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Old 01-30-2003, 07:27 PM
  #1  
swampthing
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Default Batteries

I have a flight pack that is a 600mah for my Rx.What is it susposed to read when it is fully charged? I have checked it with my voltmeter that puts a 300ma load on the battery and it will drop to 4.2 4.3 When I check it with another one of my volt meters that does not put a load on it it will read 5.5 5.6 volts. I guess my question is does it sound like the tester is reading wrong,the one that puts a load on the batteries? These are Ni-cads batteries. When they are fully charged,how low of voltage can I safely go to fly? I am not sure weather the batteries are no good,and by the way they are new and I have charged them 20 hours, or the tester from Hanger 9 is bad. Thank you for your time.....Swampthing
Old 02-07-2003, 11:15 PM
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jack01
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5.5 to 5.6 is good without a load. That 300 mha load on a 600 mha battery is pretty stout. Although the unloaded tester will work fine, I'd be more comfortable with a slight load on it. I've got a Hobbico digital voltmeter that has an LED that turns green when the vattery is charged and red when it is too low. It also has a LCD screen to show you how far the voltage drops when you put the load on it.
Old 02-08-2003, 05:55 AM
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FHHuber
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The 300 mah load will get the battery wire harness to start heating up... Too much current for the fine wires. Don't use that test very much.

As above... the unloaded 5.6 v reading is typical for a fully charged 4 cell NiCd pack. I've seen them read up to 6.2 v if you get the meter on immediately after taking the pack off the charger... but that drops VERY fast.

Using the unloaded ESV: You are usually safe to fly until the pack reads 4.8 v unloaded. Below 4.6 v the voltage drops rapidly. The majority of the power curve wil be in the 5.2 to 4.6 v range.

I take my readings after leaving the RX on for at least 30 sec to clear the voltage rebound. If you let the NiCds rest more than 1 min afterf lying before connecting the ESV... you can get a false high reading.

Loaded ESV's don't have the voltage rebound problem, but you need to use .05 to .1 times the capacity for the load... Excess load gives false low readings. At high loads even the battery leads will give you a significant voltage drop.
Old 02-08-2003, 09:07 AM
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Rodney
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Really, 300 ma is not an excessive test current. Any single servo (on a typical 40 sized plane) can draw a momentary current in excess of 1000 ma for a brief period or if stalled. I would double check the voltage reading you are getting with the loaded meter by simultaneously reading that voltage with the other meter; the two voltage reading should be the same at that time. It may be that the loaded meter is reading low. If not, I would suspect at least one marginal cell in your battery pack; it should not load down that low with a 300 ma load right after charging. If these measurements are being made downstream of the switch, it could also mean you have a high resistance switch. Check the voltage on each side of the switch while under load, if there is a difference, replace the switch.

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