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e-Electric Batteries & Chargers > how low to run 11.1V 3 cell?
 
 
pirellip
Heliman
Location: Toronto, Ontario, Canada

My Posts This: Topic  Forum		I know you shouldn't go below 9.6V no matter what, but how low do ppl run them on your x400/Trex? At a field I was flying at they're all like "don't go below 11.2 or you'll damage your pack" is this true?
03-12-2006 Over year old.
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leslie
Key Veteran
Location: Hollis, NH - USA

My Posts This: Topic  Forum		Hi All,

My experience, the bird will almost land itself when the battery is near the end of its cycle.

I used to have a beeper/warning circuit installed but it was added weight and the behaviour of the bird tells me when to pack it in.

I find when I have to really push the throttle to get her to hover, it's probably time to land. When I get the battery back into the charger the voltage is 10.8-11.5. I've never had problems with my packs as long as I pay attention to the diminished performance = land now

Cheers,
Leslie

Protecting those who protect us
03-12-2006 Over year old.
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Rob_T
Elite Veteran
Location: ..

My Posts This: Topic  Forum		Much better than relying on the voltage is to check the amount of current you need to charge back into the battery before its full. If you have to charge more than 85% of the nominal capacity of the battery then you're flying it too long, and you should cut back on your flying time.
03-12-2006 Over year old.
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leslie
Key Veteran
Location: Hollis, NH - USA

My Posts This: Topic  Forum		Hi All,

Great tip Rob_t! I've always eyed the voltage when I came in from flying.

Out of curiosity, how does a balancer effect this? The balancer (tp205 for me) seems to occasionally discharge a couple cells. so I'm thinking if I'm charging and its discharging my mah put back in is going to be a little artificially high.

Cheers,
Leslie

Protecting those who protect us
03-12-2006 Over year old.
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Rob_T
Elite Veteran
Location: ..

My Posts This: Topic  Forum		In theory (!) the TP 205 should only ever discharge at most 2 of the cells, so you'll still measure the amount fo charge that went into the 3rd cell.

In practice there probably is a slight increase in the current you need to charge because of the balancer (if nothing else, the balancer actually takes power from the battery to operate the "brain" of the balancer). I dont think it's so much that I'd worry about it though, and if it does make a difference, it will be in the direction of making you a little more conservative in how much you discharge the battery, so it definitely wont do any real harm!
03-13-2006 Over year old.
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N111KX
Heliman
Location: Atlanta, GA USA

My Posts This: Topic  Forum		An above post mentions disregarding voltage for battery care. If it is true that low voltage that actually damages the cells (<3V per cell) then I would pay MOST attention to voltage. A conservative figure for maximum battery life seems to be not allowing the pack to fall under pack rated voltage with no load (ie, after a flight noting 11.1 volts and not less). If you wish to push them harder then theoretically you could go lower but you must consider how much time during flight load that you are at or near the killer 9V mark or 3 volts per cell.
Just my two cents...
Kip
03-14-2006 Over year old.
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leslie
Key Veteran
Location: Hollis, NH - USA

My Posts This: Topic  Forum		Hi All,

I don't believe Rob_T or myself advocate disregarding battery voltage. But paying attention to both the discharged voltage and the amount of current you put back into the battery are BOTH good indicators of battery health.

Cheers,
Leslie

Protecting those who protect us
03-14-2006 Over year old.
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Rob_T
Elite Veteran
Location: ..

My Posts This: Topic  Forum		The problem with looking at voltage after discharge is that it isn't a constant. A deeply discharged battery will pick up volts while it's sitting doing nothing, so if you check the voltage 30 seconds after flying and again 30 minutes after flying you will get different numbers, often quite different.

Because of this, open circuit voltage of the battery after flying is not such a good indicator of the amount of charge taken out of the battery as actually measuring the charge put back in.

I have no objection to using low voltage warning devices in flight to warn when you're getting near to 3V per cell (or 3.3V as advised on some batteries), it's looking at the open circuit voltage an undefined length of time after flying that I dont think is reliable.
03-14-2006 Over year old.
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drksky
Senior Heliman
Location: Bloomington, Illinois

My Posts This: Topic  Forum		Is there any way to meter how much you're putting back into a pack without using a charger with that specific function on it?
03-26-2006 Over year old.
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Rob_T
Elite Veteran
Location: ..

My Posts This: Topic  Forum		You can use something like the Wattage D.C.M. which is also usefull for checking current draw of your motor. (Astroflight makes a similar unit for a few bucks more).

In the long run though, I'd suggest moving up to a charger that does have a display of current charged and voltage etc. They're usefull for diagnosing battery problems and really dont cost that much.
03-26-2006 Over year old.
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oldboldpilot
Key Veteran
Location: Southern California

My Posts This: Topic  Forum		In my experience, there is excellent correlation between "end of flight" voltage measured more or less immediately after flight, and the recharge mah displayed on the charger.

I am "anal" on my LiPos, which are 10S2P, $$$, and I record "all" readings all the time

And I have not seen a difference in pack voltage measurement "immediately' versus "after a while."

My packs don't get really hot in flight..

Helis are Man's Defiance of the Laws of Nature - OCHC
03-27-2006 Over year old.
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e-Electric Batteries & Chargers > how low to run 11.1V 3 cell?
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