NiMH Batteries and TX Range

"mjc13 @verizon.net>"

In article , "Six_O'Clock_High" > them with an alkaline recharger. I'd *like* to switch to NiMH batteries,

NiMH on the other hand easily provides more current - check the voltage on the batteries while transmitting and it may not be 12 V anymore. You need a charger for NiMH, as the ones for NiCd charge them only about

Marc

I was afraid that I'd get 75% or so of my normal range, and would then crash the plane(s). The normal range is a pretty long walk to fully test it! Maybe I'll do a comparison with the antenna down...

In article , Six_O'Clock_High recharging them with an alkaline recharger.

Hopefully they're rechargable alkalines ...

| > I'd *like* to switch to NiMH batteries, but I'm concerned about a | > drop in range if I go from batteries producing about 12 volts to | > those producing about 9.6. Should I be concerned, or not?

Probably not.

Alkaline batteries only put out 1.5 volts/cell when they're new -- it's all downhill from there.

NiCd and NiMH cells put out 1.4 volts/cell when freshly charged, then they drop to 1.3 volts or so relatively quickly, but then take a long time to get to 1.2 volts. Once they get below 1.0 volts or so, they'll drop off fast.

I don't know how rechargable alkalines work.

Comparing 12 volts to 9.6 volts (1.5/cell volts vs 1.2 volts/cell) is hardly fair, because one is a fully charged battery, and the other is a battery that's around 80% discharged.

| MOST transmitters operate on NiCad's whose charge status should exceed 9.6 | volts. That is the cutoff point I use for NiCads, but not for NiMH.

You can really treat NiCd and NiMH the same in most respects, include that one. 9.6 volts on a 8 cell TX pack is a good time to stop flying, NiCd or NiMH.

| Read the specs carefully because I think you should be ok. NiMH | cells have lots and lots of miAH so you will need a special charger | for them.

A wal-wart for your TX can charge NiMH cells, it'll just take a lot longer, up to 4x as long. I don't think the self discharge rate is a really large concern, even if you're only charging at a C/48 rate.

Judging from past posts, mjc is talking about the low end planes that don't even have a charge jack -- he's just removing the cells and charging them in his AA charger.

NiMH batteries should be a drop-in replacement for that. You should not lose any significant range from using them. For the higher end gear, losing some range isn't really a concern because you start with

If there's any question, test it -- get some NiMH batteries, discharge them most of the way (not all of the way, just most -- like 75%) and do some range testing. Put in freshly charged alkalines, have a friend hold the TX and wiggle the sticks, and walk away with your plane until it stops being accurately controlled. Then repeat in the same place and holding the plane in the same way with the NiMH cells in the TX, and see if the ranges changes. I would not expect a large difference -- and by comparing fresh alkalines to almost dead NiMH cells, you're looking at a worst case scenario.

Thanks for the reply. The only reason I haven't just tried it is that I don't have 8 AA NiMH cells, and don't want to buy that many, plus a charger that will handle 8, if it won't work. Sounds like it probably will, though. I just hope the range doesn't drop off...

I'm using regular alkalines and a Buddy-L charger. I've recharged alkalines for years, and there's a knack to it. Some brands, like Duracell and, believe it or not, Ray O Vac, are much more tolerant of being recharged than Energizer and even some store brands. You also have to recharge them *before* they get too low. That's a PITA, though, because the 'Vulcan' TXs drain them pretty quickly.