Solar Crossroads

[JRTJH]

From an "electrical circuit vantage" there is no difference in connecting a circuit at either end of a wire. There is a "consideration" about whether that wire has the capacity to carry the load, so if it's a "undersized wire" then connecting to the end that doesn't require it to carry the amperage would be important.

That said, if a wire is sized to carry 50 amps for 25', then it can carry 50 amps in either direction. So, there's no "requirement" from an electrical current perspective, to connect to one end as opposed to connecting at the other end.

There is voltage drop on any DC circuit and amperage load capacity requires "heavier wire for larger/longer loads" but if a wire is carrying 50 amps for 25' "FROM" the battery to the converter/fuse panel, that same wire is capable of carrying 50 amps for the entire 25' "back to the battery from the converter/fuse panel. It just can't be expected to "carry both at the same time".....

[chuckster57]

I was just wondering about back feeding the panels if he hooked up the solar wires at the converter.

[JRTJH]

Most "large inverters have a transfer switch in them to prevent backfeeding. And, he mentioned installing an "A/B" switch to connect the solar when not on shore power and the converter when "plugged in".

As for the wire "from the battery to the converter" if it's heavy enough to carry 45-50 amps from the charger to the battery, it can surely carry 45-50 amps from the solar array to the battery. The key is making sure that only one system, converter or solar array is connected to the battery at any time. Either an automatic transfer switch or better yet, an A/B manual switch. I've seen lots of "automatic stuff" that got slowed down, stuck or just wore out" and has been the cause for damaged or burned out components. You won't have that issue with a manual A/B switch.

[Keystoned]

I'll have source a 'S/C' switch, lol. Or something appropriate and unmistakable because you know, humans. Actually, as long one or the other is selected, the system is protected...
I can mount it and the solar controller near the converter somewhere and be able to mount the panels at the rear of the 5th wheel.
I call that a win/win

Sort of like the Chiefs just now!

[flybouy]

Originally Posted by Keystoned

I'll have source a 'S/C' switch, lol. Or something appropriate and unmistakable because you know, humans. Actually, as long one or the other is selected, the system is protected...
I can mount it and the solar controller near the converter somewhere and be able to mount the panels at the rear of the 5th wheel.
I call that a win/win

Sort of like the Chiefs just now!

Actually all you need is an on/off switch in the wire from the solar panel.

[Keystoned]

Not too sure about that, it leaves a possible AND condition subject to human error, I think. Worst case is both chargers on at once.

The A/B is always an OR condition with no chance of error. Worst case is lack of charging by solar.

Any logics folks here to weigh in?

[chuckster57]

Like I stated before, we have always ran the solar wires to the controller and then directly to the batteries with zero issues. Tiffen motorhomes that are “prewired” have it set up this way, I was only questioning running the solar leads from the controller to the converter/inverter.

[flybouy]

Originally Posted by chuckster57

Like I stated before, we have always ran the solar wires to the controller and then directly to the batteries with zero issues. Tiffen motorhomes that are “prewired” have it set up this way, I was only questioning running the solar leads from the controller to the converter/inverter.

I'm no solar expert but here's my take. Connecting both charging sources to the same battery cable (anywhere in that cable) will have no need for any switch.

Think about it this way, the positive cable always has battery voltage present when connected, the converter's charger and the solar panel only serve to increase that voltage to replenish the battery "charge". Having both connected simultaneously in my thinking would possibly result in the solar panel (if sufficient size and sun exposure) may cause the converter to "satisfy" and shut off if the solar panel is producing a higher voltage.With clouds/darkness resulted in a lower voltage from the solar panel than the converter will supply the charge.

Last thought on this. Do you disconnect the camper from the battery while towing? Same principle, your TV is charging the batter via the 7 way umbilical. Electrically no different.

If my thinking is flawed someone step in and correct it.

[JRTJH]

Marshall,

The only "flaw" I see in your analysis is that the converter "charging circuit" is voltage dependent. It will ONLY produce a charge if the voltage sensed from the battery (the red + cable) is below a specific voltage threshold. If the solar system is "concurrently connected" to that same red cable (without an A/B switch) then as long as the sun is shining, the solar array on the roof will provide 12+ VDC, exceeding the "threshold voltage" sensed by the converter charger and keep that device "turned off".

It's the same with connecting a secondary battery charger to the battery while connected to shore power. The secondary battery charger will "inhibit charging" because the "line voltage on the red + cable" is always above the threshold, triggering the converter/charger to "believe the battery standing voltage is able the level that requires charging....

So, connecting BOTH may not cause damage to the converter/charger, but: I'm not sure about back flow DC to the converter and whether it will cause damage to the sensing circuit. I do know that if the solar panels send more than the threshold voltage to that "converter/charger/solar panel" connection site, the converter/charger will be "turned off as long as the solar panel voltage is greater than the threshold"...

[Keystoned]

While it 'may' be okay to just tie everything together, I'm still tending towards an A/B switch. One position for when plugged in and the other for when not. Just need to find one to match the system.

[JRTJH]

Originally Posted by Keystoned

While it 'may' be okay to just tie everything together, I'm still tending towards an A/B switch. One position for when plugged in and the other for when not. Just need to find one to match the system.

I agree, a manually operated A/B switch is the "foolproof way" to make sure that only one system (converter OR solar) is connected to the battery at any specific time. If I were doing the add to my trailer, I'd install an A/B switch to make sure the systems are isolated.

[Keystoned]

This one might work;

https://www.amazon.com/1-2-Both-Off-...s%2C255&sr=8-2

Open to suggestions...

[flybouy]

Originally Posted by JRTJH

Marshall,

The only "flaw" I see in your analysis is that the converter "charging circuit" is voltage dependent. It will ONLY produce a charge if the voltage sensed from the battery (the red + cable) is below a specific voltage threshold. If the solar system is "concurrently connected" to that same red cable (without an A/B switch) then as long as the sun is shining, the solar array on the roof will provide 12+ VDC, exceeding the "threshold voltage" sensed by the converter charger and keep that device "turned off".

It's the same with connecting a secondary battery charger to the battery while connected to shore power. The secondary battery charger will "inhibit charging" because the "line voltage on the red + cable" is always above the threshold, triggering the converter/charger to "believe the battery standing voltage is able the level that requires charging....

So, connecting BOTH may not cause damage to the converter/charger, but: I'm not sure about back flow DC to the converter and whether it will cause damage to the sensing circuit. I do know that if the solar panels send more than the threshold voltage to that "converter/charger/solar panel" connection site, the converter/charger will be "turned off as long as the solar panel voltage is greater than the threshold"...

I believe this is essentially what I said. I would not think that backflow to the converter would be an issue as I would think the converter, let's say a 55 amp one, would have a diode capable of the voltage & amperage designed for the converters 12 vdc capability. I would be more concerned with the charge controller in a low end say 100 watt solar charger. The solar charger should have a diode to prevent voltage backfeeding from heating up the solar cells but is it sufficient enough to handle the potential 55 amps? That's what I don't know as I'm no expert on solar chargers or arrays.

The only thing I do not like about a manual switch is the failure is wholly dependent on human thought and error. Failure of a quality electrical component is typically in a "non working" mode. That failure rate could be in the thousands or tens of thousands of cycles. The human failure rate, the possibility of someone (or child) wanting to find out "what this switch does" or thinking "this must be the speaker selector switch", or just getting distracted and forgetting to properly set the switch is a risk greater than a device failure in my mind. YMMV

[JRTJH]

I agree, manual switches do require "human thought AND action" where automatic systems require "no human interaction". We did that with photo-electric cells (so humans don't need to turn on a light) and now with "active cruise control" (so humans don't need to pay attention to the following distance or closing rate). Both are OK, but both can be controlled with a manual switch or "foot on the brake" as they've been done in the past. Either system will work, the worst scenario that I can think of with a manual switch would be a dead battery or a charging circuit that doesn't charge (until the switch is manually changed).

The "key to success" with either an automatic or a manually controlled system is assuring that the battery is connected to the fuse panel "24/7" while the charging system (converter or solar) is switched. It takes a bit of thought "beyond 1 wire/1 switch/2 inputs" as the output must always remain connected. Easy to do, but much easier to "skip over" as well....

[Customer1]

Originally Posted by chuckster57

Both systems are charging the battery(s), but I’m not an electrician or electrical engineer so I don’t know the science. Maybe the controller has some protection to prevent any hack feeding.

It isn't an issue. The RV charging system won't back feed to the panels anymore than the battery will back feed to the panels.

Think about it, whether the panel feed is connected at the batteries or elsewhere, the circuit is actually the same except one way uses more wire and the other way uses less.

[Keystoned]

https://roadslesstraveled.us/chargin...r-shore-power/

This is the best explanation I have found on this topic. In a nutshell, not a personal safety issue or equipment damage risk, just that neither system is optimal due to possible voltage reading issues. The two charging systems kind of fight each other and nobody wins...

[bbells]

Nothing has changed in 4 years, and your panels should be producing almost as much as new. But, it is hard to sell a used RV these days unless you drop the price dramatically. The solar would most likely be the reason someone would buy your trailer over someone else's. Plus filling in the holes or removing the glue marks are too big of a job to save $200.

[Keystoned]

If it sells with the trailer with added value then no problem, I'll get new stuff.
If they buyer does not value it and wants to pay too little, I will remove the panels, controller and batteries, leave the wires, replace the hold down screws with flatheads and cover them with self leveling goop. A new large battery will replace the AGMs and it will be 'solar ready'.
The value of the panels, controller and batteries is closer to $800 in parts, at least. I'm not hard up for money but I won't give stuff away either, just on principle.

[bbells]

Originally Posted by Keystoned

If it sells with the trailer with added value then no problem, I'll get new stuff.
If they buyer does not value it and wants to pay too little, I will remove the panels, controller and batteries, leave the wires, replace the hold down screws with flatheads and cover them with self leveling goop. A new large battery will replace the AGMs and it will be 'solar ready'.
The value of the panels, controller and batteries is closer to $800 in parts, at least. I'm not hard up for money but I won't give stuff away either, just on principle.

$800? Never buy panels from that dealer again. I sold 200w panels before the tariffs for $130 each. After the tariffs I see them for between $150 and $200. If you get 12v panels you only need a pwm controller, which is about $10 on ebay. If you decide to go mppt because you got a 24v panel, you can get an adequate one for about $90. Sorry. You got taken for a ride. Plus, you now have the option to go with semi flex panels. They simply tape on with permabond roof tape. No holes to drill. Remember, with a 200w panel you are only sending a max of about 17 amps to your battery (and very rarely that high). You do not need extra heavy duty wire to do that.

[Keystoned]

It's always good to get new viewpoints, but here is where I got my numbers from.
AGM batteries are about 200 each, so there's 400.
The system on the TT looks like it has gone down a bit in 4 years, but I paid close to 350;
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Misc stuff was like another 50, that makes 800.

If you can provide me links to create a new system for less, I'd appreciate it. I like the idea of flexible panels, assuming they last as long as rigid ones.