Meter for amps

[davidz71]

I'm curious about amperage draw from my factory overhead lights, numerous light fixtures the previous owners added, reading lights in the front of my 31' Excella, lights by the single twin curbside bed, the 3 ceiling fans in addition to two small fans mounted underneath overhead compartments. While I see movement of the ammeter gauge in the control panel, can I mount a small meter with a finer (more sensative) scale right off the fusebox where the 2 wires connect and go to the control panel? My Excella has a front cradenza with a Flexsteel couch on the curbside. The cradenza tambour doors slide open to expose the fusebox behind a fold down panel. Craig

[FrankR]

Amp meters have fallen out of use. Amp meters must allow current to be passed thru them or a transformer to reflect energy being used. If you merely want to know the current used by any electrical device, it maybe easier to remove the fuse cover to temporarily connect an ampmeter. An ampmeter must be connected in series to function.
Most multimeters can measure up to 10 amps. To measure any load in amps, find circuit to be measured. Disconnect wire from either end of fuse holder. Clip one wire from ampmeter at fuse, and other end of meter to wire just disconnected. If there is no electrical draw on circuit, meter will not move. As devices are turned on, the load will be seen on meter. Checking each fuse and loads will tell total load amps of that fuse/circuit. There are several circuits that could exceed ampacity of tester. Larger meters with higher amps will not acurately measure small loads. In my opinion, an ampmeter is not a good electrical tool. My choice is a digital voltmeter for ac and one for dc. A good multimeter is a very valuable tool for any electrical problems and just checking values. Frank

[davidz71]

Thanks Frank,
I guess I will take part of a weekend morning and go through every 12 volt circuit in the trailer and write the values down as I test them with my multimeter. I was just curious if some of my lights/fans were drawing more current than others.

[FrankR]

To make your quest for amp values more accurate.......first measure the dc voltage. If the voltage is either up or down will directly affect the amperage numbers. A long time ago, a really great electrician told me " electricity can be somewhat compared to a see saw" With an increase in voltage, there will be a decrease in amperage. And the opposite is also true......with a decrease in voltage there will be a rise in amperage. In making critical measurements in electrical applications, all electrical values must be considered. To get the most complete and accurite numbers, measure all voltages. From the source, measure the ac in, the converter output, and batteries standing voltage. Some math maybe required.... Frank

[tenrsingr]

Here is a site that you can use.

http://hyperphysics.phy-astr.gsu.edu...ic/ohmlaw.html


I am an electrician at a paper mill and all I can say is .... be safe. If you are not careful, this stuff can hurt you bad. I just want you to be informed. I hope the best for you on your journey for knowledge.

[Inland RV Center, In]

The formula for pure DC circuits is E=IR, which means the voltage is equal to the current times the resistance. Therefore when the voltage drops, such as from 12 volts dc to 10 volts dc, and the resistance is fixed, then the current lowers. The formula can also be stated I=E over R. As an example, a resistance of 2 ohms that has 12 volts dc placed across it, will draw 6 amps. If the voltage is lowered to 10 volts dc, then the 2 ohm resistance will only draw 5 amps.
Frank may be referring to wattage. That formula for DC circuits is W=EI, which is watts is equal to the voltage times the current. In that case if the wattage remains constant, the current will drop as the voltage increases. In the example above, a 2 ohm resistance with 12 volts across it will draw 6 amps. When the wattage formula is used (W=EI), we will be drawing 72 watts. At 10 volts the wattage draw would be 50 watts.
If anyone wants to tinker with it, here are some DC formulas.
E=IR
I=E over R
R=E over I
W=EI
W=I squared x R
E= voltage
I=current
R=resistance
W=wattage
These are for pure DC circuits only, and not for AC circuits.
AC circuits deal with impedance, which is a combination of resistance and reactance.
Confused? That's why they sell voltmeters and ammeters, so we don't have to calculate anything. Meters work every time, as long as they are calibrated. The ammeters that are in many Airstreams are not calibrated. Simply put, those meters show more or less as the case may be.
Have fun.
Andy