PWM Solar panel regulator measuring voltages

D

davidmh

Well-Known Member
Joined
30 Jan 2015
Messages
475
Visit site
I have a very simple solar panel and a PWM controller, please do not tell me I need a better controller I have what I have.
With the panel and battery connected
1. If I put a multi meter across the input terminals on the controller this will give me the voltage of the panel including cable drop. yes/no
2.If I put the meter across the out terminal that is connected to the battery this will give me the voltage the battery is seeing less any voltage drop. yes/no
3. If 1 is less than about 12.8 or so the battery will not charge the battery with 13.4 or so and it is charging yes/no
4. If the panel is not charging .no sun etc, is the voltage at 2 the real battery voltage or will it be higher due to the residual voltage from charging.

hope this makes sense I just want to know what the multi meter is really telling me

Thanks
David MH
 
Re 1 assuming you have some sun and the battery is not fully charged or you have decnt load on the battery, (lights on)the voltage you read at the input should very nearly approximate or be just slightly higher than the battery voltage. If you disconnect the battery this voltage read will be the no load voltage of the panel 18 to 20 volts. If battery is connected and fully charged you get a connection panel to battery via switch transistors which is connected and disconnected at a rate witha duty cycle depending on charge still going in to the battery. depending on the rate this may be very difficult to measure with DVM. This because DVM samples the voltage around twice per second for a short period of time. This sampling may coincide with on or off time of the controller. So not reliable. Just be mindfull the controller is intended to connect panel to battery until such time as battery is fully charged so needs to be protected from over charge. With a small panel may never happen.
Re 4 voltage at the output of the controller will also be the battery voltage. Yes if it has been on charge it will likely be higher than it will be later after it settles with no charge or with some discharge.
You seem concerned with volt drop of wiring. This is not as much a concern as you might expect for say a mast head light. If you want check again, with low charge battery or a load on battery and full sun, from pos of panel to pos of controller input. Likewise neg of controller to neg of input. Again same pos of controller to pos of battery then neg of controller to neg of battery. Should all be quite small less than .1 volt. ol'will
 
ol'will ^^ has given you the best answer ,but yes you are about right on your thinking.

As for (3) I understand what you say,but your battery will charge up to 12.8 ( if battery is lower) equalising the input (thereabouts)
but at 12.8 your battery will not be fully charged.

(4) it will be the battery voltage
 
Last edited:
Many thanks for your replies, I have managed to find and download a manual and this gives me more information. The unit can be set for Sealed Lead Acid, Gel or flooded, by flooded I assume they mean lead acid can you can top-up. For sealed lead acid which is what I have they give the following
Equalization 14.6v, Boost 14.4 v, Float 13.8v , reconnect at 12.6v. Thanks for the tip about measuring with a digital meter.
davidMH
 
davidmh said:
I have a very simple solar panel and a PWM controller, please do not tell me I need a better controller I have what I have.
With the panel and battery connected
1. If I put a multi meter across the input terminals on the controller this will give me the voltage of the panel including cable drop. yes/no
2.If I put the meter across the out terminal that is connected to the battery this will give me the voltage the battery is seeing less any voltage drop. yes/no
3. If 1 is less than about 12.8 or so the battery will not charge the battery with 13.4 or so and it is charging yes/no
4. If the panel is not charging .no sun etc, is the voltage at 2 the real battery voltage or will it be higher due to the residual voltage from charging.

hope this makes sense I just want to know what the multi meter is really telling me

Thanks
David MH
Click to expand...

Short answer... basically yes.

Long answer

1 .... yes at that point in time with that load.

2 .... what you see will depend on battery state and the frequency of PWM controller, if battery is low you will see charge voltage, if battery is charged you have pulses of charge (PWM), so battery voltage goes up and down depending on charge pulse cycle, multi meters measure close to the voltage between charge not the peak charge voltages.

3 .... a lead/acid flat battery will need 13.0 volt to take a charge, as as charge level increases so does the voltage up around 15.4 volt.

4 .... you will see battery voltage, but this varies, a) voltage will be higher immediately following charge, b) after say 12 hours with no load draw you will see true battery voltage around 12.8 fully charged, c) battery voltage varies with temperature, d) the fully charged voltage of a new will rise, it can be 13.1 volt instead of 12.8, over a period of time ( months ) it will fall back to 12.7/12.8.

No cable volt drop is considered in above.

Brian
 
You must log in or register to reply here.

Share this page

Top