DMM voltage tester vs. battery tester

[ltiu]

I just realized, why does my DMM have separate voltage testers and battery testers?

The voltage settings: 200mv, 2000mv, 20v, 200v.

The battery tester have settings: 9v, 1.5v.

Can't they just use the voltage tester to test battery voltage and not have redundant features?

What's the difference?

 

[Mr Happy]

The battery tester puts a small load on the battery while measuring the voltage, in order to give a more accurate estimate of the battery condition.

 

[Lynx_Arc]

what he said..... some batteries are somewhat elastic when it comes to voltage and even though they are mostly used up the voltage will bounce back to close to what a less used cell has. I have had batteries that measured 1.5v that wouldn't run a tv remote they were dead enough that a battery tester had them at 0.3v

 

[Light Sabre]

One thing that i have noticed is that the "load" varies on different battery testers. Refering to the ones that test alkaline batteries. I have a cheapie here that IMO puts too much of a load on the BUT and all sizes get the same load. I have an older Radio Shack one that puts a 1ma load on button and coin batteries, 50ma load on N and AAA's, and 150ma load on AA, C, and D, and 10ma load on 9V. Not sure if the loads are appropriate for the different size of batteries.

 

[Lynx_Arc]

those loads are acceptable... they are typically fixed resistors. Mine has 3 settings or resistors and the loads vary according to the resistance of the cell added into the testing circuit. You want just enough load to get the battery to work some which if it is weak it won't be able to work and the voltage will drop a lot from start.
my digital battery tester has 3 loads
for C/D it is approx 75ma (high load)
for lithium coin cells AA/AAA and alkaline 9v cells it is 20-120ma or medium ( I suspect 120ma for 9v)
for button cells and lithium 3v cells and non alkaline 9v and alkaline 12v (which are 8 ag3 I think in series) the load is 2.5ma to 20ma) or Low
I typically keep mine set on low most of the time as I am more interested in the sitting voltage than the load voltage most alkalines I can judge well without a load I have two categories... New and used. New is 1.45v+ and below that is used for 1.5v cells

 

[ltiu]

How can I tell what load my DMM is putting on the batts using the batt tester?

Using two in-line DMM? The other one set to measure current?

 

[Nos]

just measure the "short" circuit current with your dmm. on my dmm ~2,5A is full and ~500ma and dropping rapidly is empty

 

[ltiu]

How can I tell what load my DMM is putting on the batts using the batt tester?

Using two in-line DMM? The other one set to measure current?

OK, I did just that and found that the current is dependent on the battery voltage, higher voltage, greater current.

So current is not constant on my DMM.

 

[ltiu]

just measure the "short" circuit current with your dmm. on my dmm ~2,5A is full and ~500ma and dropping rapidly is empty

This is scary and dangerous!

 

[Nos]

AA NiMh's should be fine with 2,5A. I cant see anything dangerous there :shrug:

 

[Mr Happy]

AA NiMh's should be fine with 2,5A. I cant see anything dangerous there :shrug:

2.5 A is for alkaline. NiMH will approach 10 A on a single cell. Multi-cell packs will be 20, 30, 40+ amps. More than enough to blow the meter fuse or damage the internal shunt.

 

[Mr Happy]

OK, I did just that and found that the current is dependent on the battery voltage, higher voltage, greater current.

So current is not constant on my DMM.

This is because the load will be a simple resistor. The resistance is constant and the current naturally increases with higher voltage. For that reason there is a separate setting for 9 V batteries using a higher resistance than the setting for 1.5 V batteries.

 

[Nos]

Notthing new here A single cell doesnt have enought voltage to blow a unfused dmm, the internal resistance is too high for a unsafe current flow.

max current on a hot of charger eneloop was 2,7A i cant see any problem with that.....any hotwire puts more stress on the cells.. ..... i lstill my method :tinfoil:. at least for NiMh's

 

[Mr Happy]

max current on a hot of charger eneloop was 2,7A

Actually it seems like you have a resistance problem with your meter or test leads. Under good conditions with low resistance connections an Eneloop fresh off the charger should give a short circuit reading of 9-10 A.

 

[Nos]

my other dmm shows 0,15Ohm internal resistance on the 1st dmm+leads...................

something is wrong here. that should make the 9-10A :scowl:

my calculated resistance is 0,545Ohm ..............the dmm can take 20A but i guess i allready blew it :ironic:

 

[Light Sabre]

My better battery tester (Radio Shack, ~20 yrs old) has the ma written next to the voltage setting (only for the most common batteries) on the front cover . I found out what resisters it uses by just placing an ohm meter across the leads and measure the resistance on each setting. When I test a battery I also hook up a voltmeter in parallel with the battery tester (which has leads attached to it) to give me a more information than just good/marginal/replace. I can then match a set of batteries by voltage.

 

[ltiu]

I got one of these:

http://www.thesource.ca/estore/Prod...B9E2D6FCBECC43522FF2215442CC4E2134D0219770109

I wonder if it puts a load? I tried to measure it but hard to do with two hands. Need a second pair of hands to place the DMM leads on the contacts ...

 

[ltiu]

I got one of these:

http://www.thesource.ca/estore/Prod...B9E2D6FCBECC43522FF2215442CC4E2134D0219770109

I wonder if it puts a load? I tried to measure it but hard to do with two hands. Need a second pair of hands to place the DMM leads on the contacts ...

OK, doing a voltage reading comparison between a DMM with a loaded batt tester and the NexxTech batt tester, on a few different batteries. I conclude the NexxTech batt tester does not put a load on the batteries when testing.

 

[Light Sabre]

Just wondering if it's like the ZTS battery testers ZTS, Inc. Product Information. They only put a 2 second pulse on the battery under test. The resistor type of battery testers only really work on alkaline and carbon zinc batteries. Lithium, lithium ion, and NMH batteries can't really be tested accurately on that type of battery tester since their discharge curve is a lot flatter than alkaline and carbon zinc. The resistor testers go by battery voltage. On yours the test might already be over by the time you try to put a DVM across the battery.

 

[ltiu]

I wonder if it's like the ZTS, but then I got it for under $5 on sale from The Source (Radio Shack). The price tells me it is dumber than the ZTS.