specific solar charging question

[Mayne]

I working on building up my old m416, and one of the areas I know little about
is recharging the optima blue tops I want to add to it. The only real power draw I would have would be a fridge/freezer of the Engle-ish kind. I'd like to go solar, as I'm running a flat 4 plug and wire harness for the trailer, so I don't see it charging off the jeep unless I rewire both units. What kind of solar system would I be looking at to keep things going for a max of 10 days.
Or, do I have overly high expectations for this kind of set up.

Thanks

Mayne

[Martyn]

I working on building up my old m416, and one of the areas I know little about
is recharging the optima blue tops I want to add to it. The only real power draw I would have would be a fridge/freezer of the Engle-ish kind. I'd like to go solar, as I'm running a flat 4 plug and wire harness for the trailer, so I don't see it charging off the jeep unless I rewire both units. What kind of solar system would I be looking at to keep things going for a max of 10 days.
Or, do I have overly high expectations for this kind of set up.

Thanks

Mayne

On the 12 volt section of our web site http://www.adventuretrailers.com/12volt_solar.html are all the equations for working out what your power requirements are. Once you have calculated your draw you can work backwards and see what size panel you need to keep things afloat for 10 days.

Your fridge will have the amperage stated on it, you then have to try and calculate what percentage of the time the compressor is running over a 24 hour period to calculate the energy draw. (It would be a whole new thread to discuss how to keep this down to a minimum, and why some people can run their fridges for 7 days with no recharge and others only 3 days).

Value for your $ the 80 watt panels are your best buy. Prices fluctuate on panels but sometimes you can make a great deal when a company changes from say an 80 watt panel to a new 85 watt panel.

In addition to the panel you will need a control box to regulate the charge to the battery. You can buy simple units or LED units that show the charge coming in from the panel and the battery voltage.

You would need to fabricate a stand for the panel.

As you are not charging the battery in the trailer from the vehicle it would be very important that the battery in the trailer was fully charged before you leave on a trip. We use the Power Tender unit as it is a 6 amp charger and a trickle or float charger. It will charge most styles of battery.

[RunninRubicon]

Thanks for this information I know many of us debate about which way to go (gen. vs solar vs just battery). Nice to know about your source for advice on this challenging problem of power. So many just want to sell us something and not provide us with data to determine our own needs. Do you have thoughts on wind generation as well? I have seen some data and products via catologs, but this direction seems so variable as one never knows about the windage at one's destintation. Seems 80 amps of power should "fit the bill" for most of us utilizing solar. Especially so here in the southwest.

[Martyn]

Thanks for this information I know many of us debate about which way to go (gen. vs solar vs just battery). Nice to know about your source for advice on this challenging problem of power. So many just want to sell us something and not provide us with data to determine our own needs. Do you have thoughts on wind generation as well? I have seen some data and products via catologs, but this direction seems so variable as one never knows about the windage at one's destintation. Seems 80 amps of power should "fit the bill" for most of us utilizing solar. Especially so here in the southwest.

We are working on wind generators. Small wind generators are very few and far between, and then getting companies to work with you is an other challenge.

AirX is a nice unit produces 400 watts. They have a 15 ft telescoping pole that the generator fits onto the base is set up so you drive over it and the vehicle or trailer acts as the anchor.

Noise with these small units is a problem as the rotor turns so fast. Fitting a kill switch to stop the rotors is a good idea so you can sleep.

Lots of new ideas coming forward but few in production.

Having the facts so you can make an informed decision is essential. It's not that I'm adverse to making a sale, but I want you to come to that conclusion after you have done all the research. We don't by any means carry the cheapest equipment on the market, we do carry what we consider to be the best, that will perform in the harshest conditions, and is extremely reliable.

Saving a few bucks and having a product malfunction is not our game.

[Mayne]

So if I get this right, from the reply Martyn had and the info off your trailer site, I can figure an Engle 45 fridge will suck up 30 watts/hr @2.5amp/hr.
If I assume (yes I know, very scetchy when one assumes) that the fridge compressor will run constantly. Then I need at least 60watts/hrs to replace what I've sucked down overnight. And this is if I have a full 12hrs of sunlight, to counter act 12hrs of night. Giving that situation is pure theory and is a bit black and white.
If I have 200amp/hrs worth of power at 12volts = 2400watt/hrs
I should have 2400watt/hrs divided by 2 = 50% drain on batteries and therefore have 1200watts/hrs of power divided by 30watt/hrs usage.
to = 40watt/hrs of burn time.

Am I even in the ball park?

Mayne

[Martyn]

So if I get this right, from the reply Martyn had and the info off your trailer site, I can figure an Engle 45 fridge will suck up 30 watts/hr @2.5amp/hr.
If I assume (yes I know, very scetchy when one assumes) that the fridge compressor will run constantly. Then I need at least 60watts/hrs to replace what I've sucked down overnight. And this is if I have a full 12hrs of sunlight, to counter act 12hrs of night. Giving that situation is pure theory and is a bit black and white.
If I have 200amp/hrs worth of power at 12volts = 2400watt/hrs
I should have 2400watt/hrs divided by 2 = 50% drain on batteries and therefore have 1200watts/hrs of power divided by 30watt/hrs usage.
to = 40watt/hrs of burn time.

Am I even in the ball park?

Mayne

Your compressor does not run all the time, not even close, even if you are running the unit as a freezer. It's just like your fridge at home you can hear the compressor cycling on and off. I don't have my copy of the Overland Journal to use as a reference, but do they state anything about the power draw in use as the compressor cycles on and off??

My experience with an Engle 45 liter running just on the battery is that I can get 5 days + out of a group 31 deep cycle battery at day time temperatures of 90' The battery will power the fridge down to as low as 10.8 volts of charge.

I know other people have different experiences, and things like how often you open the fridge, if it's in direct sun light, how full the fridge is, if you are replacing items that are removed so you are cooling something rather than air all make a difference.

[Mayne]

Your compressor does not run all the time, not even close, even if you are running the unit as a freezer. It's just like your fridge at home you can hear the compressor cycling on and off. I don't have my copy of the Overland Journal to use as a reference, but do they state anything about the power draw in use as the compressor cycles on and off??

My experience with an Engle 45 liter running just on the battery is that I can get 5 days + out of a group 31 deep cycle battery at day time temperatures of 90' The battery will power the fridge down to as low as 10.8 volts of charge.

I know other people have different experiences, and things like how often you open the fridge, if it's in direct sun light, how full the fridge is, if you are replacing items that are removed so you are cooling something rather than air all make a difference.

Okay, so in that case with the fridge running a fraction of full time, say even a third off the time on the high end, then an 80watt panel set up would more than take care of my needs. As it is any other electrical use would be far and in between.
I do like the idea of a mini windmill, that does sound cool....

[RunninRubicon]

We are working on wind generators. Small wind generators are very few and far between, and then getting companies to work with you is an other challenge.

AirX is a nice unit produces 400 watts. They have a 15 ft telescoping pole that the generator fits onto the base is set up so you drive over it and the vehicle or trailer acts as the anchor.

Noise with these small units is a problem as the rotor turns so fast. Fitting a kill switch to stop the rotors is a good idea so you can sleep.

Lots of new ideas coming forward but few in production.

Having the facts so you can make an informed decision is essential. It's not that I'm adverse to making a sale, but I want you to come to that conclusion after you have done all the research. We don't by any means carry the cheapest equipment on the market, we do carry what we consider to be the best, that will perform in the harshest conditions, and is extremely reliable.

Saving a few bucks and having a product malfunction is not our game.

Knowledge is power, point well made. Your knowledge on this subject matter is duely appreciated and obviously seen in your companies products. This web-site is a real asset because of informed members such as yourself, making contributions. Thanks again for your continued input.

[Howard70]

On a recent 3 week trip we did a "hybrid" system for our ARB 40 refrigerator/freezer. When driving we powered the fridge from our Tacoma's alternator via the starting battery. When stopped we powered it from an auxiliary battery. The auxiliary battery was charged via a pair of 55 watt Siemens solar panels (about 7 total amps at 12-14 volts with good sun) mounted on top of our ARE shell. The system worked flawlessly and I suspect would have gone on indefinitely. Here's a summary of the system and the power data:

Background

We started the trip with the fridge full of frozen stuff and we set the fridge on freeze for 12 hr (120v connected to an outlet in our garage) so that everything was cold at the start and the system wasn't starting out by freezing stuff. Our daily cold, but not frozen, food and drinks were carried in a small igloo cooler (maybe 15 quart size) with 3 quarts of frozen water in plastic jugs.

Every morning before breaking camp we would move the partially thawed three quarts of water from the igloo to the ARB fridge and take 3 quarts of freshly frozen water out of the fridge and put them into the igloo. We did this whether or not the water in the igloo was thawed or not.

Whenever we purchased new food that we wanted to freeze or that was frozen we would place in the ARB. If we wanted to keep food cool we placed in the igloo. We generally kept the ARB set at 3 to 5, but in the morning after placing the partially thawed water containers in the fridge we'd set it on freeze if we were driving. We'd leave it on freeze until about 3 or 4 in the afternoon, or until we stopped driving.

Power consumption

We monitored current and voltage with a Xantrex Link 10 (http://www.xantrex.com/web/id/237/p/1/pt/5/product.asp) battery monitoring system. Depending on how late we drove before setting up camp and how hot the night temperatures were, the ARB fridge consumed between 15 and 26 amp/hours (settings between 3 and 5). Our shortest "night" was probably about 8 hours and our longest "night"was probably about 16 hours. The coolest night was around 40 and the hottest probably around 85.

Power Production

The two solar panels could easily fully charge the auxiliary battery during the following day, sometimes by as early as 1 pm and sometimes it took through the afternoon. That depended on the cloud cover (we had a few days with nearly complete cloud cover, but we usually had several hours of strong sunlight); whether we were in forest or the open; and whether or not we parked in the shade to keep the truck cooler. In general we simply drove normally and didn't try to park in favorable solar conditions.

We almost always produced at least 1 amp unless it was before 8 am, after 5 pm, or actually raining. Usually we were producing between 4 and 6 amps, occasionally slightly over 7. 9:30 to 3:30 were the peak hours when we'd see the highest output. One problem with monitoring "real time" like this is that the charge controller we use for the solar panels, maintains voltage and adjusts current depending on the batteries state of charge. Thus when the batteries are getting "full" the controller reduces the current and so you rarely see the full output of your solar panels unless your battery is really drawn down. We never discharged the battery below 50% (it was a 55 ah Optima Yellowtop).

Balance - Could we have run the system completely solar?

Remember that we were using the solar panels to recharge amp hours used at night and we used the alternator while underway in the daytime. We wanted to test the system before trying a completely solar trip (which we'll do next). However, I think that we could run the system almost completely solar now that we've upgraded the battery to a 100 ah Lifeline. If the fridge uses 60 amp hours in a day and the solar panels can produce 45 amp hours in a day, then there's a 15 amp hour deficit per day. with a 100 amp hour battery drawing it down to 45 or 50 amp hours (approximately 50%) is a good target. That would give us about three, maybe four days completely solar before we'd need to run the fridge on the truck in the daytime and allow the solar panels full output to go into the battery for a day or so to bring it back up to a full charge. If you worked at reducing the amp hours required by the fridge (keeping it cooler, open it less, etc.) you could extend that time.

Cost

Solar is more expensive that a generator to purchase. We were lucky because Heidi traded some work for the two solar panels and we didn't have to purchase them. I would guess that our 110 watt set up with the charge controller would probably cost about $800. I prefer two panels totaling 110 watts to a single panel of 110 watts. While solar panels are tough they can break if hit by a rock or really large hail. With one panel a single break takes down the whole system. With two, you will decrease your output by 1/2 if one panel breaks but you'll still have some current produced.

We're really happy with the solar system. Once we get the auxiliary battery wired into the truck's charging system then we'll have the best of both worlds since the battery will charge when the truck runs - we almost always drive some within a three to four day period which will top the battery back up.

Howard L. Snell

[Tucson T4R]

Excellent write up! Thank you. For longer stays, I have been using honda generator to recharge my trailer batteries. Setting a solar solution would be so much better. :-)

Last week, I saw a 400Watt Solar system at Costco for about $220. It was four pannels and the electronics to attach and monitor a battery charging system.

Seemed a little on the cheep side but maybe it was a good deal. Still researching before I buy.