Solar panels for dummies

[Wingedryder]

Originally Posted by LoveToCamp

Winged, I ordered my panel post-delivery, but the TM came completely wired for solar. All I did was connect my panel to the special connectors that were zip-tied by the rear-street torsion bar.

When I installed my battery cutoff, I was able to do it without interrupting the charge line into my batteries. Should be a relatively simple matter to see if your solar is wired directly to the battery, or if it is part of the cutoff. Should be independent of the cutoff, I believe.

LoveToCamp: That was nice that the TM came prewired for solar panels (makes me thinketh the dealer may actually have installed my panels - there were a lot of "we" sell our units with this & that, so this may have been an item I took for granted that the factory installed and assumed the dealer was also taking credit for). Re cutoff switch: As I think back, I hooked up mine using cable leads bolting them together w/battery connector end, rather than by splicing. In which case I would have also captured the solar wire to the cutoff. I may wanna redo that in order to leave the solars panels connected whenever cutoff is switched 'off'. Thanks for that!

Originally Posted by Bill

WingedRyder -

Are the panels mounted on the front or rear shell? (Sorry, I have not been able to find a picture.) As I'm sure you realize, the panels must be exposed to direct sunlight in order to generate a charge. So if you have indoor storage (or outdoor storage with shadows on the panels), they won't charge. Similarly, if they are mounted on the rear shell, and the front shell covers them when the TM is closed, they won't charge. But if they are on the uncovered part of the rear shell, or on the front shell - and exposed to the sun - they should charge whether the TM is open or closed.

This should be true regardless of whether the tow vehicle is plugged in.

Bill

Bill:
1) My panels are mounted to the REAR shell top, streetside - exposed whether or not shells are collapsed (Sorry, I have no pics either). And, yes, I understand solar panels require actual sunlight to operate.

2) Though my TM has been covered this winter, I'm interested in the possibility of leaving battery connected, with TM uncovered for solar 'drip charge' to the battery over winter. I have no shore power at the lot, and lifting battery out from under dinette bench and over the front slide-out wall with front shell raised for access, after parking for the season is a chore. AND, I have an elec tongue jack. It helps to position trailer with a slight rake for snow/rain run off toward the rear of roof, but of course the slant makes it even more difficult to raise either shell to access the battery inside (I didn't think about losing ability to raise/lower tongue when battery is pulled or switched off, as it was during camping season when I upgraded, ha!). The 2720 is a learning curve, that's for sure, and obviously there are a few compromises I didn't think about before-hand. I just remember how easy it was to pull the battery at storage time on my previous camper, where it was mounted on the exterior frame front.

3) My additional question is this: Assuming battery is receiving some charge from the solar panels while traveling with some sunlight present, wonder if the solar panels could be enough to help alleviate discharging either TM or TV battery during stops, as talked about here on the forum, when running the frig on 12V?

[rickst29]

Originally Posted by Wingedryder

3) My additional question is this: Assuming battery is receiving some charge from the solar panels while traveling with some sunlight present, wonder if the solar panels could be enough to help alleviate discharging either TM or TV battery during stops, as talked about here on the forum, when running the frig on 12V?

Simple answer: Any power which the Solar system provides, at the charge controller's battery terminals, DOESN'T have to come from ANY of the batteries. It may be providing everything the Fridge needs, or a "large proportion", but it might also be a lot less (depending on Charge Controller programming "limits".)

A more complex answer follows:

Don't think of the battery "receiving some charge" at the same time it is being discharged, because their is a gap in voltage between between these processes. Instead, think of wht happens at the +12V bus within the power distribution center -- that's where the TV battery and alternator (via bargeman) and the Fridge +12V lead, and the net power drawn from the battery AND charge controller all come together.

With no Solar power and the TV turned off, the TV discharges at 12.8V - and goes down from there, as it's State Of Charge decreases. The same thing will happen at the TM batteries, but the two battery sources don't fall together: As current increases, there's usually more voltage drop along the TV--> Baregeman --> TM +12V "bus bar" path, than there is along the TM battery --> 12V "bus bar" path. While power is being drawn from the Fridge, the TM battery gets discharged a bit more quickly than the TV battery, obeying the constraint that voltage at the bus bar (battery voltage - voltage drop on the corresponding path) is equal. aso that the voltage right at the bus (battery voltage minus voltage drop).

But, when the Fridge 12V circuit is opened (turned off), the Fridge will stop drawing power - and power will be drawn from the TV battery, directly to the TM batteries, until they have equal voltage. (Ignoring everything else, and some power gets lost in wires, too.) While the voltage differential is large, the current is substantial, but it declines as the batteries become more equal.

Now add Solar, via the Controller. The Controller will try to feed power into the TM battery terminals with some constraints- power delivery can't exceed either the maximum power of the Array, *or* the maximum power which can be delivered at the maximum Voltage for that charging mode. (The fastest, most powerful charging rules, called "Bulk Mode" or "Absorb Mode", will try to reach 14.5-14.8 Volts, depending on the Controller programming. But the power might be further limited by a "max current" and/or "maximum Bulk-Mode time" limits). Then, it typically drops to maximum of 13.3V or less, and might also be power/current limited - which would be non-optimal mode for the situation where the charger thinks that the "nearly full" batteries should be limited to only a small amount of current, but a huge amount of current is being drawn by the Fridge - and not going into the batteries at all.

The batteries won't begin to drain until their voltage is "pulled down" to less than about 12.8 Volts - and, with 120-130W being drawn by the Fridge Heater, but that will happen if your Solar Charge Controller is delivering less than 120-130W. If your Solar system delivers more than that, you will stay it it's float charge Voltage -roughly 13.3 Volts.

At less than 12.8V on the bus bar, your TV battery will also become involved - exactly as before - but both sets of batteries are greatly protected by the whatever Current (and Power) which your Solar Controller is pushing onto the battery terminals. If it's less than 120W, all of your batteries will still go down - but they'll go down slower than they do without Solar assistance.

[Bill]

Originally Posted by Wingedryder

3) My additional question is this: Assuming battery is receiving some charge from the solar panels while traveling with some sunlight present, wonder if the solar panels could be enough to help alleviate discharging either TM or TV battery during stops, as talked about here on the forum, when running the frig on 12V?

Yes, it will certainly help alleviate, though whether it will totally prevent is of course dependent on the capacity of the panels and the amount of sunlight falling on them. However, I would urge you to install an isolation relay to protect the tow vehicle battery during stops. And that way, besides protection of the
TV battery, all of the solar charge can go into the TM battery and loads.

Bill

[Wingedryder]

Originally Posted by Bill

Yes, it will certainly help alleviate, though whether it will totally prevent is of course dependent on the capacity of the panels and the amount of sunlight falling on them. However, I would urge you to install an isolation relay to protect the tow vehicle battery during stops. And that way, besides protection of the
TV battery, all of the solar charge can go into the TM battery and loads.

Bill

Thnx Bill, that's at least the tree I was barking up. I know there are variables here such as capacity of the panels (which I can't discern from the literature I've been provided) and amt of sunlight available for absorption. Which is why I had hoped someone else with a newer TM w/the already installed solar panels like mine might respond with their thoughts/experiences here on the Forum.

Re an 'Isolation Relay' - if I remember past discussions correctly, addition of an isolation relay to protect the TV battery can be a rather expensive proposition, in which case, I'm inclined to merely keep the frig off while traveling. Seems I'm getting used to a boatload of nuances with the TM, so one more is no big deal, I guess.

rikst29: Seems my Biz grad degree and parmaceutical industry background have ill prepared me for the theory behind your electrical explanations, sorry to say. But thnx, I appreciate your efforts anyway.

[LoveToCamp]

rickst29, thanks so much for the explanation. I don't grasp all of it (bus bar drawdown), but it does make sense. Someday, probably after I am done using a TT, I may understand more about electricity. Seems like it should be simple, but I have never tried to understand all the nuances. I appreciate the explanations you give. I pick up a little more each lesson you give.

[Bill]

Originally Posted by Wingedryder

... capacity of the panels (which I can't discern from the literature I've been provided) ...

I think TM was installing 80 watt panels, at least for a while. Can you measure the overall size of the panels (length and width)? This should lead us to a pretty close estimate. Is there no writing, no labels, at all on the panels?

Re an 'Isolation Relay' - if I remember past discussions correctly, addition of an isolation relay to protect the TV battery can be a rather expensive proposition ...

Not necessarily so. If you buy one of the expensive isolators discussed earlier (>$100), you have to mount it under the hood somewhere, and make
2 connections to the device - Power In From Alternator and Power Out To Trailer. If you are willing to make two more connections, you can get a relay for $5-$10. Once installed, this is a very reliable approach. I did this on my first Explorer, and put 160K miles on it before I traded it in.

http://www.walmart.com/ip/Directed-E...Relay/21190763
http://www.walmart.com/ip/Install-Ba...Relay/28829772

One of the extra connections is to ground - any ground under the hood.
The other extra connection is 12 Volts when key in is ON. You would pick this up in the fuse box, which is easily accessible.

Several of us can provide more installation details if you would like. Or keeping the refrig off is perfectly good, too, if that works for you (it does for us).

Bill

[rickst29]

My "cheapo" PWM controller likes to fall into Float mode and stay there, without regard to battery voltage being pulled down by subsequent heavy loads. The power was thus limited to no more than 13.2/18.9 * 200 Watts (just enough to run the fridge, with no extra for charging the batteries while the Fridge was running. My "200 Watts" of PV panels became only 140W at the battery terminals of the Controller.) If it stayed in Bulk mode, it would have offered about 14.4/18.9 * 200W (another 12 Watts or so.)

My new controller is MPPT, it converts nearly all of the power delivered by PV at "excessive voltage" into more current at the right voltage. It's "bulk mode" will deliver a full 200W (i.e., significant battery charging at the same time a Norcold Fridge would be running at roughly 140W).

My new one has also much more advanced programming, it's happy to start a new "bulk mode" cycle when the battery voltage is being pulled down by high loads. (This "switch-back" is limited only by timer considerations and temperature at the battery terminal post.) I can also change ALL of it's programming parameters, by connecting it to a Windows computer program and using the program to set whatever values I like.

Of course, my new Fridge runs at only 70-90W. But for everyone else, the PWM power loss versus high Norcold power consumption is a big deal - roughly 1/3 of your PV power is not going to get through the Controller. Everything else must come from batteries (and the TV alternator, while actually driving).

[Wingedryder]

Thanks Bill & rickst29!
I'll have to ponder your latest posts a bit, not being the electrical engineer that I know Bill is, and prolly rickst29 as well.

I'm at least a little more encouraged. Though the relay idea may not be the first mod I tackle, appreciate knowing it could be a practical remedy for not discharging TV or TM battery w/o spending $$$$! I recall that my solar panels (2) are 80watt panels (still covered for storage, so can't measure right now). Beyond that, I have no clue what to expect from them, nor do I know the type of controller, though I'll dig a little deeper in my pile of TM literature.

Thanks again for the responses, guys - I gather there aren't many on the Forum with experience with as new a TM.

[tentcamper]

Just wondering, with fixed panels if there are any issues of two charging systems trying to charge at the same time? Is there any thing special you need do such to isolate between the two different power supplies. ie, the panels controller, the TV alternator or camper converter? Will they work in tandem without one of the power supplies stepping down because it senses the voltage of the other power supply?

[Bill]

Originally Posted by Wingedryder

Though the relay idea may not be the first mod I tackle, appreciate knowing it could be a practical remedy for not discharging TV or TM battery w/o spending $$$$!

Be sure you undertsand that an isolator or isolation relay will prevent discharge of the tow vehicle battery when you are stopped (thus assuring that you can start the tow vehicle), but will not prevent discharge of the TM battery by loads, such as refrig, in the TM.

I recall that my solar panels (2) are 80watt panels (still covered for storage, so can't measure right now).

Good to know. As noted above, 160 watts (nominal) of panels won't power the refrig top full power, but will certainly prevent it from sucking the TM battery dry as you travel.

Bill