Brymen Crest and Min/Max Function VDC Capability - Page 1
Forum section: electronics / testgear

author: splat2030
author_rank: Contributor
timestamp: September 17, 2022, 12:59:02 pm
content: Hello All,I have been looking to purchase a multimeter for automotive/general usage, but I would like something with a very good min/max function that is capable of measuring the instantaneous max. voltage drop at my 12VDC car battery when under the load of cranking the starter. The overall application of the meter is personal use, so unfortunately the higher end meters like the Fluke in the video below are out of the budget. The Brymen BM-829s has caught my interest because the manual states that their crest function is capable of a 1ms (1000X/s) sampling rate, and the normal min/max function is capable of a 50ms (20X/s) sampling rate. This meter has signifiantly better specs than other similar meters I have looked at such as the UNI-T UT161D, which has a min/max function with a sampling rate of only 333-500ms (2-3X/s). Does the Brymen 1ms crest function work with DC voltage, and would it be fast enough to capture the max. voltage drop in this application? Does anyone have any real world experience using either the Bryman crest or min/max in this application that can provide any further input as to its suitability?Below is a link to a video showing this starting system/battery test:

author: unknownparticle
author_rank: Frequent Contributor
timestamp: September 17, 2022, 01:56:41 pm
content: How about Dave's 121GW, that has bluetooth data logging, so you can be remote from the meter and view on your phone.

author: splat2030
author_rank: Contributor
timestamp: September 17, 2022, 02:27:18 pm
content: I did peruse the manual for the 121GW, but I'm not sure it would be suitable for my application because it states that the 1ms peak button is only for AC voltage. It also does not list a specific sampling rate for the min/max function, so I assume that it defaults to the 5X/s update rate listed in the general specifications. The Brymen BM-829s manual does not state whether the 1ms crest function works for DC voltage, but even if it doesn't it would appear that the min/max function is on the order of 4X as fast than the 121GW if it functions per spec. under real world conditions.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 17, 2022, 02:46:03 pm
content: Depending what you are trying to measure, maybe you could just make a simple peak detector probe.

author: unknownparticle
author_rank: Frequent Contributor
timestamp: September 17, 2022, 03:34:51 pm
content: I admit to only skimming the text in your post, so excuse me for that.So, there maybe a better solution than a DMM. I have a battery analyser which can test the battery and charging system of a vehicle and record data in real time and hold it for examination. Mine is a Konnwei KW600, which I think has been superseded by the KW650. Check it out on Amazon, and the manual is available as PDF from the manufacturer. I haven't gone through it in detail but it may suit your purposes, at a low price. Mine has worked very well and has predicted a failing battery a couple of times. First time I sort of took the result of the test with a pinch of salt, that battery then failed suddenly 2 months later! Second time, on another vehicle, I changed it before that happened!

author: splat2030
author_rank: Contributor
timestamp: September 17, 2022, 04:19:03 pm
content: I know there are other faster/better methods of checking the charging system such as with a dedicated tester or an oscilloscope, but I'm just trying to keep it simple and relatively cost effective at this stage with one piece of equipment since I need to buy a decent multimeter for doing other things as well.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 17, 2022, 04:41:28 pm
content: Looking at the following:https://www.richtek.com/Design%20Support/Technical%20Document/AN066?sc_lang=enYou want to detect a dip with a minimum time of 13.5ms (t6). It would be easy enough to create a simple test pulse to demo it but I don't have the meter you are asking about.

author: mqsaharan
author_rank: Regular Contributor
timestamp: September 18, 2022, 04:41:25 am
content: Check out the reviews onhttps://lygte-info.dk/info/DMMReviews.htmlby HKJ. He has reviewed many cheap as well as expensive meters. He is also a member here.Under the section "Measurements" you'll find the details about min/max/peak functions.

author: splat2030
author_rank: Contributor
timestamp: September 18, 2022, 09:46:01 am
content: Quote from: joeqsmith on September 17, 2022, 04:41:28 pmThanks for the reference to the 13.5 ms, so now I know what level of accuracy I need. I am pretty new to the world of electronics, so it's probably outside of my current ability to make something to test this.

author: splat2030
author_rank: Contributor
timestamp: September 18, 2022, 09:48:10 am
content: Quote from: mqsaharan on September 18, 2022, 04:41:25 amThanks for the link, lots of good data there. I see he has tested the Brymen BM-829s min/max function, and states it needs 570ms to capture a voltage. The Brymen manual states that the min/max function takes a reading every 50ms, so any ideas why there would be such a large discrepancy?

author: Fungus
author_rank: Super Contributor
timestamp: September 18, 2022, 03:21:41 pm
content: Quote from: splat2030 on September 18, 2022, 09:48:10 amThat page also says:"Peak (Creast) needs about 0.7ms to capture a DC voltage, it may use multiple captures to get the final value. "Reason: "Min-Max" isnotthe same as "Crest" on a Brymen."Min-Max" works with the values displayed on screen, Crest uses raw/unprocessed ADC readings and is much faster.You can see the difference if you use it on AC voltage. Min-Max gives TRMS values, crest doesn't.https://www.eevblog.com/forum/testgear/brymen-bm257s-minmax-vs-5ms-crest-capture-mode/

author: joeqsmith
author_rank: Super Contributor
timestamp: September 18, 2022, 03:22:24 pm
content: If you check the manual for the meter used in the video you linked, it should be fast enough to capture that 13.5ms dip.https://assets.fluke.com/manuals/87______umeng0800.pdfThe Brymen BM789 and BM869s can both easily measure it (yes in DC crest mode). Guessing they offer other meters that could measure it as well. I looked at their automotive meter. The one thing I did not like about it was it would not save every parameter and required more fiddling than I would have liked.**Should add, when I wrote both meters can easily measure this, I set up a one-shot pulse (single pulse) that idles at 11V, then jumps to 16V for 5ms, then down to 6V for 5ms, then returns to 11V.

author: splat2030
author_rank: Contributor
timestamp: September 18, 2022, 03:59:52 pm
content: Quote from: Fungus on September 18, 2022, 03:21:41 pmThe problem is that the tested signal duration required to record the correct voltage value was longer than the manual specified screen refresh rate of 5X/sec or 200ms. If the min/max simply recorded the minimum value displayed to the screen, then I would think it should be able to record the correct voltage value in 200ms, and not require the 570ms that was measured. If it does truly work the way you described, then the screen refresh rate is actually 1.7X/second, and not the 5X/second specified in the manual.It seems that min/max on any of these meters is going to be much too slow, however, I am concerned about the accuracy when using the crest function. BM829s Manual states +250 digits for signals greater than 1ms in crest, and I would be in the 60.00V range to measure 12.6 volts. This would result in a tolerance of approx +/- 2.5 volts (.01*250), which pretty much would make it useless for this reading with that poor of accuracy.

author: splat2030
author_rank: Contributor
timestamp: September 18, 2022, 04:22:55 pm
content: Quote from: joeqsmith on September 18, 2022, 03:22:24 pmThe interesting thing I noticed after watching that video again closer is that he just pressed the min/max button one time, which would have put the Fluke 87 in the 100ms nominal response setting, and not the peak 1ms setting. This setting requires a minimum signal duration of 200ms per the Fluke manual from your link, so I don't think his reading of 9.96 volts is actually the true minimum voltage if the signal is only 13.5ms.I have also been looking at the BM789, and the crest function appears to have the best specs. of all the Brymen meters I have looked at. Manual states it can record with an accuracy of +100 digits at a duration of .35ms, however, the tolerance would still be quite large at +/- 1.0 volts when measuring 12.6 volts in 6000 count mode. What kind of accuracy did you see when you took those measurements?Would it be possible for you to test the minimum signal duration in VDC for the regular min/max mode as well? Manual states that min/max records 10X/second or 100ms, but also states that the min signal duration is 300ms, which seems pretty slow compared to their spec for the BM839 at 200ms. Very interested to know how close this would come to the spec.

author: Fungus
author_rank: Super Contributor
timestamp: September 18, 2022, 04:54:31 pm
content: Quote from: splat2030 on September 18, 2022, 03:59:52 pmMy Brymen BM857s is +100 digits on 50,000 counts. That's 0.1V accuracy on the 50V range.It's one of Brymen's "professional" meters (ie. designed to be thrown in toolboxes) and it only costs 10 Euros more than the BM829s.https://brymen.eu/shop/bm857s/I'm sure there's other Brymens with similar specs.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 18, 2022, 05:30:31 pm
content: Quote from: splat2030 on September 18, 2022, 04:22:55 pmThe min/max function on both meters (BM869s/789) would be far too slow to measure your 13.5ms. For accuracy, I would defer to the manual.I have a Fluke 189 which has something called a Fast Min/Max mode. This is a 5000 count mode with +/-100 count accuracy. I don't own the 87 referenced in your video. Looking at the manual they show a +/-40 count but then have a typical of +/-100 count for some modes.https://dam-assets.fluke.com/s3fs-public/87______umeng0800.pdf

author: joeqsmith
author_rank: Super Contributor
timestamp: September 18, 2022, 07:07:09 pm
content: Quote from: splat2030 on September 18, 2022, 04:22:55 pmGuessing that is true but he may know that and the number he tossed out for a minimum was based on that. Hard to say. You could write them and ask.

author: splat2030
author_rank: Contributor
timestamp: September 19, 2022, 12:54:26 am
content: Quote from: Fungus on September 18, 2022, 04:54:31 pmIt seemed like all of the meters I have looked at so far state that they revert to 4 digit display when in the crest/peak mode. I took a look at the manual for the BM857s, and oddly it doesn't list any specs for the meter at all. I had to pull the catalog brochure which states +100ms for changes greater than .8ms, but does not specify which scale the meter uses. Can you confirm with your meter that when you put it in crest mode you have a 5 digit display rather than 4 digit?Neither the manual nor catalog brochure give any specs on the performance of the regular min/max function, did yours come with any other documentation that lists this?

author: splat2030
author_rank: Contributor
timestamp: September 19, 2022, 01:19:23 am
content: Quote from: joeqsmith on September 18, 2022, 05:30:31 pmI was wondering how close you got to the true voltage value with the BM-789 in crest mode when you were measuring the 11V-16V pulse? Considering my calculation shows a tolerance of +/-1 volt when in the 60.00volt scale, was the meter actually capable of returning a value closer to actual than the stated tolerance?My confidence in the accuracies of regular min/max reported in the manual without 3rd party verification isn't great at this point considering that the two Bryman meters tested at the website referenced by mqsaharan (BM-829s, and BM-869s) both were way off compared to spec. The BM-829s took 570ms vs 50ms stated in the spec, and the BM869s took 350ms vs 50ms stated on the website. The BM789 seems to be their newest meter and has a much more detailed spec. for the min/max function in the manual, so I am curious whether this meter will actually perform closer to the spec. than the others. I will be using the regular min/max for other applications, so I would like to ensure whatever meter I get performs well in this function in addition to the crest/peak function.https://lygte-info.dk/review/DMMBrymen%20BM829s%20UK.htmlhttps://lygte-info.dk/review/DMMBrymen%20BM869s%20UK.html

author: Fungus
author_rank: Super Contributor
timestamp: September 19, 2022, 01:22:11 am
content: Quote from: splat2030 on September 19, 2022, 12:54:26 amIt's the "datasheet", not the "brochure", and it's +/-100 digits.Quote from: splat2030 on September 19, 2022, 12:54:26 amIf I manual range to the 50V mode then press "crest" I get two digits before and two digits after the decimal point.I find itveryhard to believe the accuracy is 1V though, that would be completely useless.I think we're not fully understanding the phrase "+100 digitsfor changesgreaterthan .8ms".I can understand that a changelessthan .8ms could be missed but what's meant by that wording?I could do some measurement experiments but they won't prove much until that's cleared up.

author: splat2030
author_rank: Contributor
timestamp: September 19, 2022, 02:04:17 am
content: Quote from: Fungus on September 19, 2022, 01:22:11 amMy understanding of the accuracy statement is that the crest function is capable of measuring changes in a measurement parameter that last for longer than .8ms, which is why they only assign a tolerance to values greater than this threshold. Any change in the parameter less than .8 ms does not get an assigned tolerance because the meter is not capable of registering it. I could be wrong, but this is how I interpreted it.I looked at the specs for all of the 5+ digit display meters that Brymen lists on their website (860 series, 830 series, 780 series, and 850 series), and all but the 850 series explicitly state in the spec that they use a 4 digit resolution in crest mode, which would give a tolerance of +/- 1 for the best performing meters with +/- 100 digit accuracy in the 50.00 range (see attachments). A meter with a 4 digit display such as the BM829 has a statement similar to the 850 series catalog where it just lists the accuracy, I assume because the meter is only capable of displaying 4 digits. It would seem to me that perhaps this was a mistake with the 850 series documentation, and it should perform like the BM869 and BM789 in crest mode considering yours switches to 4 digit display just like the others. I have a hard time believing that Brymen's newest, most advanced, and more expensive meters like the BM789 and BM869 would be so much less capable than one of their oldest meters.This video shows that the BM869s switches to 4 digit display in crest mode, but the measurement he takes is low enough to be within the 5.000V range. Low voltages like this should result in +/- .1 (.001*100) tolerance since there would be 3 decimal places of resolution.

author: radiolistener
author_rank: Super Contributor
timestamp: September 19, 2022, 03:10:21 am
content: Quote from: splat2030 on September 17, 2022, 12:59:02 pmyes, CREST works with DC and works with AC. In both cases it has the same meaning - it captures min and max amplitude Voltage. For example if I measure mains in AC mode with CREST I see:max=328.2 Vmin=-328.3 VAC = 240.3 VrmsBut you're needs to note that precision is significantly worse in CREST mode. Also this mode has some noise, so you will not be able to capture exact value, just min/max values of ADC noise around signal.Also note that there is bandwidth limitation, so the error will be higher for shorter pulse.Here is a short test, how CREST function of Brymen BM867S measures pulse with different length.Actual max Voltage is 1.0142 V.Actual min Voltage is -0.0130 V.pulse duration = max Voltage / min Voltage1000 ms = 1.031 / -0.029100 ms = 1.026 / -0.02910 ms = 1.028 / -0.0275 ms = 1.021 / -0.0294 ms = 1.016 / -0.0293 ms = 1.006 / -0.0292 ms = 0.899 / -0.0291 ms = 0.566 / -0.029Noise during measurement was about ±0.025 V, it means that it can show 0.566 V and after a second seconds can jump to 0.591 V.As you can see measurement error starts to grow very significantly at about 2-3 ms pulse. And at 1 ms pulse measurement error is up to 50%

author: radiolistener
author_rank: Super Contributor
timestamp: September 19, 2022, 03:17:28 am
content: Quote from: splat2030 on September 19, 2022, 02:04:17 amYou're needs to understand that CREST mode shows raw ADC value at about 1000 times per second rate. There is no way to keep 5-6 digits precision at so fast measurement. This mode is not intended for precise measurement, it is intended to catch short Voltage pulses or to estimate amplitude Voltage of AC waveform. Other DMM cannot do that at all.

author: Fungus
author_rank: Super Contributor
timestamp: September 19, 2022, 10:20:43 am
content: Quote from: radiolistener on September 19, 2022, 03:17:28 amObviously, but people are suggesting it drops down to less then 2 digits.Quote from: splat2030 on September 19, 2022, 02:04:17 amOK, so a changethat lasts for at least .8ms.That makes sense.Quote from: splat2030 on September 19, 2022, 02:04:17 amBut this makes no sense. My Brymen drops down to 4 digits in crest mode so if I put it in the 50V range and tap a 9V battery with the probes, you're suggesting it can read anywhere between 8 and 11 volts?It's an easy test to do...I've got a 9V battery here and if I set it to the 50V range and measure the voltage I get "09.465V".I pressed the crest button and tapped the battery terminal with the probe and I got "09.59V" on screen.I did it again and got "09.62V".Third time gave "09.60V".Fourth time: "09.60V"..Fifth time: "09.62V".OK, it's a tiny bit high (1.4%) but the error is consistent with "10 displayed digits", ie. 0.1V.The exact phrase use in the datasheet is:"Specified accuracy +/1 100 digits for changes > 0.8ms in duration"I think that "specified accuracy" refers to the meter's accuracy in 50,000 count mode, not the "visible accuracy" of the number of digits displayed in crest mode.It's consistent with my quick test and much more believable than the meter only having +/-1V accuracy (which would be completely useless!)

author: splat2030
author_rank: Contributor
timestamp: September 19, 2022, 12:04:11 pm
content: Quote from: Fungus on September 19, 2022, 10:20:43 amI agree with you that this accuracy level would be practically useless for my measurement, so I hope someone can point out where I have gone wrong in my understanding.I am not suggesting that every meter will necessarily read to the limits of the tolerance range when taking a measurement, but any random meter could read at the max. or min. published tolerance and still be considered to be within spec. I assume that if these meters are tested for quality at some point during the manufacturing process, then one that reads say 10 volts in crest mode would pass and be sold to a customer assuming my interpretation of this accuracy statement is correct. Every meter is going to read a little differently due to manufacturing variances.I'm not sure using a 9 volt battery like you are describing would adequately test the function of crest mode, because you are simply taking multiple measurements of a constant 9 volt source that doesn't see any rapid changes once you have the meter connected to the battery. I think a more accurate test would be to simulate a short duration voltage spike on a constant voltage source at varying time intervals.The exact statement for the BM857s is "Specified accuracy +/- 100 digits for changes > 0.8ms in duration", but this is the only meter with a greater than 4 digit display in Brymen's lineup that doesn't also include an additional caveat statement "6000 count mode only", or "Resolution 5000 counts" when describing crest mode. I would be surprised if this meter is capable of .001 resolution in crest mode when the flagship BM869s is not.My understanding is that the number of additional counts has a different effect on accuracy based on the resolution of the range you are measuring in. The resolution is .001 in 6.000V range, and the resolution is .01 in 60.00V range, so the effect on accuracy of +/- 100 counts is the difference between .1 and 1 in those two ranges. Since your BM857 meter switches to a resolution of .01 when you enter crest mode measuring 9V (09.00V), then +/- 100 digits should result in +/- 1V of tolerance, regardless of the normal screen resolution.As an example calculation, if we assume that we are limited to the 6000 count mode for the crest function as is stated in the BM-839 manual, then the only ranges available in DCV are 6.000, 60.00, 600.0, 1000. To measure 9 V, the meter would have to be in the 60.00 V range, otherwise it should show an overload in 6.000 V range. The "specified accuracy" in the 60.00 V range for the BM-839 is +/-(.045% + 1D), so a reading of 9 V would give +/- .014 V (.00045*9 + .01*1), then because we are also in crest mode we need to add the additional +/-100 digits to this (.01*100) = 1 V. The total tolerance per spec for reading for 9 volts in crest mode using the 6000 count range would be +/- 1.014 V.If we were reading say 5 V in the same 6000 count crest mode, then we would have a resolution of .001 (5.000V) because we are in the 6.000 V range, and the +/- 100 counts would only amount to +/-.1 V (100*.001). The specified accuracy would also be less at +/-.005V (.00045*9 + .001*1), resulting in a total tolerance of +/- .105 V.

author: Fungus
author_rank: Super Contributor
timestamp: September 19, 2022, 12:27:16 pm
content: Quote from: splat2030 on September 19, 2022, 12:04:11 pmWould make it useless foranymeasurement.Quote from: splat2030 on September 19, 2022, 12:04:11 pmYou're assuming the 100 counts is applied to the numbers shown on screen in crest mode, not to the "specified accuracy" of the meter.Quote from: splat2030 on September 19, 2022, 12:04:11 pmThat's exactly what's shown in the video you posted.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 19, 2022, 12:43:43 pm
content: For any questions regarding the specifications, you could always contact Brymen.It seems there is something in the manual for the BM869s where you can place the meter into the 500k mode prior to selecting crest. This will enable an extra digit but it seems it requires the signal to be stable for a longer period. I have not checked to see if Brymen has a newer version of the manual and it seems mine was pretty sparse on details.

author: splat2030
author_rank: Contributor
timestamp: September 19, 2022, 12:57:14 pm
content: Quote from: Fungus on September 19, 2022, 12:27:16 pmIt would make it useless for any measurement above 6 V (Assuming 6000 count mode). Measurements under 6 V would have an accuracy of +/- .105 V like I showed.The specified accuracy is the normal accuracy for the range you are measuring in. For the BM-839 its (.045%+1D) in the 60.00 V range, resulting in +/- .014V when reading 09.00V.The 100 counts are applied in addition to the specified accuracy in the range that the meter is measuring in. They would apply to 09.00 V in the 60.00 V range in 6000 count mode resulting in +/-1.00 V.Total accuracy for 09.00 V in 60.00 V range in 6000 count crest mode is specified accuracy + accuracy due to additional counts = +/- 1.014 volts.The video I posted shows a test of the crest function with a BM869s using voltage under 5 volts, so we would expect the accuracy to be approximately +/- .1 due to the .001 resolution in 5000 count mode. I have yet to see someone do the same test with a voltage that requires this meter to be in the higher 50.00 volt range with .01 resolution.

author: splat2030
author_rank: Contributor
timestamp: September 19, 2022, 01:29:25 pm
content: Quote from: joeqsmith on September 19, 2022, 12:43:43 pmThe manual for the BM869s states that it has a 5000 count resolution in crest mode.

author: armandine2
author_rank: Frequent Contributor
timestamp: September 19, 2022, 03:54:27 pm
content: Going back to the vehicle battery test - just checked my copy of Dan Sullivan'sFundamental Electrical Troubleshootingpp.168-169[He has >9.5Volts as a good battery] hedoes not include anything regarding sample rate and min/max but advises making up some long leads and watching the meter in your lap as you crank test. Which kind of says to me this procedure works with a technician grade DMMs and without min/max.I'd watch testing of min/max on DMMs measuring short duration signalsmy own quick test indicates I'd should probably use my Gossen Metrawatt Metrahit AM Xtra for the measurement (not my Fluke 28II or 287).

author: bdunham7
author_rank: Super Contributor
timestamp: September 19, 2022, 04:04:17 pm
content: Quote from: splat2030 on September 17, 2022, 12:59:02 pmI don't think you need a very fast MIN/MAX function to do this test and it actually might be confusing or yield wrong results if it were too fast. The 13.5ms figure mentioned is from a specification regarding the ability of automotive electronics to operate properly in a worst-case momentary voltage drop during starting and isn't intended as a battery test--and if it is used as a battery test, you need different numbers than given in your video.Your youtuber is giving you a rough rule-of-thumb method that may work on many modern cars with PM starters and modern electronic engine controls. I don't know where the 9.6 volts comes from, but from experience I can tell you that very early electronic fuel injection cars would sometimes have long crank times because the controllers went offline at ~9.6V and would only come back to life when the engine was spinning fast enough so that the starter load was reduced enough that the battery voltage would come back up. So a 'crank, no-start' complaint would be caused by a weak battery, something unthinkable on older models.The Fluke 98 Scopemeter had a built in battery test function that would graph out the battery voltage during the startup cycle. I just went out and tried my car, a 2010 Honda Accord I-4 that has been sitting for about a week. The car starts promptly and the battery is known to be good. The initial OCV was 12.41V, which dropped to 11.9 when the ignition was turned on. Ambient temp is 64F after an overnight low of ~56F. I'm sorry the picture isn't better, but the backlight is weak on the 30-year old Scopemeter and although I have the FlukeView software and cable, it hasn't worked since Windows 95. As you can see, the voltage briefly drops way below 9.6V, but then pops back up to 10V+ right away.A Fluke 27 using MIN/MAX gives a MIN of 10.19 volts and a MAX of 14.05 which indicates a good battery and a good charging system according to the test mentioned--both of which are correct results. That might be a good meter to start with for your usage, or if you are really interested in automotive, start scouring eBay looking for a Fluke 98.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 19, 2022, 04:24:16 pm
content: Quote from: splat2030 on September 19, 2022, 01:29:25 pmCould have been Rec mode or that I am confusing it with a different meter. Easy enough to download the manual and look. Sure enough, min/max mentions it.

author: armandine2
author_rank: Frequent Contributor
timestamp: September 19, 2022, 04:28:03 pm
content: Fluke 98 was re-badged as the Bosch PMS 100Looking through my copy of Bosch'sEngine Test: Fault detection with the oscilloscopethey don't mention the crank test - which might indicate that there is some difficulty in the interpretation of trace?

author: Fungus
author_rank: Super Contributor
timestamp: September 19, 2022, 04:33:21 pm
content: Quote from: splat2030 on September 19, 2022, 12:57:14 pmWhich is why I don't think they'd ever make a single meter that works that way, never mind a while range of them.It would be like making a car whose wheels turn square if you go past 50mph.Quote from: splat2030 on September 19, 2022, 12:57:14 pmOr ... they might have an accuracy of +/- 0.01V, as shown in joe's video.I just tried it with some 1ms, 2ms, 3ms... pulses and my meter seems to be about 0.1V high on the 50V range, ie. Specified DCV accuracy+100 counts.I can do more tests but practical testing only tells me aboutmymeter. My metermightbe the golden meter in a million that just happens to work well.The only way to be 100% sure is to write to Brymen and ask them to clarify the statement in the manual.(Which they probably will - they respond to email).Please let us know what they say.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 19, 2022, 04:36:28 pm
content: If my cars go "click", I know the battery is dead. No need for anything too fancy. If it dies often, I would be looking for the current draw. I seem to get about six years out of them.bdunham7's scope shot is nice. With a better scope, you should be able to see the compression stroke of each cylinder. We would expect them to be balanced. Maybe some monkey math applied to determine a weak cylinder. Certainly we could see if one was totally gone with a hole in it.

author: Fungus
author_rank: Super Contributor
timestamp: September 19, 2022, 05:01:33 pm
content: Quote from: joeqsmith on September 19, 2022, 04:36:28 pmYep, it's a car FFS.You don't need to know the exact dip to two decimal places, you just need to knowifit dips badly during starting.7V or 6V? It doesn't matter. You just need to know if it happens or not.Plus: No matter how accurate a meter's min/max function is it's not going to tell youhow long the voltage dipped fororthe shape of the dip. That's far more important than knowing the dip voltage to several decimal places.What's needed is a graph of voltage over time. Only an oscilloscope can do that.Get the right tool for the job.Quote from: joeqsmith on September 19, 2022, 04:36:28 pmYep.Waymore useful than a single number on a multimeter.

author: bdunham7
author_rank: Super Contributor
timestamp: September 19, 2022, 05:19:04 pm
content: Quote from: joeqsmith on September 19, 2022, 04:36:28 pmAnd when that happens in an airport parking lot after 14 hours of security, customs, gate changes and mediocre premium seating in an airplane not of your choice, you may wish you'd been more proactive.QuoteBetter scope? It's ancient but in some ways still unmatched, IMO. The Fluke 98 has that compression function as well, implemented in voltage or current configuration with a nice trace or 'relative compression' bars displayed. Voltage mode seems to not work very well with modern cars and I don'tcurrentlyhave an appropriate amp clamp. It's good enough to spot single burned exhaust valves on V8 engines that don't have very obvious running problems.

author: bdunham7
author_rank: Super Contributor
timestamp: September 19, 2022, 05:34:32 pm
content: Quote from: armandine2 on September 19, 2022, 04:28:03 pmI've used the feature many, many times and if it gets a good signal it gives you your choice trace or bars and both are typically quite easy to interpret. Obviously since you aren't directly measuring compression, there can be things which will interfere with the process. b/t/w I don't know if the Bosch PMS100 used the same firmware as the Fluke 98, I think the Bosch was an OEM-specified tool for some makes/models and it may have had different specs as a result.

author: armandine2
author_rank: Frequent Contributor
timestamp: September 19, 2022, 07:14:10 pm
content: "easy to interpret" because the car starts or doesn't?"

author: bdunham7
author_rank: Super Contributor
timestamp: September 19, 2022, 08:02:00 pm
content: Quote from: armandine2 on September 19, 2022, 07:14:10 pmNo, easy to interpret as in "oh look, cylinder number 3 is down 40%, that explains the rough idle". Provided, of course, that you can do a synced test, otherwise it is "oh look, one of the cylinders is down 40%, I wonder which one?"

author: joeqsmith
author_rank: Super Contributor
timestamp: September 20, 2022, 12:33:43 am
content: Quote from: bdunham7 on September 19, 2022, 05:19:04 pmWhat ever the circumstances are involving a dead battery, that would be my problem not yours but I appreciate the concern. I can tell you that I have never had a battery fail that was life changing...Quote from: bdunham7 on September 19, 2022, 05:19:04 pmReferring to the very low res.

author: splat2030
author_rank: Contributor
timestamp: September 20, 2022, 03:05:22 am
content: The reason I like the multimeter cold cranking test is because it is not simply a battery load test, but rather a quick and easy whole starting system health check. Failing this test does not necessarily mean you have a bad battery, it could also indicate that the starter motor is beginning to fail. You would need to separately load test the battery to 1/2 CCA rating to determine if the problem is with the battery, because a starter motor won't typically put a large enough load on the battery to fully test it. The whole point of doing any of this testing is to identify a failing starter or battery so you can replace them before they are completely nonfunctional and result in a breakdown.I like the suggestion of the Fluke 98 scope or the Fluke 27, but those meters are out of my budget. My vehicles service manual gives a minimum spec of 9.6 volts for a cold cranking test, so I would suggest that a true minimum reading of 7.12 volts is likely indicative of a developing problem with the starting system that has not yet manifested in any drivability issues. The regular min/max function on the Fluke meters needs a duration of 200ms to capture a voltage, so not using the peak function could allow you to show a passing result when in fact you failed the test. If the cold cranking test fails when monitoring voltage but the battery load tests properly, I would recommend retesting with an amp clamp to verify that the max current draw for the starter is in spec.After all of this research into the Brymen meters I am leaning toward the BM789, but I still would like to confirm the accuracy of min/max and crest. I will try to contact Brymen to see if they can clarify the statement in the manual and give an update.

author: bdunham7
author_rank: Super Contributor
timestamp: September 20, 2022, 04:09:44 am
content: Quote from: splat2030 on September 20, 2022, 03:05:22 amFluke 27 can be had reasonably on ebay. There was a seller a while back with brand new units with case and HV probes for $140. I realize it is a bit primitive in some ways, but it has its good points like beingverydurable.https://www.ebay.com/itm/155101904381One of the reasons I put the scope shot up is to show that the 9.6 volt specification doesn't include that initial short current surge and resulting large voltage drop. My battery and starting system are in good condition, that's just what things look like on a scope vs the MIN/MAX feature of a DMM. The car sits a lot and the battery was a bit discharged, so a I took the opportunity to charge it, top off the water and retest it. Not much difference and still below 9.6 volts. That initial surge just what you get when you apply power to a DC motor at standstill when there's no back-EMF yet.

author: splat2030
author_rank: Contributor
timestamp: September 20, 2022, 04:30:13 am
content: I was looking at the Fluke 27 II which is about $500 new, and the Fluke 98 scope which is about $1000 used. I hadn't really considered used just due to the potential of getting something that was knocked out of tolerance from to the way it was treated by the last owner. That Fluke 27 used for $70 doesn't look too bad, but something like the BM789 new for $175 seems like it would be much more useful due to the additional features. I am hoping I can just buy one multimeter that will meet all of my current and future needs, but I have also been debating back and forth whether I would be better served with both a cheap multimeter and a cheap scope like the Pico 2204a or the Hantek 6074BE rather than just a decent multimeter.From what I recall my factory service manual recommends using a specific diagnostic tester that has a built in amp clamp for doing the cold cranking test, but also gives that minimum 9.6 volt spec. I'd be interested to see if the results you are showing to 8 volts for that instantaneous drop are typical across multiple different vehicles at different ages, or if your vehicle is an outlier.

author: bdunham7
author_rank: Super Contributor
timestamp: September 20, 2022, 04:56:12 am
content: Quote from: splat2030 on September 20, 2022, 04:30:13 amI've tested many vehicles, and while they all have their unique characteristics, mine is not an outlier by any means. It actually is pretty undemanding of the battery--PM gear reduction starter motor, fairly puny battery cables. Probably less than 150A cranking current (not the initial surge) cold, less warm.Edit: here is an entirely different car, also in known good condition and it only sat overnight

author: splat2030
author_rank: Contributor
timestamp: September 21, 2022, 11:29:39 am
content: As an update from my previous post, I have attached the email response I got today from Brymen technical support regarding the accuracy of the crest and min/max modes for the BM789 meter. Unfortunately, they confirmed my calculations that the meter accuracy decreases significantly as you range up in crest mode. I asked them to provide me a calculated accuracy for a crest measurement in each of the 3 lower ranges of 3 volts, 12 volts, and 80 volts. The results are as follows:The accuracy of a 3 volt measurement is +/- .101 volt, the accuracy of a 12 volt measurement is +/- 1 volt, and the accuracy of an 80 volt measurement is +/- 10 volts. Looks like the crest function is pretty much useless for readings over 6 volts.They also confirmed that regular min/max/avg mode cannot pick up a signal with a duration less than 300ms regardless of the fact that the meter samples every 100ms in this mode.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 21, 2022, 11:43:45 am
content: Happy to see you going to the source. Brymen has proven to be very helpful when it comes to having an open dialog.

author: splat2030
author_rank: Contributor
timestamp: September 21, 2022, 12:03:19 pm
content: Kind of a bummer though...I was secretly hoping Mr. Fungus was right on this one!

author: Fungus
author_rank: Super Contributor
timestamp: September 21, 2022, 12:12:54 pm
content: Quote from: splat2030 on September 21, 2022, 12:03:19 pmYeah.

author: NoMoreMagicSmoke
author_rank: Regular Contributor
timestamp: September 24, 2022, 04:48:14 am
content: I have to ask the dumb question. Why not just buy the correct tool for a battery load test... AKA a carbon pile??? They can be had for cheap from HarborFreight/NorthernTool/Amazon, and will be much more accurate of a battery health test than trying to measure the voltage while cranking the starter.Something like this...https://www.amazon.com/WINMAX-TOOLS-AUTOMOTIVE-Alternator-Regulator/dp/B082PNSRXN/ref=sr_1_2?crid=YUD2LHFE8TGY&keywords=carbon+pile&qid=1663994835&qu=eyJxc2MiOiIzLjExIiwicXNhIjoiMi41NiIsInFzcCI6IjEuNzkifQ%3D%3D&sprefix=carbon+pile%2Caps%2C89&sr=8-2&ufe=app_do%3Aamzn1.fos.08f69ac3-fd3d-4b88-bca2-8997e41410bb

author: splat2030
author_rank: Contributor
timestamp: September 24, 2022, 10:06:57 am
content: Quote from: NoMoreMagicSmoke on September 24, 2022, 04:48:14 amA voltage drop of <9.6 volts during cranking is a quick check that indicates you have a healthy battery, starter, and starting system wiring/connections. Simply load testing the battery tells you nothing about the health of the starter and associated components. I needed to purchase a multimeter anyways, so I was looking for something that would work for this test.

author: bdunham7
author_rank: Super Contributor
timestamp: September 24, 2022, 02:15:03 pm
content: Any of the 'slow' models you've discussed will work fine in place of the Fluke 87 in your linked video. Your quest for the right multimeter may result in you getting one that gives you wrong results on this very rough rule-of-thumb test. Here is a Fluke 289 in MIN/MAX PEAK mode, again on a perfectly good car and battery.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 24, 2022, 02:48:08 pm
content: If I put the meter at the starter and try to crank the motor (which doesn't roll over) and I see a reasonable voltage, the starter is getting pulled. A 12V lamp is about all I need. I've had a few of my personal starters go bad. It's always the brushes. Tough to tell how much life is left on them with a meter. Same for the solenoid. Wiring and terminals are easy enough to inspect.

author: splat2030
author_rank: Contributor
timestamp: September 24, 2022, 02:53:53 pm
content: Quote from: bdunham7 on September 24, 2022, 02:15:03 pmI'm just going to go with the Uni-t 161D with a regular "slow" min/max based on the information you provided in this thread. I like that it has the temperature probe, and I should be able to pick one up for about $70.

author: splat2030
author_rank: Contributor
timestamp: September 24, 2022, 03:03:27 pm
content: Quote from: joeqsmith on September 24, 2022, 02:48:08 pmI am only looking at performing this test maybe once a year as a simple preventative health check, so I hopefully don't get to the point of the starter not cranking. If this test passes and reads >9.6 volts, then I shouldn't have to do anything further. If this test fails and reads < 9.6 volts, then I would load test the battery separately. If the battery load test passes, then I would do voltage drop testing along the circuit to rule out any bad connections. If that checks out, then I would check the starter current draw and if necessary pull the starter for further inspection and bench testing.

author: armandine2
author_rank: Frequent Contributor
timestamp: September 24, 2022, 03:56:44 pm
content: Fluke 287 on min/max - just tested the battery on start - 3 timesfirst min reading was negative, under a volt -not sure what that was about?- ghost voltage, as I set min/max prior to attaching leads to batterysecond reading min was over 10 voltsthird reading - savedI'm thinking may be my 287 isn't so quick as other's 289?Ed to add Peak info from manual

author: chebo
author_rank: Contributor
timestamp: December 02, 2024, 09:36:29 am
content: Let's raise a forgotten topic... I couldn't find a newer topic about this Crest mode.I recently purchased a BM789 and decided to use it to check my car battery. And at the same time I compared it with what the oscilloscope shows. This is what happened.The result is more or less the same, but there is still a small difference.Then I decided to conduct a small experiment at home with this scheme.I manually closed and opened the switch shown in the diagram, simulating a voltage drop. The average value for several measurements in the Crest mode was 7.60 V. As a result, the relative error was approximately 4%.