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Discussion Starter · #1 ·
Last night I tested both my old (1987) and new (1997) nicad chargers (the 7.2v r/c car racing type) using my trusty multimeter and got fast charging voltages of 12 volts and 16 volts respectively. Funny thing was, when I set them on trickle charge, I got no reading at all. :confused:


Is it generally too low to measure on these units, or do I have a problem here?



Thanks.
 

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Hi Peter.
What is the chemistry and capacity of the battery packs?
A standard trickle charge current for NiCd chemistry is 10% of the capacity in ma for 14 hours from a discharged state.

Voltage is not really important as long as it is higher than the rated battery voltage. The voltage will drop as soon as the charging is taking place.
It is regulation of the current that is important.

I use a Maha charger for my 14.4 volt sub C NiCd packs. The rated capacity of the cells is 2,400 ma.
Tonight the Maha was showing 3,575 ma charged capacity in two brand new packs.
50% more run time sure impressed me.
 

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Discussion Starter · #3 ·
Thanks, Tony

The packs are 7.2v Nicad packs of 6 c cells, rated at 1500mah.

Yeah, I guess it all about amps not volts.

I found this info on the web...

To sum it up: (Where C = battery capacity)
Overnight charge = C/10
Quick charge = C/3
Fast charge = 3C
Trickle charge = C/50

Since going back to nicad packs from AA NiMh cells I've had tons of trouble. I really have to sort out my battery woes.
 

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Unless your current draw is very low, The AA cells are not a good idea. The internal resistance of those cells will waste a lot of your energy.

The charging voltage will vary, depending on the characteristics of the cells. Some take more voltage to provide the desirable trickle charge current. Really good chargers will control the charge current in each phase of charging. If all of your batteries are the same capacity and brand, you might be able to figure out the desired voltage by hooking a fully charged pack to a variable power supply and a milliampmeter.
 

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In trickle charging, it's the current, not the voltage that's important.

If you every get hold of a precision power supply, try hooking it up to charge a battery, and vary the voltage by one hundredth of a volt, you will see a very large change in charging current.

So, charging systems must pay attention to the current drawn.

Regards, greg
 

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Peter.
If you really must use AA size cells, the only ones worth considering nowadays are a mixture of NiMh and Alkaline chemistry and are guranteed to retain 85% charge over 12 months and not to self discharge.
I use the ENELOOP brand made by Sanyo.
The same sort of chemistry is also available from Panasonic and other battery manufacturers.

Please bear in mind Bill is correct about the maximum curent draw AA cells can handle.
About 500 ma continuous is OK. Any more and the life of the AA cells will be curtailed. Life, as in the number of recharges they can achieve.
NiMh already are behind the 8 ball compared to NiCd.
The life expectancy of NiCd is about double that of NiMh.
 

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Discussion Starter · #7 ·
Thanks, guys.

I started out years ago with 6-cell nicad sealed packs in trailing cars, then went to onboard 4 cell AA racks as all my locos turned into teeny weeny four wheel critters pulling one or two light cars.

However, as I have built up my rolling stock, I have gone back to trailing nicad packs since -- you are right -- AAs simply lack the necessary oomph.

Lately my problem has been really short run times from my (supposedly fully charged) 1500 mah 7.2v nicad packs.

I believe my problems may be traceable to my A/C wall jack peak charger cutting out long before my packs are fully charged. Last night I charged one pack with my old 15 min charger hooked up to my car battery, and another pack using an overnight charger. I monitored closely for hot cells, and there were none.

Today we'll see if I get back to the long run times I used to enjoy.
 

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Discussion Starter · #8 ·
Posted By pdk on 05/15/2008 10:50 AM
Thanks, guys.

Lately my problem has been really short run times from my (supposedly fully charged) 1500 mah 7.2v nicad packs.

I believe my problems may be traceable to my A/C wall jack peak charger cutting out long before my packs are fully charged. Last night I charged one pack with my old 15 min charger hooked up to my car battery, and another pack using an overnight charger. I monitored closely for hot cells, and there were none.

Today we'll see if I get back to the long run times I used to enjoy.



Short update, for the record.

All is well again with the nicads now that I've stopped using my peak-detecting fast charger. It was cutting out too soon.

I've found that my simple 7.2v 120 mAh continuous "overnight" charger works best and is most convenient. May not be good for racing R/C cars, but it's right for my locos. Slow and steady, just like a train.
 
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