Adding a voltmeter to a battery charger

The objective is to add a voltmeter to a charger. The final result is this:


http://imageshack.us/a/img267/4476/img0793oz.jpg


ADVANTAGES:
* You can check quickly the charge of a battery. It is not needed to plug the charger. .
* To monitor the charging process.
* The charging can be stopped to about 50-60%. This is the best charge for a long store period. About 3.8V.
* To check that there is no overcharge during charging.
* This mod is quite easy.

DISADVANTAGES
* I think that the voltmeter cannot be connected all the time, when charging. It consumes about 20mA and the charger can be "fooled" by this current. For example, the charger I am using in this mod takes wrong decisions due to this extra current. That is the reason I am using switches to connect the voltmeter, only when it is necessary a reading.

* For that reason, you have to add two switches if the charger as to slots, and so on. These switches complicated a bit the mod.


PROCEDURE
A micro voltmeter is required. The power has to come from the battery to be checked. With a model with this characteristic the mod is easier. A voltmeter with only two wires.

The large majority of the models only work from 3V. However, I have found one that works from 2.4 / 2.5 volts, what it is very convenient for this mod. And it is very accurate. SKU 187376, about $3, from dealextreme.







It is better to remove the two screw holders that previous pictures show. Just use scissors and a file to finish.

Next step is soldering negative wire of the voltmeter to the charger:



Now two small switches are connected to each positive terminal of the charger. These switches are very common in electronics. Just search for "momentary" switch

And each switch connect the positive of the voltmeter to the positive of the charger:







I have fastened the voltmeter with tape. Of course you can improve the mod making a hole in the charger to place the voltmeter. However, for me the result is good enough, and quite robust.




Final result:



http://imageshack.us/a/img267/4476/img0793oz.jpg

Two remaining oversize images converted to links - Norm

:welcome:


Your images are oversize, when you post an image please remember Rule #3

Rule #3 If you post an image in your post, please downsize the image to no larger than 800 x 800 pixels.

Please resize and repost. - Thanks Norm

My thoughts: when a charger with a built in voltmeter checks the voltage it does it in an off cycle (the charger temporarily stops charging to check the voltage and/or resistance, this could be as short as a fraction of a second) because otherwise the meter would be reading the chargers voltage and not the battery's.

Would this not just be reading charger voltage?

edit: I guess if you unplug the charger it would only be reading battery voltage, good for checking batteries without plugging in the charger, it would be really cool if it would read down below 1v, that way you could check NiMH's too.

I modded a Pila IBC charger here. I like the button idea too.

Cereal_Killer said:

My thoughts: when a charger with a built in voltmeter checks the voltage it does it in an off cycle (the charger temporarily stops charging to check the voltage and/or resistance, this could be as short as a fraction of a second) because otherwise the meter would be reading the chargers voltage and not the battery's.

Would this not just be reading charger voltage?

edit: I guess if you unplug the charger it would only be reading battery voltage, good for checking batteries without plugging in the charger, it would be really cool if it would read down below 1v, that way you could check NiMH's too.

Click to expand...

yes, when the charger is off you are measuring just the battery. This is the way I am using to check my batteries.

I could not find voltmeters reading very low voltages taking the power form the voltage to be measured. There are more model very similar to the one I have just used. However, this one begins to measure from 2.4V. The rest of models i tried from 3V.