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Plane_freak
09-08-2005, 12:07 AM
I have never really used Nimh batteries but I use Ni-cd a lot more. My Nimh gets pretty warm while charging it. how hot is too hot for a nimh battery?:confused:

batman
09-08-2005, 03:58 AM
When you can't hold one in your hand for longer that a second that is getting hot. Mine come out of the plane like that. Off the charger they can get hot but not too hot to hold in your hand. hope this clears things up for you.

Warden
09-08-2005, 01:23 PM
When charging or discharging, Nimh batteries get a lot hotter than Nicd's.

Matt Kirsch
09-09-2005, 04:58 PM
Plane Freak,

Are you charging the NiMHs too fast? They should get warm, not HOT. Charge at 1C, which is one times the Capacity of the pack, for best results.

Hot enough to make you uncomfortable (mentally or physically) is too hot, unless you're a total lunatic and anything above ambient is "too hot" for you :D

Plane_freak
09-09-2005, 11:32 PM
I have never even charged the battery past .8c. every time I get it up to almost 1c it gets hot. I don't want to charge it to fast and get it to hot and damage it. So I'll probably let it charge at .5c-.8c just so it doesn't get to hot.

Jason T
09-10-2005, 02:39 AM
I charge my GP2200 pack from 4 to 5 amps but I want them hot before they go in because the resistance is lower and they put out more power. I am constantly heating mine up to about 160 F while flying. I realize that I will probably shorten the life of the pack but its worth the extra performance.

GeraldRosebery
09-10-2005, 12:51 PM
I have never really used Nimh batteries but I use Ni-cd a lot more. My Nimh gets pretty warm while charging it. how hot is too hot for a nimh battery?:confused:

When I charge at 1C the batteries get to better than 180-200F unless I cool them. My cooling box keeps them to a perfect for flight 140F. I did fry a pack (blew the cell seals) by allowing it to get to 240F. So I advise - keep them under 200F.

FYI - I warm up the packs (3300 mah) on the way to the field by charging them at 1 amp. It warms them nicely to about 140F outside my cooling box.

AEAJR
09-11-2005, 04:58 PM
I have never really used Nimh batteries but I use Ni-cd a lot more. My Nimh gets pretty warm while charging it. how hot is too hot for a nimh battery?:confused:

I fly mostly NIMH. Depending on the charger, they will come off warm when they are fully peak charged. Some chargers will sends that peak sooner than another.

My HobbyZone charger finishes them warm. My Triton charger finihses them warmer. My Hitec charger finishes them warmer still. But none are too hot to handle.

Based on magazine reports in QuietFlyer, nimh can come of as high as 130 degrees which is pretty warm, but should not burn you.

The faster you charge them the hotter they tend to get. 1.5C is typical max for average motor packs. High performance packs might be able to take 2C, but don't push that far unless you know these are high performance packs.

Plane_freak
09-11-2005, 06:17 PM
What is the point of warming of your batteries? I what for mine to cool fully before making my way to the field. I usuallly put my nimh next to a fan just to keep it cool. I don't want to shorten the life of my battery and all I use this pack for is a Hyper wing. It is a 9.6 volt 800 mah AAA 5/4 pack. I am unsure what the 5/4 stands for. It is a great pack and a great plane. I can fly around at 1/3 throttle. It usually stays pretty cool in the Wing. I don't use a temp gauge. i go by how cool warm or hot the pack is.
I like lithium better than Nimh or Ni-cd. Lasts longer in the airplane weighs less and provides plenty enough amps.:D

AEAJR
09-11-2005, 11:58 PM
5/4 stands for the length of the cells. The cells you have are the same diamater as AAA cells, but longer.

GeraldRosebery
09-25-2005, 07:07 PM
What is the point of warming of your batteries? I what for mine to cool fully before making my way to the field. I usuallly put my nimh next to a fan just to keep it cool. I don't want to shorten the life of my battery and all I use this pack for is a Hyper wing. It is a 9.6 volt 800 mah AAA 5/4 pack. I am unsure what the 5/4 stands for. It is a great pack and a great plane. I can fly around at 1/3 throttle. It usually stays pretty cool in the Wing. I don't use a temp gauge. i go by how cool warm or hot the pack is.
I like lithium better than Nimh or Ni-cd. Lasts longer in the airplane weighs less and provides plenty enough amps.:D

NiMH cells internal resistance goes down as they warm up and they become more efficient. The ideal starting temperature is about 140F. Also, although LiPoly are very good they come with their own sets of issues and are hugely expensive in big packs.

hoppy
10-04-2005, 07:56 PM
Here's what a manufacturer has to say. It's a long read but tells a lot.
http://www.hardingenergy.com/techmanual.htm

GeraldRosebery
10-05-2005, 12:35 AM
Here's what a manufacturer has to say. It's a long read but tells a lot.
http://www.hardingenergy.com/techmanual.htm

Unfortunately the company provides the usual technical gibberish. Clearly no one at the company has ever conceived of drawing 10-15C out of a NiMH cell. It is the specialty applications we use that makes the information less than useful. Yes, we are not going to get 1000 cycles out of our hard used NiMH cells. Yes, if we allow them to get to 240F, they blow a seal. In the meantime, we all get a lot of fun doing things the cells were never expected to be able to do.

hoppy
10-05-2005, 03:07 AM
Plane_freak,
Some manufactures do conceive of that.
Here are the manufacturer's specs for a 15C NiMH battery.
http://sanyo.wslogic.com/pdf/pdfs/HR-43AAUP.pdf

Some modelers believe in maximizing performance and others believe in maximizing the useful life. I prefer cool with a long life, Gerald apparantly likes maximum watts to the motor. Both paths can be used and both are right for the purpose intended. You just can't have both.

Here is another source for technical information.
http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf
If nothing else, after reading it you'll have an excellent knowledge of how they work.

Oh, one other thing, there are a lot of so-so performing NiMH cells out there (even from RC/Battery shops) that won't take kindly to abuse. When you look at all the sizes and brands available, not many will stand up to high temperature usage. Maybe Gerry will report on which cells he has been using.

N3CLI
10-05-2005, 12:55 PM
Where did you get the parts for a cooling box?

Radio Shack has lots of nice fans, but what did you make the box material from?

Fred AMA68196:)