Connecting a couple of 12Volt Computer Power Supplys together to get 24 Volts

[linuxpower]

Hi,
I am currently working through the "Build Up" to a project. What I am wanting to do is to build a remote controller car/truck which is controllable over wireless networking (Complete with web cam). The Wireless control bit I have sorted out, the problem I am having is I want to use 24Volt motors as they offer a good torque/cost ratio. I will be needing to have a power supply on the vehicle to run the motherboard. This Brings me to my question:

If I have two computer power supplies on the "Vehicle" is it possible to wire the 12Volt rails in each one to get 24 Volts on the motor. I have an idea that if I were to put a diode on each line would this deliver 24 Volts to the motor without "cooking/hurting" the power supplies.

Thanks

 

[3lectrokid]

this is generally not possible. this is because computer power supplies are not line isolated. this means that the output of the power supplies ground is connected to your house ground.

i guess you are thinking about putting the power supplies in series to acheive your goal. however as i said earlier connecting the 12v to the other supplies ground will efectivly be a short circuit cutting power to the supply.

do not despair though because depending on the amperage there is a -12v line also so if you use the +12v and -12v line it will equal 24v. this is not really a good option though because the -12v line cannot take much current. look at the big sticker on your power supply

dave

 

[cowana]

Usually the -12v line is limitted to something small like 500mA.

However, PC power supplies offer so much current on the 12v line, I'd have thought you could run some pretty beefy 12v motors from them.

Andrew

 

[linuxpower]

Thanks for the replies,
What I was hoping to do was to wire a diode to the +12volt Line from Power Supply A and a diode to the +12volt Line from Power Supply B. These Lines would then be connected to the Motor. Same would be done for the negative line. Having the diodes in the lines, shouldn't this stop the power supplies shorting out?

Thanks

 

[Boncuk]

Hi,

Laptop power supplies are normally primary switch mode power supplies.

You might check if they are isolated from mains by measuring conductivity between the mains power plug and the low voltage output.

If there is no conductivity you can wire the outputs in series for 24V.

I assume that both power supplies have the same power output. If not the maximum load depends on the weakest power supply used.

Boncuk

 

[ben7]

Thanks for the replies,
What I was hoping to do was to wire a diode to the +12volt Line from Power Supply A and a diode to the +12volt Line from Power Supply B. These Lines would then be connected to the Motor. Same would be done for the negative line. Having the diodes in the lines, shouldn't this stop the power supplies shorting out?

Thanks

That won't work! You'll have +12volts with double the amps output. You can however put the power supplies in series.

 

[ben7]

this is generally not possible. this is because computer power supplies are not line isolated. this means that the output of the power supplies ground is connected to your house ground.

I've taken many computer power supplies apart and they all seem to have the output ground connected right to the mains power ground via the metal cover too.

 

[tcmtech]

So for the more obvious question, where is the higher voltage for the input side power coming from to power the computer power supplies on the mobile vehicle?

 

[ben7]

Probably from an invertor.

 

[linuxpower]

Yea, the idea was to use an inverter from a 12 volt battery. I am thinking that an easy and not two expensive way out of this would be to buy 2*12Volt batteries and wire them in parallel for the inverter, then wire then in series to the motors.

Thanks for all the Help

 

[4pyros]

You will want to rethink that all for effechency. The motors should have thare own power source, so if the batterys die the computer will not stop. Your computer should run off low voltage DC, inverters wast alot of power. Trying to run motors off your computer power supply that is run off a inverter all from one 12 volt battery is just wrong in so many ways. Can you use a lap top and run it off its own battery? Andy

 

[linuxpower]

Yea, I have a laptop that I can use, my only reason why I don't really want to is that I need my laptop for everyday use.
However as I will be using a linux non-gui system it is possible that I could get a cheapy laptop with a busted screen and use that.
Then depending on the battery condition in the laptop I could get one of those cheap laptop car chargers from ebay and just connect it to the 12Volt battery/s.

Thanks for the Ideas

 

[engineernate2782]

Depending on your budget there are ATX power supplies available with a 24Vdc input and standard power supply outputs for use in marine or renewable energy applications. This would allow for 24V motors and remove the necessity of an inverter.

 

[4pyros]

You should still have separate supplys for the motors and logic. Andy