Solar panel wire

Thanks for the reply. We dont intend to connect to the car to charge the batterys , the same as we havent with our present van , but rely on solar for the house batterys. Our normal daily drive time is only 2 or 3 hours and have not had a problem.
Den and Col

Hi Frank. The panels will be in parallel and i guess the run from the panel would be at least 25 ft, and the regulator is a Xantrax 35 amp reg.
Just one question with regards wire size as i have read that there are a few different ways that are used to measure automotive wire. Is 8 B&S (i believe that stands for battery and starter but happy to be corrected ) the same as 8AWG. I did see on the table that 8AWG has a conductor that is 3.26 mm but i havent purchased the wire that was recommended so not sure if 8 B&S is the same or different size conductor.
Den and Col

Hi Den and Col,

B&S stands for Browne and Sharpe (dunno about the "e"s on the end, one or other has it I think :-) ) Anyway, B&S is interchangeable with AWG.

If your panels put out 8 amps each and the cable run is 25 ft of 8 B&S, the voltage drop will be 0.78, about 19 watts loss out of 390. I imagine that is acceptable.

Cheers

Frank

Thanks for the replys Frank.
Guess you are talking about missing out on about 8 amps for the whole day.
The problem is that every time i think about the van i seem to find a reason to spend another couple of hundred dollars.The overall cost just seems to keep climbing. Will talk to the manufacturer about going in series with the panels but i do like the idea of the reg being fitted in the boot with a remote readout. From memory you are talking about a MPPT regulator? Will do some more research to see if i can get one that will give charge rate /volts and load via a remote head.
De and Col

Den and Col,

It's pretty hard to specify how many amp-hours a day you'd lose, as it depends on conditions - shade, cloud, air clarity, season, latitude, the angle of your panels to the sun - I assume they will be flat on the roof.

I think with 390 watts of panels flat on the roof and with the panels in series feeding an MPPT controller through 8 B&S cable you'll be doing ok.

In good sun the output from an MPPT regulator hooked up to your panels in series could be around 27 amps. Make sure the regulator is big enough and also the cable from the reg to the battery for that sort of current. If you have a 2 metre run from the reg to the battery, I'd be going for 6 B&S, only because on the charging side, tenths of a volt are important for multi-stage chargers, and a good MPPT regulator will be multi-stage.

BTW, how big are your batteries (amp-hours)?

Frank

Will ring the manufacturer on Monday after i have sussed out a suitable reg. We're having 3x120 amp hr AGM batterys fitted and have decided to go with a 3 way fridge so no high current draw from that angle. Have one in the present van and works great.
You don't have any tips re MPPT regulatorwith a remote readout?
Den and Col

One other question Frank, having a quick look i note that the regulators are for 12,24,or 48 volt, therefore does this mean that you cant run 3 panels in series and have 36v.
Also if you have shade on one panel when in series is this going to drop the charge drastically. That is to say do you only miss the output of that panel or does it mean that the resultant drop in overall voltage means little output due to a low total voltage.
Thanks again for the help.
Den and Col

When you see a regulator rated at 12/24/48V, then this is most likely the battery voltage.
So if your system has a 12V battery, select a 12V regulator.
If you want to wire 3 12V panels in series which gives you minimum current hence minimum voltage drop between the panels and the regulator, but maximum input voltage (up to 66V), select a MPPT solar regulator which 'transforms' the high input voltage to the lower battery voltage, making extra charging amps in the process.
This MPPT regulator needs to be specced 80V or higher on the input side(under cold conditions the solar input voltage can creep up quite a bit).
B&S8 will be sufficient if you use the panels in a series configuration.

And to answer your other question about shading:
No, shading of one or two panels won't affect the other panels as long as each panel has a bypass diode.

cheers, Peter

Den and Col,

In this thread I mentioned the GSL brand. They make a 15, 30 and 60 amp MPPT regulator, all with a remote display option. I have had good results with their 30 amp model, despite the opinions of some posters in that thread.

In that topic others mentioned Morningstar which do have a remote monitor option on some models.

There are plenty with displays, but fewer with remote displays. Maybe some others here can help?

The 12, 24 or 48 volts regulators refer to the nominal voltage of the battery system they are connected to. My regulator can auto-detect whether its connected to a 12 volt or 24 volt system. Others may detect a greater range, and others may be good for only one specific nominal voltage.

So-called 12 volt panels have a typical open circuit voltage of about 22 volts (some more, some less) which drops under load. If you put 3 in series you will have up to 66 volts going into your regulator. Fine - in fact, better - as long as the wiring meets the required standard safety-wise and the regulator is designed to take that input voltage. Simplistically, an MPPT regulator will mess around with the combination of volts and current to get the maximum watts out of the panel - and that is what you want.

Panels the size of yours connected in series need bypass diodes. By-pass diodes help to control the effects of shade on part of a panel. I have found that after changing my panels from all parallel to serial, shade on part of a panel has less effect on the output that when they were all in parallel.

Larger so-called 12V panels like yours usually have them built in, so setting them up in series is as easy as setting them up in parallel - it's just a matter of where the wires go. Best to check for the diodes, though - open the junction boxes and have a look.

Without the diodes, shade on part of a panel will drastically affect the output of the system and in the worst case can damage cells or panels. Heaps of infohere if your a techie person.

Cheers

Frank

Thanks for that info.I am doing more reading on the net and getting a better understanding of things now. Can see where the benefits are in using the MPPT.
A 30 amp MPPT is too low i feel and 60 is an overkill .Thanks for your info as well Peter. The better informed i am the easier to make the correct choice
Den and Col.

Hello again,

....a 30A MPPT is too low....

Yes, but only on paper.

Real situation:

Max theoretical solar power is 3x135W=405W, but only if the sun is perpendicular to the panels, and if the cells are cooled to 25 degrees.
In real life, the solar wattage will be at least 10% lower (at perpendicular), due to cell heating, dropping the max available output to 365W.
The wires and the solar regulator gobble up around 5% of this, leaving only 346W of charging power.
If the battery's deeply discharged, this will result in a charging current of max 346W/12V=29A, less if the depth of discharge was lower.
But again, only while the sun is perpendicular to the panels.
You can't do any damage by maxing out a MPPT regulator.
In a nutshell, forking out extra Dollars for a higher specced MPPT doesn't really make sense in this case.

cheers, Peter

This has been an interesting and informative thread. When I hooked my 3x80w panels up I never gave any thought to wiring them in series. I have a Plasmatronics PL20 which is not an MPPT Regulator. Is there any benefit in me changing to series? I believe the PL20 can handle 100v input.

Regards,
Bob

Hi Robert,

I had a quick look through the PL series reference and user manuals. It was a quick look, not a thorough read, but I didn't find anything about connecting the panels in series. Might be worth asking Plasmatronics.

I think perhaps the main benefit would be reduced losses in the cable between the panels and the regulator, because if you connect them in series the current will only one third of what it is now.

If your cables are fat enough to give you minimal losses now, you probably won't see much benefit. However if they're long and a bit on the thin side, then you could well pick up a worthwhile benefit.

Have a play with the calculator mentioned in my reply at the top. I'm guessing your panels output about 4.8 amps, call it 5 for easy maths. In parallel, in a perfect world, you have a total current of 15 amps in the cable from the panels to the reg. In series it would be 5 amps.

Choose a wire gauge, choose a one-way cable length, choose a current (5 or 15) and calculate. The voltage drop times the current will be your wasted watts, which you want to be a low as practicable.

You may need a wire gauge conversion chart to help.

Frank

Thanks Frank,

I have used 8mm2 cable all round so using your tables and calculator I shouldn't see much of a voltage drop. Two of my panels are side by side and are paralleled panel to panel with only a 1 meter cable to the regulator. The other panel is down the end of my canopy and the cable is about 4 meters so I would be seeing 10A in one cable and 5A in the other. The distance from regulator to batteries is about 1 meter. After doing the sums there is probably no good reason to change my setup.

I wish the panels were as cheap when I bought mine as they are now. I would love to have a couple of 200w panels powering my gear. Even with 240w I still have to manage my power consumption carefully at times.

Thanks again,
Bob

Bob,

I envy you your rig :-)

Is there room in there for, say, a 120 watt fold-up portable array. Give it 10 metres of decent sheathed twin core cable (Repco sell it as Narva 50 amp), terminate with an Anderson plug, provide an Anderson input to your reg in parallel with the other panels.

In VERY favourable conditions you may max out your reg, but as Peter from Battery Value said, that's ok - the reg will just deliver what it can but on the odd occasion when there's more available it'll just be lost. You'd have 360 watts which isn't too far off 400, you don't need to upgrade your expensive and very good reg and you have a portable panel which you can move around to maximise input that you might not be getting from your roof-mounted ones.

Just a thought

Frank

Bob,

Is there room in your rig for, say, a 120 watt fold-up portable array. Give it 10 metres of decent sheathed twin core cable (Repco sell it as Narva 50 amp), terminate with an Anderson plug, provide an Anderson input to your reg in parallel with the other panels.

In very favourable conditions you may max out your reg, but as Peter from Battery Value said, that's ok - the reg will just deliver what it can but on the odd occasion when there's more available it'll just be lost. 360 watts is close to 400, you don't need to upgrade your expensive and very good reg, you have a portable panel which you can move around to maximise input that you might not be getting from your roof-mounted ones and better output in less than perfect conditions.

Just a thought

Frank

Frank,

I am like a boy in a lolly shop. I fill my pockets up and I still want more. I probably don't need any more but I have thought of doing as you suggest and getting a fold up panel. I am sure I can find a spot for it somewhere.

Regards,
Bob

Therefore placing the regulator in the boot near the batterys would be the way to go? In the photos of the display van that we have it appears as though the voltage display in the van is a remote display unit so i assume the reg is in the boot. Will add that question to the list for the builder.
Thanks for the reply.
Den and Col

If you lose volts in a circuit carrying current, you lose watts, doesn't matter where the loss is. You're right in the sense that a volt lost before the regulator is less of a loss than a volt lost after the regulator because you lose fewer watts. However, it's a risky statement to say, without qualification, "Voltage drop between the panels and the regulator is really not an issue worth worrying about"

The 6 amp example was too low. Those panels are more likely to deliver about 8 amps. In parallel they would total 24 amps. With 2.5mm2 cable over 40 ft at 24 amps there would be a 5 volt drop.

That IS a concern, it's 120 watts that will never get to the regulator - 120 watts wasted out of 390, about 30%.

If he wants to save on copper he should install the panels in series. Then the cable he has already bought will be fine. In a parallel array, at 24 amps he will lose 1.25 volts over a 40 ft run - that's 32 watts lost from a 390 watt array, probably acceptable if an 8% loss is acceptable to him. (He did ask for negligible loss - it's up to him to decide what is negligible, I guess.)

Thanks Peter and Margaret. Will file that away in the computer for future reference.
Den n Col

I was wanting to stick with Xantrex if i go with the series installation and mppt train of thought, but as they are 60 amp, and over $900 i think it is a bit of an over kill.Trying to find something around 40 amp so there is a bit of capacity for expansion and is of reasonable quality.At $900 would probably go back to parellel and spend the money on an extra panel.
With regards the excess wire, we plan on getting them to use the 7.9 sq mm wire for the 12 volt outlets as well.
Den and Col