More data re solar panels and running the fridge on 12V

[Mike Lewis]

Today I pulled my trailer from Townsend, TN to Charleston, SC. I have 355W total of solar panels, three rooftop panels that are fixed in a flat position. As an experiment I put my fridge on twelve volts for the trip. I left at 9:00 a.m. and arrived at my destination at around 6:00 p.m. It was a sunny day. The panels were able to maintain the batteries' charge despite the drain from the fridge-- they were at 95% capacity when I arrived, down from 100% when I left Townsend.

So-- 355 watts of solar panels will keep the batteries from being depleted on a sunny day while running the fridge on 12V. In April, in the South.

[padlin]

Start and stop time have a lot to do with it too. I only see top output for about 5 hours in the middle of the day. Chances are you are running a deficit early and late for your travel time. Having 355w you make up your early deficit during the noon hours but are left with the 5% deficit from late in the day.

I was thinking of adding another 100w for similar reasons, but running on propane is so easy I haven't.

[Mike Lewis]

Yes, I did stop for gas. I believe that my Tacoma's alternator provides very little charging to the trailer's batteries when towing, but I haven't measured it.

[cpaharley2008]

I assume you have dual six volts, Mike and Bob? What about adding another set of batteries vs another panel? I was thinking of getting a double set in the front box.

[thoer]

Originally Posted by Mike Lewis

Yes, I did stop for gas. I believe that my Tacoma's alternator provides very little charging to the trailer's batteries when towing, but I haven't measured it.

Mike depending on what year your Tacoma is, if you have the tow package, it actually has an alternator with enough capacity to provide a good deal of charge to the trailer batteries. Our 2008 used to fully recharge our dual 6V whenever we would do more than a couple hours of driving.

[Rossue]

Originally Posted by cpaharley2008

I assume you have dual six volts, Mike and Bob? What about adding another set of batteries vs another panel? I was thinking of getting a double set in the front box.

Four 6-volt batteries weigh 240 lbs. Front box on my 21 has a sticker that says "Do Not Exceed 100 LBS.".

[Brian B-P]

I think just about any vehicle capable of towing a trailer and built in the last decade or two has more than enough alternator capacity to power the refrigerator and add some charge to the battery... but the alternator doesn't run at full capacity because the correct voltage at the truck's battery is too little at the other end of the long wire to the trailer. This is highly dependent on wiring details.

Apparently some vehicles boost their voltage setting to a higher level when in tow-haul mode - or at least doesn't drop the voltage to help fuel economy - and that would help. Maybe some Toyota models and years keep the voltage up - mine doesn't have a tow-haul mode but it's not a truck.

The solar panels have two advantages over the tow vehicle's alternator: the panels are more directly connected to loads in the trailer; and in full sun their open-circuit voltage is much higher than any 12V vehicle's voltage regulator setting.

[Klem]

Originally Posted by Brian B-P

The solar panels have two advantages over the tow vehicle's alternator: the panels are more directly connected to loads in the trailer; and in full sun their open-circuit voltage is much higher than any 12V vehicle's voltage regulator setting.

All good points and consider this:

The TV alternator 'looks' at voltage and the solar array 'presents' a higher voltage. But the flat mounted panels can't produce anywhere near the load of the refrigerator.

So the alternator 'sees' a higher voltage on the battery wiring circuit ... and assumes all is well. In this case (refrigerator on DC) the result is undercharged batteries.

[Mike Lewis]

The combined length of my Tacoma + Escape 21 is 39 feet, one inch. The truck's alternator is in the front and the trailer's dual six-volt batteries are in the back. This is why I assumed the alternator has little effect charging the batteries. Someday I'll get a friend to watch the trailer's battery monitor while I rev the truck's engine to highway speeds. On a sunny day, of course, to get the influence of the panels as well.

[LeonW]

Doesn't it also depend upon the thickness of the wire from the alternator to the trailer? I seem to remember reading a thread about that, smacking my head, and saying 'Duh, another thing I should have done...'

[padlin]

Different truck, different trailer, but at 35' I get 10A from the truck according to the monitor.

[thoer]

Originally Posted by LeonW

Doesn't it also depend upon the thickness of the wire from the alternator to the trailer? I seem to remember reading a thread about that, smacking my head, and saying 'Duh, another thing I should have done...'

According to my local Toyota dealer, when they wired our new Highlander for the 7 pin, they used the same gauge wire for power supply that Toyota does on factory wiring, 10 gauge. I believe that ETI uses that same wire size for that power wire from the 7 pin.

[alanmalk]

Originally Posted by Brian B-P

I think just about any vehicle capable of towing a trailer and built in the last decade or two has more than enough alternator capacity to power the refrigerator and add some charge to the battery... but the alternator doesn't run at full capacity because the correct voltage at the truck's battery is too little at the other end of the long wire to the trailer. This is highly dependent on wiring details.
...

I did a little experiment a while back. With the Escape battery switch in the "disconnect" position and the refrigerator set to 12v, all the power was being supplied by my alternator. The voltage drop from the car battery to the distribution panel at the rear of the trailer was 1.75 volts. That is a very significant drop and it means that had the Escape batteries been connected they would have been providing some power to the 'frig, rather than being charged by the car.

The moral of the story, as others have pointed out is - the wiring between the car to the 'frig is not thick enough to both run the 'frig and charge the trailer batteries. Based on a guestimated 75 foot round trip from alternator to 'frig and back to alternator, and on a 15 amp load to run the 'frig on 12 v, the wire guide at West Marine suggests that 6ga is more appropriate. Real world measurements and experiences seems to verify this.

Current solutions - solar on the trailer or simply run on propane while driving.

--
Alan

[paulk]

In my trailer, I am planning on installing a DC to DC charger to resolve the 12 volt fridge operation issues. What these little devices do is convert any reasonable voltage on the input side to a nice 14.5 volts (absorption) or 13.3 volts (float) on the output side. They do this by essentially exchanging amps for volts.


So as an example, say the voltage drop from the alternator to the trailer battery would have been 1.75 volts, bringing it down from about 13.25 volts at the alternator to 11.5 volts at the trailer battery. If the trailer battery was requiring 14.5 volts to charge during the absorption phase, and the draw from the battery and the fridge was 25 amps, then a DC to DC charger would need 14.5 volts * 25 amps = 362 watts, which it can get from a 11.5 volt input source by drawing 362 watts / 11.5 volts = 31 amps.


The specific device that I plan on using is the Redarc BCDC1225-LV, which can output up to 25 amps. 25 amps is sufficient to run the 15 amp fridge AND simultaneously recharge the battery with the remaining 10 amps. Alternatively, if I'm low on battery and want to charge it up quickly, leaving the fridge on propane will allow the full 25 amps to go into the trailer battery.


There are other advantages too if you have a solar panel. The Redarc model above can replace the standard GoSolar charge controller that comes with the Escape solar package. The benefit in doing so is that the Redarc is an MPPT charge controller which is significantly more efficient at converting solar energy than a PWM solar charge controller like the GoSolar. The increase in solar collection should be in the range of 20%-40%, so the effect is like instantly upgrading your solar panels from 160 watts to the equivalent of 200-260 watts.


PWM (pulse width modulation) charge controllers are not very efficient in that they just pulse on/off the 18.5 volt input from the solar cells and then smooth the output down to 14.5 volts, so they essentially waste (18.5 - 14.5) / 18.5 = 21% of the available power. MPPT (Maximum Power Point Tracking) charge controllers on the other hand work by constantly searching to find the optimal draw from the input that will obtain the highest amount of power in terms of watts and then converting that to the 14.5 volt output during charging.


My trailer is due in 2017. Once I have all of the above installed, I'm hoping to use my vehicle as a kind of "emergency" generator. With two solar panels on the top, I don't expect to need a generator very often, if ever. In the unlikely event that do I run out of batteries, I figure that running the engine on idle for 3-5 hours won't significantly damage it compared to the countless hours that it'll be driven getting between beautiful locations. Keeping a generator and replacing unused diesel at a disposal center every year seems like a chore that I can do without given how little I plan to need non-solar power.


Ctek also sells an MPPT solar/alternator DC to DC charge controller, but I’ve heard bad things about the solar side of their unit. Supposedly, it doesn’t do a good job searching for the optimal load to apply to the solar input, so you get an inefficient power conversion.

[cpaharley2008]

Welcome PaulK to our little world. You lost me above in your description other than it is a better controller than the stock one. What are the prices and installation procedures?

[Brian B-P]

Originally Posted by paulk

In my trailer, I am planning on installing a DC to DC charger to resolve the 12 volt fridge operation issues. What these little devices do is convert any reasonable voltage on the input side to a nice 14.5 volts (absorption) or 13.3 volts (float) on the output side. They do this by essentially exchanging amps for volts.
...
The specific device that I plan on using is the Redarc BCDC1225-LV, which can output up to 25 amps...

Great idea; it has been discussed here (and in the FiberglassRV forum) before...

Originally Posted by Brian B-P

If you want to get significant charging while driving, I suggest seriously looking at a DC-to-DC charger, rather than expecting the voltage that happens to result from the tug's charging system operation to be suitable. It should be no problem to pump 30 amps into the trailer's batteries with a suitable charger, but just a wire to the tug's battery won't do that.

Originally Posted by NJ Joe

I think you are having trouble keeping up because of the voltage drop in the long run for the charge cable from the truck to the back of the 21. I am planning to try this DC to DC charger once I pick up my 21 next year.

ctek d205S

I'm looking forward to hearing about the results.

[paulk]

Originally Posted by cpaharley2008

Welcome PaulK to our little world. You lost me above in your description other than it is a better controller than the stock one. What are the prices and installation procedures?

They're fairly expensive, which is why they seem to still be fairly niche.

The Ctek D250S DUAL, which I do not recommend unless you don't care too much about your solar input, is $239.97 on amazon -> Amazon.com: CTEK (56-677) D250S 5-Step, Automatic DUAL 12 Volt 20 Amp Battery Charger: Automotive

The much better Redarc BCDC1225-LV seems to not be sold in the USA, but you can import it easily. Redarc themselves will ship it to the USA, and they sell it for $659.93 Australian Dollars. I've seen it new on ebay for $390 Australian Dollars. That would make it $300 USD at today's exchange rate.

https://www.redarc.com.au/products/p...ulator-25a-lv/

Installation should be fairly easy. It needs to be close to the battery, just like other chargers, so I'm putting it under the dinette seat. It should be secured to the floor or something else solid.

For the alternator only installation, just disconnect the +12 volt wire coming from the vehicle and attach it instead to the input on the DC-DC charger. Attach the output of the DC-DC charger to whatever the +12 volt line was attached to originally. Attach the DC to DC unit's ground to ground. Done.

Installation for solar requires an additional SPDT relay to switch between the solar input and the alternator input. Attach the relay's switch controlling terminal to the +12 volt wire from the vehicle, so that it selects the vehicle's alternator input whenever the vehicle is providing power. Attach the +12 volt line to input #1 on the relay. Attach the solar cable to input #2 on the relay. Connect the common output of the relay to the DC-DC charger. Remove the GoSolar charge controller since the solar cells attach directly to the DC-DC charger. Done

The Redarc manual accessible from the link above has some visual diagrams showing various installations. I omitted a few minor details above for clarity, but those details are in the manual.

Redarc also sells a Relay that you can use, but these are commodity items and Redarc charges $100 for that component. I'd just get one from a hardware store.

In addition to the above, I'd recommend getting a Trimetric as neither the Redarc nor the Ctek has a display to show solar amps. A trimetric can show that after deducting the trailer loads, which you could argue is a better metric anyways.

So yes, in summary, DC-DC charge controllers are expensive, but still less than a $800 Honda 1000 watt generator if you are contemplating buying one for just occasional use. I should mention though that you would get a faster charge on a generator (85 amps vs 25 amps).

[yardsale]

Originally Posted by LeonW

Doesn't it also depend upon the thickness of the wire from the alternator to the trailer? I seem to remember reading a thread about that, smacking my head, and saying 'Duh, another thing I should have done...'

Escape recommended running #10 ground wire but my local installer said it wasn't possible--should have persisited. I think our fridge draws about 4 amps per hour as I was able to run the fridge on 12v during a sunny day when my 160w panel was producing that much power.

[NJ Joe]

I have had the Ctek D250S Dual installed in my slide-in camper for about a year now. It has been able to fully charge my 2 group 31 batteries and keep up with my 12v compressor frig and freezer while I am underway, even when my F150's alternator drops down to the 12.9v float charge.

I am hoping to get one installed in my Escape 21 sometime this year. The frig in the Escape will put a larger load on the system then what I have in my slide-in camper (about 8 amps + charge current for the battery). Also, the cable run from the 7 pin trailer connector will be longer (only about 6 ft in the slide-in), so I'm still not 100% sure this is going to work.

[Losangeles]

Originally Posted by yardsale

Escape recommended running #10 ground wire but my local installer said it wasn't possible--should have persisited. I think our fridge draws about 4 amps per hour as I was able to run the fridge on 12v during a sunny day when my 160w panel was producing that much power.

I had my local (expert and trusted) trailer guy run #10 wire from the engine in our SUV to the power connection at the back of the tug.

(When I finally got ahold of the right tech at Acura, they admitted that the super thin wire they use to the hitch power connection is only sufficient for trailer brake lights)

Adding the #10 wire to the tug made a HUGE improvement. We run the medium sized Casita fridge freezer when towing on 12v, not propane (don't start that debate here)

and with the "factory tow" kit from Acura (before the $100 mod) we'd arrive after 1 day of towing with 2/3 depleted Casita battery.

after the #10 wire was in, we'd arrive with a FULL Casita battery. Makes a huge difference when boondocking!!!