Battery Voltmeter Installation Question

Thanks folks.

on my trailer... 30 foot.. battery in the nose and panel behind rear axle .
main wire run. is 35 feet.. with a steady draw of 20 amps. I have a 0.5 volt drop from battery to panel.. and my unit is 11 years old.

and I am using a Fluke meter. accurate to 0.002 volts.

but the drop is normal and within specs.. look on the web, for voltage drop for 12 volts an its different than 120 volts... ac and dc...

low voltage DC is harder to travel in wire.
that is why the world uses AC in everywhere... power loss in wire.

mabynack wrote:

JWRoberts wrote:

Bill.Satellite wrote:

JWRoberts wrote:
There will be NO difference in readings at the battery or the panel.

There certainly can be differences depending upon the coach wiring. The OP will need to give the easy option a try but if that's not accurate the OP will need to find a better option.

As a retired electrical engineer, I assure you there will be NO difference. A digital meter draws micro amps of current from the measuring point so no significant voltage drop will exist.

That's where I'm a little confused. If I wire the meter in parallel across the leads going to the voltage monitor in the panel, won't I just be measuring the voltage drop across the monitor panel and not the full battery voltage?

You will be measuring the voltage present, not dropped, at the panel. If properly wired, there will be negligible voltage drop in the wires from the battery to the panel. With every 12V device on, the difference in voltage at the battery and the panel will typically be 0.1V.

mabynack wrote:

JWRoberts wrote:

Bill.Satellite wrote:

JWRoberts wrote:
There will be NO difference in readings at the battery or the panel.

There certainly can be differences depending upon the coach wiring. The OP will need to give the easy option a try but if that's not accurate the OP will need to find a better option.

As a retired electrical engineer, I assure you there will be NO difference. A digital meter draws micro amps of current from the measuring point so no significant voltage drop will exist.

That's where I'm a little confused. If I wire the meter in parallel across the leads going to the voltage monitor in the panel, won't I just be measuring the voltage drop across the monitor panel and not the full battery voltage?

You will be measuring the voltage present at the panel. If properly wired, there will be negligible voltage drop in the wires from the battery to the panel. With every 12V device on, the difference in voltage at the battery and the panel will typically be 0.1V.

The issue is not current draw of the meter. The issue MAY be, current draw of any other components on the same wiring. Where the terminations may be, and the condition of those terminations. Real world results will be, slightly lower voltage at remote locations.

If you run new wires between the battery and the meter, and make good connections, then there would be no issue and you could put the meter anywhere. But I don't think that is what the OP is proposing. He wants to tap into existing wiring.

JWRoberts wrote:

Bill.Satellite wrote:

JWRoberts wrote:
There will be NO difference in readings at the battery or the panel.

There certainly can be differences depending upon the coach wiring. The OP will need to give the easy option a try but if that's not accurate the OP will need to find a better option.

As a retired electrical engineer, I assure you there will be NO difference. A digital meter draws micro amps of current from the measuring point so no significant voltage drop will exist.

That's where I'm a little confused. If I wire the meter in parallel across the leads going to the voltage monitor in the panel, won't I just be measuring the voltage drop across the monitor panel and not the full battery voltage?

Bill.Satellite wrote:

JWRoberts wrote:
There will be NO difference in readings at the battery or the panel.

There certainly can be differences depending upon the coach wiring. The OP will need to give the easy option a try but if that's not accurate the OP will need to find a better option.

As a retired electrical engineer, I assure you there will be NO difference. A digital meter draws micro amps of current from the measuring point so no significant voltage drop will exist.

JWRoberts wrote:
There will be NO difference in readings at the battery or the panel.

There certainly can be differences depending upon the coach wiring. The OP will need to give the easy option a try but if that's not accurate the OP will need to find a better option.

There will be NO difference in readings at the battery or the panel.

When I installed mine, I just placed it where it would be most convenient to monitor at a glance. That was near the control panel at the entrance door. Made for easy wiring too.

I'm sure it reads a one or two tenths of a volt less than it would at the battery terminals. But it still registers by tenths of a volt when the pump turns on or we hit a light switch, so the info of relative loads is useful. I would find it much less useful if it were hidden in a compartment with the batteries.

Try to make sure you connect the negative to a wire that runs all the way back to the battery bus. Not a chassis ground.

If I want to check actual battery condition, I'll dig out a digital VOM for that occasional task.