Author Topic: why did the 600mA fuse break.. but the 200mA didn't?  (Read 2606 times)

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Online JPortici

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why did the 600mA fuse break.. but the 200mA didn't?
« on: November 04, 2016, 11:33:22 am »
posting this to the beginners section because i think i'm missing something basic..

so, we were messing around with the electronics of a car engine. the turbo pressure valve actuator got stuck in a position and the ecu refused to move it after barely trying
moving it manually was out of the question, we tried applying power to it

(SPOILER ALERT: at the end it got unstuck and all has gone back working as if nothing happened  :phew:)

one of the motor input at gnd and because we didn't want to blow something up, the other to the battery, thought a multimeter in amp mode.

BRYMEN 867s, 1kV 600 mA fuse for the mA range. didn't work. later i checked and the fuse blew open. I was actually expecting it but...
BRYMEN 867s, 1kV 11A fuse for the 10A range. didn't work either. the fuse is ok by the way and verified that the multimeter works in the Amp range

UNI-T UT33D, 200mA fuse, mA range. it worked. the motor moved. fuse didn't blow up. tried several times.

but why?
 

Offline P90

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Re: why did the 600mA fuse break.. but the 200mA didn't?
« Reply #1 on: November 04, 2016, 11:45:10 am »
Leads plugged in the wrong jacks???
 

Online JPortici

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Re: why did the 600mA fuse break.. but the 200mA didn't?
« Reply #2 on: November 04, 2016, 11:48:15 am »
of course not!
 

Online rsjsouza

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Re: why did the 600mA fuse break.. but the 200mA didn't?
« Reply #3 on: November 04, 2016, 11:59:05 am »
Can you double-check and see if your Uni-T actually has the fuse in series with the mA jack and not with the V inputs?

IIRC joeqsmith saw that before in an el-cheapo DMM...
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Online JPortici

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Re: why did the 600mA fuse break.. but the 200mA didn't?
« Reply #4 on: November 04, 2016, 12:12:37 pm »
the uni-t has two inputs.
10A, unfused
v/ohm/ma, fused with 200mA (allegedely)

aaaaaand we have no fuse. a very small wire soldered there instead. somebody here may have done something that stupid, i asked, let's see. (yes, somebody did that.)

but then, why the brymen wouldn't read anything in the A mode? could it be that the 11A fuse + meter resistance was so high that the voltage at the motor collapsed?
« Last Edit: November 04, 2016, 12:40:25 pm by JPortici »
 

Offline P90

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Re: why did the 600mA fuse break.. but the 200mA didn't?
« Reply #5 on: November 04, 2016, 03:14:59 pm »
That wire you're referring to is the 10amp current shunt.

No.
 

Online JPortici

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Re: why did the 600mA fuse break.. but the 200mA didn't?
« Reply #6 on: November 04, 2016, 04:07:57 pm »
If you say so :-+



So, why did the brymen not work with the motor even in 10 amp mode? Combined fuse/shunt resistance respect the modor impedance?
 

Online rsjsouza

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Re: why did the 600mA fuse break.. but the 200mA didn't?
« Reply #7 on: November 04, 2016, 06:02:44 pm »
So, why did the brymen not work with the motor even in 10 amp mode? Combined fuse/shunt resistance respect the modor impedance?
I wonder if the A jack of the BM867S is defective on the circuit/PCB and not the fuse. Can you measure the conductivity between the A and the GND inputs using your Uni-T? Make sure to connect the cables to the BM867S first, as the input sense may influence things.
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 


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