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Old Aug 01, 2012, 07:04 PM
Space Coast USA
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Hi Norm,
To make an IR meter you just need a known resistance and a volt meter. http://www.rcgroups.com/forums/showp...&postcount=272

I used 100W, 2 ohm resistors I got off the internet from China.

IR
Vu = unlaoded V
Vl = voltage under load

IR = (Vu - Vl) x R/Vl Don't forget to divide the answer by the number of cells in the pack.

The IR will probably not match other meters but, it can be used to effectively grade your own packs. Mine varied from 8 mohms to over a 100 mohms.
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Old Aug 01, 2012, 11:15 PM
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MetroWest, Massachusetts, USA
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Quote:
Originally Posted by hoppy View Post
Hi Norm,
To make an IR meter you just need a known resistance and a volt meter. http://www.rcgroups.com/forums/showp...&postcount=272

I used 100W, 2 ohm resistors I got off the internet from China.

IR
Vu = unlaoded V
Vl = voltage under load

IR = (Vu - Vl) x R/Vl Don't forget to divide the answer by the number of cells in the pack.

The IR will probably not match other meters but, it can be used to effectively grade your own packs. Mine varied from 8 mohms to over a 100 mohms.
Oh, that's easy. I'm embarrassed to admit that I'm an electrical engineer and should have been able to figure this out myself

I read the post you referenced but I don't know anything at all about LiPo chemistry; do you know if it matters how much current you're pulling or if the IR changes as the cells heat up? I've got a 47ohm 5W load but that's not going to pull much current, so its probably not too good for this. Guess its time to pick up some power resistors.
Thanks a lot.
-norm
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Old Aug 02, 2012, 07:48 AM
Space Coast USA
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My tests at 10A and 20A showed little difference in the IR. My setup can give me either a 1 or 0.5 ohm load.
A 1 ohm resistor would yield a 12A load with a 3s pack. That would be 24C for a 500mah pack and a 3C load for a 4000mah pack. Using the 0.5 ohm load would increase that to 6C with the 4000mah pack.

The IR meter uses a 16A load. I assume the chargers with built in IR circuitry use less than a 5A load.

Good luck.
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Old Aug 02, 2012, 07:49 AM
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I do believe that battery manufacturers specification sheets state AC ohs as the ohms is measured using AC 1khz. There may be a slight difference by using DC ccts.
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Old Nov 02, 2012, 10:15 PM
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Canada, ON, Toronto
Joined Oct 2012
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Hoppy and others, thanks for posting and maintaining all this information on LiPos, chargers and their care. For a newby like myself just getting into RC and specifically planes, remember that there is a lot to take in. Glow engines are not this complex!

I have been crazily reading stickies and boning up on my electrical math. The stickies on how to prevent a campfire while charging your LiPos was most enlightening (literally). These batteries are like nothing I have ever used, and their care and feeding have no similar counterpart with any other common battery type, and this may be the problem. To treat LiPos like you do other batteries might burn your house down.

I continue to madly read but not post just yet.
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Old Nov 03, 2012, 07:27 AM
Space Coast USA
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Thank you. Enjoy the hobby, it's a great time to be getting into electric flight.
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Old Nov 26, 2012, 10:37 PM
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Australia, New South Wales, Fernmount
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Very helpful info. Have managed to salvage one battery so far and am about to resurrect some more.

Thank you all
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Old Feb 13, 2013, 04:23 AM
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hi. I have 3.7 battery that unlike other 1 cell batteries have 3 contacts. One is +, another is -, but can't understand what is 3rd one b/n them.
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Old Feb 13, 2013, 05:46 PM
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id pins.
used to identify the battery to the phone.
plug in the wrong battery and it won;t work
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Old Feb 14, 2013, 06:27 AM
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thanks for the tip. this battery must be also used in other devices, it came with my miniDV camera (the same like 808 but in other body) which works fine with 2 wires of any 3.7cell too. I just soldered cables to contacts in camera and it works from LiPo cell. I'll check if I can recharge that battery from other charger through 2 cables
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Old Apr 20, 2013, 11:24 AM
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does voltage matter when recharging battery? I know that ma matters but don't know about voltage. I measured chargers and found that one designed for small batteries (it's written 200ma 6V) gives 8.4V, while 500ma gives 4.2V and another one gives 6.4V. if I have small 200mah battery is one with 200ha ok if it has 8.4V voltage?
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Old Apr 20, 2013, 07:23 PM
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Voltage is important. Open circuit voltage is not very useful. Use chargers specifically intended for the batteries you want to charge.
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Old May 09, 2013, 10:19 PM View Post
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Old May 26, 2013, 09:38 AM
John
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Thanks for the info. I did a search and found this thread because I was doing some testing and forgot to unplug a 3s. Lipo went totally dead and I though it was headed to the trash. Slightly puffy but still works.
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Old Jul 20, 2013, 06:29 PM
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Steinbach, MB, Canada
Joined Nov 2004
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What is the minimum voltage per cell for Nicads?

Hi guys, I should know this off the top of my head as I have been involved in this hobby for over 30 years, but as age creeps up on all of us, I can't remember for certainty. I think the voltage is 1.1V per cell for Nicads, can anyone confirm this?...

I have a Futaba transmitter battery that has a non servo type plug (circuit board two pin type) and I need to cycle it a few times but can't remember the minimum voltage for an 8 cell NiCad. I will have to use the transmitter voltage readout (digital one) and turn off the transmitter once that voltage is reached, then recharge and do it all over again as I can't find any place that would sell a male 2 pin connector of that type, seems most (read as no places) places are no longer stocking these types of items. I can't cycle by connecting it to my battery charger/cycler because of the plug type on the pack....

Sackie
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