Solar dilema

[dkwilson]

My dilemma.

I have 5 solar panels, 2 new 40w and three old Solarex 40w panels. They are all 12v panels – approx 19-20v open circuit. Are they compatible to hook up together. I intend to use a Morningstar 15 amp Sunsaver MPPT regulator. I propose to use two sets of panels each hooked up in parallel and then connected together in series then to the regulator or controller. Would the “parallel then series” set up improve the compatibility of the two sets of panels given that the voltage would be the sum of both sets. The controller apparently can handle the voltage.

Next question. My vehicle, Disco 2, has a calcium battery and I think a 140 amp alternator. For vehicle charging of the leisure battery when underway will the Disco set up harm an AGM if it whacks it with some heavy amps? Isolator and cables are more than adequate (Redarc and 2 B&S).

[d2dave]

If it was me I would just run them all in parallel.
Just make sure you mount the regulator near the battery not on the panel.

If your aux battery is a medium to large the alternator won't hurt it.

Dave.

[Blknight.aus]

depending on the input voltage of the regulator I would suggest that a full 12v in parrallel setup with high quality blocking diodes would be the best bet although thats potentially going to cost you a couple of hundred mA per diode/panel.

But it does stop partial shading causing headaches.

If you can set the array up so that all panels get lit you can do without the blocking diodes and run a parallel setup but when one panel dies it will pull the power out of the system.

if you flatten the AGM and then dump 140 amps from the alternator into it its not going to like you very much. Id suggest putting something in that will act as a current limiter if you plan on flattening the battery too much but this wont be a problem if you keep the battery inside its normal operating spec.

[d2dave]

Dave,
Can you explain what these blocking diodes are for?

I have two 80 watt panels which I take when I go camping. I have one connected to the car to run the engle and the other to the caravan to run lights and water pump.

As 80 watts is a bit of overkill for the caravan I have made up a lead to connect the two in parallel to run the engle on a cloudy day.

This will deliver about 5 amps each when sunny to about one amp each when heavy cloud.

Ok, lets say the sun is shining and I am getting five amps x two and the wind blows one of them over and therefore one is out of action, don't I still get five amps from the other one?

Dave.

[fraser130]

The only advantage to running them in a series then parallel config would be to double the voltage, which would reduce the current, which means longer cable runs for the same voltage drop, but you have 5 panels, which means one panel left over. you should only series identical panels(same age etc), so two sets, one set of new panels in series, one set of old panels in series, then parallel the outputs of the two sets.
Thats a lot of wiring to put together on site!
If you just parallel the lot, they can all "piggy-back" off each other, so you can add and remove panels as you wish.
The MPPT regulator will pull the voltage down to the point where you are getting maximum total output from whatever panels you add.

Cheers,
Fraser

[Blknight.aus]

the panel may still be outputting 5 amps but the one thats fallen over will now be drawing current.

if you think of it like a pair simple permanant magnet generators in parralell while both are being driven your getting power out of both of them. If you remove the drive from one it will carry on spinning becasue its gone from being a generator to a motor. The output from the generator thats still being driven goes to making the undriven generator turn instead of into the batteries.

a blocking diode also forms the simplest form of charging regulator because it stops the battery from discharging into the panel when its not providing charge.

[adonuff]

Hi I was wondering if or how do I measure amps, I have a digital multi meter and it tells me how many volts my panels are putting out but have no idea how many amps??
Andrew

[d2dave]

Andrew,
Most digital multimeters usually have a current measurement of ten amps.
If you have this you will need to unplug the non common lead and put it into the current measurement jack. You then remove one of your solar panel leads from the battery and connect it to one of the multimeter leads. Then connect the other lead to your battery. Don't worry about which way round the leads are. If it is wrong you will just get a minus before the reading.

The above procedure is known as connecting the multimeter "In series"

Dave.

[adonuff]

Thanks Mr Whippy I will try it out soon as the sun comes up.
Andrew

[d2dave]

Andrew,
I assume then that your multimeter has amp measurement.

It is easy for me as I have a hi tech solar regulator which tells me amp input as well as many other things.

Dave.

[adonuff]

It does I have 10 amp outlet, fiddling about under the flouro lights at the moment, its telling me I;m getting 7.5 volts and .1 of an amp, bit inconclusive will try it with sun in the morning

Would be good if someone could enlighten me as to parallal and series connections ? I assume it would be simular to parallal and series battery wiring?

If there is a good web site that deals with this I would love to know.

Thanks Andrew

[Blknight.aus]

thats exactly right.

if you join all the positives to all the positives and all the negatives to all the negatives then its all in parallel

if you go positive of one to the negative of the next then from positive to negative and make a big long chain then thats in series.

try these for the basics in batteries

Battery Wiring (http://www.otherpower.com/otherpower_battery_wiring.html)
Learn how to wire solar panels and battery systems (http://partsonsale.com/learnwiring.htm)

panels work on the same basic principales but need extra care when it comes to where the regulators and/or blocking diodes go.

[d2dave]

It does I have 10 amp outlet, fiddling about under the flouro lights at the moment, its telling me I;m getting 7.5 volts and .1 of an amp, bit inconclusive will try it with sun in the morning

Thanks Andrew

That would be about right.
You cannot get anything worth while from a solar panel under artificial light.

Dave.

[adonuff]

Thanks everyone going out to try it out in the sunlight, Learning lots, going to eventually set up the caravan with batterys and solar panels. Soon as funds become available.

Andrew

[Blknight.aus]

when it comes to buying panels ebay and auction sites are your friend be wary of panels that are over about 3-4 years old.

FME its at about that age that they start to degrade, they still work, just not as well.

[d2dave]

the panel may still be outputting 5 amps but the one thats fallen over will now be drawing current.

if you think of it like a pair simple permanant magnet generators in parralell while both are being driven your getting power out of both of them. If you remove the drive from one it will carry on spinning becasue its gone from being a generator to a motor. The output from the generator thats still being driven goes to making the undriven generator turn instead of into the batteries.

a blocking diode also forms the simplest form of charging regulator because it stops the battery from discharging into the panel when its not providing charge.

Dave,
I have to disagree here. I have just tried this;

I connected my two panels in parallel. I put a huge load on my battery to make sure panels would work to full capacity.

Total current into the battery was 8.6 amps. I then turned one solar panel face down and placed a blanket over it.

Charge into my battery was then 4.1 amps. The other panel was not taking the current.

Dave.

[fraser130]

Dave,
I have to disagree here. I have just tried this;

I connected my two panels in parallel. I put a huge load on my battery to make sure panels would work to full capacity.

Total current into the battery was 8.6 amps. I then turned one solar panel face down and placed a blanket over it.

Charge into my battery was then 4.1 amps. The other panel was not taking the current.

Dave.

If you put them in series and try it, without bypass diodes you will get a very different result, give it a try!

[d2dave]

If you put them in series and try it, without bypass diodes you will get a very different result, give it a try!

This may be correct but in Daves(blknight) post on this he was talking in Parallel.

Dave.

[Blknight.aus]

Dave,
I have to disagree here. I have just tried this;

I connected my two panels in parallel. I put a huge load on my battery to make sure panels would work to full capacity.

Total current into the battery was 8.6 amps. I then turned one solar panel face down and placed a blanket over it.

Charge into my battery was then 4.1 amps. The other panel was not taking the current.

Dave.

ummm yes it was...
assuming you used the same panels

8.6/2=4.3 the blanketed panel was pulling down 200ma.

[fraser130]

All the panels I have owned have already had diodes in them to stop them drawing current if they are not producing voltage higher than the battery/circuit voltage.

Fraser

[d2dave]

ummm yes it was...
assuming you used the same panels

8.6/2=4.3 the blanketed panel was pulling down 200ma.

They aren't identical. One is 85 watt and one is 80 watt. The 80watt is also two years older.

I am going to have to do this again now and see what each panel is doing individually.

Dave.

[Blknight.aus]

They aren't identical. One is 85 watt and one is 80 watt. The 80watt is also two years older.

I am going to have to do this again now and see what each panel is doing individually.

Dave.

yep and if your panels dont match up nearly exactly in output dont try putting them in series.

[dkwilson]

G'day to all, and thank you for your comments. Parallel is the way to go.

Thanks again and cheers, travel safe, David