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Old 01-24-2006, 03:40 PM   #1
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Default Converting a PC Power supply to use with RC Charger

Hello, i would liek to convery my ATX pc power supply to use with my duratrax Intellipeak (on its way) charger. Now here is a tutorial i found on the web:
http://reckerclub.tripod.com/id105.html

Now for the people that have the done this, is this process correct? I also have a few questions if you dont mind. Thanks
Ron
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Old 01-24-2006, 03:50 PM   #2
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Looks about right. I suggest getting atleast 400 watt PS or even a 500 watter as you might even get away without using a resistor to bump up the voltage. I have also seen those mini PS they now have for smaller computer cases which looks more compact.
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Old 01-24-2006, 03:51 PM   #3
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Use search, I got some good results.

But that process is almost exact.
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Old 01-24-2006, 03:59 PM   #4
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perfect! the psu i have is a 450 watter, so i think iam good? I just have a few questions, I should test for voltage first? And, what he did, is he cut the wires on one psu, and then used the other psu to show the voltage using the resistors. Now, if i cut the wires, where will the resistor go? should i leave one connector to use with a resistor? and what is i put more yellow wires together? will that increase the voltage or the amps? thanks
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Old 01-24-2006, 04:09 PM   #5
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From memory the resistors go to the 5 volts line. Voltage won't go up by joining the 12 volts line but its good to have atleast more than one.

Leave atleast 10 wires for each 5 , 12 and negative line. That should be enough and also makes it alot cleaner. Cut everything else down to its root
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Old 01-24-2006, 04:14 PM   #6
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I modified a 450watt PC power supply to use with my ICE and a Integy 16X8v6. The PC power supply I got has 32amp max on the 12v line. I didn't use a resistor to bump up the voltage, but I have absolutely no problem powering both charger plus a few other fans.

I was just charging with both chargers at 7 amps and with a few fans turned on. It work perfectly even though on the ICE it shows that the input voltage was 10.99v.
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Old 01-24-2006, 08:26 PM   #7
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I built one of these and it is working fine.

I bundled 4 yellow wires to the 12V+, 4 black for 12V-, 4 red for 5V+ and 4 black for 5V- and connected each of those to a banana plug. I added two 10 ohm resistors in parallel across the 5V + and - lines for the load.

My 12 V lines read 12.05 V, but when I run my charger, this voltage drops to about 11.6V (Duratrax Intellipeak Digital). Charger seems to run fine.

Follow all instructions, be careful, and build yourself a decent power supply for just a few bucks.
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Old 01-24-2006, 09:36 PM   #8
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Bundling more yellow wires together will not do anything for increasing voltage. It will increase the amount of current that will be able to flow out of your power supply.

An analogy that is often used is to think of thickness of the wire (or number of wires) like the cross section of a river: the bigger the cross section, the more water (current) can flow through the river.

A 10 amp power supply will still be 10 amps, but it will flow more efficiently to your charger through 4 wires than through 1.

Hope that makes sense. I'm sure someone else can probably say it better. The bottom line is bundle 3 or 4 wires together.
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Old 01-25-2006, 12:42 AM   #9
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I also have modified some PC PSU's just put a resistor between 5 volts and ground, and also between 3,3v and ground.
Found at my PSU datasheet that the minimum currents were 1 amps out of 5 volt and 0,3 amps out of 3,3v
And you have to connect the power on wire to ground for the psu to switch on.

works ok, but sometimes one of my psu's shut down in error.
Think that's caused by the effect that psu's are protected for large current fluctuations.
When i pull of a battery which is at charge on my novak millennium of run a powerful motor on the much more motor master the PSU occasionally dies.

Futhermore it is a very cheap method for power, mainy use is for one charger and tyre warmers and fans, for the others i have a Much more PSU...

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Old 01-25-2006, 01:16 AM   #10
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Quote:
Originally Posted by Erikderaaf
works ok, but sometimes one of my psu's shut down in error.
Think that's caused by the effect that psu's are protected for large current fluctuations.
When i pull of a battery which is at charge on my novak millennium of run a powerful motor on the much more motor master the PSU occasionally dies.
That's normal if youre running an ATX power supply as most of them have inbuilt overload protection.

Usually there is no problem running any motor off the 3.3v line, but if you run a Mod on the 5v line (especially if also charging at the same time) then it can overload and switch off.
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Old 01-25-2006, 04:09 AM   #11
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The resistors are not used to bump up voltage but to place a small load on the psu. They do not like being run with no load on them.

You should use something like a 25watt 20r for 12v rail and a 25watt 6r for the 5v rail. These should be connected directly between one ground wire and the corresponding 12v (yellow) or 5v (red) wire.

I have used thes types of psu for many applications in the past and they work very well for running charges etc. Just recently built on up (480w Hiper atx) which I ran for the first time at the weekend. It ran two people charging, motor coolers, soldering iron and lathe with no problems.

I prefer to dissassemble the psu and re wire directly on the board to a connector mounted on the case. I then use a mating connector and cable up to a breakout box sitting on the table so the psu can sit underneath out of the way.

I would however recommend that you DO NOT take the psu to pieces unless you are very experienced in electronics as they can be very dangerous. A much safer option is to use the supplied cables.
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Old 01-25-2006, 12:49 PM   #12
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When I built my first one (using instructions off rcrcacechat) I used a resistor on the 12v line - but since then I've discovered that it isn't necessary as long as there is a load on the 5v line.

I've found that the actual value of the resistor/s vary greatly with the brand/quality/wattage of the PSU used.

On my cheap PSU, I could not get enough volts out of the 12v line when using a 6 ohm resistor, and eventually had to go to a 2 ohm resistor to keep the 12v line above 12v under load.
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Old 01-25-2006, 05:38 PM   #13
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Mine has been very touchy.....Sometimes it will just flash the fan for a half second and not turn on. I have to let the caps drain then try again. Getting to be pain in the butt. Any idea why it's doing this and how to stop it? I have a small red bulb on 1 set of 5 volt lines and a heatsink resistor on the other set. I also have to have my charger or motor checker plugged in before I try to turn it on or it just shuts down. Any ideas or should I scrap it?
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Old 01-25-2006, 06:34 PM   #14
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Is the PSU new? - if it's 2nd hand it may simply be stuffed.

Is it an ATX type? If it is, have you joined the green wire to one of the black wires?

How much load do the resistor and bulb put on the PSU?
What is the wattage rating of the bulb and ohms value of the resistor?

Once you've got it switched on, read the vollts on the 12v line.

Then start charging a battery at 5 amps and take another reading on the 12v line. What is that reading?

The fact that yours doesn't seem to stay on unless it is pre-loaded (with your charger etc) seems to indicate that the 5v load isn't good enough.
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Old 01-25-2006, 08:08 PM   #15
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It is a 12volt bulb on the 5 volt line, and a 1 ohm resistor on the 5 volt line. When it stays on, I can charge a battery at 6 amps and break in a motor etc. It is a 3oowatt supply that was new.
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