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Old Mar 04, 2012, 01:17 PM
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United States, MA, Walpole
Joined Dec 2003
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Quote:
Originally Posted by ggtronic View Post
i suggest you to open the camera & measure actual battery voltage...

as mention before, the camera charge system let it go above 4.2v and may
dammage most of these camera lipo battery wich may lead to your problem
(it happend to me , i had to replace the battery) i'v install an external battery
+ futaba plug to monitor charge voltage :
http://www.rcgroups.com/forums/showp...postcount=8717

Maybe Tom could give an important advice about this camera charge circuit at the
first page ? as soon as a little battery this size gets hot, it mean overcharge ... my opinion...
all my coaxial heli & 1s airplane lipo never charge enought these 1s battery to heat them...
There is a charge management IC on the main circuit board of both the #11 and #16 cameras. I don't have a spec sheet on it, but it reportedly has a typical lipo CC/CV charge cycle to limit the current during the initial charge until the voltage reaches the recommended battery max. (typically 4.2V), then switches to a constant voltage mode with diminishing current to maintain that voltage until the current is a pre-defined fraction of the of the initial current. It is unknown how accurate that charge management chip is in terms of the max. voltage allowed. On the #11, the charge current was on the high side according to the manufacturer, and that was why the battery life was shortened, not because of excessive voltage. The #16 camera has a lower charge current, and therefore takes longer to charge, as well. There has not been enough time since the #16 was released to tell how much additional life the battery will have due to the lower initial charge current.

In addition to that charge management IC, the camera battery also has a small protection circuit board soldered to it tabs. In short, the protection circuit will shut down the charge if the voltage rises to 4.3V (+- .05V) for a period of 80-200 ms. When the detected charge voltage drops to 4.1V (+- .05V), the charge cycle will automatically resume. While 4.2V is the widely accepted maximum voltage for continued charging, many lipo manufacturers claim a maximum and minimum voltage of 4.23 and 3.0 volts per cell, respectively. Taking any cell outside these limits can reduce the cell's capacity and ability to deliver full rated current. So it appears possible for the voltage to exceed the manufacturer's claimed limit if the charge management IC is off spec., but it would only be for a VERY brief fraction of a second before the charge cycle would terminate, and the charge would not resume until the voltage dropped back down to 4.1 (nominal) volts. It's unknown whether the charge management IC will even allow an excess voltage high enough to trigger the protection circuit to occur. I think some users have reported voltages in excess of 4.2V on a battery after a full charge, but it is unknown if this is real or a meter accuracy issue.

The battery protection circuit board also has an over-current trip (e.g. short circuit) and low voltage cutoff (LVC) while discharging. The LVC trip point is also on the low side based on conventional practice, but the camera will shut down due to insufficient voltage for the circuit board long before the LVC limit is reached, so it's not a factor.

Also, Since a battery has an internal resistance, heat is inevitable when current flows into or out of it, with more heat as the current increases. It is NORMAL for a lipo to get warm when charging and discharging with most consumer devices like this camera. A greater risk, in my opinion, is when an external battery is connected in series with the internal battery, such as is possible with a hack that uses the #11 "special" cable or that simply runs parallel wires from the circuit board battery connection pads to an external lipo. If the internal battery is at a lower voltage than the external battery, current will flow from the external cell to the internal cell with nothing to limit the current other than the voltage differential and battery internal resistances. And since a hack like that bypasses the circuit board charge management IC, it's possible that an even higher charging current can occur than would have come from the charge management IC. The safe way is to always be sure the internal cell is fully charged BEFORE connecting an external cell in series with it.
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Last edited by Tom Frank; Mar 04, 2012 at 01:32 PM.