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Home made Batteries very hot during charging!

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Home made Batteries very hot during charging!

Old 11-19-2020, 09:56 AM
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Default Home made Batteries very hot during charging!

Hi to all.
I have made battery packs for my old RC toys, their batteries were dead. One was a 3x 1,2v 2/3AAA so 3.6v and the other a 5x1.2v 2/3AAA so a 6v battery. I made several battery pack (rather well now I finally mastered the soldering technique, using hot soldering (I saw it was better to make yourself a special soldering kit with a 12v battery and a condenser, but I went for the lazy option)). They work well BUT:
-when I charge the 6v ones on their original charger (it is a timer charger with a 30min timer, you plug in the car 12v plug). It charges but the batteries HEAT A LOT! And one 30 min charge isn't enough to charge them fully.
I am supposing that the original batteries had a lower amperage (maybe 200 mAh per cells) and I suppose the ones I bought are greater in intensity (Amperage), so I suppose it takes longer to charge. Can that be correct?
Also, I am having to charge them twice... Isn't that not very good for the battery? (should I rather set the timer to 30min and come back before the 30min are finished to add another 15-30 minutes to it? (Even if the battery is very hot??) Or can I let it stop, and then later dd another 30 min charging?

(any ways of calculating the time of charge required knowing the voltage and amperage??)

Thanks a lot for all you help...

Best!!

PS: the batterie are NiMh 400 mAh each.

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Old 11-19-2020, 10:17 AM
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Originally Posted by makehobbyrc View Post
Hi to all.
I have made battery packs for my old RC toys, their batteries were dead. One was a 3x 1,2v 2/3AAA so 3.6v and the other a 5x1.2v 2/3AAA so a 6v battery. I made several battery pack (rather well now I finally mastered the soldering technique, using hot soldering (I saw it was better to make yourself a special soldering kit with a 12v battery and a condenser, but I went for the lazy option)). They work well BUT:
-when I charge the 6v ones on their original charger (it is a timer charger with a 30min timer, you plug in the car 12v plug). It charges but the batteries HEAT A LOT! And one 30 min charge isn't enough to charge them fully.
I am supposing that the original batteries had a lower amperage (maybe 200 mAh per cells) and I suppose the ones I bought are greater in intensity (Amperage), so I suppose it takes longer to charge. Can that be correct?
Also, I am having to charge them twice... Isn't that not very good for the battery? (should I rather set the timer to 30min and come back before the 30min are finished to add another 15-30 minutes to it? (Even if the battery is very hot??) Or can I let it stop, and then later dd another 30 min charging?

(any ways of calculating the time of charge required knowing the voltage and amperage??)

Thanks a lot for all you help...

Best!!

PS: the batterie are NiMh 400 mAh each.
The old timer chargers will for NiCad batteries. With NiMh you will want a peak detection charger. Although, they still got pretty warm during charging, but not hot.
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Old 11-19-2020, 11:01 AM
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Since the cells are rated at twice the capacity of the original cells, given the same charge rate from that charger, yes, it should theoretically take twice as long to charge given that they are rated at twice the capacity. That being said, the commenter above is correct. You might want to invest in a reasonable smart charger. Most LiPo chargers that Iíve seen out there have a NiMh mode, so Iíd say shop around for one that suits your need and budget.

As for the heat, you might want to see if itís the whole pack or any specific cells in the pack you built. There might be either a bad cell in there, or maybe a bad solder joint that is producing resistance, hence heat. A half-decent smart charger might even monitor resistance while charging to let you know if itís a problem with the pack or not.
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Old 11-19-2020, 12:08 PM
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  1. I echo what's been said above - get a modern charger. Not only do they allow you to optimise your charge settings, they give a lot more information and that makes them a lot safer
  2. I'm concerned you have done something wrong when building your custom packs. I don't honestly know what "hot soldering" means in this context. But new, higher capacity cells should not be getting hot when charged with the same settings as an old, low capacity cell. As a first step, I would check the individual voltages of the cells to make sure they are well balanced.
Trust me, you don't want a hot NiMH cell to become an exploding one. Even a 2/3AAA will give a nasty injury if it happens in your hands.

A 400mAh cell would normally tolerate a 0.4A fast charge (although on those small cells it is better to go lower rather than higher). Check the old charger's label to see what rate it is charging at.
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Old 11-20-2020, 02:59 AM
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Originally Posted by trilerian View Post
The old timer chargers will for NiCad batteries. With NiMh you will want a peak detection charger. Although, they still got pretty warm during charging, but not hot.
Oh that's interesting thanks! What does a peak detection charger looks like? Can I find some for 6v batteries easily?
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Old 11-20-2020, 03:01 AM
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Originally Posted by TurnNBurn View Post
Since the cells are rated at twice the capacity of the original cells, given the same charge rate from that charger, yes, it should theoretically take twice as long to charge given that they are rated at twice the capacity. That being said, the commenter above is correct. You might want to invest in a reasonable smart charger. Most LiPo chargers that Iíve seen out there have a NiMh mode, so Iíd say shop around for one that suits your need and budget.

As for the heat, you might want to see if itís the whole pack or any specific cells in the pack you built. There might be either a bad cell in there, or maybe a bad solder joint that is producing resistance, hence heat. A half-decent smart charger might even monitor resistance while charging to let you know if itís a problem with the pack or not.
Great thanks! It is the hole lot of the cells in the pack that heats a lot! Concerning charger.. I have Li-Po charger, but for 7.4v... I suppose I can't and SHouldn't use that for my 6v battery packs... Will have to invest... to do that properly...
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Old 11-20-2020, 03:07 AM
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Originally Posted by trilerian View Post
The old timer chargers will for NiCad batteries. With NiMh you will want a peak detection charger. Although, they still got pretty warm during charging, but not hot.
Does this look good:

https://fr.aliexpress.com/item/34543...archweb201603_

?
Any ways of knowing if it is a "PEAK DETECTION CHARGER" and will it do the job properly??/ thanks!
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Old 11-20-2020, 07:51 PM
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Originally Posted by makehobbyrc View Post
Does this look good:

https://fr.aliexpress.com/item/34543...archweb201603_

?
Any ways of knowing if it is a "PEAK DETECTION CHARGER" and will it do the job properly??/ thanks!
According to the description that will work with NiMH batteries. But I canít tell how many cells.
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Old 11-21-2020, 02:05 AM
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Be aware that is a fake one, it is a lower quality.
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Old 11-21-2020, 08:27 AM
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Originally Posted by trilerian View Post
According to the description that will work with NiMH batteries. But I canít tell how many cells.
You count the cells. then you can adjust charger for that many cells and adjust the delta peak to what that pack needs..1-15 cells in nimh mode....
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Old 11-21-2020, 11:18 AM
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Originally Posted by Roelof View Post
Be aware that is a fake one, it is a lower quality.
Oh dear, thanks a lot! Why? How do you know it's a fake..?
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Old 11-21-2020, 01:01 PM
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No holographic label.and it really wont matter for that price..seen the fakes last longer than the real imax chargers
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Old 11-21-2020, 02:30 PM
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Old 11-22-2020, 05:52 AM
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Originally Posted by the rc guy View Post
No holographic label.and it really wont matter for that price..seen the fakes last longer than the real imax chargers
Oh ok thanks so its not the iMax brand (I don;t mind), but does it seem to be a Peak Detection charger?
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Old 11-22-2020, 05:52 AM
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Originally Posted by Roelof View Post
great tutorial thanks!!
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