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Rechargeable batteries for electrical testers.

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Rechargeable batteries for electrical testers.

Posted by Sparkingchip on Jan 17, 2020 5:17 pm

I am considering buying some Eneloop batteries for some of my electrical testers.

The question is which version and rating?

Andy Betteridge 

Re: Rechargeable batteries for electrical testers.

Posted by mapj1 on Jan 18, 2020 9:38 am

For each size, there are various optimisations - ones that cram in as much capacity (run time before flat) at the penalty of thinner metal and a lower peak current,  ones that can deliver a higher current, at less capacity or those that have a long shelf life  (low self discharge rate) versus capacity.

Now you need to decide how you will use and charge your devices - will they be charged and forgotten for weeks, or kept on charge until needed,  and is your kit especially demanding?
Also be aware that some equipment designed for 1.5v cells that start new at 1.6v and fall to 1.1-1.2 when nearly dead sees a fully charged rechargeable at 1.2- 1.3 volts as half flat and will warn of low battery, even if it is really in perfect working order. It may be worth checking with the makers if 1.2v rechargeable cells are likely to cause issues..
regards Mike

Re: Rechargeable batteries for electrical testers.

Posted by Sparkingchip on Jan 18, 2020 7:51 pm

I have a Megger MFT1741 which has a built in charger and was supplied with the batteries already installed, so I decided having a look inside it might be a good starting point. 

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Andy Betteridge 

Re: Rechargeable batteries for electrical testers.

Posted by Sparkingchip on Jan 18, 2020 8:22 pm

Megger MIT420/2

Replacement battery types are:
6 x LR6 (AA) 1.5 V Alaline
or 6 x 1.2 V NiMH

Warning: Do NOT use AA size LiON (Lithium Ion) rechargeable cells as these are 3.4 V each and could permanently damage the instrument.

Note. NiMH rechargeable batteries show a lower charge than alkaline batteries, and may not give much warning before becoming exhausted.

Re: Rechargeable batteries for electrical testers.

Posted by Sparkingchip on Jan 18, 2020 8:37 pm

So these seem appropriate.

1.2 V 1900 mAh Ni-MH

Andy B.

Re: Rechargeable batteries for electrical testers.

Posted by mapj1 on Jan 18, 2020 11:22 pm

almost certainly fine,  and as an addition  a car or van charger may be worth considering.
You could try the ones out of the the other meter in the kit you want to use,  just to verify you do not get an erroneous flat battery waning.
regards Mike

Re: Rechargeable batteries for electrical testers.

Posted by Sparkingchip on Jan 18, 2020 11:43 pm

I will put the Megger MFT1741 on charge then swap the batteries into the MIT420/2 and see what the voltage display indicates.

There are some industrial AA batteries that could catch the unwary out being 3.6 volts.

Andy Betteridge

Re: Rechargeable batteries for electrical testers.

Posted by davezawadi on Jan 19, 2020 11:22 am

You can buy various AA batteries in bulk at good prices, such that rechargables become more trouble than they are worth. I use Duracell industrial ones which wholesale are much cheaper than shop prices, or bulk ones from CPC for Radio Microphones. Sometimes I use 30 or 40 a day for productions, and the capacity is little different from the more expensive D* ones. I have tried rechargables and they take a lot of effort and time to charge and the life of the kit power ends up the same as a normal AA, although the advertised capacity may be more. This is as Mike says the voltage monitors don't like rechargable 1.2 nominal voltage. Equipment designed for rechargable batteries has a switch mode, wide input range converter from the batteries so that they may be fully discharged properly, which may not be there in older equipment.
Regards David CEng etc.

Re: Rechargeable batteries for electrical testers.

Posted by Sparkingchip on Jan 19, 2020 12:27 pm

I was doing a cost comparison last night, a current example is  Argos twenty batteries for £10.49

The MFT knows which type of battery it has in it and I presume the voltage indicator adjusts accordingly. I constantly have a bag of old batteries in my van to leave in a recycling bin, usually the one at a Screwfix, it does seem a inefficient way of working. The number of batteries from smoke alarms is decreasing significantly as the new alarms generally have sealed batteries, the next biggest quantity of old batteries are from the testers, it has also dropped as the MFT has rechargeable batteries in it, so swapping over the batteries in the other testers seems logical as a green measure and as a cost saving in the long term.

Andy Betteridge.

Re: Rechargeable batteries for electrical testers.

Posted by AJJewsbury on Jan 19, 2020 2:05 pm

I did have a try with Ni-Zn rechargeables a while back - the big advantage being that their cell voltage is 1.6V rather than 1.2V so a lot of equipment can function much further into the discharge cycle. I've mostly given up with them for the moment - partly because of the high failure rate after only a couple of dozen cycles (at least one of a set of four would seem to loose a lot of capacity) and partly because my local supplier (Maplin) is no more. It might be worth a look if you can find a source of better quality ones though.
   - Andy.

Re: Rechargeable batteries for electrical testers.

Posted by Sparkingchip on Jan 19, 2020 7:19 pm

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MFT1741 battery indicator 

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The same rechargeable batteries transferred in a Megger MIT420/2 does not show as being fully charged. 

Andy Betteridge 

Re: Rechargeable batteries for electrical testers.

Posted by mapj1 on Jan 19, 2020 9:09 pm

That is I fear to be expected. But if it works ok on the NiMH - even if it says 'half full', you will still  get most of the benefit -  the discharge curve of voltage vs state of charge  is quite flat until the last 10% or so. BUT will not get much warning, as the change from half -full to dead will occur quite sharply, compared to the primary cells. From the electronics designer's perspective it makes it hard to do an accurate battery indicator on NiMH cells, as voltage is not reliable, so when it really matters, then we have to resort to something more like an electricity meter, and integrate and record  the current in and out.

nice plot in the article here
regards Mike

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