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        Discussion 3.7v 150mAh LiPos and charger

#1 Master_Dirt Apr 29, 2007 01:37 AM

3.7v 150mAh LiPos and charger
 
I'm sure ya'll are tired of hearing the question, 'What charger do I need?" so I'll just change the wording but ask the same :D

What I want to do is take 2 or more individual LiPos, specifically 3.7v 150mAh (TOBN 150s) and put them on the charger at the same time (end of day for example)

Each battery would power a different r/c receiver and fly a variety of time.. e.g. Battery 1, 35 minutes, Battery 2, 70 minutes, Battery 3, 12 minutes...etc... Point is, each would have different drain for the day.

At the end of my flying day I want to throw all 3 batteries on the charger (as in one charger) This charging session might have a fully charged battery still in the charger and only 2 need recharge. Or I might only put one on the charger. These batteries would not have leads and/or plugs attached rather only the tabs that came on the battery. I don't forsee charging any big power batteries just the 3.7 single battery.

Can I do this safely with a single charger? That is, 1 or 2 or 3 batteries at a time? Is this a common application for LiPo chargers? Any suggestions who might sell something along this line?

Thanks in advance, all these numbers and letters for a battery is driving me nuts. (I just recently finally figured out the difference between AA and AAA) I'm a little slow, I studied electronics before we had electricity :D

#2 Cirip Apr 29, 2007 10:18 AM

Yes, what you want it is possible.
Connect the negative of the cells together. Attach a 4.7ohm resistor at each individual positive tab at the cells. Connect all three other ends of the resistors together and apply the charger at that point and at the common negative.

Initially, the most charged battery may be discharged a bit, but eventually all cells will settle at 4.2V. Also, the resistors will prevent currents higher than 100mA to flow in the circuit, therefore no shorting or damage to the cells.

Cirip

#3 Master_Dirt Apr 29, 2007 11:06 AM

I figured something along those lines Cirip, thank you.

Of course, that begs another question. Would something like the Apache 2020 "http://www.b-p-p.com/proddetail.php?prod=b_a2020" meet my needs then? Again, no big charging requirement, just those around 150 mAh. Could this also handle 250mAh in the same manner?

#4 Cirip Apr 29, 2007 01:02 PM

Although I am not familiar with commercial chargers, I am tempted to say it should work. I would choose 250mA (maybe 500mA, not sure) charging rate for the three cells connected as shown above. The charging process might take a bit longer and the capacity displayed (if available) might not be correct because of the extra power dissipated in the series resitors that don't actually go into the cells. Also, the current decrease slope towards the end of the charge might be somehow slower because of the higher series resistance the charger sees, but I expect no harm done to the cells.

Cirip

#5 rampman Apr 30, 2007 12:59 AM

You could also use a balancing charger like the DN http://www.xushobby.com/servlet/Detail?no=210
or CSRC
http://www.commonsenserc.com/product...f5bcf6b8b2db33
charger to do this. You would need to install a balancing tap or adapt your connector to the charger using the supplied adapters like the ones that come with the CSRC charger.
The way I would do this is to make one adapter to fit the single cell port of the charger, another to fit the two cell port but use only the pins for the second cell, same with the three cell but use the third cell pins... You could do this to charge up to four cells separately at one time, all balanced to 4.2V/cell.
These will charge down to .2A, slightly higher than your 150mah packs should have but many on here say it is OK to charge at 2C (300mah)

This would show how to connect these. The "X" is a don't connect, the "I" is a connection.

1 cell port: II
2 cell port: IIX
3 cell port: IIXX
4 cell port: IIXXX

Verify my wiring before connecting these as I have never done this exact connection but to the best of my knowledge, it is correct.

Rick
www.commonsenserc.com


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