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RE: How to convert an ATX power supply to rc use - 10/10/2007 12:00 PM

mrasmm

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quote:

ORIGINAL: Savage03

Just put a load on it with 2 resistors and its showing 12.11v, good grief more?

looks like you put them in series, that should make your voltage go down, run them in parallel and it should make it go up =)

The higher you are above 12v the better you are because chargers run more efficient at higher voltages, which basically means less heat in the charger. As long as you are above 12v though for most chargers you will be good to go =)

As far as amp draw check out the ammeter in your dmm, those are usually rated to 10A, and mine measures about 18 to 20 before the fuse blows =P (shh I didn't tell you that)

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RE: How to convert an ATX power supply to rc use - 10/10/2007 12:02 PM

mrasmm

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quote:

ORIGINAL: NM Bob

Hey Guys, I need some help-I'm making a DC power sourse from a computer power supply. I have read all types of helpfull info and have even done this before but this time I got a Dell power supply ( circa 2000) and I can't figure out which wire I need for on/off function. This model of PS does not follow the industry standards so I don't know what colors to use. Anyone out there have experience with an old Dell?

sounds like that other guy has got you taken care of, but you could also match the wire colors to the molex conntectors, take some readings, and also you could match the 20 pin mobo power connector

that's taken off of this site
http://www.marcee.org/Articles/PCPowerSupply.htm

That's how I ended up doing mine. I jsut cut off the mobo connector and made sure to leave about an inch or two of the color coding in the mobo connector, then make sure to reverse it because you are looking at it from the top instead of the connector side =)

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RE: How to convert an ATX power supply to rc use - 10/10/2007 12:26 PM

Savage03

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quote:

ORIGINAL: mrasmm

looks like you put them in series, that should make your voltage go down, run them in parallel and it should make it go up =)

The higher you are above 12v the better you are because chargers run more efficient at higher voltages, which basically means less heat in the charger. As long as you are above 12v though for most chargers you will be good to go =)

As far as amp draw check out the ammeter in your dmm, those are usually rated to 10A, and mine measures about 18 to 20 before the fuse blows =P (shh I didn't tell you that)

Sorry for the newbness but how do I wire them?

Tried the meter on the 10amp setting and it kicks off my PS, whats that mean? Im sure its more then capable for me, its a 650watt ps and I bought lesser PS alread coverted off a guy on another forum and I run 3 chargers off it with no probs.

< Message edited by Savage03 -- 10/10/2007 3:39 PM >

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RE: How to convert an ATX power supply to rc use - 10/10/2007 7:07 PM

Andrew

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If your DELL powersupply was manufactured between 1996 and 2000, there is a high probability that the PSU is one of the DELL proprietary supplies and that it will not conform to the INTEL Design Guide standards.

The pinouts (colors) that were used in this time frame are:

GRAY -- PS_ON (power supply on) equivalent to ATX standard GREEN. This should be switched or hardwired to GROUND.
BLACK -- ground plane (the same as ATX black)
RED -- +5v rail (the same as ATX red)
YELLOW -- +12v rail (the same as ATX yellow)

Tie the GRAY to GROUND (BLACK) through a switch or hardwire it.

Pre-load the +5v rail with a power resistor (RED to BLACK). Use the highest ohm rating that will give you a satisfactory voltage level on the +12v rail.

Your charger connections (binding posts) will be YELLOW and BLACK.

andrew

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RE: How to convert an ATX power supply to rc use - 10/10/2007 10:56 PM

Savage03

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Ok tried this, just added extra leads off the black and red ones so basically a Y then ran each lead to the resistors, I know get 12.29 with no load and 12.22 with a 5amp load. Need more:?

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RE: How to convert an ATX power supply to rc use - 10/11/2007 10:40 AM

mrasmm

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quote:

ORIGINAL: Savage03

Ok tried this, just added extra leads off the black and red ones so basically a Y then ran each lead to the resistors, I know get 12.29 with no load and 12.22 with a 5amp load. Need more:?

sounds pretty good to me, it's all just about what you want and what you're looking for. If that's close to how many amps you'll be using max on a regular basis then I would probably say that is pretty much good =)

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RE: How to convert an ATX power supply to rc use - 10/11/2007 10:51 AM

Savage03

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Well if I were to wanna run anohter charger off it would it drop below 12v? To be safe I just should add another resistor? Easy enough now that I know how to do it.

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RE: How to convert an ATX power supply to rc use - 10/11/2007 10:55 AM

mrasmm

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I'd just find a good dummy load that is gona pull your max load on the charger (test for verification with a shunt if it's over what your ammeter is capable of, and just see what the voltage comes out to be, if it's below 11 I'd put in another resistor =) If you don't want to go to all of that, probably just put in another one =) make sure they are in parallel, because series actually adds the resistive capacities together and would go the opposite way that you are looking for

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RE: How to convert an ATX power supply to rc use - 11/25/2007 10:20 AM

nano__

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Where did all the pictures go?

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RE: How to convert an ATX power supply to rc use - 11/29/2007 9:10 AM

markind

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Mod under way

Hi guys thanks for all the great info!

My PSU is a fairly new Antec 550W and I have it running with all the un-needed wires cut short to the board, with nice banana jacks mounted in the case for 12V out, and one standard wire set with 5V and 12V available on that standard 4-pin Molex connector.

I have tested it with a 5 ohm dummy load across the 5V line, and my 10W sand bar resistor gets up to 190 deg. F. after a couple minutes.

Not a problem but the 12V out is only boosted to 12.06V under load. I was hoping to get 12.2ish.

Should I try for 3 ohm dummy load? With no dummy load, she runs just fine but only at 11.97V

I'll post up some pics when done. This one is neat and easy.

Edit:

Well I needed my 4 batteries charged so I hooked up the whole system with a DMM reading the 12V output and once the charger really got going, it drops to 11.89V

The sand bar 5 ohm resister got just under 200 deg. F. Not terrible but a bit too hot to handle.

This is boogers. I will try the 3 ohm dummy load to try to boost the 12V out.

End result: All 4 batteries went through the charge cycle fine but only 12.46V to 12.56V. I will 'top off' the packs before flying asI like to see 12.6V at launch. That's lame though. I want it right the first time!!

< Message edited by markind -- 11/30/2007 6:15 AM >

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RE: How to convert an ATX power supply to rc use - 12/1/2007 7:18 AM

mrasmm

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I think you're gona have a hard time getting an ANTEC to run much over 12v. They are very good PSU's and are very accurate, it's part of the mfg process of them. A 5 ohm load should draw about 1A, which will definitely get hot, that's about 5.3 watts TDP, and the thing is only rated for 10w at something like 220C. The way to get around this is to put them in series, so you have 2 5 ohm resistors for a total of 10 ohms, and then you can run two of those setups in parallel for a net resistance of 5 ohms and a TDP that is the same 5.3w but divided between 4 resistors, or about 1.32w each which will run alot cooler.

if you want to go to 3 ohms total, there are many ways to get there, but one single 3 ohm resistor is not gona work unless you want it to get really hot

the reason for it not getting to 12.6v is your charger rather than the PSU. make sure to balance the packs, and really anything over about 12.4 will work, the difference between 12.4 and 12.6 is only about 3 to 5% on most packs.

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RE: How to convert an ATX power supply to rc use - 2/16/2008 4:57 AM

rob1234

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Guys,
I use a 32 amp computer power supply and charge 4, 6 or 8 1800mah bats at one time for my little kids traxxas rustler.
I simply use a 5 amp diode bridge on each and select whatever charge current I want with a simple door spring (This serves as a high power resistor. To turn the supply off, you just switch that one wire from ground.
I don't have pictures, I'm new here. But I may take some this weekend to post here if i have time.
It will charge 4 in about 25 min. or longer if I choose.

Never use this method and charge your bats too fast, they will not last very long if you pump 4+ amps into them. But it works very well if you charge at 2.5 or 3 amps and keep a close eye on the charging. It works just like the cheap chargers that cost $29.00.

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RE: How to convert an ATX power supply to rc use - 2/20/2008 8:19 AM

K-OS

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Just did the mod on an Antec 400 watt power supply. When I connect the charger while the unit is on, the unit shuts down completely. However when I connect everything and THEN power on the unit it works.

Just wanted to share this info so no one does the same mistake as me (dismantle the unit 3 times and try over and over)

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RE: How to convert an ATX power supply to rc use - 2/20/2008 4:12 PM

Andrew

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quote:

ORIGINAL: K-OS

Just did the mod on an Antec 400 watt power supply. When I connect the charger while the unit is on, the unit shuts down completely. However when I connect everything and THEN power on the unit it works.

Just wanted to share this info so no one does the same mistake as me (dismantle the unit 3 times and try over and over)

This is a fairly common occurrence and is tied to the overload protection circuitry built into the PSU. Some chargers have fairly hefty ripple suppression capacitors built into the front end and when discharged represent a significant current sink when attached. To the PSU, this is sensed as a short and it latches off. However, because most motherboards are populated with a large number of capacitors, the Design Guide states that PSU's should be able to power up with an attached 5000 uF load on the 12v rail and stabilize.

When the charger is attached first, the load seems typical and the PSU comes up to full power. When attached later, the high current sink is atypical and the PSU shuts down.

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RE: How to convert an ATX power supply to rc use - 2/20/2008 4:48 PM

K-OS

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Quite a detailed explanation Andrew. How much does NASA pay a guy like you?

One more question, my PSU has an output voltage of 12.12 volts using 2 fans. 12.20 with one fan, and 12.30 without any fans. Is there a way to maintain the 12.30 volts without affecting my output voltage and using both (or perhaps even 1) fans? Or is 12.12 volts sufficient to run my Duratrax ICE charger.

FYI at 5amp draw it drops to 12.05 volts.

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RE: How to convert an ATX power supply to rc use - 2/20/2008 7:53 PM

Andrew

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quote:

ORIGINAL: K-OS

One more question, my PSU has an output voltage of 12.12 volts using 2 fans. 12.20 with one fan, and 12.30 without any fans. Is there a way to maintain the 12.30 volts without affecting my output voltage and using both (or perhaps even 1) fans? Or is 12.12 volts sufficient to run my Duratrax ICE charger.

FYI at 5amp draw it drops to 12.05 volts.

The 12.12v should be sufficient, but voltage levels are set by charger manufacturer specification, albeit on the conservative side. What pre-load are you running on the 5v rail?

It is worth discussing cooling, however. Most of the dual fan Antec supplies use 80mm fans running under noise suppression/thermal management circuitry. The average flow rate for 80mm fans is around 30 CFM. Taking into account airflow impedance, low fan speeds due to noise suppression and out and out lying by the manufacturers about their fan capacities, let's cut that figure by 2/3 to 10 CFM. A typical ATX supply case runs about 125 cubic inches in volume -- with components, the actual air volume is much less. Given the 10 CFM flow rate, you can expect to evacuate the PSU case around 135+ times/minute with a single fan which is more than sufficient cooling. Keep in mind that PSU fans many times are the primary ventilation source for the entire computer case, consequently, cooling capacities are well above the needs of the PSU alone. I would be inclined to run only a single fan.

If the converted supply does not have a noise suppression circuit, you can easily drop the speed of the fan, and reduce the associated fan noise, by running it on 7 volts. Just attach the negative lead from the fan to the 5v rail and the positive lead to the 12v rail -- it will run just fine.

quote:

Quite a detailed explanation Andrew. How much does NASA pay a guy like you?

Well, if I gave that out, then we would have to send a Predator up that way guided by one of the 3 geo-synchronous targeting satillites floating over SE Canada. Oh, and by the way, you might want to pull the shades on that back bedroom window.

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RE: How to convert an ATX power supply to rc use - 2/20/2008 8:37 PM

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This might help some.

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RE: How to convert an ATX power supply to rc use - 2/20/2008 9:15 PM

Andrew

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quote:

ORIGINAL: snellemin

This might help some.

Those images are mine, BTW.

I've been preparing an update to the website that will give some tips on getting more current from the newer ATX12V supplies based on multiple rails. As an aside, the 6 pin auxiliary power connector has been dropped from the more recent Design Guide specifications and a 4 pin connector has been added. The 4 pin connector is an add-on the the existing 20 pin motherboard connector and is used to convert the 2x10 into a 2x12 MoBo connector to support the newer power hungry PCI-Express boards.

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RE: How to convert an ATX power supply to rc use - 2/20/2008 10:16 PM

snellemin

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If it is, then I will give you the credit. I got the color images about a year ago to help decode the wires faster.

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RE: How to convert an ATX power supply to rc use - 2/20/2008 10:31 PM

Andrew

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ORIGINAL: snellemin

If it is, then I will give you the credit. I got the color images about a year ago to help decode the wires faster.

That's quite alright -- I put the site up to hopefully be of some help and to give back to a hobby that I've enjoyed for many years.

Converting a PC Power Supply

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RE: How to convert an ATX power supply to rc use - 2/20/2008 11:22 PM

K-OS

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I'm running a 10 ohm 10 watt resistor across the 5 volt line. I tried adding another 10 ohm 10 watt resistor across a seperate 5v line and the voltage remained exactly the same, maybe something I didn't do properly.

Also, I ran 2 motors plugged in parallel and in series and always notice a 5 amp draw, does this mean my 400 watt PSU only supplies 5 amps?!??! Because when I charge a 5 cell 700mAH pack I also get a 5amp draw from the psu.

Thanks Andrew! *closes his blinds*

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RE: How to convert an ATX power supply to rc use - 2/26/2008 1:58 PM

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I use a 250W and it reads 11.6V. I tried adding a 5ohm resistor on the 5V plugs and it went to 11.8V-11.9V but the resistor was way too hot so i just use it with the 11.6V on my Triton and it works just fine!!!

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RE: How to convert an ATX power supply to rc use - 2/27/2008 1:07 AM

OldRookie

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I wasn't quite getting the voltage I wanted. I tried the 4 10 ohm 1 watt resistors in series and got pretty good results. The next thing I tried is putting two sets of 10 ohm 1 watt resistors in parallel, and then put the two parallel resistor sets in series. What type of load does this put on the system compared to the 4 10 ohm 1 watt resistors in series? I don't know the formulas for series and parallel circuits.

Greg

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RE: How to convert an ATX power supply to rc use - 2/28/2008 9:11 AM

mrasmm

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ORIGINAL: OldRookie

I wasn't quite getting the voltage I wanted. I tried the 4 10 ohm 1 watt resistors in series and got pretty good results. The next thing I tried is putting two sets of 10 ohm 1 watt resistors in parallel, and then put the two parallel resistor sets in series. What type of load does this put on the system compared to the 4 10 ohm 1 watt resistors in series? I don't know the formulas for series and parallel circuits.

Greg

hey there, I got your PM, so here it goes.

The formula for TDP is voltage squared over resistance, so it's 5.15^2 or 26.5/resistance. For series you add all the resistance together to put it on the bottom, and for parallel, you do two different equations and then add them together

so in your case four 10Ω resistors rated at 1w each, will give you a total resistance of 4 x 10Ω or 40Ω then 26.5 / 40Ω = 0.66w TDP between all 4 resistors, so if you divide that 4 ways, then it is 0.165w per resistor, or about a 16.5% load, which is a good range to keep them running cool.

In the second case you would really up the amount of power draw. Two 10Ω resistors in series will give you a total of 10Ω + 10Ω = 20Ω then you take 26.5 / 20Ω = 1.33w per two resistors, or 0.66w per resistor, or about 66% of the capacity on a 1w resistor, so that puppy is gona get hot. Then when you add the second set in there, you'll get a total TDP of 2.65w, and 0.66w per 1w resistor.

so the first one you'll get 0.66w load on the 5v rail and the second example you'll get 4 times that at 2.65w load on the 5v rail. The temp diff in the resistors between the two is going to be very different. I'll bet in the second example you'll be getting close to 180F or 200F for each resistor, especially without a heat sink.

Hopefully that answers your q

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RE: How to convert an ATX power supply to rc use - 2/29/2008 5:36 AM

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Im having a problem with my power supply shutting off when i try to charge 4s packs. The psu is out of a compaq pc and is rated 8 amps at 12v. It works fine charging 3s and im getting about 12.6v under the charge load. Does it take that much more juice to charge 4s packs? or ??

Allso I had the same problem as edwal07 on page2
""and the 5v sense to the 5v. In this configuration I had voltage but no current. I removed the 5v sense and it latched on perfectly. ""

I had 12v+ but it wouldnt power anything until i disconnected the grey and red wire.

This is the charger im using if that matters. http://www.allerc.com/etecchargers.htm

Thanks
Rob

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