Measuring output during the day....

[SheepRustler]

Hello all,

I'm keen to create a small display to show the current (bad word!) output of my panel at any time of the day. I'm sure you can buy something, but I like making stuff based on Arduino's. I have a small weather station made from a basic anemometer, a temperature probe and a atmospheric pressure sensor and an Arduino Nano. The whole thing cost less than £20 ($30) plus a bit of soldering time and I'd like to do something similar for my small solar powered pump system so I can monitor its performance and what the current draw on the system is. Here's what I have:

50w panel Like the attached image.jpg

A controller like the attached image.jpg

An (old) 130Ah battery from a Land Rover.

What I'd like to measure and display is the real time output from the panel (watts would be good), the battery voltage and the current draw from the Shurflo water pump attached.

Measuring the volts ( with the panel disconnected ) I get about 35 v ( dull winter day) but when connected to the controller I get about 13 v on both the panel screw terminals of the controller and the same on the battery, regardless of the weather. This drops to zero on the panel terminals when the green charging light goes out on the controller at night. (No surprise there!)

I can measure the current draw on the pump easily enough using the 30a version of the sparkfun acs 712 current sensor connected to my Arduino NANO and, using a voltage divider fed from the battery terminals, I can get a relative 5v input onto an Analogue Arduino pin to display the battery voltage, but how can I measure (or calculate) the realtime voltage/current/power out of the solar panel when it's connected to the controller? Researching this a bit I now realise it's not as straightforward as I first thought.....

Any advice? Once up and running I'll happily post my Arduino code and sensor hardware setup if anyone's interested. (Ditto for the weather station code if anyone wants it)

[Sunking]

All you need is a current and voltage transducer, plus writing a program. Otherwise you just use a volt and current meter to read it at any specific time.

[jony101]

all you need is some led meters, some wires and toggle switch. Also a dc wattmeter. Easy to make and tells you everything you want to know.
the 0-99 dc volt led cost me 7 dollars (this reads panel voltage)
the 90 volt 30 amp combo led meter cost me 20 dollar (this connects between battery and controller reads volts/amps going to battery)
the 60 volt dc 100 amp wattmeter cost 13 dollar (this connects from battery to your load reads amps/watts/peak amps used)
the yellow xt60 connectors handle up to 60 amps cost 10 dollars for 10 sets.

during the day you can tell whether your in float mode or bulk mode by reading the voltage, at night time you can read the battery voltage and get a rough idea its charge status. Consumes very little power and i leave mine connected to battery 24/7.

xt60 connector large a.jpg
a dc wattmeter.jpg

[SheepRustler]

all you need is some led meters, some wires and toggle switch. Also a dc wattmeter. Easy to make and tells you everything you want to know.
the 0-99 dc volt led cost me 7 dollars (this reads panel voltage)
the 90 volt 30 amp combo led meter cost me 20 dollar (this connects between battery and controller reads volts/amps going to battery)
the 60 volt dc 100 amp wattmeter cost 13 dollar (this connects from battery to your load reads amps/watts/peak amps used)
the yellow xt60 connectors handle up to 60 amps cost 10 dollars for 10 sets.

during the day you can tell whether your in float mode or bulk mode by reading the voltage, at night time you can read the battery voltage and get a rough idea its charge status. Consumes very little power and i leave mine connected to battery 24/7.

[ATTACH=CONFIG]5631[/ATTACH]
[ATTACH=CONFIG]5632[/ATTACH]

Thanks Jony101,
I like that setup. The measurement that I'm finding it difficult to get is the panel voltage, 32.2v I guess in your picture, if I measure this at the panel input terminals on the controller it floats around 13.5v (the same as the battery) if I disconnect the panel I get about 32v (during the day).

I notice you have a switch - is this to swap over to measurement mode or do you have two kinds of controller?

[inetdog]

Thanks Jony101,
I like that setup. The measurement that I'm finding it difficult to get is the panel voltage, 32.2v I guess in your picture, if I measure this at the panel input terminals on the controller it floats around 13.5v (the same as the battery) if I disconnect the panel I get about 32v (during the day).

I notice you have a switch - is this to swap over to measurement mode or do you have two kinds of controller?

That voltage behavior is perfectly normal for a PWM type charge controller. If you think that you have an MPPT controller you are mistaken or deceived.
With a Voc of 32V your panels will have a Vmp somewhere above 25V, so you are losing half of the potential power output of your panels because of the way your CC works.

You definitely want to measure the panel voltage at the CC input terminals. It should be very close to what you would measure at the panels themselves unless you have severely undersized the connecting wiring.

[SheepRustler]

That voltage behavior is perfectly normal for a PWM type charge controller. If you think that you have an MPPT controller you are mistaken or deceived.
With a Voc of 32V your panels will have a Vmp somewhere above 25V, so you are losing half of the potential power output of your panels because of the way your CC works.

You definitely want to measure the panel voltage at the CC input terminals. It should be very close to what you would measure at the panels themselves unless you have severely undersized the connecting wiring.

inetdog,
Yup its definitely a PWM charge controller - it says so on the outside - maybe I should invest in a MPPT as I need every last millivolt due to a lack of sun around here.......

[Amy@altE]

Is there a label on the back of the solar panel that gives you any information like the brand and model? The panel you gave the link to is a 12V nominal panel, which should put out about 22V when disconnected. You are describing the output for a 20V nominal panel with 35V. If you don't have a label, count how many cells it is made from. Are there 36, 60, or 72 squares of silicon on the front? If anything other than 36 cells, you need an MPPT to get the full output of the panel.

[Sunking]

inetdog,
Yup its definitely a PWM charge controller - it says so on the outside - maybe I should invest in a MPPT as I need every last millivolt due to a lack of sun around here.......

Here is the good news you will absolutely love.

You have a panel with a VMP that approx = 25 volts means you rPWM controller turns your 50 wat panel into a 25 watt panel. Told you would love it.

[SheepRustler]

Is there a label on the back of the solar panel that gives you any information like the brand and model? The panel you gave the link to is a 12V nominal panel, which should put out about 22V when disconnected. You are describing the output for a 20V nominal panel with 35V. If you don't have a label, count how many cells it is made from. Are there 36, 60, or 72 squares of silicon on the front? If anything other than 36 cells, you need an MPPT to get the full output of the panel.

Yes, there a label on the back Amy, but I cant recall what it says... I'll unbolt it and have a look as soon as the snow disappears off the roof...

[SheepRustler]

Here is the good news you will absolutely love.

You have a panel with a VMP that approx = 25 volts means you rPWM controller turns your 50 wat panel into a 25 watt panel. Told you would love it.

I don't (yet) understand the difference twixt PWM other CC's (I'll research it...) so perhaps I'll put off buying another panel just for now as I may not yet need it.... Thanks Sunking for the pointer!

[Amy@altE]

I don't (yet) understand the difference twixt PWM other CC's (I'll research it...) so perhaps I'll put off buying another panel just for now as I may not yet need it.... Thanks Sunking for the pointer!

There's several YouTube videos on the subject, including one I made. Search on YouTube for "MPPT vs. PWM Charge Controllers"

[SheepRustler]

There's several YouTube videos on the subject, including one I made. Search on YouTube for "MPPT vs. PWM Charge Controllers"

Amy, A nice informative video, thanks for posting that, it much clear to me now. With future expansion in mind I'm going to invest in a MPPT controller I think, especially as (even though my system is very low demand) I seem to be on the edge of not achieving a decent charge during the day during the short winter days. Suspecting a tired battery I borrowed a new leisure battery for a week and found that this too didn't seem to be able to cope with the draw from the pump. Hopefully I'll get a a bit more efficiency from a MPPT.

Thanks

[inetdog]

Amy, A nice informative video, thanks for posting that, it much clear to me now. With future expansion in mind I'm going to invest in a MPPT controller I think, especially as (even though my system is very low demand) I seem to be on the edge of not achieving a decent charge during the day during the short winter days. Suspecting a tired battery I borrowed a new leisure battery for a week and found that this too didn't seem to be able to cope with the draw from the pump. Hopefully I'll get a a bit more efficiency from a MPPT.

Thanks

An MPPT CC also lets you expand your system using lower cost per watt panels made primarily for grid tie systems.