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post #11 of 17 (permalink) Old 05-01-2020, 00:06 Thread Starter
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Originally Posted by bc109 View Post
A 12V system is normal for European Motor Homes, although there will be exceptions to the rule. Perhaps someone can suggest a few.
A charging voltage for a 12V system( meaning battery voltage ) is about 14 to 15 volts. A "12V" solar panel will provide this easily in broad daylight. Any thoughts of a 24V system would mean items like fridges, heaters and so on would be special, meaning expensive and hard to source.

If you are concerned about insufficient voltage in Winter weather, then I suggest a small voltage solar panel, say 4V, in series would provide a little extra boost. But if you search through the technical topics on this site, then no-one seems to have the problems you are anticipating.

The more likely problem would be insufficient electrical storage, meaning insufficient batteries on board. You will get extra storage by normal voltage solar panels in parallel with batteries to handle the extra current input and a controller also happy with the extra current capability. The batteries must be in parallel and of the same type in all respects.
I hope this info is helpful
Bill
Hi Bill, thanks for your reply...

I get that there'll be enough solar light power to give over 12v (as you say, 14 to 15v) at the optimum times, but from what I read the UK on average has, summer, around 5hrs of (charging) daylight hours, down to much less than that in winter. There's more daylight hours than this of course but from what I read the average is 5hours of charging hours, and the goal of series (from the folks that suggest series) seems to be that you can extend those hours - so the times earlier in the day when there's not quite enough voltage kicked out from the panels in parallel yet would, in series, kick out enough and so start charging quite a bit earlier in the day, or on quite cloudy days too.

With 220ah of batteries and a lot of power use during winter & colder months (diesel heating firing up once per day takes 10ah in it's initial start-up, then a fair bit until van is up to temp, then much less to maintain warm van), plus laptop charging, fridge running on 12v sometimes (may opt for a 3-way though), etc etc, I think I'll need a fair amount - see here: http://tinyurl.com/sfbculp for an example of the calcs I've been running, this one is for winter so a worst case scenario).

So worst case I'll draw 163amps over a 24 hour period. With panels max output at 50a (and 50a MPPT), but likely in winter only a couple of hours at a decent output (likely then less than 50a still in winter even at peak daylight hours as I understand it), I'll be lucky to replace 100amps into the battery bank. Unless I'm wrong?

I'd get more batteries as you mention... BUT the issue as I understand here, is you're meant to charge with at least 15% of the battery bank's total capacity in ah, as the charging current... and up to 25%. So if I add more panels, I'll need more solar (and I've run out of roof space ) Source of this: https://www.mastervolt.com/charging-batteries/ (it's for gel or AGM, my batteries are tubular gel).

So the series vs parallel is basically just trying to figure out what'll give me most ah charge put into the bank over daylight hours, in order to minimise needing to go for a drive just to charge up Of course I'll likely be driving a fair bit anyway which will help, but I want that to be a choice as much as possible, and less dictated by needing some charge. I'll also have a backup little suitcase genny too, I reckon.

Lots to think about! I was leaning towards parallel as each panel is more independent then, but some make valid arguments for series - I'm just struggling to decide! Still, I guess I can keep the config based externally anyhow, so I can always change that even once fitted, so long as I make sure cables can take parallel wired panels (which I'd likely do anyway - nice thick cables to avoid any voltage drop, especially after the MPPT part of the circuit where it's on a lower voltage. MPPT will also be next to the batteries).

Sooooo. Still wondering
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post #12 of 17 (permalink) Old 05-01-2020, 07:14
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I had a couple of 508d and 608d Merc vans in the 80s and both had two 12v batteries in series for 24v starting. But the vans other electrics were only 12v so tapped midway. They were great motorhome conversion vans but not fast.

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post #13 of 17 (permalink) Old 05-01-2020, 07:26
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hi mike

something to consider is that the panels work best if the panels are pointing exactly at the sun and the output is not so good if they are fitted flat on the roof

is there a mppt controller that works on say 40v input and 12v output i thaught

i will ask a guy here on site that has some big panels pointing to the sun and he should know as he works for the local m/home repair shop


barry
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post #14 of 17 (permalink) Old 05-01-2020, 11:47
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Quote:
Originally Posted by MikeVan View Post

Lots to think about! I was leaning towards parallel as each panel is more independent then, but some make valid arguments for series - I'm just struggling to decide! Still, I guess I can keep the config based externally anyhow, so I can always change that even once fitted, so long as I make sure cables can take parallel wired panels (which I'd likely do anyway - nice thick cables to avoid any voltage drop, especially after the MPPT part of the circuit where it's on a lower voltage. MPPT will also be next to the batteries).

Sooooo. Still wondering
Why don’t you wire each of the two panels independently from the roof to the location of the MPPT controller. This will then give you the option to connect them in parallel or series immediately before the connection to the controller. In this way you can easily experiment with which suits you best.

If you need a connection diagram then just shout. It will take two minutes to change from parallel to series if you need to.
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post #15 of 17 (permalink) Old 05-01-2020, 13:40
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post #16 of 17 (permalink) Old 01-08-2020, 00:30 Thread Starter
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Originally Posted by kabundi View Post
Why don’t you wire each of the two panels independently from the roof to the location of the MPPT controller. This will then give you the option to connect them in parallel or series immediately before the connection to the controller. In this way you can easily experiment with which suits you best.

If you need a connection diagram then just shout. It will take two minutes to change from parallel to series if you need to.
Quote:
Originally Posted by kabundi View Post
Why don’t you wire each of the two panels independently from the roof to the location of the MPPT controller. This will then give you the option to connect them in parallel or series immediately before the connection to the controller. In this way you can easily experiment with which suits you best.

If you need a connection diagram then just shout. It will take two minutes to change from parallel to series if you need to.

Oooops! I missed that reply, so sorry!

That sounds like a good idea! Guess I'd need to isolate the panels before doing the change, rather than hot-swapping. Hmmm you've got me thinking now, I saw a thread about using a DPDT 'break before make' switch switch to make it possible to change it on the flick of a switch. Will try to find the thread/image of the diagram (different forum).
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post #17 of 17 (permalink) Old 01-08-2020, 11:05
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Easiest way to ‘isolate’ the solar panels is to throw a blanket over them for the period that you are working on the connections. This will stop any output from the panels so you can work safely.
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