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Shunt resistor wanted

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05 Oct 2021 08:34 #51879 by juergen.scholl
Shunt resistor wanted was created by juergen.scholl
Does anybody know where to get a 1ohm or 0.1 ohm shunt resistor fro?. I want it for long term current drain measurements by voltage drop. It should have a suitable wattage. Thanks for your help, any links are welcome.

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19 Oct 2021 11:45 #52131 by juergen.scholl
Replied by juergen.scholl on topic Shunt resistor wanted
!!!BUMP!!!

Anybody?

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19 Oct 2021 15:26 #52135 by Matt T
Replied by Matt T on topic Shunt resistor wanted
I just 'scope voltage drop across the current shunt of a DMM. The meter doesn't need to be powered up for this. IIRC there is a thread on this somewhere on the forum.

Or if you need/want to buy something you can get cheap current shunt resistors from the usual vendors of chinesium. Or you can get 100W power resistors from the same sources which'll probably work.
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19 Oct 2021 16:22 #52136 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Shunt resistor wanted
Loads on ebay

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19 Oct 2021 20:31 #52147 by juergen.scholl
Replied by juergen.scholl on topic Shunt resistor wanted
Thank you Matt, thank you Andy!

the issue I have with the ebay resistors is the reliability. A typical spec would be 75 mV at 20A, which results in 0,00375 ohms. I don`t feel confident with this kind of precision required to get an accurate result.

The meter idea is slick, I checked a couple today and most seem to use an 0,1 ohm shunt resistor on the meters´ highest amerage setting. Again, I do not have a miliohmmeter, so 0,1 could be anything from 0,05 to 0,14 ohms. Nevertheles, it would be possible to get very close to the true value with some measurements of the VD with known loads/controlled current flows.

Finally it dawned on me that I simply can wire a fuse in series between the battery cable and the battery post and measure the VD over the fuse. I then will be able to use the known fuses voltage drop charts.

Anyhow, I will play around with all three options - shunt resistor, ampmeter, fuse - and update later on the outcome.

Once again: Thank you!

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20 Oct 2021 08:38 #52164 by Noah
Replied by Noah on topic Shunt resistor wanted

I just 'scope voltage drop across the current shunt of a DMM. The meter doesn't need to be powered up for this. IIRC there is a thread on this somewhere on the forum.

I don't get it. Why not just turn on the amp meter and measure the current?

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I guess that's why call me The Working Man.-

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20 Oct 2021 09:27 #52165 by Matt T
Replied by Matt T on topic Shunt resistor wanted

I don't get it. Why not just turn on the amp meter and measure the current?

That's what I normally do for parasitic draws Though I am using Flukes which are fast enough to catch pulses and also have a MIN/MAX/AVERAGE function I can leave running.

Volt dropping the DMM is just one option when you need a shunt for use with a 'scope or data logger.
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20 Oct 2021 09:31 #52166 by juergen.scholl
Replied by juergen.scholl on topic Shunt resistor wanted

Why not just turn on the amp meter and measure the current?

Noah, the overall idea is to catch these pesky, often intermittent drains where you´ll need pacience and time to find them. So instead of running low the ampmeter´s or current clamp´s battery (specially if it can log data) in an overnight intent to find the problem a voltage drop measurement in streaming mode with a dso over a resistor can run the time neccessary to get conclusive results.

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20 Oct 2021 11:13 #52167 by juergen.scholl
Replied by juergen.scholl on topic Shunt resistor wanted
I forgot to mention amp clamp drifting.....

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20 Oct 2021 11:24 #52168 by Noah
Replied by Noah on topic Shunt resistor wanted
Oh, I get it.
Old school Vantage baby! I can graph amperage on a16hr screen.

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