I hooked a bunch of meters into the same circuit.

I got spoiled. It used to be, many years ago, that Volt Meters were expensive and not very accurate. Now that they are cheap I can’t stop buying them. They seem like such a good deal in comparison. Anyway, I rounded up a quite a few and hooked them up to see how their readings compared to each other. Since the first time I opened one of these cheaper meters up, I noticed that they seem to be built around a “DMM on a chip” That is, all the important stuff in on one I.C. with a few other parts hanging off. Of course there is the readout, switch and banana jacks. Here is a pic of an opened, typical Harbor Freight DMM.

The black dot on the right is the DMM chip. In the upper left hand corner are the 3 banana jacks. They are soldered directly to the circuit board. Notice that there is a wire soldered connecting the left most jack and the right most. This is the shunt resister that is passes the current when using the 10A mode. That wire has to pass all of the current that is being measured. Typically this shunt wire is a .01 ohm resistor and to measure current passing through, the meter measures the voltage drop across it. It will be very small.
To the right of the battery is a replaceable fuse and in the lower right corner you can see an adjustment. I would imagine that it is a global calibration setting that after the meter is assembled, a technician adjusts a voltage reading to a known source. I am guessing that adjusting this once on a certain scale will also adjust for all the other scales as the digital circuits all use this one adjustment. So it would once and done. The only other calibration would be for the 10A scale, more on that later.
With cheap meters, the mechanical components are the weakest link. The switch, battery connector, jacks, and especially the test leads.
To see how 10 different meters compared, I first measured ordinary US household voltage. In this measurement it isn’t that important to have good test leads. They are only measuring voltage, very little current will pass through them, so I used the stock test leads. Here is the pic

Included in the picture are 5 Harbor Freight Meters, 2 Sears Craftsmans, a large digit Excel, an “Ideal” and a Cal-Hawk. All meters measured within 1% of their collective mean.

However, what seems to concern us most on BLF is current measurements. Can cheap meters read current levels accurately? Well the answer is no, not with the stock test leads. As many of us know, it is VERY important to have excellent electrical connections in higher current applications such as high powered LED lights. For this reason, I did not use the cheap, junky test leads that came with these meters, but rather used 14 gauge copper wire. For this current test, I connected 14! meters in series with each other, and then to a TMart C-8 XM-L running on a laptop pull cell, a Sanyo 2200mAh unprotected. Here is a pic before the light is connected, all meters read 0.00

This next pic shows the readings of all 14 meters as the current passes through each one. Normally this light draws 3.2A on this cell, but in this case, inserted into the circuit is 14 meters and 28 physical connections. Even though I used 14 gauge wire, the 28 connections and 14 x .01 ohm shunt resistors have taken a toll.

What’s important here is that for the most part, all the meters agree with each other! What this means is that all of these meters were calibrated at the factory. Only the HF meter in the upper right corner and the large digit Excel read a little low.

In the past, when I have changed out the battery in the Harbor Frieght meter, I have noticed either notches or gobs of soldier on the shunt resistor. At the time, I assumed that the notch was put there during calibration to increase ever so slightly, the resistance of the shunt and the gob of soldier was put there to reduce it. It turns out I was probably right. What I am about to do now, I have never done before. I will attempt to adjust the current reading of the HF meter that is reading too low (1.40)
Notice that I had put a black line on the switch of the meter in the upper right corner. Here is a pic of the unmodified shunt resistor.

The current reading of this meter is too low. This meter is reading the voltage drop across the resistor according to Ohms Law, E=IxR. If the reading is too low, (E) then R must be increased. Squeezing some notches in the wire will increase resistance!

Now I test again. Now the reading is too high! Those 3 notches increased the resistance too much. Again notice the black line on the switch.

Now the resistance needs to be lowered, a bit of solder can do this. This next part wasn’t easy, it took several tries. I’m sure the technicians know just how much will do in each instance. Experience makes hard work easy.

This next pic is after some fussing and a cell change. The important thing is that the meter now reads the same as the others.

I believe what all this means is that these cheap meters can be used for our casual purposes. If I was a professional, I certainly would own and use the very best meter I could afford i.e. Fluke or some such.
BTW, please don’t get the wrong impression. I own a lot of tools and when it really matters, I get the very best. I enjoy using them and owning them. Maybe someday I will own the very best meter, but for now, these will do.

For those intersted, Here is a pic of my EICO, bought in kit form in 1966. $39.95 and it had to be calibrated after it was assembled. The calibration consisted of connecting it to a wall socket and adjust for 117V. The DC calibration was the measure a fresh Carbon-Zinc D cell and adjust for 1.65V.

This next pic is of a Digital Volt Meter that I bought in 1975 for $69.95. It also was a kit, Sabtronics Model 2000

8 HF meters…I don’t know what to say. :wink: This is a cool comparison/test either way, thanks for putting out this data point (or 14 points…)

Wow, that is some collection!

I am actually surprised to see how close they agree to each other. Really, that’s pretty cool.

Thanks for doing this. Now we know the limiting factor for cheap DMM is the lead and its connection.

Heh, my current multimeter looks similar to that Eico.

I was planning on grabbing one of these eventually…


The super low price of the HF meter has been a game changer for me. Being free, or next to nothing allows me to spread them around like you would a screw driver. I have them in the shed, garage, kitchen drawer, my van, my electrical tool box, various tool bags, with my computer, etc. Where ever I am, I have a meter not too far away. I have even hardwired them into some portable power supplies that I have.

And they come with the battery already installed

Thanks much. We know it takes effort to put good info up for our benefit. You have spoken volumes to the utility of the HF meter.

If I didn’t thank you, I would burst. Kudos to you.

Thanks. great and informative test. Fun to see 14 meters in series .

Thanks for posting! I also have several of the HF meters. Time to build a good set of leads for them for current measurements.

Wow. Very interesting and informative. Thank you for all the effort you put into this. I think you are one meter short of being scientifically valid though.

Actually, I shouldn't joke. I think I have about 7 meters, not counting an oscilloscope.

It’s funny, I waited 3 weeks for 10 Banana Plugs to arrive from FastTech so that I could make some good test leads. I was disappointed with them, they were not of the greatest quality. So instead I used them to make the first 5 “jumper” leads. They didn’t work so well, I had to add soldier to each tip to get them to connect well. After I ran out, I used the plain 14 gauge wire stripped and folded in half at the bare wire portion. They worked well as is.

What I need to mention here is that there are other things to be concerned about with meters, that being SAFETY. These cheap meters are not as safe as the professional meters. I would not use them to measure high voltages i use them for light household and low voltage measurements. That is flashlights and automotive type measurements. I know some of them have the CE rating, but I wouldn’t trust that.

:smiley: I at first thought you were going to say ” I think you are one meter short of a full range digital multimeter
You would not be the first one to think that :slight_smile:

There probably is a “BudgetVoltmeterForum.com” somewhere in an alternate Universe :bigsmile:

What is really sick, is that I have many more, a lot of them unopened except that I have taken the test leads out because the crappy set that comes with it broke. Also for years, whenever Sears had a sale on meters, I would buy one. My price point for them was $10. There are 3 in play, one of them is auto ranging. Believe it or not, I don’t like auto ranging. Makes you think twice what you are actually reading. To me, it can be dangerous!

Do what Pulsar13 does, dedicate one of the HF meters to 10A current readings by soldiering the leads directly to the inside of the banana jack! See how free or cheap can be a game changer? What a great idea!

That’s a great idea. Thanks! :slight_smile:

Those red meters look like the same as my DT-830D (left), which is okay for a cheap meter. It’s internal resistance is 0.03 ohms (only 0.01 ohm more than the Uni-T UT33B on the right), so with decent cables and probes (clean the sockets too) it is good enough for current draw measurements. Good to know they’re calibrated!

You could use “the cheap, junky test leads”, get a reading perhaps 1A on your 14 meters, this number would be accurate.

Yes you are absolutely right! Point well taken, and the point is exactly what I was trying to show. That these meters measure accurately the amount of current that is passing through them. Of course we would not want to influence that amount downwards by using the stock test leads. Good catch on your part, proves you were paying attention! :slight_smile:

Yes, the major difference is that the red meters have a slide switch to turn them on and off and the DT830 has the on-off built into the selector switch. If you look closely at the voltage test pic, you will see your DT830. Bottom row, second from the right :wink:

Here are pics of the insides of my DT830 and a recent HF meter. The DT830 I thought was about 6 years old. That could be, there is a date of 2005 on the circuit board. The HF meter is the most recent one I picked up (free) on Sept 25, 2013.

Notice that the shunt resistor on the DT830 is twice as long as the one in the HF. and also that the shunt resistor in the HF is soldered directly to the same pads that the banana jacks are soldered to. 2 major improvements in reducing the internal resistance.
BTW, if you search around on the circuit boards, you will find “830B” printed on each of them. They are both generic type 830B meters. A lot of cheap meters will include the numbers 830 in their model number.

My 830D is quite old too. I will check inside for date etc. I am sure there is a trim pot. I see yours has no trim pot on the PCB compared to the red one.

There is no date on mine(I checked under the beeper). There is a date 20060909.

I see your meter has the shorter shunt resistor, but it is not close to the banana jacks. The fuse is soldered in place, not easily replaceable. I do see the 830B imprinted on the circuit board however, so this meter belongs in the club. That is weird about my 830D, no trim pot.
Also, notice the notch in the shunt resistor on yours, it was calibrated!

Thanks for the entertainging and informative post dchomak!

I’m missing the point to this thread, why would you invest in fourteen cheap meter instead of consolidating the same cash into something quality?

Because… It’s the American way!

(this is intended to be a joke)