How many watts needed from solar to maintain battery w/ Engel fridge

[teotwaki]

Martyn, good info and not adding to the misinformation either.

Looks like at least three of us with hands on experience plus an understanding of the numbers have done well with 53-60 watt panels. I would hate to see the OP waste cargo space and money building a solar system in excess of his actual needs and budget.

There are good points on being aware of ambient temps and not cooling a fridge full of air. If too much time goes by without sunlight the car's engine can be run and the battery charged rather than have a bunch of heavy batteries that are rarely needed.

 

[Robert Bills]

. . .Our in field experience has shown that a good 60 watt solar panel (Aspect Solar or Powerfilm) will produce enough energy in a 24 hr period to run an Engel 45 indefinitely in the continental US. In all cases we paired the solar panel with a group 31 battery to act as a reservoir for energy and to power the fridge overnight.

^^^ What Martyn said.

I looked at my notes from 10 years ago when I was restoring my Bantam trailer and first thinking about solar to power my Engel 45. I found an exchange of emails with Martyn, who was helping me analyze my power needs. His recommendation at the time was a 60 or 80 watt panel for a 95 aH Group 29 marine battery (the largest that would fit in my battery box).

I never got around to finishing my solar setup and made do with charging the battery at home with a bench charger and on the road by the tow rig alternator (and often by borrowing power from a buddy's RV generator/charger). That limited me to about two days use between bench charges, and I also ruined several Wallyworld batteries by drawing them down to empty rather than following the 50% maximum discharge rule.

Now that I have retired I have more time to use my trailer and am updating my power system:

I just purchased a Renogy 100w suitcase solar kit. Of the Group 29 batteries on the market I have decided on the Costco/Interstate DC27 at $85 as the best value (I still have the same battery box limiting battery size). My rationale is that if I take care of my battery I should get an average of 3 years from it, which means that I can buy a Costco battery every three years for 9 years before I spend the same as for one high-end deep cycle battery. On the other hand, if I abuse my battery and destroy it (as my past history proves is quite likely) I will only throw away $85 at a time rather than $275.

The only piece to the puzzle that I haven't solved is an onboard charger/maintainer to run the fridge and maintain the battery when hooked up to shore power. I am open to suggestions for one of those.

 

[teotwaki]

This is the updated version of the charger that I built into my trailer: http://www.marinco.com/en/28106

About $64 http://www.boatersland.com/mrn28106.html?gclid=CKvq9ZiR5MwCFY9hfgodue8OOQ

 

[calicamper]

^^^ What Martyn said.

I looked at my notes from 10 years ago when I was restoring my Bantam trailer and first thinking about solar to power my Engel 45. I found an exchange of emails with Martyn, who was helping me analyze my power needs. His recommendation at the time was a 60 or 80 watt panel for a 95 aH Group 29 marine battery (the largest that would fit in my battery box).

I never got around to finishing my solar setup and made do with charging the battery at home with a bench charger and on the road by the tow rig alternator (and often by borrowing power from a buddy's RV generator/charger). That limited me to about two days use between bench charges, and I also ruined several Wallyworld batteries by drawing them down to empty rather than following the 50% maximum discharge rule.

Now that I have retired I have more time to use my trailer and am updating my power system:

I just purchased a Renogy 100w suitcase solar kit. Of the Group 29 batteries on the market I have decided on the Costco/Interstate DC27 at $85 as the best value (I still have the same battery box limiting battery size). My rationale is that if I take care of my battery I should get an average of 3 years from it, which means that I can buy a Costco battery every three years for 9 years before I spend the same as for one high-end deep cycle battery. On the other hand, if I abuse my battery and destroy it (as my past history proves is quite likely) I will only throw away $85 at a time rather than $275.

The only piece to the puzzle that I haven't solved is an onboard charger/maintainer to run the fridge and maintain the battery when hooked up to shore power. I am open to suggestions for one of those.

Check out the Marine shore power options. Same kind of amps in vs needed numbers. I replaced our 10amp shore power / charger on my 28ft Sail boat last yr with a 12 amp unit. Simply given prices had come down. I recall it was like $180. They typically last 5-6yrs. Though mine is always plugged in except when were out sailing. You do have a isolator switch, non of these shore power units like to see alternator current, when you fire up the engine or have solar power coming in.

 

[teotwaki]

You do have a isolator switch, non of these shore power units like to see alternator current, when you fire up the engine or have solar power coming in.

I've had my Guest/Marinco charger without an isolator switch for almost 6 years and had no problems. Both the solar charger and connection to the car system are wired across the battery too.

 

[calicamper]

I've had my Guest/Marinco charger without an isolator switch for almost 6 years and had no problems. Both the solar charger and connection to the car system are wired across the battery too.

Most will tolerate power coming in from another source, but they typically dont like it. If watch them close you'll see they do some goofy modes when they detect other power sources.

 

[teotwaki]

Most will tolerate power coming in from another source, but they typically dont like it. If watch them close you'll see they do some goofy modes when they detect other power sources.

How can it get into a "goofy mode" without AC power on the line cord to power up the charger's circuitry? If AC power is on the line cord why would solar or vehicle charging be putting DC into the circuit?

 

[calicamper]

Simply sharing my 25yrs of shore power experience from the sailboat world. The good units do quite a bit of battery health via logic in the unit. I havent encountered one yet that doesnt get cranky and unhappy when other power sources start dumping power into the house batteries. This was actually an interesting talk a few of us had two yrs ago with a marine elecrician working systems for several boats getting set to race SF to Hawaii. During the race many use the Diesel to deep charge the house batts if solar isnt cutting it. To avoid causing the shore power unit trama ie showing an error for the trip, we simply put them on a switch and shut them off.
No big deal.
But yes they typically dont agree with alternate sources dropping power into the battery as they are "managing the battery", just confuses their logic.

 

[4x4junkie]

60-80W of solar indeed should be able to keep a fridge going indefinitely, AS LONG AS each & every day remains sunny throughout the day (and your panel remains free from shading).

Me, I like to have some reserve capacity built into the system to keep going through those not-so-sunny days, as well as to be able to recover from a string of such days within a reasonable amount of time (very warm weather can cause a fridge to exceed your solar capacity too). For this you really need more than 80W of solar.

I have 170W, and though I have a little more than just a fridge going (LED camp lighting, playing the stereo, occasional charging R/C model batteries), there has been times on the first sunny day after a couple cloudy days it still doesn't fully recover my two batteries (it'll take a 2nd sunny day in a row before it's fully recovered).

And I have yet to see a simple solar controller that didn't simply shut itself off (or shut off charging) when another charging source such as your alternator or a shore charger comes online. I only have experience with one shore charger (a Xantrex unit) that was "seeing" other charge sources, however it too had no issues with it either. Maybe many many years ago systems were less "smart", but nowadays I think pretty much anything made for off-grid use is designed to work with other charging systems being present on the same battery (or battery bank).

 

[Rockrunner]

Hi Rockrunner
Based on our experience with 2.000+ clients who face the same question what size solar array needed to sustain the operation of a fridge, in your case you want to run it 24/7 during summer, you most likely will be looking at 158W or more. Less and your battery will be discharged in 1 week. That is during days with sun.

For days without sun (overcast, rain etc.) your fridge will run from the battery solely and you need to consider how many days autonomy you want as this will determine how many batteries you would need to install. Example: if your fridge draws an average of 3A/h and you have a 100Ah deep cycle battery, after 24h total load drawn is (24 x 3Ah) 72Ah and your battery would be 72% discharged (not counting battery losses), i.e. empty.

If you frequently open and close the fridge the suggested 3A value will increase.

Our suggestion would be to ensure the vehicle is parked in the shade (cooler for the fridge and vehicle), whilst the solar panels are in the sun. Size wise you should consider a 158W array more and avoid partial shading. On the battery side you should consider at least 2 x 100Ah deep cycles (parallel) to have 2 days autonomy.

For more reading, there are some relevant posts on our website

Thanks, lots of great info and things to figure out. I am trying to keep the footprint as small as possible and think I have figured out what I am going to do once I get an answer back from Arkpak.

 

[Rockrunner]

Thanks for all the great info guys, as usual it isn't as simple as one would hope and I ended up changing one of the variables last night. I am now the new owner of an ARB 50, bought it from a fellow member.

After reading a bunch of posts and other articles online I have come to a decision. I am going to get an Arkpak 730 and a solar supply to keep the unit charged. I like the Arpak because it has 110v and 12v an while I am on the boat I like to watch some TV, not a lot but there are days when it is cold and or windy when I go below and will watch a game or movie. I like that it it portable and can be moved to my truck when I take it camping, usually for 4-6 days, with the ability to charge it three ways I should have no problem keeping power the entire trip. I have a generator but hate running it due to the noise, easier when camping but not so much when on the boat in my slip.

Here are some of the details some of you asked for;

Littleton CO
ARB 50
19" LCD TV
Insulating blanket ordered
Cooler is used for two days then two-three days closed then used for a day and shut till the weekend again

So now I am hunting for solar set up for the Arkpak, a little easier to do I think. If anybody has one and has it hooked up to Solar please LMK what works for you and what hasn't, cheaper to learn from other peoples mistakes (I have made plenty :-0 )

 

[plh]

Arkpak 730.... assume you are adding a group 31 to that being they don't come with a battery?

 

[calicamper]

My little 15inch LCD tv is actually 12volts but has a box on the cord to step it down from 110. I've been wanting to try setting it up for a direct 12volt plug vs running through the inverter which is really inefficient.

Just a general device thought.

 

[Rbertalotto]

All the TVs in my camper run off 12v "wall warts". I simply disregarded and wired directly to 12v. ( Best Buy house brand InvictaTVs) I also did the same with a Sony Blue Ray player. Works great. No issues. You can read all about my solar and lots more here:
Www.rvbprecision.com

 

[dcg141]

I have the big Dometic fridge. Its a 65 quart cooler and I use a 31 agm and one 100 watt panel and in bright sunlight it takes until about noon to bring my battery back to full charge from an overnight run. That's if I just run the fridge. I carry a 2000W Honda gen but I rarely have to pull it out anymore.