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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> 6 Volt NIMH 2700 Mah pack
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6 Volt NIMH 2700 Mah pack - 6/29/2002 7:18:13 AM   
goatnick



Posts: 80
Joined: 1/6/2002
From: Demotte, IN, USA
Status: offline 		Need help on how far you can run a 2700 Mah Nimh battery down
and still be on the safe side.Took off charge today after 16 hr at C-10 rate using DDVC at 270, reading was 730, After two flights of 12 minutes reading was down to 6.14, I am using two 5945 digitals on ailerons, two 945 coreless on Elevator, One 134 on Rudder and 148 on throttle,I have it on a cycler now to see what is remaining, Any help appreciated , Thanks
Bob

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Re: 6 Volt NIMH 2700 Mah pack - 6/29/2002 10:57:53 AM   
thomasb



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From: Private, CA, USA
Status: offline 		[QUOTE]I have it on a cycler now to see what is remaining[/QUOTE]That is what you need to do to determine where you stand. If you apply a 500mA load (12 ohms or so), then a cut off voltage of 5.92V would be about it.

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6 Volt NIMH 2700 Mah pack - 6/29/2002 5:32:49 PM   
Geistware



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From: Locust Grove, GA, USA
Status: offline 		Why not put it on a fast charger to get more energy in the battery initially then do your experiment.

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6 Volt NIMH 2700 Mah pack - 6/30/2002 2:28:42 AM   
goatnick



Posts: 80
Joined: 1/6/2002
From: Demotte, IN, USA
Status: offline 		Thanks gentleman for your response, Reading on accucycle after discharge was 232 minutes, this was with setting on 5 cell pack and discharge set at 500 MAH, Appears I had plenty in reserve,Do you know if discharge terminates at 5.5 discharging a 5 cell pack, says in instructions to make sure that switch is in proper setting but dosen' t say at what voltage it kicks out,Geistware are you saying battery wasn't fully charged after 16hrs on DDVC at 270 MAH.I'm not hep on electronics but does fast charging put more in battery,Thanks again Bob

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6 Volt NIMH 2700 Mah pack - 6/30/2002 2:53:42 AM   
Geistware



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Status: offline 		NO, 16hrs at 270ma on a is more than enough to charge a 2700maH battery. When I saw the 730. I was thinking it was 730maH not 7.30 volts. Fresh off the charger you should be above 1.25 volts per cell. After a short period of discharge you should be stay around 1.2-1.25 volts until you have reached discharge condition which is around 1.15 volts. Some people will discharge down to 1.1 but I don't like that.

Most voltage monitors will indicate a discharged condition at 1.2 volts per cell.

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6 Volt NIMH 2700 Mah pack - 6/30/2002 3:38:23 AM   
thomasb



Posts: 343
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Status: offline 		[QUOTE]Do you know if discharge terminates at 5.5 discharging a 5 cell pack,[/QUOTE]Accu-Cycle uses 1.05V/cell cut off. Therefore, five cell pack terminates at 5.25V.

This is a bit higher than is used by the cell makers, so Accu-Cycle will under-report the capacity by a small bit. I guess that is better than the other way around.

Your results indicate that you had over 1900mAH remaining. I would say that you had PLENTY reserve.

[QUOTE]Most voltage monitors will indicate a discharged condition at 1.2 volts per cell.[/QUOTE]I use 1.185V/cell (C/5 loaded) for my cutoff, and that leaves a small reserve in the pack.

< Message edited by thomasb -- Jun 29 2002 11:09PM >

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6 Volt NIMH 2700 Mah pack - 6/30/2002 4:46:06 AM   
goatnick



Posts: 80
Joined: 1/6/2002
From: Demotte, IN, USA
Status: offline 		Thanks again fellows for the help. Sorry I forget the dot after the 7, Now I feel I can fly more than a couple of times and have piece of mind, Thanks Bob

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6 Volt NIMH 2700 Mah pack - 6/30/2002 6:35:24 AM   
Geistware



Posts: 12946
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Status: offline 		thomasb,
I understand what you are saying but the Vol****ch and the hobbico expanded volt meter both indicate an unsafe condition for a 4 cell pack at 4.8 volts. This equals 1.2 volts per cell. I don't know about the expert unit but I would expect the same thing. My 5 cell unit (expert) goes to red at 5.9-6.0 volts. That is right at 1.2 volts per cell as well.

Which unit do you use that indicates a critical condition at 1.185V/cell? That is 4.74 volts per 4-cell pack or 5.925 per 5-cell pack. I guess for my expert, 5.925 does fall within the range of 5.9-6.0 volts

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6 Volt NIMH 2700 Mah pack - 6/30/2002 7:07:04 AM   
thomasb



Posts: 343
Joined: 6/6/2002
From: Private, CA, USA
Status: offline 		[QUOTE]I understand what you are saying but the Vol****ch and the hobbico expanded volt meter both indicate an unsafe condition for a 4 cell pack at 4.8 volts. [/QUOTE]I can confirm that the Volt.Watch goes to the first Yellow on 4.8V. But in this situation, the pack is not expected to be loaded much. Five idle servos do not draw a predictably large current. As such, the measured voltages need to account for this (unloaded voltages will rise slightly).

I load my packs with a C/5 load and use a Digital Voltmeter. I have confirmed that when I stop for the day that there is a small reserve in the pack, as measured on my cycler. I usually have >20% reserve.

The nominal voltage from a NiMH is a bit lower than a NiCD and its discharge curve is a bit steep at the end-of-charge area. For this reason, the Volt.Watch is NOT recommended for use on a NiMH pack, per Hobbico.

I noticed that the GEM2K monitor is using 1.187V for the cutoff. I believe it attempts to measure this under load by using a bit of averaging. My 1.185V is really the same thing. GEM2K: [url]www.electrotekrc.com/specs.htm[/url]

[QUOTE]That is 4.74 volts per 4-cell pack or 5.925 per 5-cell pack.[/QUOTE]According to GEM2K, at 4.75V and higher, you have 30% or more remaining capacity. Anything less means that you have less than 30%. That is as much as you will be able to tell by reading the volts under load (the voltage method is not very informative, other than pass/fail).


As an experiment, fly until you reach the Volt.Watch's first yellow. Take the model home and measure the remaining capacity. I would be interested in what you find. I think you will be surprised. If you ask me, this is the best way to tell what is really going on.

< Message edited by thomasb -- Jun 30 2002 4:17PM >

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