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Author Topic: Battery Usage - Cutting it too close?  (Read 492 times)

Offline Heman Lee

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Battery Usage - Cutting it too close?
« on: August 23, 2011, 09:29:04 AM »


I flew my E-Ringmaster at the Goyet contest this weekend.  I am using a 4S 1800mah Lipos.  I measure the battery voltages after each flight.  It averages 3.74 v +/- .01v for each cell on all 5 of my batteries.    I always touch the battery after each flight, barely luke warm.  When I look at the charger after a complete charge it puts back about 1530mah.  According to my charger come out to about  85%, even though the volts is above the minimum.   Is the charger (Hyperion 0606i) showing me the correct number?

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Offline Howard Rush

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Re: Battery Usage - Cutting it too close?
« Reply #1 on: August 23, 2011, 01:07:32 PM »
That's a good question, I think. What do chargers measure?  If they only account for the amount of charge they put out, it wouldn't include the amount lost in heating the battery during charging.   
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Offline Tim Wescott

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Re: Battery Usage - Cutting it too close?
« Reply #2 on: August 23, 2011, 01:14:23 PM »
LiPo batteries are supposed to be very efficient with the charge that goes in -- something like 99% of the charge that you stuff in during charge comes out during discharge.  (This is quite unlike NiCd, NiMH, lead-acid, and most other battery technologies that suck up significantly more amp-hours than they deliver).

So if the charger accurately measures amp-hours, then it should be a fairly trustworthy number.
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Offline William DeMauro

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Re: Battery Usage - Cutting it too close?
« Reply #3 on: August 23, 2011, 02:16:36 PM »
Herman,
Using 1530 is pushing the limits of your 1800's for sure. Without more info(basically flight time,motor and prop) its hard to advise you what to do. If you can, shorten the time till to get your usage to around 80%. Your best option may be to get some 4S 2200's and then you will be fine.
Howard,
Chargers measure what goes into the battery in mah. So assuming we are starting with a fully charged battery, It will be the amount that goes back in after the flight. The better chargers are very accurate. The inexpensive ones lose some accuracy during the balancing phase but are still close enough to let you know if you have any sort of problems. The inaccuracy is usually to the high side which at least means you would be using less mah which is better for the battery. Also a lipo should NEVER EVER GET HOT OR WARM DURING CHARGING!!!!!!
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Offline Dennis Adamisin

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Re: Battery Usage - Cutting it too close?
« Reply #4 on: August 23, 2011, 03:17:57 PM »
My Triton Charger/Equinox balancer displays total pack voltage & MAH put back into the pack.  I have seen it get to peak voltage then use up to 45 minutes and an additional 150 mah to finish balancing the pack.  My GT-A6 does not do that but does  a great job balancing.

Don't know how the Hyperion charger acts but you might watch for the behavior I described.

I guess I would expect to see lower cell voltages if you were drawing 85%.
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Offline Heman Lee

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Re: Battery Usage - Cutting it too close?
« Reply #5 on: August 23, 2011, 06:13:02 PM »
I just calculated the 85% based on 1530/1800.  The only thing the charger said is is the amount it put in (1530).  I can not find any definitive chart on exactly what voltages represent the percentage of charge.  Is 3.7v 10% or 20%?
Update:
This was posted on Wattflyer Forum:

       1S1P  2S1P 3S1P  4S1P   5S1P  6S1P
100% 4.20 8.40 12.60 16.80 21.00 25.20
90% 4.15 8.3 12.45 16.60 20.75 24.90
80% 4.10 8.20 12.30 16.40 20.50 24.60
60% 4.00 8.00 12.00 16.00 20.00 24.00
40% 3.90 7.80 11.70 15.60 19.50 23.40
20% 3.80 7.60 11.40 15.20 19.00 22.80
10% 3.70 7.40 11.10 14.80 18.50 22.20
« Last Edit: August 23, 2011, 10:08:08 PM by Heman Lee »
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