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how to check battery for mah???

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Old 12-23-2005, 01:12 PM
  #1
tiktock
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Default how to check battery for mah???

is there a way to check how many mah are left in a nimh battery?

thanks
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Old 12-23-2005, 01:36 PM
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Default RE: how to check battery for mah???

Discharge it with a good charger with LCD display. They'll say how much has been discharged from the pack..see sig, my charger will display when testing/cycling NICD/NIMH packs.
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Old 12-23-2005, 01:49 PM
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Default RE: how to check battery for mah???

as for my charger ..... I'm using the Hobbico Quick Field Charger MK ll and i don't think it's capable of displaying that information.
is there a way to use a multimeter to get that info?
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Old 12-23-2005, 02:25 PM
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Default RE: how to check battery for mah???

You could simply time it with fixed discharge rate, ie with Futaba BR-2000 (packs only)- discharge at 1A. Time it until the unit stops (0.9v) you've got the mah then.
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Old 12-23-2005, 08:57 PM
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Default RE: how to check battery for mah???

Does your millimeter have the ability to measure DC current?

The best results are realized by repetitive charge discharge cycles (three typically). Record the last charge/discharge mA readings, charge-fly and discharge you now have a baseline for comparisons.
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Old 12-23-2005, 09:35 PM
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Default RE: how to check battery for mah???

As Mad Wax and MGlavin have said you'll need to use the milliamp portion of a DVM and another DVM to measure the voltage across the cell. Most cell manufactures use a discharge current of C/5 or 1/5 the current rating of the cell and a low limit discharge voltage of 1 or .9 volt per cell. It is a lot easier to use the cycle functions of charger that has cycle capablities such as a Triton or a Multiplex LN 5014 or the Auto-Cycle Elite. Sirius makes a standalone unit.

http://www2.towerhobbies.com/cgi-bin...&I=LXCJG7&P=ML
http://www2.towerhobbies.com/cgi-bin...&I=LXKSY1&P=ML
http://www2.towerhobbies.com/cgi-bin...&I=LXEYD4&P=ML
http://www.siriuselectronics.com/ind...a0d1f56bcd7aeb

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Old 12-23-2005, 10:02 PM
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Default RE: how to check battery for mah???

What do you mean by current rating? Would a 500 ma battery have a different discharge rate than a 900 ma battery?
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Old 12-24-2005, 02:44 AM
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Default RE: how to check battery for mah???

What John was referring to is C/5 or 1/5 of the battery capacity. For example, if the battery has a rated capacity of 1000mA, then 1000/5=200. 200mA is the typical discharge current used by manufacturers to rate the capacity.
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Old 12-24-2005, 11:50 AM
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Default RE: how to check battery for mah???

I would like to know if it s possible to find out how much capacity is available in a battery pack which I am flying with.
For example, my notebook computer has a battery capacity of 4400 mAh. At all times I can get a reading of the current charge and can tell how long I will be able to use the battery. It would be great to have an accurate idea of the capacity left in the battery pack to know whether or not its good for more flights.
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Old 12-24-2005, 12:05 PM
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Default RE: how to check battery for mah???

It is safer to base fly/no-fly decisions using a voltwatch or a loaded voltmeter. When a battery pack voltage drops to the critical level of just below 4.8V, it may still have 15-20% capacity left.
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Old 12-24-2005, 04:00 PM
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Default RE: how to check battery for mah???

You're notebook computer uses a Li-Ion battery that is very linear with voltage as to it's capacity. the same cannot be said of NiMh batteries. Different chemistry. There is no accurate battery guage like on your laptop. I use a voltwatch on all my planes. I read the voltage when I land. If I wait 10 minutes before the next flight the voltage rises. Do some reading at Red's battery clinic.
www.rcbatteryclinic.com
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Old 12-24-2005, 05:35 PM
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Default RE: how to check battery for mah???

Is it really worth using a battery pack with a unknown storage capacity? How much is that model? And any damage to property/persons if it goes out of control? Just buy a £50 new charger!

I had a new NICD pack, charged with 2100mah put into it and reported ok on the LED monitor but car went into failsafe after 5 minutes! LED monitor showed red! Did a discharge/cycle and it only kept 200mah of charge. This was a model car not a plane...so at least the fail safe works and just stops the car...not like in a plane.
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Old 12-24-2005, 08:29 PM
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Default RE: how to check battery for mah???

Mad Wax - Hey the fail safe for planes works too. Kit to kindling 2 seconds!
You can do a load test with a voltwatch the same as a loaded meter if you exercise the servos for 2 minutes and the see how much capacity you've lost. Should still be in all the way in the green if the pack is good.

I agree that cycling the pack for capacity is the best way to know capacity. I always do it a the start of the season and write the test method and results on a label on the pack. I try to do another cycle test each month into the season. I've can see how a pack runs by how many 10 minute flight sessons I can get out of it before the voltwatch goes down. It's a pretty good indicator for $11.00!

John
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Old 12-24-2005, 09:38 PM
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Default RE: how to check battery for mah???

A charger that cycles down and records the mah is probably a good investment. Over the past ten years cycling down has probably saved 6 airplanes for me. Occasionally after a flying session I cycle the battery down after I get home to determine the remaining mah. Twice there has been less than 15mah when I expected several hundred mah. The batteries turned out to be way below rated capacity and were replaced. If it is difficult to determine the battery capacity testing will simply will not performed often enough.

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