Solar Charge Control
Good Morning
I've just ordered a 100w system for my pvc and will be installing it myself. I have a question regarding the position of the charge controller. Does it need to be near the batteries or can I put it somewhere "convenient"? You can appreciate there's not much spare space in a panel van!!
Any advice / opinions appreciated
Cheers
JK
Comments
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The theoretical answer is to put the controller as close to the battery as possible. Reasons for this. Less power loss from the cables by maximising the input cable length from the panel to the controller because the voltage is higher and shorter length to the battery when the voltage is lower. Also some controllers have temperature compensation. Real world I’m not sure it will make any appreciable difference. Almost every factory fitted panel I have seen the controller is normally stuck high up in a cupboard and on a folding panel the controller is stuck on the back of the panel. Is it worth considering a dual output controller so you can charge both the habitation and vechicle battery?
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We have a coach built and the battery is right at the back of the van, the charge controller is in a overhead locker above the front habitation seating some 4 to 5 mtrs away.
we have just spent 10 weeks in Spain and most of this has been off grid with no problems at all (100 watt)
Idealy close but not a real issue in our case!
Kev
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Evening
Thanks for informative replies. I was concerned about cable length and voltage drop but I guess in the scheme of things having the controller in the wardrobe about a meter fom the leisure battery and two from the vehicle battery won't matter at all. Boff, yes I've gone for a dual controller as I need I've had problems while in storage so need both batteries topped up. We mostly wild camp when away here in Spain so I'm after peace of mind. I'll let you know how the install goes.
Kev, enjoy Merrose again, we're not back until May so I'll let you know how warm it's been!
JK
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Just crossed the border from Spain yesterday, went through Somport tunnel this year, wow what a fascinating drive lovely scenery. We don’t start for a couple of weeks yet but the warmth of the coast of Spain has already disappeared for another 9 months.
Have a safe journey back and will pop up sometime in the year
Kev
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As far as I remember form my O-Level physics. Power loss is the Square of the Current x the resistance (I^2xR). The amount of current is more important than the resistance because if you double the current that is a factor of 4 where as if the resistance it is only a factor of 2. With a solar panel a typical output voltage is something like 17.5v and the charging voltage is 14v ish. Therefore there is a theoretical advantage in having the wiring from the controller to the battery as close as possible. In the real world not sure it makes much difference to a solar panel on top of a MH. But obviously it makes a huge difference in powelines which is why mains electricity is transmitted long distances at very high voltages and very low currents.
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The solar controller regulates its output to the battery, so the last thing you want are cable losses, reducing what the battery gets. It is far better it gets what the controller wants it to receive. Plus, as stated many controllers contain the battery temperature sensor for altering the charging values, so ideally it should be where it sees the temperature the battery sees.
That some commercial installers put it anywhere, including on portable panels the poorer designs simply stick them on the back, does not make them correct, normally it is no more than expedient. On the back of the panel then any included temperature compensation facility within the controller is fooled to drop the output voltage, as a byproduct of solar panels is heat, so they get hot!
There will be cable losses in the panel to the controller, but those don't affect what the controller determines the battery needs, the battery still gets what it should,
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You don’t get a lot of current output from a 100 W panel even at peak sunlight so although it’s good to have reasonable sized cables the volt drop should be fairly small in which case it doesn’t matter too much where the controller is.
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Morning
Thanks for some very informative replies. I'll let you know how the install goes. What is the best cable size please?
I'd add photos but that would probably take longer than the install!
JK
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I used, 4mm solar cable from the panel to the controller. The controller is next to the battery. Solar cable is relatively bulky similar to coax aeria cable. I was able to route my cable invisibly to the controller. I think that this is the best way of doing it. But as I stated before I am not sure how much real world difference it makes.
My shopping list included the following.
A length of solar cable which has a male mc4 at one end and a female at the other.
A MC4 disconnection tool (cost a couple of ££’s)
A port cable entry gland
A hole saw to make a neat hole in the roof 19mm iirc
Adhesive/ sealent I used Sikaflex 512
All of which is available online.
Fitting is straight forward Drilling the hole takes nerve. Cut the solar cable in half mark up the end that will be connected to the +ve output from the solar panel run the cables to your controller. NB the controller should be connected to the battery first. Connect up the cables from the solar panel and you are done. Don’t forget to seal the entry gland to the roof, friend had a panel fitted to his new caravan by the dealer and the didn’t do this and his ceiling came down!!!
It is an easy job, must be if I can do it!
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Cable size will depend on how far your controller is away from the battery. Mine is less than 1 meter and I think I was supplied with 4mm square with the kit I bought. i wouldn't use anything below 2.5mm square but that is not based on any scientific calculation just my own feeling.
peedee
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"NB the controller should be connected to the battery first."
I agree in that my controller's instructions labour that point, however, with most portable units the controller is stuck on the back of and pre wired up to the panel, so can't be used that way. Even stranger, it that one brand used the same controller as I was!
As I said so much commercial stuff takes an expedient rather than an optimised route.
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TBH. I have had the situation whereby the panel has been connected and the battery hasn’t been and no harm has occurred. But I think you might as well do it according to best practise but not to panic if you don’t . Actually I think that the installation and operation is quite be quite sub-optimal and still work.
After posting about optimal cable sizes I remembered that my first portable panel was wired in with a cable harvested from a scrap flymo 1.5mm still worked.
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I use my EHU cables as the panel to van connection, with the panel and van wiring configured to exploit all three cores. So can set the panel 10, 15 or 25 metres away seeking optimum avoidance of shadows.
I take the view not both an EHU and a solar panel are going to need the leads at the same time and I already carry all that heavy lot of copper anyway neatly on reels, so why another very heavy cable?
All part of de-cluttering this hobby as much as practical.
Before any body screams unsafe, I use the right polarisation so have the solar "socket" [not plug] at the van, and I am still bright enough not to connect a live EHU lead into my panel. Plus the panel would never be deployed from its cassette if there was an EHU, so no other dumb mischievous individual could do that either.
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