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| Testing batteries with multimeter |
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| edy:
Hi, This is perhaps a simple question but aside from measuring voltage of batteries (i.e. AA, AAA, C, D, 9V etc...) with a multimeter, how do I make sure they actually perform under load properly? A bunch of batteries would all show the normal 1.5V terminal difference, but if I switch the multimeter to AMP, I may get 5-7 A reading straight from the terminals, but some batteries have much less (1-2 A). For example, my 9V battery tests 9.31V on the terminals but as soon as I check AMP on the terminals, I am getting 0.040 A and dropping. Is this a good secondary way to check? Is there a rating system I can use... for example, if 5-7A it's fresh and good for some heavy-duty toys, and in the 1-2A rating it may be ok for remote-controls or low-energy devices? Does it make sense to first filter my batteries by voltage on the terminals... and then a secondary test under load or AMP through multimeter on the ones that test within good voltage parameters? Or should I set up a circuit and test the voltage when under load and see how far it drops? What would be an easy way to do this? Set up a battery holder hooked up to a number of different resistors and test the voltage across the battery when it runs through different resistor values? |
| barry14:
It is not a good idea to directly place an ammeter across the battery terminals. This is close to shorting them out which is why you get such high current readings. It can reduce the life of the battery. Instead, your second suggestion is a good approach. Place a resistor across the battery that will draw a reasonable amount of current (ideally equal to the actual load the battery will see in service) and measure the voltage. This is exactly what is done in commercial battery testers. Most of these testers have a rotary switch that places a resistor across the battery that is suitable for the battery being tested (AAA, AA, C, D and 9 volt batteries are usually accommodated; some will also test button batteries ). You could build your own tester but commercial ones are low in cost and include a meter so they are self contained. |
| edy:
Thanks, yes I agree I should be using a resistor to check AMP. I made sure my multimeter probe was on the Max 10A unfused jack but still it was getting terribly close at 7A to reaching that limit as well. :phew: I thought for a few seconds just to read I wasn't going to cause much of an issue but it is still better not to. I will check out a commercial battery tester if they are relatively cheap and have all the resistors built in. Sounds like a better idea than trying to cobble something together myself. I found a bunch on eBay but I am worried all they do is test voltage, which is exactly what I am doing with my multimeter: How do I make sure they are actually doing a thorough test under lsome selectable load? I'm guessing those cheap ones aren't doing anything to check amps across some variable resistor based on size of battery. |
| malagas_on_fire:
There are also some multimeters that includes 1.5V 9V and/or 12V battery testing with a resistor load in series mentioned in the manual. eg uni-t ut33b+ or uni-t 139A ( True RMS) |
| edy:
--- Quote from: malagas_on_fire on August 23, 2019, 09:14:50 pm ---There are also some multimeters that includes 1.5V 9V and/or 12V battery testing with a resistor load in series mentioned in the manual. eg uni-t ut33b+ or uni-t 139A ( True RMS) --- End quote --- :palm: I just realized my multimeter has that function!!!!! :-DD It's a Velleman DVM860BL: I didn't even see those 3 "BATT" ranges for 9V, 3V and 1.5V. So when I test the batteries it is not giving me the voltage on the battery (like the voltage range does) but really chokes it down to 0V if the battery is no good. For example, here are readings using normal V and the Batt 1.5V setting: V Batt 1.5V ------- -------------- 1.24 1.15 1.27 1.19 1.15 1.02 0.06 0 1.55 1.45 -0.07 0 -0.18 0 1.31 1.24 0.66 0.65 1.15 1.02 0.48 0.43 1.36 1.30 1.36 1.31 1.57 1.45 0.11 0 1.57 1.49 0.07 0 1.30 1.21 So what am I supposed to make of these numbers? If I use the Batt 1.5 V setting versus the regular voltage reading, how am I getting any more information? Is it changing the way it is testing the battery? Is it drawing some current (leakage through a resistor) through multimeter and therefore adding some load? I'm assuming that is what it is doing, hence the lower V's on the Batt 1.5V range setting. |
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