Looking for Brushed DC Motor Supply (~8V 10A)

[metrologist]

Basically, I'm looking for where I may likely salvage an 8V, 10A DC supply (I'm cheap).

I am planning to use a brushed 540 sized RC car motor in a Dremel kind of application. It will be used to drive a small rotary cutting tool through a 1:1 metal gear. I have a decent variety of RC motors from which to choose, "stock" 27 turn to 11 turn performance motors. The load on the cutting tool will generally be light as they are small tools, about 1/8" (3 mm) or less. I do want at least 10k RPM.

The stock motors run fine with my 5V bench supply, but could use a bit more voltage. The performance motors don't quite spin up with 5V. Most of these motors will overheat with a typical 12V supply.

I'm planning a direct connect, no speed control.

[Ian.M]

High current 9V supplies are rare like hen's teeth, as most consumer 9V kit was designed to run from dry batteries in the days before USB 5V and LiPOs took over, so you are lucky if you can even find a 1A one.

Instead I suggest a simple MOSFET + CMOS 555 PWM circuit from a beefy 12V supply.  Use an adequately rated MOSFET + a Schottky diode anti-parallel to the motor to let the current recirculate, PWM it as fast as you can drive the MOSFET without it heating excessively and adjust for 8V average at the motor.  For 10A you'll probably need a MOSFET gate driver chip between the 555 and the MOSFET as the CMOS 555 can only sink/source about 100mA and you need that PWM to be *FAST* due to the relatively low motor inductance to maintain a near-constant motor current.

[Alex Eisenhut]

A nice 2S lipo pack will do fine, and you can get brushed motor controllers real cheap too.

http://www.ebay.ca/itm/320A-Brushed-Speed-Controller-ESC-For-RC-Car-Boat-Truck-Motor-R-C-Hobby-HOT-/161997563512?hash=item25b7cea678:g:XMsAAOSwu1VW2QyC

I don't know, maybe for that price you won't mind speed control, you'll also need something to drive the throttle signal.

[metrologist]

Forgot to mention I need longer duty cycles. About an hour off and on, all day long.

If this works out well, later I'll be putting brushless on this. Don't want to sink a bunch into it at first.

How about a 12V with a high power Zener? Is that just silly?

[Ian.M]

How about a 12V with a high power Zener? Is that just silly?

Really silly.  Even if you do an amplified Zener using a 2N3055 transistor^* with the Zener wired base-collector and 100R base-emitter to give the Zener enough current, it will be dropping 4V at up to 10A so the combo will be dissipating 40W. Better put a *LARGE* heatsink and a PC fan on that!   I don't even want to think about the price of a real 3.9V 40W Zener - if you can even find one.

If/when you go to brushless motors and ESCs, simply select ones designed for operation on up to 4s or 5s LiPO packs (4s doesn't give you much margin for 13.8V opeeration though) and use a 13.8V 10A 'CB'ers' bench PSU.

* Most modern 2N3055 transistors wont hold up at 10A Ic - you have to make sure you get a GENUINE one direct from the official distributor of a known reputable manufacturer or a genuine USA or European made N.O.S one.

[NiHaoMike]

Old PC PSU with output voltages trimmed down?

[Kleinstein]

If it is just a temporary solution, an old PC supply and some 4 V voltage drop might be an option. This could be a kind of simple regulator circuit (a real 2N3055 should be Ok), or just 6-8 beefy diodes.

[metrologist]

I know I have a couple spare PC supplies, so it would be interesting to look into modding one for variable output, as that would be useful in several ways.

I did find a 6.25V supply. I'll have to check into what RPM I can get with that.

I think these motors are actually designed around 7V and for higher current draw, which means I should likely look into gearing it up.

[Euphyllia]

Meanwell makes some nominal 7.5V power supplies that can be trimmed up to your desired voltage. Model SP-100-7.5, SP-320-7.5, etc. Seventy bucks at Mouser, and there are probably cheaper knockoffs of them somewhere.

[All2skitzd]

A computer power supply will put out around 7V when you hook positive to 12v+ (yellow) and negitive to 5V+ (red) and can usually be adjusted out some. An older one would probably be better because a lot of the newer ones will shut off to easy. If you get a ATX power supply that don't have trim pots to adjust it just look at the wires going to the ATX 20 or 24pin connecter and look for one's that have a big wire and small wire in the same pin, cut the small wire and put a 10K VR on it with it set to 0, then turn it on (connect green to black) and slowly adjust the VR

[Ian.M]

Ignore that.  The 5V rail on a PC PSU is not specced to sink current, so the total load you connect between +12V and +5V must *ALWAYS* be less than the existing load on the +5V rail. 

[daqq]

You could abuse VICOR modules - pricey, but worth it.

[metrologist]

I found a TDK RAX12-14K switching supply rated 12V 14A. It adjusts down to 7.65V and up to 13.75V. That's a huge range and should be very well suited for this. Now all I need is to made a final gear spacer and give it a run.

Poor supply running aweful DC motors. Is this a good supply? I'd hate to burn out a good supply doing something silly. I was using it for Ham radio a while back.

http://www.kepcopower.com/specs/raxspecs.pdf

I also found a multiple output switching supply with two 16V 8A, one 24V ?A, and one 6.25V 24A output. I need to find a cord and see if it works.

[metrologist]

My test run revealed 7.95V @ 15.95A, and that is with a wimpy motor. I think this TDK supply will not handle this. My other supply is burned out. 

[Pack34]

Does it have to be really compact?

You could always use one of these cheap SMPS from Amazon and then just trim your output of your motor controller so it doesn't give it the full 12V.

https://www.amazon.com/XINCOL-Switched-Switching-Transformer-Adapter/dp/B01LWUQH3E/ref=sr_1_1?ie=UTF8&qid=1475697528&sr=8-1&keywords=10a+smps

[metrologist]

It does not need to be compact, but my initial guess as to the current requirement was too low.

I have an ATX PC power supply and will see how it goes with the 5V supply - as soon as I figure out how to get it to switch on...

[CM800]

Where are you based? I have a few high current 15V VICOR modules (500W iirc) that would be perfect for this. You can adjust the voltage.

You will need a smoothed 300V input however.

These are used units still attached to the PCB. If you are in the EU I could send you 1 or 2 for £20 + P&P each.

[metrologist]

Thanks for the offer. I had to look up what those were. 300V might be just as hard for me to produce, and I'm in the states.

So, I got the ATX PC supply hooked up and it powers the motors OK, they only hit ~7k RPM. Any kind of load brings the amps up to 15. I think I have one more supply buried around here somewhere, then it's time to hit the surplus store.

[_Wim_]

I would go for a cheap 12V led power supply and put a dimmer in series. Then you have a speed control also. Just do not put it at max speed...

Example of a cheap dimmer that can handle the power: https://www.aliexpress.com/item/LED-Dimmer-DC-12V-24V-30A-360W-Adjustable-Brightness-Lamp-Bulb-Strip-Driver-Single-Color-Light/32728242475.html?spm=2114.01010208.3.369.sqnz71&ws_ab_test=searchweb0_0,searchweb201602_4_10056_10065_10055_10068_10054_10069_10059_10073_10017_10070_10060_10061_10052_10062_10053_10050_10051,searchweb201603_1&btsid=98f6a52a-bdca-45f7-9a08-8bf416725786