EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: GerGa on December 08, 2024, 10:35:27 pm
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Hello,
I am replacing the AA NIMH cells in a Hotronic ski boot heater.
I want to use Tenergy flat top AA NIMH batterys. https://power.tenergy.com/tenergy-aa-2000mah-nimh-flat-top-rechargeable-battery/?gad_source=1&gclid=Cj0KCQiApNW6BhD5ARIsACmEbkUyff2aXzB_H6VGTd-OJDmU1k4rXBKhZWTJMBxiM_QIdG20eTOIvpYaAn-2EALw_wcB (https://power.tenergy.com/tenergy-aa-2000mah-nimh-flat-top-rechargeable-battery/?gad_source=1&gclid=Cj0KCQiApNW6BhD5ARIsACmEbkUyff2aXzB_H6VGTd-OJDmU1k4rXBKhZWTJMBxiM_QIdG20eTOIvpYaAn-2EALw_wcB)
The old pack had .2x4mm nickel strips, and I don't want to spend a fortune on a spot welder, while the cheaper spot welders don't have the power for 0.2mm strips.
I'm wondering if 0.1x4mm strips will work but no idea:
A: how to calculate nickel strips ampacity
B: how much current my battery pack will be capable of. Cells are 1.2v, 2000mah, pack is 4 in series, so 4.8V, 2000mah. In the link to Tenergy, the cell reads "standard discharge: 380mah to 1.0V. Not sure that means anything for this.
Any help on this problem?
Thanks
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The maximum current a battery cell can deliver depends on its voltage (which you know) and its internal resistance (which Tenergy doesn't list). Since NiMH battery has low internal resistance its maximum current is quite high. But for the device that you use it with how much current would that device draw? It may not be a lot.
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The maximum current a battery cell can deliver depends on its voltage (which you know) and its internal resistance (which Tenergy doesn't list). Since NiMH battery has low internal resistance its maximum current is quite high. But for the device that you use it with how much current would that device draw? It may not be a lot.
Thanks for the reply.
I received the datasheet for the Tenergy battery.
It reads:
Internal resistance (IEC61951-2 (2017) 7.10.1)
Within 1 hour after being standard charged, the internal resistance is not greater than 38mΩ, as tested by 1000Hz AC source.
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You can probably find some tests online for the high current performance of AA cells. It depends a lot on the design and quality of the cell, but most good quality AA cells should manage 5 A comfortably, and some can get up to 10 A. But at that discharge rate the cells are quite stressed and will also get warm. Consumer products are unlikely to run to such high discharge rates, since if you did run a 2000 mAh cell at 5 A discharge it would barely last for 20 minutes. Not very useful if you want to wear the ski boots for a few hours.
Your best estimate would be to divide the battery capacity by the run time and use that to estimate the current draw. And I imagine the thinner nickel strips would be fine.
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You can see some data here: https://envodrive.com/blogs/articles/lithium-ion-battery-pack-how-is-it-made
If its 380mA discharge then thats fine.
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The simple Ah divided by hours..the heater specifies it will last 2.5 to 4 hours at the hottest setting.
2Ah/2.5 = only 0.8amps