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Charging NiMH

Hi folks,

I bought the Yaesu FT-270e and I’m totally over the moon with it! Very, very pleased! Thanks to all the advice that was given on here pointing me in this direction!

So, last weekend we went up Fan Fawr in Wales and had a great time… worked 160 miles on 2m / 5w which I think is a pretty good result.

What do I do now? Off to the Welsh borders tomorrow and the Yaesu is half dis-charged. I don’t want to get up Brown Clee Hill and run out of juice, but the manual says charging the battery before it’s empty “reduces battery efficiency.”

Do I just leave it on, receiving nothing for 30 hours a week until discharged and then charging it up?

Advice appreciated,

Rob GQ7LAS

In reply to G7LAS:

Yes you can just leave the set on and run down the cells if you want then charge it up. But I wouldn’t worry much, partial charging will result in a shorter life than perfect charging and discharging. The cost of a new pack is pennies in reality so don’t waste effort worrying about it. Just get on the air and enjoy yourself.

Andy
MM0FMF

In reply to MM0FMF:

Thanks Andy… I like that answer! :slight_smile:

It’s going on charge right now!

All the best,

Rob

In reply to G7LAS:

What do I do now?

Recharge it. NiMH batteries do not show the memory effekt known from NiCd batteries. Some investigations find a much less pronounced “lazy cell effekt” but this can be removed by fully discharging the battery.
Always fully discharging your battery pack can harm it more than it uses: At a voltage of 7.2 V there are probably 6 cells in series in it. At NiMH packs single cells are not monitored separately. When fully discharging the pack the weakest cell is already at 0.9 V while the others still are e.g. 1.1 V. You do not realize this as the sum voltage is still 6.4 V. Further discharging the pack results in deep discharging and in the worst case reverse charging the weakest cell. By this treatment the weakest cell deteriorates even more and in the next cycles this effekt gets worse.
To avoid this the R/C model builders use matched battery packs where all cells have the same capacity.
So if you fear the lazy cell effekt discharge fully e.g. every fifth cycle and recharge rest of the time.

73 de Michael, DB7MM

In reply to G7LAS:

Hi Rob

Most problems with NiCd and NiMH battery performance are due to chronic overcharging. I suspect the warning in your radio’s manual is probably prompted by the high likelihood of causing overcharging by unsophisticated charging systems (like that in the FT817, not sure how your radio handles it) that rely on the length of time the batteries have been on charge to determine charge cutoff(which is particularly difficult with NiMH).

It is very wasteful to unnecessarily fully discharge batteries prior to charging just so that you don’t overcharge them, and as pointed out in Michael’s post potentially damaging. Provided it’s treated right a battery that will last 1000 full discharge cycles will last 2000 half discharges!

73 de Paul G4MD

In reply to G7LAS:
I don’t know what charger you are using but I would invest in a good quality unit, they don’t come cheap but as with everything you only get what you pay for.
The good quality chargers can discharge and also switch over to trickle charge when the battery is fully charged so no danger of over charging. Best place to look for reviews on which are good is on the Model Car forums, thought those guys are now increasingly moving towards LiPo that offer move punch for less weight. Their forums also offer a wealth of advice on how to look after NiMh Batteries.

I was involved in model cars for few years so have some experience on how to treat NiCd and NiMh batteries or show I truthfully say how NOT to treat them :wink:

73
Darius OK7OK

Just charge it when you can, for best performance run the battery empty perhaps ever 20-30th cycle.
With NiMH you just cannot know how empty the battery really is, do not blindly rely on what the battery meter says.

But…
Good charger is as important as a good battery.
Timer based overnight chargers easily overcharge the battery which is propably the reason why the manual says to run it down before charging.
A smart few hour charger is best for battery life, it’s up to you if you need one or do you want to save that money for a replacement battery every year or two.

Whatever your charger is, do not use it as a stand, do not keep your battery trickle charged, it’s the easiest way to ruin it.

I use AA NiMH batteries in my flashlights, camera, FT-817ND and many other gadgets so I have run a few tests with them.

When you need to replace your NiMH battery, try to find a LiPo battery, or at least stay away from those high capacity batteries(AA 2500 or up) because those are very very fragile.

Jani OH9FZU