rmuckley

My Feedback: (1)

I'm looking for a cheap, simple power supply (120vac to 12vdc) for my LiPo charger/balancer, for use at home.
I've been searching the web, but have only found ones that are $50+. Why are they so expensive? It seems like it would be a simple thing, but they cost as much or more as the darn charger! Can anyone recommend one? Thanks in advance.

Rob

Loswave

I bought one from ebay. I got a brand new SSI psu that has 1 5 V output rated for 60 amps, and two 12 volt outputs rated at 10 amps a peice, so I strung the 12s together in parrellel, so I effectively have 12 v at 20 amps, it works great and I only paid 20 bucks for it, plus 15 for shipping, but still 35 bucks for 20 amps of 12 v not to mention the 5 volts as a bonus. Just look on ebay for a week or two, something will show up.

VinceHerman

Or, if you like FREE!!! you can use a power supply from an old computer. The line sets going to the drives have a 12v set, I believe yellow and black.

Loswave

That depends on what kind of amperage the +12 rail on the PSU has. If you have any laying around check the numbers, and if the +12 V rail has the juice you need use it. The only spares I had were old and could anoly put out a couple amps, so I bought my PSU and don't think I'll be needing anther one, ever, I hope.

rmuckley

My Feedback: (1)

Interesting ideas....thanks.

HighSierra

My Feedback: (2)

I went the cheap route with a computer power supply.... I had a 300W one from an old computer just collecting dust (but i'm sure you could get one from a used computer store, or a place that fixes peoples computers for $10-$20.

Here's what you do to make it work (most power supplies are switched on thru the mother board so you need to do a little wire jumping work to make it fire up when you thow the switch on the back.

First, cut off all the plastic connectors on it so you just have a bundle of wires (with it unpluged of course), You'll do nothing with the orange wires ( you can twist them all together and wire nut and tape them off), You also won't use the white wire, the blue wire, or the grey wire (I just sut them down short and put a piece of shrink tube on each one and pinched the end shut...but don't tie different colors together! )

Now the yellow wires are all +12 volts, the red wires are +5 volts, and the blacks are all the common negative, so you can bundle them all together and pigtail it down to one wire on both the yellows and the blacks (except leave 1 Yellow wire out of the bundle)....this will be where you hook up your charger (yellow = pos and black = neg ..... I had a few deans connectors around so I used those for the connection between the power supply and my charger, and used an additional female deans connector to make a set of wires for the field with alligator clips on the other end (If you use deans connectors use the same logic you use on your heli for what gets the male connector and what gets the female).

Now group up all but one red wire and pigtail them together and wire nut and tape them off ( you only use one red wire), So now take the one yellow wire you left out of the bundle, and connect it with the purple wire, pigtail, wire nut, and tape it, and finally connect the one red wire you left out of the big bundle to the only green wire and pigtail it etc.

Plug it in and it should fire up, and pat yourself on the back....you just made a 12 volt power supply, that's probably able to put out right around 14 amps with a very clean line voltage for next to nothing in price!!


I learned about this little cheap power supply trick from a HAM radio guy who do this for their transmitters or whatever (I'm no HAM guy)...... What they do is buy 3 of them, and use the +5 volt wires (the red ones, which carry nearly twce the amperage as the 12 volt wires) and hook them up in a series so you get an end voltage of 15 volts, and right around 30 amps (or more!!).... Anyhow those are big bucks to buy new, but easily made at a fraction of the price!

It's worked great for me!

Good luck!

Loswave

Most computer PSUs will have a label on them that will give you the amperages they will yeild on each rail. Something around 480 Watts will give you about 18 amps on 12 btw.

rmuckley

My Feedback: (1)

Thanks for the ideas!

reades

Hello.

HighSierra, could you possible post some pics of this set-up? I have a few "old" power supplies laying around. Plus, I have churning over the power supply question since I ordered the 600.

Thanks,

reades

HighSierra

My Feedback: (2)

Here's my setup before I put the deans connectors on it (just for convience).... I'd probably go back and change the pigtail leads on the positive and negative to a thicker wire if I were charging packs with more than 3 cells.


The multiplex charger I've got works great and I highly reccomend it for all your different battery charging needs.

WhtBronco

Being a Network Engineer I have access to lots of PSU's and have tried to make 3 different ones to no avail. Well they all work, but they only produce 11.8v so when I connect a 3S li-po to my Astro 109 charger the charger shuts down due to low voltage. Charging a 2S li-po is no problem using the modified computer PSU's. I gave up and just use old UPS batteries that are laying around. Besides a UPS makes a nice charger that you can foget about and worry.

FWIW, the mod is pretty easy to do and doesn't take long. I went a step further and unsoldiered the unused leads form the circuit board for a bit cleaner look on the first 2 units, the 3rd I didn't bother since I didn't expect to get 12v and that turned out to be correct. I never got any of the 3 to put out more than 11.7v.

I plan to produce my own PSU with an output of 13.0v or a bit more. I don't like the idea of using a PSU with lower voltage than the battery requires at full charge anyway since it requires the charger to output more power than it's recieving.

HighSierra

My Feedback: (2)

My PS only puts out around 11.7 volts as well.....doesn't seem to bother my charger (allthough I only have 3 cell lipos, so I can't say how it would preform on 4, but It has no problem stepping the voltage up when using the same charger to charge my 12 volt field battery (peaks at 14 volts)...

If you've got an ample supply of power supplys, then you should go the route of a 30+ amp 15 volt setup (connect the +5 in serries)

AJsToyz

If I can find the link I'll post it, but it states you need a small load on one 5v tap to get true 12 volts.

rcboosted

I have the $15 Esky lipo charger that takes both 2S and 3S lipos. The input voltage on the charger said 10V~15V. I had always thought if I charged a 3S lipo but only gave it 10V, it'll step up the voltage (while drawing more amps or course) for the 3S. Is this true for this particular charger?

TooLy

I use computer ps.
I also load the 5V port to raise the 12V.

rcboosted

Would it work if I use yellow for +, and white (-5v) for - on the charger? This would give me 17V, but the -5V rail is only rated at .5A, would this fry the rail? Not sure if both the + and - would need to have high amperage.

Karyn

It wouldn't fry the -5v rail, it would simply limit your 17v supply to the 0.5A available from the -5v rail.

rcboosted

That's unfortunate. I loaded the 5V rail and was surprised that .15v bump was enough to keep my cellpro 4S happy.

xeliman

hallo.i have a pc power supply that i want to convert to charger supply.as i see in your photos .you put four yellow and four black wires as possitive and negative? if my power supply has more than four i put them all?.and about the other wires of the same color you merge them together? i mean each one of the same color touch the other of the same color? thanks

Dynamic

Also remember that the amp rating is for burst (a few seconds) not continuous. If it says 20 amps your probably only getting 6 in reality. Spend $1000+ (and thats a big +) on a copter and cheap out on the power, bad idea. Spend the money and get a good quality power supply with more amps then you need. It will be able to charge your batteries faster (if wanted) and not cause problems. I've played around with the computer PS's but they don't have the power of a real one. Novak has some nice stuff.

PlaneHeli

I picked up three new 400W computer PSU when I stopped off in Bangkok.
180THB each ($5USD)

Found instructions on the web how to convert them.

The modern switching PSU require the green and black wire to be connected. (to start the PSU and fan).

Use all the yellow wires as positive. An equal number of black for negative.

You must put a load on the red wire to increase the voltage from around 11.7V to what you want. (mine around 12.5V)

Ive used 5W resistors (2.2 - 4.7 ohm) wired in parallel. (or you can use a light / lights).
Connect a digital voltmeter to the yellow and black wire, then experiment with the resistors (or lights) to get the voltage you want.
Dont use too high a resistance or it will not do anything. The red wires are only 5V.

I used all the yellow wires to spread the load. Supposedly a 400W PSU outputting 12.5V should be able to supply 32A. as mentioned in reality their output rating (eg 400W) may be only for a short period. But as i only charge my 2200MaH Lipos at 2.2A, and my 3900MaH NiMh at 3.9A im well under the rated output.

Ive made two so far for my two LCD chargers. Theyre still working.
I paid less than $10USD all up for each charger (PSU, resistors, a light, rubber grommets, 2 bolts).

Do a search on the internet for instructions.

robotronski

Finally someone mentioned the required load resistor !!!!!

Thank you

PlaneHeli

Yes, I bought a bunch of 5W resistors from 2.2 Ohm, 3.3, 4.7, to 5.6 Ohm. The 5.6 Ohm seemed a bit high even in parallel, (no increase in voltage) so I settlled using about 4 2.2 and / or 3.3 Ohm in parallel.

Just buy a bunch of 5W resisitors from say 2.2 - 3.3 Ohm, and experiment with them in parallell to get the Output Voltage you want.

The voltage is 12.5V on one and 12.6V on the other.

The resistors do get hot, so is positioned them by the aluminium heatsink behind the fan. When I close the lid, they press against the heatsink.

Caution the resistor wires dont short out when you close the lid.

KamikaziRcPilot

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