EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: electrodacus on February 25, 2015, 03:17:03 am
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I decided to share my Solar BMS case design made exclusively from PCB's only.
Most are FR4 except for the PCB at the bottom that is a metal core PCB.
People mostly use metal core PCB's for power LED's but this are really great for high power electronics no idea why not more people use them.
Anyway the case is made on that 2.5mm Aluminium metal core PCB for the power components then there are two spacers or 1.6mm FR4 followed by the main board with all the smaller parts then another two FR4 1.6mm spacers and on top the front PCB with the capacitive buttons and cut out for the LCD.
This is really great since it can be mounted on a larger heatsink able to take that 20W max TDP if the Solar BMS (Battery Management System) is used at full load.
My new design will use a very similar construction but a bit more complex with about double the number of parts for the case.
Here are some photos that should make things more clear.
(https://ksr-ugc.imgix.net/assets/003/311/441/32fe5a33e06d4784fa245d8f3a751d48_original.jpg?v=1424386951&w=700&h=&fit=max&auto=format&q=92&s=04f0f4d032e82d9ba8e035843efc15dd)
(https://ksr-ugc.imgix.net/assets/003/311/452/42ceddce4c52ed757a24023e633ce617_original.jpg?v=1424387055&w=700&h=&fit=max&auto=format&q=92&s=f179e5b49b41950e90a7e84012dcc368)
(https://ksr-ugc.imgix.net/assets/003/311/472/7398000037821e11438e604b15a7f884_original.jpg?v=1424387247&w=700&h=&fit=max&auto=format&q=92&s=54600354221b9d728a4f38248366387f)
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I like it.
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I like it.
Thanks. Maybe more will use something similar for small compact electronics.
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That looks absolutely amazing.
The main reason that this is not widespread, I think, is the price of enclosures. A hammond extruded box costs about 50% more at 100 pieces as a Eurocard IMS PCB, at least that is what I've calculated just now. Did you solder the standoffs on the IMS somehow, or are these special standoffs?
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That looks absolutely amazing.
The main reason that this is not widespread, I think, is the price of enclosures. A hammond extruded box costs about 50% more at 100 pieces as a Eurocard IMS PCB, at least that is what I've calculated just now. Did you solder the standoffs on the IMS somehow, or are these special standoffs?
Mersi :)
It depends how you calculate the cost this is actually extremely inexpensive because you need those 3 PCB's anyway for the capacitive buttons the main PCB and the power PCB so only those smaller PCB's with no traces are needed (in some applications you can have those made of acrylic or similar things but I need FR4 just to be sure is fire proof)
Here is a photo I managed to find from the back and a closer look from the front
(http://electrodacus.com/SBMS4080/back11.jpg)
(http://electrodacus.com/SBMS4080/front11.jpg)
Also my new design is at the moment just a 3D render made all just of PCB (much more PCB's almost 2x)
(http://electrodacus.com/images/open4-680.jpg)
(http://electrodacus.com/images/SBMS100anim.gif)
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i like too :-+
Thanks. PCB manufacturers also love it :)
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That's very slick. I'm a big fan of the clear mask and black silk you chose as well. :-+
What are you using for board-to-board connections?
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That's very slick. I'm a big fan of the clear mask and black silk you chose as well. :-+
What are you using for board-to-board connections?
I use some small 60pins connectors not the best choice but those where 3.2mm thinners I needed for this version also a bit expensive.
I will be using spring contacts for the next version the advantage is that you do not need all traces routed to a connector on a one layer board like the aluminium metal core PCB. I can have each spring where I needed in contact with the main board above that will be 4 layers this time. I have much more components and I hope the quality of 4 layer will be better especially for that annoying 0.4mm QFN package that I have.
The bottom layer will only have those about 12 gold plated pads or so that will contact with the springs mounted on the power board.
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That looks very good, quite eye catching!
Top job! :-+
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i like the design but is that board really passing 77A and charging with around 40A !!!
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i like the design but is that board really passing 77A and charging with around 40A !!!
Yes it dose and the new design can charge with 120A while at the same time discharge with 120A and the total TDP in that case is just 22W
I use the best technology available to get to this performance levels.
Happy to talk about more since is open source.
You need to mount the Solar BMS on a small passive heat sink able to dissipate those 20 to 22W without any heatsink it can only do half that 20A charging and 40A discharging on the old version.
The charging was just 26A when I took that photo (I have just 3x 240W PV panels connected) and discharge as you see 77.8A.
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That looks very good, quite eye catching!
Top job! :-+
Thanks.
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Interesting, out of curiosity is pin that dissipates heat. Are they electrically connected to the aluminum or does it go though some kinda insulator in the pcb..?
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That is a really nice looking design. And I love the creativity in construction :-+
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Interesting, out of curiosity is pin that dissipates heat. Are they electrically connected to the aluminum or does it go though some kinda insulator in the pcb..?
Hi the way metal core PCB is build is like this. A 2.5mm Aluminium plate in my case then a 0.1mm layer of Teflon and then your copper layer so no electrical contact between your pads and aluminium plate but a really good thermal transfer do to that thin 100um layer of Teflon.
I hope more people to find about this and work with this.
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That is a really nice looking design. And I love the creativity in construction :-+
Thanks. Maybe more people get inspired by this deign.
The cost is better also than any alternative for 100+ units.
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i like the design but is that board really passing 77A and charging with around 40A !!!
Yes it dose and the new design can charge with 120A while at the same time discharge with 120A and the total TDP in that case is just 22W
I use the best technology available to get to this performance levels.
Happy to talk about more since is open source.
You need to mount the Solar BMS on a small passive heat sink able to dissipate those 20 to 22W without any heatsink it can only do half that 20A charging and 40A discharging on the old version.
The charging was just 26A when I took that photo (I have just 3x 240W PV panels connected) and discharge as you see 77.8A.
thanks for info :-+ since it's an open source is it possible for you to share schematics on the blog :D
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i like the design but is that board really passing 77A and charging with around 40A !!!
Yes it dose and the new design can charge with 120A while at the same time discharge with 120A and the total TDP in that case is just 22W
I use the best technology available to get to this performance levels.
Happy to talk about more since is open source.
You need to mount the Solar BMS on a small passive heat sink able to dissipate those 20 to 22W without any heatsink it can only do half that 20A charging and 40A discharging on the old version.
The charging was just 26A when I took that photo (I have just 3x 240W PV panels connected) and discharge as you see 77.8A.
thanks for info :-+ since it's an open source is it possible for you to share schematics on the blog :D
Yes but this is more about the case if there is an interest in the solar BMS I can open another thread about that or actually use the one in the Open Source projects
This was a successful Kicstarter project last year so if you search for Solar BMS on Kickstarter and look at my first version not this new one you will find updates and in the latest updates there are links to both software and schematic.
Hope Dave will not delete this as considered advertising.
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:-+
Neat design! Nice to see the creativity!
Her's a link to a company that even buries the components inside multi-layer boards. For me, it fell on the cost of making prototypes :-X
http://www.hofmannlp.de/fileadmin/dokumente/Hofmann_AML.pdf (http://www.hofmannlp.de/fileadmin/dokumente/Hofmann_AML.pdf)
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:-+
Neat design! Nice to see the creativity!
Her's a link to a company that even buries the components inside multi-layer boards. For me, it fell on the cost of making prototypes :-X
http://www.hofmannlp.de/fileadmin/dokumente/Hofmann_AML.pdf (http://www.hofmannlp.de/fileadmin/dokumente/Hofmann_AML.pdf)
Thanks for that link. Looks interesting but is probably expensive to even in larger volumes. A single layer metal core PCB will perform probably better at keeping the component temperature lower and cost way less.
In fact it cost about the same as a regular 4 layer PCB at least for my small volume and thick 2.5mm Aluminium with less thick aluminium it will probably be a bit less.
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Are ALU boards available with plated through holes? Or just for surface stuff?
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Are ALU boards available with plated through holes? Or just for surface stuff?
This are for surface parts only with a single layer. There are dual layer and some more exotic metal core PCB's but those are not used as much so more expensive and you don't get this great thermal transfer as with this one layer surface mount boards.
Also if you use true hole then the ability to mount this on a larger heat-sink is not there do to protruding pins.
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What an awesome idea, thanks for sharing!
I made good use of it in one of my hobby projects, photo attached.
I originally had planned to solder the layers together using solder paste and hot air, but I ended up using a drop of Epoxy instead.
cheers, Werner
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What an awesome idea, thanks for sharing!
I made good use of it in one of my hobby projects, photo attached.
I originally had planned to solder the layers together using solder paste and hot air, but I ended up using a drop of Epoxy instead.
cheers, Werner
Thanks, it seems to be the same general idea not sure why not more people use this.
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great design!
What software did you use to make the animated gif/3D model/PCB layout?
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great design!
What software did you use to make the animated gif/3D model/PCB layout?
Thanks,
For the 3D renders I used Blender 3D is a free software tool.
Animated gif is made out of still 3D renders from Blender 3D using GIMP another free software tool. I think both are available for Windows but I use them in Linux.
You should check out this video since that gif animation was done for kickstarter so no real render just viewport snapshots and gif is limited to 256cloors anyway
https://www.youtube.com/watch?v=lqDD0X5twFE (https://www.youtube.com/watch?v=lqDD0X5twFE)
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Very innovative ... great work! :-+
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Very innovative ... great work! :-+
Thanks.
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Interesting, out of curiosity is pin that dissipates heat. Are they electrically connected to the aluminum or does it go though some kinda insulator in the pcb..?
Hi the way metal core PCB is build is like this. A 2.5mm Aluminium plate in my case then a 0.1mm layer of Teflon and then your copper layer so no electrical contact between your pads and aluminium plate but a really good thermal transfer do to that thin 100um layer of Teflon.
I hope more people to find about this and work with this.
PFOA is toxic if its heated above certain temperatures. Its also (I think) an endocrine disruptor
http://www.ncbi.nlm.nih.gov/pubmed/?term=pfoa (http://www.ncbi.nlm.nih.gov/pubmed/?term=pfoa)
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Interesting, out of curiosity is pin that dissipates heat. Are they electrically connected to the aluminum or does it go though some kinda insulator in the pcb..?
Hi the way metal core PCB is build is like this. A 2.5mm Aluminium plate in my case then a 0.1mm layer of Teflon and then your copper layer so no electrical contact between your pads and aluminium plate but a really good thermal transfer do to that thin 100um layer of Teflon.
I hope more people to find about this and work with this.
PFOA is toxic if its heated above certain temperatures. Its also (I think) an endocrine disruptor
http://www.ncbi.nlm.nih.gov/pubmed/?term=pfoa (http://www.ncbi.nlm.nih.gov/pubmed/?term=pfoa)
You will nor get to those temperature in normal operation unless some components decide to exhale magic smoke and Teflon itself is not suspected of causing cancer PFOA is used in the process of making Teflon
FR4 may be even worse above some temperatures so you should not buy any electronics :)
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I've just seen this on Julian Iletts YT channel, or a similar model anyways! Good job!
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I've just seen this on Julian Iletts YT channel, or a similar model anyways! Good job!
Yes this is the same model the new model is just 3D render as of now. That one will probably look way better in real life.
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wow, that is really well executed! :-+
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wow, that is really well executed! :-+
Thanks. I will have posted this here earlier if I knew people find it so interesting.
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Anyone got a recommendation for a company that you can send gerbers too and they will produce pretty much the same thing as a PCB with holes, silkscreen and stuff, but no copper tracks and maybe not even FR4.
I'm looking for somewhere cheaper than a PCB house to get boards made that are to be used for cases and front panels. ie, non electronic uses.
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Anyone got a recommendation for a company that you can send gerbers too and they will project pretty much the same thing as a PCB with holes, silkscreen and stuff, but no copper tracks and maybe not even FR4.
I'm looking for somewhere cheaper than a PCB house to get boards made that are to be used for cases and front panels. ie, non electronic uses.
If you are not interested in the FR4 and temperature resistance there are those that do 2D shapes out of acrylic or similar plastic sheets (I'm sure they can convert Gerber in to SVG or whatever they use).
Like you seen my spacers are just simple FR4 no copper and they where not that expensive but they do not take much material since they are small and L shaped so can be optimised with not much material loss.
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Genius! Except you made me spend all day thinking about a project where I could do something similar. |O
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Genius! Except you made me spend all day thinking about a project where I could do something similar. |O
:)
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That's pretty beast ;D
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may i pick your brain about that direct-FET i see on the PCB?
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may i pick your brain about that direct-FET i see on the PCB?
Yes ask your question :)
I will not be using that in my next design I will be using the one you see next to those direct-FET the IPT007N06N much better value.
The problem with direct-FET is that PCB trace from the Source can not be wide enough so the loss there will make the small RDSon of the FET quite useless.
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Maybe some via stitching and another trace on the other layer to help lower the resistance of the trace?
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Maybe some via stitching and another trace on the other layer to help lower the resistance of the trace?
If you look closely I use a single layer metal core PCB so no via are possible. But I can also do 80A with just 35um (1Oz) of copper because of excellent thermal performance of the metal core PCB.
The solder points are also quite small on the direct-FET when you are working with 1.1mohm RDSon FET PCB resistance plays a huge role and can cancel all the advantage of a low RDSon FET.
The IPT007N06N is probably the best in the world at this moment with max 0.75mohm and measured typical of 0.66mohm also do to case construction it works way better on a single layer PCB.
The direct FET just dose not work in my application. I used those at up to 40A in that configuration and that was really the limit and did not liked the performance.
That short trace connecting the Source of both mosfets together doubles the loss.
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But I can also do 80A with just 35um (1Oz) of copper because of excellent thermal performance of the metal core PCB.
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The IPT007N06N is probably the best in the world at this moment with max 0.75mohm and measured typical of 0.66mohm also do to case construction it works way better on a single layer PCB.
When looked into its datasheet while I might be interested in using this Datasheet IPT007N06N - Infineon (https://www.infineon.com/dgdl/Infineon-IPT007N06N-DS-v02_01-en.pdf?fileId=db3a30433e9d5d11013e9e4618320118) and calculated contact area under dren (~50mm2) and source (~15mm2) it looks like this under dren is ~3.3 times bigger than under source, but on PCB with 35um copper layer when we take contour of IPT007N06N dren (7.5mm x 7mm ) contact area (there is no other way for current to flow if there is no via stitching possible in your smart design) than we find that this contour is ~29 mm long, so multiply by 1oz copper width we get 29mm*0.0347mm= 1mm2 pf cross section copper thin layer for 100A ? :palm:
Do you plan use few of those "best in the world" IPT007N06N in parallel on this 1oz PCB?
Else I smell "magic smoke" and IPT007N06N desoldered itself surfing over teflon surface on hot aluminium base :o
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But I can also do 80A with just 35um (1Oz) of copper because of excellent thermal performance of the metal core PCB.
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The IPT007N06N is probably the best in the world at this moment with max 0.75mohm and measured typical of 0.66mohm also do to case construction it works way better on a single layer PCB.
When looked into its datasheet while I might be interested in using this Datasheet IPT007N06N - Infineon (https://www.infineon.com/dgdl/Infineon-IPT007N06N-DS-v02_01-en.pdf?fileId=db3a30433e9d5d11013e9e4618320118) and calculated contact area under dren (~50mm2) and source (~15mm2) it looks like this under dren is ~3.3 times bigger than under source, but on PCB with 35um copper layer when we take contour of IPT007N06N dren (7.5mm x 7mm ) contact area (there is no other way for current to flow if there is no via stitching possible in your smart design) than we find that this contour is ~29 mm long, so multiply by 1oz copper width we get 29mm*0.0347mm= 1mm2 pf cross section copper thin layer for 100A ? :palm:
Do you plan use few of those "best in the world" IPT007N06N in parallel on this 1oz PCB?
Else I smell "magic smoke" and IPT007N06N desoldered itself surfing over teflon surface on hot aluminium base :o
I have one SBMS4080 powering this computer :) The SBMS4080 has a single IPT007N06N for the output (max output current 80A) here is a photo with SBMS4080 outputting 77.8A while also having at the input 26A (that is with the direct FET) (https://d15chbti7ht62o.cloudfront.net/assets/003/311/472/7398000037821e11438e604b15a7f884_large.jpg?1424387247)
This is mounted on a metal core PCB quite different form a normal FR4 the trace will not usually get more than 3 to 4C above aluminium plate since all there is between the two is a 100um of Teflon.
While at above 75A for over 20 minutes the heat sink temperature was under 40C absolutely no problem with the design.
The new SBMS100 will be able to handle 120A (overcurrent protection limit) with two of this IPT007N06N in parallel and 3Oz (100um) copper almost no length to copper trace with the new design at most 5mm distance between power components.
While handling 100A nominal in and 100A out so 200A total with 6 IPT007N06N the entire SBMS TDP will be 22W easy to dissipate with a small passive heat-sink.
I know any PCB trace calculator will be on the red with this values but metal core PCB is quite a different class.
The SBMS4080 has already some months used to power my house and with normally 50 to 60A on Load for one or two hours during the day that 77.8A is not that often I do not like to stress my LiFePO4 batteries.
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While at above 75A for over 20 minutes the heat sink temperature was under 40C absolutely no problem with the design.
Did you checked temperature of IPT007N06N itself? For short period of time at low ambient temperature with huge thermal capacity maybe it works.
Anyway 75A for this IPT007N06N is of course nothing and ~4W loses easy to disipate, but 1mm2 of copper in best case scenario for huge currents looks bad and I do not like it at all.
This is not PCB calculator, just raw math and physics based on physical dimensions of IPT007N06N and copper layer ;)
Probably additional copper plate (1mm) cut on CNC, on top of regular PCB, under IPT007N06N or a few other low RDSON in parallel will do the job much better.
IPT007N06N is quite expensive, so we can buy many low RDSON's for the same price.
BTW: 25A fused home grid 230VAC with 2.5mm2 wires we have 10A/mm2 and ~6kW , so for 100A a lot of copper lost for wiring the house with such low voltage high power outputs and very difficult to transfer this energy for longer distances, so such low voltages are good for.... welding :-DD
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To be honest I find interesting, that you would use such big mosfet in your design. As far as I understand you are not switching it at high frequency, because it works like a chopper, so gate capacitance and switching losses are less significant. In my designs, where I have to do similar tasks, I usually use multiple smaller fet in parallel. For that 6 dollar Infineon, you could get 8-10 Power SO8 FET, which can switch much higher current, you just have to make sure that you know how to parallel FETs. Not to mention, because you use higher quantities, you get a lot better discounts at the suppliers.
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While at above 75A for over 20 minutes the heat sink temperature was under 40C absolutely no problem with the design.
Did you checked temperature of IPT007N06N itself? For short period of time at low ambient temperature with huge thermal capacity maybe it works.
Anyway 75A for this IPT007N06N is of course nothing and ~4W loses easy to disipate, but 1mm2 of copper in best case scenario for huge currents looks bad and I do not like it at all.
This is not PCB calculator, just raw math and physics based on physical dimensions of IPT007N06N and copper layer ;)
Probably additional copper plate (1mm) cut on CNC, on top of regular PCB, under IPT007N06N or a few other low RDSON in parallel will do the job much better.
IPT007N06N is quite expensive, so we can buy many low RDSON's for the same price.
BTW: 25A fused home grid 230VAC with 2.5mm2 wires we have 10A/mm2 and ~6kW , so for 100A a lot of copper lost for wiring the house with such low voltage high power outputs and very difficult to transfer this energy for longer distances, so such low voltages are good for.... welding :-DD
The worst case scenario is a few hundred ms for the overcurrent protection to act or a few hundred microseconds in case of short circuit currents.
The entire Load circuit includes the IPT007N06N a 0.25mohm current shunt resistor (two 0.5mohm in parallel each rated at 3W) the copper trace and connectors. All this together have a 2mohm measured resistance or 2mV/A voltage drop.
At full 80A the total voltage drop is 160mV so 12.8W total that need to be dissipated. All this Load circuit uses a total footprint of about 40x40mm on the metal core PCB but the metal core PCB is 121mm x 87mm and gets mounted on a heat-sink able to dissipate at least the 20 to 22W worst case TDP.
As you already made the calculation out of this 12.8W about 4 to 4.8W will drop on the IPT007N06N then 1.6W on the current shunt resistors (0.8W each) the rest of the loss is on the PCB trace and connectors so about 6.4W and all this uses quite a bit of surface on the metal core PCB that is as I mentioned before made out of 2.5mm Aluminium plate and just 100um of Teflon.
The thermal performance of the metal core PCB is around 0.13°C cm^2/W to 0.5°C cm^2/W (I took the worst case value since you do not know exactly what you get from a PCB manufacturer in China :) ) so you can see that the temperature delta between the heatsink and copper trace and components is really small at most a few single digit °C above heatsink temperature.
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To be honest I find interesting, that you would use such big mosfet in your design. As far as I understand you are not switching it at high frequency, because it works like a chopper, so gate capacitance and switching losses are less significant. In my designs, where I have to do similar tasks, I usually use multiple smaller fet in parallel. For that 6 dollar Infineon, you could get 8-10 Power SO8 FET, which can switch much higher current, you just have to make sure that you know how to parallel FETs. Not to mention, because you use higher quantities, you get a lot better discounts at the suppliers.
What is the RDSon on those 8 or 10 SO8 also there will be longer copper traces to connect them all and if you look at my replay above that is quite significant part of the power loss.
I use the FET as a switch mostly so I'm interested in the smallest loss so small RDSon.
I did had in my initial design (just prototype) 4 smaller FET that cost almost the same while they where just 40V not 60V
Yes that discount for larger number is a good thing but I do this in low volume anyway so saving even 1$ at 100 units will save me 100$ not even worth the manual placement of all those SO8 :) Not to mention I have no space for more than 4x SO8 in my design.
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may i pick your brain about that direct-FET i see on the PCB?
Yes ask your question :)
I will not be using that in my next design I will be using the one you see next to those direct-FET the IPT007N06N much better value.
The problem with direct-FET is that PCB trace from the Source can not be wide enough so the loss there will make the small RDSon of the FET quite useless.
after sleeping ... i forgot what i wanted to ask ... something about thermal dissipation :palm:
ahhh YES ! ... at what Tcase do you approx design those power packages at? 70oC ?
or at what Tj alternatively if thats the number you go for?
Look at the earlier replay I made to eneuro
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so you can see that the temperature delta between the heatsink and copper trace and components is really small at most a few single digit °C above heatsink temperature.
teflon has ONLY 0.2W/mK, while Cu 400W/mK, Al 250W/mK, so I'm, still sceptical about better performance of thin a few oz copper layer with 0.1mm teflon insulation to aluminium heatsink than 8-10 fets in parallel while those fets has huge drens surface to help disipate heat-copper heatsink can be used soldered to.... copper pipes filled with oil like in home thermal heating systems, but ok maybe for mass production it is not the cheapiest solution to ship, but messing with teflon...no :-\
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so you can see that the temperature delta between the heatsink and copper trace and components is really small at most a few single digit °C above heatsink temperature.
teflon has ONLY 0.2W/mK, while Cu 400W/mK, Al 250W/mK, so I'm, still sceptical about better performance of thin a few oz copper layer with 0.1mm teflon insulation to aluminium heatsink than 8-10 fets in parallel while those fets has huge drens surface to help disipate heat-copper heatsink can be used soldered to.... copper pipes filled with oil like in home thermal heating systems, but ok maybe for mass production it is not the cheapiest solution to ship, but messing with teflon...no :-\
Like I mentioned manufacturer spec for that PCB is at most 0.5°C cm^2/W and based on my observation seems to be real. It really is a big difference between a SO8 package with heatsink on top and a IPT007N06N mounted on a metal core PCB.
They use this metal core PCB for Power LED's up to hundred watt LED's that need to have the die at no more than 60C for long life.
Thermal resistance of the IPT007N06N is just 0.2K/W for junction to case.
The metal core PCB is also a really inexpensive solution compared to multilayer FR4 and heatsink (I have no invested interest in promoting this metal core PCB) but may point sharing the case design was to show what is possible with this solution.
Hope more people will take a closer look at the metal core PCB for their high power applications.
Not sure what you want to say with "messing with Teflon".
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Interesting, out of curiosity is pin that dissipates heat. Are they electrically connected to the aluminum or does it go though some kinda insulator in the pcb..?
Hi the way metal core PCB is build is like this. A 2.5mm Aluminium plate in my case then a 0.1mm layer of Teflon and then your copper layer so no electrical contact between your pads and aluminium plate but a really good thermal transfer do to that thin 100um layer of Teflon.
I hope more people to find about this and work with this.
PFOA is toxic if its heated above certain temperatures. Its also (I think) an endocrine disruptor
http://www.ncbi.nlm.nih.gov/pubmed/?term=pfoa (http://www.ncbi.nlm.nih.gov/pubmed/?term=pfoa)
Sure but Teflon (PTFE) doesn't contain PFOA. It is used in the manufacture, but is almost completely absent in the final product.
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To be honest I find interesting, that you would use such big mosfet in your design. As far as I understand you are not switching it at high frequency, because it works like a chopper, so gate capacitance and switching losses are less significant. In my designs, where I have to do similar tasks, I usually use multiple smaller fet in parallel. For that 6 dollar Infineon, you could get 8-10 Power SO8 FET, which can switch much higher current, you just have to make sure that you know how to parallel FETs. Not to mention, because you use higher quantities, you get a lot better discounts at the suppliers.
What is the RDSon on those 8 or 10 SO8 also there will be longer copper traces to connect them all and if you look at my replay above that is quite significant part of the power loss.
I use the FET as a switch mostly so I'm interested in the smallest loss so small RDSon.
I did had in my initial design (just prototype) 4 smaller FET that cost almost the same while they where just 40V not 60V
Yes that discount for larger number is a good thing but I do this in low volume anyway so saving even 1$ at 100 units will save me 100$ not even worth the manual placement of all those SO8 :) Not to mention I have no space for more than 4x SO8 in my design.
Say, you have 40mm space for the FETs, you can put 7 of those SO8 packages there, plus some spacing. IRFH7085 (conveniently selected for you) has about 2,3Ohm Rdson if you drive it with 15V. A pcb trace 20mm wide 40mm long with 35um plating has half a milliohm resistance, lets calculate with half of this, because the current distribution. That is 0,57mOhm DC resistance. But yes, I get that manual placement is not fun.
I see that you used the open hardware symbol. Is there schematic somewhere? This stuff is quite interesting, even that I dont have a solar system.
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To be honest I find interesting, that you would use such big mosfet in your design. As far as I understand you are not switching it at high frequency, because it works like a chopper, so gate capacitance and switching losses are less significant. In my designs, where I have to do similar tasks, I usually use multiple smaller fet in parallel. For that 6 dollar Infineon, you could get 8-10 Power SO8 FET, which can switch much higher current, you just have to make sure that you know how to parallel FETs. Not to mention, because you use higher quantities, you get a lot better discounts at the suppliers.
What is the RDSon on those 8 or 10 SO8 also there will be longer copper traces to connect them all and if you look at my replay above that is quite significant part of the power loss.
I use the FET as a switch mostly so I'm interested in the smallest loss so small RDSon.
I did had in my initial design (just prototype) 4 smaller FET that cost almost the same while they where just 40V not 60V
Yes that discount for larger number is a good thing but I do this in low volume anyway so saving even 1$ at 100 units will save me 100$ not even worth the manual placement of all those SO8 :) Not to mention I have no space for more than 4x SO8 in my design.
Say, you have 40mm space for the FETs, you can put 7 of those SO8 packages there, plus some spacing. IRFH7085 (conveniently selected for you) has about 2,3Ohm Rdson if you drive it with 15V. A pcb trace 20mm wide 40mm long with 35um plating has half a milliohm resistance, lets calculate with half of this, because the current distribution. That is 0,57mOhm DC resistance. But yes, I get that manual placement is not fun.
I see that you used the open hardware symbol. Is there schematic somewhere? This stuff is quite interesting, even that I dont have a solar system.
All the space I have there is at most 30mm for FETs. I looked at your recommended FET http://www.irf.com/product-info/datasheets/data/irfh7085pbf.pdf (http://www.irf.com/product-info/datasheets/data/irfh7085pbf.pdf) that has 2.6mohm typical so say I can somehow fit 6 but probably realistic just 5 is possible to have some space between them.
So 2.6/5 is 0.52 mohm that is not big improvement over 0.66 mohm typical on the IPT007N06N and where is the cost gain that is still over 1$ each in quantities so it will be more expensive than IPT007N06N or at least there will be no gain. Sorry I looked at CAD $ still you need exactly 4 to replace one IPT007N06N that costs $4 US at 500pcs where IRFH7085 cost 0.76 X 4 = 3$ but more parts so you need a larger PCB to fit them that will add to cost also longer PCB trace that will negate the use of 4 or even 5 smaller FETs to replace the IPT007N06N
For the new design I have even less space is just enough to fit two parallel IPT007N06 on the output and of course much higher current 120A.
The entire SBMS100 will be using 6 of those IPT007N06N so if I need to replace with the smaller ones I will need at least 24 of them.
The SBMS 25 and SBMS40 will actually use something similar a smaller FET but that will need to be in a DPak case so that it can fit on the same footprint of the IPT007N06N probably IPD034N06N3 or similar I will decide when I get closer to the components order.
Yes is open source the schematic for the current model is available you can find the link on youtube in the description of the SBMS4080 HW video or in the latest updates on the first kickstarter project just search for Solar BMS on Kickstarter.
Just noticed you are from Romania :) Salut.
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i face similar problem when trying to squeeze alot of things into 5cmx5cm to make a PSU controller ... good Tjc component vs more smaller cheaper component. in the end the real estate problem is something so hard to get over when it comes to thermal dissipation :-// (that was where i started to explore mounting alot of SMD NMOS on heatsink and not on PCB ... https://www.eevblog.com/forum/beginners/smd-on-normal-heatsinks/ (https://www.eevblog.com/forum/beginners/smd-on-normal-heatsinks/))
i did see 1 of the tear down i think is shahriah on the keithley SMU parrallel SO8. but @ 80A ... i mean SO8 is so easy to overheat :-//. ... but at hobbyist level it would be a dream if its a it would never breakdown design :-DD
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i face similar problem when trying to squeeze alot of things into 5cmx5cm to make a PSU controller ... good Tjc component vs more smaller cheaper component. in the end the real estate problem is something so hard to get over when it comes to thermal dissipation :-// (that was where i started to explore mounting alot of SMD NMOS on heatsink and not on PCB ... https://www.eevblog.com/forum/beginners/smd-on-normal-heatsinks/ (https://www.eevblog.com/forum/beginners/smd-on-normal-heatsinks/))
i did see 1 of the tear down i think is shahriah on the keithley SMU parrallel SO8. but @ 80A ... i mean SO8 is so easy to overheat :-//. ... but at hobbyist level it would be a dream if its a it would never breakdown design :-DD
metal core PCB is a really great use in this sort of applications but even my large 121 x 87mm x 2.5mm pcb can only handle around 5 to 6W as passive without getting over 50 to 60C (I never design things that go over 60C at full load)
But the nice thing on metal core PCB is that you can mount your device on a larger heatsink as large as you need to dissipate the power. In fact any flat metallic surface will do.
My new SBMS will be 110mm x 80mm a bit smaller than first and needs to handle 2x the power (TDP will be the same max 22W).
Is nice for shipping also new SBMS at around 340g so I can keep the parcel under 500g probably one of the smallest devices able to handle 2x 120A simultaneously for unlimited amount of time. Trick is that it needs an external heatsink or a a piece of flat aluminium plate. Is somehow similar to a modern CPU :) at 22W TDP will be one of those low power mobile versions.
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All the space I have there is at most 30mm for FETs. I looked at your recommended FET http://www.irf.com/product-info/datasheets/data/irfh7085pbf.pdf (http://www.irf.com/product-info/datasheets/data/irfh7085pbf.pdf) that has 2.6mohm typical so say I can somehow fit 6 but probably realistic just 5 is possible to have some space between them.
So 2.6/5 is 0.52 mohm that is not big improvement over 0.66 mohm typical on the IPT007N06N and where is the cost gain that is still over 1$ each in quantities so it will be more expensive than IPT007N06N or at least there will be no gain. Sorry I looked at CAD $ still you need exactly 4 to replace one IPT007N06N that costs $4 US at 500pcs where IRFH7085 cost 0.76 X 4 = 3$ but more parts so you need a larger PCB to fit them that will add to cost also longer PCB trace that will negate the use of 4 or even 5 smaller FETs to replace the IPT007N06N
For the new design I have even less space is just enough to fit two parallel IPT007N06 on the output and of course much higher current 120A.
The entire SBMS100 will be using 6 of those IPT007N06N so if I need to replace with the smaller ones I will need at least 24 of them.
The SBMS 25 and SBMS40 will actually use something similar a smaller FET but that will need to be in a DPak case so that it can fit on the same footprint of the IPT007N06N probably IPD034N06N3 or similar I will decide when I get closer to the components order.
Yes is open source the schematic for the current model is available you can find the link on youtube in the description of the SBMS4080 HW video or in the latest updates on the first kickstarter project just search for Solar BMS on Kickstarter.
Just noticed you are from Romania :) Salut.
That seems to be justified in that case. Interestingly, I was working with smaller voltages, and I came to a different conclusion when I was making my design. I think the main reson behind this is the huge market of the DC-DC converters inside PCs. If you want to make a design which works at 12V, you have FETs with 3mOhm Rdson for 30 cents and you can parallel as many as you want, but if you increase the voltage, not so much anymore.
The MOSFETs on metal core is a very interesting design concept. I have designs which dissipate over 300W, with water cooled heatsinks, I always toyed with the idea of the IMS PCB but never got the boss to agree to launch a prototype.
There is very little talk on the web about high current FETs unless it is in SMPS, so I take any chance to talk about it.
BTW I'm living in Belgium, but I'm originally from Hungary, not Romania.
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have you considered just using vias? lots of it? if say the thermal resistance could work ... so the PCB could be thin? maybe 0.4mm? i saw a page selling bare 0.3mm thick PCB, i didnt think there is such thin boards :-//
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Hope more people will take a closer look at the metal core PCB for their high power applications.
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Not sure what you want to say with "messing with Teflon".
For high power apps experimenting rather with direct connecting TO-220 case to aluminium/copper heatsink by http://en.wikipedia.org/wiki/Brazing (http://en.wikipedia.org/wiki/Brazing) using short high energy pulses (spot welding) to melt filler metal ;)
Brazing is a metal-joining process whereby a filler metal is heated above melting point and distributed between two or more close-fitting parts by capillary action.
So, actually teflon might be really good in my method to seperate electrically coper case and aluminium/copper heatsink which will allow easy heat filler metal which has much higher resistance than copper or aluminum.
Additionally teflon will help limit brazing bondary to element case.
(http://s17.postimg.org/fcon57kd7/heatsink_teflon_tape_on_aluminium_between_copper.jpg) (http://postimg.org/image/fcon57kd7/)
It looks like that even thin teflon tape 0.075mm~0.1mm should be fine while there is no electrical contact between case and heatsink elements, also tried this tefon tape in fire - it is not flammable 8)
Probably teflon used on those metal core PCBs is very different than cheap teflon tape for pipes, but teflon might be this what I needed for spot welding brazing :-+
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That seems to be justified in that case. Interestingly, I was working with smaller voltages, and I came to a different conclusion when I was making my design. I think the main reson behind this is the huge market of the DC-DC converters inside PCs. If you want to make a design which works at 12V, you have FETs with 3mOhm Rdson for 30 cents and you can parallel as many as you want, but if you increase the voltage, not so much anymore.
The MOSFETs on metal core is a very interesting design concept. I have designs which dissipate over 300W, with water cooled heatsinks, I always toyed with the idea of the IMS PCB but never got the boss to agree to launch a prototype.
There is very little talk on the web about high current FETs unless it is in SMPS, so I take any chance to talk about it.
BTW I'm living in Belgium, but I'm originally from Hungary, not Romania.
Where you use normal FR4 multiple parallel FETs make more sense since all that heat is better distributed. I prefer to keep the power dissipation as low as possible even if involves more expensive FETs since the additional heatsink or water cooling will probably be even more expensive.
Those metal core PCBs dropped in price significantly thanks to modern high power LED's.
Sorry :) for some reason that black stripe on the Belgium flag looked blue on my screen.
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have you considered just using vias? lots of it? if say the thermal resistance could work ... so the PCB could be thin? maybe 0.4mm? i saw a page selling bare 0.3mm thick PCB, i didnt think there is such thin boards :-//
Then you need some electrical isolator between the vias on the other side and a heatsink that will be nowhere near as good as that 0.1mm Teflon. It will probably also cost more.
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Hope more people will take a closer look at the metal core PCB for their high power applications.
...
Not sure what you want to say with "messing with Teflon".
For high power apps experimenting rather with direct connecting TO-220 case to aluminium/copper heatsink by http://en.wikipedia.org/wiki/Brazing (http://en.wikipedia.org/wiki/Brazing) using short high energy pulses (spot welding) to melt filler metal ;)
Brazing is a metal-joining process whereby a filler metal is heated above melting point and distributed between two or more close-fitting parts by capillary action.
So, actually teflon might be really good in my method to seperate electrically coper case and aluminium/copper heatsink which will allow easy heat filler metal which has much higher resistance than copper or aluminum.
Additionally teflon will help limit brazing bondary to element case.
(http://s17.postimg.org/fcon57kd7/heatsink_teflon_tape_on_aluminium_between_copper.jpg) (http://postimg.org/image/fcon57kd7/)
It looks like that even thin teflon tape 0.075mm~0.1mm should be fine while there is no electrical contact between case and heatsink elements, also tried this tefon tape in fire - it is not flammable 8)
Probably teflon used on those metal core PCBs is very different than cheap teflon tape for pipes, but teflon might be this what I needed for spot welding brazing :-+
I do not think that Teflon used on metal core PCB is any different. I just have no idea what sort of glue they use to stick that Teflon to copper and aluminium. You can also order metal core PCB with copper instead of aluminium but of course is more expensive.
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You can also order metal core PCB with copper instead of aluminium but of course is more expensive.
Those MCPCBs are copper on white surface due to this teflon layer on aluminium base like in this video below?
Soldering Cree Leds to a MCPCB (https://www.youtube.com/watch?v=7rNm8lN5YWU#ws)
Probably need review this thread to see estimated pricing per square inch of such aluminium MCPCB, but maybe I will be able using spot welder brazing join a few mm aluminium/copper plates cut on CNC to classic cheap 1oz double layer PCB with help of teflon tape between PCB copper<->teflon contour<->aluminium/copper heatsink<->teflon contour<->element case and additional 3mm in diameter rivets througth vias and TO-220 case to ensure mechanical stability at accidential high temperatures >:D
(http://www.aeroassemblies.com/images/pop/rivets.jpg)
"May the Force be with us" :-DD
Note: Teflon countour I mean there is no 0.1mm teflon isolation over whole joint area of course, but only contours required to keep electrical isolation between brazed elements in spot welder pulses, but let brazing fill metal most of contact area between element case and heatsink-in the case of copper to copper solder itself, copper to aluminium brazing with help of brazing past etc ;)
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Those MCPCBs are copper on white surface due to this teflon layer on aluminium base like in this video below?
That is a metal core PCB but is white instead of black do to paint colour of the solder mask you can not actually see the Teflon.
If you look on eBay you can get 50 pcs of those 16mm diameter metal core PCB's for LED with $12 so is like 25cent/pcs you can build your custom PCB's and if they are in sufficient volume you will get at about same price.
My board is quite a bit larger 121x87mm and the aluminium is thicker 2.5mm vs those usually 1.6mm or less for LED and mine in relatively low volume 100pcs was about $6.
I will say is a decent price and is hard to find a better or more cost effective solution for high power stuff.
That LED in the video is probably a 10W LED so TDP around 8W or over while keeping the LED die under 60C
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Please be careful with teflon/PTFE, when heated beyond a few hundred degrees it produces really toxic fumes.
https://www.ncbi.nlm.nih.gov/pubmed/?term=ptfe (https://www.ncbi.nlm.nih.gov/pubmed/?term=ptfe)