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Solar controller tie in

mtnman1000
Explorer
Explorer
I am getting ready to install a couple solar panels on my 28' Keystone Springdale and am trying to determine how to get the charging to to the front mounted 6V batteries. I was thinking of running the MC4 wiring down the fridge vent then to the wardrobe closet where the controller will be. From there my thought is to wire the controller to the 12V input lugs on the fridge. There is about a 23' run from there to the breakers (15 amp) then battery battery but I don't know the AWG of that wire.

Would this work OK? I figure if it's 8 AWG it get a 2.5 % drop. Also if I installed more than 2 100W panels, the breaker to fridge would be too small I think.

Outside of this I'd need to figure out how to get the controller in the front storage then charge cable tray from there to the batteries. That would be a bit out of my league though.
15 REPLIES 15

BFL13
Explorer II
Explorer II
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.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

CA_Traveler
Explorer III
Explorer III
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
Hereโ€™s the full quote and note that he has a MPPT controller which converts the panel power to battery power minus losses โ€“ ie watts. Any voltage drop in the wiring results in less amps delivered to the battery for a given voltage. For him itโ€™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.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

ajriding
Explorer II
Explorer II
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.

mtnman1000
Explorer
Explorer
@naturist Thanks for the link. I think that will be perfect for the intrusion into my rv.

BFL13
Explorer II
Explorer II
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.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

CA_Traveler
Explorer III
Explorer III
"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.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

naturist
Nomad
Nomad
This: Entry gland

Lwiddis
Explorer II
Explorer II
โ€œMy controller is over 25 feet from my batteries...โ€

Thatโ€™s not the advice of WindyNation - โ€œMounting 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.โ€
Winnebago 2101DS TT & 2022 Chevy Silverado 1500 LTZ Z71, WindyNation 300 watt solar-Lossigy 200 AH Lithium battery. Prefer boondocking, USFS, COE, BLM, NPS, TVA, state camps. Bicyclist. 14 yr. Army -11B40 then 11A - (MOS 1542 & 1560) IOBC & IOAC grad

mtnman1000
Explorer
Explorer
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.

RLS7201
Explorer
Explorer
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
95 Bounder 32H F53 460
2013 CRV Toad
2 Segways in Toad
First brake job
1941 Hudson

CA_Traveler
Explorer III
Explorer III
Drop the notion of pre existing wiring convience. The critical path is from the solar controller to the battery where small losses can cause significant loss of battery charging. Mount the controller as close to the batteries as possible.

12V panels produce about 18V and that wiring can tolerate significant voltage drop w/o power (battery charging) loss if you're using a PWM type controller. MPPT controller are a different consideration.

The key paths are panels to controller and controller to batteries. The refer and it's DC wiring is not involved.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

corvettekent
Explorer
Explorer
The fridge breaker would be 120 volt so do not run your charge controller there.
You want as short of a wire run as possable so you should mount the solar panals on the front part of the roof, drop the wires down in conduit into a forward closit or bathroom. Mount the charge controler the forward storage compartment and then run those wires to the batteries.

When you shut off the main battery switch the solar should still be charging the batteries.
2022 Silverado 3500 High Country CC/LB, SRW, L5P. B&W Companion Hitch with pucks. Hadley air horns.

2004 32' Carriage 5th wheel. 860 watts of solar MPPT, two SOK 206 ah LiFePO4 batteries. Samlex 2,000 watt Pure Sine Wave Inverter.

agesilaus
Explorer III
Explorer III
I was told to use one of these breakers on the line into the controller: solar breakers. And 15 amp is too small. I got the type they show as a 40 amp with the lever. You can use it as an on/off switch too.
Arctic Fox 25Y Travel Trailer
2018 RAM 2500 6.7L 4WD shortbed
Straightline dual cam hitch
400W Solar with Victron controller
Superbumper

BFL13
Explorer II
Explorer II
Need a link to your floorplan. A utube of a 2013 28ft Springdale TT was for a bunkhouse model, didn't make it clear where the converter is, eg.

More info on that would help with your options. It would be better to run the controller in parallel with the converter than from the back of the fridge for amount of voltage drop.

Usual way to get wiring from tongue to front storage is drill hole in floor up front and go down and up to the tongue instead of going through the front cap.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.