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How are 4-wire precision resistors wired?

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Boncuk

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Hi,

I need a 30mΩ shunt resistor for a solar charger to determine charge current into the battery.

The power rating should be 3W for 10A max current flow.

Two wire resistors are difficult to get for that power rating and their series start at 0.18Ω normally.

There are four-wire precision resistors being manufactured with a range of 0.5mΩ to 1Ω.

Searching in the internet there are lots of descriptions why 4-wire resistors are used, but I didn't find any application about how to connect the terminals.

Here is the data sheet of the ISA-PLAN type PBV resistors. It doesn't contain any wiring diagram as well.

It's pins are labeled 2XI and 2XU. That's all I can find.

Can somebody shed some light on it?

Thanks to all

Boncuk
 

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Last edited:
Hi,

I need a 30mΩ shunt resistor for a solar charger to determine charge current into the battery.

The power rating should be 3W for 10A max current flow.

Two wire resistors are difficult to get for that power rating and their series start at 0.18Ω normally.

There are four-wire precision resistors being manufactured with a range of 0.5mΩ to 1Ω.

Searching in the internet there are lots of descriptions why 4-wire resistors are used, but I didn't find any application about how to connect the terminals.

Here is the data sheet of the ISA-PLAN type PBV resistors. It doesn't contain any wiring diagram as well.

It's pins are labeled 2XI and 2XU. That's all I can find.

Can somebody shed some light on it?

Thanks to all

Boncuk

Morning Hans,.
Look at these two links.
One pair of wires is for the load current and the other pair are usually used as the voltage across the resistor as a sense pair.



Four Wire Kelvin Testing (A Description)
 
Thank you Eric,

I figure I don't need the two voltage pins then.

The resistor is used as a shunt and the voltage drop across it is then amplified for 350mV/A which is used in the A/D converter of the MCU to calculate for current flow.

Regards

Hans
 
Thank you Eric,

I figure I don't need the two voltage pins then.

The resistor is used as a shunt and the voltage drop across it is then amplified for 350mV/A which is used in the A/D converter of the MCU to calculate for current flow.

They are there for good reason - use them - it doesn't make your task any different.

Basically it gives you an accurate point to measure across, bear in mind you're talking tiny fractions of an ohm, trying to do it otherwise might introduce considerable errors (which is why it's done that way).
 
Thank you Eric,

I figure I don't need the two voltage pins then.

The resistor is used as a shunt and the voltage drop across it is then amplified for 350mV/A which is used in the A/D converter of the MCU to calculate for current flow.

Regards

Hans

hi Hans,
I have marked up your resistor pdf, you should use the blue wires for the MCU voltage sense take off point.
 

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)0.03 ohms at 10 amps is 3 watts. You need to derate your power resistor by a factor of 2 or 3 so it stays cool. A 3 watt resistor will be too hot.
 
)0.03 ohms at 10 amps is 3 watts. You need to derate your power resistor by a factor of 2 or 3 so it stays cool. A 3 watt resistor will be too hot.

That's already been taken care of. I'll purchase a resistor with heat sink able to dissipate 10W without derating.

Thanks anyway.

Boncuk
 
To measure low resistance, you need to measure the current through the device and the voltage across it. Note the the terminals are labeled V and I. The resistance is guaranteed between the two V terminals. Hence, you passthe current being measured through the I terminals and measure V across the resistor across the V terminals. The V&I next to each other have the same sign.
 
To measure low resistance, you need to measure the current through the device and the voltage across it. Note the the terminals are labeled V and I. The resistance is guaranteed between the two V terminals. Hence, you passthe current being measured through the I terminals and measure V across the resistor across the V terminals. The V&I next to each other have the same sign.

Thanks for your input.

I will buy that awefully expensive resistor (with heatsink EURO12) and check out its accuracy with the "V" terminals connected.

Regards

Boncuk
 
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