New Brymen BM2257 Multimeter

[mwb1100]

It would be, except...

But what's more popular than a YT where things blow up?

(though fuses popping might not be so exciting)

[EEVblog]

It would be, except...

But what's more popular than a YT where things blow up?
(though fuses popping might not be so exciting)

Sadly you don't get to see anything with sand filled HRC fuses

[mwb1100]

Sadly you don't get to see anything with sand filled HRC fuses

of course...   

[geralds]

@eevblog, @mwb1100, @bdunham7 (not sure whether "@" + user works like in Outlook?)

Many thanks for your super fast replies, which are very helpful indeed! What a forum!

I will then look again at the AN870, despite my tendancy for the BM2257 as it seems more robust and thus should hopefully last substantially longer. Plus a set of ProbeMaster and Hirschmann leads/probes.

Re Fluke 115/225 set, there seems to be a promotion in Europe for around EUR 250. But noted about (lack of) Auto-Hold function, LoZ and usefulness about probes/test leads for electronics, so it seems the BM2257 has more useful features/functions for my requirements. And the promotion/set does not seem to be available for the 116/117.

I have no intention to do any mains works (nor microwave ovens!) - I know my limits and prefer to leave that work to the professionals.

I will keep you posted once I have finally decided (may take a few weeks).

Thanks again, your response time and helpfulness is really impressive!

[tautech]

Pop quiz: How many mA does it take to blow a 400mA fuse?

In theory, 401mA after quite some time.
At 400mA the fuse should not break after an infinite time.
In practice, any random value if you bought a fake off ebay, or if genuine follow the parametric charts and add your own window, add salt to flavour.

Good topic for a video.
Quality vs no name vs Normal vs Slow blow vs Fast blow.

It would be, except it's basically a statistical thing, so you have to run a lot of them.

Apply KISS principles as to many new entrants a fuse is just a fuse.

[EEVblog]

I forgot I had done this video!

[bdunham7]

(though fuses popping might not be so exciting)

I just finished the first round with the fuses you sent me.  You're right, it's not that exciting.   

[jj5]

Maybe change the package to:

    2 x HV110 11A 30kA 1000V HRC (10x38mm)
    2 x HV620 400mA 10kA* 1000V HRC (6x32mm)
    3 x HV620 630mA 10kA* 1000V HRC (6x32mm)

I think that's a great idea. This set would suit me as I have a BM2257 and am planning to get 121GW and maybe some others. Not sure how much it would suit others though!

[jj5]

I think that's a great idea. This set would suit me as I have a BM2257 and am planning to get 121GW and maybe some others. Not sure how much it would suit others though!

p.s. I would also be happy to buy one 11A+400mA set plus one 11A+630mA set.

[Fungus]

Against this backdrop / intended use, would the BM2257 be fit for purpose?

Easily.

[CustomEngineerer]

From the bm235-loz-mode thread:

FYI, the new BM2257 will autorange down to 6V range in LowZ mode, so you get the full 1mV resolution all the way down to 0V.
Completely changed from the BM235

Wondering if anyone has anyone tested this? The user manual suggests LoZ only works down to 1.5V. Testing on mine it seems to work down to about 0.930V. If I'm not reading to much into the above quote it seems Dave is suggesting it goes all the way down to 0V? Or maybe he just meant that you get the full 1mV resolution until it cuts out, which it does. Not a big deal either way, but was curious if I was missing something.

This is what the BM2257 user manual has to say about it.

When a signal above the voltage threshold of 1.5V DC or AC up to the rated 600V is present, the meter displays the voltage value in the appropriate type DC or AC, whichever is larger in peak magnitude.

[EEVblog]

From the bm235-loz-mode thread:

FYI, the new BM2257 will autorange down to 6V range in LowZ mode, so you get the full 1mV resolution all the way down to 0V.
Completely changed from the BM235

Wondering if anyone has anyone tested this? The user manual suggests LoZ only works down to 1.5V. Testing on mine it seems to work down to about 0.930V. If I'm not reading to much into the above quote it seems Dave is suggesting it goes all the way down to 0V? Or maybe he just meant that you get the full 1mV resolution until it cuts out, which it does. Not a big deal either way, but was curious if I was missing something.

This is what the BM2257 user manual has to say about it.

When a signal above the voltage threshold of 1.5V DC or AC up to the rated 600V is present, the meter displays the voltage value in the appropriate type DC or AC, whichever is larger in peak magnitude.

I stand corrected. Just measured one and only got down to 0.93V.
In practice, that's plenty low.

[CustomEngineerer]

Agreed, thanks for verifying. Hope a few others do as well just to see if the 0.93V is consistent.

[Furna]

I just received mine today ...
I can go down to 0.928V
The image has been captured when it was at 0.929V but I can guarantee 0.928V
Sorry for the low quality photo.

Super happy!

Actually for the low amp fuse I went for EKSA 632.415 630mA
Sorry Dave I didn't buy the fuse from you; at the time of the order you only had the 600mA

[bdunham7]

I stand corrected. Just measured one and only got down to 0.93V.
In practice, that's plenty low.

It would be interesting to know what design quirk makes it work that way as I don't see an obvious reason for it on DCV.  Is the input impedance still low below 0.93V?

[EEVblog]

Actually for the low amp fuse I went for EKSA 632.415 630mA
Sorry Dave I didn't buy the fuse from you; at the time of the order you only had the 600mA

I've ordered 630mA fuses from ASTM but have not heard anything back yet. Resent the email to new people and still nothing. Not sure what's going on...

[floobydust]

I stand corrected. Just measured one and only got down to 0.93V.
In practice, that's plenty low.

It would be interesting to know what design quirk makes it work that way as I don't see an obvious reason for it on DCV.  Is the input impedance still low below 0.93V?

What are we talking about?  I got lost here.
That there is a deadzone of +/-0.93V before a reading is displayed, or for the LowZ load to engage? The Brymen manual does not say what happens below "1.5V".
You found the transistor clamp are in-series with the LowZ PTC load (on a different Brymen model) so nothing much is happening at below say 6V for the input impedance to decrease on them. (There may be a MOV-like action with these HV PTC's, as a faint theory of mine, as they have similar construction.)


As far as the fuses go, I see very little difference from 500-630mA when the relevant BM2257 range is 600mA.
Those fuses don't even consider blowing until currents are 2-4x times above that, and the i²t times are not so different.

[bdunham7]

What are we talking about?  I got lost here.
That there is a deadzone of +/-0.93V before a reading is displayed, or for the LowZ load to engage? The Brymen manual does not say what happens below "1.5V".

Well, both and how they might be related.  The BM2257 auto-ranges down and I'm really curious to know why it would not read below 0.93V just because there is a PTC across the inputs.  I'm presuming it is because the input layout just isn't that simple.  The input impedance issue is just another angle that might give a clue as to the input setup.  It just seems a bit...weird.

Fluke's straightforward approach means it will read down to the last digit in DC Lo-Z, although it only has a 1000V range.  And the input impedance is about 3.2k no matter how little the input voltage is.

[Furna]

Is the input impedance still low below 0.93V?

Ohm's law says at 2V impedance is around 2KΩ (see picture).
For lower voltages I get unreliable A values.

[EEVblog]

What are we talking about?  I got lost here.
That there is a deadzone of +/-0.93V before a reading is displayed, or for the LowZ load to engage? The Brymen manual does not say what happens below "1.5V".

Well, both and how they might be related.  The BM2257 auto-ranges down and I'm really curious to know why it would not read below 0.93V just because there is a PTC across the inputs.  I'm presuming it is because the input layout just isn't that simple.  The input impedance issue is just another angle that might give a clue as to the input setup.  It just seems a bit...weird.

Yeah, I'm surprised.
I can understand the BM235 with the input arrangement it uses, but this is a bit puzzling. Sounds dual diode droppy...

[floobydust]

If there is a deadzone for the LowZ to engage - then I'd need to know about it and probably say ick.
It sounds like input impedance is 10MEGΩ when input voltage is less than 2-3 diode drops, and above that the PTC is present and 2.1kΩ when LowZ is selected. It does simplify the rotary switch design and that is why I think Brymen is doing it.
To test/prove it you could inject a sine-wave with series sense resistor observed on a scope, to see if this is the case.

This will cause a problem when troubleshooting low voltage such as automotive. You'll get say a 1.5V ghost reading outside of the pristine laboratory, in the mud and dirt.
Do the armchair experts here know what this means? 

[bdunham7]

It sounds like input impedance is 10MEGΩ when input voltage is less than 2-3 diode drops, and above that the PTC is present and 2.1kΩ when LowZ is selected. It does simplify the rotary switch design and that is why I think Brymen is doing

I don't think there's that sort of direct correlation between the input impedance and the minimum reading.  Does the BM235 stop reading below about 7V or does it just go high-impedance?  Those really are somewhat independent issues although the design may work in some sort of relation between the two.  Dave just needs to break out a screwdriver and have a look....

[EEVblog]

I don't think there's that sort of direct correlation between the input impedance and the minimum reading.  Does the BM235 stop reading below about 7V or does it just go high-impedance?  Those really are somewhat independent issues although the design may work in some sort of relation between the two.  Dave just needs to break out a screwdriver and have a look....

In progress...

[Furna]

One of the armchair experts here, doesn't have (yet) an AWG ... it's on the buy list althought not on the top.
 

[floobydust]

   It would be great if we knew the two PTC part numbers, somebody cut off the heatshrink tubing over them to see that.
I also note Fluke ditched using clamp transistors for a while now in their newer models and instead is using diode arrays but they are not symmetrical. Clamp is +6V_f and -2V_f on the (PTC) Ohm's source channel and Dave might see something odd like that if Brymen is indeed running the LowZ PTC in series with a clamp.
I could draw the BM2257 schematic if I had one or loosely based on board pics but that would cause trouble.

Hey this is new silicon? Brymen got the (Hycon) LCD driver and DMM IC into one 100-pin package it seems.