Multimeter!

Not being an electronics guru whatsoever, I have a rather ridiculous question...

For testing LIon voltage, does the multimeter I purchase have to have any particular setting or range?

I was thinking of hopping down to my local crappy tire and buying this one (looks a little more robust than DX's testers):

http://www.canadiantire.ca/browse/product_detail.jsp?FOLDER%3C%3Efolder_id=1408474396672448&bmUID=1237051001437&PRODUCT%3C%3Eprd_id=845524442132041&assortment=primary&fromSearch=true

(use postal code N1R8C4)

And for pulse load testing, I already have a ZTS tester on the way....

I've accumulated about 5 Multimeters over the years, and this is my primary DMM. Granted, I don't do much more than test batteries. As long as it tests DC voltage in the range of your batteries, it will work fine.

coppertrail said:

I've accumulated about 5 Multimeters over the years, and this is my primary DMM. Granted, I don't do much more than test batteries. As long as it tests DC current in the range of your batteries, it will work fine.

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For $14, can't go wrong.

Purchased.

Mod's, please close! Unless anyone wants to discuss multimeters! I do I do! lol

coppertrail said:

As long as it tests DC current in the range of your batteries, it will work fine.

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Don't you mean DC voltage? Granted DC current has its uses, but voltage is the main test applied to batteries.

foxtrot29 said:

For $14, can't go wrong.

Purchased.

Mod's, please close! Unless anyone wants to discuss multimeters! I do I do! lol

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Actually, I would have purchased the Innova meter from Canadian Tire. The general quality of construction is better on the Innova/Equus meters, meaning they will probably be more reliable overall.

foxtrot29 said:

...For testing LIon voltage, does the multimeter I purchase have to have any particular setting or range?

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From my Sig Line LINKs:

RadioShack 22-802 DMM: pocket-sized, easy to keep clean and safe by simply closing the lid, has held up for years of use and goes about anywhere in a tool box, glove box or pocket. Got a couple of them on sale years ago and haven't used my expensive fragile analog since.





Link to product manual pdf: http://www.radioshack.com/graphics/uc/rsk/Support/ProductManuals/2200802_PM_EN.pdf

oregon

Mr Happy said:

Actually, I would have purchased the Innova meter from Canadian Tire. The general quality of construction is better on the Innova/Equus meters, meaning they will probably be more reliable overall.

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Yeah, and it seems to only be 3 1/2 digit, so I cancelled the order.

I'm on the fence here, don't know what to buy....

You can do load testing using a digital multimeter and some Radio Shack scraps:



You just have to create a circuit that puts a load on the battery, which is what resistors do. Above, I've put two 1 Ohm/10 Watt resistors in series for a total of 3.0 Ohms tested/displayed.

This circuit tests freshly charged Li-Ion cells at 1.38 amps, and NiMHs at .45 amps (or .91 amps if using only one resistor). It can also test 123 cells at exactly 1 amp draw.

Parts cost:

- Multimeter $3
- Resistor 2-pack $2
- Alligator clips $.60

Total cost: $5.60

Please note that the multimeter in the photo is set to display the resistance of the circuit - never use this setting for battery testing! Always set your meter to DC Volts when testing batteries

Ok, found one on ebay that is 3 1/2 digit, and for DC this is the accuracy listed:

DC. Voltage 200mV / 2V/ 20V / 200V / 1000V ±1%, ±2digits
+- 2 digits? Is this a bad thing?

StarHalo said:

You can do load testing using a digital multimeter and some Radio Shack scraps:

Click to expand...

For those less familiar with circuits, it may be worth pointing out that that picture is really dangerous. The meter is on a resistance range with the meter probes right next to a battery. It is just inviting someone to set it up like that and then put the probes on the battery.

For this test the meter needs to be on the DC volts range. If the probes are touched to a battery with the meter on a resistance range it could damage the meter.

foxtrot29 said:

Ok, found one on ebay that is 3 1/2 digit, and for DC this is the accuracy listed:

DC. Voltage 200mV / 2V/ 20V / 200V / 1000V ±1%, ±2digits
+- 2 digits? Is this a bad thing?

Click to expand...

Well unfortunately for really reliable measurement of lithium ion voltages you need a meter that is 4 1/2 digits with a basic DC accuracy of about 0.1%.

To see why, suppose the battery has a true 4.20 V measurement. On the meter you have to use the 20 V range, which means you have readings up to 19.99 V. The uncertainty in the meter reading will therefore be 1% of 4.20 V (0.04 V) + 2 digits (0.02 V) giving 0.06 V total.

In the worst case the meter could therefore read anywhere between 4.14 V to 4.26 V. In reality most meters will not be right at the edge like that, but a good rule of thumb is never to trust the last digit.

I said unfortunately at the beginning because a 4 1/2 digit 0.1% meter will cost a lot more than a 3 1/2 digit 1% meter. However, you might like to buy a low cost but reasonable quality meter to get familiar with using it, and then decide later on if you want to spend a lot more on a more accurate one.

Mr Happy said:

The meter is on a resistance range with the meter probes right next to a battery. It is just inviting someone to set it up like that and then put the probes on the battery.

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Very true, I've edited the post, ty for pointing that out.

Mr Happy said:

Well unfortunately for really reliable measurement of lithium ion voltages you need a meter that is 4 1/2 digits with a basic DC accuracy of about 0.1%.

To see why, suppose the battery has a true 4.20 V measurement. On the meter you have to use the 20 V range, which means you have readings up to 19.99 V. The uncertainty in the meter reading will therefore be 1% of 4.20 V (0.04 V) + 2 digits (0.02 V) giving 0.06 V total.

In the worst case the meter could therefore read anywhere between 4.14 V to 4.26 V. In reality most meters will not be right at the edge like that, but a good rule of thumb is never to trust the last digit.

I said unfortunately at the beginning because a 4 1/2 digit 0.1% meter will cost a lot more than a 3 1/2 digit 1% meter. However, you might like to buy a low cost but reasonable quality meter to get familiar with using it, and then decide later on if you want to spend a lot more on a more accurate one.

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Understood. I went with the canadiantire version, and it is 3 1/2 digit, 0.5%. Seems like a solid quality meter (linked in one of my first posts above...)

This setup will give you wrong results as you measure the voltage drop of the contact points to the battery.
Do a search for Kelvin, 4 wire measurement method.

Mr Happy said:

Don't you mean DC voltage? Granted DC current has its uses, but voltage is the main test applied to batteries.

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I did mean voltage :-S . Post edited.

get yourself a fluke DMM, cheap DMM is unreliable, do notice cheap one will read incorrectly when the battery level is low.

One could get a calibrated voltage reference and probably use that in combination with an inexpensive meter.

ebay often has ones for auction from a seller named zildjianboy7. He also sells them direct from his web site at voltagestandard.com. He sells a trimmable version and a less-expensive, non-trimmable one (or he used to).

Most likely such a 5V reference will give you a good idea of your measurement error at 4.20V. If you are really lucky and your 3 1/2 digit meter specs out a little better than advertised, you might be able to use your meter's "relative" function to get 3 decimal places, even if your meter's voltage ranges jump from 4V to 40V. For this hypothetical example, take a 3V Li primary and measure its resting voltage. Your meter hopefully can read that voltage out to 3 decimal places. Press the Relative button to zero the meter relative to the voltage of the Li primary cell. Then measure the voltage of your Li-ion. Add that relative value to the voltage measured for the Li primary to get the absolute voltage of the Li-ion.

Normally, if your meter range goes from 4V to 40V (for example), the Li-ion voltage measurement will be at 2 decimal places. But by using the relative feature, you might fool the meter and obtain 3 decimal places since the nominal 3V measurement of the Li primary should be at 3 decimal places.

Another approach could be to compare your meter to the measurements from a known-accurate meter like a Fluke 87 V.

foxtrot29 said:

I was thinking of hopping down to my local crappy tire and buying this one (looks a little more robust than DX's testers):

http://www.canadiantire.ca/browse/p...4442132041&assortment=primary&fromSearch=true

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That one goes on sale quite regularly for under $10. Next sale should be coming along in a few weeks.

I have 2 of them.

Black Rose said:

That one goes on sale quite regularly for under $10. Next sale should be coming along in a few weeks.

I have 2 of them.

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Canadian tire was having a huge sale while I was there.... Clearance, 40-75% off! But alas, that item was not on sale.

I'll stick with this one for a while, my next one will probably be a fluke! lol

I have a ZTS tester enroute anyway...