Question about battery chargers...

[homestarmy]

Ok, let's say you have two NiMH battery chargers, and both of them have an output of 200mAh. But then let's say that one's output is 1.2v and the other's output is 2.0v. Does this mean that theoretically (or also in real life) the 2.0v charger would charge 1.66 times as fast as the 1.2v charger? I am assuming this because voltage times amperage equals wattage, which is total power, no?

But the NiMH cells are 1.2v. Does that mean that they will not input at another voltage?

Any insights on this?

 

[Eli]

No.

A battery will hold the chargers voltage to [whatever the cells voltage is].

It is amperage that matters.

At 200mA, it will take appx. 5 hours to charge a 1000mAh battery, 8 hours to charge a 1600mAh battery and 11 hours to charge a 2200mAh battery.

 

[homestarmy]

Ok, I completely understand that. So what you're saying is that the 1.2v battery only can accept 1.2v inwards also.

So why is it that on one of my chargers, it shows an output of 2.0v? Where is that extra .8v going?

Sorry if these questions sound dumb. I never took any of this in school and have recently learned a bit about electric power consumption.

 

[Eli]

Err.. let's see.. I forgot to say..

Since the cell is bringing the 2.0V charger's voltage down, it is also increasing it's amperage output....

But that is only while the cell is low voltage. The closer it gets to full, the less current it will draw.

But in the case of the 2.0V charger, the cell will only reach 1.2V ... so it will keep drawing current. Unless the charger is smart and switches to trickle, you will kill your battery.

This is a new area for me, so please someone else come in here and correct me.. I doubt I'm 100% right, just trying to explain it as far as I know it.

 

[Eli]

So.. hmm, I do believe that you were actually correct in your OP.. It was just your terminology that made me say "No".

The 1.2V charger is putting 0.24 watts into the battery

The 2.0V charger is putting 0.40 watts into the battery.

 

[homestarmy]

Thanks very much for your insight. I am in the same shoes as far as being somewhat of a new area.

Here's a new question. Lithium Ion battery packs that I work with are 3.7v with 1090mAh of power total. Does this mean that in an equivalent situation with the same power draw, a 1.2v NiMH battery would need to have 3360mAh to run out of power at the same time? I do understand that the highest power of a AA NiMH is only 2500 mAh btw .

I have heard people throw around a term... was it nominal power output or something like that? Is that a word that would have to do with this situation?

 

[Eli]

I'll have to let someone else tackle that one.....

I suck at teh electronic theory as of now.. lol

I'm having trouble grasping the question, though... I'm not sure there's enough info, or something?

Hmm.. well, with the same amperage draw...

The 3.7V, 1090mAh LiOn battery pack would last appx. 22 hours with a 50mA draw.

A 1.2V, 3360mAh NiMH cell would last appx. 67 hours with a 50mA draw. That's all basic stuff, I think you understand that.. I guess I don't get your question, lol. Like if you stepped the 1.2V up to 3.7V or something?

Hard to compare the different voltages....

 

[homestarmy]

someone else out there has to have some info about this...

 

[nwfsnake]

You probably couldn't use a single 1.2v battery in place of a 3.7volt pack, you would need three 1.2v in series. The circuitry probably requires 3 volts to operate (if you do indeed have circuitry involved). By using high capacity AA cells (2000mAh or so), you could build a pack better than the one you are trying to replace. It would help to know the application to give better direction.

 

[homestarmy]

I understand that you would use 2-4 AA NiMH batteries in place of the battery pack, but that was for illustrative purposes.