Adaptor showing a higher voltage, normal?

[Serge 125]

Hi all!!

I've just changed the rechargeable batter in my little beard razor with the same type and value (Nicad, 1000mah, 1.2v) and made sure that the + - was correct before soldering it and I fully discharged the battery and recharged it over night as per instruction BUT today I tried it and it didn't even held a charge as if it wasn't charged. So the first thing that I did is check
how much output that the adaptor had and on the label it says 1.2vdc out but on my meter I'm getting 1.9vdc, is this normal? Why didn't the battery fully charged is it because of this problem or just a no good battery (1 out of a pack of 4 that I bought). I didn't crack it open yet to check the inside to see if it's something wrong.
Thanks for any info on this!!!

Serge

 

[sagor1]

Adapter output of 1.9V may be normal since there is no load. Once you put a load on it, the voltage will probably drop. Big question is, is there a regulator in the razor? That may regulate to a proper charging voltage and prevent overcharging.
What did you "solder"? One should not solder to the battery terminals directly, it can damage the battery. Replacement batteries should have tabs already spot welded onto them, and one solders to those tabs only.
If you soldered directly to the battery terminals, I suspect you may have damaged one of the cells, and it is preventing a proper charge.

 

[Nigel Goodwin]

Yes, perfectly normal - you can't charge a 1.2V cell with only 1.2V, it must be higher - 1.9V sounds fine.

 

[Serge 125]

What did you "solder"? One should not solder to the battery terminals directly, it can damage the battery. Replacement batteries should have tabs already spot welded onto them, and one solders to those tabs only.
If you soldered directly to the battery terminals, I suspect you may have damaged one of the cells, and it is preventing a proper charge.

Yeah I did solder it because I don’t have anything to spot weld. Gee I don’t understand why it would damage the battery by just soldering. So now I must try to find a way to fix it without soldering. Now I know not to do this again.

Thanks!!!

 

[sagor1]

Damage to the battery from soldering comes from the heat applied. I've seen it done, though I don't recommend it. What some people do is "tin" the battery quickly with some heat and solder, then let it cool fully. One end at a time, let it cool. Too much heat is bad. Then, tin the wire separately, let it cool. Once that is all done, all it takes is a quick touch of the wire to the battery with a soldering iron to tack the two together. This minimizes the heat to the cell. This is not the best way, batteries with proper solder tabs are the proper way to do soldering of wires.
If you held a big soldering iron to the cell to melt the solder to the wire all at the same time, there would have been excessive heat. Check each battery separately with a voltmeter with a small load (10-20 ohm resistor will do), see if any cell is "dead". That may help identify a bad battery.

 

[Nigel Goodwin]

Yeah I did solder it because I don’t have anything to spot weld. Gee I don’t understand why it would damage the battery by just soldering. So now I must try to find a way to fix it without soldering. Now I know not to do this again.

It's perfectly fine to solder to batteries - as long as it's done competently and quickly - clean the ends of the battery with abrasive paper first, so it solders easily.

And as Sagor1 mentioned, tin the ends of both battery and wire first before connecting the wire to the battery. I've soldered hundreds of batteries over the years, has as anyone involved in electronics - I've never seen or heard of any damage been caused by any vaguely competent soldering.

We now use a small spot welder at work, but prior to that we soldered battery packs there as well - the main point of the spot welder is that it's MUCH, MUCH quicker to use, and makes a more professional looking job.

It's really another of those 'urban myths' - like overheating semiconductors while soldering - in both case you 'can' damage them by excessive heat, but it's very unlikely unless you can't really solder.

 

[audioguru]

I suspect that you changed the battery without knowing that it is the charger that is faulty, not the battery.