New Nimh first Charge?

[QUADDRA]

Hi,
Just bought a new 1050mAh Nimh and need advice on the first charge.

I have a multiplex 5008 DC charger that is quite basic with one button to set NiMH or NiCd and a dial to set charge current (from 0.1A - 5A)

On my old Nimh, it instructs you to set the charger to 1.2A for an hour. The charger automatically switches to trickle at end of charge.
Therefore, it takes about an hour to recharge the battery, which is why I have purchased a second, so I can fly whilst the other is charging.

Anyhow, back to my question, I’ve just bought this new 1050mAh and it says that a slow charge is required for the first charge so how do I set the Multiplex charger to do this? do I just set the charge current to min 0.1A or not?

[Alistair Taylor]

Yes

0.1 A is 100Ma, which is 1/10 of 1050Ma, and the 1/10th C rate that you're advised to charge NiMH batteries at for the first charge.

1.2A is the "fast" charge rate for these cells - best not to exceed this or risk damaging them.

AlistairT

[QUADDRA]

Thanks Alistair.
So does the charger still automatically turn to trickle? and roughly how long will this charge take?
Thanks again

[Alistair Taylor]

100 Ma is more or less a trickle charge for this battery pack.

Time-wise, as a rule of thumb, most battery packs are supposed to be charged at 1/10 C for 14 - 16 hours. This is the standard slow charge rate (NiMh and NiCad).

Your 1050MaH battery pack is therefore supposed to be charged at 105Ma for 14 - 16 hours (Call it 15 hours (for ease of maths).

105Ma x 15H = 1575 MaH (Call it 1600 for ease of maths again).

Divided by the 100Ma that your charger will be suppling = 16 hours.

So a 16 hour charage at 100ma should see your battery fully charged, but don't sweat about leaving it on for an extra 30 mins or so, this low charge rate shouldn't damage the cells, although it's not advisable to leave cells (particularly NiMH, but not so much NiCAds) on charge for extended periods or permanently.

If you've got solar garden lights, these use NiCads and are left on charge all day every day, and discharged every night. They don't use any fancy charge-control circuitry.

AlistairT

[Tim Mackey]

But my lights never seem to have enough power to leave the ground :(

[QUADDRA]

Hi Alistair,
Thanks,
Just read the instructions for my charger and it says that for safety reasons main charge process is limited to 2 hours after this the unit switches to trickle charge then trickle charge is limited to max 3 hours. So do I just keep restarting after every 5 hours? Means getting up at 4AM!!!! Oh No!!!!

[Tim Mackey]

you haven't actually said how many cells are in your battery, but if it is for tr or receiver , then just put it on charge with the wal-wart charger from your radio set...these are usually set to a very low "trickle" style rate.

[QUADDRA]

Hi Timbo,

9.6v 8 cells and its for receiver & power.

Also I put it on charge at 6pm and the charger that Ive spoken about above has just started beeping. Normally it beeps then switches to trickle. I dont know why it didnt this time. Anyhow just reset it charging at 0.1A
Am I doing this right or should I just take it off charge completely?

[Alistair Taylor]

Blimey, what a limited charger!

This sounds totally inappropriate for first-charging your NiMH battery, although fine for subsequent fast charging.

A first charge is supposed to be at a low rate, and therefore continue for some time - so shutting off after anything less than 15 hours is pretty useless!

However, you may still be able to use your transmitter/receiver charger to charge this battery. I've done this successfully several times.

First - check your TX/RX charger. It almost certainly does not incorporate a delta peak cutoff, and probably charges at between 50 - 100ma. As per the calculation above, at 100ma you'll need to leave it on for 16 hours, at 50ma for 32 hours(!). You'll probably need to make up a fly lead that connects your power battery to the charger output, or to the TX battery socket in the transmitter. This can be easily achieved with choc-block connectors (don't ever use these for connections on flyin models - they can vibrate loose, cause interference, and high-speed air-to-ground encounters).

NB: DO NOT REVERSE THE BATTERY POLARITY OR YOUR TRANNY WILL BE DEAD, YOU WILL LOSE THE WILL TO LIVE, SHRIVEL UP AND EXPIRE!!!

If the charger does not incorporate delta peak (likely) you'll just need to make sure you switch off after the appropriate time - but don't sweat an extra 30 mins or so.

Hope this helps


AlistairT

[QUADDRA]

Cheers Alistair

[Alistair Taylor]

Oh - and only fast charge the 1050MaH battery at a max 1-amp. This should be OK for it

Glad to have been of help

Alistair