Charging circuit

[sambo]

I am designing a hand cranked charging circuit for a NiMH battery.

I have used a LM317 voltage regulator however im not sure exactly what output voltage to use for charging a single 1.2V AAA cell.

Can anyone help?

 

[alec_t]

Have a read of this article.

 

[audioguru]

An LM317 is a voltage regulator, not a battery charger circuit. It would probably explode a little AAA Ni-MH cell.
Energizer Battery Company have a Tech Info section on their website with a manual about how to charge and discharge their batteries.

I suspect that your arm will fall off before an AAA cell is fully charged. How about using a windmill, waterwheel or solar panel instead?

 

[dknguyen]

An LM317 is a voltage regulator, not a battery charger circuit. It would probably explode a little AAA Ni-MH cell.
Energizer Battery Company have a Tech Info section on their website with a manual about how to charge and discharge their batteries.

I suspect that your arm will fall off before an AAA cell is fully charged. How about using a windmill, waterwheel or solar panel instead?

I think the LM317 is meant to be wired up with it's output going to a sense pin on opposites sides of a resistor that is in series with the output and load so than it operates as a current source rather than a voltage regulator. With that regard to the OP's question, you don't wire up the LM317 in it's regular configuration as a voltage regulator which means you do not pick an output voltage. You pick a safe, low, charging current and wire up the LM317 as a current source that produces that. This current has to be low enough that even if it's pumping current into the battery when it's overheated, it doesn't cause it to overheat and explode before your hand gets tired of cranking it.

 

[audioguru]

A proper battery charger IC designed for a Ni-MH cell detects a full charge then shuts off. An LM317 current regulator will keep trying to overcharge the cell and damage it instead.

 

[dknguyen]

A proper battery charger IC designed for a Ni-MH cell detects a full charge then shuts off. An LM317 current regulator will keep trying to overcharge the cell and damage it instead.

Well, it's never going to reach full charge anyways since his arm will fall off first.

 

[Nigel Goodwin]

As with your other thread, you're simply wasting your time - do you really want to wind the handle for 24 hours at a time?.

 

[sambo]

As with your other thread, you're simply wasting your time - do you really want to wind the handle for 24 hours at a time?.

Well I don't need to fully charge the aaa battery, I just need 25mAh so i can then trickle it into a coin cell, thats the project.

 

[sambo]

An LM317 is a voltage regulator, not a battery charger circuit. It would probably explode a little AAA Ni-MH cell.
Energizer Battery Company have a Tech Info section on their website with a manual about how to charge and discharge their batteries.

I suspect that your arm will fall off before an AAA cell is fully charged. How about using a windmill, waterwheel or solar panel instead?

I want to store 25mAh+ in the aaa battey and then trickle this into the coin cell. Surely if the aaa battery is 950mAh i can charge it at around 200mA for 5 minutes before filtering it in? The hand crank can only produce at most 200mA so no risk of any explosion surely?

 

[sambo]

I want to store 25mAh+ in the aaa battey and then trickle this into the coin cell. Surely if the aaa battery is 950mAh i can charge it at around 200mA for 5 minutes before filtering it in? The hand crank can only produce at most 200mA so no risk of any explosion surely?

And i used the voltage regulator to smooth the output voltage from the variable hand crank speeds

 

[rjenkinsgb]

If you connect a schottky rectifier between the output of the LM713 and the cell positive, the adjust the LM317 to get about 1.45V after the diode, you should be able to get a reasonable percentage charge in to the cell without risking overcharge.

 

[dknguyen]

What makes you think the coin cell is any more immune to overcharge than the AAA is? If anything it's even more vulnerable to overcharging. Using a battery to charge another battery is just pointless and inefficient. Just use the AA as is.

 

[sambo]

What makes you think the coin cell is any more immune to overcharge than the AAA is? If anything it's even more vulnerable to overcharging. Using a battery to charge another battery is just pointless and inefficient. Just use the AA as is.

The coin cell is the battery that needs to be charged, the idea is just using a aaa to store the charge in a few minutes

 

[sambo]

If you connect a schottky rectifier between the output of the LM713 and the cell positive, the adjust the LM317 to get about 1.45V after the diode, you should be able to get a reasonable percentage charge in to the cell without risking overcharge.

Ok thanks, what is the role of the schottky rectifier?

 

[alec_t]

200mA for 5 mins gets you about 17mAh of charge. If the generator is indeed limited to 200mAh, and the AAA was discharged sufficiently initially to accommodate that charge, then you should be good to go.

 

[crutschow]

And i used the voltage regulator to smooth the output voltage from the variable hand crank speeds

The battery doesn't care if the voltage is "smooth".
A battery looks like a large capacitor and will do a lot of smoothing all by itself.
Just connect the rectified voltage from the generator directly to the NiMH battery.
It's quite unlikely that you can crank enough to damage the battery in any reasonable time-frame.

 

[audioguru]

When do you stop cranking? When your arm falls off?

 

[ronsimpson]

When do you stop cranking? When your arm falls off?

I usually stop when blisters appear. I have never tried going until the arm falls off. I am interested in determining if over charging happens at the same time as the arm falls off. Not interested enough to try it.

 

[audioguru]

Energizer battery company says that Ni-MH batteries should have a full charge detected (by an IC) then have the charging turned off. If a trickle charge is needed then its current should be reduced to 1/40th the mAh rating.

 

[gophert]

I usually stop when blisters appear. I have never tried going until the arm falls off.

There was also a rumor that hair would grow on your palms