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Author Topic: Lithium batteries to replace NiMh cells  (Read 673 times)

craggle

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Lithium batteries to replace NiMh cells
« on: June 13, 2017, 02:40:11 PM »

Hi all

Bit of a non boating question here but I have one of the Tamiya Tiger one tanks which hasn't been used for a few years now, needs a repaint, new batteries and reassembly. I was mulling over the idea of replacing the hard to get at NiMh 7.2v stick batteries with 7.4V 2S Lithium Polymer batteries.

I'm sure a fully charged 7.2V battery can be over 7.2V so not sure if the extra 0.2V will make a difference or not and a volt is a volt right, no difference what make of battery it comes from? If I stick with a similar capacity as the NiMh cells, maybe 2000 mAh cell, can anyone see a problem changing over?

The batteries in the tanks are not over worked really, fairly low demand on them as the motors are only small 380 type motors and everything is done at fairly low speeds.

Craig.
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tsenecal

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Re: Lithium batteries to replace NiMh cells
« Reply #1 on: June 13, 2017, 04:54:22 PM »


you are correct that voltage is voltage, most things don't care if it is voltage from a lipo, nimh or PB for that matter... but...

three things to look out for:


1) fully charged voltage for lipo is actually 8.4v, so verify that the ESC(s) built into the tamiya tank controller and the other electronic bits can safely handle that.

2) the internal resistance for lipos is much lower than average nimh, so a lipo can dump more amps into the esc, which may cause it to overheat... and cause a thermal cutoff...  if the tamiya electronics don't have a thermal cutoff, PLEASE get rid of the cheap white plastic tamiya connectors...  they are only rated for 10 to 15 amps, and will literally weld themselves together.

3) the low voltage cut-off for lipos is 3.3v per cell, so for a 2 cell pack, that would be 6.6v, if you go below 3.0v per cell, you most likely have destroyed the cell, and it is useless. most brushed ESCs do not have a low voltage cutoff, or it is set for nimh - a voltage below 6v, so you will want to buy a low voltage lipo saver or lipo alarm to make sure you don't kill your lipos by discharging them too far.   you can find lipo alarms for under $4.00 on ebay
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Netleyned

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Re: Lithium batteries to replace NiMh cells
« Reply #2 on: June 13, 2017, 05:13:47 PM »

A NiMH pack can be safely charged in situ,
but a LiPo will have to be removed for safety's
sake for each charge.
An uptodate NiMH pack carrys a lot less baggage
even if it is hard to get at and you don't need the
the extra power delivery which would be the only
advantage IMHO


Ned
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