Solar Charge Control

I did my own installation JK and the advice I was given was to keep the leads to the battery as short as possible. I put mine on a vertical surface above the battery ensuring that air could circulate around it for heat dissipation.

peedee

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? 

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

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

It's all down to resistance, increase the size/capacity of the cabling itself and thus increase wiring distance. A bit too scientific for me to guess requirements but others I'm sure will explain.

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

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. 

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, 

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.

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