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Old 28-01-2016, 14:18   #1
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Wiring solar charger to ?

I bought a small pair of 100 watt flex solar panels and a 20 amp mppt charger controller today. My problem is that it would be a nightmare to run the wires all the way to my 320ah house bank. My Catalina 320 has all of the wiring in Plastic conduits with very little extra room. My 20 amp charger is in the port stern locker where I plan to install the controller. The cables that run back from the batteries look to be 1/0. I would like to connect the controller directly to the existing cables at the lugs.

I don't know squat about how these systems work.

Thanks, Woody
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Old 28-01-2016, 22:00   #2
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Re: Wiring solar charger to ?

1/0 wire on a 20a charger??.... maybe 10awg.


I would connect the MPPT output to the post on the charger for the house bank. as that wire should be going straight to the batteries bypassing any switch. make sure that charger wire is fused at the battery. it's probably 30a if there is one. and I wouldn't go any higher if it's 10awg.


depending on the actual wire and fuse size. you'll probably blow it if you run the charger on a sunny day... as the system will only handle one or the other if it's 10awg with a 30a fuse. but that will be your limitation of not running wires all the way.
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Old 29-01-2016, 07:10   #3
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Re: Wiring solar charger to ?

Thanks, I wasn't sure if it was acceptable to wire the the controller to the house bank there. I also checked the wire size to make sure it was the right size. It's 4 awg with a 20 amp fuse. The run from the charger to house bank is about 18 Ft. It seems like overkill but everything on this boat is that way.

Thanks again, Woody

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Old 29-01-2016, 07:14   #4
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Re: Wiring solar charger to ?

Correction, it's a 30 amp fuse.

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Old 30-01-2016, 19:56   #5
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Re: Wiring solar charger to ?

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Originally Posted by Drift Woods View Post
Thanks, I wasn't sure if it was acceptable to wire the the controller to the house bank there. I also checked the wire size to make sure it was the right size. It's 4 awg with a 20 amp fuse. The run from the charger to house bank is about 18 Ft. It seems like overkill but everything on this boat is that way.

Thanks again, Woody

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technically speaking, piggy-backing the connections through the shore charger is not allowed. the MPPT should have its own dedicated connection (fused) to the battery bank.
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Old 31-01-2016, 23:43   #6
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Re: Wiring solar charger to ?

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technically speaking, piggy-backing the connections through the shore charger is not allowed. the MPPT should have its own dedicated connection (fused) to the battery bank.
the charger is just a junction point. it's just a bus bar for a battery connection.

I would fuse the wire from the charger to the mppt with the correct fuse for the solar, and make the battery one bigger to handle both since the wire is so big. the charger is already fused internally for the device itself. and the battery fuse is protecting the 4awg.


if you wanted to make it slightly better, you could remove the house wire from the charger to a post below it, and then fuse from the post to the charger and to the mppt. then make the 4awg battery one bigger for both.
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Old 01-02-2016, 05:29   #7
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Re: Wiring solar charger to ?

The installation instructions call for a fuse between the panels and the controller, and one between the controller and the battery. For wire sizing per run length I've been using the attached chart. It calls for a minimum 6 awg from the charger to the battery @ 40 amps in a critical circuit. The 4 awg installed according to the chart is good for 60 amps in a critical circuit.

I do think adding a small bus bar is a smart idea. I may decide to add two more panels and a second controller later on.

Thanks for the help, Woody
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Old 01-02-2016, 05:36   #8
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Re: Wiring solar charger to ?

Everything to a buss bar then one big wire from buss to battery. One positive and one negative buss bar

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Old 01-02-2016, 06:17   #9
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Re: Wiring solar charger to ?

This is the wiring chart I'm using. Don't know why it didn't load the first time.

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Old 01-02-2016, 06:43   #10
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Re: Wiring solar charger to ?

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Originally Posted by Drift Woods View Post
The installation instructions call for a fuse between the panels and the controller, and one between the controller and the battery. For wire sizing per run length I've been using the attached chart. It calls for a minimum 6 awg from the charger to the battery @ 40 amps in a critical circuit. The 4 awg installed according to the chart is good for 60 amps in a critical circuit.

I do think adding a small bus bar is a smart idea. I may decide to add two more panels and a second controller later on.

Thanks for the help, Woody
This is a land based NEC requirement where panels will be run at significantly higher voltages often with micro inverters right at the panel.... Your panels are "self-limiting" and thus any fuse and wire that can handle the loads, and not induce performance robbing voltage drop, won't trip on the PV side of the controller because the panels can't develop enough short circuit current to do that...

The battery is the current source you are protecting the wires from and a fuse is a safety requirement, preferably within 7" of the battery positive post....

So long as the charger wire is large enough to handle both charge sources at once, with minimal voltage drop, adding positive & neg busbars at the charger is a suitable choice, just be sure they are covered.

With 4GA wire at 18' to the bank the round trip circuit length is roughly 36'. 36' of 4GA wire at 20A & 14.4V will net you about a 1.3% wire voltage drop excluding connections/terminations. Even adding 200W of solar to the 20A charger, and calling it a max potential of about 32A, your voltage drop in a 36' 4GA circuit at 14.4V is still about 2%...

Also the chargers AC terminations (butt splices) should be made inside the charger case, or in a j-box. The white wire connected to the chargers case/frame grounding point should be no more than one GA smaller than the DC charging wires. It should also be green or green with a yellow stripe and run directly back to the ships ground bus.
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Old 01-02-2016, 06:49   #11
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Re: Wiring solar charger to ?

Im sure you know, but measure to and from too figure wire size. If 15 feet from fuse to appliance then 30 foot wire run. It makes a difference. Thanks

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Old 01-02-2016, 08:46   #12
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Re: Wiring solar charger to ?

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Im sure you know, but measure to and from too figure wire size. If 15 feet from fuse to appliance then 30 foot wire run. It makes a difference. Thanks

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That was a big mistake on my part. I still have the required wire size for what I'm installing now but no further expansion.

The boat won't be used for full time cruising so the 200 watts of solar hopefully will be sufficient.

Thanks, Woody

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