Digital Multimeters (Also Brymen BM869 repair)

[retiredcaps]

Re: Digital Multimeters

http://www.digikey.com/short/3ztpm7

You may want to order extras/spares for future use?

[retiredcaps]

Re: Digital Multimeters

that ptc that is 500v. does that mean at 500v the fuse will trigger and the meter will read nothing until it resets? and will the lower voltage affect accuracy of the meter significantly?

As the reading approaches 500V, the PTC resistance should start to get higher. If the voltage goes past 500V, the PTC resistance should continue to go higher. The meter should continue to function, but your accuracy results could be affected.

The lower voltage rating on the PTC should not affect the accuracy of the meter for readings under 500V.

BTW, making an "oops" moment like having the meter on resistance while the probes are plugged into mains (120V) may affect the accuracy of the meter until the PTC cools down. See Dave's eevblog ohms overload video (10 minute video).

https://www.youtube.com/watch?v=UX7xmA7F5bc

[jasonbay13]

Re: Digital Multimeters

I have added the items in my digikey cart. and have made 2 changes to the suggested items. i changed out the resistors to something closer to the original size and is 1% tolerance, though it is not fire rated.
the 1kv varistor is CNR 10D102K (10mm diameter), so i picked based on the diameter.

that ptc that is 500v. does that mean at 500v the fuse will trigger and the meter will read nothing until it resets? and will the lower voltage affect accuracy of the meter significantly?

http://www.digikey.com/short/3ztpm7

[stj]

Re: Digital Multimeters

dont forget to put heat shrink over the new varistors to contain the blast if you blow them again!
it may be good to sleeve the resistors too.

[retiredcaps]

Re: Digital Multimeters

Here is a suggested list of replacements. I tried to pick the big name/well known/reputable brands.

1) Bourns 820V varistor - 17 cents each x 2 = 34 cents total

http://www.digikey.com/product-detai...7D821KTRCT-ND/

2) Epcos 500V PTC 1.1k ohm - $2.31 each x 2 = $4.62 total (NOTE: This is a 500V PTC, not 1000V)

http://www.digikey.com/product-detai...3890-ND/652053

3) Vishay 1k ohm 3W resistor wirewound flameproof - 87 cents each x 4 = $3.48 total

http://www.digikey.com/product-detai...KCT-ND/1587922

4) Bourns 1000V varistor - 49 cents each

http://www.digikey.com/product-detai...02K-ND/2798254

0.34 + 4.62 + 3.48 + 0.49 = $8.93 + whatever shipping (I'm guessing $4 USD for first class).

Please note that while there is a 1000V PTC that 1.1k ohm, it is not available for purchase anywhere that I can find. The part number is YS4020. Datasheet at

https://cdn.badcaps-static.com/pdfs/...52b8cf1a8b.pdf

As such, I would consider this repaired BM869 NOT a UL listed 1000V meter anymore. While the repaired meter is likely okay for normal househould mains use (120V), I would urge caution and practice good safety like wearing goggles, using hand-free probes and not working alone.

I will leave it to the OP to double check part numbers and specifications, but more importantly, check the dimensions of each components. I don't have a BM869 so I cannot verify if these replacement parts are the same size or larger.

Email from Brymen re components ...

"Those components are:
R1 ~ R4: 1k ohm/3W wire-wound resistors
PTC1, PTC2: 1.1k ohm/1kV PTC
SPG1, SPG2: 820V Zinc Oxide Varistor
SPG3: 1000V Zinc Oxide Varistor"

[wraper]

Re: Digital Multimeters

BTW, as BM869 clamps the voltage to 1.8 kV (DC) by MOVs after those burned resistors and PTCs which are rated to 1kV, seems that OP had put well above 2.8 kV (peak, not RMS) into the meter.

[wraper]

Re: Digital Multimeters

but would a ut-61e explode?
if you have no mov's creating a short, the most likely outcome of a couple of kV would be burning out the silicon and releasing the magic smoke

ut-61e will start arching between the contacts in the dial switch somewhere between 1000V and 2500V applied (output voltage settings on the HV tester in the video). As it seems OP had some high energy high voltage source, I wouldn't be surprised if a huge plasma arc appeared inside the meter and it would blow up in pieces. Here is ut-61e HV test:
https://www.youtube.com/watch?v=hhBbvIf3E0s
And here is how multimeter explodes in pieces from 4kV limited energy source (capacitor). In the OP's case, that probably would not end just like that because there was continuous power source, not just charged cap.
https://youtu.be/M-FZP1U2dkM?t=367

[stj]

Re: Digital Multimeters

but would a ut-61e explode?

if you have no mov's creating a short, the most likely outcome of a couple of kV would be burning out the silicon and releasing the magic smoke.

frankly, i would be more afraid to use a meter that was going to intentionally short the probe cables together while i'm holding the probes!!

[wraper]

Re: Digital Multimeters

Don't blame Brymen, that is a plain user ignorance, not the issue with multimeter at all. It have done it's job fine, failed in the safe way and didn't explode in your face. Learn to think twice about what you are doing before killed yourself out of plain ignorance.

get a UT-61E
good spec, but cheap enough to not throw a fit if you break it.

The issue is, if it was UT-61E, OP could get harmed himself when that thing would explode in his hands. Turns out is easier to damage Fluke 87 V with HV, rather than BM869:
https://www.youtube.com/watch?v=x2Dg1QA71wU

[retiredcaps]

Re: Digital Multimeters

cant you ask brymen for a schematic?

I stand corrected. I didn't ask for a schematic, but I did ask for the values of those input components and I got an answer in less than 24 hours.

I will list the digikey/mouser equivalents sometime Friday. It is 12:33AM and I have to get some sleep now.

I already know the PTC will be problematic in terms of getting the equivalent.

[stj]

Re: Digital Multimeters

get a UT-61E
good spec, but cheap enough to not throw a fit if you break it.

[retiredcaps]

Re: Digital Multimeters

this is completely separate, but my Milliamp range is inaccurate. by a lot. say my meter shows 200ma, but the load is really 100ma. this is based from an harbor freight cheapo and the 10A range of the 869.

Can you actually get some real measurement values as to the error?

A picture of the BM869 and your Harbor Freight in series measuring the same current load would be idea. In an earlier post, I referenced

http://mrmodemhead.com/blog/yokogawa...03-multimeter/

In that blog, you can see the Yokogawa and Fluke 189 both in series measuring the same current so we can see side by side.

[ivtec]

Re: Digital Multimeters

looks like i should have just bought the fluke. killed my $250 bm869 trying to measure the voltage of a step-up transformer. still dont know the voltage but i thought it could handle over 1kv without exploding.

anyway, since i've no longer a decent meter, what should i get? some of those harbor freight meters so i dont feel like driving off a cliff when i fry one or something more expensive so when i kill it i can curl up and start crying myself to sleep hoping it will all be better when i wake up?

stupidity is ridiculously expensive

yes you should have,i did buy fluke 87 and i'm very satisfied ,i also have blown the fuse by wrongly checking amps,but it survived just by replacing fuse,it costed me much money, but it's worth every penny.

[TechGeek]

Re: Digital Multimeters

Who knows... just another horror show because of price-cutting measures.
Manufacturer:

[stj]

Re: Digital Multimeters

exactly, the protection shorted out, so the cables had to handle the maximum current at maximum voltage till something gave - probably those resistors.

i dont know why meters dont have a fuse behind the main input to cut the current as soon as the mov's trip

[TechGeek]

Re: Digital Multimeters

How come? Because of the current draw of the meter with the input protection frying?

[stj]

Re: Digital Multimeters

if the mov's shorted and took out the resistors then i expect the probe cables to be untrustable.

[TechGeek]

Re: Digital Multimeters

Sounds like either the probes/probe wires have been damaged and/or that something else in the meter has gone bad.

[stj]

Re: Digital Multimeters

something else.

[jasonbay13]

Re: Digital Multimeters

this is completely separate, but my Milliamp range is inaccurate. by a lot. say my meter shows 200ma, but the load is really 100ma. this is based from an harbor freight cheapo and the 10A range of the 869. is it possible a slight overcurrent (say ~800ma) could damage the fuse without blowing it? or would this be something else?