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Rustler View Drop Down
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Posts: 100 		Direct Link To This Post Topic: Solar Power System for RPod 171
    Posted: 10 Jun 2017 at 11:27pm
Originally posted by GlueGuy

Originally posted by Tars Tarkas

Originally posted by Rustler

  Yes, I'm obsessive about maximum efficiency. 

It makes perfect sense to me to try your best to minimize losses due to wire length, gauge, connections, etc., but it seems to me that the bottom line is to get enough juice to recharge your battery.  So if, say, a 100w panel is what you need to do that, but it loses 5% or 10% of it's output to all that resistance, why not just go with a 120 panel?  I know you can continue to worry about the 5% to 10% loss with your 120w panel, but you're getting everything you need, and a little more.

Of course one of the reasons to strive for maximum efficiency with your set up is to try to counteract the things that are much harder, or impossible, to control, like a cloudy day, or not wanting to hang around the campsite all day to turn your panels to follow the sun.

TT
One of the things that might not be intuitively obvious is that when using an MPPT controller, you can go for maximum voltage. You could string together a pair of small 75 watt 37-volt panels in series for ~~ 74 volts. Sounds ridiculous, but the two panels could be getting partial sun and only putting out 18 volts each (total of 36 volts), yet because of the MPPT controller, you can still be getting a decent charge to your 12 volt battery. If you had a 300 watt 18V panel and use a PWM controller in the same circumstance, the panel would only be running about 8 volts, and you'd get zilch to the battery.

Even if you're only using one 37 volt panel under similar circumstances, the 18 volts would still be enough to juice up your battery.

So it's not just efficiency, but also being able to squeeze out some power under not-ideal solar situations.

Good food for thought. Thanks for the insight. 

The biggest problem I find with the higher voltage panels is finding one with suitable small power rating. Many are being made for grid-tied solar systems running 150 to 200 watts or more. I had a spare 185-watt, 36-volt panel from my home solar system. But finding a 120-watt, 36-volt panel took some searching. But the benefits of that panel with a MPPT controller are worth the effort and cost.
Russ
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Rustler View Drop Down
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Posts: 100 		Direct Link To This Post Posted: 10 Jun 2017 at 11:15pm
Originally posted by Tars Tarkas

Originally posted by Rustler

  Yes, I'm obsessive about maximum efficiency. 

It makes perfect sense to me to try your best to minimize losses due to wire length, gauge, connections, etc., but it seems to me that the bottom line is to get enough juice to recharge your battery.  So if, say, a 100w panel is what you need to do that, but it loses 5% or 10% of it's output to all that resistance, why not just go with a 120 panel?  I know you can continue to worry about the 5% to 10% loss with your 120w panel, but you're getting everything you need, and a little more.

Of course one of the reasons to strive for maximum efficiency with your set up is to try to counteract the things that are much harder, or impossible, to control, like a cloudy day, or not wanting to hang around the campsite all day to turn your panels to follow the sun.

To me, anyway, the solution is to go with a bit of overkill and not worry about the rest.

TT

That is a quite valid way of looking at the overall picture, Tars. But as a certified "techno-nerd" I enjoy fussing with the details. Who knows (LOL). Maybe this summer will be unexpectedly cloudy like "nuclear winter". Then every amp and watt will be important in keeping the battery topped up. Oh Yeah, I could charge the battery with jumper cables from the tow vehicle. But its still fun squeezing every watt out of the solar system.
Russ
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GlueGuy View Drop Down
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Posts: 2654 		Direct Link To This Post Posted: 10 Jun 2017 at 10:08pm
Originally posted by Tars Tarkas

Originally posted by Rustler

  Yes, I'm obsessive about maximum efficiency. 

It makes perfect sense to me to try your best to minimize losses due to wire length, gauge, connections, etc., but it seems to me that the bottom line is to get enough juice to recharge your battery.  So if, say, a 100w panel is what you need to do that, but it loses 5% or 10% of it's output to all that resistance, why not just go with a 120 panel?  I know you can continue to worry about the 5% to 10% loss with your 120w panel, but you're getting everything you need, and a little more.

Of course one of the reasons to strive for maximum efficiency with your set up is to try to counteract the things that are much harder, or impossible, to control, like a cloudy day, or not wanting to hang around the campsite all day to turn your panels to follow the sun.

TT
One of the things that might not be intuitively obvious is that when using an MPPT controller, you can go for maximum voltage. You could string together a pair of small 75 watt 37-volt panels in series for ~~ 74 volts. Sounds ridiculous, but the two panels could be getting partial sun and only putting out 18 volts each (total of 36 volts), yet because of the MPPT controller, you can still be getting a decent charge to your 12 volt battery. If you had a 300 watt 18V panel and use a PWM controller in the same circumstance, the panel would only be running about 8 volts, and you'd get zilch to the battery.

Even if you're only using one 37 volt panel under similar circumstances, the 18 volts would still be enough to juice up your battery.

So it's not just efficiency, but also being able to squeeze out some power under not-ideal solar situations.
bp
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Tars Tarkas View Drop Down
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Posts: 1447 		Direct Link To This Post Posted: 10 Jun 2017 at 9:33pm
Originally posted by Rustler

  Yes, I'm obsessive about maximum efficiency. 

It makes perfect sense to me to try your best to minimize losses due to wire length, gauge, connections, etc., but it seems to me that the bottom line is to get enough juice to recharge your battery.  So if, say, a 100w panel is what you need to do that, but it loses 5% or 10% of it's output to all that resistance, why not just go with a 120 panel?  I know you can continue to worry about the 5% to 10% loss with your 120w panel, but you're getting everything you need, and a little more.

Of course one of the reasons to strive for maximum efficiency with your set up is to try to counteract the things that are much harder, or impossible, to control, like a cloudy day, or not wanting to hang around the campsite all day to turn your panels to follow the sun.

To me, anyway, the solution is to go with a bit of overkill and not worry about the rest.

TT
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Posts: 10 		Direct Link To This Post Posted: 10 Jun 2017 at 7:42pm
Originally posted by Rustler

Originally posted by Codex1554

Originally posted by Rustler

Shortly I'll be leaving to go to the Golden State Star Party (for amateur astronomers) near Mount Shasta, CA.

Hi Russ,

My son and I will also be going to GSSP.  We'll be leaving Tuesday evening and staying near Crescent, OR, then the rest of the way on Wednesday morning.  Perhaps we can meet?

Jim

That would be nice, Jim. I'll be traveling from the Oregon coast to the GSSP on Wednesday. It should be easy to find each other. Last year there were only two or three Rpods at the gathering. I'll be parked in one of the rows next to my cousin, who has a Ford travel van with canvas sided pop-up lid. I'll have a Celestron-11 on go-to mount. My telescope is quite modest compared to all the really large telescopes present. But I would be pleased to share what can be seen with all who come by. 
I'll look for you.  Even if we can't park nearby we can still get together ;-)

Jim
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Rustler View Drop Down
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Posts: 100 		Direct Link To This Post Posted: 10 Jun 2017 at 7:12pm
Originally posted by henryv

OK Russ, I have the same 2016 171 as you. The main question I have is should we alter the set up or go with what Forest River did? Personally, I'm looking for the easy way out...

The easy way is to go with the existing setup. And as has been mentioned there would be minimal power loss. You can always opt for installing a more efficient entrance socket at a later time. I tend to do everything reasonably possible to maximize the power reaching the battery - somewhat of an obsession. The SAE connector on the Zamp port is not noted for its low voltage drop compared to Powerpole connectors. Once you start using Powerpoles, you'll never go back to other connectors.

Just be aware of the polarity of the Zamp port. Someone mentioned that it was reversed compared to other setups. Also you'll need a controller somewhere in the line. As can be seen from my other posts, I'm a great fan of high voltage (36-volt) panels and MPPT (Maximum Power Point Tracking) charge controllers. Yes, I'm obsessive about maximum efficiency. This does come at a cost, however. YMMV.
Russ
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Posts: 100 		Direct Link To This Post Posted: 10 Jun 2017 at 4:51pm
Originally posted by Codex1554

Originally posted by Rustler

Shortly I'll be leaving to go to the Golden State Star Party (for amateur astronomers) near Mount Shasta, CA.

Hi Russ,

My son and I will also be going to GSSP.  We'll be leaving Tuesday evening and staying near Crescent, OR, then the rest of the way on Wednesday morning.  Perhaps we can meet?

Jim

That would be nice, Jim. I'll be traveling from the Oregon coast to the GSSP on Wednesday. It should be easy to find each other. Last year there were only two or three Rpods at the gathering. I'll be parked in one of the rows next to my cousin, who has a Ford travel van with canvas sided pop-up lid. I'll have a Celestron-11 on go-to mount. My telescope is quite modest compared to all the really large telescopes present. But I would be pleased to share what can be seen with all who come by. 
Russ
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Posts: 10 		Direct Link To This Post Posted: 10 Jun 2017 at 2:59pm
Originally posted by Rustler

Shortly I'll be leaving to go to the Golden State Star Party (for amateur astronomers) near Mount Shasta, CA.

Hi Russ,

My son and I will also be going to GSSP.  We'll be leaving Tuesday evening and staying near Crescent, OR, then the rest of the way on Wednesday morning.  Perhaps we can meet?

Jim
Jim McP
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Posts: 259 		Direct Link To This Post Posted: 10 Jun 2017 at 9:11am
OK Russ, I have the same 2016 171 as you. The main question I have is should we alter the set up or go with what Forest River did? Personally, I'm looking for the easy way out...
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Rustler View Drop Down
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Posts: 100 		Direct Link To This Post Posted: 09 Jun 2017 at 11:50pm
Originally posted by sailor323

I can't speak for your pod, but the zamp wiring on our 2016 179 is 10 ga wiring. I suspect that the same is true for your pod.  Power loss over the short distance covered by the wires is negligible. Where is the controller located?

I can certainly appreciate your viewpoint, Sailor323. That larger wire would help alleviate the problem a bit. I agree that for the 15-25 of 10 gauge wire there wouldn't be a tremendous power loss (maybe 2-3 watts). But there is a significant voltage drop. The overall voltage drop is the sum of all wiring and connector losses between panel and battery. For that reason it is best to minimize the amount of wiring. If the wire run from battery to Zamp port is 18 feet, you can double that to 36 feet, since there are two wires. In choosing that location, Forest River unnecessarily added a lot of wire.  There's no reason the entrance socket couldn't have been closer to the battery. Perhaps there was some marketing reason.

As an example of how much effect that much extra wire causes, one can use the voltage drop calculator in this link. Using 18 feet of 2-conductor 10 gauge copper wire with a 100 watt panel (putting out 7.5 amps at 13.3 volts), the voltage drop is 0.34 volt (2.6%). While that by itself is acceptable at less than 3% drop, one must add all other voltage drops caused by other wire and connectors. The overall voltage drop could easily exceed 3%, the standard for acceptable voltage drop. If the drop exceeds 3%, it is best to use larger gauge or shorter wire. So the extra wire does matter.

The power loss in that 18-foot run of wiring is about 2.6 watts (7.5 amps X 0.34 volts).

My MPPT controller is located near the battery on the wall behind the dinette seating at the front of the 171. That location is preferred since the controller more correctly reads the voltage conditions at the battery. If the controller is located some distance away (i.e. at the panel), it can get a significantly inaccurate reading of the actual battery voltage. For proper battery charging, even a tenth of a volt difference is significant.

I don't mean to overwhelm forum members with a bunch of math. But it has been my intent to show the electrical consequences of some decisions we might make regarding implementing our solar power systems. Even if we make some decisions that are not optimum (but perhaps less expensive), things will still work adequately. As long as we don't do something that might cause a fire.
Russ
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