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Posted by _ on July 20, 2008, 6:52 am
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On Sun, 13 Jul 2008 15:31:49 +0100, Richard wrote:
> On Sun, 13 Jul 2008 15:14:38 +0100, Duncan Munro
>
>>Tim Leech wrote:
>>> The battery pack on my ultrasonic thickness tester is dying.
>>> It consists of six AA NiCd cells strapped together.
>>> I went to Maplins this morning planning to get some new cells, but
>>> virtually all their rechargeables are now Nimh or what they call
>>> 'hybrid'. They had a couple of NiCd cells but not enough, and they
>>> seem to be discontinuing most of them. The gormless youths in charge
>>> couldn't tell me anything useful about what these 'hybrids' are, or
>>> how well either type would do as replacements for NiCd cells in kit
>>> with a built-in charger.
>>> Any suggestions how well they would work, especially with reference to
>>> the charging?
>>> The charger is labelled 'NiCd charger for up to 10 cells, 50mA'
>>
>>Tim, NiCD cells are out of favour now due to the Cadmium content and
>>associated disposal issues. The two replacements as you've found out
>>are the NiMH and Hybrid batteries.
>>
>>NiMH works the same as NiCd but has a higher self discharge. This means
>>that if you leave it to one side fully charged, it will flatten itself
>>quicker than the NiCD which is about the only significant disadvantage.
>>
>>The Hybrid batteries are NiMH batteries that have a different internal
>>construction which lowers the self discharge rate. They do, however,
>>have a lower capacity as a result.
>>
>>Hybrid is better suited to things like clocks, air fresheners, the kind
>>of things that you want to stay charged for 6-12 months as the normal
>>NiMH would be flat in that time. RC models, digital cameras, and other
>>high drain / short turnround applications might benefit from NiMH but to
>>be honest I'm just using Hybrid for everything now.
>>
>>The 50mA charger is a tiny trickle charge and is perfectly suitable for
>>the newer batteries, although it will take some time to charge up the
>>higher capacity batteries. To get a full charge into 2100mAh Hybrid
>>batteries from empty would take 3 days, but the bonus is you can leave
>>the thing connected on charge for as long as you like without damaging
>>the them.
>>
>>Finally, if you are after hybrids, Wilkinsons do a bargain price on
>>Uniross Hybrio batteries, 4 x AA for a fiver, a lot less than Maplins.
>>Another place I've found helpful (they do tagged packs as well) is
>>www.vapextech.co.uk
>>
>>Hope this is some help to you.
>
>
> I doubt it matters for your application, but NiMH's have a more
> gradual loss of voltage with discharge ie they loose more voltage
> earlier whereas NiCd's are pretty flat until the last moment when they
> go dead in moments.
No.
http://shdesigns.org/batts/battcyc.html
You may be thinking of primary cells, which do show a steady voltage loss
with usage.
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Posted by Richard on July 20, 2008, 6:50 pm
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On Sun, 20 Jul 2008 10:52:00 GMT, _
>On Sun, 13 Jul 2008 15:31:49 +0100, Richard wrote:
>
>> On Sun, 13 Jul 2008 15:14:38 +0100, Duncan Munro
>>
>>>Tim Leech wrote:
>>>> The battery pack on my ultrasonic thickness tester is dying.
>>>> It consists of six AA NiCd cells strapped together.
>>>> I went to Maplins this morning planning to get some new cells, but
>>>> virtually all their rechargeables are now Nimh or what they call
>>>> 'hybrid'. They had a couple of NiCd cells but not enough, and they
>>>> seem to be discontinuing most of them. The gormless youths in charge
>>>> couldn't tell me anything useful about what these 'hybrids' are, or
>>>> how well either type would do as replacements for NiCd cells in kit
>>>> with a built-in charger.
>>>> Any suggestions how well they would work, especially with reference to
>>>> the charging?
>>>> The charger is labelled 'NiCd charger for up to 10 cells, 50mA'
>>>
>>>Tim, NiCD cells are out of favour now due to the Cadmium content and
>>>associated disposal issues. The two replacements as you've found out
>>>are the NiMH and Hybrid batteries.
>>>
>>>NiMH works the same as NiCd but has a higher self discharge. This means
>>>that if you leave it to one side fully charged, it will flatten itself
>>>quicker than the NiCD which is about the only significant disadvantage.
>>>
>>>The Hybrid batteries are NiMH batteries that have a different internal
>>>construction which lowers the self discharge rate. They do, however,
>>>have a lower capacity as a result.
>>>
>>>Hybrid is better suited to things like clocks, air fresheners, the kind
>>>of things that you want to stay charged for 6-12 months as the normal
>>>NiMH would be flat in that time. RC models, digital cameras, and other
>>>high drain / short turnround applications might benefit from NiMH but to
>>>be honest I'm just using Hybrid for everything now.
>>>
>>>The 50mA charger is a tiny trickle charge and is perfectly suitable for
>>>the newer batteries, although it will take some time to charge up the
>>>higher capacity batteries. To get a full charge into 2100mAh Hybrid
>>>batteries from empty would take 3 days, but the bonus is you can leave
>>>the thing connected on charge for as long as you like without damaging
>>>the them.
>>>
>>>Finally, if you are after hybrids, Wilkinsons do a bargain price on
>>>Uniross Hybrio batteries, 4 x AA for a fiver, a lot less than Maplins.
>>>Another place I've found helpful (they do tagged packs as well) is
>>>www.vapextech.co.uk
>>>
>>>Hope this is some help to you.
>>
>>
>> I doubt it matters for your application, but NiMH's have a more
>> gradual loss of voltage with discharge ie they loose more voltage
>> earlier whereas NiCd's are pretty flat until the last moment when they
>> go dead in moments.
>
>No.
>
>http://shdesigns.org/batts/battcyc.html
>
>You may be thinking of primary cells, which do show a steady voltage loss
>with usage.
_I_ am certainly thinking of NiCd's/NiMH's, but possibly the reference
from which I got the info was not. I'll try to look it out as it was
(apparently) directly relevant to my application (RC aircraft range)
and the curves shown were certainly nowhere as similar as your
reference - indeed the dissimilarity was the thrust of the article as
I recall.
I can't remember at present where it was, but expect I've kept it
somewhere. It was what I perceived to be a reputable source, probably
the BMFA, but I'm not sure.
Thanks for the additional info.
Richard
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Posted by Tim Leech on July 13, 2008, 11:33 am
Please log in for more thread options On Sun, 13 Jul 2008 15:14:38 +0100, Duncan Munro
>Tim Leech wrote:
>> The battery pack on my ultrasonic thickness tester is dying.
>> It consists of six AA NiCd cells strapped together.
>> I went to Maplins this morning planning to get some new cells, but
>> virtually all their rechargeables are now Nimh or what they call
>> 'hybrid'. They had a couple of NiCd cells but not enough, and they
>> seem to be discontinuing most of them. The gormless youths in charge
>> couldn't tell me anything useful about what these 'hybrids' are, or
>> how well either type would do as replacements for NiCd cells in kit
>> with a built-in charger.
>> Any suggestions how well they would work, especially with reference to
>> the charging?
>> The charger is labelled 'NiCd charger for up to 10 cells, 50mA'
>
>Tim, NiCD cells are out of favour now due to the Cadmium content and
>associated disposal issues. The two replacements as you've found out
>are the NiMH and Hybrid batteries.
>
>NiMH works the same as NiCd but has a higher self discharge. This means
>that if you leave it to one side fully charged, it will flatten itself
>quicker than the NiCD which is about the only significant disadvantage.
>
>The Hybrid batteries are NiMH batteries that have a different internal
>construction which lowers the self discharge rate. They do, however,
>have a lower capacity as a result.
>
>Hybrid is better suited to things like clocks, air fresheners, the kind
>of things that you want to stay charged for 6-12 months as the normal
>NiMH would be flat in that time. RC models, digital cameras, and other
>high drain / short turnround applications might benefit from NiMH but to
>be honest I'm just using Hybrid for everything now.
>
>The 50mA charger is a tiny trickle charge and is perfectly suitable for
>the newer batteries, although it will take some time to charge up the
>higher capacity batteries. To get a full charge into 2100mAh Hybrid
>batteries from empty would take 3 days, but the bonus is you can leave
>the thing connected on charge for as long as you like without damaging
>the them.
>
>Finally, if you are after hybrids, Wilkinsons do a bargain price on
>Uniross Hybrio batteries, 4 x AA for a fiver, a lot less than Maplins.
>Another place I've found helpful (they do tagged packs as well) is
>www.vapextech.co.uk
>
>Hope this is some help to you.
Many thanks to all for suggestions.
Is it OK to leave that charger on indefinitely with Nicads?
Tim
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Posted by Peter A Forbes on July 13, 2008, 12:56 pm
Please log in for more thread options wrote:
>Many thanks to all for suggestions.
>Is it OK to leave that charger on indefinitely with Nicads?
>
>Tim
The standard continuous charge rate is C/10 or 50mA.
However, cell water/moisture loss can occur due to heating if they are enclosed,
so normally 14 hours is the longest you should leave them, assuming an unknown
state of charge at the beginning.
Note that AA cells are 600mAH these days, so 50mA is less that C/10 charge rate.
Dry AA cells are 1500mAH with less self-discharge, worth remembering.
Peter
--
Peter & Rita Forbes
Email: diesel@easynet.co.uk
http://www.oldengine.org/members/diesel
http://www.stationary-engine.co.uk
http://www.oldengine.co.uk
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Posted by Tim Leech on July 13, 2008, 1:07 pm
Please log in for more thread options On Sun, 13 Jul 2008 17:56:35 +0100, Peter A Forbes
>wrote:
>
>>Many thanks to all for suggestions.
>>Is it OK to leave that charger on indefinitely with Nicads?
>>
>>Tim
>
>The standard continuous charge rate is C/10 or 50mA.
>
>However, cell water/moisture loss can occur due to heating if they are enclosed,
>so normally 14 hours is the longest you should leave them, assuming an unknown
>state of charge at the beginning.
>
>Note that AA cells are 600mAH these days, so 50mA is less that C/10 charge rate.
>
>Dry AA cells are 1500mAH with less self-discharge, worth remembering.
>
>Peter
The manual specifies a charge time of 16 hours, though I don't know
what the original battery capacity was. Those currently fitted are
800mAh.
I did try some time ago running the instrument from a 9V dry battery,
it didn't seem to like the higher voltage much!
Thanks
Tim
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