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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 03-02-2012, 03:19 PM   #1
g725s
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Default charging 1300 3S 25C with 10 amp supply?

First off I'm new to charging Lipos. I picked up an iCharger 106b+. I have at home a 10amp linear power supply. As of now I'm charging 1300 3S 25C batteries.

At what charge rate (or is it charge current) should I charge these batteries with. I see a place in the iCharger menu to set the "Charge Current", it goes from .05 to 10 amps. I assume this is the setting I need to adjust.

I've done some searching and it seems for best longevity of my batteries I should charge at 1C, for these batteries would be 1.3 amps.

Does that sound about right? I was told by an iCharger rep that I could charge these batteries at up to 8 amp with this supply.
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Old 03-02-2012, 03:30 PM   #2
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Originally Posted by g725s View Post
(snip)

Does that sound about right? I was told by an iCharger rep that I could charge these batteries at up to 8 amp with this supply.
You are correct that 1C for your battery is 1.3 amps. For setting your charger at 1C, simply use the battery rating in AMPS. Battery voltage or number of cells does not figure into the C rating here.

The iCharger rep was also correct. You "could" charge your batteries at up to 8 amps, but that is a rating of your charger and power supply. That doesn't mean your battery is capable of that charge rate.

8 amps would be just over 6 C for your pack. Some lipos can be charged at up to 10C. Depends on your particular battery. Best to read any paperwork (or label on battery) for the MAXIMUM charge rate.

You can't go wrong at 1C....you can shorten your battery life considerably, or worse, by charging at too high a charge rate.

Hope this answers your concerns.

Cliff
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Old 03-02-2012, 04:15 PM   #3
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If you need a bigger power supply for charging multiple cells or at a higher C rate just strip one out of an old PC case, on the power supply it will tell you the colour of the wires connected to the 12V rail and how many amps you can draw off the 12v rail. Just bunch together all of the 12v+ wires and solder them together use those wires and the bunch of Neutral wires to feed your charger. There are a couple of other wires you will have to join together to make the PSU start as they would normally be connected to the switch on the PC. Then cut all of the other wires short bunch and insulate them as they're not needed. There are plenty of tutorials on the net showing what to connect where. It's pretty simple and very cheap! I've been using a 25A supply for 2 years in this way without any problem with a 4 cell charger charging 4 lipos of varying sizes at 1C and 2C rates.

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Old 03-02-2012, 07:47 PM   #4
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Originally Posted by Davethebluessinger View Post
If you need a bigger power supply for charging multiple cells or at a higher C rate just strip one out of an old PC case, on the power supply it will tell you the colour of the wires connected to the 12V rail and how many amps you can draw off the 12v rail. Just bunch together all of the 12v+ wires and solder them together use those wires and the bunch of Neutral wires to feed your charger. There are a couple of other wires you will have to join together to make the PSU start as they would normally be connected to the switch on the PC. Then cut all of the other wires short bunch and insulate them as they're not needed. There are plenty of tutorials on the net showing what to connect where. It's pretty simple and very cheap! I've been using a 25A supply for 2 years in this way without any problem with a 4 cell charger charging 4 lipos of varying sizes at 1C and 2C rates.

Dave
Not completely true. For the most part, what was said above is correct. The parts missing are :
Most PC power supplies require that a load be placed on the 5 volt bus to get good regulation on the 12 and 5 volt bus. Usually, a 5 ohm 10 watt resister on the 5 volt bus will do the job. This resister will get quite warm (hot) so mount it accordingly. You will have to connect one wire (usually the green colored one) to ground to get the supply to turn on. The amount of current you can pull off the 12 volt bus is not the same for all power supplies, some are as low at 5 amperes but most are around 10 amps or a little more. The sticker on the side of the supply will give you the maximum currents you can draw under ideal conditions, one of which is adequate cooling. Keep the vents open and clean and the fan working.
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Old 03-03-2012, 01:54 AM   #5
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Thanks for the replies about charging and the power supply.

So I get that charging at the 1C rate is best. I will do that for now.

I will use this power supply for now since it can do fine with the 1C rate for one battery.

But a couple more questions....

How many 1300 3S 25C batteries (currently have three Gens Ace) can I do in parallel with my 10amp power supply at the 1C rate?

I'm guessing that I can lower the charge current for multiple batteries in parallel? And how low of a rate can you charge at for a Lipo?
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Old 03-03-2012, 05:51 AM   #6
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Originally Posted by g725s View Post
Thanks for the replies about charging and the power supply.

So I get that charging at the 1C rate is best. I will do that for now.

I will use this power supply for now since it can do fine with the 1C rate for one battery.

But a couple more questions....

How many 1300 3S 25C batteries (currently have three Gens Ace) can I do in parallel with my 10amp power supply at the 1C rate?

I'm guessing that I can lower the charge current for multiple batteries in parallel? And how low of a rate can you charge at for a Lipo?

If you've got a 12 VDC supply, the watts output is P=E times I, or 12 times 10, that's 120 watts.

Now, your Gens Ace battery can be charged at say 1C or 1300 milliamperes, that's 1.3 Amps. Again, watts equals volts times amps so W = 3 (cells) times 4.2 Volts per cell times 1.3 Amps. That's 16.38 watts per 3S battery. The efficiency of your chargers is generally something like 80% so that would be 16.38/0.8 or 20.4 watts per battery.

Next, 120 watts divided by 20.4 watts per battery shows you can charge 5 packs at once. Leaving a safety margin, I'd keep it to three or four packs maximum.

If you're doing this with just one charger, you've got the problem of just having one balance cable for those four packs. IMHO, I'd not parallel that many packs. Just because if anything goes wrong, it's going to be expensive. (Not counting the potential fire issue)

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Old 03-03-2012, 12:13 PM   #7
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Thanks Rodneh, I never knew about the 5V rail needing the resistor. However I've used 2 separate chargers without that mod and they've both worked fine. My PSU has 25A on the 12V rail and has no restriction on the cooling as it sits on my bench with the charger alongside.
Always great to get pointers to increase your knowledge of these things though!

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Old 03-03-2012, 05:39 PM   #8
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Originally Posted by Davethebluessinger View Post
Thanks Rodneh, I never knew about the 5V rail needing the resistor.
I've also got these power supplies to work without that loading resistor on the 5 VDC output. There is a wide variety of power supplies out there from decades old to fairly new, so they must also have a wide variety of requirements for powering up.

If anyone wants to buy one of these things, take a look.

http://www.mpja.com/Computer-Type-Po...s/products/36/
http://www.mpja.com/650Watt-ATX-Echo...info/17980+PS/ (This one has a 22 Amp output on its 12VDC line)

http://www.jameco.com/webapp/wcs/sto...001_2094928_-1

www.mpja.com as well as www.jameco.com sell a wide variety of power supplies, including dedicated units that have a 120 VAC input, and a 12 VDC output. They are also available in 5 VDC, 24 VDC, and a number of other fixed voltages. They tend to be expensive though.

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