What happens if...

[PeterDove]

Hi All,

I just want to straighten out a few items about battery charging in my head - so if some kind soul could enlighten me that would be great.

1) What happens if I have a 1.2V Nimh and charge it by putting 2.5v and 150ma through it? Will it cope OK with the 2.5V ?

2) What happens if I have a 1.2V Nimh and am attempting to charge it but it only received 1V and 50ma? Will it charge?

Thanks - just running through solar panel scenarios

Peter

 

[Hero999]

1) providing you limit the current and stop it when it reaches 1.6V not harm will be done, there again if it's a 1500mAh cell then it can take less than 150mA indefinately.

2) No, of course it won't charge, learn Ohm's law, charge always flows from a high potential to a low potential so a 1.2V cell will discharge into a 1V supply.

 

[PeterDove]

2) No, of course it won't charge, learn Ohm's law, charge always flows from a high potential to a low potential so a 1.2V cell will discharge into a 1V supply.

Thanks for the heads up on question 1

Of course! But in this case it cant flow from the 1.2V to the 1V as there is a diode stopping it from doing so.

 

[Hero999]

I'm assuming from the other thread that the diode is a 1N4001, in which case the voltage drop will be 800mV; have you accounted for this?

Of course the diode will stop it, because it's reverese biased no current will flow, apart from a very small leakage of course.

 

[audioguru]

You can charge a 1.2V Ni-MH cell from 1 million volts if you limit the charging current with a resistor or electronic circuit. The voltage across the battery cell will slowly rise until it is near being fully charged, then its voltage peaks then drops slightly before rising higher as it is overcharged.

Here is a graph from www.energizer.com who have datasheets for all their batteries:

 

[Sceadwian]

Uhh no, actually a million volts will fry just about anything. =) Even the best insulators breakdown at those voltage, but that's beside the point. What audioguru is trying to say is that current is the important part of charging a battery, not the voltage.

 

[Hero999]

This isn't true, some of the largest electrical transmission lines use peak-peak voltages higher than 1MV.

Dielectric strengh is mainly governed by the type of insulation and its thickness, you could build GV insulators if you wanted to but they'd be very big.

 

[audioguru]

Some high voltage transmission lines I see have glass insulators at least 5m long. There is no salt spray from the nearby lake and the lines are about 50m above the ground.