Author Topic: high power-ish power supply  (Read 5223 times)

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Offline FrankT

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high power-ish power supply
« on: April 23, 2015, 06:34:58 am »
I'm playing around with brushless RC motors.  Some of the high voltage ones - 50v 100amps ~ 5kW.

I suspect these numbers are BS as their wires are too thin and I suspect they'd melt, but I'd like to try to at least power them up to 1.5kW but I'm not sure what the best choice for PS is.

1) Aliexpress 1500W 48V LED switch mode power supply (http://www.aliexpress.com/store/product/Free-shipping-LED-power-supply-48V-30A-1500W-CE-ROHS-certification-By-sending-the-terminal-block/614366_762829597.html)
2) Paralleling smaller 500VA transformers then adding a bridge rectifier and caps. http://www.altronics.com.au/p/m5730-powertran-30-30-500va-toroidal-transformer/
3) Winding my own 1500VA http://www.ebay.com.au/itm/Toroidal-laminated-core-for-AC-power-transformer-1500VA-/171764320687?pt=LH_DefaultDomain_0&hash=item27fdf389af  (He also has larger ones.  I'm not sure where I'll find thick enamelled copper wire.).

Any thoughts?

As this is to power a motor, it doesn't have to be too clean.
 

Offline electr_peter

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Re: high power-ish power supply
« Reply #1 on: April 23, 2015, 07:25:39 am »
If you want to get full and consistent power, use Li-ion or Pb batteries - much better current capacity than any comparable size power supply.

I am not sure why you want to limit power to 1.5 kW. Those supplies you listed seems to have 1.5kW available as max rating - you have to add 20-40% nonsense and/or safety factor and get only 1-1.2 kW. 1500VA transformer also does not equal 1.5kW power.
I suggest getting something more powerful and reliable.
 

Offline PSR B1257

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Re: high power-ish power supply
« Reply #2 on: April 23, 2015, 07:43:33 am »
This one should be not bad http://www.us.tdk-lambda.com/hp/product_html/genesys2u5.htm  8)

Quote
where I'll find thick enamelled copper wire.
Typicly there are multiple thinner wires in parallel. But I would not reccomend to build your own high power transformer, especially not a single phase one. If you need such power, you should go for a three phase (auto) transformer. Through a 6 puls rectifier you get a almost ideal DC voltage.
In theory, there is no difference between theory and practice. But, in practice, there is.
 

Offline peter.mitchell

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Re: high power-ish power supply
« Reply #3 on: April 23, 2015, 07:44:48 am »
here is an option;

go on ebay, find high power used server power supplies, disconnect their negative output from chassis earth and put them in series - this is fairly safe, as they are all fully isolated, very well constructed designs, and their chassis is still connected to mains earth. as each supply is its own separate converter, you can supply each unit with its own connection to mains, allowing you to spread the several kW load across multiple circuits. Additionally, they have very fast acting built in OCP, so if you short the outputs accidentally you aren't as likely to end up with a smouldering mess.

2x http://www.ebay.com.au/itm/301593331744
2x http://www.ebay.com.au/itm/121624371980


This is just an option. This is given with no warranty, nor is any implied. I am not responsible for your actions etc.
 

Offline FrankT

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Re: high power-ish power supply
« Reply #4 on: April 23, 2015, 08:15:56 am »
Thanks for the replies.

Firstly I should have mentioned "cheap" as a requirement ($ hundreds, not $ thousands).
And secondly, the motor will be driving a CNC spindle, so rechargeable batteries aren't a long term solution.

I like those server power supplies - 12.2V 147.5A.  Originally I started looking at high voltage motors (around 40v) because I didn't think I could provide 2kW at 12v ~160A, but maybe that is an option.

Thanks,
Frank
 

Offline peter.mitchell

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Re: high power-ish power supply
« Reply #5 on: April 23, 2015, 08:36:56 am »
As you can easily isolate the outputs and slightly trim the output voltages i'd expect you to be able to get a reliable 50v+ at 100+A from a setup like that if you got 4 units.
 

Offline Psi

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Re: high power-ish power supply
« Reply #6 on: April 23, 2015, 08:39:33 am »
I'm playing around with brushless RC motors.  Some of the high voltage ones - 50v 100amps ~ 5kW.

I suspect these numbers are BS as their wires are too thin and I suspect they'd melt, but I'd like to try to at least power them up to 1.5kW but I'm not sure what the best choice for PS is.

They can handle a fair bit.

I was pushing 1kW through this $20 875W rated RC brushless motor for a while.
http://www.hobbyking.com/hobbyking/store/__15169__NTM_Prop_Drive_Series_35_36A_1800Kv_875w.html

RC plane worked awesome for ~9x 20min flights (with <5sec speed runs at 1kw) before it smoked itself and left a beautiful white bloom across the sky. (was totally worth it)



« Last Edit: April 23, 2015, 08:41:49 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline PSR B1257

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Re: high power-ish power supply
« Reply #7 on: April 23, 2015, 09:41:15 am »
Quote
the motor will be driving a CNC spindle, so rechargeable batteries aren't a long term solution.
And the BLDC motor most likley neither.
In theory, there is no difference between theory and practice. But, in practice, there is.
 

Offline rob77

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Re: high power-ish power supply
« Reply #8 on: April 23, 2015, 01:47:49 pm »
i don't get th epoint here...
why to spend money on a powerfull RC BLDC + ESC + powersupply if the goal is to have a CNC spindle ? it's far far more efficient to buy a spindle suitable for CNC. i would rather buy a regular 220V AC driven CNC spindle with quality bearings rather than spending the money on something not suitable.
the RC grade BLDC motors are useless for CNC - (not acceptable outrun/eccentricity, low grade bearings...etc..)
 

Offline PeterFW

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Re: high power-ish power supply
« Reply #9 on: April 23, 2015, 02:13:21 pm »
Firstly I should have mentioned "cheap" as a requirement ($ hundreds, not $ thousands).
And secondly, the motor will be driving a CNC spindle

You will not want to hear that but starting at 150 Euros you get complete 1KW motors with collets and mounting brackets that will work in most home CNC mills without anny modifications. You just have to screw it to the gantry, put the right collet in the chuck and you are good to go.
They are designed to take the lateral force and run reasonably true.
I can drill 0.6mm holes without shattering the bit with a Kress FME1050.

And if not, real small lathe spindles are only in the 300 Euro range, iirc.
 

Offline mrflibble

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Re: high power-ish power supply
« Reply #10 on: April 23, 2015, 02:33:00 pm »
go on ebay, find high power used server power supplies, disconnect their negative output from chassis earth and put them in series - this is fairly safe, as they are all fully isolated, very well constructed designs, and their chassis is still connected to mains earth. as each supply is its own separate converter, you can supply each unit with its own connection to mains, allowing you to spread the several kW load across multiple circuits. Additionally, they have very fast acting built in OCP, so if you short the outputs accidentally you aren't as likely to end up with a smouldering mess.
Seconded. :-+

I use 4 leftover dodgy-but-not-too-dodgy PSUs in series like this. Makes a nice power supply for messing about with motors. The one thing you do have to be aware of is regenerative braking. If you rapidly decelerate, then your motor suddenly decides to explore new career options as a generator. So the excess voltage gets dumped on top of the rail, and your typical computer PSU doesn't really like that. But luckily this will not cause any lasting damage, it will just trip the OCP. So if this happens a few times while experimenting, no problem. If it happens more often, then that is just a hint that you should build an external brake circuit. ;)

You will not want to hear that but starting at 150 Euros you get complete 1KW motors with collets and mounting brackets that will work in most home CNC mills without anny modifications. You just have to screw it to the gantry, put the right collet in the chuck and you are good to go.
It's been a while since I last looked into it. Back then it was still too expensive for my hobby use, but maybe now prices have come down. If you have some links to examples of those 1 kW motors, that would be much appreciated. :)

 

Offline PeterFW

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Re: high power-ish power supply
« Reply #11 on: April 23, 2015, 02:40:29 pm »
It's been a while since I last looked into it. Back then it was still too expensive for my hobby use, but maybe now prices have come down. If you have some links to examples of those 1 kW motors, that would be much appreciated. :)

I bought mine... oh... a long time ago, but i got the FME800, not the FME1050.

This one is very popular for small CNC mills, there you get even the brackets:
https://damencnc.com/en/tools/kress/kress-milling-motor

Edit: They have "cheap" spindles too:
https://damencnc.com/en/tools/teknomotor/electrospindle

That is plenty of power for non-iron metals, shure you can not run it a 10cm/s in a block of 7075 but they will do the job just fine.
Since i could not afford a CNC i have to hand crank annyway :-)
« Last Edit: April 23, 2015, 02:43:39 pm by PeterFW »
 

Offline mrflibble

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Re: high power-ish power supply
« Reply #12 on: April 23, 2015, 04:23:52 pm »
Thanks. :)

And cheap spindles was indeed what I was looking for, I wasn't clear enough in my question. And looks like that's still 400+ (ex VAT), darnit! Still, that damen cnc site has some nice goodies. Must ... close ... browser tab.
 

Offline PeterFW

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Re: high power-ish power supply
« Reply #13 on: April 23, 2015, 06:29:32 pm »
And cheap spindles was indeed what I was looking for

Not saying you are dooing annything wrong, im just curious, why do you want a "proper spindle"? :)

The runout of the kress is >0.01mm with a proper collet, at least thats what the quick google search said (i am too cheap to buy a dial indicator myself :'( )

The bearings in a proper spindle will be much better in the long run, but as long as you just mill ne-metals...

Geetings,
Peter
 

Offline FrankT

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Re: high power-ish power supply
« Reply #14 on: April 23, 2015, 08:14:55 pm »
The die grinder as a spindle are great when the material you are cutting is can be cut at high speed (20krpm), but if you need to cut harder material, or use a larger cutter, you need to drop the rpm below 5k.  These machines stall at low rpm.

I'm tinkering with using the motor either via pulley (2:1 ratio), or a "low" speed 5krpm 5kw direct drive of a spindle.

The example below is an inrunner, with a straight shank ER11 replacing the existing shaft.  The end will be machined to hold 2 angular contact bearings.

This is for a cheap spindle (compared to $5k industrial spindle).  I want to machine steel (1/4 carbide cutters at about 2-5krpm) and aluminium/plastic etc at 25krpm.  I may need 2 spindles for that, but if this design works that will be cheap.

There are some examples on the net showing other designs like this.
 

Offline PeterFW

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Re: high power-ish power supply
« Reply #15 on: April 23, 2015, 08:41:20 pm »
The die grinder as a spindle are great when the material you are cutting is can be cut at high speed (20krpm), but if you need to cut harder material, or use a larger cutter, you need to drop the rpm below 5k.  These machines stall at low rpm.

Ah... ok, but the CNC spindles are all designed for high RPM, at least as far as i know.
I thought that was the idea behind a spindle, to run at very high rpm.

Low RPM usually has another motor and/or gears.
At least everything i have come across that was supposed to mill steel never had a high rpm motor.

Might i ask, do you want to build the CNC machine yourself? Last year i had plans to buy a gantry cnc mill wich could to light work on steel for about 5K to 6K Euro and could not find one that was sturdy enough.
 

Offline FrankT

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Re: high power-ish power supply
« Reply #16 on: April 24, 2015, 02:38:16 am »
Might i ask, do you want to build the CNC machine yourself? Last year i had plans to buy a gantry cnc mill wich could to light work on steel for about 5K to 6K Euro and could not find one that was sturdy enough.

That's exactly what I want to do.  Currently I have a CNC router.  I do wood, and PCBs on it.  I can also machine aluminium but it sprays chips all around the room.  If I try to use larger cutter 1/4" or more, the aluminium sticks to the cutters and they snap off, unless I sit there and spray it with WD40  - that becomes tiring. 

I also have a manual mill-drill on which I do the heavy work on.

I want to build a 5-axis mini-gantry mill.  Something that is self enclosed so I can use flood coolant and not worry about bits breaking and not flooding my room.  Automatic tool changer too, but I can't find something small.  You can get ATC belt drive spindles on Aliexpress starting ~$700 but for milling capable bearing models its over $1500.  For a complete powered ATC its over $3k with ISO30/ISO40 tool holders.

I'm planning to do something like this...

http://www.cnczone.com/forums/linear-and-rotary-motion/72261-backlash-free-rotary-table-post1574382.html#post1574382

There's a lot of dreaming in there.
 


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