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post #1 of 17 (permalink) Old 02-01-2020, 16:54 Thread Starter
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Question Solar panel fuse/breaker question :)

A question/advice requested re: solar panels ...

I've got a question re: fusing/breaker for a solar panel setup I'm installing on a van conversion - just want to sense-check my thoughts against someone else's brains, maybe someone with more experience of solar than me Thanks in advance!

So, my panels are 2x 270w Perlight Delta All Black ones… These: https://midsummerwholesale.co.uk/pdf...ack-54-270.pdf

As I understand it, it's good practise to fuse any power source as early as possible, be that a battery or solar panel.

I obviously don't want a fuse on the outside, that'd be a pain! So am thinking that as the solar cable will come in via an entry gland that's above a top side cupboard (cupboard yet to be built!), then I could pop a circuit breaker in that cupboard - nice & convenient.

My calcs, then some questions:

- Panels state open circuit voltage of 36.07v, so I guess that's the max volts.
- They seem to say (on the PDF linked above) current at Pmax is 9.06a per panel, so that’s 18.12 amps max.
- I'll be connecting the panels in parallel (argued with myself on this... series would increase the voltage and this may be good in low light UK conditions to make sure the voltage is higher than the battery, and so enable the batts to charge... But then again if then ONE panel is shaded, I think it'd mess up the other if in series... Parallel won't increase the volts but will work better if one panel in partial shade, if I'm correct? Plus, doesn't the MPPT serve to increase the volts if needed, provided it has sufficient amps being delivered to it, to ensure the volts are sufficient for the battery to accept a charge? Of course the MPPT will be very close to the batteries to avoid any further V drop, nice thick cables too).

So with all of the above in mind, fuse/breaker size I think is:

9.06a per panel, parallel so doubled as above would be 18.12amps. Could I get away with a 20a breaker? (keen on using a breaker as I'm a bit crap at losing fuses!).


QUESTIONS

1 - Anyone sense-check my thoughts & calcs above? All opinions welcome... If I've messed up somewhere or am wrong, please do say so! Getting this right is more important than my pride for sure

2 - With cable thickness/amps capacity calcs I believe you need to add 25% as a safety margin, I'm imagining the same is NOT true of a fuse, as the fuse is intended to protect the cable (not the appliance) from overload/overheating - am I right about this? If so, what are the thoughts about a 20a breaker when the max amps is 18.12a? All good? (I doubt the MPPT would complain if somehow 20a was delivered to it, it's a 50a MPPT - plus the cable I used will be rated above that anyway)...


3 - What are thoughts on fusing both the + and - cables from the solar to the MPPT? Overkill/not needed or advisable? Been told both by solar folks in the past! Opinions appreciated.

4 - If I did go with a breaker of 20a, do you think a car audio one would work, like: https://www.amazon.co.uk/Buwico%C2%A...0175T00AS?th=1 ? (NOT an affiliate link! genuine question)... Issue is that the breaker linked is a 12v to 24v breaker, from what I understand this MAY be fine, the only risk being the plastic isn't rated to the (max) voltage of the panels, so a risk of arcing through the plastic... But surely there's a tolerance here?). Or would this maybe be better: https://www.amazon.co.uk/Circuit-Bre...15&sr=8-4&th=1 ?

Hmmmmm that's it, I think!

Cheers in advance

Last edited by MikeVan; 02-01-2020 at 17:21.
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post #2 of 17 (permalink) Old 02-01-2020, 21:04
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There are experts on here will be able to answer your questions - I'm not one of them! Just giving your post a gentle bump.

Jean
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post #3 of 17 (permalink) Old 02-01-2020, 22:05 Thread Starter
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Quote:
Originally Posted by jiwawa View Post
There are experts on here will be able to answer your questions - I'm not one of them! Just giving your post a gentle bump.
Thanks Appreciate the bump
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post #4 of 17 (permalink) Old 03-01-2020, 07:26
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I doubt whether an MPPT controller would be happy with double the usual voltage input. I don't think solar panels in series is a good idea.
Not sure whether the picture I have posted will show up. If not, I will put up some more piccies later.
These circuit breakers come in various amperages and are not expensive. They are ideal for thick solar cables. Have a look for them in the usual Fleabay.
Twenty amp fuse on an 18 Amp line is likely to trip/blow. Look on Google for fusing details in general practice.
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post #5 of 17 (permalink) Old 03-01-2020, 08:36
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Since my previous post, I have had a look at your solar panel details.
Are you putting together a 24V system for your new MH ? If not, then solar panels suggested are very high in voltage.
Bill
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post #6 of 17 (permalink) Old 03-01-2020, 10:06
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My thought for what it is worth:

A single panel at 270w seems more than adequate. I have a single 120W with 2x110ah batteries and have no problems in maintaining power even at New Year for 4 days.

I can see nothing useful in connecting panels in series to give more volts only for the regulator to reduce it.
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post #7 of 17 (permalink) Old 04-01-2020, 18:22 Thread Starter
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Quote:
Originally Posted by bc109 View Post
I doubt whether an MPPT controller would be happy with double the usual voltage input. I don't think solar panels in series is a good idea.
Not sure whether the picture I have posted will show up. If not, I will put up some more piccies later.
These circuit breakers come in various amperages and are not expensive. They are ideal for thick solar cables. Have a look for them in the usual Fleabay.
Twenty amp fuse on an 18 Amp line is likely to trip/blow. Look on Google for fusing details in general practice.
Bill
Thanks for your reply

This is the MPP - https://www.photonicuniverse.com/en/...p-to-150V.html it's rated up to 150v, so should be okay with the panels in any configuration I think?

Quite a few are pushing to do the panels in series, the idea being on cloudy days when normally there wouldn't be enough volts to give a charge (autumn, early spring, def. winter), then with the panels in series, there's a chance of enough volts still.

Personally I'm leaning towards parallel, as in series if one panel is in shade or has an issue, the circuit is gone pretty much = no charge.

Will check those breakers - thanks
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post #8 of 17 (permalink) Old 04-01-2020, 18:33 Thread Starter
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Quote:
Originally Posted by bc109 View Post
Since my previous post, I have had a look at your solar panel details.
Are you putting together a 24V system for your new MH ? If not, then solar panels suggested are very high in voltage.
Bill
12v system (2 x 110 tubular gel batteries in parallel to give 220amp hour).

MPPT should take the voltage from the panels though I think? (unless I've worked something out wrong!) - It's this MPPT: https://www.photonicuniverse.com/en/...p-to-150V.html - takes up to 150v.

In theory the MPPT should accept the extra volts fine (up to 150v) and convert it to (up to) 50a charge for the batteries. As I understand it, ideally a charing current should be 15% to 25% of the battery (bank) total capacity (for gel or AGM anyway). So that'd be 33a to 55a... So the MPPT should match the battery bank capacity I think - and hopefully I've not made a mistake re: the max volts the panels will kick out and max the MPPT linked above is happy with? Hope I haven't! :S

Of course in low light UK, likely not to get the 50a except in high summer (and even then... who knows!), but hopefully even in autumn & winter I'll get SOME output... I hope (may have to move to Spain for winters if not! Ha!).

What do you think bc109?

Quote:
Originally Posted by rayc View Post
My thought for what it is worth:

A single panel at 270w seems more than adequate. I have a single 120W with 2x110ah batteries and have no problems in maintaining power even at New Year for 4 days.

I can see nothing useful in connecting panels in series to give more volts only for the regulator to reduce it.
I have 2 at 270 as am being cautious - I'll be living in the van fulltime for a bit, possibly over winter, and will need to run a fridge & charge a laptop etc (I work online). Of course I'll do the obvious & charge laptop when driving as much as possible (split charging with a voltage moderator too to ensure good charging), but still, just want to make sure

Re: Connecting in series, I mentioned just now above but it's been suggested to me by a few people, that series is good for low-light in winter/autumn/sprint, if you need to get charge as it'll ensure a higher chance of enough volts to charge the battery when perhaps there wouldn't normally be enough - but I prefer parallel usually as in series if one is shaded it reduces the charge to next to nothing... and 2 panels on a van roof takes up a fair amount of space so there's a chance of shading on one etc, whereas trying to ensure one is in full light seems an easier task (if parking between trees etc etc).

Hopefully with 2 x 270 panels I'll be fine anyway, but I'm leaning towards parallel

Thanks for the info on NYE - was it especially sunny for you where you were, or overcast etc? Would be really interested to know any charging stats if you had them (max current given, how many charging hours you had etc) - Absolutely no worries if not though! Just really interesting to hear facts of how someone's solar is working in winter
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post #9 of 17 (permalink) Old 04-01-2020, 20:49
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Much too complicated for me I just ensure the battery voltages remain as close to 12.7 under no sunlight as possible. I can see some merit in connecting two panels in parallel but for the life of me not in series.
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post #10 of 17 (permalink) Old 04-01-2020, 21:25
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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
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