Voltmeter and Ammeter

Jakachira

Hello, guys

I planning to buy cheap analog volt and amp meters for my small system

My system is 300Watts of panels .. maximum current is 16.5Amps and its a 12V system.

so my Voltmeter range will be 0-30V,
Ammeter: 0-30Amps both DC.

My question is I would like to connect the meters preferably between the controller and the battery. Do these analog meters withstand a permanent connection? I want know how much power power i'm drawing from the battery so which position should i put the ammeter here? (btwn inverter & battery? or controller and Battery?) I want to monitor in DC only. For exmple if i have a TV on an inverter, my Ammeter should be showing a negative ~6Amps. I'm not concerned about the power stored in the battery but the power that goes in and out. esp current.

I guess i do not need a shunt because my system is small.

Thanks guys

Cariboocoot

Re: Voltmeter and Ammeter

The Voltmeter won't be much of an issue, except that "cheap" tends to mean "inaccurate" in instruments. Many charge controllers have a built-in Voltmeter or have an accessory meter unit.

The Ammeter is another issue. When you talk about running a TV, there's a big difference between sets. The Ammeter would have to be able to handle the total maximum current draw for your inverter. 30 Amps @ 12 Volts is 360 Watts, which would be something like the Morningstar 300. Here you should really plan on spending the money, because you expect to put all the current through the meter. This is why the shunt-type battery monitors are better. They also keep cumulative data; a built-in analog "automotive" type Ammeter will only tell you what's happening now. As a result, you won't really have any good information about how well your battery has been charged or how greatly it's been discharged - unless you sit there all day and watch it, taking notes. :roll:

What sort of charge controller will/do you have? My advice would be that if you're not going to go with a battery monitor then get a controller which has metering functions. It will at least tell you what the charge rate and Voltage is. I'd be a bit leery bout hard-wiring automotive gauges into a system for the reasons mentioned (they'll usually only accept 10 Gauge wire connectors too, which might be too small for your hook-up).

Just my opinion. Feel free to disagree.

Highland_Fling

Re: Voltmeter and Ammeter

Cariboocoot wrote: »

I'd be a bit leery bout hard-wiring automotive gauges into a system for the reasons mentioned (they'll usually only accept 10 Gauge wire connectors too, which might be too small for your hook-up).

Just my opinion. Feel free to disagree.

well i do really - if an old style (no shunt) car ammeter was sized to handle 60A FSD why would you worry about using that - apart from it will only give you a now reading.

BB.

Re: Voltmeter and Ammeter

With a automotive amp meter--typically, you have to route the wires capable of 60 amps from the battery to the meter (if you follow NEC recommendations, that would be somewhere around 6-4 AWG cable). And that would only be recommended for around a 5-10 foot total cable run (1-2% voltage drop for 6 awg cable at room temperature).

Of course, if you accept higher voltage drop and current flow, you can have the wiring somewhat longer/lighter gauge.

If you want the amp meter anywhere else, other than next to the battery bank, it would be much better (and probably safer) to run a shunt and remote wire the meter using the shunt sense connections (very small gauge wire from shunt to meter).

-Bill

And, you should fuse the cable (or the positive lead off the battery) for 60-75 amps or so to reduce the possibility of overheating/fire in the event of excess loads and/or short circuit.

Highland_Fling

Re: Voltmeter and Ammeter

BB. wrote: »

With a automotive amp meter--typically, you have to route the wires capable of 60 amps from the battery to the meter (if you follow NEC recommendations, that would be somewhere around 6-4 AWG cable). And that would only be recommended for around a 5-10 foot total cable run (1-2% voltage drop for 6 awg cable at room temperature).

Of course, if you accept higher voltage drop and current flow, you can have the wiring somewhat longer/lighter gauge.

If you want the amp meter anywhere else, other than next to the battery bank, it would be much better (and probably safer) to run a shunt and remote wire the meter using the shunt sense connections (very small gauge wire from shunt to meter).

-Bill

And, you should fuse the cable (or the positive lead off the battery) for 60-75 amps or so to reduce the possibility of overheating/fire in the event of excess loads and/or short circuit.

OKIDOKI but my auto ammeter is in the system with no more than two feet of wire much less than were it installed in a car - and of course there is a C/B in the circuit from the controller to the batteries. Also my main engine ammeter is also a direct reading type - the alternator is less than a foot from the batteries well the battery combiner actually BUT the ammeter is at the back end of the cockpit so vis a vis a direct link alternator to batteries that wiring is considerably longer - the boat meets all the appropriate CE/EU and USA Boat building regulations and yes i have a factory installed shunt for the ammeter on the main panel.

System2

Re: Voltmeter and Ammeter

Hi fellows and fellowines,
I have a question along the lines of this thread. I have a straightforward 600 w, 24v system. I have 2 analog ammeters to measure what is going in and what is going out. The solar side ammeter got bypassed when some work had to be done and I installed a new regulator a couple of years ago.
I would just like to know how to wire in the "in" ammeter. There isn't any distance problem as others mentioned, and I see that probably I will go from the positive solar terminal, but where to then?
Thanks,
David

Cariboocoot

Re: Voltmeter and Ammeter

David;

Ammeters go "in line". Something like this:

Charge Controller (+)

---

Ammeter

---

Battery (+)

OR (added by niel for clarity)

Charge Controller (-)

---

Battery (-)

Does that help?
If the Ammeter is installed backwards it will read backwards. With a "plus/minus" type (as in automotive use) this isn't a problem. One that reads only 0 and up can be damaged by reversed polarity.

RCinFLA

Re: Voltmeter and Ammeter

Jakachira wrote: »

Hello, guys

I planning to buy cheap analog volt and amp meters for my small system

My system is 300Watts of panels .. maximum current is 16.5Amps and its a 12V system.

so my Voltmeter range will be 0-30V,
Ammeter: 0-30Amps both DC.

You can buy 200 mV LCD modules cheaper then an analog meter these days. They draw less then 1 mA at 9vdc (unless you get backlight version).

http://www.web-tronics.com/test-equipment-panel-meters-digital-panel-meters--lcd---led-.html

Many come with the divider resistors for normal DVM voltage scales.
For the ampmeter use the same module with a 100 amp shunt.

http://www.solar-electric.com/mka-100-100.html

Most analog meters are 50 uA movement, meaning 50 uA is full scale needle deflection.

niel

Re: Voltmeter and Ammeter

Jakachira wrote: »

Hello, guys

I planning to buy cheap analog volt and amp meters for my small system

My system is 300Watts of panels .. maximum current is 16.5Amps and its a 12V system.

so my Voltmeter range will be 0-30V,
Ammeter: 0-30Amps both DC.

My question is I would like to connect the meters preferably between the controller and the battery. Do these analog meters withstand a permanent connection? I want know how much power power i'm drawing from the battery so which position should i put the ammeter here? (btwn inverter & battery? or controller and Battery?) I want to monitor in DC only. For exmple if i have a TV on an inverter, my Ammeter should be showing a negative ~6Amps. I'm not concerned about the power stored in the battery but the power that goes in and out. esp current.

I guess i do not need a shunt because my system is small.

Thanks guys

one can use analog meters if one has them on hand, but they are general in their readings as you won't discern values with any real accuracy. i should point out that the ammeter will not give you a negative reading as it will just pin the meter in the negative direction. if the ammeter were a 30-0-30 type then the needle would point to 0 in the middle of the meter with negative readings going to the left and positive readings going to the right. (noting that this can be reversed if connected as such)

also note the ammeter is a realtime meter and is not cumulative to read amphours and that there's no harm leaving them connected providing you secure against any possible shorts from these being connected.

System2

Re: Voltmeter and Ammeter

Cariboocoot wrote: »

David;

Ammeters go "in line". Something like this:

Charge Controller (+)

---

Ammeter

---

Battery (+)

OR (added by niel for clarity)

Charge Controller (-)

---

Battery (-)

Does that help?
If the Ammeter is installed backwards it will read backwards. With a "plus/minus" type (as in automotive use) this isn't a problem. One that reads only 0 and up can be damaged by reversed polarity.

Thanks, Cariboocoot & Neil,
However, Won' t this measure what is actually going into the batteries? Whereas I want to measure (directly) what is being put out by the solar panels, before any regulating. Does that mean I should go solar (+ or -) > ammeter> battery (+ or -)?
[My meter only measures (+). ]
David 8)

Cariboocoot

Re: Voltmeter and Ammeter

cloudy sun wrote: »

Thanks, Cariboocoot & Neil,
However, Won' t this measure what is actually going into the batteries? Whereas I want to measure (directly) what is being put out by the solar panels, before any regulating. Does that mean I should go solar (+ or -) > ammeter> battery (+ or -)?
[My meter only measures (+). ]
David 8)

Yes, that would measure the current flowing into the batteries from the charge controller. This is usually what you'd want to measure, as it is relevant to how well the batteries are being charged. Measuring the current from the panels to the controller can be done, but it's questionable what value that would have as it is the power actually going to the batteries that gets stored: charge controllers use up a bit of power themselves. Perhaps you want to compare the in and out current to see how much?

Think of an off-grid system as having three separate circuits: 1) the PV's to the charge controller (and back); 2) the charge controller to the batteries (and back); 3) the batteries to the inverter (and back); 4) the AC side of the inverter. Placing a properly oriented Ammeter capable of handling the potential current within any of these circuits will show you the current flowing within that segment of the system.

Usually one uses a clamp-on DC Ammeter for checking systems. Permanent installations are more likely to be of the battery monitor type so that you can keep track of the in and out cumulatively and get an idea of the state of charge of the batteries at any point in time.

BB.

Re: Voltmeter and Ammeter

By the way, Battery Monitors typically install the shunt in the negative lead of a negative grounded battery bank.

That way, if there is ever a short for the shunt sense wires to ground--there is very near to zero voltage on the wires (no fuse/resistor needed at shunt to limit short circuit flow).

-Bill