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Old 03-08-2018, 05:36 PM   #1
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More solar questions....

I have been hijacking other threads so I decided I would start my own.

y'all have been very helpful in improving my understanding. I do have a few more questions and really hope you don't mind.

Situation: I am looking to place one 265w solar panel on my PH roof. Only one panel because that is all that I can conveniently fit on my boat.

A comment that psneed made in a solar thread a while ago has stuck with me. He said something along the lines that while his solar system may not be "perfect" it works well for him. Mathew 5:48 notwithstanding, I don't need to get a perfect system, just something that will help me keep the batteries charged when we stray further from home.

1. Placement of controller.
My limited understanding is that the charge controller should likely be located near the batteries as opposed to near the panel. The panel will put out higher voltage than the charge controller and so current from the panel to the controller will be less than from the controller to the battery. Putting the controller next to the battery means a shorter run for the larger wire needed for the higher current and using a smaller AWG wire for the run from Panel to controller. I think I would use 8 AWG from panel to controller in this scenario.

I would like opinions on another option. There is a DC panel in the PH. There is a 2/0 (maybe a 1/0 I will need to check) cable running from a bussbar there to the battery bank. Couldn't I just connect the controller output to that? This would make installation a lot easier. Instead of running 8 AWG wire from the pilothouse roof to the aft lazarette, I could just run the wire from the panel to the controller in the PH and connect the controller output to the bussbar.

Unless I am missing something, this should charge the batteries just fine. The only downside would be that I would't have temperature monitoring of the batteries. However, the batteries are in an aft space that is shaded and sitting in water that is normally right around 50 degrees. Also, the max that the charge controller would be putting out would be 30 amps, nothing like the 125 amps that my shore charger kicks out.

2. Running wire through the PH roof.
This is a simple and simpleminded question. I will need to run the panel wire through the PH roof. How do I do that without creating leaking issues?
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Old 03-08-2018, 08:26 PM   #2
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If you have a significant (more than a half volt) voltage drop from the solar panel to the controller, no big deal. The panels are putting out lots of voltage and all you are losing is a little power, not performance.

But a half volt drop in the wire from the controller to the batteries is a big deal. The controller is adjusting its voltage output based on its charging algorithm. If you have a 0.5 volt drop then the battery is seeing less voltage than the algorithm expects so your batteries will not charge as fast as they should.

I would try to keep the voltage drop at 0.2 volts or less in the controller to battery circuit, whatever size is required to do that based on the distance.

As you note you can hook your controller up anywhere in its circuit as long as the wiring is large enough to keep the voltage drop low as above. The main DC panel is a good spot. You can often use a spare breaker and back feed the battery through it. Or tie in to the main buss through a properly sized fuse. Size the fuse or the breaker so it protects the wire to it.

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Old 03-08-2018, 10:00 PM   #3
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Thanks David, that makes sense. Even with the connections (which I can clean) I think I will get less voltage drop using the large cable connecting the DC panel to the batteries.

I’ve read the same suggestion you just gave about “back feed the battery through a breaker”. To be honest, I don’t fully understand what that means. My guess is that it means the charge controller feeds DC back towards the battery from the panel that normally is getting DC current fed to it from the batteries.

If the controller will put out a max of 30amps, that means that I would need a spare 30amp breaker to connect between the charge controller and the positive buss?
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Old 03-08-2018, 10:21 PM   #4
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My solar is wired exactly as you are proposing. It works great.

You can use a panel breaker, or a separate fuse or breaker.
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Old 03-08-2018, 10:23 PM   #5
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My solar is wired exactly as you are proposing. It works great.

You can use a panel breaker, or a separate fuse or breaker.


Thanks Twisted.

Any ideas on how to get the wire through the PH roof without creating a potential leak problem?
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Old 03-09-2018, 06:32 AM   #6
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While its not a problem for everyone , some solar systems make RFI on AM ad FM radios.

Its a PIA to not be able to use the fun radio, just because the batt needs a wee bit more juice.

A way of cutting off the solar charger can add to the delights of being onboard.
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Old 03-09-2018, 06:38 AM   #7
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Quote:
Originally Posted by dhays View Post
Thanks Twisted.

Any ideas on how to get the wire through the PH roof without creating a potential leak problem?
I have seen an installation that uses these:



Newmar RA-2 Cable FEED-THRU 0.27-0.35 Inch Cable Diameter - Newmar RA-2 - Terminal Blocks Bus Bars & Feed Thrus - Electrical Parts - Electrical - Boatersland Marine

They are very elegant-looking solution over the old standby. No knowledge of how they hold up, however. They may be available elsewhere - that was the first link that Google produced. No affiliation, etc.
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Old 03-09-2018, 09:21 AM   #8
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Without knowing the controller it is hard to answer the question accurately, other than to generalize.

Does the controller have remote volt-sensing?

Does the controller have remote on-battery temp compensation?

What brand and model?

Many controllers these days use local-ambient temp sensing to compensate charge voltage. It is a cheap way of doing it but can actually be harmful to the batteries. This is why most of these controller makers suggest as close to the batteries as possible..

I have seen numerous installations where the batteries were one temp and the controller was another thus giving the battery bank an incorrect charging voltage.

I had one trawler customer who's house batteries were in the engine room and his ambient-sensing controller in a much cooler compartment up in the v-berth. When his Trojan batteries were 116F, due to engine room heat, the controller was feeding them over 15V because it was at about 50F.... It should have been compensating voltage DOWN, not UP.. Oops....

With an MPPT controller you want as little voltage drop as possible, on both sides of the controller....

I use the ScanStrut deck glands almost exclusively... This one is a DS30-S..

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Old 03-09-2018, 11:13 AM   #9
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Quote:
Originally Posted by FF View Post
While its not a problem for everyone , some solar systems make RFI on AM ad FM radios.

Its a PIA to not be able to use the fun radio, just because the batt needs a wee bit more juice.

A way of cutting off the solar charger can add to the delights of being onboard.


I have heard about the RFI from some controllers and that is a reason I will want to stick with a known manufacturer. (BTW, anyone experience RFI with the Victron?)

I have wondered about putting a switch between the panel and the charge controller. If the sun it out, and I need to disconnect the panel or controller, it might be nice to be able disconnect it.
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Old 03-09-2018, 12:06 PM   #10
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265 watt is ok. What if you were just installing one panel, why not put as large as panel as possible in the same footprint. Something like 300 or 330 watt
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Old 03-09-2018, 12:40 PM   #11
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Don't buy a no-name ebay or amazon controller and you will be fine.

Lots of different cable glands are available from Blue Seas and others.

One thing to watch out for is if you have one or more ammeters. I have one at my panel that measures current through through panel. I connected the solar charger to the battery side of the shunt and used a separate breaker. That way the panel current meter still shows panel current. The solar charge current goes straight to the batteries, and is picked up in the battery net current meter. So I see the effect on the batteries, but it doesn't distort teh consumption figures. If I backfed to a breaker on the panel, it would have messed up the panel current meter readings.
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Old 03-09-2018, 12:59 PM   #12
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Quote:
Originally Posted by CMS View Post
Without knowing the controller it is hard to answer the question accurately, other than to generalize.

Does the controller have remote volt-sensing?

Does the controller have remote on-battery temp compensation?

What brand and model?

Many controllers these days use local-ambient temp sensing to compensate charge voltage. It is a cheap way of doing it but can actually be harmful to the batteries. This is why most of these controller makers suggest as close to the batteries as possible..

I have seen numerous installations where the batteries were one temp and the controller was another thus giving the battery bank an incorrect charging voltage.

I had one trawler customer who's house batteries were in the engine room and his ambient-sensing controller in a much cooler compartment up in the v-berth. When his Trojan batteries were 116F, due to engine room heat, the controller was feeding them over 15V because it was at about 50F.... It should have been compensating voltage DOWN, not UP.. Oops....

With an MPPT controller you want as little voltage drop as possible, on both sides of the controller....

I use the ScanStrut deck glands almost exclusively... This one is a DS30-S..
Thanks Rod.

I am looking at the Victron BlueSolar MPPT 100/30 charge controller. It has internal temp sensing. My boat is such that I shouldn't ever have the situation you describe where the controller is sensing a temperature much lower than that of the batteries. My batteries are in an aft lazarrette that is below a covered cockpit. The top of the lazarette is therefore shaded and is sitting in a hull that is in water that is a relatively constant temperature year round. The controller in the pilothouse would be warmer than the batteries. On a hot summer day, the controller could be 25F degrees warmer than the batteries. This would result in the controller sending a lower charge voltage to the batteries than they might otherwise accept. Not ideal, but the alternative is a very long, and frankly difficult, wire run from the single panel on the pilothouse to the batteries.

I also think that I will get less voltage drop by using the existing 0/1 or 0/2 cables that are there and back feed the batteries from the DC panel.

I had looked at the Scanstrut glands so it is nice to get a knowledgeable endorsement for them. One of the reason I love this community is that there are so many folks with so much more knowledge and experience than I have. Ignorant questions;

Since I need to run two wires through the PH roof, + and -, can I use just one deck seal? I believe it is possible to use a blank seal and drill a hole for each wire. However, if I did this I wouldn't be able to pass a connecter through the seal. But, if I make the MC4 connections from the panel I suppose I could just get a premade MC4 extension cable, cut it in half, and pass the cut ends through the seal. The cut end would then just be wired directly to the controller.

Secondly, I was hoping that I could get some type of deck gland that I could affix to the roof without more screw holes using something like 4200. Have you seen this work well?
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Old 03-09-2018, 01:02 PM   #13
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Quote:
Originally Posted by boathealer View Post
I have seen an installation that uses these:

Newmar RA-2 Cable FEED-THRU 0.27-0.35 Inch Cable Diameter - Newmar RA-2 - Terminal Blocks Bus Bars & Feed Thrus - Electrical Parts - Electrical - Boatersland Marine

They are very elegant-looking solution over the old standby. No knowledge of how they hold up, however. They may be available elsewhere - that was the first link that Google produced. No affiliation, etc.
Thanks, I've seen those as well. I do like the horizontal orientation, just not sure if I could run two wires through one gland.
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Old 03-09-2018, 01:06 PM   #14
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Did a bit more looking. These, https://scanstrut.com/products-22/el...plastic-detail, are really sexy!
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Old 03-09-2018, 01:07 PM   #15
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265 watt is ok. What if you were just installing one panel, why not put as large as panel as possible in the same footprint. Something like 300 or 330 watt
Rats. You found one of my many typos. I meant to type 365w panel. My thought was the same as yours, since I can only fit one panel, I'd rather put one on with the highest output that I can. It appears that it has been to long and I can't edit my own post at this point.

The panel I was looking at is the LG365Q1C-A5. It is a 365w, 60 cell panel with very high efficiency. NOT inexpensive however.
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Old 03-09-2018, 01:11 PM   #16
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Did a bit more looking. These, https://scanstrut.com/products-22/el...plastic-detail, are really sexy!
Yes, I saw those as well. I have the same concern in that I'm not sure I can run two wires through them.

There are a number of dual roof pass through connections for solar installations on RVs. They may be another option.
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Old 03-09-2018, 02:29 PM   #17
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Dave-

You can run the numbers to determine an ideal wire size between the panel and your controller. Also when running the numbers remember that batteries that have low charge will accept large currents while as the charge increases, the charge acceptance decreases. This means you can actually have some voltage drop in your wiring without system degradation.

OK but engineering the new system can be a PITA! A simple approach I would use is to use a higher Vmpt panel to reduce the voltage drop between the panel and the controller and remember, the wire length is times 2 between the panel and the controller for calculating voltage drop. Back to higher voltages. At a minimum I would use 32Vmpt so your current is almost 1/2 that of a so called 12V panel which usually has a Vmpt of 18V.

And battery temperature monitoring. The probability of a 350 watt panel being able to get 30 amperes to the batteries for an extended time is small. I have only seen about 50 amperes going to my batteries once or twice and I should be getting upwards of 70 but again, it depends a lot on the batteries' acceptance. I have Canadian mono panels, four each 295 watts. I have them connected in parallel/series. That is 2 panels in parallel forming two banks with two banks in series. So my point, if running a temperature sensor gets to be a pain, I don't think it will be a big deal.
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Old 03-09-2018, 03:29 PM   #18
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Secondly, I was hoping that I could get some type of deck gland that I could affix to the roof without more screw holes using something like 4200. Have you seen this work well?

If 4200 is your sealer of choice why not simply feed wire through hole and as you push the last few inches through load the wire up with 4200 and then finish off neatly.

Its not as if you'll see it and you won't be removing it.
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Old 03-09-2018, 04:11 PM   #19
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My solar is wired exactly as you are proposing. It works great.

You can use a panel breaker, or a separate fuse or breaker.
+1 On wiring to the panel, so's mine. Not a problem. I have a main that runs from the battery that lives in the aft part of the engine room to the panel up in the pilothouse. My solar panels (480W) float the batteries out after I bring them up to about 90% with the genset. It's been great for the batteries; we spend lots of time at anchor, and it's significantly reduced our genset run time since I don't feel compelled to keep the gen running to try to float the bank. It's also enabled me to eliminate the cumulative loss of capacity as a result of chronic undercharging.

Regarding David's concern over voltage drop to the bank, I'd expand on it that since the objective is purportedly float charging, with the wattage you're proposing, it's not likely you'll overcharge the bank, so the controller could be programmed at a float voltage to offset that drop, if any. Keep in mind, you'll probably only get 75-80% capacity on a good day. Here in the Bahamas, I'll see a max of about 365W from my 480W panels.

FWIW, an MPPT controller will yield more energy output than a PWM type. You can add a breaker between the controller and the connection to the bus. The purpose of the breaker is to protect the wire-could also use a fuse. Keeping that focus will help make sense of when/where one is appropriate.
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Old 03-09-2018, 07:13 PM   #20
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Dave,

As a retired EE, I concure with Steve's setup. In fact I just copied it with a single LG 315W panel and a Victron 100/30 mppt controller. To solve the issue of controller being in PH and batteries in the ER, Victron is releasing a remote battery temp sensor. It is called the Smart Battery Sense and should be available in the US by this summer. Manual at: https://www.victronenergy.com/live/s...y_sense_manual

For the PH roof penetrations (2 MC4 cables) I am using a 2 gland horizontal unit
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I also added a MC4 inline fuse next to the panel for a little extra protection.

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