• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

How are 4-wire precision resistors wired?

Status
Not open for further replies.

Boncuk

New Member
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
 

Attachments

Last edited:

ericgibbs

Well-Known Member
Most Helpful Member
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.

Kelvin (4-wire) resistance measurement : DC METERING CIRCUITS

Four Wire Kelvin Testing (A Description)
 

Boncuk

New Member
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
 

Nigel Goodwin

Super Moderator
Most Helpful Member
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).
 

ericgibbs

Well-Known Member
Most Helpful Member
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.
 

Attachments

Jaguarjoe

Member
)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.
 

Boncuk

New Member
)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
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
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.
 

Boncuk

New Member
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
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading

 
Top