Yet another solar wiring question

[Serapium]

Socaldmax, that's great info. Thanks! When you say that you turn on your loads during the day (ice maker etc), are you powering those directly off the 'load' terminals on the charge controller or are those wired directly to your 12V system? I've wondered several times as I was designing the electrical whether I would gain some life out of the batteries by running the intermittent 12V loads I can turn on and off (like your ice maker or a 12V watermaker) from the charge controller instead of the battery bank. Seems to me that if I run it from the charge controller I will ultimately have few electrons going in and out of the battery bank and thereby reduce the overall usage of the bank over time... thus lengthening battery life from what it would have been otherwise. Thoughts?

[socaldmax]

Originally Posted by Serapium

Socaldmax, that's great info. Thanks! When you say that you turn on your loads during the day (ice maker etc), are you powering those directly off the 'load' terminals on the charge controller or are those wired directly to your 12V system? I've wondered several times as I was designing the electrical whether I would gain some life out of the batteries by running the intermittent 12V loads I can turn on and off (like your ice maker or a 12V watermaker) from the charge controller instead of the battery bank. Seems to me that if I run it from the charge controller I will ultimately have few electrons going in and out of the battery bank and thereby reduce the overall usage of the bank over time... thus lengthening battery life from what it would have been otherwise. Thoughts?

If the loads are on at the same time the batteries are getting charged, the electrons aren't going into and out of the batteries. If the batteries get charged and the load draws power from the batteries at a later time (like overnight) then the electrons flowed in and out, with the attendant losses.

My ice maker is one of those portable 120v units, so it runs off of the inverter, as well as TVs, DVRs, media servers, etc. I don't run anything off of the "load" terminals on the solar controller. If I did have some 12v loads that I wanted to control at certain time intervals I could run them off of those terminals, but so far I'm manually turning the ice maker on and off.

[steve77]

Originally Posted by GrahamHO

I use the largest size tinned cable that will easily fit the terminals. No need to do calculations. The manufacturer has already done that when they sized the connection terminals.

I would respectfully disagree with this statement. The designer has sized the terminals, but when doing so he had no idea of the details of your particular installation. For example, he had no idea of the length of your cable runs. For longer runs, the cable resistance can lead to high voltage drops, which can require larger cable than the designer foresaw.

If you run your panels in series, then you can run a lot smaller wire. I chose not to do this because I did not want a large loss of power from partial shading. It's an option that you may want to consider.

Okay, I'm an engineer. I just think doing the calculations before buying and running the wires is a good idea.

Cheers!

Steve

[GrahamHO]

Originally Posted by steve77

I would respectfully disagree with this statement. The designer has sized the terminals, but when doing so he had no idea of the details of your particular installation. For example, he had no idea of the length of your cable runs. For longer runs, the cable resistance can lead to high voltage drops, which can require larger cable than the designer foresaw.

If you run your panels in series, then you can run a lot smaller wire. I chose not to do this because I did not want a large loss of power from partial shading. It's an option that you may want to consider.

Okay, I'm an engineer. I just think doing the calculations before buying and running the wires is a good idea.

Cheers!

Steve

Sure, I've also got an engineering background and calculations are good but it also comes down to practicalities.

How many times have you calculated that a good controller requires heavier cables than can fit the terminals. Calculations may tell you that you can run lighter cable.

The controller designer envisaged an average installation with average length cable runs. If we keep our cable runs as short as possible and use the largest tinned cable to fit the terminals it will work fine.

I do agree with both your statements in principal though; including wiring panels in series. That may be OK for a terrestrial installation but as we know a vessel moves around and shading changes.

[Maine Sail]

Originally Posted by GrahamHO

The controller designer envisaged an average installation with average length cable runs. If we keep our cable runs as short as possible and use the largest tinned cable to fit the terminals it will work fine.

The reason many terminals on controllers are often smaller than we'd like is because they are built to be in compliance with NEC & land based UL standards. So a 30A controller only gets a terminal strip / lug sized for 30A regardless of the voltage drop in your particular installation. With some creativity you can often fit up to 6GA terminals into these small terminals....

[GrahamHO]

Originally Posted by Maine Sail

The reason many terminals on controllers are often smaller than we'd like is because they are built to be in compliance with NEC & land based UL standards. So a 30A controller only gets a terminal strip / lug sized for 30A regardless of the voltage drop in your particular installation. With some creativity you can often fit up to 6GA terminals into these small terminals....

Yes you can remove a few strands from a heavier cable. Not best practice but it works. Or you can have a junction box near the controller which is what I do.

[Maine Sail]

Originally Posted by GrahamHO

Yes you can remove a few strands from a heavier cable. Not best practice but it works. Or you can have a junction box near the controller which is what I do.

I meant that I will sometimes modify a 6GA lug to fit a 30A terminal using a Dremel to make it narrow enough to fit the slot. For screw/pressure fit terminals I use tongue/blade terminals or ferrules unless it has a built in pressure plate. I also use an external busbar to step down to controller size terminals when I need to....

[boatsmith]

Originally Posted by steve77

I would respectfully disagree with this statement. The designer has sized the terminals, but when doing so he had no idea of the details of your particular installation. For example, he had no idea of the length of your cable runs. For longer runs, the cable resistance can lead to high voltage drops, which can require larger cable than the designer foresaw.Steve

I agree with this. In fact the Morning Star 30 amp controllers we just installed would not accept #8 ring terminals without sanding the terminals narrower. This IMO is very crappy design

[Norfolk Is]

Hey Guys
Can I ask a question, because I am very green when it comes to solar,
I want to add as much power I can to go off grid, I have measured my real Estate on my boat and I can fit 2 x 200w solar panels, given that how many amps in batteries could I charge? I know it depends on conditions, but I am just wondering how much to spend on batteries, no good putting in 600amps if I can only recharge 400..

[GrahamHO]

Originally Posted by boatsmith

I agree with this. In fact the Morning Star 30 amp controllers we just installed would not accept #8 ring terminals without sanding the terminals narrower. This IMO is very crappy design

I run 2 reasonably heavy cables from each of 2 panels to a junction box close to a Morningstar controller. Then connect short cables sized for the controller terminals from the junction box to the Morningstar. This works just fine. The controller should be installed close to the battery to avoid voltage drop in the regulated charging voltage.
In fact I have 4 panels and 2 controllers with each pair wired as above.
It's just another way of skinning the cat.
Everything works well which is all that needs to happen.

[Maine Sail]

Originally Posted by boatsmith

I agree with this. In fact the Morning Star 30 amp controllers we just installed would not accept #8 ring terminals without sanding the terminals narrower. This IMO is very crappy design

Don't forget that the MS PS MPPT controllers have a dedicated voltage sensing circuit. About 80% of them I see installed are not using it....

[Stu Jackson]

Originally Posted by Norfolk Is

..but I am just wondering how much to spend on batteries, no good putting in 600amps if I can only recharge 400..

Understand that you're new to this, but you're missing the point about bank capacity and charging.

The larger the bank means that WITH THE SAME DAILY LOADS you can go longer without recharging.

The size of the charging source, in general, means shorter charging times.

[Paul Elliott]

Originally Posted by Norfolk Is

Hey Guys
Can I ask a question, because I am very green when it comes to solar,
I want to add as much power I can to go off grid, I have measured my real Estate on my boat and I can fit 2 x 200w solar panels, given that how many amps in batteries could I charge? I know it depends on conditions, but I am just wondering how much to spend on batteries, no good putting in 600amps if I can only recharge 400..

There is a point of diminishing returns if you want to use solar as your primary charging source, but in general you can use small panels with a large battery bank.

For example, I have about 1000Ah worth of 12V house batteries, and 3x 100W panels. These would take a long time to fully recharge my batteries, but they more than keep up with my daily at-anchor power consumption so the big battery bank never gets very much discharged. Having a big battery bank lets me ride out a couple of cloudy days without needing to run the engine for charging, and when the sun comes back the panels eventually recharge the batteries.

At sea I use more power than the panels can deliver, so I run the engine every couple of days to fully recharge.

[motion30]

[ QUOT E =Maine Sail;1913987]Don't forget that the MS PS MPPT controllers have a dedicated voltage sensing circuit. About 80% of them I see installed are not using it....[/QUOTE]

could you Please explain more I have an Outback 60 amp controller and not familiar with any such device

[GrahamHO]

Originally Posted by Maine Sail

Don't forget that the MS PS MPPT controllers have a dedicated voltage sensing circuit. About 80% of them I see installed are not using it....

I'm not aware of a voltage sensing circuit on my Morningstar. Perhaps in my ignorance I assume that the controller senses the battery voltage from the cable attached to the battery; and that it senses the panel voltage from the cable attached to the panel. I know the controller also has a couple of terminals labeled "load" with I think a graphic of a light bulb. Is that what you are thinking of? That is an extra accessory connection I believe and probably 80% of owners including myself don't use it.