Charging lipo with desktop computer power supply

[mikejbb]

My van leaves the cig ligher hot even when the van is off and since the charger is using about 2+ amps, that's not a problem. So I charge the lipo in the van.

I lent my van to my son this past weekend and don't have it back yet so I don't have a vehicle to use to charge my lipo. I was going to buy a 12vdc power supply from radio shack, but looked on the internet first. I found a couple 5-7amp power supplies for about $35 after shipping. That would have been ok.

But while I was surfing, a computer power supply came up in the results. That got me thinking, I am a pc person since before the radio shack trash80 was produced so I have lots of parts in my basement just ready to reuse. I found 2 computer power supplies and tested both. One was old enough to have a power sw, but it mush have been bad because I only got 3v out of it so it's in the trash now. The second one is newer but no power sw. So I found an old motherboard (mb) and plugged in the power supply and turned on the mb and the power supply showed 12v so I put on a cig lighter female and charged my battery. A bit of an overkill, but I can't find out how to turn on the power supply without the mb attached.

Mike

[mikejbb]

When I was looking for parts for the desktop I found an old power supply for a laptop (a brick). The bricks output was 16v 2.2a so I figured it would work and be WAY smaller. So I connected and it all works great.

I'd recommend this method if you have an old laptop brick laying around. It's currently working just fine and the brick is not overheating.

Mike

[duck9191]

only thing to watch with using a laptop power supply is that some put out 19 volts, which would more then likely kill your charger. 16 volts is in the higher limits of what you wanna run so that one you have should work with out damaging it.

first is this a atx, or at power supply? if its an atx you need to short the green wire on the 20 or 24 pin mobo connector to a ground wire. this will turn on the psu. simplest way is to find the wire in side the case and permanently short the green wire and use the switch on the back or add a switch on the out side of the case. also make sure you are using the 12+ and the 12 volt ground off a molex. if you pull off the mobo connector you need to make sure you didnt get a 3 or 5 volt wire and sometime arnt on the same rail. the 12 volt accessory will have the strongest output rail (should at least).

[mikejbb]

Yes absolutely watch out for the output voltage, my current laptop bricks are 20v so I didn't try them.

The one psu that worked is atx and I did read to short out the green wire. However I didn't understand that you had to keep it shorted. I tried it before and I didn't notice it was running, very quiet, but if you look, the fan runs. Now that you've replied, I tried it again and as long as I keep the green wire attached to the psu case, it stays running. Thanks!

And yes I took the 12v off one of the hd connectors and it worked just fine. Now I wouldn't even need the motherboard. However, I'll use the 16v laptop brick until it fails. It's a lot smaller.

I just thought people should know there are options.

Mike

[duck9191]

the laptop brick is a good idea, i might hunt around ebay and see if i can find a 12-15 volt one. it would look nicer and be alot smarter then the old CB radio power supply i am using now.

[mikejbb]

I used to have one of those old cb psu's when I was a teenager and had a "portable" cb in my beetle and took it out for use in the house. That was in the 60's, long gone. The portable was really inside the "trunk" in the front of the vw and I got to it by trashing the glovebox. The car was small enough so I could reach.

Mike

[flydiver]

Apr 29, 2008 18:59:43 GMT 1 mikejbb said:

I can't find out how to turn on the power supply without the mb attached.

Mike

Start here:
www.rcgroups.com/forums/showthread.php?t=446764

or here:
www.wattflyer.com/forums/showthread.php?t=22583

or here:
reckerclub.tripod.com/id105.html

The higher voltage laptop PS will run the NiMh chargers OK-not sure where the upper voltage limit is. They will fry the lipo charger FAST if much over 15v. Learned that the hard way. Many other lipo chargers will NOT function if over 15v and need at least 3A+ to work right.

fly

fly

[mikejbb]

I have the Hextronics lipo charger and it says 9v-15v input but does not say the amps needed. I have it set to 2a chg rate. The laptop ps is rated 16v 2.2a output. It's been used in much higher demands on laptops and it would get very hot then. Now it just gets warm like it's turned on. I've charged my 3s 2400mha lipo 4 times using this method and the battery is getting fully charged based on 20+ minute flight times, and the charger is staying cool, the laptop ps is only a little warm so not overloaded and the balancing charger says the cells are being charged good too. I watched and each cell stops charging at a different time sometimes so I believe that tells me the balancing circuit is working.

I did notice when I ran it on 12v and lots and lots of amps the cooling fan in the charger runs a little slower than it does now with the 16v. It depends on the innerds if it converts the higher volts to amps then less amps are needed. I won't recommend anybody exceed specs, but it works well for me.

Of course putting a 3s lipo in the cub is very much over specs and it works for many people if they do the other things that are necessary for it to work.

Mike

[flydiver]

Apr 30, 2008 5:42:38 GMT 1 mikejbb said:

I have the Hextronics lipo charger and it says 9v-15v input but does not say the amps needed. I have it set to 2a chg rate.
Mike

If you have a Wattmeter it's worth checking the output. I've checked 3 of them now using 7A PS. They are all under spec:

Setting Actual
0.5A 0.2A
1.0A 0.68A
1.5A 1.1A
2.0A 1.32A

That's why it takes so long. It also does not charge 100%, more like 93%. This does NOT hurt the battery, probably better for it in the long run but it does ding performance a tad. Balancing seems to be satisfactory. Another case of cheap Chinese electronics not living up to spec. Don't believe it, test it.

fly

[mikejbb]

Thanks, You're right, I need to order that wattmeter, I forgot. So the underspec is probably why the 2.2a laptop psu works just fine then. If the charger was up to spec, then the psu would probably fail or the charger would not function correctly.

It take 1.5 hrs to chg my 2400mah lipo, but I suppose the 2400 is also suspect since it's a "mystery" brand.

Mike

[flydiver]

Apr 30, 2008 20:45:22 GMT 1 mikejbb said:

Thansk, You're right, I need to order that wattmeter, I forgot. So the underspec is probably why the 2.2a laptop psu works just fine then. If the charger was up to spec, then the psu would probably fail or the charger would not function correctly.

It take 1.5 hrs to chg my 2400mah lipo, but I suppose the 2400 is also suspect since it's a "mystery" brand.

Mike

Once you have a Wattmeter you'll wonder how you got along without it.

Assuming the charger itself needs a certain amount of those Amps to function it's probably it's underperformance that keeps it from stressing the low powered PS.

Mystery.....you just have to wonder.
I think I'd knock off 20-30% of all specs on principal. I tend to do that with all lipos anyway. I think there is C inflation going on.

fly

[mikejbb]

Sounds about right
Mike

[duck9191]

i have the mystery 2400 12c's and i only get 2000-22000 out of them. also running them in the cub pulling around 20-24 amps they sag a bit more then i would like, but i only paid like $20 for two so im happy. i also have a 1500mah 20c cheapo and i get about 1450mah and it seems to hold voltage better underload.

i have found my duratrax ice is only about .05-.1 amp off from the display and the battery lead. good enough for me.