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Recharging non-rechargeable batteries

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Noitoen:
I remember the ZN414, a 3 legged am radio ic :thumbup:

NickG:
Brilliant, I too have seen them advertised but didn't know how they worked or whether they did. Just chucked loads of duracells and bought 4 more rechargables  :doh:

Andromedac:
Thanks for the welcome!

I was very wrong about the timings posted in the magazine article, they referred to the lower and upper
capacities of zinc carbon and alkaline, and gave a rough guided time for each – I was sixteen!:-(

I have since done a fair amount googleing and have found a formula for a guide:
Charging time = mAh / mA

Monitoring the battery voltage in the last 4 hours or so down to make sure I don’t over charge them past
100%, then adjusting the timing cct accordingly.

The magazine was not totally fruitless. The diagram shown is slightly different than the reconstructed
one done on page one, I have attached a screen print from expresssch/easypcb.
I think the idea is have at least two batteries charging at any one time, and have them in either the 1
& 2, or the 3 & 4 positions, to ‘balance’ out the cct.

I have dug out all the various incarnations of the project and was pleased to find two printed cct
boards made for the timer and timing selection, albeit that there were omitted tracks for power – bloody
sixteen year olds! I also found I’d bought a 12VA with two secondary outputs, coupled with enough
ZN1034E’s and RS 348-582 reed relays I’m cooking with gas.

In true Darren style I have not tested the ‘AA’ resistor array that I found already constructed, I have
calculated Ra/b values for a PP3 9V battery after finding an old 30VA 13V(16.5VAC) transformer and am
currently testing my timer cct with it! I’ll let you all know if there is any success.

I was a little puzzled with the original writer’s W values for the resistors?!? Take the ‘AA’ Rb value
of 47R posted at 1W. If you use the original formula I=(Vsupply-Vdiode-Vbatt)/Rb:

I=(4.5-0.7-1.5)/47=49mA
P=I2*R=0.0024*47=113mW – not even a 1/8W and P=IV=0.049*2.3(Vs-Vd-Vb)=113mW

Anyone who can corroborate my sanity eitherway, please post…!

PekkaNF:

--- Quote from: Andromedac on October 15, 2012, 03:38:04 PM ---....
I was a little puzzled with the original writer’s W values for the resistors?!? Take the ‘AA’ Rb value
of 47R posted at 1W. If you use the original formula I=(Vsupply-Vdiode-Vbatt)/Rb:

I=(4.5-0.7-1.5)/47=49mA
P=I2*R=0.0024*47=113mW – not even a 1/8W and P=IV=0.049*2.3(Vs-Vd-Vb)=113mW

Anyone who can corroborate my sanity eitherway, please post…!

--- End quote ---

I reached for dictionary and then skratchen my head - got splinters under my nails. That circuit looks a little dodggy (not really a current regulator or anything of that nature) - I believe succes depends on fitting the battery and transformer characteristics close enoug. Something similar to tricle charge e.g. when battery voltage rises "full", very little charge current is left over battery, making charging SLOW but dispenses with delta cutout and timers and such.

RE: resistance and wattage ratings of the shunt resistor you are calculating. You are assuming in your calculation nice constant book value of battery internal resitance. Real life batteries always don't behave well. The ones building and using circuits don't behave taht well either.

What about if the battery has short circuit or fully charged battery is inserted wrong way? Or someone changes resistanced for big fat D-battery and then accidentaly rams in NiCd? Your variables here are transformer and resistors.

And resistors are not that ideal either, sometimes fairly much bigger wattage resistor is choosen to prevent it heatting (bad for circuit, fire, or resistance changes too much) and sometimes bigger is choosen because wirewound might suplly a inductance needed (very unlikely in this app). Then again if the writer/designer does not tell, it just might be what he had in the box and what worked for him!

PekkaNF

vtsteam:
I used to recharge alkaline cells a couple years ago, and found that I could typically recharge AA cells 4 to 6 times. However their tendency to leak was increased to the point that it was a bad idea to leave them in anything unless you were using it within a month. I was only using them to fly small $29 store bought R/C planes, so a leak wasn't a major tragedy. And it was certainly more ecopnomical to recharge hem.

I wouldn't want to put them in important equipment, unless there was a pressing momentary need for a battery. And I'd take them out afterwards.

My guess is that the charge cycle does take a toll on the case or seals, and the batteries probably don't hold a charge as long in storage -- thus the greater tendency to leak.

Just my experience -- others may differ.

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