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.?
Reply to
The Observer
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Red Scholefield participates in this group and has a place called The Battery Clinic:
There's a page on NiMH. Scroll down the menu on the left and you'll see the link.
Marty
Reply to
Martin X. Moleski, SJ
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
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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.
Reply to
Ted Campanelli
| 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
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...
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.
Reply to
Doug McLaren
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:
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Michal
Reply to
Michal
| 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: |
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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.
Reply to
Doug McLaren
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
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us out for "revolting" information.
fiction.
Reply to
Red Scholefield

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