Resistor power values for Ohm meter

Hi All

I have built an Ohm meter using voltage divide. It works well and as expected the resistor get hot. (0.5W carbon film)

Question is what power value would be best for the resistor to keep the heat generated low?

The circuit is for my vehicle LPG (aka CNC, Propane) tank gauge that reads 0-95 Ohm and is powered up when driving and acts like a fuel gauge.

Also is there a better way to measure resistance?



Sorry, as you have provided no useful information - and a poorly-cited dead link - no-one has the slightest idea about what you are talking! :roll_eyes:

Question is what power value would be best for the resistor to keep the heat generated low?

You calculate power as follows:
Power = voltage * current
Power = current squared * resistance
Power = voltage squared / resistance

Use the appropriate formula to calculate the power dissipation in your resistors and buy appropriate resistors.

Rule of thumb: If your component is not too hot to keep your finger on it then it's not too hot.

Cheers Perry

Didn’t realise it that simples ;D 5V 22Ohm spot on 1.14W

And thanks for you Nextion work as i’m using that to get info on a screen.


You're welcome!

Since your resistor got noticeably hot, you might want to check it to see how much it's value has changed.


Just how much accuracy do you need? If you're setting up a voltage divider to measure the voltage with a microcontroller you can increase the value of the fixed resistor, which sacrifices resolution, but reduces current consumption and heat considerably.

You could also add a MOSFET into the voltage divider to switch on the measurement only when needed. It's not like you need to constantly measure the fuel might only need to measure once per second...and the measurement will only take a brief moment.

Assuming you use an Uno/Nano.
Power the resistor/sensor from the 3.3volt pin.
Then you can get near max resolution of the A/D with a 220 ohm resistor and with 1.1volt Aref enabled.
The 220 ohm resistor would dissipate only 0.05watt.

If a resistor gets hot, that usually means you're doing something wrong.

If that resistor is part of a voltage divider or similar type of sensing circuit you're quite certainly doing something very wrong.

If that resistor is close to a highly flammable substance, you're asking for disaster.

It appears you're in the third category.

General solution: seriously lower the current you're pumping through that resistor.

Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Thanks.. Tom.... :slight_smile: