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Measuring 100A DC current

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pdenisowski:

--- Quote from: tooki on June 08, 2024, 08:28:14 pm ---I truly don’t get it: why would anyone order electronic components on Amazon? Aside from it being a scummy company, it’s not even a good price! For the same price, you can get name-brand resistors from Digikey for example.

--- End quote ---

Because if you live in a medium- to large-sized city in the United States, you can get many "basic" (and some not-so-basic) electronic components the same day or overnight, with free shipping if you're a Prime member.  If you need something quickly with low to zero shipping cost, Amazon is sometimes a very logical choice. 

But yes, I use Digikey, Mouser, etc. for things that I don't need right away or when I do a "bulk" buy of components, cables, etc.

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.

Psi:
It's very rare that I need a part today/tomorrow. I usually know I will need parts in 2 weeks when the PCB turns up.
But then, I do have a good stock of generic parts already. I guess anyone starting out would have that issue.

The first thing anyone starting out should do though is spend $100 on a resistor SMT/TH book, capacitor  SMT/TH book, box of electrolytics and a collection of generic jellybean ICs. Build up some basic parts inventory.

egonotto:

--- 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

--- End quote ---

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

johansen:

--- 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

--- End quote ---

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

--- End quote ---

So spend 50 more cents for 0.1ohm resistors

nctnico:

--- 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

--- End quote ---

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

--- End quote ---

So spend 50 more cents for 0.1ohm resistors

--- End quote ---
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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