My funky power system build

[Skyjim73]

We should take delivery of our new 3124KB in February, and I've begun acquiring the major hardware for the solar charging system. Since I'm going slightly against the grain with a few of my choices, I'll list what I'm using and then once we get some experience with the system next year, let any interested forum members know if my system is working for us or if my theories have crashed and burned...

We'll hopefully be all over North America, but we do a lot of dry camping in the desert southwest. I am a pretty serious amateur astronomer, so I like to go to fairly isolated places for dark skies. My wife enjoys many of the national park campgrounds when we do "normal' camping, and at least in the western states most campgrounds in the parks lack hookups. I have a Honda EU-2000 we've used with our old hard-side trailer, which had four 6V golf cart batteries and a 2KW Heart inverter-charger with a 100 amp four stage charger. I've gotten used to managing my battery bank, doing regular equalization charges, and so forth, and my last set of Trojan T-105s lasted 8 years. But one thing we learned was that we really did not use the AC power capability except for stuff like wall chargers that a tiny, cheap inverter could have handled. But having a good DC charging system is a must for me.

I'm not going to take my new lightweight TM and burden it with a huge battery bank - at least not right away. But I will need reliable 12 volt power since I'm committing to a 12VDC/115VAC compressor fridge rather than the 3-way. So my version 1.0 battery bank is going to be a pair of 6 volt Trojan T-145 "tall" golf cart batteries giving me a 260 amp/hr bank to draw from. Trail Manor has agreed to fab me a slightly lower slung set of battery rack rails to get me an inch lower so the T-145s in their boxes are out of the way of the forward bed section when it folds down.

At first I figured I'd buy a Magnum inverter/charger, but I really don't need most of it's capability - and it's a really pricey way to get a good charger into the system, and the only one they have with a 65 amp or under charger output (using the 25% rule of thumb for charging rate vs bank size) only has 20 amps of AC pass-through rating. That worried me when looking at air conditioner startup loads - wanted to allow at least 30 amps to match the AC service the system is designed for and the common low amperage hookup in most RV parks. So, I could spend a lot more money for a bigger inverter/charger than I needed, and deal with the complexity of an AC sub-panel for the fridge and air conditioning, which I would NOT want pulling power from the inverter. We would only use the air with AC hookups and the fridge will only switch from DC when AC power is present - no point in incurring conversion losses making AC power via an inverter. Anyway, I'm instead going to try another setup.

I also REALLY didn't want to completely redesign the DC setup, but wanted at least some control over the battery charging. The converters typically installed, including the WFCO TM uses, have three stage charging now incorporated, but they taper out of bulk charge stage VERY quickly - just the opposite of what you want for quick replenishment in a campground via small generator. I knew I'd want some solar charging capability to extend my dry camping endurance and offset the power the fridge consumes en route to a campsite, but there just isn't that much roof area available on a TM, and I didn't want to deal with portable arrays. So, I want a fixed set of panels, preferably with pretty high low-light/partial shade performance to better deal with the variety of sun exposures in typical campgrounds.

So, Version 1.0 of my system:

Batteries: 2 x Trojan T-145 (260 amp/hrs at 20 hr rate)

Custom battery rails, 2 Sea sense tall GC battery boxes.

Replace the charger module of the factory 12 volt converter with a 55 amp Progressive Dynamics 3 stage unit, with PD control pendant installed to allow me to manually control charge stages during short AC availabilities. Automated but very conservative charging option for longer term hookup situations.

TM is upgrading the DC charge cabling - still waiting to confirm whether we can go to my desired 2 gauge from the factory 10 gauge, but as Fun Pilot has found out, at least 4 gauge is definitely possible. Happy to pay for this type of upgrade at the factory!

2 x Unisolar 64 triple junction amorphous solar panels. Unisolar made these panels, as well as sheet-style flexible arrays with self-adhesive backing for metal roof setups, in Michigan before they went out of business after the 2008 economic meltdown and the flood of cheap Chinese panels. The design isn't as efficient in full sun as typical crystalline arrays, but they have really excellent shade-tolerance and low light performance. You can still find new in box US-64s on E-bay last time I checked.

Morningstar Sunsaver 15 Max Power Point Tracking charge controller. Went with the pricier MPPT controller to run the panels in series for higher voltage to minimize wiring losses to the controller, which can down-convert to the needed voltage while utilizing more of the panel output, since MPP for the Unisolars is 16.5V. Normally it's more cost-effective on small systems to buy more panels and use a cheaper controller, but I want the panels hard mounted to the roof and I've got mass and space constraints, so I'm going to try for max real-world efficiency in less than ideal light conditions. Theoretically ought to work, but we'll see how it goes in practice. I might be wrong on this choice but I want to test that.

Edit: Almost forgot:Morningstar battery temp monitor cable and remote monitor. May not give me as much information as I want, andI could wind up wanting a Trimetric monitor for comprehensive info, but this was a good deal and I'll see how it goes.

Can't wait to get things assembled after delivery and see how it all works!

Jim

[scrubjaysnest]

We have gotten on well with two 80 watt poly crystalline panels which in low light conditions preform better then the amorphous solar panels. I wouldn't try to keep the batts up with 128 watts because there is no way to reach C/20. C= batt aH capacity. We can't do it with 180 watts. We also would never try running the refrig on DC and charge only with the solar. But all that said it is refreshing to see a different approach and we will have to compare notes as we will be spending a good part of the winter in the AZ/NM/NV area.

[Padgett]

Don't forget that a compresser fridge uses about half the DC power of a gas absorption.

Only disconnect (and may be me) is the "desert southwest" with no mention of AC. My sister lives outside of Bisbee, AZ and it tends to get a tad warm there. but does cool down at night. Is probably easier to sleep than with the 90/90 we get in the summer.

In any event I founf the EU2000 (2000/1600) to be marginal and grunted starting the roof AC which is hard on everything while my Pred (2500/2200) handled it a lot better/faster.

[scrubjaysnest]

A look at the numbers is the concern. If the compressor frig draws half, say 6 amps@ 12 volts that is 72 watts times 24 hours that is 1728 watts. The panels at best will produce 128 watts times 6 hours = 768 watts. There for the batteries have to make up the difference of 1728 - 768 = 960 watts.
If the batteries are 225 aH @ 12 that is 2700 watts. Since we really don't want to go below 50% soc that is 2700 times .5 = 1350 watts. 1350 watts minus the 960, which is a deficit is 390 watts for lights and pumps and the heater maybe. This is why we prefer the three way absorption refrig. That 960 watt deficit per day is hard to make up.
The above example is best case. Throw is cloudy or rainy days and it gets worse. One has to be very conservative to get by on solar alone. We are right at the ragged edge with 180 watts. This means we don't use the fresh water tank and pump, a couple of 2 1/2 gal jugs for water. Use the furnace to take the chill in the morning, not run all night. All LED lighting. Also careful position of the solar panels. Out west in the dessert its not so bad but on the east coast or in WA or OR one will have to really look at it closely.

[tentcamper]

Is that the power rating for the compressor frig? It sounds like that little eu-2000 will be running most of the day.

Scrubjaysneste you may know the answer? If you are running the generator and recharging through the converter and the solar is charging the battery at the same time. Will either one, the converter or the solar control go into bulk charge? I would think they will trick each other with the 13.x float mode applied to the battery and just sit in float mode? I would think they would never go into bulk charge if both are producing 13.x???

[LoveToCamp]

Seeing all the concern over solar charging from those of you who camp with clouds or tree canopy, it makes me a bit happier that I don't have as much shade to camp in!

I have gone 7 nights at a time in the summer with mostly-shade, and my battery seems to top-off daily (my original TM had a lights-only controller, so I never really knew the state of charge). I got my new 2417 this spring, and that controller showed me I was up to at least 13.1 every day.

A few weekends ago, I took our TM out with 4 guys (yes, it was tight, but 3 of us had comfortable beds). Kept the heater at 65° in the evening, then 45° overnight each night. Through the evening, the heater was on about half the time. Overnight, it ran about 25% of the time, with outdoor temps of 30°. Each day, we were back up to 13.1, even with the sun low on the southern sky.

This weekend, I put a second 12v battery in, so I should have even more capacity going-forward. One of these years, I will be camping in New England, or Oregon, and will get to see if I get close to a full re-charge daily. But, for now, my 100w panel seems to keep me fully-charged daily.

[tentcamper]

Originally Posted by LoveToCamp

Seeing all the concern over solar charging from those of you who camp with clouds or tree canopy, it makes me a bit happier that I don't have as much shade to camp in!

I have gone 7 nights at a time in the summer with mostly-shade, and my battery seems to top-off daily (my original TM had a lights-only controller, so I never really knew the state of charge). I got my new 2417 this spring, and that controller showed me I was up to at least 13.1 every day.

A few weekends ago, I took our TM out with 4 guys (yes, it was tight, but 3 of us had comfortable beds). Kept the heater at 65° in the evening, then 45° overnight each night. Through the evening, the heater was on about half the time. Overnight, it ran about 25% of the time, with outdoor temps of 30°. Each day, we were back up to 13.1, even with the sun low on the southern sky.

This weekend, I put a second 12v battery in, so I should have even more capacity going-forward. One of these years, I will be camping in New England, or Oregon, and will get to see if I get close to a full re-charge daily. But, for now, my 100w panel seems to keep me fully-charged daily.

I would try the norther camping before I bought an additional battery. I know we would all like a fully charged battery every day; But what we have found is we need enough battery to get us through our camping. So each day the battery is a little lower but we are still in the safe zone.

For many years we would go 7+ days warm weather without heat and be OK and that was without any solar or recharging. Now when we left CG the battery was near 50% and it would recharge from the TV when traveling. If I had solar I could have gone maybe 14 days.

In cold weather we need to recharge after 2 nights with the auto jumper cables We just got solar for our cold weather camping. Our belief is with solar we can push it to 4 nights in cold weather, which we never say anywhere in cold weather more then 3 nights. The battery is fine to discharge to slightly above 50%. Since we live in the north every automobile we have has a set of jumper cables. Only twice in 25+ years of having a camper in warm weather, have I had to recharge the battery with the jumper cables.

[Bill]

I have a 10-year-old Engel 43-qt frig/freezer with the Sawafuji compressor. This is a single-compartment unit, so it is a refrig OR a freezer, unlike your Dometic frig/freezer, which has a separate freezer compartment. Currently we are using our Engel as a home freezer.

It has an uncalibrated thermostat. Since we use it as a freezer, I simply set it to MAX COLD and let it run. It has settled at a temp of about -5 degrees F. This is in an ambient of 75 degrees, with no direct sunlight on the unit, and good ventilation for the cooling mechanism.

When the compressor is on, it draws about 2.3 amps on DC power. In the conditions outlined above, the compressor seems to run about 60% of the time.

So what does all this mean to you? My intent is to highlight the things that will have an effect on your unit’s energy consumption.

The factor that influences energy consumption the most is the thermostat setting. In other words, how cold do you want the unit to be inside? In my example above, I just set it to MAX and let it run. You can’t be nearly as cavalier about the setting.

If you demand a refrig temp of 35 degrees (in other words, a 40 degree drop from a 75 degree ambient), you will use a certain amount of energy. If you are willing to raise the thermostat to 45 degrees (a 30 degree drop from a 75 degree ambient), then you will cut the unit’s energy consumption by 25%. And similarly in between. This decision is complicated by the fact that although your unit has both a refrigerator and a freezer, it has only one thermostat. This means that you set the thermostat to the temp you want in the refrig, and take what you get in the freezer. If the freezer is too warm, you have to juggle. Get a good refrigerator thermometer.

The next major element in calculating energy use is what percent of the time the compressor actually runs (called duty cycle). It certainly will not run 100% of the time. If the compressor draws 6 amps when running, but runs only half the time, the equivalent current for calculation purposes is 3 amps. And if it runs only 1/3 of the time, then the equivalent is 2 amps. These are the numbers you would use in the battery-life calculations. As you would expect, compressor run time is determined by thermostat setting, as well as by ambient conditions.

Among the other factors that affect energy consumption are ambient temperature - how warm is it in the room? If you park your TM in the shade and open the windows for a good cross breeze, the ambient in the TM will be about as low as you can get it. If you go away for the day and close all the doors and windows to deter thieves, the temp inside the trailer will rise, and so will the energy consumption of the refrig.

Next is venting the refrigerator’s cooling mechanism. The TM’s 3-way refrig generates a lot of heat, so TM uses a relatively big fan to suck the heat out of the refrig mounting compartment. The Dometic 2-way will generate a lot less heat, but it is still important not to let it build up. Otherwise the refrigerator is fighting an uphill battle. Especially on a hot day, it might be wise to have a low power fan built into the compartment.

Along a similar line is sun loading. If you park the TM so that the refrig is in the sun, you are pumping heat into the compartment. You should either park the TM in a different direction, or at very least rig up a sunshade over that area of the wall.

So my refrig draws 2.3 amps DC, while yours draws 6 amps DC. Mine is set for really cold, so the duty cycle is high, while yours will be set warmer, so the duty cycle will be less. Since you are looking at solar as your exclusive source of power, you'll need to be aware of, and manage, the other items carefully.

My apologies for the length of this post. I hope it helps clarify some of the issues under discussion.

Bill

[Padgett]

About post #4. That might be true if the compressor ran continuously but just taint so.

Part of the reason the stock gas absorption fridge requires such a large energy budget is that it is really very inefficient in many ways. So on electric it pulls 150-180W almost continuously to cool not very much, even more than a Peltier plate.

OTOH a modern compressor fridge is very efficient, pulling 60-70W but with a 30-50% duty cycle. Once it is cold and the door stays shut it really does not use much power. With a top freezer, circulation does not need much help.

As a rule of thumb I'd figure 30W continuous or 60-70AH/day at 12v. Meanwhile a 200W array providing 140W @ 13v for 6 hours is about 65 AH so close to a wash.

Now that is just a SWAG so I'd be interested in hearing real world numbers but personally think a GA fridge is really a poor choice unless always on LP.

[tentcamper]

If bills numbers are in the ball park? And the fridge compressor runs 1/2 the time, it sounds like the compressor fridge could be in the 50-60+ amps per day load.

I think we all would like the faster cooling fridge like a 12v compressor fridge. But it all comes down to your style of camping and if it's a lot of dry camping or being connected to a shore power or a generator?

Plus's
- Gas absorption fridge runs on propane and use no 12V energy and does not do well holding temps in the 30's when outside temps are above 95 degrees.
- Compressor fridge cools faster and hold a cold temp better in hot weather.