Best Volt meter

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teklektik
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Re: Best Volt meter

Post by teklektik » Jan 18, 2015 5:09 pm

spinningmagnets wrote:... I would like to know what my best DMM options are in the different categories for an upgraded second DMM. How much do I have to pay to accurately check individual cell voltages down to 0.01V? Can it be done with a $30-DMM?, $40, $50...?
An experiment in Cheapie Data Logging:
A year or so ago I wanted to log some charger temperature data and so sprang for a TekPower DT9602R - another $50 DMM similar in features to the UNI-T UT61D. As I mentioned before, inexpensive autorangers are not my favorite, but this one does have a 'range' button so the readings are workably responsive if you dial in the range a priori.

As I said, the reason I went after the unit was data logging - a feature that has been called out in this thread for $600 meters. So - how do they do it for $50? Well - the meter doesn't actually save the data - it shoots it out an optically isolated RS-232 port and you hook up a PC and a little app saves the data. I found this to be an interesting approach that avoided paying for storage that I already have in my laptops.

Here's a snap of the little app they give you:
TekPowerDataGrab.png
TekPowerDataGrab.png (87.68 KiB) Viewed 1557 times
As you can see, this is just a straight dump of the LCD screen data - 4 digits of precision and a max sample rate slightly under a second but adjustable to any longer sample rate. The sample rate pretty much sucks for many logging applications, but for temperature or battery charge/discharge monitoring, it's fine. The generated log files can be pulled directly into Excel.
TekPowerDataFile.png
First line is meter setup info
TekPowerDataFile.png (7.53 KiB) Viewed 1557 times
The app lets you configure/save ranges, etc for all the different meter LCD screens but lacks a means to purge data to start a second run from the 'zero count'. A PITA, but it's easy to either restart it or adjust the collected data in Excel. A more ambitious (or possessed) person could replace the app with their own - the transfer format is very simple.
TekPowerConfig.png
TekPowerConfig.png (85.26 KiB) Viewed 1557 times
In general the meter does what is claimed although I found the temp reading to be about 2 degrees high. This wasn't troubling enough to see if it could be adjusted out or if it was the supplied K thermocouple. For relative comparison purposes between runs it was just fine.

Anyhow - as I mentioned before, I prefer a simpler meter for common tasks and this one shows the sluggishness of autoranging and a busy little processor - probably not any worse than other autorangers in this price range. But, it does have 4 digit precision, comes with a temp probe, and the logger works on any LCD display setting - just add you own PC. For on-the-road monitoring tasks I use the Cycle Analyst with Analogger which picks up a dozen parameters five times a second, or use a logging CellLog for multi-cell-level voltage debugging, but this meter is pretty serviceable for the specific tasks of logging common (slow-changing) ebike stuff in bench experiments.

So - this is just sort of an FYI. There seem to be more than one unit in this price range with these capabilities - if you have similar logging needs or aspirations they might be worth checking out for $50 - even if it's just for specific dedicated use.

An alternative might be something like the DI-145 multi-channel USB analog data acquisition device, but I went the meter route for better or worse.... :D
Last edited by teklektik on Jan 19, 2015 1:39 am, edited 1 time in total.
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Re: Best Volt meter

Post by friendly1uk » Jan 18, 2015 8:08 pm

spinningmagnets wrote: However, I would like to know what my best DMM options are in the different categories for an upgraded second DMM. How much do I have to pay to accurately check individual cell voltages down to 0.01V? Can it be done with a $30-DMM?, $40, $50...?
The $30 vichy and a fluke are seen in this video measuring 5v and the vichy is about 10 times more accurate. https://www.youtube.com/watch?v=3y5wjaNusr0 ( 2:30 )
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Re: Best Volt meter

Post by teklektik » Jan 19, 2015 1:19 am

friendly1uk-
Thanks! Interesting comparison... I had seen that comparison made by a number of eBay vendors, but the video brought the point home.

It got me snooping on YouTube and I ran into this: Review: Mid Range / Priced Multimeter Shootout / Buyers Guide
  • see: 29:30 for recommendations
The UT61E is part of the shootout review which has links in the video itself to more extensive reviews of all the contenders.

I have no particular affection for the UT61E but it got a lot of play on the Test Equipment Forum and has some good-looking specs and features for the price. Here's the links to the truly huge 4 Part YouTube Review which was glowing except for caveats about cheap probes and an input protection issue (don't use it above 220V EU mains voltage). It's frankly more than the minimum for ebike work, but at less than $60, it looks like a pretty nice meter for more demanding 'electronics' applications....

Amusingly one commenter said this:
YouTube viewer wrote:This is amazing... 3 parts on an inexpensive multi-meter. I guess I'm not the only one to look at things a bit close and over think things.

Wait a second.... part 4? No way.... LOL
Links to the nifty little reference standard PCBs in the vids:
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Testing Controller and Motor with or without DMM

Post by teklektik » Jan 19, 2015 4:02 pm

spinningmagnets wrote:5) possible short in one of the three phases inside the motor.
Check Ohms resistance between the phase wires. If one phase is bad, there should be a huge difference in one of the three readings, it should have a much lower resistance because the amp test signal has a shorter distance to flow through.
(do I understand this correctly?)
SM-
Yep. But although your suggestion sounds good in principle, measuring phase resistance is something a common meter typically cannot do because of the extremely low resistance. However, you can use your basic strategy by going after phase resistance with an external power supply or iCharger:
  1. Unplug the motor from the controller
  2. Hook a constant current supply or iCharger (set for 2V and 10A) across two phase leads.
  3. Use the meter to measure the voltage across the phase wires.
  4. Resistance = V/A (e.g. 0.8V/10A = 0.08ohm).
That said, there are alternative strategies to diagnose controller/motor issues that don't require a power supply - or even a meter....

Here's some common failure modes so we know what to look for:
  1. shorted FETs
  2. open FETS (not too likely)
  3. winding shorted (either adjacent turns or through stator)
  4. winding open (not too likely)
  1. Diagnosis With a Basic DMM:
    Here's the general idea for identifying controller failures:
    ShortedFetDetectionMeter2.png
    ShortedFetDetectionMeter2.png (29.78 KiB) Viewed 1492 times
    This test relies on the fact that the FETs have internal body diodes.
    1. Unplug the controller from power and disconnect the phase leads.
    2. Using the DIODE TEST mode, check the high-side FETs by testing the {A,B,C} phase connections to the controller V(+) connection.
    3. Using the DIODE TEST mode, make the same tests in the reverse direction.
    4. Using the DIODE TEST mode, check the low-side FETs by testing the {A,B,C} phase connections to the controller V(-) connection.
    5. Using the DIODE TEST mode, make the same tests in the reverse direction.
    • A GOOD FET will show about 0.4V in one direction and 'OPEN' in the other direction
    • An OPEN FET will show OPEN in both directions.
    • A SHORTED FET will show 0.0V in both directions.
    As mentioned above, testing the motor for shorts with a basic DMM on a resistance setting can be problematic because of low winding resistance, although simple stator shorts can be detected by unplugging the controller and doing a continuity or diode test from each phase lead to the axle (not the side plate). (The diode test is just sleazy means to get a readable voltage impressed instead of relying on the continuity criteria of the meter). Open windings are pretty unlikely but can be easily detected by doing three continuity tests across the possible combinations of two phase leads. If these tests don't yield results, you can pursue the 'cogging' test in the next section, or resort to the power supply strategy mentioned above.
  2. Diagnosis Without a Meter:
    Many motor/controller failures can be diagnosed without any test equipment at all.
    ShortedFetDetectionRegen.png
    ShortedFetDetectionRegen.png (30.62 KiB) Viewed 1492 times
    Here we exploit the facts that (1) the motor acts a generator when turned and (2) the generator electrical load determines the amount of turning resistance. Good or open FETs cannot present a load in this test and so create no rotational resistance; a shorted FET (the most common failure mode) creates a (partial) generator short circuit which appears as a heavy load and so causes turning resistance. Shorted turns generate less current and so cause less turning resistance.
    1. Unplug the controller from power but leave the motor connected to the controller.
    2. Turn the wheel by hand (backwards if a gear motor to engage the clutch) and get a feel for the cogging resistance.
    3. Unplug the motor phase leads from the controller.
    4. Turn the wheel by hand and compare the cogging resistance to the first test.
      1. If the motor spins much more freely, then there are one or more shorted FETs.
        Localization of the exact FET may be possible by plugging in the phase wires two at a time, but further efforts are best done with a meter.
      2. If the resistance is the same, then the controller has no shorted FETs and the problem may be in the motor.

        With the motor leads unplugged from the controller, use either of these two techniques:
        1. Pair-wise Cogging Comparison:
          1. Short together any two phase wires, turn the wheel and note the cogging resistance.
          2. Repeat the 'shorted phase wire' tests for the other two combinations and compare the cogging resistance.
            Reduced force for a particular combination indicates an open or shorted winding.
        2. 3:2 Cogging Comparison:
          1. Short all three phase leads together and turn the wheel to evaluate cogging force.
          2. Disconnect a phase lead and test cogging again.
            If the force is the same and not reduced, then that phase is open or has a short.
          3. Reattach the phase wire and repeat the 3-wire vs 2-wire comparison for the remaining two phase leads.
So - many common controller/motor failures can be diagnosed without fancy equipment although exact FET or phase localization may require a bit more effort than outlined here. That said, many folks will simply determine which of the controller or motor has failed -- that will be enough to go directly to 'replacement' as the solution.
Last edited by teklektik on Mar 13, 2015 2:50 am, edited 3 times in total.
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Re: Best Volt meter

Post by JEB » Jan 20, 2015 6:38 pm

Analog in volt meters, or clocks, if all you need is a indication , reading a analog clock takes a split second, a analog meter on a fluctuating voltage a analog easier to read, my old Simpson is the one I grab, the digital when it is necessary for a very accurate reading, my best Fluke went bad with a black LCD, never fixed it, who needs 4 digits anyway around bikes, or normal use. The taut band analog Simpson still is very accurate (10 inch movement~) with many scales to choose from, it was the state of the art back in the 60's. Some times a little more load other then 10m ohm's gives a more actual accurate reading, when hi sensitivity is not required. -my .02-

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Half-Ohm DMM Adapter (Winding Resistance)

Post by teklektik » Jan 21, 2015 3:58 pm

The post above about testing motors/controllers talks about using an external power supply to measure motor winding resistance (typically in the neighborhood of 100mOhms) because resistances of this scale are out of reach for common DMMs.

I ran across a little gadget that plugs into a DMM and allows you to measure milliOhms as milliVolts directly on any DMM. This looks pretty handy for measuring motor winding resistance - certainly more than enough for phase comparisons. It should also be handy for debugging PCB connection issues if your tinkering lies in that direction. Unfortunately, it's not going to be much help measuring shunts because they are in the 1 mOhm range and require greater accuracy than this device can afford.

Anyhow - it seems pretty cool for about $17 US. The circuit is simple/reliable and the device has been around for a few years (mature). Mine is in the mail... :)

Half-Ohm MilliOhm Adapter Page
halfOhmAdapter.jpg
halfOhmAdapter.jpg (28.04 KiB) Viewed 1431 times
[ Skip ahead to 2:45 -- Adapter is first item in "mailbag review" ]


Anyhow - this doesn't fall in the category of 'basic' tools to address common ebike tasks, but it looks like an inexpensive meter enhancement for those who desire the capability...
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Re: Best Volt meter

Post by friendly1uk » Jan 21, 2015 8:29 pm

teklektik wrote:friendly1uk-
Thanks! Interesting comparison... I had seen that comparison made by a number of eBay vendors, but the video brought the point home.

It got me snooping on YouTube and I ran into this: Review: Mid Range / Priced Multimeter Shootout / Buyers Guide
  • see: 29:30 for recommendations
The UT61E is part of the shootout review which has links in the video itself to more extensive reviews of all the contenders.

I have no particular affection for the UT61E but it got a lot of play on the Test Equipment Forum and has some good-looking specs and features for the price. Here's the links to the truly huge 4 Part YouTube Review which was glowing except for caveats about cheap probes and an input protection issue (don't use it above 220V EU mains voltage). It's frankly more than the minimum for ebike work, but at less than $60, it looks like a pretty nice meter for more demanding 'electronics' applications....

Amusingly one commenter said this:
YouTube viewer wrote:This is amazing... 3 parts on an inexpensive multi-meter. I guess I'm not the only one to look at things a bit close and over think things.

Wait a second.... part 4? No way.... LOL
Links to the nifty little reference standard PCBs in the vids:
I didn't like the UT61E's 10A limit. 20A is common now and can measure the effectiveness of soldering 15A shunts. The leads would need work, but that is easy enough. Good to see it in a more expensive lineup as little more than a benchmark, and giving the most accurate reading. Just not quite right for me though. Where most things have a 13A plug and I'm not just buying for the bike.


Hint for newbs: When test probes have their full shiney lengths exposed to daylight, the chances of crossing them while taking readings from something like a jst connector are high. Always cover your probes except for the very point. Exposing enough shiney metal to get on a jst plug, but not enough to reach a neighbouring probe. Only then can you stab in both probes with one hand without fear of crossing the streamers
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Re: Best Volt meter

Post by spinningmagnets » Jan 21, 2015 9:29 pm

teklektik, thanks for posting these troubleshooting procedures. I know how time-consuming it must have been to write all of that out. I will bookmark this thread and go back over it when I have some time and parts to experiment with, to solidify my understanding.

edit: here is a good $15 beginners Digital Multi Meter (DMM)

https://www.sparkfun.com/products/12966

"Testing MOSFETs with a DMM"
https://endless-sphere.com/forums/viewto ... 16&t=19645

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Re: Best Volt meter

Post by ddk » May 26, 2015 1:19 am

since I took the time to write this I'm just gonna bumper up with My Opinions

Any multimeter is better than no multimeter. Spend what you will but get one.

I Has:
-Protech 90something- measures almost everything. The A/C RMS measurement is inaccurate above 150Hz. The DC volts is accurate to 0.00X although it can only display 3.5 digits on it's internal LCD. note: RS232 utility software displays the complete measurement range of 4.5 digits.
-picked it up on sale a decade ago for about $75
...it's my 'accurate' standard
- not one, not two, but four of those Harbor Freight meters I managed to pick up for free or $1 during visits to the store.
These are accurate within a...lol...volt but are the meters I use most for basic troubleshooting.
I keep thinking I'll break one someday, but whatever.
*All the meters run on 9V batteries*
but I'm pretty good about turning them off
oh, and the Protech has a defeatable auto-shutoff, which I only defeat if logging something via the RS232 port.

If you've gotten bored using your meter to measure that electrical stuff only, you might look at this one that pretty much measures anything.
I've always been fascinated by meters that measure everything.
I plan to pick one of these up soon, not that I'm unhappy with the meters I already own.
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Re: Best Volt meter

Post by spinningmagnets » May 24, 2017 3:27 pm

Here's a new option, a $60 DMM with bluetooth, so the data-logging of checking many tests can be saved automatically onto a smart-phone?

https://www.amazon.com/Digital-Multimet ... B010Y71G1K

https://www.youtube.com/watch?v=7BpODKbTyZE


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Re: Best Volt meter

Post by 999zip999 » May 24, 2017 6:27 pm

For a back up how about a FREE harbour freight multi meter. I have three free meters one still in the box with free battery ( with coupon ) Also have a fluke, but loved old my fluke77 should have not loaned it out but given away a free h.f. mm instead.
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Re: Best Volt meter

Post by tiny_n_terrible » May 24, 2017 7:56 pm

My favorite multi meter is a Wallyworld 19.00 everyday price one.

I tried a harbor freight meter it has solder blobs for the rotary contacts and cheap probe socket contacts that oxidize after every use. Not for me.

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Re: Best Volt meter

Post by methods » May 24, 2017 9:57 pm

A used mid-range fluke is the only meter I will use.
All others have wasted my time with erroneous readings in the face of stray current... Or slow setting times.

The fancy fluke units are slow to start up... I go for the basic units that click on quickly. Just bought two at Fry's when I did not have time to shop used.

Always glad I spent the extra money. Fluke has never failed me.

-methods
"One test is worth a thousand opinions"

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Re: Best Volt meter

Post by Overclocker » May 24, 2017 10:29 pm

Image

my favorite "everyday" DMM so far. autorange. cheap. really compact and i like the auto-off so i just press select to wake it up again (no dial wear etc). out of the box calibration is very good.

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Re: Best Volt meter

Post by methods » May 24, 2017 11:09 pm

Ack lol :D

I just hang up when doing phone support and I hear someone say "what range do I set my Radio Shack meter to?"

Accuracy
Precision
Reliability
Pedigree
Confidence
Calibration
Noise immunity
Never a false reading ... Say when measuring resistance in a hot circuit...

I don't fool around where it comes to test and measurements
I will save money by wiping my butt with newspaper... But my meter is not a place to skimp.

-methods
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Re: Best Volt meter

Post by Overclocker » May 24, 2017 11:47 pm

ok fluke fans show me a scenario where, for an average ebike builder NOT doing rocket science, a UNI-T is going to give really bad measurements relative to a fluke

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Re: Best Volt meter

Post by tomjasz » May 25, 2017 2:20 am

Overclocker wrote:ok fluke fans show me a scenario where, for an average ebike builder NOT doing rocket science, a UNI-T is going to give really bad measurements relative to a fluke
Probably true, but happy i was gifted a fluke. It has an air.... Ha.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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Re: Best Volt meter

Post by bigmoose » May 25, 2017 8:40 am

My starting point for people is the same I gave my kids about their cars... any oil is better than no oil...

That said, I too have a couple of mid price range Flukes. Great reliability and accuracy, and after 20 years when the display gets funky, you can get new zebra stripes and make it new again.
"Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God..." all the best, Dave

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Re: Best Volt meter

Post by methods » May 25, 2017 10:21 am

Overclocker wrote:ok fluke fans show me a scenario where, for an average ebike builder NOT doing rocket science, a UNI-T is going to give really bad measurements relative to a fluke
I am sure your meter is fine. Don't wish to attack your choice, only advertise mine.
If we were to test head to head I would repeat what I just said:

* Measuring resistance with stray current... Does it go OL or does it show an arbitrary false reading?
* Settling time with capacitance in the circuit... How long does it take to settle?
* Is it precise across temp and range?
* Is it accurate across temp and range?

I have sat in a lab and measured meters against each other point by point. Voltage, current, resistance. I was surprised to find errors. In my case I just added a sticky note to the non-linear meter and kept using it with an offset factor.

May be the best meter on the market for all I know and I do not wish to speak I'll of it without testing myself. :mrgreen: I will look it up and test it if I have time and money.

-methods
"One test is worth a thousand opinions"

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Re: Best Volt meter

Post by tomjasz » May 25, 2017 4:11 pm

methods wrote: I have sat in a lab and measured meters against each other point by point. Voltage, current, resistance. I was surprised to find errors. In my case I just added a sticky note to the non-linear meter and kept using it with an offset factor.

May be the best meter on the market for all I know and I do not wish to speak I'll of it without testing myself. :mrgreen: I will look it up and test it if I have time and money.

-methods
I'd be happy is the people I help just had enough of a meter to read voltage within 1 volt. And continuity. Sadly to many come for help and refuse to invest in this most basic of all tools. Much less a fluke. Points well taken. Even my mid range fluke would leave someone as advanced as you disappointed..
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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Re: Best Volt meter

Post by methods » May 28, 2017 11:48 am

I understand your pain.

I try to get people to invest the $50 in a used Fluke because often... as they try to understand Volts, Amps, Ohms... how capacitance and current affect those readings... how to deal with range and range errors... it can be so hard with a meter which is manual.

I guess I would set the absolute minimum at a Meter which is Auto Range and can measure current. You are correct that it need not be accurate or precise... but it certainly must garner results which are not "insane"

Most guys asking me for help are trying to calibrate a shunt or measure leakage current... things we want to be accurate and precise for.
I support ya'll effort to get people to buy the tools needed.

Let me be rude and say... "Anyone who dabbles in Ebikes and does not own a DMM is retarded" :mrgreen:

Its like... going to the card house to play poker and not even knowing what hands beat other hands. Impossible to win. A meter is REQUIRED for this work just like a socket wrench set is required for working on a modern car. Yes... you can work on a modern car with an adjustable wrench only... and your knuckles will be bloody, time wasted, etc.

-methods
"One test is worth a thousand opinions"

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Re: Best Volt meter

Post by tomjasz » May 30, 2017 9:31 pm

Spot on.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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