Ohms Law not working.

I have a very basic breadboard circuit with a 1.5 (reads 1.6) volt alkaline battery, and 10 Ohm, 1% resistor, (reads 10.1 ohms)
I will expand it with more components as I prove out steps in Ohms Law.

According to the law, I should be measuring 160 ma current. Instead I am getting 125 ma. I checked for any additional resistance in the components
but all check out OK. I am using a $100 digital multimeter.

Why am I not getting 160 ma?

Thanks

 

How did you measure the battery voltage? Was it in-circuit (10Ω resistor connected) or standalone? Under load, the voltage from a battery will drop.

Given your results, I’d expect that under load, the battery voltage will read about 1.25V.

 

How did you measure the battery voltage? Was it in-circuit (10Ω resistor connected) or standalone? Under load, the voltage from a battery will drop.

Given your results, I’d expect that under load, the battery voltage will read about 1.25V.

Hold on let me check now.

With the resistor the voltage is reading 1.47 across R and 1.53 across the cell.

 

The is a huge difference between a weak small AAA battery cell and a powerful D size battery cell.

 

The is a huge difference between a weak small AAA battery cell and a powerful D size battery cell.

It's a AA.

I'm just going over elementary projects and happen to have a lot of AA alkalines with holders just to observe different scenarios with cells & batteries.

 

You must measure the voltage across the resistor while it it is being heated by the battery cell.
1.6V x 160mA= 256mW then a 1/4W resistor gets too hot so use a 1/2W or larger resistor.

 

According to the law, I should be measuring 160 ma current. Instead I am getting 125 ma. I checked for any additional resistance in the components

I can guarantee you that Ohm's law is working and this is operator error. The ammeter is perturbing the circuit. What is the meter's burden voltage?

 

Is the 10.1 Ohm measurement including the resistance of the meter leads? Does your meter have a 'relative' setting to zero out the leads?

Since your resistor is 1%, measuring the VOLTAGE across the resistor and using ohms law will give you a close true value for the current in the circuit. As mentioned above, the meter's amp range burden voltage is likely to cause errors in a low voltage circuit when measuring current in-circuit.

 

Ohms Law not working.

I have a very basic breadboard circuit with a 1.5 (reads 1.6) volt alkaline battery, and 10 Ohm, 1% resistor, (reads 10.1 ohms)
I will expand it with more components as I prove out steps in Ohms Law.

According to the law, I should be measuring 160 ma current. Instead I am getting 125 ma. I checked for any additional resistance in the components
but all check out OK. I am using a $100 digital multimeter.

Why am I not getting 160 ma?

Thanks

10 ohms is pretty low resistance, you're probably loading down your battery too much. Try 100 ohms and look for 16ma

 

So how do you determine " the meter's amp range burden voltage"?

In the meantime I'll get the manual and check.

Thanks

 

So how do you determine " the meter's amp range burden voltage"?

In the meantime I'll get the manual and check.

Thanks

That would be a battery spec, not the meter's

 

10 ohms is pretty low resistance, you're probably loading down your battery too much. Try 100 ohms and look for 16ma

I'll try that.

However I only have 1/4 watt resistors.

 

I'll try that.

However I only have 1/4 watt resistors.

Those are far more than adequate.

 

1.6V/100 ohms= 16mA. Then the resistor heats with 1.6V x 16mA= 0.0256W which produces very low heating in a 1/4W resistor.

 

Those are far more than adequate.

Audioguru recommended I use a 1/2 watt as 1/4 watt gets too hot (and it was hot).

I find no metion of "the meter's amp range burden voltage" in the multimeter specs.
Is there another name for that?

 

From the Fluke Service manual for my older meter:

 

unfortunately it is very common that the Burden Voltage is not given in a meter's specs.

 

From the Fluke Service manual for my older meter:

View attachment 301519

There is no mention or listing of Burden Voltage in my spec sheet like it is in yours.

Is there another term for that parameter?

 

The 100 ohm resistor is reading 154 ma good but trying to locate the missing 6 ma is interesting for learning.

No doubt its taken up somewhere in the hardware, but where? No big deal except for learning.

Also I would like to know the burden voltage for my meter for general purposes if anyone know how to determine that?

Additionally, knowing the internal resistance of the 1.5 (1.6) V cell.

This is all a foundation for future circuits.

Thanks

 

All meters have resistance. What is the resistance of the ammeter?
From your data, you can calculate the resistance of the meter.