# Help with Basic Circuits

#### RUSTYWIRE

Joined Aug 28, 2023
61
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 #### djsfantasi Joined Apr 11, 2010 9,129 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. Thread Starter #### RUSTYWIRE Joined Aug 28, 2023 61 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. Last edited: #### Audioguru again Joined Oct 21, 2019 6,437 The is a huge difference between a weak small AAA battery cell and a powerful D size battery cell. Thread Starter #### RUSTYWIRE Joined Aug 28, 2023 61 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. #### Audioguru again Joined Oct 21, 2019 6,437 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. #### dl324 Joined Mar 30, 2015 16,127 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? #### boostbuck Joined Oct 5, 2017 416 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. #### KL7AJ72 Joined Apr 15, 2021 22 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

#### RUSTYWIRE

Joined Aug 28, 2023
61
So how do you determine " the meter's amp range burden voltage"?

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

Thanks

#### KL7AJ72

Joined Apr 15, 2021
22
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

#### RUSTYWIRE

Joined Aug 28, 2023
61
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.

#### KL7AJ72

Joined Apr 15, 2021
22
I'll try that.

However I only have 1/4 watt resistors.
Those are far more than adequate.

#### Audioguru again

Joined Oct 21, 2019
6,437
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.

#### RUSTYWIRE

Joined Aug 28, 2023
61
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?

#### boostbuck

Joined Oct 5, 2017
416
From the Fluke Service manual for my older meter:

#### boostbuck

Joined Oct 5, 2017
416
unfortunately it is very common that the Burden Voltage is not given in a meter's specs.

#### RUSTYWIRE

Joined Aug 28, 2023
61
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?

#### RUSTYWIRE

Joined Aug 28, 2023
61
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

#### MrChips

Joined Oct 2, 2009
29,832
All meters have resistance. What is the resistance of the ammeter?
From your data, you can calculate the resistance of the meter.