A "minimal" solar kit for a nOOb? (LONG!)

[Martinjmpr]

So, yes, I have read through the other "help me figure out a solar power setup" threads and I'm still somewhat befuddled. I also should point out that my solar needs are a little different from what most of the other people seem to be wanting. I'll apologize in advance for being somewhat long-winded.
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Our needs are actually fairly minimal: We need a setup that will keep a 12v fridge running for, at most, 5 days with ambient temps in the 70 - 90 degree (max) range. .
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The 12v Truckfridge (AKA Indel B TB 41) is a 41 quart fridge and normally sits in the tow vehicle, currently a 2004 Suburban. Right now I have it plugged in to the aux power outlet on the back of the center console (more about this in a minute.)
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Our trailer, a 2014 T@B Clamshell, has a 12v fridge (I think it's a Norcold but not sure) however, we don't normally run it because it is very noisy and the back of the fridge is directly behind where my wife's head is when we sleep! If we are at a developed campsite with 120vAC power, we sometimes run that fridge during the day only and shut it off at night. Needless to say we don't keep "spoilable" food in there (no meat, cheese, milk, etc), the only thing in there normally are bottled water, soda or beer. I really don't need/want to run that fridge all the time anyway because of the noise issue.
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The trailer does have a battery of unknown specification. If I get a chance later today I'll pull the cover off and take a look to see what group size it is, type, amps, etc. But the bottom line is that we do have a battery and there is even an input on the side of the battery cover for the ZAMP solar power kit.
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Now, as I said, the fridge normally stays in the truck. There are a couple of reasons for this, the biggest one being that floor space in our little T@B is already minimal so we don't want to diminish it further by putting the fridge inside. Putting the fridge outside the door is also something we want to avoid as we often camp in "critter country" and the thought of leaving a fridge outside doesn't seem like a smart idea. Also having the fridge (and food box) in the truck means that if we leave camp to go explore, we will have all our food and drinks with us.
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Since I got the Suburban in December we've been camping about 5 times at 9 different locations, and we had 120vAC power at all of them. Since the fridge is in the truck, if we take a day-long excursion, the fridge normally sits in the truck while we are out and about. At night when we are camped I run a regular 120v extension cord directly to the fridge to keep it powered. A couple of times after day excursions I've come back to find the display on the fridge reading "E1" which is the error code meaning that voltage has dropped below the "safe" level and the fridge has shut itself off. When my 4runner would do this, it almost always meant a dead battery but my Suburban fired right up. I think what happened was that the voltage cutoff setting has accidentally moved from "low" to "medium" or "high" and my assumption is that the wiring to the 12v outlet in the center console was causing enough voltage drop to make the fridge shut off. From now on I'm careful to make sure the cutoff switch stays at "low" which I believe will allow voltage to drop as low as 10v before cutting off (I think the medium and high settings are 11 and 12v respectively, but I'll have to check.)
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I should probably note that I put a new battery in the Suburban as soon as I got it, it's an AGM "Super Start" from O'Reilly (which I think is just a re-branded Deka.) Rated at 775 amps.
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OK, so that's the background. Now, as to an actual power setup: The lights in the T@B are LEDs and the fan consumes very little power, so the only real need we have for electrical power is for the truckfridge. We have a couple of camping trips coming up where we will not have access to shore power.
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When we did this trip last year (which has us sitting, static, at the same campsite for 4 days) I would start my 4runner and run it for about 30 minutes, twice each day to charge the battery. I normally did this during or right after breakfast and dinner. The only day I didn't do this was the day we broke camp to come home, and in that case I waited until about 11am to start the truck and sure enough - dead battery (I carry a portable jump starter and was able to jump start myself but this showed how important it was for me to do my twice daily engine start-ups.)
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I'd rather not get a gasoline generator if I don't have to (don't want to carry a noisy/smelly generator in my truck or trailer) so I'd like to figure out if I could get some kind of minimal solar setup, just enough to keep the fridge from running my battery down on a warm day (it can get up to 75 degrees or so outside, but if the windows on the truck are closed the interior temp of the Suburban can easily exceed 90 degrees at mid-day.) I could put the fridge outside (in the shade) during the day and then put it in the truck at night (when it would obviously be cooler.) We could also, possibly, put the fridge inside the T@B although as I've said, that's not a preferred solution.
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And that's really the other question WRT solar: Should I leave the fridge hooked up to the truck (which presumably has a bigger battery than the T@B) and run solar to the truck, or should I plug the fridge into the trailer's 12v power outlet (it has both 12v and 120vAC outlets but if we are not plugged into shore power the 120vAC outlets don't work.) Another option might be a bigger battery (or a pair of batteries) on the trailer.
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I do have a very minimal amount of electrical knowledge (enough to get a basic HAM ticket but not much more than that.) Anyway, thanks in advance to those who read this long post, and I'll appreciate any input you can give.

 

[Martinjmpr]

Looking at maybe something like this: https://www.amazon.com/Renogy-Watts...35827&sr=8-4&keywords=renology+100w+solar#Ask

 

[Martinjmpr]

Hmmm....just read through the FAQ again regarding solar and fridges.
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Maybe I'm over thinking this?
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Seems like a basic 100w setup would probably be sufficient to keep the truck battery charged up with the fridge running and that would be all I need. I see mentions of inverters but assuming everything I'm running is 12v, I don't see how an inverter would be needed?

 

[DiploStrat]

Martin,

Shortest answer is that yer doin't backwards:

-- Determine how many Ah your load demands in 24 hours.
-- Multiply by the number of days you need to run the load.
-- Buy the battery(s) that can carry this load.

Now figure out how you will recharge - vehicle, solar, shore/generator. Do it this way and your system will always work and your beer will always be cold.

For solar, the big variable is at the amount of sun available, but, if you have done the other part correctly, it is not mission critical as you will always have enough power within the window you define.

So, the real question is, how much solar does it take to recharge a battery of x size within the amount of time that I have available?

 

[jonyjoe101]

danfoss compressor 12 volt fridges consume about 25 amps of power during a 24 hour period when set to 40 degrees. I use to keep my fridge edgestar fp430 in the back of my van where the temperature was over 90 degrees. I measured the consumption using a 12 volt wattmeter.

I use to run it 24/7 with a 120 watt solar panel and a 75ah agm aux battery, but i'm in southern california where the sun is always out. The few times that it was overcast or raining, the fridge would quit working at about midnight due to low battery, but the items in fridge would stay cold till morning.

120 watt panel gave me about 6 amps of charge power when the sun was overhead. Usually you can get about 1 amp from every 20 watt of solar panel. mppt controller will squeeze every amp out of your panel but they only work on the high voltage panels (30 volts or higher). 240 watt panel with mppt will give you about 13 amps. You want to have a big enough panel to quickly charge your battery when the sun comes out. On my system it was 100 percent solar, I never charged the battery with generators/alternators/shore power. I use to go months without any problems, bad weather was the only time I got the battery low warning on the fridge blinking.

if your fridge keeps cutting out when the battery still reads good, you might have a weak connection. On my fridge I replaced the 12 volt plug with xt60 connectors and connected directly to battery. These connectors make a solid connection and can handle 60 amps, your fridge wont be losing any power from a loose connection. If your cigarette plug is getting warm, its wasting power. When you are relying on batteries you dont want to waste it on heat.

 

[Martinjmpr]

Martin,

Shortest answer is that yer doin't backwards:

-- Determine how many Ah your load demands in 24 hours.
-- Multiply by the number of days you need to run the load.
-- Buy the battery(s) that can carry this load.

Now figure out how you will recharge - vehicle, solar, shore/generator. Do it this way and your system will always work and your beer will always be cold.

For solar, the big variable is at the amount of sun available, but, if you have done the other part correctly, it is not mission critical as you will always have enough power within the window you define.

So, the real question is, how much solar does it take to recharge a battery of x size within the amount of time that I have available?

OK, that seems reasonable. The next issue for me is how to find out the information needed.
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New battery on the truck is a SuperStart (Deka), according to the web page it's rated at 55ah
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Fridge is an Indel-B TB41. Now this is where I am having difficulty finding info: I can't find anything that addresses the average amp draw on this fridge. According the manual, it has a 45w power supply.
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So let me ask a dumb question: Would 45w power supply / 12v = 3.75 amps? And would that be the max or the average?
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3.75a x 24 hours = 90ah for a 24 hour period which is almost double the AH of my battery, right?
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But a 100w solar panel, operating at (let's say) 72% efficiency, would be 72w / 12v = 6a. If I have 11 hours of good sunlight (very possible in Colorado in the Summer) that could potentially mean 66ah going back into the battery, yes?
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Have I figured this out right?
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So IF I've figured this out correctly, my 55ah battery isn't likely going to be enough unless I get a big enough solar panel to keep it "topped off" during the day. Even then I could potentially be looking at 13 hours at 2 - 3 ah which would draw my 55ah battery down to 50% or less, not good, from what I've heard (of course, here in CO it cools off rapidly at night so maybe the fridge would be running at <1ah during hours of darkness? Is there a way to measure this?)

 

[Martinjmpr]

danfoss compressor 12 volt fridges consume about 25 amps of power during a 24 hour period when set to 40 degrees. I use to keep my fridge edgestar fp430 in the back of my van where the temperature was over 90 degrees. I measured the consumption using a 12 volt wattmeter.

Is the 12v wattmeter something I can get at an electronics store? Is it fairly easy to use (i.e. can I just hook it up between the power source and the device being powered?) Our Indel-B is normally set at 30- 32 degrees (I do this because I've noticed there can be a wide fluctuation of temps between the bottom and the top. The thermostat is apparently located in the bottom, i.e. coldest, part of the fridge, so 30 degrees at the bottom keeps the top of the fridge below 40.)
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On my fridge I replaced the 12 volt plug with xt60 connectors and connected directly to battery. These connectors make a solid connection and can handle 60 amps, your fridge wont be losing any power from a loose connection. If your cigarette plug is getting warm, its wasting power. When you are relying on batteries you dont want to waste it on heat.

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Do you have a link for the XT60 connectors?

 

[AndrewP]

Tons of cheap power meters:
https://www.amazon.com/Makerfire®-P...TF8&qid=1465925916&sr=8-4&keywords=watt+meter

The battery in your truck is far too small. Ideally, you want about 100 amphours, which is about as big as common 12 volt batteries get, with a few exceptions. A panel of 100 watts will likely be enough to run a refrigerator but not much else.

Do you have space to add a second battery in the Suburban? If you could separate start functions from "house" functions you'll be miles ahead.

You have to remember the duty cycle of your fridge is not 100%. It's likely running only 30% of the time, depending on ambient temperature. The power meter will have a recording function, and you can measure the power use of your fridge in a typical 24 hour day. Then you'll have a good number to use for calculating your loads/needs.

Your math is basically right but ignores losses when charging the battery. I'd be surprised if you see 6 amps off the panel. Good rule of thumb is that 100 watts = 5 amps into the battery 6-7 hours per day, and less another 6 hours per day.

While you can get the XT 60 connectors on Amazon, you might want to look at Anderson Power Poles too. That's how I make the connections for my solar system.

 

[Martinjmpr]

Tons of cheap power meters:
https://www.amazon.com/Makerfire%C2%AE-Precision-Power-Meter-Analyzer/dp/B00ORGDQOK/ref=sr_1_4?ie=UTF8&qid=1465925916&sr=8-4&keywords=watt+meter

The battery in your truck is far too small. Ideally, you want about 100 amphours, which is about as big as common 12 volt batteries get, with a few exceptions. A panel of 100 watts will likely be enough to run a refrigerator but not much else.

Do you have space to add a second battery in the Suburban? If you could separate start functions from "house" functions you'll be miles ahead.

You have to remember the duty cycle of your fridge is not 100%. It's likely running only 30% of the time, depending on ambient temperature. The power meter will have a recording function, and you can measure the power use of your fridge in a typical 24 hour day. Then you'll have a good number to use for calculating your loads/needs.

Your math is basically right but ignores losses when charging the battery. I'd be surprised if you see 6 amps off the panel. Good rule of thumb is that 100 watts = 5 amps into the battery 6-7 hours per day, and less another 6 hours per day.

While you can get the XT 60 connectors on Amazon, you might want to look at Anderson Power Poles too. That's how I make the connections for my solar system.

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Thanks for the info. As far as the battery goes, yes, there is space under the hood for a 2nd battery but I don't think I have the skills or the time to get a system like that properly set up. Does anybody make a 100AH battery in group 78/31?

 

[DiploStrat]

Grossly ...

Martin,

You are getting some good advice. Remember, refrigerators suck power. My NovaCool, with a freezer section, demands anywhere between 3 and 5 amps per hour.

Assuming that you use a lead acid battery,

-- You want a true deep cycle battery, not a starter battery or a "marine" battery. As the name implies, they are designed for deep cycling.

-- You may want to follow the 50% rule - that is for the best cost/benefit, never discharge you battery more than 50%. (I actually run about 20%.) You can go deeper, say 80%, but you will greatly reduce the battery's life. This may be worth it if your space is REALLY limited; it is up to you.

If you are going to be hammering the camper battery, you really need to isolate it from the starter battery. Chevrolet's have really good battery chargers so use properly sized cables and a relay based isolator, either key controlled or, if you want your solar kit to charge the starter battery, an "intelligent" relay.

 

[Martinjmpr]

OK, so thank you again to everyone who chimed in. I'm zeroing in on a solution. A few conclusions/discoveries have changed my focus:
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First of all, the dual battery plan for the 'Burb is on hold.
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So let me run this by the group and see if I'm forgetting anything or if this plan makes sense:
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I'm going to bypass the truck entirely and rely on the trailer battery. As near as I can tell, my battery is either 75ah or 80ah capacity. It is a deep cycle marine/RV battery, of the FLA type (i.e. it is not a sealed or AGM battery.)
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Instead of running dual batteries in the 'burb and hooking my solar panels there, my short term plan is to aqcuire a 100w Renology solar panel with a 40a MPPT charge controller and hook it to the trailer battery (there's already a connection for the ZAMP type fittings, I'm assuming that if the ZAMP fitting is not universal then I can either put a ZAMP fitting on the Renology panel or install a different fitting.) If we are stationary at a campsite (which is the only place we would need/want solar anyway) the fridge will come out of the Suburban and go into the trailer.
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Since I always leave the trailer plugged in at home, I should, (theoretically anyway) be starting with a fully charged battery. If I can figure that on average the fridge will draw 3-4a per hour during the hottest part of the day, and a 100w panel can put 4 - 5a per hour back into the battery, then the battery should stay nearly charged up through the day. Of course it will be getting no charge at night - but neither will the fridge be working at max capacity (the place we boondock is roughly 7500'+ in elevation so it cools off rapidly once the sun goes down - in fact, last weekend camping at similar altitudes, while daytime highs hit 85 it was cool enough to need a sweater by the time we went to bed.)
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I'm hoping (knock wood) that this will be sufficient for a 4 day/3 night trip. Fridge will be set at the lowest cutoff level and I will be monitoring the battery with a volt meter. Unfortunately I don't have a way to charge the trailer battery but if the worst happens, and voltage in the trailer drops low enough for the voltage cutoff to kick in and shut off the fridge, then I will move the fridge to the 'Burb and either try to connect the solar panel controller to the 'burb's battery or (in case of absolute failure) run the engine on the 'burb until the battery is charged up.
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So what have I not considered? Any holes in this plan? Should I bite the bullet and get 2 x 100w panels instead of one (the "in-for-a-penny-in-for-a-pound" philosophy?)
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Also before anyone suggests it: Eventually the 12v battery in the trailer will be replaced with a pair of 6v golf cart batteries. A friend of ours who has the exact same trailer has done this and according to him, his 2 x 6v batteries give him a whopping 208ah of capacity! :Wow1:

 

[dwh]

mppt controller will squeeze every amp out of your panel but they only work on the high voltage panels (30 volts or higher)

That's a pretty common misconception, but it's not correct.

MPPT works on anything. All it does is do a load test on the solar panel to determine what is the optimum voltage to get the most from the panel right this minute, and then adjust the load to keep the panel working at that voltage. Some check and adjust every hour, some do it more frequently.

The Vmp of the panel doesn't matter, as long as the MPPT controller is rated to operate at that voltage.

 

[dwh]

OK, that seems reasonable. The next issue for me is how to find out the information needed.
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New battery on the truck is a SuperStart (Deka), according to the web page it's rated at 55ah
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Fridge is an Indel-B TB41. Now this is where I am having difficulty finding info: I can't find anything that addresses the average amp draw on this fridge. According the manual, it has a 45w power supply.
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So let me ask a dumb question: Would 45w power supply / 12v = 3.75 amps? And would that be the max or the average?

Max. You figure average by figuring out the "duty cycle". I.e., what percentage of the time, is the compressor actually running.
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3.75a x 24 hours = 90ah for a 24 hour period which is almost double the AH of my battery, right?
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But a 100w solar panel, operating at (let's say) 72% efficiency, would be 72w / 12v = 6a. If I have 11 hours of good sunlight (very possible in Colorado in the Summer) that could potentially mean 66ah going back into the battery, yes?
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Have I figured this out right?

Yup. Though I think your 11 hours of good sun is unrealistically optimistic. Of course, by having a portable panel and moving around frequently to keep it centered on the sun you might actually get that, but I wouldn't count on getting full power out of the solar for 11 hours/day.



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[dwh]

Instead of running dual batteries in the 'burb and hooking my solar panels there, my short term plan is to aqcuire a 100w Renology solar panel with a 40a MPPT charge controller

You sure don't need a 40a rated charge controller for a 100w solar panel. 10a would be big enough for that.

If we are stationary at a campsite (which is the only place we would need/want solar anyway) the fridge will come out of the Suburban and go into the trailer.

Or, what I would do, is bring along a decent battery charger and just hook it to the truck battery when shore power is available. Then you only have to move the fridge to the trailer when boondocking.


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Unfortunately I don't have a way to charge the trailer battery

Sure you do, you have two ways - solar and the truck.

So what have I not considered? Any holes in this plan? Should I bite the bullet and get 2 x 100w panels instead of one (the "in-for-a-penny-in-for-a-pound" philosophy?)

I would. Especially considering what you say in this next quote...

Also before anyone suggests it: Eventually the 12v battery in the trailer will be replaced with a pair of 6v golf cart batteries. A friend of ours who has the exact same trailer has done this and according to him, his 2 x 6v batteries give him a whopping 208ah of capacity! :Wow1:

 

[4x4junkie]

×2 on the solar controller, you shouldn't need more than a 20A controller even for two 100W panels.

A 20A MPPT controller with one or two 100W panels connected to it is also likely to be more efficient on cloudy days than a 40A MPPT controller.