NiCD or NiMH as a replacement

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#2
The issue with NiMH is that they do not stand overcharging.
NiCD will trickle charge all day long: NiMH won't.
When NiMH were a new thing, marketing said they could replace NiCD & use same trickle charger.
I ruined many cells in this way.

I have a hair trimmer supplied with embedded NiMH cells equipped with a trickle charger.
The cells didn't live long.
I suspect the product was originally designed for NiCD and the manufacturer changed the cells without consideration of the different charging requirements. .

A smart charger for NiMH may have a very low trickle rate (after charging is complete) of C/40.

There should be no safety issue, just battery longevity.

It is cheap to try.
 
#6
What about a Supercap? Many tuners use those. 0.47 F 5.5V should be OK. No risks as they can not be overcharged. Just do not short-circuit them when charged.

Just to be sure it would be good to show the schematics.
 
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#8

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#10
The circuit is very unusual in that the battery actually runs an astable multivibrator to generate the backup supply.

I'm going differ here and say you should stick to a NiCad cell in this instance as the oscillator will need a constant supply voltage (the 1.2v). Never seen anything like this before tbh. Normally the 1.2v cell would directly backup the memory. It would be interesting to know the current draw of this backup supply.

However 🙂

Screenshot 2022-09-19 200958.jpg
 
#13
if they are not Tenergy NiCD then I will just do an easy amazon return and drop them off at Kohls
I will also test them when I get them
if they don't work as they should then back to amazon
I love buying form amazon because the returns could not be easier
just go online then click return and then drop them off at Kohls or whole foods !!!!
no risk involved, no hassles like buying on eBay !

also note they are shipped by amazon and sold by tenergy so no third party crooks involved
 

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#15
Mooly said:
The circuit is very unusual in that the battery actually runs an astable multivibrator to generate the backup supply.

I'm going differ here and say you should stick to a NiCad cell in this instance as the oscillator will need a constant supply voltage (the 1.2v). Never seen anything like this before tbh. Normally the 1.2v cell would directly backup the memory. It would be interesting to know the current draw of this backup supply.

However 🙂

View attachment 1092465
Click to expand...
It would be interesting to know what voltage is produced. It is just a way to transform the 1.2V to a higher voltage. If that is around 4 to 5V then a Supercap could replace the circuit alltogether with some changes like the series resistor.
 
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#16
Mooly said:
...unusual in that the battery actually runs an astable multivibrator to generate the backup supply. I'm going differ here and say you should stick to a NiCad ...
Click to expand...

I had suspected that. RAM to work on 1.1V was unavailable until quite recently. PC CMOS/BIOS batteries were 3-cell Ni-Cad. While an always-on oscillator seems extravagant, watches with single cell had become common.
 
#19
NiMh prefer to be charged at more than 0.1C, but trickle charging at 0.001C or less is no problem: they have an inbuilt recombination process changing the excess charge into heat. It might not be advisable regarding the performances, but it is completely safe, and losing half of your backup capacity shouldn't be a problem.
Other chemistries, like Lithium or alkaline are much less tolerant, and will outgass/explode as soon as the main recombination path is exhausted. Those should never be trickled-charged (and there are others).
Lead batteries also tolerate overcharging/trickle charging, but they belong to the previous century, and are not environmentally friendly
 
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#20
Lead acid batteries are alive and kicking in the industry. Slowly lithium variants become more popular but lead acid is still leading with regards to reliability and also sales numbers. At the moment lead acid batteries are greener than lithium batteries as they are fully recycled and almost none of the materials end up in the environment. Worn out batteries have a value because of the lead prices and also the sulphuric acid is recycled in new batteries. Recycling sites should be closely examined and checked as things are sometimes not as good as they should be over there (especially as sites are generally in 3rd world countries and China). Unfortunately this counts for mining of raw materials/ores, production sites of metals and for metal recycling sites.

Lithium batteries were unrecyclable until recently and thus they were thrown on landfills in the Far East. Production of lithium batteries has some very sharp edges too. They are certainly not an example of circular design! The acceptation of lithium variants is high for electrical mobility and mobile devices for obvious reasons.
 
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