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Replacing NiCd AA rechargeables with NiMH AA rechargeables

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Replacing NiCd AA rechargeables with NiMH AA rechargeables

Post by ken » Fri Dec 13, 2013 4:39 pm

I have an old scanner which takes 4xNiCd AA rechargeables which as you know are no longer available. The ones which I have been using I bought at the end of there availability but are only 350mAh and will eventually fail. The manual states that It can be powered from an external DC supply of 11-16V at approx 300mA. The external PSU it came with is 12V 500mA unregulated which is also use to charge the batteries. It is in no way "smart". I am thinking of replacing the NiCds with 2000mAh NiMH. I have chargers that charge both NiCd and NiMH. One is manually switched between the two types. The other is not. I suppose it might be able to sense which type its charging but I don't think it is that sophisticated. I do not want to have to remove the new batteries to charge them in an external charger. I would like to be able to charge them while they are installed using the above mentioned PSU. Am I right in thinking I can do this as long as I take account of the time for which they are charged and check they are not overheating? Are there any drawbacks to this? Obviously I do not wish to risk damage to the scanner.

Regards,

Ken.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by Michael Watterson » Fri Dec 13, 2013 4:55 pm

You can use NiMH in place of NiCd. The charge time to fully charge will be longer with the NiCd built in Charger.

Other Aspects: There are three main kinds of NiMH (capacities are for AA only):
1) Regular type, between 1800 and 2500mAH usually, may self discharge much faster than NiCd. Can be left on NiCd trickle charge indefinitely.
2) Eneloop or "Pre Charged" type, can hold 50% charge for a year! But MUST NOT be left on charge when fully charged.
3) High Capacity. 2500mA to 3000mAH or even more inflated claims. These are rubbish! Often the capacity is less than claimed. They are for short use high power, self discharge often in less than 10 days! Must not be left on charge.

The terminal voltage is about 200mV to 250mV higher per cell, not a problem.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by boyblue » Fri Dec 13, 2013 5:08 pm

Hi Ken, Poundland (in Paisley!) sells 800 ma/h nicads, 2 for £1. Might be easier than changing your current ! charging arrangements. Peter

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by ken » Fri Dec 13, 2013 6:20 pm

Hello Gents,

Thanks for your replies.

Michael

The NiMHs I am thinking of I think are here http://www.maplin.co.uk/c/batteries-and-power/rechargeable-batteries/rechargeable-nimh-batteries#Capacity:2000mAh&sort=&page=1&productsPerPage=12 .The code on the 4-pack is NO48W or N048W but I can't find them on Maplins site. They are £4.99 for four. I don't think they are anything special so the self-discharge issues you mention could be a problem.

Peter

I recently bought 4x 800mAh AA rechargeables from Poundland in Glasgow at two for a pound but they were NiMH. They are marked "FUSIONMAX" and dated 06/2018. I thought it was no longer possible to by NiCds. Are you sure the ones in Paisley are NiCd? If I get a chance I will take a run into Paisley over the weekend as if they are NiCd they might solve the problem.

Regards,

Ken.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by Michael Watterson » Fri Dec 13, 2013 6:24 pm

NiCds in a Retail shop? Also 800mAH is unlikely for AA NiCd.

I'd avoid those and stick with 1800mAH to 2200mA quality NiMH, just takes longer to fully charge (which would be the case with the dubiously labelled 800mAH NiCd.

Quality NiMH are not a problem.

Many places have decent NiMH cheaply. Avoid less than 1800mAH or more than 2500mAH.

NiCd are available for specialist applications. But not in Retail. There is no point to them for a Scanner. I use regular NiMH in my Radios and Scanners that were from NiCd era with no problem.

The main issue with the high self discharge ones is finding it flat unless you are recharging every few days. I have two sets for more heavily used stuff.

These are panasonic version of the Sanyo Eneloop
http://www.maplin.co.uk/p/panasonic-evo ... pack-n30na

The only limitation is that if orginal NiCd were 300mAH to 500mAH, the charge rate will be about 30mA to 50mA. So don't leave them on charge for more than 70 hours. It may take 25 to 60 hours in the original charger circuit to fully charge due to higher capacity. But as there is little memory effect compared to NiCd, partial use and charge overnight isn't a problem.

About 4 to 5x longer use than NiCd. At low consumption (< 30mA) though, Alkaline still beat them for capacity. Only at > 100mA load is NiMH going to look a lot better.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by ken » Fri Dec 13, 2013 7:02 pm

Hello Michael

Thanks for the very full reply and the link. I have seen these in Maplin. I think I will give the NiMH a go. The higher capacity is definately an advantage. I might initially charge them using an external charger.

Regards,

Ken.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by boyblue » Fri Dec 13, 2013 7:18 pm

Hi Ken, Had a look at the poundland site again, they are 800ma/h Ni Mh not NiCad, sorry. Not bad price though. Peter

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by ken » Fri Dec 13, 2013 8:04 pm

Hi Peter,

I think they must be the ones I've got. They also had chargers to charge two AAs for a pound!

Regards,

Ken.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by Refugee » Fri Dec 13, 2013 9:02 pm

I have been using 8 pre-charged AA cells for a TR82 with no problem.
They are Tesco branded 2000ma/h.
The reason I went for 9.6 volts is because chargers only work with the batteries are charged in two's.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by Michael Watterson » Fri Dec 13, 2013 10:12 pm

boyblue wrote:Hi Ken, Had a look at the poundland site again, they are 800ma/h Ni Mh not NiCad, sorry. Not bad price though. Peter


At 800mAH they are rip off AAA in a AA box. That's why they are cheap. The worst is the D cells with AA NiMH in them, waste of money if you need a D cell.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by Michael Watterson » Fri Dec 13, 2013 10:23 pm

Refugee wrote:The reason I went for 9.6 volts is because chargers only work with the batteries are charged in two's.


A layer PP9 is about 10.5V when fresh and 6V when dead. NiMH are not actually 1.2V (actually NiCd are only 1.2V at a particular point on discharge). But they are significantly lower voltage than Zinc Carbon or layer type. More compatible 9V packs do have 7 or 8 NiMH cells in them. Using 8 cells is fine as long as never on trickle charge while in the set, as the voltage would peak at about 12V! On load without simultaneous charge the 8 x NiMH will quickly fall to 10.8V then rapidly to 10.4 with a gradual discharge to about 8V (end point for NiMH cells in series should be 1V or more).

Alkaline AA should be close to 200 hours, more than 150 in a transistor set replacing PP9. The 2000mAH Tesco NiMH should give about 120 hours per charge. Depends on listening volume if Class B or Class AB.

Make sure no leaky caps.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by Goleudu Gwyn » Sat May 24, 2014 10:08 pm

I recently cut open a Poundland Ultramax AA and there certainly was no AAA inside! It contained the usual layers you would find inside a battery, however, this didn't extend all the way to the bottom of the case. These Fusionmax/Ultramax batteries are good value for money and are fine in low/medium drain applications e.g. low powered led lights, solar lights etc. but I wouldn't use them in digital cameras or high powered Cree type torches.

The AA are rated 800mAh and the AAA at 350mAh which works out at 1600mAh/£1 and 700mAh/£1. If you want more capacity then Lidl are selling Varta precharged AA (2100mAh) and AAA (800mAh) for £3 a pair. They wouldn't suffer any memeory effect from partial charge/discharge (did memory effect ever exist?) but would benefit from being taken out once a year and given a few charge/discharge cycles just to keep to 'freshen' them up.

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by Michael Watterson » Sat May 24, 2014 11:53 pm

Yes, memory effect did exist on NiCd and does exist on Lithium. But it's very very complex.

Also Nickel Dendrites are a problem.

I would avoid any NiMH that are either much less than normal capacity (poor quality) or claiming much more than normal (can be real, but high self discharge, shorter life and can't be left on trickle charge).

 
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Re: Replacing NiCd AA rechargeables with NiMH AA rechargeabl

Post by Herald1360 » Tue May 27, 2014 10:56 pm



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