Recharging Batteries

[theinfamousbob]

OK, I got a laptop at a garage sale for free (wasn't working), and brought it home. A couple tries got me a POST screen, but it died after that. Upon destruction, I found the battery pack was filled with Toshiba batteries (see pics). I know a lot has been asked about charging batteries, but I was wondering if anyone could help me with charging voltage/current. The batteries are arrayed for 12V output. There's a board on the batteries with a fuel gauge IC and a microchip EEPROM. The fuel gauge is supposed to be able to write to and EEPROM, along with pseudo-SPI comm over serial lines. For charging, would I just pump the voltage into the battery +/- terminals?

(On a side note, I love my new Nikon Coolpix L12. I took the pictures about 4 inches away, without a tripod.)

 

[things]

they are not lithium ion batteries are they?? if they are not lithium ion batts, they can be charged with just a normal battery charger that takes those kinds of batteries

 

[things]

oh, i just saw your second pic those batteries can be charged easily, although the circuitry makes it a bit more difficult???

 

[things]

sorry for the 3 posts, i don't want to confuse anyone, but yes, you can pump 12 volts into the battery outputs, but be careful not to fry the circuitry or the batts

 

[kchriste]

For charging, would I just pump the voltage into the battery +/- terminals?

You would apply a constant current to the +/- terminals or go through the connector that went to the laptop (red and black wires). It looks like the circuit monitors battery current via R6 & R10 on the negative side of the battery and voltage via R3 on the positive terminal. The case of the battery should state the capacity in mAh so just charge them at the stated mAh for one hour if they are fully discharged. Monitor the temperature and stop the charging if they get hot before the 1hr is up. You might also want to check for shorted cells with a voltmeter during the charging process. But why not just charge it via the laptop?

 

[things]

he said he got it from a garage sale, so maybe the charger wasn't with it?? if this is the case, it would be much easier to make your own with just a plug pack?

 

[theinfamousbob]

Found this site just now:
https://www.powerstream.com/NiMH.htm

But why not just charge it via the laptop?

The laptop doesn't exist anymore...

Wasn't sure about its history anyway. When I took it apart to see what was wrong, the hard drive adapter board connector was ripped halfway out, making me wonder if the laptop was dropped. It may have shorted and just never came back.

I'll try charging them @ output current & output voltage, check for bad cells, and watch the temp.

They may all be shot anyway, I'm getting a reading of 4V total across all 10 cells.

Thanks for your help.

 

[theinfamousbob]

Ok I'm confused. On all of the circuits on **broken link removed** , the charging voltage is 3.6 volts (ideal). Would that be for a single cell? My guess right now is yes, based on how the battery pack I'm looking at is wired.

 

[kchriste]

O

k I'm confused. On all of the circuits on **broken link removed** , the charging voltage is 3.6 volts (ideal). Would that be for a single cell?

No, that is for 2 cells in series.

Top charging voltage of a battery pair: TCV < 3.1V

NIMH batteries have a nominal cell voltage of apx 1.25V when "resting". During charging they can go up to apx 1.6V per cell.

 

[Oznog]

The "4/3A" is the cell type. It does NOT mean 1.333 amp-hrs.


This type varies a lot in capacity. A quick search shows 2.8AH and 4.2AH batts on the same page.

Charging at a 1 hr rate is probably excessive, try a 2 hr at least.

It is difficult to charge these properly. They don't rise in voltage and thus the current doesn't drop off when they reach full charge. Your simple charge circuit won't be able to figure out when to stop charging and it will keep overcharging them, the overcharging will permanently damage them and they'll get quite hot.

 

[theinfamousbob]

The "4/3A" is the cell type. It does NOT mean 1.333 amp-hrs.


This type varies a lot in capacity. A quick search shows 2.8AH and 4.2AH batts on the same page.

Charging at a 1 hr rate is probably excessive, try a 2 hr at least.

It is difficult to charge these properly. They don't rise in voltage and thus the current doesn't drop off when they reach full charge. Your simple charge circuit won't be able to figure out when to stop charging and it will keep overcharging them, the overcharging will permanently damage them and they'll get quite hot.

So I could use the bq2092 to monitor the charge and instead of using the serial comm just tie the cut-off to the 100% LED output.

I think I have an 18V source, but I'd need more if I'm going to limit the current to the batteries. Back to what kchristie said, the board does have current limiting resistors on it. I've never seen "R1F" as a resistor designation for SMDs.

Based on **broken link removed** it looks like they're 4Ah batteries (The notebook was a Toshiba T-something or other, but wasn't a T2500.)

My original idea was to split the pack into 2 packs of 5 cells for a robot. I have to research the fuel gauge some but I might just be able to reprogram it or something.

Thanks!