BB and Photowit: Help, I need somebody, Help, not just anybody, Won't you please, please help me

blueskies · June 2019

Hello! I'm still pretty new to forums so as my changes occur to my system, I hope it's not faux pas to start a new post.

(PICTURES below) It's late and I've been researching so please excuse any mistakes.

I have a 7 foot by 16 foot cargo trailer and have completely covered nearly every inch of the roof with 4 solar panels. (Canadian Solar CS3U-355P - each panel: pmax 355 Watt / vmp 39.4 volt / imp 9.02 amp / voc 46.8 volt / isc 9.59 amp).

As advised recently, l plan to wire them in two strings / two panels in series times two. Although a display would be nice, I plan to use the Morningstar MPPT TS 60 as the manual is so thorough and I didn't have luck finding good information with outback, schneider, etc. And if it's good enough for photowit, it's good enough for me.

These will be going to 4 12 volt deep cycle batteries wired in a 24 volt configuration.(I have 4 batteries wired 2 parallel and 2 series equaling 24 volts (Universal Power Group 12v 100Ah Solar AGM SLA). I plan to use a diversion relay to be added later.

Obviously the thing is on wheels but I'm in Illinois and the record low was -36 F in 1999. (who knows with this weather) The average high is about 60 F.

The primary use of the system is to operate a rooftop a/c unit (Dometic Brisk, Compression locked (startup) Rotor Amps (Alternating current) 70 Amps / Normal compression operation 13 Amps, Fan 6 amps.

I will only be using the a/c for about an hour or so a day around noon.

Converting the 24 volts to 120 volts ac I figure I need a 24 v 3000 watt continuous and 6000 watt surge inverter. If this doesn't run the air conditioner, I suppose I could cut a hole for a lower watt window air conditioner but I hate to do that.

I am looking at the samplex PST-3000-24 pure sine wave for nearly $1000 (ouch ... but I want off grid and to travel).

I think I could run the AC on low and be below the specs. The whole cargo trailer is insulated "over the top" but I could still build another insulated "resting area" in the AC area to conserve more on air conditioning energy.

PICTURES:

This is before I added the last panel in front (the 2 little panels on the left and right of the a/c are just for 12v toys. Re-enforcements coming as far as brackets. There is an infrastructure I built to keep everything together from the inside. I believe the space between the roof and panels allows the roof to have shade and helps the panels stay cooler.

rubber spacers / shock absorbers:

Deck wood coated with roofing sealer:

Image: https://us.v-cdn.net/6024911/uploads/editor/gf/gvfg9wobfmqk.jpg

Adding r-22 insulation:

And the batteries balanced over the double axles:

Oops. That's not really beer. It's just pepsi in a beer box.

BB. · June 2019

Interesting installation... A 200 AH @ 24 volt AGM battery bank (~4,800 WH bank capacity) driving a 3,000 Watt inverter--Nominally, at 1,600 Watt load (assuming A/C runs at 100% for 1 hour), you would not expect, not much more, than ~1 hour or a bit more from the battery bank to near 50% state of charge.

At least during sunny weather (and assuming no shade on trailer), the 4x355 Watt panels will do a good job of keeping the A/C running and not discharging the bank too deeply.

This does raise the question of a mini-split or "inverter" based window unit to reduce surge (to not much more than running current) and allow the system to reduce running current (if/when 100% cooling is not needed).

Assuming a good quality AGM battery bank, nice/heavy cables to carry upwards of 168 amps (*1.25 for NEC derating of ~210 amps wiring and branch circuit breakers--3 kWatt) and low voltage drop (~1 volt max @ 168 amp for 24 VDC wiring)--It does seem workable.

Does a Genset make any sense (noise/fumes/etc. are not great)? An inverter based mini-split and (possibly) a Honda eu2000i or similar inverter genset for 1 hour a day running an inverter-A/C system.

-Bill

blueskies · June 2019

Thank you BB, I admire you and know you only post what is true to the best of your super human .... ; Everyone else - The topic were references to Beatles songs, but I am old. All input welcome. Don't stigmatize me if I have Asberger's - Solar is my interest, social interaction is my downfall. I don't want to lose this forum!

BB. · June 2019

No problem BlueSkies starting a new discussion. Works well when you have a new starting point in the project.

If being proficient at human interaction was(were?) required here--I would probably be the first person kicked out the door.

Some of this is really a guess on my part.... I use the rules of thumbs because they work well. And with the new inverter-style A/C and Heat pump systems (as well as "well pumps"), they really change solar landscape.

However, things that heat and move simply take a lot of energy. It is like putting a 10 gallon tank in an aircraft that can use 300 gallons per hour on take off--Yea, it will take off, but it will not take you far.

Following the design rules, generally a system that has enough AH to run 2 days + 50% discharge, gives you a FLA battery bank large enough to support your surge power requirements.

When you go off the reservation (such has a high power draw for "short" periods of time--Then our "cabin/home" rules of thumb don't work well, and you have check each "corner" of your loads (peak, average, hours of use, hours to recharge, etc.) and make sure that each is sized for your needs.

Li Ion batteries are like that--The batteries themselves can supply very high surge current. However, if there is a Li Battery Management Systems, it may impose its own limitations.

-Bill

mike95490 · June 2019

It looks like you are winding the battery cable wires around the bolts ? Using a proper crimp on lug would be much better

And wrap a bunch of tape around that socket wrench, it's a great tool to use to short out a battery and cause a plasma ball to burn your face off. With tape around it, it's insulated. Battery may be only 24 V, but in a short circuit it can dump thousands of amps, and vaporize parts of that wrench and your body part holding the wrench.

BB. · June 2019

Mike is correct... You need to use some sort of crimps for those battery connections (and bolt up bus bars).

Some options:

https://www.solar-electric.com/hacrtoforlal.html Hammer Crimping tool
https://www.harborfreight.com/hydraulic-wire-crimping-tool-66150.html inexpensive hydraulic cimper
https://www.amazon.com/TMS-Crimper-WL-YQK-300-Hydraulic-Terminal-Crimping/dp/B00GXQ2E5E another hydraulic crimper
https://www.grainger.com/product/THOMAS-BETTS-24-L-Hydraulic-Crimper-3LT09 ($2,500 + ~$200 per die set

People have used soldered connections as an alternative... People on both sides of the argument, and I have soldered large cables when I was young... Today, I would recommend against solder and use swage / crimp terminals.

You might also check with a battery distributor or welding supplies... Many offer cable services.

-Bill

PNW_Steve · June 2019

Until I bought crimpers I would run down to the local stereo shop. The one here crimps up to 4/0.

PNW_Steve · June 2019

I am curious what kind & how much insulation you used to achieve R-22?

BB. · June 2019

This link has rough R value per Inch for various types of insulation:

https://www.todayshomeowner.com/insulation-r-value/

Spray polyurethane foam is supposed to be very good (I think this is closed cell--You may have to apply at 1" at a time then let cure between coats):

https://www.homedepot.com/s/spray%2520foam%2520insulation%2520kit?NCNI-5

Don't know anything about the product--But if you are interested in DYI for a fridge/freezer, urethane spray foam is supposed to be very nice (obviously, for larger installations, spray foam contractors are out there too).

-Bill

Photowhit · June 2019

Some how I missed the R-22 reference. perhaps in a former thread?

The black trailer in the sun pretty much defines a bread box solar water heater, abit without the glass top and internal reflectors.

Did we ever understand what this 1 hour of cooling is for? I don't think there is much of a chance to store the cooled internal area. If the area is small enough and the insulation really R-22, I think you are likely to be able to run a smaller AC longer, mostly directly off solar energy and cool the trailer off and have a smaller duty cycle (the dang air conditioner won't have to run continuously...lol) Also the smaller air conditioner is likely to run off a much smaller inverter (just a thought on the over all costs....). I suspect it will heat up very quickly after the Air conditioning stops.

Just some random thoughts tonight.

Estragon · June 2019

I did spray foam on the crawlspace joist underside, not only for insulation but also for earth gas and moisture containment. Messy, tenaciously sticky stuff, especially working overhead. It did the job though.

Apparently polyiso rigid foam board is better suited to air contioning applications as its r-value is higher at room temp, something I didn't know when I used it to build fridge and freezer boxes

blueskies · June 2019

well, the r22 insulation is doing amazing. I ordered Morningstar TS-MPPT-60M MPPT Solar Controller with Meter and

Samlex 3000W Pure Sine Wave Inverter - 24V. If you think these are bad choices, please let me know. As I undrstand it this is the mppt controller my friend recommended and with a display. I may be mute until photowit gets back from vacation or speaks to me.

littleharbor2 · June 2019

At least two of the three panels that are snugged up to the A/C unit will be partially shaded most/some of the time. This will reduce the potential output of those panels and whatever panels that are in series with them.

blueskies · June 2019

I realize if not parked and reparked, there will be some shading. not too much i can do about that. Just got up after a double shift. The insulation is 3 inch rigid polyiso. It would cost a fortune brand new but mine is reclaimed from a farmer. Smelled like cows but I coated it with shellac meant to cover smoke damage. It is closed cell, does not absorb water and releases it's internal cell gas that puts out fires if you try to burn it (which of course i tried on a scrap - it really did extinguish itself.) It is even marked R22. If anyone is close to springfield, il i may be able to help them get some at very low costs. I plan to use spray foam and caulk to reduce thermal bridging around the 2x4' structure. (refer them to guy who reclaims this stuff - I think he's still on craigslist). It's durable too. You're not supposed to but you can walk on it. The ceiling is a bit more tricky. I started layering thinner polyiso from the cull cart at home depot but I have enough of the good reclaimed stuff to do the job so that will be better. Below the trailer between the steel beams I plan to screw up 3 inch styrofoam that someone was going to use on a dock but never got around to it. less chance of fire down there (I can only hope) and R value not so critical.
well, i have replaced most of the r3 value at the ceiling with the r22. the difference is obvious, especially if you open the door. if you have ever had an insulated coffee cup that you came back to two or three days longer and said to yourself, "dang, this is still hot" - that is the idea. Of course, I'm not expecting days, just hours

blueskies · June 2019

i think it might be better to keep the panels in parallel. i'm really not comfortable with the amount of voltage in parallel and this will reduce the shading issue? I really do get many hours without any shading at all. the ac isn't very tall. i've been watching it from the beginning.

blueskies · June 2019

You all saved me from major mistakes. I cancelled the order within hours. Sharp pencils are going on new paper. Thanks.

lc16 · June 2019

mobile-solarpower.com has written instructions re: a/c installation and more.
if you are in the desert at noon , https://www.southwest-solar.com/kar-kool-truck-cool has modern cooling for about 600 to 700 dollars for your size cargo trailer. I have a cargo trailer about that size and was planning on doing the same as you and have been reading ebooks on the subject for sometime.....and just ordered 600 panels and almost all needed to begin in that direction of a/c cooling for a limited time of day that is the hottest.

BB and Photowit: Help, I need somebody, Help, not just anybody, Won't you please, please help me

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