Author Topic: Testing batteries with multimeter  (Read 795 times)

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Offline edy

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Testing batteries with multimeter
« on: August 23, 2019, 08:32:08 pm »
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?
« Last Edit: August 23, 2019, 08:39:33 pm by edy »
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Offline barry14

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Re: Testing batteries with multimeter
« Reply #1 on: August 23, 2019, 08:58:37 pm »
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.
 

Offline edy

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Re: Testing batteries with multimeter
« Reply #2 on: August 23, 2019, 09:05:31 pm »
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.
« Last Edit: August 23, 2019, 09:09:53 pm by edy »
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Offline malagas_on_fire

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Re: Testing batteries with multimeter
« Reply #3 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)
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Offline edy

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Re: Testing batteries with multimeter
« Reply #4 on: August 23, 2019, 09:23:31 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)

 :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.
« Last Edit: August 23, 2019, 09:37:51 pm by edy »
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Offline mariush

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Re: Testing batteries with multimeter
« Reply #5 on: August 23, 2019, 09:25:08 pm »
A fun and easy project for you would be to make your own constant current load.
It's basically a potentiometer, a mosfet on a heatsink, an opamp and a bunch of capacitors and resistors... easy to make on a prototyping board.

I made one following the schematic on sleepyrobots.com (the site is dead now but linking to archive.org copy of it and attaching the schematic below) : https://web.archive.org/web/20160714214350/http://www.sleepyrobot.com/wp-content/uploads/2012/01/currentload-rev2.pdf

Here's the pdf : * currentload-rev2.pdf (215.82 kB - downloaded 32 times.)

I used the same opamp as it's cheap, but used another mosfet because it was easier to find : fqp50n06

Here's how my tool looks on cheap prototyping board: https://www.eevblog.com/forum/projects/problem-with-constant-current-dummy-load-design/msg383407/#msg383407   (pictures attached to the message i posted years ago)

A tool like this would allow you to adjust the current using the potentiometer (you can read the actual current value you set with the potentiometer by measuring the voltage drop across the resistors in the circuit) ... so then you can connect the battery to the constant current load and see how much the voltage drops at a particular current amount.
 

Offline Audioguru again

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Re: Testing batteries with multimeter
« Reply #6 on: August 23, 2019, 09:26:42 pm »
A battery tester is designed by a battery manufacturer to overload and kill a disposable battery so that you buy a replacement battery.
A battery tester can be used to test and kill the charge on a rechargeable battery then it can be recharged.

There are a few different kinds of ordinary household disposable batteries:
1) Cheap Chinese "super-heavy-duty" batteries are garbage and should not be purchased. They have a short life and a very low maximum current.
2) Name-brand alkaline batteries are excellent when used according to their datasheet.

I use Energizer or Duracell alkaline batteries and their spec's are shown on their websites:
a) A 9V battery has 6 or 7 tiny cells in series and are designed for a load current of almost nothing (a smoke detector) to 20mA for powering a little radio for a few hours.
b) An AAA cell can produce 50mA for a short time.
c) An AA cell can produce 200mA for a short time.

Some C or D size alkaline cells have a little AA cell inside.
 

Offline gbaddeley

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Re: Testing batteries with multimeter
« Reply #7 on: August 26, 2019, 09:14:35 am »
Rather than measuring current, it’s ok to measure voltage across a suitable resistive load. New alkaline cells will be >1.45v, reusable >1.25v, exhausted <1.1v. I use 33 ohm on AAA, 18 on AA, 10 on C, 4.7 on D, 560 on 216 sized 9v. YMMV
Glenn
 

Offline Kleinstein

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Re: Testing batteries with multimeter
« Reply #8 on: August 26, 2019, 11:20:21 am »
Alkaline cells can be tested open circuit. So just measuring the voltage can tell if the batteries are full or empty. Full/new is slightly above 1.5 V and empty is at around 1.2-1.3 V, depending on where they are used. However this can not tell the difference between different brands / types. There are  special ones for high current load and low current (e.g. clock). Even when down to some 1.2 V an AA cell max sill deliver 1 A short circuit current.

The other battery type is the old dry cell (zink carbon). These cells are kind of junk and are normally not work buying. With these cells the open circuit voltage does not give much information. Even a 99.9% dead (hardly enough to run a clock) cell still reads near 1.5 V. However with these cells the internal resistance and thus maximum current they can deliver will get worse over time. Even when new they are not good for high current, but when old the maximum current goes down a lot. So these should be tested with a load resistance - for s short time one can also measure the current, if one is sure not to have a alkaline cell or even rechargeable.
 

Offline ThickPhilM

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Re: Testing batteries with multimeter
« Reply #9 on: August 27, 2019, 08:21:11 am »
Pretty sure this has been covered in another thread, but it's worth mentioning a couple of things anyway.

You should NEVER test any cell or battery by shorting it. It will reduce its life, and may damage it internally. Some types are capable of delivering very high currents (most secondary/rechargeable types) and can potentially ignite or even explode (mainly lithium types).

Some larger lead-acid cells/batteries may be tested using a very high current tester (several hundred amps), but even this is not a direct short, it is a carefully calibrated milliohm load.

The useful life of a primary cell varies depending on the application, by and large, even 'dead' cells will continue to power an infra red remote control for example, often to the point of around 0.8v/cell, while it takes quite fresh cells to run things with motors in them.
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Offline bc888

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Re: Testing batteries with multimeter
« Reply #10 on: August 27, 2019, 08:52:14 pm »

I recall Dave Jones doing a You Tube on how to charge batteries with a Power Supply Unit, but don't recall if he detailed discharging or measuring with a multimeter first, you might do a search on Daves videos. To add to the subject, there are battery chargers that will first fully discharge and then charge batteries if you need an accurate number. Folks doing laptop pulls to reuse old 18650 lithium for example. Litokala 500S comes to mind. HKJ has some great info on his web site.

https://lygte-info.dk/info/indexBatteriesAndChargers%20UK.html

Clicking first on the chart you want, then you can click the header to sort for what you are looking for.  He lists the 500 but not the more recently released 500S. https://lygte-info.dk/info/roundCellChargerIndex%20UK.html

If you sort by "analyzer" you get the discharge current he measured. Quite a remarkable amount of good information. Link https://lygte-info.dk/info/roundCellChargerIndex%20Analyzer%20UK.html

« Last Edit: August 27, 2019, 08:56:59 pm by bc888 »
 


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