Author Topic: Battery Tester's Readings Fluctuate  (Read 1558 times)

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Offline Boris_yoTopic starter

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Battery Tester's Readings Fluctuate
« on: November 19, 2021, 10:29:32 am »
Hello,

Why battery tester's readings fluctuate? I bought it over a decade ago. Since it didn't fall down, could contacts degrade? https://streamable.com/rk3yp2

Tested lithium AAA battery and it seems okay but when attempted testing rechargeable AA readings started going back and forth.
« Last Edit: November 19, 2021, 03:22:14 pm by Boris_yo »
 

Offline electr_peter

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Re: Battery Yester's Readings Fluctuate
« Reply #1 on: November 19, 2021, 11:55:05 am »
Not familiar  with this type of battery testers. It seems they have no internal battery and uses test battery as a source for display. White battery may be too discharged - with low output voltage and high internal resistance, that may be not enough to light display properly.
Or connection is bad somewhere.

Do you have regular DMM to test voltages and compare? Is white battery any good otherwise (is it discharged)?
 

Offline Boris_yoTopic starter

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Re: Battery Tester's Readings Fluctuate
« Reply #2 on: November 19, 2021, 03:41:29 pm »
Actually I just wanted to test with multi-meter but one of probes got its cord torn out. Can it be fixed or to the trash it goes?
 

Offline electr_peter

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Re: Battery Tester's Readings Fluctuate
« Reply #3 on: November 19, 2021, 04:08:48 pm »
It is difficult and not worthwile to repair, regular probes almost never break in this way. Much better option is to get new probes for DMM, pretty cheap item.
You still could measure battery voltages with broken wire end.
 

Offline Boris_yoTopic starter

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Re: Battery Tester's Readings Fluctuate
« Reply #4 on: November 19, 2021, 04:31:45 pm »
It is difficult and not worthwile to repair, regular probes almost never break in this way. Much better option is to get new probes for DMM, pretty cheap item.
You still could measure battery voltages with broken wire end.

Is black probe good with red probe from another set?

I managed to measure and here is what I found:

With multi-meter: voltage fluctuates between 1.22 - 1.23
With battery tester: voltage fluctuates between 1.14 - 1.15

My assumption is that multi-meter does not put load on battery while battery tester does.
 

Offline tszaboo

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Re: Battery Tester's Readings Fluctuate
« Reply #5 on: November 19, 2021, 04:39:46 pm »
The tester loads the battery with a resistor.
Your battery might be somewhat weak, or it's just the immediate voltage drop for a load.
 

Offline tooki

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Re: Battery Tester's Readings Fluctuate
« Reply #6 on: November 19, 2021, 07:00:35 pm »
Hello,

Why battery tester's readings fluctuate? I bought it over a decade ago. Since it didn't fall down, could contacts degrade? https://streamable.com/rk3yp2

Tested lithium AAA battery and it seems okay but when attempted testing rechargeable AA readings started going back and forth.
A rechargeable AA that starts at 0.95V is already basically empty. There’s practically no energy left in it, so any load just drags down the voltage. The fluctuation is likely due to the variable contact of the battery contacts. I bet if you squeezed on the contacts to give it a better connection, you’d get a more stable reading.

I also expect that with a new battery, the voltage would remain much more stable.

Is black probe good with red probe from another set?

I managed to measure and here is what I found:

With multi-meter: voltage fluctuates between 1.22 - 1.23
With battery tester: voltage fluctuates between 1.14 - 1.15

My assumption is that multi-meter does not put load on battery while battery tester does.
Yes, you can mix and match probes, but why? I can tell from the picture that those are very cheap probes. Do yourself a favor and get something a bit nicer.

You are exactly right about the load: that’s what makes a battery tester a battery tester and not just a voltmeter. A battery tester applies a load so that you don’t get tricked by a no-load high voltage in a nearly dead battery, while a multimeter is designed to apply as little load as possible (so as to not affect the circuit under test).
 

Offline Boris_yoTopic starter

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Re: Battery Tester's Readings Fluctuate
« Reply #7 on: November 20, 2021, 06:31:24 am »
A rechargeable AA that starts at 0.95V is already basically empty. There’s practically no energy left in it, so any load just drags down the voltage. The fluctuation is likely due to the variable contact of the battery contacts. I bet if you squeezed on the contacts to give it a better connection, you’d get a more stable reading.

What is variable contact of the battery contacts?
 

Offline Boris_yoTopic starter

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Re: Battery Tester's Readings Fluctuate
« Reply #8 on: November 20, 2021, 06:58:46 am »
Yes, you can mix and match probes, but why? I can tell from the picture that those are very cheap probes. Do yourself a favor and get something a bit nicer.

What makes quality probes better than cheap probes for home DIY? Are they more reliable when measuring mains voltage for example?
 


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