snewpy

I've read on several occaisions that consumer sized NiMh cells (AA and AAA) have too much internal resistance for e-flight. Doesn't the maH rating determine the output of a battery? Is it simply the physical length of them? Too much heat?

The reason I ask is I just put together an 8 cell pack using sanyo 2300 maH AA NiMh's and plan to use this in my e-glider. Will I be disappointed? (Can't try it until I get some radio gear for it.)

U2Steve

Internal resistance determines how fast the energy in a battery can be pulled out of it and used. Things like radios and CD players sip electricity; airplane motors guzzle it. If your batteries can't keep up with the demands of your motor, they'll cook, and as they heat, their resistance goes higher, so you lose flying power...ouch.

You don't mention what motor you're using. I've seen rechargeable batteries from the Wal-Mart sale bin that worked fine in an IPS setup, flying LiteSticks and Tiger Moths. If you're using a Speed 400 or 500, especially direct-drive, you might be disappointed.

Hope this helps,

Steve

Uncas

My Feedback: (1)

Not all Nimh's are created equal. The more internal resistance a battery has the less current (AMPS) it will be able to produce. Mah is milliamp-hours and is more a measure of how much ENERGY the battery has and not how much POWER it can deliver.

You probably need a battery that has low internal resistance. I do not know if the Sanyo 2300's can deliver what you require. I use them in my transmitter - but it does not pull a lot of current. I always use KAN batteries for my plane power batteries. A good place to evaluate different battery types is [link=http://www.cheapbatterypacks.com]cheapbatterypacks.com[/link]. I highly recommend them.

My 8 cell KAN 650's can deliver 13amps. Keep in mind that battery terminal voltage drops to 7.3 volts. How do I know this? Because I measured it with a Whattmeter. While I was doing this I also measured the thrust the power system delivered with a small fish scale.

I have found the electric power system design to be somewhat challenging. With all the combinations of gearing and prop sizes, speed controllers and battery types. They all have to be optimized to get good performance.

Good Luck!

Charley

My Feedback: (2)

Milliamp hour ratings are usually stated at the one hour rate. So if the cells are loaded to draw 2300 mA (2.3 Amps) they should do it for 1 hour - presuming a 100% charge - not likely. Pull current out of them faster than their rating and they'll heat up. That's because the power lost across the internal resistance is dissipated as heat. As they heat up the internal resistance increases, a vicious cycle. So you need to know the internal R of the cells in question and at what rate and temp, etc.

Cheers,

CR