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QSIMDO
01-01-2013, 09:20 AM
Any recommendations for a 12 volt, 25 amp DC power supply?

It's to run a DC gear motor with 25 amp max draw.

Speed control is not a factor, just on/off running.

TIA.

ikdor
01-01-2013, 09:37 AM
If you're not running it full time, a deep cycle battery and a cheap charger could get you there for not too much cash. Otherwise lots of the computer power supplies will supply that.

Igor

BigJohnT
01-01-2013, 10:08 AM
That's only 300 watts at 12v...

John

MaxHeadRoom
01-01-2013, 10:29 AM
Pick up a suitable wattage Toroid Transformer from Antek, if they don't have the correct rating, put your own winding on, only ~24 turns needed with 50amp bridge, no capacitor needed to run a DC motor.
Max.

bewards
01-01-2013, 10:32 AM
One of the roll around battery charge car starter like the car lots use might do it. Schumacher makes one that advertises 200/100/40/10/2 amp.
I have one that runs 7 50watt 12v lights on my pier so I didn't have to run 110 in conduit along the water.


bedwards

MaxHeadRoom
01-01-2013, 10:46 AM
The thing to watch with battery chargers is only use the most simplest/basic types, controlled charge types, and the ones that sense the charged voltage may not work.
Max.

SteveF
01-01-2013, 12:17 PM
Even the simplest types may not be a good idea.

I went through this last year wanting to use my 12v chain saw sharpener (CSS) in my shop and tried using an older battery charger to power it. The motor in the CSS sounded noticeably rough compared to running it off a battery. Don't have an oscilloscope to measure how smooth the 12v supplied was but I suspect it was not a very constant voltage as a battery wouldn't care.


Steve

Paul Alciatore
01-01-2013, 01:36 PM
Even the simplest types may not be a good idea.

I went through this last year wanting to use my 12v chain saw sharpener (CSS) in my shop and tried using an older battery charger to power it. The motor in the CSS sounded noticeably rough compared to running it off a battery. Don't have an oscilloscope to measure how smooth the 12v supplied was but I suspect it was not a very constant voltage as a battery wouldn't care.


Steve

That's why Igor said to get a charger AND A 12 V BATTERY. The battery acts like a filter instead of using capacitors. And besides, battery chargers are designed to ... wait for it ... wait for it ... wait for it ... CHARGE BATTERIES. They are optimized for that task and it should be no wonder that they may not be good at directly powering a motor.

I also like MaxHeadRoom's transformer and rectifier suggestion, but you will have to package them in something.

Fasttrack
01-01-2013, 05:25 PM
Otherwise lots of the computer power supplies will supply that.

Igor

Yep - you can get a cheap or used computer power supplies just about anywhere. However, keep in mind that the wiring harness and connectors may not be rated for 25 amps. Computer supplies have several pigtails coming out and most range from 5v to 12v. The supply is designed to deliver it's power distributed over all of these pigtails so to get one tap at 25 amps, you may have to break into the box and attach heavier gauge wires to the 12 volt rail or make other modifications. I've got a 500 watt computer power supply around here somewhere that has a 12 volt 20 amp pigtail, which would probably get you close enough if your motor is driving a large load continuously.

tyrone shewlaces
01-01-2013, 05:34 PM
This is usually where I start looking when I need a dedicated power supply.:
http://www.mpja.com/Power-Supplies/departments/1/

If you want to go cheap though, a PC power supply ought to do the trick with just a little hacking.

Scottike
01-01-2013, 07:18 PM
+1 on the PC power supply. A single rail supply rated for 450 watts should give you between 30 - 35 amps on the 12volt rail.
plus give you a source for 5 & 3.3 volt as well. Check the label on the side of the supply - It should give you amperage for the
various voltages on the side of the case.
As shewlaces said it takes a little hacking (leads/jumper for remote on/off sw.,etc.) but it's not difficult.

MaxHeadRoom
01-01-2013, 07:41 PM
PC power supplies are typically high current for the 5v, the 12 is rated at very much less, typically 8 - 12 amps.
Personally I would never use one for a DC motor controller.
Max.

darryl
01-01-2013, 07:45 PM
I think I'd opt for the computer power supply as well. You can take all the 12v output wires and parallel them to get the current. Also parallel the negative wires. You don't have to break into the box at all. But you will need to ensure that the current rating on the 12v output is high enough. Normally you would want a large excess current factor- if the motor is going to draw 25 amps, the supply should be rated at at least 30 amps.

You could opt for the brute force, transformer, rectifier, filter approach, but it will take tens of pounds of parts and will certainly cost. It's easy to get various voltage outputs from a power supply, but where the current requirement is more than 5 amps or so, especially in the 20+ amp range, the parts need to be very beefy.

I would look at the required duty cycle of the motor first, and base the solution on that. A battery and simple charger could be the most viable way to go.

Scottike
01-01-2013, 07:56 PM
The power supply I looked at (just an old spare I have kick'n around)
is rated 33 amp on the +12 rail, 34 amp on the +5, and 28 amp on the +3.3
for a max combined load of 450 watts, and a 60 sec. peak load of 570 watts.
It is (or was in it's day) a quality unit. OCZ brand , Single rail supply.
The old split rail units have a lower amperage output per rail but have mulitple rails.

All12Huskies
01-02-2013, 02:53 AM
See if you can find some ham radio operators in your area, especially ones that own/operate repeaters. I have 4 12v, 50amp continuious duty power supplies stacked in my shed. If you were closer I'd let you have one for scrap $$, but I think shipping would be prohibitive........

Just my $0.02

ikdor
01-02-2013, 02:58 AM
A decade ago the 12V rail was weak on computer power supplies, but current systems use quite a lot on that rail so it has plenty of oomph.
Just note that you need to tell the power supply to switch on (connect the green wire to ground IIRC). Check online how people wire them as a bench supply.

Igor

hitnmiss
01-02-2013, 09:13 AM
quick (very quick) search on ebay found this:

http://www.ebay.com/itm/36-AMP-13-8V-Power-Supply-Adjustable-Voltage-12-Volts-05-/170966592378?pt=LH_DefaultDomain_0&hash=item27ce672b7a

QSIMDO
01-02-2013, 09:18 AM
quick (very quick) search on ebay found this:

http://www.ebay.com/itm/36-AMP-13-8V-Power-Supply-Adjustable-Voltage-12-Volts-05-/170966592378?pt=LH_DefaultDomain_0&hash=item27ce672b7a

Thanks mate!
Fingers crossed...

Paul Alciatore
01-02-2013, 01:02 PM
If you just want to power a DC motor, a fancy, regulated, switching power supply (computer or otherwise) is WAY overkill. These devices have dozens of parts, all of which have an individual probability of failure. These failure probabilities add together to increase the overall chances of a problem. As said before, a simple transformer and bridge rectifier will do the job and be a LOT more reliable.

And if you search, you can find bargains either way.

mickeyf
01-02-2013, 10:08 PM
A couple more points about PC power supplies.

1) The stated amperage rating for each voltage output does not mean that you can draw that much on all outputs simultaneously - Just that that's the maximum for that particular output.
2) There is a "power good" line that you will have to hold low to enable any output at all.
3) These are switching power supplies, and require a (possibly dummy) load, possibly on every output, depending on the particular design.
4) As stated, generally the 5V output is the highest rated, the 12V does not come close to 25A even on a relatively high-wattage unit.

MaxHeadRoom
01-02-2013, 10:32 PM
One other thing to consider, when connecting a DC motor full on, rather than any ramp up, the motor presents a virtual dead short across the supply until the generated DC opposes the supply, with a start-on-load condition the length of high current will be extended.
Max.

QSIMDO
01-03-2013, 09:17 AM
If you just want to power a DC motor, a fancy, regulated, switching power supply (computer or otherwise) is WAY overkill. These devices have dozens of parts, all of which have an individual probability of failure. These failure probabilities add together to increase the overall chances of a problem. As said before, a simple transformer and bridge rectifier will do the job and be a LOT more reliable.

And if you search, you can find bargains either way.

I wouldn't know the first damn thing about putting something like that together, but I'd sure give it a shot if someone would draw the schematic and provide the component values!

It was my brother that did all the electronic stuff. ;)

MaxHeadRoom
01-03-2013, 10:37 AM
See Q 6&7.
http://www.allaboutcircuits.com/worksheets/supply1.html
Two components, transformer and bridge rectifier, plus switch.
Digikey for 50amp bridge and Antek for the Toroid transformer, he may have one at the rating or put one together for you, he manuf. Toroids and supplies.
He lists on ebay as Jonango.
Max.

QSIMDO
01-03-2013, 12:46 PM
See Q 6&7.
http://www.allaboutcircuits.com/worksheets/supply1.html
Two components, transformer and bridge rectifier, plus switch.
Digikey for 50amp bridge and Antek for the Toroid transformer, he may have one at the rating or put one together for you, he manuf. Toroids and supplies.
He lists on ebay as Jonango.
Max.

Thanks Max.
I appreciate your help.