Solar Charge Controller and Load Output

[Mostly Harmless]

G'day, all;

I'm planning on installing a solar charge controller in line with the 12V lines from the battery -- with the 12V lines to the trailer hooked up to the load output on the controller (to cut power to the trailer if battery voltage drops below safe limits).

In a typical setup, this wouldn't be a problem, but when the trailer is on shore power, the converter will be supplying 12V into the OUTPUT of the controller -- which will sounds like it'll be a problem.

The solution I have in mind is to install a bypass switch that will feed the converter directly to the battery when I'm on shore power (bypassing the controller), but that depends on me remembering to flip the switch if I go from solar charging to shore power. And Mr. Murphy (with whom I am quite familiar) has taught me that any system that relies on human reliability is unreliable.

Does anyone have any suggestions for a solution that would be more automated? Or is feeding power to the battery via the output of a controller not the problem I am making it out to be?

Thanks in advance for your insights.

Cheers!

[TucsonJim]

It is not a problem at all. The output of the solar controller can be tied directly to a battery bank (remember to install a fuse). And the converter output can be directly tied to the battery bank also.

Jim

[jmbopp]

My solar controller is directly connected (& fused) to the batteries. Never had an issue when running on shore power.

[Mostly Harmless]

In the setup I am looking at, the current from the battery to the trailer load passes through the controller, as in the graphic below. This way, if the battery voltage drops below a certain point, the controller disconnects the load (i.e., the entire trailer) from the battery in order to avoid excessive battery discharge.

In other words, there is no direct line from the converter to the battery -- power flows from the battery THROUGH the charge controller, to the trailer's main 12v bus.

Thus, since the load is the converter, power from it must flow BACK through the charge controller output... something I doubt it's designed for.




The only way I can see around that is to put a bypass switch that takes the controller out of the circuit when on shore power.

[howson]

Thus, since the load is the converter, power from it must flow BACK through the charge controller output... something I doubt it's designed for.

Your attachment is not accessible?

This may come across as blunt, so please do not take offense but I've never seen a diagram that shows a solar controller in series between the batteries and the load. I'm not an expert nor an engineer, but I suspect if it's wired as suggested you will get a visit from "Mr. Murphy".

This graphic from Bay Marine shows the only (to my knowledge) correct way to hook up a solar charge controller:


Picture clipped from : https://baymarinesupply.com/victron-...ontroller.html

The best recommendation I can give you is to give the guys at AMSolar a call and tell them what you want to accomplish (battery disconnect at x charge) and let them suggest a solution. https://amsolar.com/

[Mostly Harmless]

That complex setup is fine if you're driving huge loads (inverter, appliances, etc.) with your 12V system. In my 2150RB, there isn't anything on the 12V system that draws so much current that needs anything close to that level of complexity. Solar charging to run a few lights, fans, fridge, and (maybe the furnace) while boondocking isn't worth the multi-thousand dollar investment depicted in the graphic above.

And pretty much every solar charge controller I've looked at has load outputs through which your 12V system draws power (at least for things like lights, radios, and other low-current items). And pretty much everything in my small trailer will not draw anything close to the max current limitations of the controllers I'm looking at (unless I retract the awning while closing the slide with the fridge and furnace on).

The controllers I am looking at are specifically designed to:

1) control the charging of the battery (or batteries) from a PV array
2) protect the battery from over discharge by cutting off the load when battery voltage drops below a pre-set level

Again, I'm not running an inverter or any high-current devices off my battery -- just the usual 12V stuff found on a small trailer (the slider is the biggest draw at ~7 Amps).

However, none of the usual systems in which these devices are used also pushes charging current from the load to the battery. The setup I suggested WILL work fine if not for the fact that charging current will flow backwards through the device when on shore power -- hence my initial question.

I'm beginning to think that a solution is going to be too complex, and will just use my charge controller only for charging, and simply monitor the battery voltage, myself. Maybe run a few auxiliary 12V circuits off the load outputs for other uses (e.g., outlets in the bedroom for a fan).

... I was hoping this would be an easier fix.

[howson]

And pretty much every solar charge controller I've looked at has load outputs through which your 12V system draws power...

Maybe we're caught up in semantics? A solar charge controller only has one job: it controls the charge going to your batteries from the solar array. The batteries power the 12V devices in your trailer.

The electrical engineer at AMSolar has a video on this very topic. Go to the 1:00 mark in this YouTube video and he says the exact same thing. https://www.youtube.com/watch?v=aLi-sujpFZs

Something like this https://www.amazon.com/Volt-Voltage-.../dp/B00KI1Z8TY between your batteries and load should do what you want to protect from undervoltage. I can't think of a circumstance where you'd want to disconnect the solar charger from the batteries (though it is fused for circuit overload). Note the device linked is for reference only--there are probably a dozen better devices available that I'm not aware of.

I hope this is making some sense...

[Mostly Harmless]

You're right -- I am being a little loose with my terms. The charge controllers I am looking at also have have the cut-off for the load in case battery voltage drops -- but doesn't cut off the battery from charging. In other words, if battery voltage drops below "safe" limits, the load is removed from the battery, but charging continues (if sunlight is available, of course). For example, this is one such controller: https://www.amazon.com/PowMr-Control.../dp/B074WNXPZ6

I've decided to skip that option -- at least for now. I'll just keep an eye on voltage (I'm adding a digital voltage readout at the control panel to get a better read on battery level). Eventually, I'll construct a battery saver circuit using the controller (with battery saver) load output to manage the cut-off between the battery and load. (Sure, I could buy one, but where's the fun in that??? )

[jh.xsnrg]

Most of the charge controllers that also have load control will only control a very minimal amount of load, say 15A. The controllers themselves are usually on the smaller size in the amp handling category as well. That could be why there is some disconnect here, as many folks have the larger charge controllers, and these do not have the DC load posts on them. I would not hook the load control up to the camper directly, but instead use it to control a relay to protect the battery. Using a relay will make sure your furnace fan, for example, will always have enough amperage to start. If you overload the load control directly on the charge controller, nothing will get through until you replace the fuse, and 15A is not a lot of juice at only 12v. I see you have chosen to not go the route your are thinking. I think that is a good choice.

Jim