Author Topic: Harbor Freight Multimeter Add-on  (Read 4917 times)

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Offline WimberleytechTopic starter

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Harbor Freight Multimeter Add-on
« on: June 19, 2019, 06:23:12 pm »
I use the freebie Cen-Tech multimeter (Harbor Freight gives away from time to time) for testing batteries because it tests them under load.  I have a few of them.  So I designed this 3D-printed add-on so that this meter is a dedicated battery tester.  Still thinking of ways to improve it but works well in the current configuration.
 

Offline tooki

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Re: Harbor Freight Multimeter Add-on
« Reply #1 on: June 21, 2019, 06:47:56 pm »
That’s cool I guess, but what is the scale used? The manual’s description makes no sense to me:



1.5V at 4mA is 6mW, not 370mW. And I’ve never heard of displaying battery capacity by current, always by voltage under load.
« Last Edit: June 21, 2019, 06:50:04 pm by tooki »
 

Offline Gyro

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Re: Harbor Freight Multimeter Add-on
« Reply #2 on: June 21, 2019, 07:07:21 pm »
A load current of 25mA for a 9V battery and only 4mA for an AA cell doesn't sound right. That's a moderately heavy load for the 9V but insignificantly low for the AA.  :-\

I assume it's using the same resistor for both. The AA reading is going to give a misleading (high voltage) result.
Best Regards, Chris
 
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Offline Stray Electron

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Re: Harbor Freight Multimeter Add-on
« Reply #3 on: June 21, 2019, 07:11:17 pm »
  How/why is it reading 3.5 with only a single 1.5V battery in the adapter?
 

Offline Gyro

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Re: Harbor Freight Multimeter Add-on
« Reply #4 on: June 21, 2019, 07:14:22 pm »
3.5mA?

It looks weird. It should be measuring the battery voltage while it is under load, not asking the user to try to extrapolate from the current.  :-//

A pretty useless function.
Best Regards, Chris
 
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Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #5 on: June 21, 2019, 08:19:52 pm »
Geez
1) the battery being tested is bad (less than good).  That is why it reads 3.5.
2) the red knob in the center can be rotated left to Volts DC and measure open-circuit voltage (add a load resistor of your choice)
3) Given Ohms law and a fixed known resistor, measure current or measure voltage--does not matter
4) 25mA and 4mA makes sense to me.  A bad battery is application dependent, so there is no PERFECT test.

 

Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #6 on: June 21, 2019, 08:20:38 pm »
  How/why is it reading 3.5 with only a single 1.5V battery in the adapter?

It is current, not voltage
 

Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #7 on: June 21, 2019, 08:26:43 pm »
3.5mA?

It looks weird. It should be measuring the battery voltage while it is under load, not asking the user to try to extrapolate from the current.  :-//

A pretty useless function.

Does the user know what is a good voltage or a bad voltage?  This is just one metric...maybe good...maybe not so good.
 

Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #8 on: June 21, 2019, 08:28:30 pm »
That’s cool I guess, but what is the scale used? The manual’s description makes no sense to me:



1.5V at 4mA is 6mW, not 370mW. And I’ve never heard of displaying battery capacity by current, always by voltage under load.

I think the manual should have said 370 OHMs, not mW. 
 

Offline tooki

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Re: Harbor Freight Multimeter Add-on
« Reply #9 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?
 

Offline Gyro

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Re: Harbor Freight Multimeter Add-on
« Reply #10 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.

Best Regards, Chris
 
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Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #11 on: June 22, 2019, 02:26:09 pm »
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?

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.
« Last Edit: June 22, 2019, 02:30:56 pm by Wimberleytech »
 

Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #12 on: June 22, 2019, 02:27:01 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.

See my post with the Linden attachment
 

Offline tooki

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Re: Harbor Freight Multimeter Add-on
« Reply #13 on: June 22, 2019, 02:57:46 pm »
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?

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

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.
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!
 

Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #14 on: June 22, 2019, 03:10:12 pm »

Quote
I meant the battery contacts. I wasn't asking about the banana plugs.
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!
OK...we can still be friends  :phew:
 
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Offline Gyro

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Re: Harbor Freight Multimeter Add-on
« Reply #15 on: June 22, 2019, 03:22:52 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.

See my post with the Linden attachment

Sure, there are all sort of load profiles and the useable battery capacity will vary with each one. Actually, rather than the Linden attachment, you're better going to the battery manufacturer websites particularly Duracell and Energizer and downloading the technical datasheets. There you will find quoted capacities and discharge curves for all sorts of conditions, constant current, constant resistance etc. together with the sort of effect storage and pulse loads have. Very informative when you're designing something that uses them and establishing realistic battery life.

Certainly testing the battery voltage under some sort of dummy load gives some sort of idea, as it reflects the internal resistance, which tends to increase as the battery ages.  Hopefully we can agree that a 'one size fits all' approach doesn't really work and that maybe Harbor Freight's implementation of sticking a 370R resistor in series with the battery, regardless of voltage, and displaying the resulting current is probably the worst possible implementation.

P.S. That's where an external add-on, with integrated push-button loads would come into its own.
« Last Edit: June 22, 2019, 03:26:06 pm by Gyro »
Best Regards, Chris
 

Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #16 on: June 22, 2019, 03:39:28 pm »
Quote
Hopefully we can agree that a 'one size fits all' approach doesn't really work and that maybe Harbor Freight's implementation of sticking a 370R resistor in series with the battery, regardless of voltage, and displaying the resulting current is probably the worst possible implementation.
It is a big world...we don't have to necessarily agree--might be boring if we did.

Quote

P.S. That's where an external add-on, with integrated push-button loads would come into its own.

Yes, indeed...this would be a nice feature and it is something I am pondering.

Maybe this is the proper test to perform, no? 
 

Offline Gyro

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Re: Harbor Freight Multimeter Add-on
« Reply #17 on: June 22, 2019, 03:49:10 pm »
Haha, maybe. I think I'd put that one slightly ahead.  :P

I've seen cheap meters with individual  1.5V and 9V battery test positions. Maybe they do a better job of reading voltage under load. Of course that still doesn't differential between an AAA and a D cell.

I remember many years ago, back when I was a teenager, I used to work Saturdays in the photographic department of a big store. We had a battery tester supplied by (I think) Ever Ready. It had a 3 zone moving coil meter - bad, ok, good, switch positions for all the various battery sizes HP2, SP2, SP11, HP11, HP7, PP3 etc. and a whole bunch of load resistors inside. This was in Zinc-Carbon days, 'copper tops' were only just beginning to surface.
« Last Edit: June 22, 2019, 03:59:31 pm by Gyro »
Best Regards, Chris
 

Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #18 on: June 24, 2019, 01:49:52 pm »
Well, I redesigned the battery tester so that it now looks pretty  :clap:

I printed wiring channels at the bottom of the battery holder.

I also shrunk the X dimension so that it does not hang over the edge.  I am done with this now!
 
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Offline tooki

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Re: Harbor Freight Multimeter Add-on
« Reply #19 on: June 24, 2019, 04:46:43 pm »
That looks great!
 

Offline mikerj

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Re: Harbor Freight Multimeter Add-on
« Reply #20 on: June 24, 2019, 05:38:26 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.

This is true for a single cell, which is all your adapter appears to cater for.  For a multi-cell battery voltage under load is a more useful measurement since a battery with a shorted cell may still be able to supply sufficient current, but you'd have no idea the voltage was incorrect.
 

Offline floobydust

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Re: Harbor Freight Multimeter Add-on
« Reply #21 on: June 24, 2019, 06:51:55 pm »
This works for me, a few seconds to test. 50mA AA load and the manual has the pass/fail voltages.
« Last Edit: June 24, 2019, 06:53:30 pm by floobydust »
 
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Offline rsjsouza

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Re: Harbor Freight Multimeter Add-on
« Reply #22 on: June 24, 2019, 07:51:22 pm »
That is a nice adapter. I have been meaning to create something like this for my meters.

It's been a long time since I have used my pair of HF meters, but it seems this function is identical to the Aneng mini: it has both 1.5V and 9.0V battery testers that only display the measured current - a bit of a cop out. IMHO the Aneng uses much more useful currents of 40mA and 25mA respectively.

I have another meter (Mestek DM91A) that actually reports the voltage under load (30Ω and 300Ω for 1.5V and 9.0V respectively).
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Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline WimberleytechTopic starter

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Re: Harbor Freight Multimeter Add-on
« Reply #23 on: June 24, 2019, 08:32:01 pm »
That is a nice adapter. I have been meaning to create something like this for my meters.

It's been a long time since I have used my pair of HF meters, but it seems this function is identical to the Aneng mini: it has both 1.5V and 9.0V battery testers that only display the measured current - a bit of a cop out. IMHO the Aneng uses much more useful currents of 40mA and 25mA respectively.

I have another meter (Mestek DM91A) that actually reports the voltage under load (30Ω and 300Ω for 1.5V and 9.0V respectively).

The Aneng mini is $3.34 on Amazon with free shipping...lol
 

Offline tooki

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Re: Harbor Freight Multimeter Add-on
« Reply #24 on: June 25, 2019, 12:40:02 am »
And...? The DT830B like your harbor freight one are available for a dollar, including free shipping from China. Nothing to brag about.
 
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