# Simple, Analog V &amp; A Meter Install on Small System Questions

Hello, I have been lurking around this forum for a while now. Finally have a simple solar project for my remote RV and have a couple of questions on installing volt and amp meters.

Just starting out with a couple of 15 watt panels. Using them to keep the two RV batteries maintained when not in use. My plan is to move up to 105 watts max over time (for now).

Anyway, I picked up two meters that I would like to install and see just what kind of juice the panels are putting out.

1. 15v DC analog meter: #EW-GM15VDC 0-15 DC Volts
2. 5A DC alalog meter: #EW-GM5ADC 0-5 DC Amps

Now, I know the 5 amp meter is small but I wanted to see small changes in the 2 15w panels I have now (yea, I am weird that way). My question on the Amp meter is, according to the directions in the box, only amp meters 25 amps and higher need to be connected to a shunt. Is this true? On the back of the meter there is a solid half-loop wire installed between the two contacts. I am assuming that is a "mini-shunt" for this small of an amp meter. Question 2 for the amp meter, and pardon my electronic ignorance, it's my understanding that I connect the amp meter into the negative wire (plan on putting it between the controller and the battery to measure the power sent to the batt), do I "break the negative wire so that one end attaches to the meter and then another wire attaches to the other contact on the meter to complete the circuit? This may seem obvious but I just want to be sure. So, the negative wire from the controller would attach to one contact on the meter, then a new wire would connect from the 2nd contact on the meter to the battery. Same question for the volt meter below.

Question on the volt meter: Does it go on the positive or negative wire? Do I break the connection on the meter so that each contact has a different wire? Does that even make sense?

Thanks for any help.

Re: Simple, Analog V & A Meter Install on Small System Questions

The terms you will want to understand is:

Parallel: For measuring voltage you will want to place the meter in parallel with the load, source or whatever you will want to measure the voltage of...

Series: You will want to place the meter in between the load and the source (break a wire and insert the meter) to measure current.

Shunt: Used to measure current higher than a normal meter would be capable. Insert shunt in series (as above). Then use a Volt Meter (typically one that can measure millivolts, or 0.001 or 0.0001 volts minimum resolution and up to 1 volt or so). The shunt converts the current into a voltage reading.

Now the warnings:

Connecting any meter to high current (or high voltage) circuits require you to be very careful about shorting wires. Shorts can very easily start fires and completely destroy your RV/HOME/Etc. If you are installing the meters permanently, understand where to use fuses and protect the wires from shorts.

A voltage meter can be damaged by attempting to read voltages that are too high (fire, etc.).

A current meter can be damaged by attempting to read currents that are too high (or even very high voltages too--fire, etc.). A shunt is needed anytime the current is greater than the rating of the meter (or if you have a voltage meter and wish to measure current).

Voltage meters draw power and leaving an inexpensive analog meter connected all the time can actually discharge your battery over time (from a few percent to 10% of your battery capacity per month--depending on the meter and the size of your battery bank). For a panel meter you will probably want a push to test or toggle switch to only measure voltage when you are there.

A current meter (unless it has a back light or something odd) is not going to consume any power over time--you can leave it connected all the time.

Panel meters are sometimes intended to be used with shunts or other external scaling device (such as a pair of resistors) so the markings on the scale are not always indicative of the actual function of the meter (for an example a panel meter that reads 0-100 amps that has small gauge connections/wires is probably a volt meter intended for use with a current shunt).

A couple of basic electrical formulas that should be helpful:

V=I*R (voltage = current * resistance)
I=V/R
R=V/I

P=IV (power in watts = current * voltage)
P=I^2*R (current "squared" times resistance)
P=V^2/R

Watt*Hours (measure of the amount of work--or power over time--e.g. 100 watt light bulb for 10 hours would be 1,000 watt hours or 1 kilowatt hour worth of work done or required).

AMP*Hours (manytimes used to measure the capacity of a battery based system. Similar to WHr but does not include voltage (so you have to know if the system is a 12 volt, 24 volt or whatever size system).

A 100 AmpHr battery would be able to supply a 1 amp load for 100 hours (12 watt load for 100 hours) or a 50 amp load for 2 hours, etc. (note that I am being really loose with my definitions here--a battery can deliver more total energy if its loads are small and over time. The observed capacity of a 100 amp*hr battery supplying 200 amps will be much less than 30 minutes.

Note that a standard car battery should probably not be cycled for more than 20% of capacity (100 amp*hr battery should only run 1 amp for 20 hours) or risk the battery failing in months, or even a few weeks.

A true storage battery (hopefully like your RV system) should not be cycled for more than 50% of capacity (100 amp*hr would be used as a 50 amp*hr battery).

I hope the above is useful.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Re: Simple, Analog V & A Meter Install on Small System Questions
BB wrote:
The terms you will want to understand is:

Parallel: For measuring voltage you will want to place the meter in parallel with the load, source or whatever you will want to measure the voltage of...

Series: You will want to place the meter in between the load and the source (break a wire and insert the meter) to measure current.

Shunt: Used to measure current higher than a normal meter would be capable. Insert shunt in series (as above). Then use a Volt Meter (typically one that can measure millivolts, or 0.001 or 0.0001 volts minimum resolution and up to 1 volt or so). The shunt converts the current into a voltage reading.

Bill, thanks for the VALUABLE info. So here are my followup questions:

1. 15v meter: this meter will measure volts up to 15, right? And the meter should be installed in PARALLEL to the positive wire coming from the controller. Since the meter measures up to 15v I shouldn't need a shut for it right? So, installing it in parallel, would that be done with a simple jumper wire off the + wire? This would be the meter that needs an on/off toggle to avoid current drain?

2. 5a meter: this amp meter does not require a shunt and should be connected in SERIES on the negative wire coming from the controller, yes? This meter can stay connected to the circuit and constantly monitor current (amps)?

Thanks again for the electronics lesson. It is much appreciated.

Re: Simple, Analog V & A Meter Install on Small System Questions

The 15v Voltage meter is the correct range. It should be install + terminal of meter to + wire of your RV. The meter's - terminal should be connected to the metal frame of your RV (or ground wire if one is near by). The switch would typically be installed by breaking the + lead of the meter lead.

Voltage meters--for what you are doing--would never use a shunt. There is something called a resistor divider (that is not a shunt) that can be used for high voltages or in special situations--but would almost never be used by an RV'er...

The current meter should be designed to work without a shunt (really need to read the specs of the meter--or sometimes the information in printed in very small type on the front of the meter). At those small currents of a 15 to 60 watt panels, it would not hurt much to just connect the meter and see if it works correctly or not.

And you will not need a switch or shunt for your current meter--it is connected all the time.

If you have a simple solar charge controller, you can place the meter either between the charge controller and the battery, or between the panels and the charge controller. Assuming that your RV is negative ground--I would tend to place the current meter in the positive lead from the panel or to the battery... Much less confusion than the negative leads, especially when working with a charge controller (where the charge controller's negative lead does not carry the load).

The current meter can go in either the positive or negative lead of the solar panel. It does not matter. Simply cut one wire from the solar panel and insert the meter leads. If the meter reads backwards, just swap the leads and try again. If you have more than one panel, connect all of them together (+ to + and - to -), then put the meter in the one lead to the battery and you will measure the total current supplied.

In general, also use a fuse (or connected to an existing fused circuit in your RV) to protect your wiring from fire. It is not difficult to do correctly and the problems if the wiring is not fused correctly are huge if there is a short later. Lead Acid storage batteries can output HUGE AMOUNTS OF CURRENT--much more than you are used to in your AC Home wiring (think large arc welder type currents). Home AC wiring was installed and inspected by professionals with fire safety in mind--An RV power system is very easy to bypass fuses and create safety issues. You would probably never think of opening your main breaker box and connection wires directly to the 240 VAC coming directly off of your power pole--but many folks will do almost exactly the same thing when connecting wires to a large 12 VDC battery.

My normal disclaimer--It is very hard to understand the knowledge of a poster on an Internet Board when answering questions... I am not trying to be difficult, but you may wish to get a friend or pay somebody to help with your first installation so that you understand the basic safety requirements and can ask questions.

Yes, the connections are simple--but the downside of making a mistake can be property and life threatening when dealing with these power levels.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Re: Simple, Analog V & A Meter Install on Small System Questions

Exactly what I needed Bill.

I have experience with wiring 12v automotive stuff. Radios, fan's, lights, etc. I have worked with relay's quite often for high amp applications like fog lights and fans so I am not completely clueless. Just never wired in these types of measuring devices (amp meter and volt meter). Also know about fuse protection and why it's important.

I appreciate you time and effort to help me out. Just didn't want to start connecting the meters to wires! Good info.

Thanks! :-D
Re: Simple, Analog V & A Meter Install on Small System Questions

AZ,

You sound good to go... If you want to think of the meters in a different way... Think of connecting a light bulb instead.

Connecting a bulb from + to - will glow whenever there is voltage present.

Connecting a bulb by breaking a wire--it will glow only when current is flowing in the wire.

That is pretty much all there is to it.

Good Luck and have Fun! (boy, I miss camping--my wife is a city girl).
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Simple, Analog V & A Meter Install on Small System Questions

az,
do note that placing an analog meter in backwards can potentially bend the small piece of metal used for the indicator. many meters do have a provision in the front for adjustment via a screw driver. if you don't have this then you can't make corrections to the meter when it is inaccurate. a fuse is a good idea, but especially on anything placed in parallel to the voltage potential. if you accidentally place a wire accross the voltmeter you will actually short the whole battery/pv system without a fuse inline to stop it, but if you placed a wire accross the ammeter it will not harm anything and will only bypass the meter unless this goes on and touches a contact from the other polarity of the battery/pv.
analog meters are somewhat inaccurate even if calibrated right for those that can be calibrated and are more difficult to read than digital meters. these analog meters can be cheap to get sometimes, but you can't beat digitals for their accuracy per price.
as to the shunts that can happen on lower current levels too as it depends on the basic meter capabilities. analogs can have current levels rated in amps without a shunt, but digitals nearly always will need one unless the small current measured is with the basic range of the meter straight up and this you will find is almost always measured in microamps.
Re: Simple, Analog V & A Meter Install on Small System Questions

Niel,
More good information. Thanks!

Did a test setup on one of my quads with a discharged battery and a single 15W PV. Volt meter worked great +15V. Did have some issue with the amp meter. As you stated, the analog meter has a little screw in the front to adjust, however, it reads less than 0 amps and the little screw won't move it all the way to 0 (disconnected).  Output this morning 8 AM in Phoenix read less than .5 A. But, that was just with jumper wire and not a nice connection. Will tinker around some more. Will propably go digital as you suggesed for final install on the RV.

Thanks again for the assistance.

Side Note: as I move to solar for my remote RV setup it's interesting how you start looking at power use and conservation in both the RV and at home. I have switched most of the lights in the RV to LED's, and will be looking at other things so that I can count on the solar to keep the batteries charged and not use my noisy 1000W generator. I am paying more attention to power usage at home, lights, fans, TV's, etc. Who knows, maybe soon I will be contemplating solar at the house! And as anyone from AZ knows we have LOTS of sun here!

Thanks for the great forums!
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Simple, Analog V & A Meter Install on Small System Questions

it's possible the ammeter is broken if you can't get it to 0. one more note here is that if you should drop an analog meter it will break quite easily.