NiMH batteries

Well, I've started building again (after a hiatus of several years spent skydiving). I see NiMH batteries in the hobby stores now.
Are there any on-line articles on the care and feeding of NiMH batteries? Are they as reliable as NiCds? If I re-equip my models with NiMHs, will I need to buy a special charger? Etc.?
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On 4/30/2004 08:25, The Observer wrote:

Have a look at http://www.rcbatteryclinic.com
Lots of great battery info!
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On Fri, 30 Apr 2004 10:25:31 -0500, The Observer

Red Scholefield participates in this group and has a place called The Battery Clinic:
<http://www.rcbatteryclinic.com/
There's a page on NiMH. Scroll down the menu on the left and you'll see the link.
                    Marty
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On 4/30/2004 11:25 AM Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:
NiMH are as reliable as NiCads. They are somewhat lighter in weight than NiCads also. You PROBABLY will not need a special charger for NiMH. The chargers in the past several years handle NiCads and NiMH equally well.
Check http://www.rcbatteryclinic.com This site should provide you with all the information you need.
If you are doing electric planes, you need to look into LiPo batteries. These do need a special charger and have several SAFETY REQUIREMENTS FOR SAFE CHARGING, however, they are substantially lighter than NiMH.

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I have a question for you and Red. Documentation for FMA Direct Safety Guard Device states that it can be used to allow NiCd/Nimh chargers to charge 2s and 3s packs. It states that this method will not damage cells, but might not charge the cells as fully as a dedicated Lipo charger. What is your opinion about this device? I have two NiMh/cd chargers, and if these devices ($12 each) would allow me to charge LiPos, I would try them right away.
Here is the pdf documentation: https://www.fmadirect.com/support_docs/item_1133.pdf
Michal
--
u*x sys admin, programmer, aviation enthusiast, photographer

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| I have a question for you and Red. Documentation for FMA Direct | Safety Guard Device states that it can be used to allow NiCd/Nimh | chargers to charge 2s and 3s packs. It states that this method will not | damage cells, but might not charge the cells as fully as a dedicated | Lipo charger. What is your opinion about this device? I have two NiMh/cd | chargers, and if these devices ($12 each) would allow me to charge | LiPos, I would try them right away. | | Here is the pdf documentation: | https://www.fmadirect.com/support_docs/item_1133.pdf
Well, after looking at what it does, it looks like it would indeed allow you to safely charge a LiPo pack with a NiCd or NiMH charger. The reason it might not allow a full charge is that the charger might see a `peak' happen and abort the charge on it's own, as it would think it's charging NiCd or NiMH and it would think that it's done.
I wouldn't suggest buying one of these so that you could use your NiCd/NiMH charger to charge LiPo cells -- they'd probably work fine, but it just doesn't seem right. And besides, you can find basic LiPo chargers fairly cheap if you look around.
--
Doug McLaren, snipped-for-privacy@frenzy.com Fax is stranger than fiction.

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I would not use any charger for Lithium cells that is not designed for them. While the Safety Guard device may keep you from blowing them up there are just to many other peculiarities and differences between the charge protocols for lithium and Ni-Cd to make this a practice that I would recommend. -- Red S. Red's R/C Battery Clinic http://www.rcbatteryclinic.com Check us out for "revolting" information.
Fax is stranger than fiction.
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| Well, I've started building again (after a hiatus of several years spent | skydiving). I see NiMH batteries in the hobby stores now. | | Are there any on-line articles on the care and feeding of NiMH | batteries? Are they as reliable as NiCds? If I re-equip my models with | NiMHs, will I need to buy a special charger? Etc.?
To expand on what the other poster posted about www.rcbatteryclinic.com ...
They're perhaps a little less reliable than NiCds -- they don't last quite as many cycles, and handle abuse less well. And their rate of self-discharge is a good deal faster than that of NiCd. But the increased capacity helps make up for it.
If you have a fast charger, it needs to be able to charge NiMH cells -- not all can. Your slow wal-wart charger will work fine with them, but will take longer to do a full charge -- if the battery has 3x the capacity, like 600 mAh vs. 1800 mAh, a full charge will take 3x as long.
Oh, and you can't safely charge AA NiMH cells at more than 1 C.
NiMH cells are *perfect* for your transmitter. The only downside is not being able to quick charge at 2 C -- but having 2-3x the capacity helps make up for that.
For a receiver pack, they're good, but there's a few gotchas -- they have higher internal resistance, so they can't provide as much power. Normally this isn't a problem, but if your servos draw a whole lot of power (like with a stalled digital servo) it may be one. Cushioning them against vibration is more important as well.
For a power pack, be aware that NiMH cells have higher resistance, so they may not be able to dump as much power in a short time.
--
Doug McLaren, snipped-for-privacy@frenzy.com
"A good reputation is one of many tiny annoyances to which I have
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Thanks, everyone, for the excellent info. I am not planning to use for electric planes, just for Tx and Rx use.
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