Why do i need a voltmeter?

Someone said I should have a voltmeter as I'm using rechargeable's (AW RCR123's & 18650 + Pila Charger) but I'm not sure why.
1) Should I have one?
2) Is it important to know the voltage before and after charging or just interesting?
3) What action am i meant to take if the battery isn't as expected?
4) If I need one, which are recommended?

Thanks for any advice!

Burntrice said:

Someone said I should have a voltmeter as I'm using rechargeable's (AW RCR123's & 18650 + Pila Charger) but I'm not sure why.
1) Should I have one?
2) Is it important to know the voltage before and after charging or just interesting?
3) What action am i meant to take if the battery isn't as expected?
4) If I need one, which are recommended?

Thanks for any advice!

Click to expand...

I'm sure others will also respond with more details, but yes, IMHO anyone using rechargeables should have a voltmeter.

To answer your questions above ....

1) Yes, to use Li-Ion chemistry cells safely and properly, a voltmeter is indispensable.

2) Yes, voltage before and after charging is important for correct use. Cells that get overcharged don't last as long (and extreme overcharging can be a safety risk). Cells that get over discharged are dangerous to recharge.

3) If the cell is significantly out of the safe voltage range, it should be disposed of properly (recycled).

4) Voltmeters (like flashlights ... ) are available in a wide variety of features and quality, with prices to match. If you want the best, most would probably suggest a Fluke. There are other manufacturers that make simple models which are much cheaper and still adequate for this purpose, however.

Hope that helps - Cheers!

Yes, the multimeter is not optional if you're planning on using Li-ion batteries; if the voltage of your battery is quite low and you continue to use it, you can kill it. And if the voltage is unusually high and you attempt to use the cell, it will likely explode. If at any time the voltage of your battery is beyond where it should be, you have to replace it. Any multimeter will do, Harbor Freight has $2 models that do the job.

Also, don't rely on the protection of a protected cell to tell you when it needs to be recharged; the protection is just there to prevent the battery from dying completely, and once you've reached the protection voltage, you may have already damaged the cell. Keep it between 3.6 and 4.15 volts, these are the numbers the R/C community arrived at after many forums-full of debate and experiment.

This is all you need.

http://www.harborfreight.com/7-function-digital-multimeter-90899.html


Or this one which has some more features like checking temperature.


http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html

I own both of these meters, plus some high dollar Flukes. But for some reason I always grab the cheap meters when checking battery voltage.

+1 on the harbor frieght for general purpose measurements. I have three of the 7 function ones in the link above. They also have a pot on the circuit board that can be adjusted to calibrate the DMM agaisnt a known good meter or a voltage reference. I had two that were spot on and one that was off .3v. Calibrated and all are good now. Here's the thread for pot location.