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Discussion Starter #1 (Edited)
I've finally got around to designing my solar panel system. I'm going to get two of the Renology 150w panels




I do have two questions however.

Most of the information I can find suggests that Sikflex 252 is the best adhesive for this purpose. Has anyone here had any actual experience using this product? At $20 for a 10.5 oz cartridge I don't want to waste any or buy too much. Does the roof or the aluminum mounts need any prep other than a good cleaning with thinner and if so, what seems to work the best?

On the electrical side I need some kind of fuse on the positive cable from the PV panel. 30A seems correct. Does this make sense? A switched circuit breaker type would be nice but I've yet to locate a 30A self contained one, does anyone have any suggestions? I'm assuming the feed out from the charge controller to the AGM battery also needs to be fused. Any suggestions on what size cable and fuse to use? I used #2 welding wire from the alternator (starting battery) with a 175A fuse on each end but that would seem to be overkill from the charge controller. I'm guessing a much smaller cable and fuse - any suggestions?

KOV
 

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Sikaflex is what we used when I was an automotive engineer. Good stuff. Holds better than some lame caulking from Home Depot.
 

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Look into maybe using 3m VHB (very high bond) Acrylic Foam double-sided adhesive tape to bond to painted surfaces. A thicker foam tape would be better so it conforms & gives a little bit. Removing the tape can be either small wedges and let time lift it off or use a fine wire with sawing action.

Those mounting Z brackets' lower flange is on the small side to use foam tape with, but it's easy to custom make sheet aluminum "oversize feet" (OR attach a pair of brackets to a runner sheet going between them) OR attach whatever bracket made up from stock angle or box aluminum.

The VHB & UHB (ultra high bond) tapes are the go-to attaching solution for $100,000 Airstreams, etc.. eBay has many small kits of the tape for $5 or $10 shipped, Amazon is a little steeper but has 1-1/2" x 9' rolls for $16...
 

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On the electrical side I need some kind of fuse on the positive cable from the PV panel. 30A seems correct. Does this make sense? A switched circuit breaker type would be nice but I've yet to locate a 30A self contained one, does anyone have any suggestions? I'm assuming the feed out from the charge controller to the AGM battery also needs to be fused. Any suggestions on what size cable and fuse to use? I used #2 welding wire from the alternator (starting battery) with a 175A fuse on each end but that would seem to be overkill from the charge controller. I'm guessing a much smaller cable and fuse - any suggestions?

KOV
I would follow their guide lines as to wire and fuse size.
http://renogy.com/wp-content/uploads/2014/04/off-grid-general-manual.pdf
 

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Discussion Starter #5 (Edited)
Thanks for that installation link. I looked everywhere and couldn't find it!

It appears that 30 A in and out with #10 wire is all that is required (if I'm reading it correctly).

I may just go with the 3M VHB tape instead - good idea (thanks) or maybe just put two 10-32 well nuts into the roof for each bracket instead. Then I won't have to worry about if coming off. I'll use 10-32 stainless screws for sure.
 

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The 150watt panels ah output are 8.25a? short circuit is 9.25a? so you would want 10amp for 1 panel, 20amp for 2 panels and 30amp for 3panels the panel ah output is from memory so may be off a bit.
 

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Discussion Starter #7
Thanks, sounds like 20A will do it for 300W then.
 

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Nope. 150 Watts/12 volts= 12.5 Amps for each panel so I would go with 30 amp and #10 stranded wire. You can fuze either lead. Most fuze +. The feed form your alternator was WAY overkill as 10 gauge would have done that as well. I would probably go 8 gauge and fuze that at 50 amps. Same fuze for the solar although 30 Amp is ok. Try auto store or

I like the mechanical fastener if you will have the panels standing off the roof and those little tabs just look too small to trust double sided tape alone! Goop it up with Dicor lap seal and it will NEVER leak, NEVER![ame]http://www.amazon.com/Dicor-Leveling-Sealant-White-551LSW/dp/B00FFAZNYI/ref=sr_1_2?s=industrial&ie=UTF8&qid=1425680918&sr=1-2&keywords=RV+roof+lap+seal[/ame]
Must be it has warmed up in SNH?
 

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Use the largest wire you can. (Pet peeve time: obtain, install and use solar but be wimply wired)

On fixed installations a 5% drop from PV to charge controller is usual to keep sticker shock of a system minimal; then 2% drop from batteries/inverter to point-of-use. For a custom RV why not chunk it up a little?

On checking average wire gauge (AWG) choice - http://www.powerstream.com/Wire_Size.htm

So... 10awg, 12 volt, 15 feet, 9 amps... 2.31% wire loss (voltage drop)
BUT: 10awg, 12 volt, 15 feet, 18 amps... 4.63% voltage drop...

Here is a spot you can increase efficiency by 1 or 2% permanently, a small dividend you could choose to collect every minute the sun is shining...

Yearly: 250 work days, 5 peak solar strength hours per day... and that pesky 2% of 300 watts... looking at 2% over that time period that's 7500 watt hours free and clear. Of course human nature and taking battery state of charge etc. for granted, forgetting maintenance like cleaning panel glass and all that rot come into play but a few dollars more up front is a long-term payoff.

/rant off

Edit: 3m 5200 Marine caulk is what is used to keep boats afloat, about as forever sealant/glue as there is... I used a lot of it on my 1973 Airstream complete rebuild. Just wanted to add to the signal-to-noise (noise to signal?) ratio here : )
 

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Rant on.... Those panels will not produce 25 amps probably ever. Redo the calculation for the more normal Max at 20 amps and the loss will be so low you won't want to put up with that monster cable. 10AGW is fine 8 is better! I get 2% for 8 AGW Better look at the controller's efficientcy too there are controllers to gain another percent or 3. Rant off!
 

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Discussion Starter #11 (Edited)
So, 30A in and out of the controller with #10 wire.

I used the larger wire from the starting battery to the house battery as I had no plans to use solar when I did it and wanted to be able to recharge the house battery as quickly as possible and use it for starting in an emergency if necessary.
 

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So, 30A in and out of the controller with #10 wire.
I used the larger wire from the starting battery to the house battery as I had no plans to use solar when I did it and wanted to be able to recharge the house battery as quickly as possible and use it for starting in an emergency if necessary.
Yup you will be fine! I don't want to talk you down but 300 watts is a LOT of solar. Being flat on the roof and with shade it will produce much less but still alot. I had 80 watts on my truck camper and ran everything but a refrigerator. We never even came close to running out even week long no starts. Since I plan a 12 volt efficient refrigerator I think 200 watts will be enough for us but will make spacing for 300 (3X100) JIC. .... Edited out dumb comment
 

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Discussion Starter #13
RD, You are most likely correct about the 200W but I don't want to do it again and have to add more if it doesn't do what I want. For the few $100 extra it's well worth it to me to just get it done. It's all a learning curve anyhow as I have no experience at all with solar other than what I've picked up here and online.

I think I'm going to order the two PV panels, the mounts and the controller and lay them out first then decide how I'm going to secure them to the roof and then determine all my wire runs to keep everything as short and waste free as possible. Most likely I'll use a combo of mechanical and bonding tape to hold them on the roof as I don't want to see them flying down the interstate at 70 mph.

Now, if the snow will just melt and the mud dry up I can get to work!
 

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Discussion Starter #15
Thanks to all for everyones thoughts and input. I'll report back as soon as I do it, most likely within a month!
 

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This is were I came up with amp output for the Renogy 150W 12V Monocrystalline Solar Pane,l I was off -.13 and + .20
http://renogy.com/wp-content/uploads/2014/06/RNG-150D-revised.pdf
Yes you were correct. Current = Power/Voltage and in this case they rate the panels at 17.9 volts so 150 W/17.9 Volts=8.4 amps. In reality the MPPT solar controller may be able to utilize this to interface at 12Volts (up to 14 really) but to describe this as a 150 Watt panel may be a bit deceptive. It will be unlikely to get that from it. KOV will be good with his 300 watts and 10 AGW wire for sure. The reality is all solar panels have a rating under ideal circumstances and a power output in use. I took the rating at 12 volts and so... 150Watts/12Volts=12.5 Amps MAX. It will never produce that. When looking at panels it is a good idea to go through this to see what you are likely to get from the panel.
 

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So in planning my solar setup I started looking at shore power adapters to power up when plugged in and the in hit me: Why plan a solar system that requires you to plug in?

So I went with 2 Grape Solar (ordered through Home Depot so I could return them if I changed my mind) panels at 265 Watts each and then saved some money on shore power equipment. I did my power calcs and realized I use about 120 Amp/Hours per day. All of the reference sites used seem to indicate the panels would produce about 130 Amp/Hrs in my lat/long area. We'll see if I've over planned.

I'm bolting my panels to fiamma roof racks with hinges so I can tilt toward the sun if I want increased output and was going to use polyurethane or urethane to glue the combiner box to the roof, but those other suggestions sound better?

I agree with other posters that more wire is worth the investment. I'm going with 8 AWG to the junction box and perhaps 4 AWG to the charge controller. For me it's only a 10 or so feet run so I figure why not.

Here are the sites I found most useful in my research:
Great article about solar engineering:https://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/
Solar Battery Info:http://solarhomestead.com/your-first-battery-bank/
Solar Demand and Battery Bank Calculator:http://www.batterystuff.com/kb/tools/solar-calculator.html

So did you use a battery isolator? Some of them are solenoid based while others are diode. The diode ones want you to connect directly from the alternator which I'm hesitant to try. . .
 

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If you want to maximize the out put of your panels, put them in series and get a MPPT solar controller. I am currently installing (4) 100 watt panels, I set them up 2 each in series then parallel the 2 sets into a MPPT controller. Most of the solar panels have bypass diodes, "bypass in shade" so check before doing so. I'm also running 8awg to each set, overkill but wire is cheap. Also higher voltage by putting them in series means you can run smaller wire.
 

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Discussion Starter #20
If you want to maximize the out put of your panels, put them in series and get a MPPT solar controller. I am currently installing (4) 100 watt panels, I set them up 2 each in series then parallel the 2 sets into a MPPT controller. Most of the solar panels have bypass diodes, "bypass in shade" so check before doing so. I'm also running 8awg to each set, overkill but wire is cheap. Also higher voltage by putting them in series means you can run smaller wire.
Hey mojo, great job on the solar mounts! did you make them up yourself or buy them? Can you post some photos of just the mounts to the roof lugs? If you bought them what and where did you get them? I'm still uneasy about drilling a lot of holes in my roof for rivnuts and/or using VHB tape to hold them on!

kov
 
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