Electronics > Projects, Designs, and Technical Stuff
Harbor Freight Multimeter Add-on
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Gyro:
Yes, just to be clear, I was commenting on the poor meter battery test functionality, not your 3D printed add-on.

Adding (switchable) load resistors, with appropriate loads for the two types of battery to your add-on would make a great deal of sense, using the voltage range instead.

Voltage under load is the natural measure of battery health. A battery labelled 9V should read in the vicinity of 9V, likewise a 1.5V marked AA cell.

Appropriate test current for an AA cell would probably be in the 200mA region.

Wimberleytech:

--- Quote from: tooki on June 22, 2019, 10:38:09 am ---So again, what’s the scale? With a full AA it should read 4+ mA? Just making sure I understand.

As I said, I — and others, it seems — have never heard of measuring battery capacity by current. Always just voltage under load. So it’s weird.

But again, the holder itself is cool. Perhaps it’d make sense to put a load resistor in it and then just use it in volts!

Did you DIY the contacts, or use COTS ones like from Keystone?

--- End quote ---

I used banana jacks (crappy ones that I modified) with the plastic cover removed.
I believe these here from Ebay: https://ebay.to/2Fr4wmy  These are really pretty bad.  You have to solder the lantern to the post otherwise you have intermittent connectivity.

Regarding voltage/current...it is natural for us to think in terms of voltage.  However, as I said, it does not matter for a given (known) resistance as long is there is some quality metric (e.g., 4mA is good, 3mA is bad) to inform the test result. 

Voltage is no more informative than current because the usefulness of your battery depends heavily on your application.

The designers of the meter decided to add this feature...load the battery with a 370 ohm resistor and measure its current.  It could just as well have measured the voltage instead.  That was their choice--not mine.  I would argue that the ONLY bad thing about measuring current vs. voltage is that we don't have an intuitive sense of what is good and what is bad (like we do with voltage--as I said...because we think in voltage terms).  So the designers of the meter decided to give you a number, a threshold, on the dial.

I am posting a page from Linden's Handbook of Batteries which illustrates that there is no "one size fits all" method for testing a battery.
Wimberleytech:

--- Quote from: Gyro on June 22, 2019, 12:16:28 pm ---Yes, just to be clear, I was commenting on the poor meter battery test functionality, not your 3D printed add-on.

Adding (switchable) load resistors, with appropriate loads for the two types of battery to your add-on would make a great deal of sense, using the voltage range instead.

Voltage under load is the natural measure of battery health. A battery labelled 9V should read in the vicinity of 9V, likewise a 1.5V marked AA cell.

Appropriate test current for an AA cell would probably be in the 200mA region.

--- End quote ---

See my post with the Linden attachment
tooki:

--- Quote from: Wimberleytech on June 22, 2019, 02:26:09 pm ---
--- Quote from: tooki on June 22, 2019, 10:38:09 am ---So again, what’s the scale? With a full AA it should read 4+ mA? Just making sure I understand.

As I said, I — and others, it seems — have never heard of measuring battery capacity by current. Always just voltage under load. So it’s weird.

But again, the holder itself is cool. Perhaps it’d make sense to put a load resistor in it and then just use it in volts!

Did you DIY the contacts, or use COTS ones like from Keystone?

--- End quote ---

I used banana jacks (crappy ones that I modified) with the plastic cover removed.
I believe these here from Ebay: https://ebay.to/2Fr4wmy  These are really pretty bad.  You have to solder the lantern to the post otherwise you have intermittent connectivity.

--- End quote ---
I meant the battery contacts. I wasn't asking about the banana plugs.


--- Quote from: Wimberleytech on June 22, 2019, 02:26:09 pm ---Regarding voltage/current...it is natural for us to think in terms of voltage.  However, as I said, it does not matter for a given (known) resistance as long is there is some quality metric (e.g., 4mA is good, 3mA is bad) to inform the test result. 

Voltage is no more informative than current because the usefulness of your battery depends heavily on your application.

The designers of the meter decided to add this feature...load the battery with a 370 ohm resistor and measure its current.  It could just as well have measured the voltage instead.  That was their choice--not mine.  I would argue that the ONLY bad thing about measuring current vs. voltage is that we don't have an intuitive sense of what is good and what is bad (like we do with voltage--as I said...because we think in voltage terms).  So the designers of the meter decided to give you a number, a threshold, on the dial.

I am posting a page from Linden's Handbook of Batteries which illustrates that there is no "one size fits all" method for testing a battery.

--- End quote ---
Bro... I wasn't asking for a lecture on the principles of methodology. I was just asking what the scale was, since it's not self-explanatory, and their method deviates from the one commonly used, and it's not explained in the manual, which as you saw is so wrong that it actually adds to the confusion. It says nothing like "≥4mA is good, <2.5mA is empty" or whatever it would be. That the "only" downside to showing it as current is that we have no sense of it is literally my point... That's not a minor little disadvantage!
Wimberleytech:


--- Quote ---I meant the battery contacts. I wasn't asking about the banana plugs.

--- End quote ---
These, as I recall: https://ebay.to/2L8b3pZ


--- Quote ---
Bro... I wasn't asking for a lecture on the principles of methodology. I was just asking what the scale was, since it's not self-explanatory, and their method deviates from the one commonly used, and it's not explained in the manual, which as you saw is so wrong that it actually adds to the confusion. It says nothing like "≥4mA is good, <2.5mA is empty" or whatever it would be. That the "only" downside to showing it as current is that we have no sense of it is literally my point... That's not a minor little disadvantage!

--- End quote ---
OK...we can still be friends  :phew:
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