# Arduino voltmeter maximum amp input

I made a programmable Arduino that measures an input voltage. The Arduino will close or open an inverter using a relay to prevent the set of batteries from dropping below 50% to keep the batteries healthy. I currently have a set of 8 6V batteries configured to supply a total of 12V to one inverter. I used a set of 10k ohm and 100k ohm to safely measure the 12 volt input from the batteries. In the current configuration the total Amperage provided by the set of batteries is 400 amps. Is it safe to measure the voltage from a 12V/400A input or do I need some kind of protection?

• measuring 12 volts is easy, measuring 400 amps is not. Mar 20 '17 at 21:02

It is perfectly safe.

The Arduino will see the voltage reduced by the divider you have. It will see whatever current it needs to see in order to sense the voltage - which is a tiny amount.

Remember: Current is drawn on demand by the load. It is never pushed by a supply.

• Why do some DMM have a maximum input of 10A when measuring? Also, why Hall-Effect is used to measure high amp current if it's safe to directly measure it using resistance devider? Mar 20 '17 at 17:33
• That is for the current measurement mode. Measuring current and measuring voltage are two very different things.
– Majenko
Mar 20 '17 at 17:34
• You measure voltage across something, but measure the current through something. When measuring current that current has to pass through the DMM. When measuring voltage the only current that flows through the DMM is that drawn by the measuring device.
– Majenko
Mar 20 '17 at 17:38
• Thank you, I understand now. So basically a hall-effect sensor is to measure the amperage (current) that a component is drawing. Mar 20 '17 at 17:40