Computer Power Supply?

[rob_s]

I've been considering a Duratrax Ice charger, but am not too keen on having to spring for the seperate power supply. I've seen mention made of using a computer power supply, and I just so happen to have one lying around. My question is, how do I go about doing this, and what are the minimum specs I need on the computer power supply for it to work?

My particular power supply has a ton of wires sticking out of it, and I'm not sure where to begin.

[DTL]

Try this link
http://web2.murraystate.edu/andy.batts/ps/powersupply.htm

[MrCrash]

Before you start tearing into it, check how many amps it has on the +12v line.

[rob_s]

I'll have to check out the PS when I get home tomorrow or Friday. I may have to post a pic of the label as from what I recall it made little to no sense to me.

DTL, thanks for the link. It looks like it may be more involved than I want to deal with, but we'll see.

[awnelson]

Another thing to consider would be the MRC charger that does everything the ICE does but includes a temp probe and P/S for not much more money.

[rob_s]

Another thing to consider would be the MRC charger that does everything the ICE does but includes a temp probe and P/S for not much more money.
I'm looking into that as well. ;
http://forums.radiocontrolzone.com/showthread.php?t=236222&page=2

[Demon-TC3]

the modification is not very difficult, everything is obviouse once youve cracked it open.

I converted one, looks awsome, works a charm...all i need is an LED fan and im done!

[chewie]

normally its the yellow wire thats +12 v.. what you do is if it has a power turnon.. if there is a green wire.. put it on a switch that runs to the ground(black wires) thats the remote turn on.

[Demon-TC3]

there is a little more to it than that, if you want the PSU to provide more current you gota install some resistors, (i went with 6x 10watt 10Ohm resistors) and out of a 250W psu im getting at least 15A

[MrCrash]

The big thing is putting a load on the +5v line so that you keep the +12v line within a safe area. Unless the lines are independently regulated, having no load on one will cause the other to drop really low.

[c2s]

How is the longevity?

[Demon-TC3]

the what?

If you mean the lifespan, i have run mine for about....id say about a year now and has never let me down, very safe if done properly.

i will get pics up as soon as im back from the meeting tonight, seems allot of people are intrested.

[rob_s]

Here's the power supply I have. You can see from the sheer number of wires why I am a bit overwhelmed.

http://i134.photobucket.com/albums/q111/rob_s/RC/IMG_0797.jpg

http://i134.photobucket.com/albums/q111/rob_s/RC/IMG_0799.jpg

[chestnut007]

you can do what I did and buy a pre-modded pc power supply on ebay like this one (http://cgi.ebay.com/34-amp-12-5-volt-DC-power-supply-for-battery-chargers_W0QQitemZ150122723431QQihZ005QQcategoryZ3 4063QQrdZ1QQcmdZViewItem)

[MrCrash]

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

I just used the +12v line, and wired in a large resister to the +5v line. It works perfectly.

[Demon-TC3]

thats a normal ammount of wires, dont worry.
sort them out into wires of the same color and its allot less overwhelming.


The only thing i would identify is that you have no grills to cable tie resistors to...that may be a problem.
i will get a pic of my PSU up later on tonight.

[rob_s]

There are grilles on the sides, and an internal fan.

[Demon-TC3]

OK here it is, not plugged up to anything...

Basic mod, installed 6x 10watt 10Ohm resistors, a little re-wiring and installing the bananna plugs but thats about it...other than covering it in Vynal and attaching some small rubber feet onto it:

http://img518.imageshack.us/img518/6341/pics001ej9.jpg

I have not covered the very top where the resistors are as i didnt want the smell of burning Vynal should they resistors get hot (they do sometimes)

[Demon-TC3]

Just made another one yesterday (for a friend) and completed mine.

the actual modification is installing 3 lots of 2 x 10Ohm 10Watt resistors in parallel into the 5v lines. this will bring up the current in the 12v line.

Now i have an LED fan wired up to the 12v line (rather than 5 as standard) so it stays much cooler - will get a pic up later of it wired up and working.

[quick5pnt0]

Can anyone provide a wiring diagram for the resistors? Is it nothing more than wiring the resistors across the +/- 5v wires?

Has anyone tested how much fluctuation there is in the voltage/amperage? I once read that you cannot use an automotive battery charger to run your r/c batery charger because of the voltage fluctuations. I'm just nervous that something like this may burn out my battery charger, like a car charger would.

[Demon-TC3]

What you need to do is wire 2 10 watt 10Ohm resistors in paralell together, connected one side to 2x5V wires and the other side 2x ground wires. you need 3 of that set up (you can get away with 2 if your only using one or maybe 2 chargers at any given time)

The supply is extremely stable, very smooth.
Look on the net for PSU convesion or something on those lines as you need to also wire a Power good wire to a ground wire so it stays on.

[quick5pnt0]

What you need to do is wire 2 10 watt 10Ohm resistors in paralell together, connected one side to 2x5V wires and the other side 2x ground wires. you need 3 of that set up (you can get away with 2 if your only using one or maybe 2 chargers at any given time)

The supply is extremely stable, very smooth.
Look on the net for PSU convesion or something on those lines as you need to also wire a Power good wire to a ground wire so it stays on.

So I would need six of those resistors? The links above only talk about connecting one 10 watt 10 ohm resistor.

Thanks for the response

[Demon-TC3]

yea u need 6 of them, in the links they are far lower current demand opperations, since we need allot of current for things like chargers, we need to create high resistance in the 5v line so the current builds up in the 12v line...sounds stupid but it works (since current takes path with lowest resistance)

So, yea 6 resistors, now the reason you go for 6x 10 ohm resistors rather than 3x 5ohm i think its just so they stay cooler.

Good luck with the conversion.

[quick5pnt0]

Now I see, that makes sense. Thanks for the help.

[quick5pnt0]

Well I got my power supply done, but the amperage is really low. The voltage is rock solid at 12.04 volts, but when measuring the amperage I only get around 4.5 amps. Then when I run my battery charger it'll only charge at around 2.6 amps.

Maybe I missed something so I'll post what I did and if anyone sees anything wrong let me know. I had a brown sensing wire so I connected that with an orange (3.3v) wire as one of the tutorials above states to do. Then I ran six 10w 10ohm resistors, in three groups of two wired between the red (5v) and black (ground) wires. From there I wired up the green wire and a black ground to a switch. There were other wires but I think they were all just the negatives of the power sources (blue -12v, etc)

Any ideas why the amperage is so low?

Thanks again

[guver]

Before you start tearing into it, check how many amps it has on the +12v line.

response to quick5pnt0

I should've mentioned in the early part of this thread that is not uncommon to find out the 12 volt line has half the current of less than the rating plate. It is also typical to get 12 volts or less and the reason you are only getting a couple amps charge might have more to do with the input voltage on the charger than the current capacity of the ps. 4.5 @ 12 volts isn't too bad.

2 of my older ones run about half of the wattage that their supposed to. My latest one runs 200 watts just like the tag shows. go figure. :o

[Demon-TC3]

im not so sure on the sensing wire with orange, i dont remember because i did mine a LONG time ago...
Try removing that connection and see if it helps, if not, remove 3 of the resistors (one from each pair) so the load is on 3 resistors but you get much higher resistance.
this may cause the resistors to get stupidly hot...

It does seem very low current, im getting 14+ from my 240watt PSU meaning you should be getting in the reigon of 16 - 18 from a 300!

[quick5pnt0]

Alright thanks for the replies. I'm going to try removing that sensing wire connection first to see if it helps, otherwise I'll remove a few resistors and let you know how it works out.

[quick5pnt0]

Well I tried everyone I could think of but the amperage never came up. I hooked my charger to it again before and during different attempts to fix it but the charger would never charge above 1amp. I tried connecting and disconnecting the brown sensing wire, and it had no affect either way. I also tried it with three resistors and just one.

I assume the power supply is just defective or not powerful enough. I guess if I ever come across another I'll try again.

[guver]

Your current problem may be directly due to input voltage especially if you are chargeing the max number of cells with a specific charger.

[quick5pnt0]

Your current problem may be directly due to input voltage especially if you are chargeing the max number of cells with a specific charger.

Well the input voltage is over 12v, and I'm only charging 6 cells. The charger I'm also using can be used with 120v AC but I wanted to run it off a power source because then I can charge the batteries at a higher rate (it'll only charge at 3amps with ac power, 5 with dc power) Unfortunately when used with the power supply it will barely crack 1 amp.

[guver]

Ok, it sounds like you have the digital piranha and it will require more voltage , your current is probably enough.

If you can verify it with a 7 or 8 cell pack and the condition gets a lot worse .

Or you can go the other way and try a 3-5 cell pack and see if the condition gets a lot better.