# Battery Charging Help Needed

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#### AKPilot

##### Well-Known Member
Can someone explain the following to me, in the simplest of terms (I've always been lost when it comes to electricity):

- I have a Parkzone F-27. I have a field, car charger, that can be set from .30A - 1.2A.
- I have several NiMH, 8-cell battery packs, rated at 9.6V, 900mAh

So here's where I seek clarification. When I'm at the park and my batteries run out (typically I charge them all ahead of time; wall charger). I've always simply set the car charger to 1.2A, plug in the battery(ies) and wait.

Is this the optimal method, wanting both optimal time and charge? Should it be set to 1.2A, or lower? I'd simply like to stay longer at the park, and use the car charger a bit more - better.

Thanks

If I am remembering properly the 1.2Amp is for quick chargeing and the .30amp is for slow charging or maintence "Trinkle"charge. I would sugest you look up the chargers information on their webpage and see what they say.

That is correct 1.2 amps is for fast charging, but at the risk of shorter battery life. Generally speaking the faster you charge the shorter the life of the battery.

Sorry there was no Charging 101, basic instructions, with the charger, this is what prompted me to ask.

You can charge NiMH batteries with that charger if you don't leave the batteries on for too long.

Your battery packs are rated at 0.9 A-Hr and the charger is rated at 1.2 A so it will fully charge the batteries in 0.9/1.2 = 0.75 hr = 45 minutes. You usually can charge most rechargable batteries to 90% quickly (If you go beyond that point they get hot if you don't reduce the current.). If you limit the charge to 90% or 40 minutes at that rate, you should be fine.

Bob

If I am remembering properly the 1.2Amp is for quick chargeing and the .30amp is for slow charging or maintence "Trinkle"charge. I would sugest you look up the chargers information on their webpage and see what they say.

Just to clarify, it is called trickle charging, not Trinkle charging. Oddly enough, I work with someone named Trinkle and she rarely needs charging!

You can charge NiMH batteries with that charger if you don't leave the batteries on for too long.

Your battery packs are rated at 0.9 A-Hr and the charger is rated at 1.2 A so it will fully charge the batteries in 0.9/1.2 = 0.75 hr = 45 minutes. You usually can charge most rechargable batteries to 90% quickly (If you go beyond that point they get hot if you don't reduce the current.). If you limit the charge to 90% or 40 minutes at that rate, you should be fine.

Bob
That's assuming the battery is completely discharged. The proper way to charge NiMH batteries is to charge at no more than c/3 (300 ma in your case) while monitoring the charge voltage. As soon as the voltage stops increasing, terminate the charge or reduce to no more than c/30 to maintain full charge. You can charge at c/10 (90 ma) without monitoring but continuous charging at this rate will shorten cycle life. C/10 charging will charge a fully discharged battery in about 14 hours. Some batteries can accept a charge faster than c/3 but monitoring the voltage is essential to prevent overcharge and cell venting.

That's assuming the battery is completely discharged. The proper way to charge NiMH batteries is to charge at no more than c/3 (300 ma in your case) while monitoring the charge voltage. As soon as the voltage stops increasing, terminate the charge or reduce to no more than c/30 to maintain full charge. You can charge at c/10 (90 ma) without monitoring but continuous charging at this rate will shorten cycle life. C/10 charging will charge a fully discharged battery in about 14 hours. Some batteries can accept a charge faster than c/3 but monitoring the voltage is essential to prevent overcharge and cell venting.
In my post I assumed the batteries were pretty flat after beuing used in an R/C airplane. If not, the charge time should be reduced.

The procedure you describe applies to NiCad batteries, not NiMH cells. The chemistry of NiMH batteries is different and more complex than NiCad. NiMH cells should always be fast charged, and never trickle charged for extended periods.

For the details, checkout https://www.batteryuniversity.com/partone-11.htm from https://www.batteryuniversity.com/index.htm

Also articles of general interest on different types of batteries and chemistries. https://www.buchmann.ca/newarticles.asp

Bob

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NiMH batteries charge at a constant current. To do this, the charger varies the voltage as required to maintain that current. Additionally, the resistance within the battery is constantly changing during the charging process. With NiMH, internal resistance starts out increasing and therefore the charger must crank up the voltage to maintain a certain current going into the pack.

As the charge nears full, the cell resistance then begins decreasing, which is different that NiCd or Lead acid.

As the resistance decreases, the batteries heat up... or as the batteries heat up the resistance decreases... I can't remember which comes first, chicken or egg. When your resistance decreases, less voltage is required to keep the same current flowing to the cells and the charger keeps track of this. When your pack voltage drops by 10% from the peak level encountered during the cycle the charge stops.

Now, if you crank your charger set amperage up to more than the safe limit rate, your batteries heat up more severely. NiMH cells are VENTED, so you can actually boil off the electrolyte and destroy the cell. Also, since they heat up quicker, the resistance begins decreasing quicker, so you can actually get a premature cycle halt, which means your batteries don't get a full charge.

I don't ever recommend setting the parkzone charger higher than 0.9. If you plan to get more into electric planes, I highly recommend a better charging system.

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