Desktop ATX PSU suitable for LiPo Charging?

wolfdown · 10-06-2009, 07:20 PM

I have a spare 500W Antec ATX power supply from a new PC case. Has anyone converted these for using as a AC/DC charging PSU? If so, what are the steps and precautions I need to take?

There are two 12V lines rated at 22A each with a combined max output of 408W. I'm wondering if I can combine this in parallel to get the full 408W combined (34A).

If I can do this it will save me from having to drop $50 on a separate 12V PSU.

ANSWER HERE: so far this was the best info I could find. There is also a page on how to combine the 12V1 and 12V2 rails.
Desktop Power Supply from a PC

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Update: Here is a link to power supply with the specs, Antec Earthwatts 500W

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Related Form Posts: Found these after my post.

1. http://www.helifreak.com/showthread.php?t=70473
2. http://www.helifreak.com/showthread.php?t=67288
3. http://www.helifreak.com/showthread.php?t=25715
4. http://www.helifreak.com/showthread.php?t=161776

RocketSled · 10-06-2009, 07:46 PM

12V@22A=264W. I would bet that the 2 12V lines are rated at 22A *combined*, and that the other voltages consume the remaining 236W to get you to 500W total.

Most chargers won't charge with only 12V, they need 15V minimum or maybe even higher. If your charger needs more than 12V your ATX supply probably won't "cut the mustard". But if your supply's outputs are bridgeable, you could for instance combine +12 and -3 to get 15V. But you need to be sure it'll do that before you try or you might end up with smoke, it's not something you want to just "try".

If your ATX *can* power your charger, the next question is "what charge rates do you expect to use?". As computed above, the max wattage for the 12V output is 264W. You need to multiply the battery voltage and charge current (2C charging a 5000mAh battery draws 10A) and make sure that the charge wattage is less than the supply's power output capability. In this example, 2C 5KmAh 3 Cell pack would need a maximum of 10*12.6=126W, well under the Supply's limit. A 6 Cell pack would need 2x the wattage, 252W, which is too close to the Supply's limit and probably wouldn't work.

If you search in the forum, someone recently had a fairly long thread about using a PC power supply from eBay - one that had bridgeable outputs so you could get more than 12V from it.

TJinGuy · 10-06-2009, 10:39 PM

1) Yes lots of us use them and they work great. Care must be taken to convert them properly though.

2) I have found that the 2 12V bus outputs will add together. So I would assume 44A on your PS. On the one I did with dual buses, all the 12V lines were already combined on the circuit board.

3) All the chargers we use will work fine off of 12V source. They were designed this way so you can charge off your car battery. To reach their potential, some chargers do require higher input voltage. This is only if you need to maximize their output though.

4) Using a 12V and -3V will indeed give you 15V but will limit you to the current output of the -3V bus. In other words it is a REALLY bad idea.

TJinGuy · 10-06-2009, 10:42 PM

wolfdown · 10-07-2009, 02:14 AM

From what I have read there is no -3V rail, only +3.3V. Either way, I believe you are correct that trying to combine with a low current rail is a bad idea.

10-06-2009, 07:20 PM	#1
wolfdown Registered Users Join Date: Oct 2009 Location: USA	Desktop ATX PSU suitable for LiPo Charging? I have a spare 500W Antec ATX power supply from a new PC case. Has anyone converted these for using as a AC/DC charging PSU? If so, what are the steps and precautions I need to take? There are two 12V lines rated at 22A each with a combined max output of 408W. I'm wondering if I can combine this in parallel to get the full 408W combined (34A). If I can do this it will save me from having to drop $50 on a separate 12V PSU. ANSWER HERE: so far this was the best info I could find. There is also a page on how to combine the 12V1 and 12V2 rails. Desktop Power Supply from a PC -------------- Update: Here is a link to power supply with the specs, Antec Earthwatts 500W -------------- Related Form Posts: Found these after my post. 1. http://www.helifreak.com/showthread.php?t=70473 2. http://www.helifreak.com/showthread.php?t=67288 3. http://www.helifreak.com/showthread.php?t=25715 4. http://www.helifreak.com/showthread.php?t=161776 Last edited by wolfdown; 10-07-2009 at 02:18 AM.. Reason: Added link, increase clarity, add external link

10-06-2009, 07:46 PM	#2
RocketSled Registered Users Join Date: Sep 2008	12V@22A=264W. I would bet that the 2 12V lines are rated at 22A combined, and that the other voltages consume the remaining 236W to get you to 500W total. Most chargers won't charge with only 12V, they need 15V minimum or maybe even higher. If your charger needs more than 12V your ATX supply probably won't "cut the mustard". But if your supply's outputs are bridgeable, you could for instance combine +12 and -3 to get 15V. But you need to be sure it'll do that before you try or you might end up with smoke, it's not something you want to just "try". If your ATX can power your charger, the next question is "what charge rates do you expect to use?". As computed above, the max wattage for the 12V output is 264W. You need to multiply the battery voltage and charge current (2C charging a 5000mAh battery draws 10A) and make sure that the charge wattage is less than the supply's power output capability. In this example, 2C 5KmAh 3 Cell pack would need a maximum of 1012.6=126W, well under the Supply's limit. A 6 Cell pack would need 2x the wattage, 252W, which is too close to the Supply's limit and probably wouldn't work. If you search in the forum, someone recently had a fairly long thread about using a PC power supply from eBay - one that had bridgeable outputs so you could get more than 12V from it. __________________ Fly in the street hangar includes:* T-Rex 450SEV2, 250SE (MD500), Blade 400, SR & mSR & 120SR & mCPx & mCX & CX2, Walkera 4G6S & SeaCobra Parkzone Sukhoi (& XP), Centurion, Mustang (Micro and BL versions), µBeast, Mosquito

10-06-2009, 10:39 PM	#3
TJinGuy Registered Users My HF Map location Join Date: Jan 2008 Location: Socorro, NM	1) Yes lots of us use them and they work great. Care must be taken to convert them properly though. 2) I have found that the 2 12V bus outputs will add together. So I would assume 44A on your PS. On the one I did with dual buses, all the 12V lines were already combined on the circuit board. 3) All the chargers we use will work fine off of 12V source. They were designed this way so you can charge off your car battery. To reach their potential, some chargers do require higher input voltage. This is only if you need to maximize their output though. 4) Using a 12V and -3V will indeed give you 15V but will limit you to the current output of the -3V bus. In other words it is a REALLY bad idea. __________________ - Chris *To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.* heli...info...news...such Helis: TRex 450 Pro - Protos - TRex 550e Stuff: Spektrum DX7 - iCharger 208B - Hyperion G3 Last edited by TJinGuy; 10-07-2009 at 08:47 AM..

10-06-2009, 10:42 PM	#4
TJinGuy Registered Users My HF Map location Join Date: Jan 2008 Location: Socorro, NM	... __________________ - Chris *To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.* heli...info...news...such Helis: TRex 450 Pro - Protos - TRex 550e Stuff: Spektrum DX7 - iCharger 208B - Hyperion G3

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10-07-2009, 02:14 AM	#5
wolfdown Registered Users Thread Starter Join Date: Oct 2009 Location: USA	From what I have read there is no -3V rail, only +3.3V. Either way, I believe you are correct that trying to combine with a low current rail is a bad idea.