The bird man

I talked at length yesterday with a very patient individual at Hangtimes Hobbies AKA NoBS Batteries, who answered many questions that I had regarding NiMh batteries. The following is what he told me to do regarding “Form” or “Formation Charging” of new NiMh battery packs.

1) Charge the pack at C/10 (200mA for a 2000mAh pack) until the pack just starts to get slightly warm to the touch. If you are using a peak detect charger it will most likely stop the charge before the pack begins to warm. This is OK, as it will prevent overcharging. If this is the case continue to charge the pack at C10 with a wall wart or a non peak detect charger until the pack just starts to get slightly warm to the touch. Allow the pack to cool before step 2.

2) At this point set your discharge rate at 500mA with a voltage cut off at 1.0 volts / cell and discharge the pack. Again if the pack is warm allow it to cool before recharging.

3) Repeat steps 1 & 2 at least 3 times while monitoring the capacity continue with additional cycles as needed until the capacity levels off.

The discharge rate in step 2 was for a NoBS 1950mAh FAUP Pack. I would think you would need to adjust this value up or down with different pack sizes and the rate he gave me is approximately C/4. If that holds true a discharge rate for say a 600mAh pack would be 150 mA. I will confirm the discharge rate and post it here. He was very adamant about letting the pack get warm during the charge portion of the cycle. He referred to the formation charging as “Teaching the cells that they are batteries”
I hope this helps others in getting the most from their packs.

Jimmy Bananas

My Feedback: (13)

I muse the 'Sirius Pro Former' to form change my NIMH batteries...here is the web site:

www.siriuselectronics.com check it out

gerwen

Common advice around here is to charge at C/10 for 16-18 hours, and discharge at C/5 to .9V/cell (1V/cell is fine too).

Pretty close to the advice you've been given, except you don't have to figure out a way to monitor your pack's temp.

JNorton

My Feedback: (2)

I'd goto sleep if I had to hold a pack at a C/10 charge for 14 to 16 hours. Do the charge discharge cycle that Gerwin specified three times and your NiMh packs should be at full capacity ready to be fast charged.
John

guver

My Feedback: (325)

I would agree with all the advise given, and have a question . Will the pack really get warm?

JNorton

My Feedback: (2)

I've never had a pack get warm on a C/10 charge using a wall wart charger. I believe the advice was given as a matter of safety, not what normally happens.
John

The bird man

The person I spoke with specifically mentioned (more than once) to make sure it got slightly warm. I took that to mean roughly 85 -90 degrees.
The advice that Gerwin specified is so close I wouldn't think anyone would see a difference to what I was told.
I just posted this for the benefit of those that were looking for a conformation from a reliable source like NoBS as to what is recommended.

JNorton

My Feedback: (2)

J Define warm. To me it's about 99 to 102 degrees slightly warmer than the human body. Sanyo uses 113 F as the max charging temperature. My packs are room temperature after being charged. To me is this is cool. Just a matter of perception.
John

TampaRCGuy

My Feedback: (282)

A few things I would like to comment on:

1). Formation charges need more than the normal 14-16 hours at C/10. They should be charged for 18-22 hours.
2). At C/10, the pack could get warm after 22 hours, but like a few people mentioned, what is warm? Warm is when you can feel the pack is warm, not hot, not cold. This WILL NOT HURT THE PACK.
3). Cycling should be at .8-.9V per cell, Not 1V per cell. At 1V per cell, you will be very lucky to get the pack up to rated capacity. You should know what your cyclers cut off voltage is to know if this is correct.
4). The discharge rate should be high enough based on the how the battery is to be used. I cycle all my packas at 1 amp (1000 mah) when the pack is over 1000Mah in capacity. Using too low a discharge rate could falsely rate the pack.

Rodney

Mr. Norton has given you good advice above, I agree with and have experienced the same things he has when charging NiMh. If a pack is getting warm, that means it has been overcharged to a degree and that the recombination of elements at the positive terminal is giving off energy as heat rather than charging. Heat is evidence that the charge cycle has gone as far as it can and any further charging will be detrimental to the life of the cells heating up.

Alfalfameister

So, after about 3 cycles of C/10 forming (for about 18 to 22 hours), and discharging at around C/4 or C/5, then the batteries are ready to be fast charged? Or should you also take it slow on the fast charge (no pun intended)? I mean, should your first [fast] charge be at, say, 1 amp? Or can you go and give it the ol' 6 amp charge right after the 3 cycles of C/10 forming charges (am a car guy, hence the high 6 amp charge, for GP3300 and 3700, etc)?

gerwen

After 3 form charge cycles, the packs should be ok to fast charge. That said, as you charge faster, your packs lifetime decreases. It's rough on a Nimh charging at over 1C. I only charge at 1C and above when i have to (at the track and need that pack). Otherwise i go easy on it and charge at C/5 or C/10.

So, if you need that pack NOW, fast charge it, otherwise, take it easy and give it a slow charge, it will last longer.

JNorton

My Feedback: (2)

Form charging is important for car guys or airplane drivers. You'll get maximum capacity out of the cells if you form charge. For airplanes reliablity is much more important so a maximum fast charge rate of 1C is recommended for NiMh packs - 2C for NiCd. I usually fast charge at .8C You are looking for long troublefree life when you're flying.

For car guys if your looking for long life still charge it at 1C maximum, GP 3300 = 3.3 amps. If service life isn't that important to you then 2C max is all I would go. Course I like my packs to last being a frugal type (read cheap) person. You'll get longer life out of packs if you don't charge them while they are hot. Get a fan out of a defunct PC power supply it's 12VDC. Make a tube out of cardboard with a shelf in the middle. Use it to cool your packs before charging between heats.

John

JNorton

My Feedback: (2)

gerwen,
Looks like we posted about the same time. Good advise that I totally agree with. I wouldn't have repeated if I'd seen your post.
John

purple_car

To add a little helpful newb information that was discussed in another thread:

1. The wall wart charger used for the form charge can be a nicad charger. Just make sure the batteries don't stay on longer than intended (14-16 hours seems to be the consensus).

2. If your charger doesn't have a discharge function, a down and dirty discharge method is to just put the battery in your car and drive it at low speed until it starts to slow down.