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Burnt resistor’s value for MAS830L multimeter

bertus

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hello,

where in the schematic are the 0.05 and 0.15 located?
what is the reference number?

bertus
 

Jarasmus

Sep 15, 2023
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hello,

where in the schematic are the 0.05 and 0.15 located?
what is the reference number?

bertus
Not located on schematic, but located on PCB: SMD R150 survived and if there was 1Ω from 2 resistors, the burnt one should be was 1R85 (previously mistaken with R050) ? (0.15+1.85)/2

There’s now confusion between 0.1 and 1 Ω
 

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bertus

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Hello,

In all Mastech 830 schematics, the 10 A shunt is 0.01 Ohms.
When one is 0.15 Ohms, the other should be close to 0.01 Ohms.

Bertus
 

Jarasmus

Sep 15, 2023
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This is mystery to me. So how does this work then, such nearly no resistance.

The nearest value of SMD resistors I’ve got, is -O-

Why can’t I put just a thin wire, or weak fuse instead?

Serious question. Examples work better than a theory.

Thanks for your patience.
 

Jarasmus

Sep 15, 2023
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Wire: Resistance near to 0.01 (I guess)

This is (pic) the results.

I’ve tried with 0.1 ohm - numbers get lesser.

Next: I’ll see it with a 1 ohm value.
 

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Jarasmus

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Microscopic SMD 1R20, closest to 1 ohm I found.

No luck. Ammeter values jumping over limits after >0.25A applied.

Okay, how to DIY 0.01Ω resistor?
 

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bertus

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Hello,

In my DT830 the 10 A shunt is a piece of thick wire:
DT830_10A.jpg
Bertus
 

73's de Edd

Aug 21, 2015
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Sir Jarasmus . . . . .​

Initially I had no information or pics back when I first checked in.
Now let me fill you in with my ensuing observations.
I was wanting a pic of the extreme right two meter plug in terminals of the three, to confirm if center was ground and the far right was the 10A plug in.
It was confirmed . . . . with viewing a pic of the whole unit.

When the meter design gets down to ampere level current shunts, it gets touchy, with the need of the 200 ma scale requiring a paralleled resistor across it.
Look at your post # 15.

And there, observe the far right photo. (Left click MAG it on up to full size! )
Now in that photo, go to left side center and find the JF code marked fuse for your 200 ma current range and to its right you will find the SM 9 ohm current shunt resistor for your 20 ma current metering range.
Just below will be a 1ohm plus a parallel 36 ohm, to come out with a shared 0.972972972972973 ohms effective value (+or- 3 11/17 ths gobsnatches) serving as your current shunt resistor(s)for your 200 ma metering range.
On the schematics markup of the values, there is actually being a following asterisk, which is signifying an indeterminate value, as is to later be determined by test during calibration.
Now drop on down to where you have installed 3 paralleled .22 ohm SM resistor shunts, which you later found was still not a low enough resistance to serve as a 10 A range shunt.
That is visible in your same pages other photo just to the left where you have your 18650 Li-ion charger set up and you have inserted meter probes in series with a + cell output.
It reads a correct .980A whilst your meter is reading 7.69A, so that 10A combined shunt resistor cluster needs to be about 1/8 th of its present value.

NOW . . . . if this was being MY duck to pluck !

If you will take CLOSE note, SEE that there is being a most bee-yoo-ti-full tinned terminal pad * at the
11 o' clock position from the central common meter lead socket, and also over to the right side of the center R-uh tew-tew-tew SM resistor there is a like,companion * . . . . that some dolt now has being 1/2 solder encased !
Get that pad and its center hole exposed again . . . BUT if your iron even touches the Red/Black wires Q.C. police will instantly appear at your door and banish you to a remote pacific atoll. . . FOREVER .
I get my bare solid copper wire of that gauge from ROMEX cable . . . . you know the . . . AC electrical wiring in your house. BUT that looks smaller gauge than US houses are wired with, UNLESS you are a foreigner with 220'ish uppish volts being used , but with need for less amperage, so the smaller gauge might be employed.
At any rate, after having bare wire in hand of a 6 inches or so length. solder each end to a terminal and let the surplus U loop stick up.
Go back and set up just as you did before in the charger-metering scheme and see what the meter reads now as compared to the "gold standard" charger reference.
If the new reading on the meter is still too high, compared to charger reading, the newly fabbed wire shunt needs to be shortened.( 25-33-50 % ? )
Betwixt wire shortening or pulling off .22 resistors you should eventually approximate match calibration readings.
When it gets down to final "fine tuning" of that shunt wire resistance, I use wide/multiples masking tape on both sides of the central wire at a formed overlapping slit .
That then catches any grindings fall out from the use of a Dremel tool with a cut off wheel to take wide shavings from the center of the wire, while watching the DVM meter reading shift towards a match to your chargers displayed metering.
A round files drag, is used for the very final trim, on up to that cal resistance point.
Final treatment is the pulling of the shunt wire and completely solder tinning it and then de-grease / de flux with MEK or acetone or lacquer thinner or xylene or benzene or toluene or methyl methacrylate or denatured alcohol or ?.
Then wet soak a Q- tip and totally thumb press to buff the tinning, until no black residue sheds, then dry multi Q-tip thumb press buff and it will end up looking as if being chrome plated. Place on an anti oxidant coating of clear finger nail polish or clear airplane dope or clear lacquer.
Reinstall and recheck calibration against the charger.
NOW all, or most of your 10 A current will be passed thru the ADEQUATELY wattage rated, wire shunt, according to or if any of your .22's SM's ended up being left in circuit.
BTW your charger is reading 4.09V . . . . . on my charger, that would be equated with an 80% charge . . . with current pull gradually declining with time.
On my corral of 18650's, I treat them gently at a max of 200 ma charge rate. I am now recharging some 2020 charged units that are still being at 3.6V.
One could only DREAM of a ni-cad or ni-mh cell, holding a charge for 1/8 of that time period.

Any ?'s.

Read up on this fellers dealings with a Mastech 830 series . . . . wannabe . . . . . it looks like your knock off is being yet a third version.
He was satisfied with accuracy of all units and only faulted the time lag in piezo sound response on continuity check and the short on time of the displays back lite.
DON"T he KNOWS! . . . . . . .that going to its first driver transistor and changing out that 47K bleeder
resistor to a 100K-or-220K-or-330K-or-470K, would then make him one cappy hamper !

AN INFORMATIVE READ . . . .( Real MEAT . . . . . after 17 min)
(Now . . . . .denote the internal 200 Ma range fuse which we found . . . . . . maybe after a lengthy time of use, greater than the given specs shown, that you found the double duty -one shot- 10 A fuse !) ( Nevermore . . . . . if you replace with the 10A wire shunt. )




73's de Edd . . . . . .


I'm currently helping my visiting great grandson look for his misplaced half bag of Skittles . . . . ( that I fully ate, half an hour ago . . . YUMMY ! . . . . . I couldn't eat just 1 ! )


.
 
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