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Old 10-17-2021, 07:01 AM   #21
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Originally Posted by tjdonahoe View Post
I am installing 2 90 watt Zamp obsidian panels on our roof , using the 10 ga pre wire, along with AM Solar’s c box, using double sided tape and silkaflex covering the feet. Victron 100/30 smart. Using Bluetooth to phone. If I add more panels I may go with a larger diameter wire
Yes, 10 gauge wire is fine for most applications but is dependent on the length. The longer the run the higher the voltage drop. You should be good for up to 10 amps. Not sure how difficult it would be to change the wires out. May be more trouble than it's worth.
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Old 10-18-2021, 06:14 AM   #22
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Originally Posted by 92landyacht View Post
Yes, 10 gauge wire is fine for most applications but is dependent on the length. The longer the run the higher the voltage drop. You should be good for up to 10 amps. Not sure how difficult it would be to change the wires out. May be more trouble than it's worth.
Hi

It all depends on your target.

The wire that is used for the pre wire is rated for 40A per the normal safety standards. No, that's not a typo, they use high temperature insulation. Cells put out max power up around 18V. 40x 18 = 720W before it becomes unsafe / blows the fuse.

The wire is run between the skins so swapping it out likely means pulling rivets to get at the tie down points.

If the run from the panels is 8' up the wall and 8' over to the box ( which may be more distance than in your trailer) you have a 32' loop of wire. 10 gauge is 0.001 ohms per foot. The wire comes in at 0.032 ohms. Again, this is just the distance from the solar converter to the junction box on the roof.

At 10 A you would have 0.32V drop or 0.32/18 = 1.7%. The manufacturing tolerances on the panels are in the 5% range at best. A thin coat of dust is in the 5 to 10% range. If this is "barely ok" then what is the target? The wire sales guy has a spool of 4/0 sitting there ready to go ....

Bob
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Old 10-18-2021, 06:30 AM   #23
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Agreed Bob. I looked at the wire gauge chart incorrectly when I came up with the 10 amp rating. Actual max amperage comes in at closer to 55 amps. Power transmission protocol indicates that a continuous 15 amp DC is good at a length of 1000 ft. so not very likely to be a factor.

Personally I'm planning on adding a 10 gauge wire from the panels to the charge controller if I add roof top panels. Right now I'm still looking at experimenting with my small 100W system... That is, once it arrives. Fedex has been screwing around with delivery for over a week now. It's been out for deliver 3 times and in each case it was routed back to the distribution center due to some "exception" issue. Twice because the label was "unreadable and replaced". Going to be very interesting to see what the package looks like once it arrives. Scheduled for delivery for the 4th time today.
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Old 10-19-2021, 08:28 AM   #24
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Hi

Bigger is always better. If you have the inside of the trailer torn apart and can easily get here and get there, then sure go big. If you have a spool of 2AWG just sitting there, go with it. When you put those six next generation / not invented yet / $50 / 1KW each panels up on the roof, you will be glad you went big.

Bob
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Old 10-19-2021, 09:57 AM   #25
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I'm not sure how you can get 16' run with an average RV. I've got 30' on mine (8' up to roof, 15' to the front of the trailer 2' feet to the controller and 5' on the roof to the panel). But anyway you have what you have.

I made a chart based on the my spreadsheet calculations that use the wire resistance for stranded wire (not solid like all the calculators) and it takes into account for the increase in wire resistance from the quoted 20C wire resistance numbers and uses a more real world number of 30C which depending on where you live may not be enough, but anyway I have made a chart that shows the voltage loss using 15 amps in wire from AWG 0 to 10 over several distances. These numbers feed into another spreadsheet I have where I can take numerous panels and compare the efficiency and output based on different temperatures. I could run some numbers for you if you PM me, but to explain all the calculations of NOCT and Temp coefficients of VOC would take too long. But I have included a screen shot of a sample.
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Old 10-19-2021, 11:54 AM   #26
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Received my Renogy 100W solar suitcase today. It's a starting point to see how solar can be integrated into my current system. I set it out today and connected it to my older set of two batteries that have been sitting idle for about 2 weeks with no charger attached. The batteries are 12V flooded deep cycle that are about 3 years old. Once I set up the controller for the correct battery type I plugged in the solar panel and everything started working. The voltage jumped from 12.8V to about 13.8V almost immediately. Initial current was just over 2 amps. Over the course of about 30 minutes the battery voltage rose to 14.7V and remained there. At about 3 hours in the batteries were reported as full and the controller stopped supplying current and the batteries settled down at about 13.7V. Seems like a good first test. I did a little experiment on how the Renogy Eclipse panel behaved when partially shaded and was impressed with how it still provided a decent PV voltage and could still supply ample current to the battery bank.

My plan is to take the system to a week long boondock at Road Atlanta for the Petit Le Mans IMSA road race on November 8th through the 14th. I do plan to use the furnace during the evening and the fridge will be run 24/7 on 12Vdc and propane. I will have generator power if needed, but I'll be seeing how the panel gets the new 235ah bank back up to full charge during the next day. Don't plan to need much power during the middle of the day and probably will run the generator in the morning and around dinner time to run the home entertainment system and top up the batteries for the evening furnace run.

Since the race is delayed this year by a month over previous years, the need to run the furnace at night was added to the equation. In the past I had no other way to charge the bank except the generator using the power converter/charger. This year I've replaced the old 92 model converter/charger with a newer IOTA DLS-55 converter/charger with IQ4 setup for flooded batteries. I replaced the pair of old 78ah@20hr deep cycle batteries in parallel (156ah total) with a pair of GC2 6V 235ah@20hr deep cycle flooded golf cart batteries in series. Now I have solar to add to the system as a backup to charge the batteries. Should do much better than the system I had.
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Old 10-20-2021, 06:51 AM   #27
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Originally Posted by gator.bigfoot View Post
I'm not sure how you can get 16' run with an average RV. I've got 30' on mine (8' up to roof, 15' to the front of the trailer 2' feet to the controller and 5' on the roof to the panel). But anyway you have what you have.

.
Hi

The pre-wire just goes to the junction box. What happens past that is't part of the pre-wire. Since each panel has it's own cabling to the junction box, that's a totally independent issue.

On mine, the prewire terminates at the front of the trailer in the vicinity of the DC bus. If there's a bunch of extra wire there ... chop it off. The junction box isn't that far back on the trailer. The "inside wall to inside wall" distance is only about 24' on a 30' AS.....

Since there are a lot of models / lengths / setups ... who knows what each of us got.

Bob
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Old 10-20-2021, 09:48 AM   #28
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Hi

The pre-wire just goes to the junction box. What happens past that is't part of the pre-wire. Since each panel has it's own cabling to the junction box, that's a totally independent issue.

On mine, the prewire terminates at the front of the trailer in the vicinity of the DC bus. If there's a bunch of extra wire there ... chop it off. The junction box isn't that far back on the trailer. The "inside wall to inside wall" distance is only about 24' on a 30' AS.....

Since there are a lot of models / lengths / setups ... who knows what each of us got.

Bob
So you're not including the wire beyond the junction. Does it not count in length. What is it then. If you're running #10 to the roof and #10 to you're panel how do account for the wire resistance.

I admit it wasn't perhaps the most correct way of accounting for the wire on the roof, but it was the easiest. In reality you'd have to calculate the resistance of just that section of wire with the one panel unless you're creating a serial string. Just seems to complicate all the measurements.
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Old 10-21-2021, 07:20 AM   #29
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Originally Posted by gator.bigfoot View Post
So you're not including the wire beyond the junction. Does it not count in length. What is it then. If you're running #10 to the roof and #10 to you're panel how do account for the wire resistance.

I admit it wasn't perhaps the most correct way of accounting for the wire on the roof, but it was the easiest. In reality you'd have to calculate the resistance of just that section of wire with the one panel unless you're creating a serial string. Just seems to complicate all the measurements.
Hi

Each panel gets its own chunk of wire to the junction box. Since it's a "one wire per panel" sort of thing, the load is split at that point. With 4 panels, they each see 1/4 of the current. Those cables typically come with the panel and aren't part of the pre-wire.

Bob
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Old 10-21-2021, 12:18 PM   #30
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Hi



Each panel gets its own chunk of wire to the junction box. Since it's a "one wire per panel" sort of thing, the load is split at that point. With 4 panels, they each see 1/4 of the current. Those cables typically come with the panel and aren't part of the pre-wire.



Bob
Ok I see your point that it is not technically part of the prewire. But it still affects the overall equation for the losses that create the voltage drop.

Each MC4 connector also has a resistance. None of that is part of the panel specifications. You still need to account for it if you're going to get overall resistance on the loop. To be true to the actual resistance of the complete system all these things should be taken into account. Especially at lower voltages. With higher voltages it becomes more of a mute point since it won't make a large enough difference. You'd be amazed at how many losses there actually are.

So if you're just sizing the wire for current then why not just look at the NEC tables and pick the right wire for the job? But if you're looking to minimize your voltage losses then you need look beyond that.
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Old 10-21-2021, 03:54 PM   #31
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Hi

We run 4 factory installed panels through the 10 AWG pre wire. There is no problem with running that way.

Bob
Excellent….roughly 24 amps on a good day..
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Old 10-21-2021, 04:17 PM   #32
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Excellent….roughly 24 amps on a good day..


24a or 24ah?

We've seen 65ah in 9hrs of Sun with 360w of portable using 10g directly to the batteries.👍

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Old 10-22-2021, 08:16 AM   #33
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Ok I see your point that it is not technically part of the prewire. But it still affects the overall equation for the losses that create the voltage drop.

Each MC4 connector also has a resistance. None of that is part of the panel specifications. You still need to account for it if you're going to get overall resistance on the loop. To be true to the actual resistance of the complete system all these things should be taken into account. Especially at lower voltages. With higher voltages it becomes more of a mute point since it won't make a large enough difference. You'd be amazed at how many losses there actually are.

So if you're just sizing the wire for current then why not just look at the NEC tables and pick the right wire for the job? But if you're looking to minimize your voltage losses then you need look beyond that.
Hi

The point is that going from a 5% loss to a 2% loss is not that big a deal. Tearing out the walls of the trailer to redo the wiring *is* a big deal. The benefit in does not justify the work involved. You could always go for 0.2% vs 0.4% ....

Since they are all losses at peak output and you rarely are that high, it gets even more questionable .....

Bob
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Old 10-22-2021, 08:30 AM   #34
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Hi

The point is that going from a 5% loss to a 2% loss is not that big a deal. Tearing out the walls of the trailer to redo the wiring *is* a big deal. The benefit in does not justify the work involved. You could always go for 0.2% vs 0.4% ....

Since they are all losses at peak output and you rarely are that high, it gets even more questionable .....

Bob
It's not always that hard to run oversized wire. Many of the Classics (at least) run 2" pvc conduit down the streetside belly. terminates in two runs under the rear dinette seat, just forward of the wheel well.
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Old 10-22-2021, 09:50 AM   #35
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Might be helpful

TLDR:
Always use 10 gauge wire

https://www.explorist.life/How-to-Ch...trical-System/
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Old 10-22-2021, 09:53 AM   #36
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Regarding this wire size discussion, the following table may be of interest.

For RV solar system design the consensus view seems to be to use the 3% loss table, although to Uncle Bob's point, solar panels rarely, if ever, approach their maximum ampacity so following the 3% loss table should 'build-in' over capacity.

Anyhow, if you have to run wires to the roof, going bigger seems better because you only want to do this exercise once.

https://www.westmarine.com/WestAdvis...9581-_-2617611

Happy electrification:

Burnside Bob

PS I have no affiliation with West Marine, but found this wire chart useful.
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Old 10-22-2021, 10:06 AM   #37
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Regarding this wire size discussion, the following table may be of interest.

For RV solar system design the consensus view seems to be to use the 3% loss table, although to Uncle Bob's point, solar panels rarely, if ever, approach their maximum ampacity so following the 3% loss table should 'build-in' over capacity.

Anyhow, if you have to run wires to the roof, going bigger seems better because you only want to do this exercise once.

https://www.westmarine.com/WestAdvis...9581-_-2617611

Happy electrification:

Burnside Bob

PS I have no affiliation with West Marine, but found this wire chart useful.
Uh, yup. And Lewster always recommended a minimum of 6 gauge for any application, for that reason, as well as minimizing loss. The chart indicates I am at 1.5% loss with 200W in parallel and utilizing the true panel voltage and max amps I have ever seen as an output from the panels.
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Old 10-22-2021, 04:42 PM   #38
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From what I've seen, the maximum wire gauge for an MC4 connector is 8 gauge. 10 gauge is normally the largest size but there are connectors that can accept 8 gauge. If you're using MC4 connectors, I'd keep that in mind when figuring wire size. As an engineer myself, I've found that many theoretical discussions usually are curbed by practical parameters and limitations.

Since I am the original poster, I like to add this to the discussion. I just picked up a second 100W solar panel. It happened to be a great deal from Harbor Freight. 100W Monocrystalline panel. Normally sells for $109 but I was able to combine a couple of coupon offers to get it for $89. Figured for $89 I really don't have much to loose.

I've looked at how to combine the power from a single 100W panel and my Renogy 100W (twin 50W panels in series) solar suitcase. Due to potential incompatibilities between the two panel systems and trying to maximize efficiency I decided to go with two separate controllers and tie them together at the battery bank. Any input?
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Old 10-22-2021, 04:52 PM   #39
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I've looked at how to combine the power from a single 100W panel and my Renogy 100W (twin 50W panels in series) solar suitcase. Due to potential incompatibilities between the two panel systems and trying to maximize efficiency I decided to go with two separate controllers and tie them together at the battery bank. Any input?
I'm no expert, but I think 2 separate controllers is the right way to go. You certainly need to be careful and know what's what when mixing panels, and they will fight each other if you get it wrong. I also use 2 separate controllers, but my second/seperate controller is the dedicated box that is part of my portable panel set. If I deploy the portables, they have their own controller, and the roof mounted and portable both get fed into the batter bank that way. They might butt heads a bit, I dont know how that gets managed, but I do know that is far better than mixing panel voltages into the same controller (thats a big no-no).
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Old 10-22-2021, 06:37 PM   #40
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Lewster here...

We still use 6AWG for most applications. This is from 200 watts up to 500 watts. Over 500 watts we go to 4AWG up to 800 watts. Above 800 watts we use 2AWG cable. Since the majority of our work is for panels in the 400-800 watt range, the 6AWG and 4AWG both handle these well.

All cables are paired for + and - conductivity. It is really no big deal to pull a pair of new cables; usually thru the fridge vent, that gets our results. We have never had a situation where we have seen significant voltage drop, even though many installations are up to 30 feet one way.
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