Power supply design: 60V, 30A

[Centmo]

Hello, I'm an EE but a little out of element with power supply design, so I'm looking for some suggestions.

I need to charge a 14S LiPo as fast as possible from a standard 120V/20A wall plug. A fully charged pack is 4.2V * 14 = 58.8V. With the AC circuit able to supply up to 20A at 120Vrms (2400W), I figure that a DC supply could reasonably provide 30A at 60V from this circuit. Please assume that the battery pack can safely handle this charge current. The output voltage must be variable in the range 0-60V, so that I can implement a control loop to perform constant-current charging.

Ignoring the cell-balancing part of the problem (this will be done externally from the DC supply), where can I begin to design such a DC supply? I know it may have to be bulky, but the lighter, the better. Is there a development kit I can start from?

Thanks.

[KJDS]

If you just need a few, then buy an off the shelf supply.

If you need a lot, get a custom design from one of many power supply manufacturers. Even if you just need a few then putting a few pounds their way is likely to be the cheapest way forwards.

If you really need to design it in house, hire in a contractor.

If you have a few years and a lot of spare money then start reading about switch mode supplies. If you don't mind it being huge and heavy then a linear solution could be used. I know it's fun to design new things, but I don't see it as a sensible engineering solution unless there's a real commercial need to do so.

http://www.eltek.com/wip4/

Are just one of many that could provide a solution.

[jabramo]

Why don't you just buy an application specific device??

Will something like this not satisfy your needs?
http://www.thunderpowerrc.com/Chargers_2/TP1430C

I guess you still need a power supply which would cost an extra $100 on top.

This route is way safer and easier than building one from scratch. Also power electronics are not cheap. You'll need to source a high power transformer and a bunch of power transistors. You'll most likely have to design custom pcbs because there's no way you can breadboard a project like this. Thermal management will come into play no doubt which calls for heat sinking.

This project would be a pretty big undertaking even for someone experienced in power supply design. Unless your looking to put together something really crude I'd recommend ponying up for the application specific gear. And I wouldn't recommend something crude for something as explosive as lipos (I've seen youtube videos of 3S cells exploding into a ball of fire and I can't imaging what a 14S battery would look like). Lipos are no doubt extremely dangerous when mishandled, do the right thing and buy gear that was specifically designed to handle them.

EDIT: Being an EE yourself I think you will agree that keeping yourself and more importantly the people around you safe is the number 1 priority.

[digsys]

.. or pick up a couple of these - www.measureshop.co.za/buy/manson-hcs-3604-bench-power-supply-0-60v-0-15a-price-includes-vat-317729
They have analogue control inputs for V/I/on. I have a few and they work FINE. All you need then is a simple analogue controller / monitor.

[jabramo]

Even that can be dangerous.

From my limited battery knowledge LIPOs are extremely sensitive and volatile. Charging all 14 cells without balancing can be disastrous.

[ee.jmlp]

Hello, I'm an EE but a little out of element with power supply design, so I'm looking for some suggestions.

I need to charge a 14S LiPo as fast as possible from a standard 120V/20A wall plug. A fully charged pack is 4.2V * 14 = 58.8V. With the AC circuit able to supply up to 20A at 120Vrms (2400W), I figure that a DC supply could reasonably provide 30A at 60V from this circuit. Please assume that the battery pack can safely handle this charge current. The output voltage must be variable in the range 0-60V, so that I can implement a control loop to perform constant-current charging.

Ignoring the cell-balancing part of the problem (this will be done externally from the DC supply), where can I begin to design such a DC supply? I know it may have to be bulky, but the lighter, the better. Is there a development kit I can start from?

Thanks.

Get a cheap welder inverter with DC out and constant current control. Wrap some loops from low voltage secondary until you get a max of 60V with 30A.

Happy hacking

[NiHaoMike]

A 48V telecom supply would work nicely. Or 4 modified PC PSUs in series.

[Centmo]

Thanks for all the replies.

The charger is required for a commercial product, not just a single hobby unit for myself, so a hacked solution won't do. I have searched far and wide for existing products which might fit the bill, but they have all fallen short.  The ThunderPower 1430 unit mentioned by jabrano looks great from the description, but it turns out that it maxes out at 10A when you charge 14S (to the shagrin of some irked customers who only found this out after finding an addendum stuffed into the user manual).

http://rc.runryder.com/helicopter/rr/rrpv.htm?ID=681276&PG=1&IN=1

I am currently using four iChargers configured for 7S charge in 2S2P configuration to achieve 30A charging of the 14S pack. These require two large 24V DC supplies, so in total we are talking six individual components - not practical to ship with a commercial product. What I need is a single integrated solution.

Regarding the cell balancing, I have that taken care of on a separate board connected to the battery. It will not allow any of the cells to exceed 4.200V. So, all I need is a single 0-60V, 30A power supply which I can control (set output voltage) remotely with my MCU (via SPI, or otherwise). (Thanks for the tip on the 15A unit, digsys - do you know of a 30A version?)

Since I am only charging batteries, there is no stringent requirement to have low output ripple. I think this is what makes bench-top DC power supplies so expensive, and I'd prefer not to have to shell out $1000 for such a DC supply. But...I may have to. I am realizing that I don't have a year or two to design and build my own.

[AmmoJammo]

It simply can't work properly!

At the very least, you would need to monitor the voltage of all 14 cells (independently), and have the charger shut down when just one cell got to 4.20volts, or you risk overcharging and damaging that cell.

Of course, seeing you wouldn't be balance charging, you'd need to balance the pack every 5 or 10 charges, to make sure the cells are still balanced, or you risk over discharging one of the cells, and damaging it...

The only way I can see a "dumb" charger being used to quickly, and safely charge a 14 cell Lipo pack, is to charge each cell separately, with its own 4.2volt, isolated, current limited supply....

A fixed voltage supply charging all cells in series simply can't work! If it was for a home setup, and didn't really matter so much if you stuffed your own batteries, then go for it! But if its for a commercial product, you need to rethink the idea

[AG6QR]

A 20 amp 120V branch circuit normally shouldn't have a continuous load of more than 80% of its capacity, or 16 amps.  In order to produce 60V at 30A from 120V at 16A, your converter is going to need to be about 94% efficient.

I'm not surprised you're having trouble finding a commercial product that meets that requirement.

I don't have a suggestion other than to figure out where you might relax the requirement.  More input power?  Less output power? 

[pinkysbrein]

How are those balamced chargers usually constructed? One flyback based charger per cell?

[AmmoJammo]

How are those balamced chargers usually constructed? One flyback based charger per cell?

As far as I'm aware, they charge the cells in series, but monitor and discharge the cells that are charged more than the others

Which means the whole process is rather slow, as you're charging all the cells, while discharing the higher charged ones 

[pinkysbrein]

Hmm why not just temporarily take the higher voltage ones out of the string? Needs a non trivial of electronics per cell, but you could keep charging.

[Strada916]

break the battery pack down to manageable cell count, like 4,4,4,2 Never seen 14s packs. Big electric helis are the only models I have seen with anything close like 12s but they break them up into smaller more manageable packs for charging and storage.

[ConKbot]

It simply can't work properly!

At the very least, you would need to monitor the voltage of all 14 cells (independently), and have the charger shut down when just one cell got to 4.20volts, or you risk overcharging and damaging that cell.

Of course, seeing you wouldn't be balance charging, you'd need to balance the pack every 5 or 10 charges, to make sure the cells are still balanced, or you risk over discharging one of the cells, and damaging it...

The only way I can see a "dumb" charger being used to quickly, and safely charge a 14 cell Lipo pack, is to charge each cell separately, with its own 4.2volt, isolated, current limited supply....

A fixed voltage supply charging all cells in series simply can't work! If it was for a home setup, and didn't really matter so much if you stuffed your own batteries, then go for it! But if its for a commercial product, you need to rethink the idea

While its good to see people not encouraging being reckless with lithium batteries , battery cell balancing should be done by the BMS and not by the charger.  Hobbyists need high performance, eek out every last miliohm (how many planes have you seen with a fuse? )  and low cost, so they omit the balancer in the pack and just use a balance charger, and just call a low pack voltage cut off good enough on discharge. 

Power tool batteries, laptop batteries, none of these break out individual cell taps because cell balancing (in power tool packs) or cell monitoring (in laptop packs, no balancing, just matched cells) is internal.   Since the thread starter is talking about a pack which charges at 30A I'll assume its at least 10AH, and has a short circuit current in excess of 100A. Having no BMS on such a battery would be fool-hearty at best, and quite concerning

A 20 amp 120V branch circuit normally shouldn't have a continuous load of more than 80% of its capacity, or 16 amps.  In order to produce 60V at 30A from 120V at 16A, your converter is going to need to be about 94% efficient.

Not only that your mains can vary something like +15%to -10% or there abouts. Most NA PSU's have an input range of 100-138Vrms. Then there is the fact that a lot of older houses only have 15A branches not 20A. So the most you can guarentee out of a NA residential branch is 100Vrms x 15Arms = 1500VA. You would need PFC in order to get anywhere near that as well then conversion efficency etc. You could run it off the 240Vrms line that would half the input current requirment.

If this is a consumer product and it needs a 60V 30A charger for the Li-Po inside, I think I want it, doesnt matter what it actually is 

[Crazy Ape]

This thread over at candlepower should be required reading if you're messing with lithium based cells.

KABOOOOM!

http://www.candlepowerforums.com/vb/showthread.php?262234-TK-Monster-Explosion

[Centmo]

Regarding cell balancing, the cell balancing is being taken care of by a separate board, at the battery itself. Each individual cell voltage is being monitored to a 1mV accuracy by an AFE and MCU. As with any lithium charger, when any one cell gets close to 4.200V, charging will change from constant-current mode to constant-voltage mode so as to avoid an over-voltage condition (MCU will control charger remotely). When the highest voltage cell actually reaches 4.200V, it will be bypassed with a FET and power dissipating resistor in series. The FET will be switched on/off with some hysteresis to maintain 4.200V across the cell, until the rest of the cells catch up. This stage of the charging process is rather slow, compared to the constant-current charging stage, which will pump out the full 30A.

AG6QR, you brought up a good point that UL dictates I cannot exceed 80% of the branch circuit rating. 120V*20A*0.8 = 1920W. Assuming 90% efficiency, 1920W * 0.9 =  1728W. 1728W/60V = 28.8A. So, I may need to relax my 30A requirement to, perhaps 25A.

Achmed99, some good points also...I would like to design it for a 20A branch circuit, and perhaps have a variant for a 15A branch circuit (or, a switch on the back to select). Regarding PFC, you are correct, this switch-mode converter will require active PFC (PF ~ 0.97) to be able to achieve the 25A.

[Crazy Ape]

Regarding cell balancing, the cell balancing is being taken care of by a separate board, at the battery itself. Each individual cell voltage is being monitored to a 1mV accuracy by an AFE and MCU. As with any lithium charger, when any one cell gets close to 4.200V, charging will change from constant-current mode to constant-voltage mode so as to avoid an over-voltage condition (MCU will control charger remotely). When the highest voltage cell actually reaches 4.200V, it will be bypassed with a FET and power dissipating resistor in series. The FET will be switched on/off with some hysteresis to maintain 4.200V across the cell, until the rest of the cells catch up. This stage of the charging process is rather slow, compared to the constant-current charging stage, which will pump out the full 30A.

AG6QR, you brought up a good point that UL dictates I cannot exceed 80% of the branch circuit rating. 120V*20A*0.8 = 1920W. Assuming 90% efficiency, 1920W * 0.9 =  1728W. 1728W/60V = 28.8A. So, I may need to relax my 30A requirement to, perhaps 25A.

Achmed99, some good points also...I would like to design it for a 20A branch circuit, and perhaps have a variant for a 15A branch circuit (or, a switch on the back to select). Regarding PFC, you are correct, this switch-mode converter will require active PFC (PF ~ 0.97) to be able to achieve the 25A.

Parts of quote reposted in red italics.

What happens in the event the the remote MCU connection is broken (or MCU failure)?

What happens if all but one cell is in bypass and the remaining cell has only partial charge. The user of device could stop charging at any time, particularly if it's taking time and they are in a hurry. A low cell in a series configuration is very bad in high current situations, it will run down first, and then start charging in reverse polarity. You don't want this.

[Centmo]

Good questions Crazy Ape - I have also thought about this. In the event that the connection between the MCU and charger is broken, the MCU will be able to identify the problem, since it will be able to see the cell voltages and will also be measuring charge current (it has a current sense circuit). If some cells are in bypass, and the charge current is above that which the dissipating resistors can handle (power supply is not dropping output voltage as instructed), it is able to dump the power into its connected load.  I won't get into the specifics, but suffice it to say that it has a connected load which can eat this current safely, and an alarm will be activated to notify the user.

If the user stops the charging process prematurely, leaving one cell at a lower voltage than the others, the system will recognize this and signal an alarm to the user about a battery imbalance. The MCU can decide to discharge the higher-voltage cells to balance the pack, or demand that the pack be fully charged before allowing operation of the load. (The user cannot operate the load without the MCU's approval)

I have been looking for power supplies, and have found many 1U rack-mount units that can supply 0-60V, 25-28A: Eltek, Genesys GEN60-25, Kepco KLN 60-25, Sorensen XG60-28, Amrel SPS60-27. Unfortunately the quotes are coming back in the $2000-$3000 range. I think it's because these are designed for sensitive electronics, so are specially designed for low output ripple? Battery charging I would expect, could handle a noisier supply.

Anyone have any ideas for something a little more....affordable?

[Crazy Ape]

Anyone have any ideas for something a little more....affordable?

There are things like this, but you'd still need to find a source of DC, and who knows if it's specifications are accurate.
http://www.aliexpress.com/item/Free-Shipping-1pc-ZXY6020-CNC-constant-voltage-constant-current-power-supply-module-60V-20A-1200W-high/1222064373.html

[Ericho]

Itech may have somthing in their range

http://www.itech.sh/en/products.jsp?sortid=002

should be below $1000 at least

[NiHaoMike]

http://enginer.us/technologies/
Not sure how much the charger is by itself, might be worth calling them.

[Centmo]

Thanks for the suggestions.

Ericho, unfortunately, it looks like iTech only has a 1200W unit (60V, 20A), or a 3000W unit. I will see how much the 1200W unit is though.

NiHaoMike, it looks like their system is based on Li-Ion only (not LiPo), and will not achieve 60V charging unfortunately. But, it may be worth contacting them to see if they're interested in sharing how they built their charger.

Crazy Ape, I have found that product during my search as well. It is interesting, and worth considering, even if it is only 20A. I will have to look for more details on it.

[AmmoJammo]

Power tool batteries, laptop batteries, none of these break out individual cell taps because cell balancing (in power tool packs) or cell monitoring (in laptop packs, no balancing, just matched cells) is internal.

Can't say I've ever seen a Lithium Polymer powered cordless tool... those things catch on fire if you poke them with a stick 

I do like how this thread only gets half the details included until people see an issue with the original idea 

[Neilm]

A commercial design will have to pass the the relevant safety standards. This includes requirements for protection circuits in the pack. Also, with a pack this large you might run into limits with the hazardous cargoes legislation.

I have seen block diagrams of large battery packs, but they tend to be from chip manufacturers who are selling solutions to it - for example TI have a very large range of chips that are designed to work with each other to do cell balancing, charge regulation, cell temperature monitoring etc. They tend to be solution in chips that are then tested and passed as "safety critical" components. They contain separate circuitry that acts as watch dogs to attempt to ensure it fails safe. Quite often they will use use serial communication (SMbus) to communicate between the battery pack and the charger to regulate charging. It also could go to a micro to allow charge monitoring.

You would then have to produce (or purchase) a 60V 2kW or so mains PSU to power your charger circuit.

[Centmo]

I looked further into the ZXY6020, which Crazy Ape suggested. Turns out that its a buck converter, so in order to get 60V out, I would have to supply at least 60+V in. The DC input voltage range is 13-62VDC. So, I assume that you would need a 62VDC, 25A supply in order to run this thing at 60V, 20A. Good luck finding that.

So, I'm basically back to square one, staring down a $2000 telecom-grade 1.5kW DC supply. (still need to find a price on the 20A iTech unit).

NiHaoMike may be on the right track....I need to see how the EV guys are doing it.

[AmmoJammo]

All you need is two good quality switchmode 30volt, 800watt supplies connected in series. Im sure there's something fairly easily available. Meanwell maybe?

[jabramo]

This?

http://www.ebay.com/itm/Xantrex-XFR60-20-DC-Power-Supply-0-60V-0-20A-XFR-60-20-/181211771612?pt=LH_DefaultDomain_0&hash=item2a311032dc

Made in Canada 

[Centmo]

That Xantrex looks like a nice unit for a one-off, but I need something I can order hundreds of, and all be identical. So, it would have to be a new product I can order again and again.

I checked meanwell, and no 30V DC supply. Connecting AC/DC supplies in series makes me a little nervous too, unless the manufacturer explicitly says you can do so.

[Crazy Ape]

Both of these match the thread title.

http://www.aliexpress.com/item/KXN-6030D-High-Power-Switching-Power-Supply-adjustable-DC-60V-30A/1388979807.html
http://www.aliexpress.com/item/0-60V-0-30A-Maisen-MP6030D-Switching-DC-Power-Supply-Free-Shipping-by-DHL-UPS-TNT/704637719.html

[AmmoJammo]

I checked meanwell, and no 30V DC supply. Connecting AC/DC supplies in series makes me a little nervous too, unless the manufacturer explicitly says you can do so.

SP-750-27 is a 27volt, 750watt supply that can be adjusted upto 30volts

http://www.mean-well.com.au/shop/sp-750-750w-single-output-power-supply/926-sp-750-27.html

I assume they can be connected in series, but it might be worth while contacting Meanwell

I didn't realise they were so expensive new though! I paid like $35 each for some 800watt meanwell supplies :p

[Centmo]

Thanks Crazy Ape...great price on those units. I wonder if they can run on 110V. One of them says so, but gives some conflicting information. I also wonder if these would be UL/CSA approved.

AmmoJammo...good point on the adjustable output of the 27V unit. But yes, they do seem pretty pricey for a fixed output supply. Maybe meanwell is cashing in on the reputation they've built up.

[AmmoJammo]

At the end of the day, if you need availability, and reliability, I'd be going with the Meanwell. I assume the intention is to build the power supply into another larger device?

[Jon86]

Both of these match the thread title.

http://www.aliexpress.com/item/KXN-6030D-High-Power-Switching-Power-Supply-adjustable-DC-60V-30A/1388979807.html
http://www.aliexpress.com/item/0-60V-0-30A-Maisen-MP6030D-Switching-DC-Power-Supply-Free-Shipping-by-DHL-UPS-TNT/704637719.html

The chinglish on that second one is bloody awful...

[Crazy Ape]

Both of these match the thread title.

http://www.aliexpress.com/item/KXN-6030D-High-Power-Switching-Power-Supply-adjustable-DC-60V-30A/1388979807.html
http://www.aliexpress.com/item/0-60V-0-30A-Maisen-MP6030D-Switching-DC-Power-Supply-Free-Shipping-by-DHL-UPS-TNT/704637719.html

The chinglish on that second one is bloody awful...

Indeed, but it could have been worse.
http://boingboing.net/2008/07/15/chinese-restaurant-c.html

[Ericho]

Indeed, but it could have been worse.
http://boingboing.net/2008/07/15/chinese-restaurant-c.html

 

I'm currently looking into a MAAS switching power supply for the lab.
They do not go up to 60V but they may still be worth to have a look at, they are cheap

Eric

[The Bart Man]

Hi There,

I think you don't need a power supply but a battery charger!!! You want to charge a battery right?
A power supply doesn't have any current control and when charging a battery; lead, lithium or any other type you NEED current control.

I understand you will have some sort of BMS. This will have to be able to balance the cells and cut of any charger or load to protect the battery from over or undercharging.

There are many chargers available for this voltage and current range. Also OEM probably.

[ee.jmlp]

you need a power supply, but not a voltage source power supply with current limit you need a current source power supply  with voltage limit

Any switched converted will work for you with the right coil. You can use a step down converter. Get a high flux toroid like HF-300060-2 (stack two or even three for 30A) and use no less than 70kHz and no less than 300uH (litz wire), I use them if you need a proof I'll upload a photo

You can use a voltage controlled converter, if you put as load the battery in series with a shunt resistor, the feedback loop senses the voltage between shunt and ground and triying to maintain the voltage constant across the shunt (and so the current) it will maintain the current constant across the battery.

regulator out+ --- +battery- ---(fb loop node)--- shunt resistor --- GND

[mtdoc]

For a basement bargain price on a well made switch mode PSU that can put out up to 50 amps at 60 V Check This Out. Would be a project to adapt to your needs. It would need a transformer to work with 120V and BMS to limit current for LiPos.

I'm adapting one to use on my 48V 436AH AGM solar system battery bank.

[Eviltech]

I have seen pretty beefy toroidal transformers that the second hand AC sellers use to convert the 240VAC to 120VAC so they can run the japanese standart air conditioners. I have seen such that run 3000BTU AC's Those in here are not more than 100-200$ and adding a small DC-DC converter on the output to keep the eficiency and steady the voltage seems a good combo... Those toroids are a bit heavy though...

[peter.mitchell]

How about you buy 14x isolated 5v 30a powersupplies, adjust the output voltage to 4.2v, and stick 0.05 ohm power resistors on the outputs, hook each one up to each individual cell.

Should charge at about 29a~, current limited by the power resistor, and constant voltage of 4.2v, no need to worry about balancing.

http://www.meanwell.com/search/NEL-200/default.htm

http://www.amazon.com/Amico-0-05-0-05R-Aluminum-Resistor/dp/B0087ZCRQK