Solar controller tie in

Yes MPPT uses power--watts in and watts out. But the watts out is at the output of the controller. Amps to the battery from there to the battery is output watts/battery voltage. (Not sure which end of that wire's voltage to use for that!)

If there is voltage drop as seen at the battery then if output watts at the battery were the same as at the controller, then you would get more amps at the battery, so that's not right.

So you are saying to use the watts at the battery to divide by battery voltage to get amps to the battery I guess.

Yes, you do not use the power with PWM and some say that "wastes" power that MPPT does not. They forget the 10% power loss at the panel due to heat (10%) that does not affect PWM, line loss, and controller inefficiency, so when you do get to the output power/battery voltage you can be close to the same amps to the battery as with PWM.

Anyway, solar works however you do it.

RLS7201 wrote:
No need to worry about distance between charge controller and batteries. You can purchase a MPPT controller with adjustable voltage or get a charge controller with separate voltage sense leads. Just make sure the wires are large enough to carry the current.
My controller is over 25 feet from my batteries and has separate voltage sense leads & is fully adjustable. Maintains the batteries correctly.

Richard

BFL13
Here’s the full quote and note that he has a MPPT controller which converts the panel power to battery power minus losses – ie watts. Any voltage drop in the wiring results in less amps delivered to the battery for a given voltage. For him it’s an acceptable tradeoff but others may want/need more battery charging so I was just making the point that voltage loss means less amps and hence power to the battery. His point is good that his controller with remote voltage sensing allows him to accept the wiring loss and provide an easier install.

PWM controllers are different is that for example a 12V panel (18V actual) charging a 14.8V flooded battery in bulk will lose the power associated with the 3.2V since charging is restricted to panel amps and not panel power (as long as the voltage is adequate) unlike MPPT controllers. I.e. The power loss associated with the 3.2V is a given for a PWM controller as its simpler design does not harvest that power.

Certainly, once absorb charging begins battery amps and voltage (power) tapers off. However, during the entire charging cycle and beyond house loads also use power which first comes from the panels and then from the battery. So again, wiring loss can becomes a factor when camping with house loads.

I use these, $12 on ebay for about any amp breaker you want. I use it as an on/off switch to disconnect the solar, or the batt, or the power lead to the 7-pin. With solar you probably never need the vehicle power, so break that connection. breaking it also means your trailer plug will not corrode as easily, no electricl voltage potential at the plug head (positive and negative terminals), mine are not corroding anyway.
For the panel safety you disconnect the panel before disconnecting the batteries, so the breaker makes this a lot easier to do.

The blister is great, I use that on a trailer.
Use Lap sealant as needed.

Closer to the batteries is idea, but maybe you can do that long run still; here is what I suggest:
Since you will put two panels up then run them in series - positive to negative then out. This is the same "in series" as you do for two 6 volt batteries.
This doubles your voltage so you have about 37 volts running through the wire, so you can use lighter gauge wire or use the same and have less voltage drop. The MPPT (and use MPPT) controller can take the 37 volts and drop it down to the 14 needed to charge. This is better than running two 18 volt wires down. Also, if one panel is putting out less voltage, from a bad cell, or shadow, or something is physically on part of the panel, then maybe you only have 35 volts, and this is still plenty, but if running 18 volt pairs, then you have issues.

Run the solar straight to the controller then straight to the batteries. Do not try to tie it in to something, many reasons for this, but just dont.
The controller may or may not need much venting. I had one in the space under the dinnette seat and it was fine, maybe that is enough air space, so maybe you can put it very close to the battery. It does need to stay relatively cooled though. Further away is ok, and the best place is somewhere where you can look at it often, but where the green indicator light does not keep you up at night (it will be bright when everything else is pitch black).
Closer is better because after the controller it will be a lower voltage, so there is more voltage drop. 37 (or 18) volts to the controller, then 14 after the controller.

@naturist Thanks for the link. I think that will be perfect for the intrusion into my rv.

CA Traveler wrote:
"My controller is over 25 feet from my batteries and has separate voltage sense leads & is fully adjustable. Maintains the batteries correctly."

There are many installation options that produce acceptable results. However more voltage drop expecially on the battery side wiring results in less power that can be harvested from the panels.

Seems a bit muddled there IMO. Not clear anyway.

Power only matters with MPPT. And there, voltage drop only affects power output from the controller from any drop at the array side, not the battery side.

Controller output with PWM or MPPT it is all about amps to the battery to get them charged properly. It is not about power to the battery.

Voltage drop from controller to battery depends on amps flow, so as the battery is charged higher up that becomes less of a problem.

The real issue with voltage drop is that the battery will not reach the voltage set on the controller when the controller starts controlling if the amps flow is still going at that point. This might matter or not depending on what voltage the battery needs to get to.

If you have voltage drop and try to make up for it by setting the controller's voltage higher, then that will get the battery voltage higher too as amps taper. Now it matters if that voltage is too high.

As long as the battery gets to 14.4ish it doesn't matter if it gets to 14.5. (Lithiums it does matter!) There is also the time it will be at that voltage before either the charging profile drops it to a Float voltage or it gets dark.

There is some wiggle room for having longer wire from controller to battery if it will mean difficulties passing wire in the RV setting things up, and you will still have a good enough set-up, as CA Traveller said above.

"My controller is over 25 feet from my batteries and has separate voltage sense leads & is fully adjustable. Maintains the batteries correctly."

There are many installation options that produce acceptable results. However more voltage drop expecially on the battery side wiring results in less power that can be harvested from the panels.

This: Entry gland

“My controller is over 25 feet from my batteries...”

That’s not the advice of WindyNation - “Mounting is optional but for best results, locate the charge controller as close as possible to the batteries and the batteries and charge controller as close to the panels as practical.”

Thanks all for the responses. Based on all this I will try and mount towards the front and use the front storage compartment. I'll have to find someone who understands the drilling and sealing piece. I've installed plenty of solar systems for off grid cabin use but don't want to compromise my rv.

Again, thanks everyone.

No need to worry about distance between charge controller and batteries. You can purchase a MPPT controller with adjustable voltage or get a charge controller with separate voltage sense leads. Just make sure the wires are large enough to carry the current.
My controller is over 25 feet from my batteries and has separate voltage sense leads & is fully adjustable. Maintains the batteries correctly.

Richard