# NiMH Charging

• posted

I have been told that the slow chargers that come with radios will not charge NiMH packs sufficiently. Is this correct? If it is, will a Sirius Peak charger suffice? If not, what do you use? I want to replace my Futaba NiCD transmitter pack with a NiMH pack but won't do it if I have buy new charging gear.

Ted

• posted

Sounds like total bollocks to me.

My Futaba trasnmitters charge just fine on Nimh cells and the stock charger.

• posted

They will charge just fine. It will take longer, since the NiMH packs usually have a much higher milli-amp hour capacity.

If your new pack is double the capacity, it will take twice as long to charge it, assuming both were fully discharged. That is the trick.

You should do a little charting, if you want to find out how long to charge with your slow, dumb charger.

Make up a resistor jumper wire, or use a car tail light bulb, and check how many amps (or parts of amps thereof) it drains on a pack, using a voltage tester that will read amps. Take your pack and fully charge it, then start discharging it and recording the voltage every 5 minutes. When it is down to 1.1 volts per cell, or when the graph connecting the voltages starts a rapid plunge downward, quit. Multiply amps times hours divided by 100, and you have your milliamp hours.

Or you could spend a few bucks on a peak detecting charger, and know you fully charged your packs, and do it a lot faster. Your choice! :-)

I hope I have not cludged this up, too badly; especially about how to calculate the amp hours. You will get the idea that you have the wrong formula, if your 2200 milliamp hour pack calculates to 22,000 milliamp hour capacity, that I messed up the math, somewhere!

• posted

| They will charge just fine. It will take longer, since the NiMH packs | usually have a much higher milli-amp hour capacity. | | If your new pack is double the capacity, it will take twice as long to | charge it, assuming both were fully discharged. That is the trick.

The concern is that since the self-discharge rate of the NiMH cells is higher than NiCd cells, you may be charging slower than the self discharge rate. I do not believe this to be true, and believe your `twice the capicity, twice as long' rule of thumb to be just fine. Sure, it might take a little longer than that, but it's not going to hurt if your battery is only 90% charged when you have 3x the original capacity.

Still, taking 48 hours to do a full charge is excessive, and if you're serious about the hobby, you should have some sort of peak charger. Some day, you're going to want to fly, and didn't charge your batteries the night before. Do you skip flying entirely, or charge for just a few hours and hope that's enough, or don't charge at all and hope there's enough capacity left? None of these answers are ideal, and having a peak charger gives you a good fourth option -- top off your battery, probably in well under an hour. And you don't have to spend much money at all.

| After you have plotted your voltage, you should be able to read your pack | when you get back from flying, and be able to say how much you have drained | your pack.

This is likely to be very inaccurate with NiCd and NiMH cells. However, with NiMH cells that will power your gear all day long, you probably have enough extra juice that it won't bite you.

As for if the Sirius charger will do, it probably will, but if it's old it might not be able to detect the smaller peaks of NiMH cells vs NiCd cells. To be sure, contact Sirius. Or see if the instructions say it supports NiMH cells.

Your peak charger might not be able to charge through your TX charge jack (if there's a diode in there) -- some can, some can't. If it doesn't see the battery at all, remove the battery plug and charge through that. You can also short out the diode (which defeats it's purpose, which is to protect you from mistakes) or replace it with a poly-fuse, but that might not be worth the trouble.

• posted

No, it is not. However, NiMH is a little more sensitive to overcharge than NiCd, so if you leave them on the charger for too long, they will deteriorate a little quicker than NiCd.

A peak charger that is designed for NiMH will work well.

I use one of these:

I am very pleased with my charger. Earlier, I had to remember to put the batteries on charge the night before I was going to fly. Now, I have batteries that can be charged quickly (most batteries these days can), so I just stick them on the charger in the morning, and they are ready before I am done with breakfast.

The only downside with this charger is that I want another one, so that I can charge the Tx and Rx packs at the same time. I usually have enough time to do one after the other, though.

As an added bonus, you can discharge your batteries once in while to test them to see if they are in good shape. If your radio has a built-in diode to protect against incorrect polarity, you will need to bypass that if you want to discharge the battery through the charge connector.

• posted

Ah . . uh . . NiMH packs self discharge at a dramatically lower rate when compared to NiCd's. Something like 1% versus 10%...

But that is just what someone told me a few years ago. However, it does seem to fit the results I get with my Orbit...

Jim AMA 1428

• posted

In article , Six_O'Clock_High

• posted

"Doug McLaren" wrote

That isn't a problem, though. I don't know anyone that goes out to fly, without first charging their equipment!

With a quick charger, you can charge at least one up, while you are driving to the field.

Planning 45 minutes ahead, and charging with a quick charger is not a problem, for most people.

Or....

You could always go for setting your stuff up on a timer, so everything is always topped off.

If you connect some extension cords to a 7 day timer, and set your slow chargers up so that the timer runs for about 2 hours per week, then everything will always be ready.

• posted

I bought some new NiMh batteries last spring that has a membrane in them that slows down the discharge rate considerably. In fact, I just checked them, and with eleven minutes of discharge (flight time) on them last September, they still are showing 10.5 Vdc in my Eclipse transmitter. I had the eight cell pack made up at Batteries Plus out of 2100 Mah cell (new technology) Ray-O-Vacs. In the past using NiCads I had to charge the batteries half way through a one day sailplane contest. Not any more with these batteries. I can fly the whole weekend and still have plenty of battery power left.

I used an old Ace bench charger at C/10 rate for an initial 24 hour charge and have been using Towers FFC since then. A longer charge time is definitely needed if you use a NiCad charger. Also, a NiCad peak charger is verboten according to Ray-O-Vac. Only use a peak charger charger that has a NiMh capability.

BTW, you can use your NiCad charger(s) that comes with your Radio package but it is not the recommended way to go. Also, cycling the batteries like NiCads is not necessary or recommended for the NiMh packs that I have.

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