Battery question

cliff

cliff

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I am about to have to replace some battery packs in a set of cordless phones however it seems I can get either Ni-Cd at 350mAh capacity or Ni-MH at 650mAh capacity - the originals are Ni-Cd but I am tempted to go for the Ni-MH this time round. Will there be any problems with the charging of th eNi-MH using the original chargers (for the Ni-Cd batteries? (apart from taking longer to reach full charge)
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"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
 
On holiday last year my Ni-MH batteries would charge from the inverter in the truck I was riding in but my NiCads would not. The camera which takes theh Ni-Cads advises NOT to use Ni-MH batteries as they work hotter. I have separate chargers for each and I'm not planning to experiment charging my Ni-MH's from the Ni-CAD charger. Although the chargers look identical, the Ni-MH charger is rated slightly higher than that for my Ni-Cads (all AA cells). Both will charge through a fag lighter socket in the car instead of the custom transformer, but it takes longer.

The Ni-MH Batteries for out Camcorder are different sizes and both charge from the same charger, it just takes longer the charge the bigger of the two.

This probably doesn't help.
 
I have always taken NiCad as being essentially the same as NiMh in voltage and charge characteristics. As you say the Ah capacity is usually larger in the NiMh which means that the old NiCad charger will be slower to recharge flat batteries but this slower recharge rate means less current as related to total capacity which should be safer.
olewill
 
here is an interesting page - http://www.ka7oei.com/nicds.html

The problem is the charge rate of the two types, here is what this site says regarding your question.

[ QUOTE ]
Replacing NiCds with NiMH cells:

Can you simply drop NiMH cells in place of NiCd ones? It depends. For optimal cell lifetime and performance, the answer is probably no. For "good" performance (that is, where overall lifetime and charge capacity will probably exceed that of NiCd cells) the answer is likely yes - as long as a few rules are observed:

You can't use NiMH cells in very high-current devices such as power tools. These sorts of demands on the cells will result in a very short lifetime and could be hazardous due to cell overheating and venting. Note that improvements to the NiMH technology are always being made and it is likely that new types may be appropriate for certain applications.

A NiCd-only "smart charger" or "quick charger" may not be able to detect when a NiMH cell is fully charged. This could result in undercharging (the cell isn't charged completely) or (more likely) overcharging if the charger cannot detect a full-charge condition. Make sure your quick charger is specifically designed for charging NiMH cells before you use it.
Charging a NiMH cell from the original NiCd "slow" charger should work, but it will probably take more than twice as long as it did with the NiCd charger. Typically, "slow" chargers will charge a NiCd pack in 12-16 hours, but this means that the same charger will probably take 30-36 hours to charge the NiMH pack. This extra charge time is required because the storage capacity of the NiMH cells are likely to have at least twice the capacity of same-sized NiCd cells that they replace.
If you replace NiCd cells with NiMH cells there are a few things that you should keep in mind:
Dispose of the dead NiCd cells properly - do not just throw them in the trash. Do a bit of research and find out where to dispose of the dead cells. (Your local recycling or trash-collection agency can probably tell you where to go... so to speak...)
Take note of the guidelines in the above section when you charge NiMH cells: They may not charge properly in a "smart" or "quick" charger and a slow charger will take much longer to charge NiMH cells.
They have a much higher self-discharge current (see the chart above.) If you charge the battery pack and forget about it, do not expect it to still be charged months later.


[/ QUOTE ]

I can't imagine the telephone base units use fast chargers, but they may not sense that the cells have reached full charge and switch off. My cordless uses 3 nimh cells but is quite modern, it can hold a charge off the base for about 5 days out of use.

I recently bought some tagged nicds from maplin for a razor, you can solder to a cell but tags are better generally, I would hate to think what the heat does to the chemicals inside the cell while you try to get it hot enough to flow solder.

If you have the types of battery that are 3 or 4 stumpy cells in a row with a cable tag coming off I might actually have a couple in the shed that I don't need.
 
Interesting site. I think for all the difference in cost I'll try the Ni-MH this time round. The extended standby time would be handy as "Dopey & Co." tend to forget to put the handsets back on the chargers for days on end /forums/images/graemlins/blush.gif
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"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
 
It all depends on the charger circuitry. If it is designed to replace quickly the charge used then go into trickle charge mode then there is a danger that it will ruin the Ni-MH cells. This is because the end of charge characteristics of Ni-MH are different to Ni Cd, and the charger might carry on charging despite being full. I wouldn't do it if they were my phones unless the Ni Cds (when new) really did not last long enough. If you do, then keep a very close watch on them for the first few days, and check they are not getting too hot. Hopefully the charger won't provide enough power to cause a safety problem but I can't say for sure.
 
ooops, plan "B" then - I'll change one set and monitor them for a few days before risking the rest of the handsets.
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hammer.thumb.gif
"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
 
[ QUOTE ]
I used a NiMH replacement on our ancient cordless phone. A test with a load and a multimeter suggested the charging circuit consists of one resistor. i.e. about as smart as I am. /forums/images/graemlins/smile.gif

[/ QUOTE ]You were smart enough to test the charger, which is smarter than the average resistor /forums/images/graemlins/wink.gif
 
Now I am really confused - I wish I'd never asked the question.... /forums/images/graemlins/frown.gif
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Support your local You know it makes sense.
 
[ QUOTE ]
Now I am really confused - I wish I'd never asked the question.... /forums/images/graemlins/frown.gif

[/ QUOTE ] Sorry about all that - ignore it, we were talking technobabble. Unless you really do need the extra capacity buy the NiCds and you will have no problems. If you did decide to buy the Ni-MH you might have problems and there is no point in taking that risk unless you stand to benefit sufficiently to outweigh the risk that you will wreck the new batteries.
 
[ QUOTE ]
[ QUOTE ]
Now I am really confused - I wish I'd never asked the question.... /forums/images/graemlins/frown.gif

[/ QUOTE ] Sorry about all that - ignore it, we were talking technobabble. Unless you really do need the extra capacity buy the NiCds and you will have no problems. If you did decide to buy the Ni-MH you might have problems and there is no point in taking that risk unless you stand to benefit sufficiently to outweigh the risk that you will wreck the new batteries.

[/ QUOTE ]

Having gone the gamut of near all types of cells available - I was heavily into Radio Control Models .............. planes, choppers, cars, boats etc. ...... I can honestly say that I haven't found any item yet that I changed to using NiMH batterys have problem ... and that includes my Fuji Digital Camera that says don't use any Rechargeables ...
Let's put it this way - when I used to have very expensive scale models flying around - I wouldn't risk them ...... never lost one - except to failed receiver NiCD on a P51 Mustang, 60" wingspan job ...... failed due to cracked solder tag inside the "commercial" covering.

I have read the above posts about charging etc. etc. ..... interesting ...... but I've used over the counter multi-chargers based on NiCD etc. for other types ... all still working ... all still reliable .... as larger capacity come out - I buy them and use them ... same charger etc. etc.

Yep - suppose I'm a fool ?????
/forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif
 
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