Author Topic: New EEVblog BM786 Multimeter  (Read 69296 times)

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Offline EEVblog

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Re: New EEVblog BM786 Multimeter
« Reply #300 on: January 24, 2021, 09:30:29 am »
Next to the LCD controller, there is an empty footprint for an IC and its components..
By the looks of it, it might be AD8436 True RMS converter chip. Some of the multimeter chips have built in low bandwidth RMS converters, for low cost options, with option to add external higher performance RMS converter for better specced meters.
Here we might have the same situation..

Yes, that was what I thought when I first saw it, but have not checked as I don't have a 789.
 
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Offline NoisyBoy

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Re: New EEVblog BM786 Multimeter
« Reply #301 on: January 30, 2021, 08:19:06 am »
Hey Dave,

Thank you so much for getting the meter out, it arrived in the US in 3 days. 

Interestingly, the three AAA batteries arrived with the meter, so no issue with DHL. They also improve the delivery date by 3 days, a pleasant surprise as we are expecting another snowstorm this weekend.

Did some quick measurements against my EDC 522 reference, as well as against my other bench meters with current calibrations, the meter is very accurate, even in the worst case, it is only 1-2 counts off.  First Brymen I own, it is definitely a keeper when I need mobility.  Its accuracy is as good as the handheld Flukes I own, and with higher precision. 

It is a great buy for its price point, not to mention showing support for a community of nice people I enjoy. 
 
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Offline jknightandkarr

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Re: New EEVblog BM786 Multimeter
« Reply #302 on: January 30, 2021, 09:50:19 am »
Dave,
     I just got my BM235 from Amazon and my BM786  just 24 hours apart. Gotta say that I love them both!  The features they both have are really nice and I esp. love the idea that I can't mess it up if I plug the probes into the wrong sockets.  VERY VERY nice idea!  Being in school at DeVry University and for my hobby work, these will come in VERY handy!   :-+ :-+ :-+ :-+

Joe 
 
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Offline Shannon

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Re: New EEVblog BM786 Multimeter
« Reply #303 on: January 30, 2021, 03:35:38 pm »
I love this no bull shit package!

Every engineer has to spent half of the work time to naming the schametic net or value in code!

Less is more.
Nature and Nature's laws lay hid in night:
God said, Let Newton be! and all was light.
 

Offline bc888

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Re: New EEVblog BM786 Multimeter
« Reply #304 on: February 08, 2021, 08:51:18 pm »


2 things...I have a rag tag collection of things that measure Non-Contact Voltage but this BM786 is the best. Hands down. Better than anything I've ever used. Finally! no more sawing through hidden live power wires behind the walls:-)

2nd) Continuity beep is not the fastest. Wish it was.

3rd) They did not cheap out on the leads. Good stuff.

Thanks Dave!!!!
 

Offline bc888

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Re: New EEVblog BM786 Multimeter
« Reply #305 on: February 08, 2021, 08:57:34 pm »
BTW, can anyone direct me where is the BM786 manual download? It's not here now, https://www.eevblog.com/files/BM789-Manual-Original-Final.pdf, and I didn't find it via Eevblog Wiki or search. Didn't find it on Brymens site either:

Nevermind, rooted around and got it here: https://www.eevblog.com/files/BM786-Manual-Original-Jan2021.pdf
« Last Edit: February 08, 2021, 09:01:41 pm by bc888 »
 

Offline schwaggins

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Re: New EEVblog BM786 Multimeter
« Reply #306 on: February 09, 2021, 07:14:07 am »
The continuity beep is very responsive on mine i haven't noticed any lag/latching problems at all, i am using different leads with mine maybe its that.
NCV is incredibly sensitive on this meter i was able to detect live wiring in the wall quite easily
 

Offline schwaggins

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Re: New EEVblog BM786 Multimeter
« Reply #307 on: February 09, 2021, 09:37:14 am »
" Continuity beep is not the fastest. Wish it was."
You are probably referring to the Beeplit Diode test, Beeplit Continuity function is the one on the Ohms range which is instantaenous
 

Offline Frank987

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Re: New EEVblog BM786 Multimeter
« Reply #308 on: February 14, 2021, 10:39:01 am »
There is a problem with the 400 mA Fuse: The BM786 manual  says a SIBA Fuse 7017240;0.4A/1000V is used for the 600 mA range.  In the SIBA datasheet https://download.siba.de/pdf/artikel/SIBA-GSS-7017240.pdf you find that the 400 mA fuse blows typical after 0.1 s at 1,5 * 400 mA  = 600 mA. The I²t value of the fuse is 0.07 A²s, giving about 0.2 s at 600 mA. So something must be wrong as it s not possible to do measurements in less than 0.2 s. Either the manual is wrong or the 600 mA current rating of the meter or the meter is supplied with the wrong fuse, should be SIBA 7017240.0,63 with 630 mA.
 

Offline 2N3055

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Re: New EEVblog BM786 Multimeter
« Reply #309 on: February 14, 2021, 11:18:29 am »
There is a problem with the 400 mA Fuse: The BM786 manual  says a SIBA Fuse 7017240;0.4A/1000V is used for the 600 mA range.  In the SIBA datasheet https://download.siba.de/pdf/artikel/SIBA-GSS-7017240.pdf you find that the 400 mA fuse blows typical after 0.1 s at 1,5 * 400 mA  = 600 mA. The I²t value of the fuse is 0.07 A²s, giving about 0.2 s at 600 mA. So something must be wrong as it s not possible to do measurements in less than 0.2 s. Either the manual is wrong or the 600 mA current rating of the meter or the meter is supplied with the wrong fuse, should be SIBA 7017240.0,63 with 630 mA.

If you look at that diagram, that dotted line on the left is not the fuse curve.  Fuse reaction curves are those two short ones on the right (marked with white and black triangles).
Fuse will blow in 60 msec at 4X of nominal current. At 2,75xIn (nominal current) it will not even blow...
Regards,
 

Offline Fungus

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Re: New EEVblog BM786 Multimeter
« Reply #310 on: February 14, 2021, 12:56:46 pm »
If you look at that diagram, that dotted line on the left is not the fuse curve.

What's the line on the left for?
 

Offline HKJ

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Re: New EEVblog BM786 Multimeter
« Reply #311 on: February 14, 2021, 01:16:39 pm »
If you look at that diagram, that dotted line on the left is not the fuse curve.

What's the line on the left for?

I would expect it was minimum and maximum, i.e. the fuse may or may not blow in between the two curves. This also matches the table where 2.75x do not contain any values.
 

Offline 2N3055

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Re: New EEVblog BM786 Multimeter
« Reply #312 on: February 14, 2021, 02:05:39 pm »
If you look at that diagram, that dotted line on the left is not the fuse curve.

What's the line on the left for?
I wouldn't know, not my diagram. I presume that is some Joule heat (current/time integral) limit...
 

Offline Fungus

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Re: New EEVblog BM786 Multimeter
« Reply #313 on: February 14, 2021, 02:07:09 pm »
Maybe it's guaranteed not to blow to the left of that line.
 

Offline Wytnucls

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Re: New EEVblog BM786 Multimeter
« Reply #314 on: February 14, 2021, 02:24:35 pm »
No. That's the minimum line for the 1A/2A fuse. 1ms to 1 hr. (4 In to 1 In).
 

Offline Frank987

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Re: New EEVblog BM786 Multimeter
« Reply #315 on: February 14, 2021, 04:37:33 pm »
Now I have read the SIBA homepage. I agree, the left curve is the minimum time not the typical time for the fuse to break and curve is only valid for 1A  1.6A and 2A fuses. Better calculation is with the "SchmelzintegralI" I²ts Value, which is 0.07 A²s for the 400 mA fuse. Now with 0.6 Amp the time to break is 0.07 / 0.6² = 0.194 s. I can not read the Multimeter in this short time as it does only 5 measurements / s. So before 1 measurement is done the fuse is broken...
 

Offline HKJ

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Re: New EEVblog BM786 Multimeter
« Reply #316 on: February 14, 2021, 04:56:07 pm »
Better calculation is with the "SchmelzintegralI" I²ts Value, which is 0.07 A²s for the 400 mA fuse. Now with 0.6 Amp the time to break is 0.07 / 0.6² = 0.194 s. I can not read the Multimeter in this short time as it does only 5 measurements / s. So before 1 measurement is done the fuse is broken...

It sounds like the integral specified the minium time, i.e. the fuse will at least last 0.2second, but may never blow at all.
 

Offline Wytnucls

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Re: New EEVblog BM786 Multimeter
« Reply #317 on: February 14, 2021, 05:02:43 pm »
t is the time for the fuse to completely open with overcurrent.
600 mA equals 150% of In and the FF fuse must not open for an hour, by IEC regulations 60127.
UL 248 standards are different:
4 hours at 110% and 60 minutes max at 135%.

A fuse made to UL/CSA/ANCE 248-14 and operated at its rated current will
eventually open. For this reason UL fuses are customarily operated
at no more than 75 percent of their rated current.

Currents between 110 and 135 percent of fuse ratings present a
severe challenge to the designer because they can subject parts to
high heat for extended periods of time, and because fuse behavior
at these currents can be difficult to predict.
  Littelfuse
« Last Edit: February 14, 2021, 05:50:25 pm by Wytnucls »
 

Offline EEVblog

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Re: New EEVblog BM786 Multimeter
« Reply #318 on: February 15, 2021, 12:56:24 pm »
There is a problem with the 400 mA Fuse: The BM786 manual  says a SIBA Fuse 7017240;0.4A/1000V is used for the 600 mA range.  In the SIBA datasheet https://download.siba.de/pdf/artikel/SIBA-GSS-7017240.pdf you find that the 400 mA fuse blows typical after 0.1 s at 1,5 * 400 mA  = 600 mA. The I²t value of the fuse is 0.07 A²s, giving about 0.2 s at 600 mA. So something must be wrong as it s not possible to do measurements in less than 0.2 s. Either the manual is wrong or the 600 mA current rating of the meter or the meter is supplied with the wrong fuse, should be SIBA 7017240.0,63 with 630 mA.

The BM235 uses the same 400mA fuse for its 600mA range and it's never been an issue.
I asked Brymen years ago if a 500mA fuse could be used on the BM235 and their response was

Quote
Not recommended.
For measuring 600mA in short period, there is no problem to use that fuse. But for measuring 600mA continuously, it will heat and the internal ambient temperature around that fuse may reach to the one out of plastic case temperature spec.
 
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Offline Wytnucls

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Re: New EEVblog BM786 Multimeter
« Reply #319 on: February 17, 2021, 05:48:41 am »
It seems to me that Brymen is obfuscating here.
A SIBA 630mA fuse will only heat up by a few degrees when subjected to 600mA, whereas the 400mA fuse, at 150% of its current rating, could possibly melt plastics, before it opens one hour later.
The Bussmann 440mA fuse temperature only rises by 6 degrees above ambient (datasheet), when operating at its max rated current.
 

Offline fabrizio_fabrice

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Re: New EEVblog BM786 Multimeter
« Reply #320 on: February 21, 2021, 08:47:04 pm »
Just discovered the 786 doesn't have an AC (only) voltage range!?  But it has the same symbols on the face as mV, mA, and µA — and they do cycle through all three.

I thought it was just an oversight in the manual, because I hadn't heard mention of this (I don't live here).  Now I read the manual in a different light— p. 7 heading is: DCV; DC+ACV.   No AC volts!   Measuring AC gain needs some math given the usual change in DC biases present.

What's the rationale?
 

Offline Monkeh

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Re: New EEVblog BM786 Multimeter
« Reply #321 on: February 21, 2021, 08:50:25 pm »
Just discovered the 786 doesn't have an AC (only) voltage range!?  But it has the same symbols on the face as mV, mA, and µA — and they do cycle through all three.

I thought it was just an oversight in the manual, because I hadn't heard mention of this (I don't live here).  Now I read the manual in a different light— p. 7 heading is: DCV; DC+ACV.   No AC volts!   Measuring AC gain needs some math given the usual change in DC biases present.

What's the rationale?

The rationale is you rotate the switch one position counter-clockwise to the ACV position.
 

Offline fabrizio_fabrice

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Re: New EEVblog BM786 Multimeter
« Reply #322 on: February 21, 2021, 10:32:15 pm »

What's the rationale?
The rationale is you rotate the switch one position counter-clockwise to the ACV position.
Ahhhh.... thanks, Monkeh!    I'm 'challenged' |O by manuals that cover multiple versions. 

It would make more sense to me if they integrated ACV with the DC and AC+DC? settings like the other parameters.  So much for HID protocol.
 

Offline Monkeh

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Re: New EEVblog BM786 Multimeter
« Reply #323 on: February 21, 2021, 10:34:58 pm »

What's the rationale?
The rationale is you rotate the switch one position counter-clockwise to the ACV position.
Ahhhh.... thanks, Monkeh!    I'm 'challenged' |O by manuals that cover multiple versions. 

It would make more sense to me if they integrated ACV with the DC and AC+DC? settings like the other parameters.  So much for HID protocol.

Too many settings. ACV, ACV + LPF ('VFD mode'), DCV, DC+ACV, dBm. Better to have a couple more switch positions than have people cycle through so many modes by button. The mV range is less used so they just crammed them all in there, and it's a pain.
 

Offline IanB

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Re: New EEVblog BM786 Multimeter
« Reply #324 on: February 22, 2021, 12:39:19 am »
It would make more sense to me if they integrated ACV with the DC and AC+DC? settings like the other parameters.  So much for HID protocol.

Sometimes turning the dial can mechanically switch certain components in or out of the circuit. If they tried to do it using push buttons they would have to use a relay instead. The rotary dial is more reliable.
I'm a ChemE--I know all about the flow of fluids.
 


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