I'm new to this forum, and just starting my journey into projects and electronics in general. I'm into alternative energy sources, solar specifically. Currently I have a 15 watt solar panel, a charge controller, and a couple of 12v 7ah storage batteries, and a multimeter.

The open circuit voltage of the solar panel is ~22-24 volts on a very sunny day. I know that once I connect a battery to the solar panel, the voltage will drop down to the charge of the battery. Is there any way that I can (with two different meters) read both the open circuit voltage, and the charge voltage at the same time?

What I am wanting to do is install two analog voltmeters inside a project case, along with the charge controller. A 30v analog meter to measure the open circuit voltage, and a 15v analog meter to measure the charge voltage.

Basically I am wanting to be able to look at the 30v meter and tell how much power the panel is receiving from the sun, and also be able to use the 15v meter to see the charge voltage of my battery bank. Is this possible?

Any help is greatly appreciated. I'm sure I will have more questions as I continue this project.

 

The open circuit voltage won't tell you anything about power from the sun. What you need is an amp meter in series with the panel in addition to the voltmeter across before the charge controller.

A quick chart of today's solar input on my system.

 

The open circuit voltage won't tell you anything about power from the sun. What you need is an amp meter in series with the panel before the charge controller.

Thank you for the reply. I guess I could swap out the analog 30v meter with an amp meter, but I'm more interested in just being able to see both voltages at the same time. Amp output might be a better indicator of the solar power the panel is receiving, but voltage works for this purpose as well. About 9 or 10 a.m., the open circuit voltage is around 15 to 17 volts, and around 1 to 3 p.m, it increases to around 22 to 24 volts.

So, if I go in the following order, will it work? Solar Panel -> 30vdc Meter -> Charge Controller -> 15vdc Meter -> 12v Battery. Would that setup allow me to see both voltages at the same time?

 

Thank you for the reply. I guess I could swap out the analog 30v meter with an amp meter, but I'm more interested in just being able to see both voltages at the same time. Amp output might be a better indicator of the solar power the panel is receiving, but voltage works for this purpose as well. About 9 or 10 a.m., the open circuit voltage is around 15 to 17 volts, and around 1 to 3 p.m, it increases to around 22 to 24 volts.

So, if I go in the following order, will it work? Solar Panel -> 30vdc Meter -> Charge Controller -> 15vdc Meter -> 12v Battery. Would that setup allow me to see both voltages at the same time?

No, open circuit means not connected to a load so you can see max voltage with very little sunlight but once connected to a load it would drop down to almost nothing. To measure it you would have to disconnect the charge controller from the panel.
http://pveducation.org/pvcdrom/solar-cell-operation/open-circuit-voltage

 

No, open circuit means not connected to a load so you can see max voltage with very little sunlight but once connected to a load it would drop down to almost nothing. To measure it you would have to disconnect the charge controller from the panel.
http://pveducation.org/pvcdrom/solar-cell-operation/open-circuit-voltage

Thank you again. So, an amp meter before the charge controller would be a better indicator of solar power, as you said before. And if I still wanted to go with the 30v meter to measure open circuit voltage, I'd have to put an on/off switch to the charge controller in there and switch it off in order to see the open circuit voltage. As soon as I turn the charge controller on, and it started charging the battery, the open circuit voltage would drop considerably, depending on how much sunlight the panel is receiving.

Sorry for the barrage of questions, but I'm new to this. Thanks for helping. There is more that I'm planning to add to this project, but apparently I need to get the basics down first.

 

Here are a few more pieces that I would like to add to this project. I might have to get a bigger project enclosure!

I want this project enclosure to contain 1 x 12v 7 ah battery, 2 x analog meters, 2 x on/off switches, 1 x charge controller, 1 x 12v distribution bus, 1 x 5v panel mount USB connector, 1 x 12v panel mount socket, 2 x 12v terminals. One switch will be to turn on/off the charge controller, the other switch will be to select power distribution from either the internal battery or direct solar power. The 5v USB already has a built-in 12v to 5v converter.

 

I like analog displays and older looking switches and things like that. Does anyone know where I could possibly get some analog voltmeters that are backlit in amber like the old VU meters used to be? Something like these:

 

I have no source but EBay has lots of good things.

I would not advice using these as this lamp load is a significant portion of the power available from a 15 watt panel.

 

Don't forget the fuses. You need at least one on the wire connected to the battery + terminal for a negative ground system. I would also fuse any external power out plugs.
I've used that same CC (PWM type) for a solar powered light in a storage shed I built.

 

I have no source but EBay has lots of good things.

I would not advice using these as this lamp load is a significant portion of the power available from a 15 watt panel.

I understand that. I would need to have more panels or higher power solar panels for that not to take up too much of the power from the panels. Initially I didn't want anything in the box that was going to draw unnecessary current, such as LED rocker switches. But as I said, I like the old style analog look, and I was hoping that I could maybe find some of these analog voltmeters that are backlit, but I have found none so far, not in the style that I wanting them anyway.

 

Backlit meter - drill a hole in the meter and insert a bulb or LED.

No-load solar panel voltage - You have to disconnect the load to take a no-load reading. If you want automated reading, build a microcontroller circuit to disconnect the load and take the reading.

 

I like analog displays and older looking switches and things like that. Does anyone know where I could possibly get some analog voltmeters that are backlit in amber like the old VU meters used to be?

I like analog displays too for a quick reading with varying levels. A good led back-light is going to waste about 50mA on each meter, over a 24 hour period that's a lot of power from a very limited supply.

 

Ok, next question. My 15w solar panel has an SAE connector, and I found a connector that can gang four panels into one output. My question is, will this connector make the panels be wired in series or parallel? I don't have many specifics on the panel that I have, but on the back it says up to 15 watts, Current I = 1 amp. I think the panel is rated between 12vdc and 15vdc, it doesn't say anything about voltage on the back, but I have been using it just fine with a 12v charge controller.

So, will this connector hooked up to 4 panels give me 12vdc and 4 amps, or 48vdc and 1 amp? Would I then have a 60w array instead of 15w?

 

Ok, next question. My 15w solar panel has an SAE connector, and I found a connector that can gang four panels into one output. ...

So, will this connector hooked up to 4 panels give me 12vdc and 4 amps, or 48vdc and 1 amp? Would I then have a 60w array instead of 15w?

View attachment 83877

I don't know for sure, but it would seem unreasonable to me for the connector to be wiring the panels in series. Panels of the type you describe are generally used to charge a single 12-volt battery through a simple controller (if any controller at all), and there would be no advantage gained by putting panels in series. Also, if the person wanted to use only two or three panels, they would need some sort of shorting plug(s) to terminate the unused connectors. So almost certainly, the connections are parallel.

From reading your post, it seems reasonable to monitor both the input and output voltage of the controller. As others have pointed out, that's not called the open circuit voltage going into the controller, but names aside, it would be an interesting parameter to monitor, as well as current, if you can. What you might want to do, if you have not bought meters yet, is to just hook things up and use a DVM to monitor voltages and currents for a while, until you have your project sort of working.

This will be a great learning experience no matter what, but there are a couple things to look out for. 15-watt panels of the type sold at Harbor Freight are often amorphous silicon, and unscrupulously rated. I've heard that the 15-watt panels are really 5-watt panels out of the box, and that after being in the sun for a year, they may degrade to 2-watt panels. With a low power panel, it may be more efficient to simply connect the panel to the battery through a blocking diode, no controller involved. Finally, if you were thinking of ganging 4 panels in parallel, look into simply getting a single polysilicon panel for the same money. The latter will not degrade nearly as much, and has a good chance of being more conservatively rated.

 

One other thing to monitor is the actual battery current and 'direction' using an amp meter connected from the - terminal of the battery to the ground bus. To do this with an analog meter a center reading type is needed.
http://www.ebay.com.my/itm/DC-Analo...026?pt=LH_DefaultDomain_0&hash=item1c5108b76a

Current in from the panel results in a + deflection, current to the loads results in a - deflection. When there is panel current and load current the sum of the currents will be displayed as the balance of charge or discharge currents for the system on the meter.

I do this on my system but use a computer generated graphics display with PIC micro-controllers for the results instead of a meter for a quick indication of power flow. The GREEN (that turns to RED when loads exceed panel power) color cube displays power to batteries minus loads and the WHITE cube is a display of panel input power. These displays are generated from real-time data with the cube color, spin rates and size encoding basic voltage/current/power data. The system also creates simple time graphs of system parameters with bulk storage of each 30 seconds of data that can be downloaded later.
Your system is a great basic start and the possibilities of what you can do in the future is endless.