Products > Test Equipment
Measuring 100A DC current
Njk:
--- Quote from: pdenisowski on June 09, 2024, 01:19:26 am ---And I'm still mourning the loss of Radio Shack (I worked there for a short time) ... also not the best prices or selection, but you could find one in almost any town of more than 25,000 people back in the day.
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BTW there were also a bigger stories like Fry's. I recalled they'd offered affordable Windows OEM DVDs (about $40, IIRC). For distribution only with a computer system but actually it was enough to buy any HW item, like a napkin for monitor. Almost all my Windows licenses were bought in that way
2N3055:
--- Quote from: nctnico on June 09, 2024, 09:31:14 am ---
--- Quote from: johansen on June 09, 2024, 04:17:00 am ---
--- Quote from: egonotto on June 09, 2024, 01:55:18 am ---
--- Quote from: johansen on June 08, 2024, 07:50:27 pm ---
didn't look at them till now. yeah would not use those.
6$ on amazon - 100 1/2 watt resistors.
https://www.amazon.com/EDGELEC-Resistor-Tolerance-Multiple-Resistance/dp/B07XLBY5RF
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Hello,
1A per resistor gives 1 W per resistor, which has 0.5 W. And 1 V voltage drop is perhaps too much.
Best regards
egonotto
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So spend 50 more cents for 0.1ohm resistors
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Which then increases the influence of the leads + solder joints even more. Bottom line: you can't construct an accurate, high current shunt from regular resistors in parallel because in the end you can't make the Kelvin connection. Getting the Kelvin connection done right is the pinnacle of constructing a current shunt.
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Of course you can make a decent shunt from parallel resistors. It has to be carefully designed, geometrically symmetric and you can achieve good enough Kelvin connection, but you have to think in 3D. It can even be quite low inductance.
But before designing it, accuracy targets need to be clearly specified.
Martin72:
In my opinion, it's only worth the effort if you can't find anything suitable on the market.
Or if you need a shunt on a circuit board, for example we use 5 R50/3W SMD shunts in parallel on a power supply unit for current feedback.
Speaking of shunts, I actually still had 2 lying around, I didn't even remember... ;)
A 60A/60mV and a 20A/60mV shunt, class 0.5, rather “robust” manufacture.
You can see clear traces of machining on the 20A shunt to achieve the resistance value.
cv007:
--- Quote ---See for example the N4646 series from Vacuumschmelze sourceable from Mouser (say the T6044-N4646-X412) for less than 17€/pcs.
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Anyone have experience with these, something like-
https://www.digikey.com/en/products/detail/vacuumschmelze/T60404N4646X101/12530732
Its not really clear to me what these are doing, and why they are relatively inexpensive (<$20 for the above part). Obviously not the same as a flux gate current sensor of considerably more cost, but they seem to be using the same idea as they describe it as a closed loop with a zero field detector. Are these essentially similar minus the precision? I can see where precision takes a lot more effort/cost, but if that much precision is not required then maybe these are a good option?
They list accuracy as max 0.5% with typical 0.1% for the above part (at max rated current, normal temperature), but not sure where you end up considering the rest of the variables in play. A typical 100A/100mV shunt is rated at 0.25% error, so it seems these are in the same ballpark. It looks like the downside is you have to come up with a +/- 12-15V power source, the upside is you can eliminate dealing with shunt heat and connections.
Maybe I am missing something obvious, but these look like something that I would at least like to check out since the cost is reasonable. Did not know these existed.
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