Author Topic: New EEVblog BM786 Multimeter  (Read 68789 times)

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Offline Wytnucls

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Re: New EEVblog BM786 Multimeter
« Reply #150 on: November 23, 2020, 07:02:26 am »
Regardless, one needs to be careful when exceeding the fuse rated current for any length of time, especially in warm ambient condition.

I don't think Bussmann Cooper makes a 600mA fuse for Fluke multimeters, but SIBA does make a FF 630mA 1000V 32/6.3mm fuse, which would be a better match than the SIBA 400mA fuse installed at the Brymen factory.
« Last Edit: November 23, 2020, 09:08:53 am by Wytnucls »
 

Online Fungus

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Re: New EEVblog BM786 Multimeter
« Reply #151 on: November 23, 2020, 07:50:43 am »
Very common.
The Fluke 70 and 80 series are both 6000 count and use a 440mA fuse.

A 440mA fuse won't blow at 441mA. Fuses will often stand double their current, they just get very warm

Underrating the fuse in this way will make it much more likely to blow at the expected current (eg. 7-800mA in a 6000 count meter).

The best way was the way it used to be done, eg. the 600mA range would have a cheap 600mA glass fuse in series with an expensive 2A HRC fuse. The idea was to blow the cheap fuse in small slipups (we've all been there) but to still have HRC protection in industrial accidents.

I wonder why they stopped doing that, was it because of burden voltage?
 

Online Kleinstein

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Re: New EEVblog BM786 Multimeter
« Reply #152 on: November 23, 2020, 08:40:30 am »
There is a problem with a cheap fuse in series with the proper HRC fuse. With a DC source it is possible and not that unlikely that the cheap fuse can blow but not quench the arc, even with a current not large enough blow the higher rated HRC one. The extra heat will become a problem where the HRC fuse will not help with very much. The smaller fuse may still be OK, but should still be DC rated and thus not a really cheap one. This is kind of the price you have to pay for a CAT 3 rating.

A 440 mA fuse will likely not blow at 441 mA, but legally there is a chance it could. It usually takes more like twice the current to reliably blow the fuse, but some may bow earlier.

I see no real problem if the fuse would even well exceed the nominal range, like a 440 mA fuse in a 200 mA range, as long as the protection is up to it. Especially for the lower range a slightly larger fuse rating would be preferable and would also allow lower burden and less heat under normal conditions. However it still needs the protection (diodes) to be good for the higher current. This may need re-certification / testing and is thus not a change to be made easy.
 

Offline Wytnucls

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Re: New EEVblog BM786 Multimeter
« Reply #153 on: November 23, 2020, 12:18:18 pm »
I guess they assume you wouldn't be measuring at full scale for extended periods of time. Nevertheless, an interesting mismatch of values.

Very common.
The Fluke 70 and 80 series are both 6000 count and use a 440mA fuse.
The Fluke 87 V has a a range of 400mA only, with a specified limit of 400mA continuous and overload 600mA for 18 hours.
The Fluke 179 has a range of 400mA only, with a specified limit of 600 mA overload for 2 minutes maximum, 10 minutes rest.

The Brymen 786 should have a limited mA range of 400mA, not 600mA.
« Last Edit: November 23, 2020, 01:46:31 pm by Wytnucls »
 

Offline dcac

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Re: New EEVblog BM786 Multimeter
« Reply #154 on: November 23, 2020, 03:04:29 pm »
Will a blown 400mA fuse in BM786 be covered by the warranty - if customer claims it was only measuring 590mA when it happened?

 

Offline Wytnucls

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Re: New EEVblog BM786 Multimeter
« Reply #155 on: November 23, 2020, 03:16:40 pm »
Keysight 60,000 count meter manual:

Current can be measured at 440 mA continuously, and > 440 mA to 600 mA for 20
hours maximum.
To avoid blowing the multimeter’s 440 mA fuse, use the terminal only if you
are sure the current is less than 440 mA.


No warranty claim there.
« Last Edit: November 23, 2020, 03:19:36 pm by Wytnucls »
 
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Offline wizard69

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Re: New EEVblog BM786 Multimeter
« Reply #156 on: November 26, 2020, 03:11:59 am »
Will a blown 400mA fuse in BM786 be covered by the warranty - if customer claims it was only measuring 590mA when it happened?

When has a blown fuse ever been covered  by a warranty?   
 

Offline Brumby

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Re: New EEVblog BM786 Multimeter
« Reply #157 on: November 26, 2020, 08:11:52 am »
Will a blown 400mA fuse in BM786 be covered by the warranty - if customer claims it was only measuring 590mA when it happened?

When has a blown fuse ever been covered  by a warranty?   

Quite.

Besides - if the fuse blew, how would they know the current they were measuring?  Might have been a steady state 590mA and blew when a transient hit.
 

Online Fungus

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Re: New EEVblog BM786 Multimeter
« Reply #158 on: November 26, 2020, 08:43:41 am »
Will a blown 400mA fuse in BM786 be covered by the warranty - if customer claims it was only measuring 590mA when it happened?

No.
 

Online Kleinstein

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Re: New EEVblog BM786 Multimeter
« Reply #159 on: November 26, 2020, 09:07:43 am »
Keysight 60,000 count meter manual:

Current can be measured at 440 mA continuously, and > 440 mA to 600 mA for 20
hours maximum.
To avoid blowing the multimeter’s 440 mA fuse, use the terminal only if you
are sure the current is less than 440 mA.


No warranty claim there.

A similar note should be included if the range is larger than the fuse rating.
With a warranty claim, the user could receive this missing bit of text from the instructions.  :-DD
Ideally the fuse values should be noted on the meter directly. I have seen this with some meters though there it was the usual way around, like 400 mA fuse for a 200 mA range.
One could argue to change the nominal range to the fuse rating and treat the extra range only as "over-range" for short time use. Due to thermal effect the accuracy is often anyway relatively poor at the upper end. So the specs for the reduced range could get better.
 

Offline dcac

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Re: New EEVblog BM786 Multimeter
« Reply #160 on: November 26, 2020, 01:51:08 pm »
Will a blown 400mA fuse in BM786 be covered by the warranty - if customer claims it was only measuring 590mA when it happened?

No.

How about then after the third or fourth time it happens within a couple of weeks?
 

Offline dcac

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Re: New EEVblog BM786 Multimeter
« Reply #161 on: November 26, 2020, 01:52:28 pm »
Will a blown 400mA fuse in BM786 be covered by the warranty - if customer claims it was only measuring 590mA when it happened?

When has a blown fuse ever been covered  by a warranty?   

Quite.

Besides - if the fuse blew, how would they know the current they were measuring?  Might have been a steady state 590mA and blew when a transient hit.

This customer was measuring the current draw from a battery through a resistor.

Are you saying 590mA is fine as long as you have absolutely zero transients.
 

Offline AVGresponding

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Re: New EEVblog BM786 Multimeter
« Reply #162 on: November 26, 2020, 02:53:26 pm »
Will a blown 400mA fuse in BM786 be covered by the warranty - if customer claims it was only measuring 590mA when it happened?

When has a blown fuse ever been covered  by a warranty?   

Quite.

Besides - if the fuse blew, how would they know the current they were measuring?  Might have been a steady state 590mA and blew when a transient hit.

This customer was measuring the current draw from a battery through a resistor.

Are you saying 590mA is fine as long as you have absolutely zero transients.

Arguably, you'd only have a warranty claim if the fuse failed to blow, and the meter or user suffered damage as a result.
nuqDaq yuch Dapol?
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Offline EEVblog

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Re: New EEVblog BM786 Multimeter
« Reply #163 on: November 27, 2020, 06:22:58 am »
Will a blown 400mA fuse in BM786 be covered by the warranty - if customer claims it was only measuring 590mA when it happened?
No.
How about then after the third or fourth time it happens within a couple of weeks?

Then the user who knowingly installed a 400mA fuse three or 4 times and still complains about it blowing at 590mA should probably stop using a multimeter and give up electronics all together.
 

Online Fungus

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Re: New EEVblog BM786 Multimeter
« Reply #164 on: November 27, 2020, 07:58:07 am »
How about then after the third or fourth time it happens within a couple of weeks?

PEBKAC.

(ok, it should be "PEBMAC"...  :-DMM )
« Last Edit: November 27, 2020, 07:59:40 am by Fungus »
 

Offline dcac

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Re: New EEVblog BM786 Multimeter
« Reply #165 on: November 27, 2020, 11:53:04 am »
Will a blown 400mA fuse in BM786 be covered by the warranty - if customer claims it was only measuring 590mA when it happened?
No.
How about then after the third or fourth time it happens within a couple of weeks?

Then the user who knowingly installed a 400mA fuse three or 4 times and still complains about it blowing at 590mA should probably stop using a multimeter and give up electronics all together.

My mistake - I just noticed the print next to the uA/mA input jack actually says Max 0.6A and not only 0.6A. And i.e. BM869s does the same but it has at least a 440mA fuse so slightly more margin if you interpret it as 0.6A 'continuous' current.

Edit: that's actually not true either as BM786 might have a different perhaps slower type fuse.
 
« Last Edit: November 27, 2020, 12:00:24 pm by dcac »
 

Offline dcac

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Re: New EEVblog BM786 Multimeter
« Reply #166 on: November 27, 2020, 02:39:40 pm »
It seems the Bussmann 440mA fuse used in BM869s if often called 0.4A fuse. Bussmann doesn’t seem to have any 400mA rated fuse - but i.e. Siba does and have both 400mA and 440mA types.

In the datasheet for Bussmann (0.4A)/0.44A fuse it states ” Intended to carry 100% of rated current indefinitely." Looking at the characteristics curve it can handle about 1.2A for 300 seconds - beyond that time is not shown perhaps due to possible fatiguing coming into play.

https://www.elfa.se/Web/Downloads/_t/ds/DMM-B_eng_tds.pdf
 

Offline Invenis

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Re: New EEVblog BM786 Multimeter
« Reply #167 on: November 29, 2020, 10:11:57 pm »
I was just about to pull a trigger on 869s and that came up :o What a nice multimeter! The LoZ, AutoHold, NCV and BeepLit. Now I'm trying to decide which one to get  :-// Also I wonder whether Brymen has some kind of refreshed version of 869s in the works.
 

Offline EEVblog

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Re: New EEVblog BM786 Multimeter
« Reply #168 on: November 30, 2020, 02:46:52 am »
Also I wonder whether Brymen has some kind of refreshed version of 869s in the works.

Not that I am aware of.
 
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Online xavier60

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Re: New EEVblog BM786 Multimeter
« Reply #169 on: December 01, 2020, 08:58:26 am »
Really nice. I have some questions:
Does it work well with rechargeable AAA batteries?
Does it come with a Cal certificate?

It should work ok with rehcargables:
https://www.eevblog.com/forum/testgear/us$150-class-multimeter/msg3077681/#msg3077681
No cal certificate, just like other Brymens.
Well, 3.55V/3= 1.18V. That is around 50% DoD of a NiMH, so not perfect.
I guess we buy a pack of alkaline then.
If there is a problem with NiMh, then I wonder why only 3 cells when 4 is a more convenient quantity and would have very likely eliminated possible NiMh problems, space permitting.
Ill be finding out for myself.
« Last Edit: December 26, 2020, 02:41:29 am by xavier60 »
Hioki AS100D vom, HP 54645A dso, Fluke 87V dmm, AN8008 dmm, Agilent U8002A psu,  FY6600 function gen, New! Brymen BM857S-(With Battery)
 

Offline EEVblog

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Re: New EEVblog BM786 Multimeter
« Reply #170 on: December 01, 2020, 12:12:00 pm »
Really nice. I have some questions:
Does it work well with rechargeable AAA batteries?
Does it come with a Cal certificate?

It should work ok with rehcargables:
https://www.eevblog.com/forum/testgear/us$150-class-multimeter/msg3077681/#msg3077681
No cal certificate, just like other Brymens.
Well, 3.55V/3= 1.18V. That is around 50% DoD of a NiMH, so not perfect.
I guess we buy a pack of alkaline then.
If the there is a problem with NiMh, then I wonder why only 3 cells when 4 is a more convenient quantity and would have very likely eliminated possible NiMh problems, space permitting.
Ill be finding out for myself.

Not enough depth, it uses a new design vertical holder.
 
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Offline joeqsmith

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Re: New EEVblog BM786 Multimeter
« Reply #171 on: December 01, 2020, 12:18:44 pm »
The batteries are in a carrier that separates from the meter.  The three batteries are mounted side by side and the pack is perpendicular to the PCB.  The batteries themselves are located towards the very top most part of the meter.  The packs height sets the thickness of the meter.  It's well laid out, making use of every bit of space.   Using this technique while adding a fourth battery would make for a thicker or a taller meter.

Slow on the draw today...
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
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Offline rsjsouza

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Re: New EEVblog BM786 Multimeter
« Reply #172 on: December 01, 2020, 02:02:50 pm »
The batteries are in a carrier that separates from the meter.  The three batteries are mounted side by side and the pack is perpendicular to the PCB.  The batteries themselves are located towards the very top most part of the meter.  The packs height sets the thickness of the meter.  It's well laid out, making use of every bit of space.   Using this technique while adding a fourth battery would make for a thicker or a taller meter.

Slow on the draw today...
A picture is worth 78 words...  :-DD
« Last Edit: December 01, 2020, 02:04:25 pm by rsjsouza »
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Offline coromonadalix

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Re: New EEVblog BM786 Multimeter
« Reply #173 on: December 01, 2020, 08:19:42 pm »
you miss the other 922 words    :-DD,   nice pack design, or maybe 3d print another one with the batteries rotated in it, to acomodate a longer cell ??
 

Online 2N3055

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Re: New EEVblog BM786 Multimeter
« Reply #174 on: December 01, 2020, 09:37:03 pm »
This battery compartment design seems to protect meter electronics from battery leakage if meter is stored both face down and back down... Nice..
 


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