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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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Old 05-02-2011
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Help With New Electrical System

First off, thanks for all the amazing posts. I have learned so much reading all the helpful information found on this site. Here is my situation, I recently purchased a 1976 Islander 36. The boat only had a 12v system present w/ 2 cranking batteries. The 12v panel is going but the existing 12v equipment is staying (lights, instruments, and radio). The boat was repowered in 2005 where they replaced the Atomic 4 with a M25XPB.

I am installing a new 110v and 12v system. This will include all of the equipment listed on the wiring diagram. I drew up the wiring diagram to help me with the install and for future maintenance. There were a couple areas I'm not a 100% on so I'm hoping to get some constructive criticism.



Obviously, some of the wiring isn't shown or simplified such as the DC branches or 110v out from the inverter.

Here are some of the questions I have:

1. I was trying to decide what battery fuses to go with. The inverter manual suggested a 250A Class T fuse. I'm fine with using those but I saw the MRBF's which might work better for my installation. Would this type of fuse work? The Blue Seas 5118 Class T fuse is listed with a AIC at 20,000 and the Blue Seas 5189 Terminal fuse (MRBF) is listed at 10,000. For the 4x6v house system, the 10,000 AIC should be enough, right? Also, should I use the 250A fuse on both the house bank and the reserve bank or should the reserve bank use a lower rated fuse?

2. Can someone double check how I have my DC neg bus and grounding bus set up. Is it close or did I miss the mark? It got a bit confusing towards the end.

3. Along the same lines, is the galvanic isolator located in the correct place? It seemed a bit funky tying the 110v panel ground into the grounding bus prior to connecting to the galvanic isolator.

4. Any idea what the amp draw is for the starter on a M25XPB? I wouldn't think more than 200 amps but that would only be a guess.


Again, feel free to pick my plan apart. I already have most of the equipment listed and would like to use it unless it absolutely will not work. I have some basic 110v experience with houses but a boat's electrical system is new territory for me. Thanks again for everyone's time reading this,

Ron
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Old 05-05-2011
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Also, does anyone have advice on the equipment I have listed? Problems or issues during install or operation? Any information would be greatly appreciated! Thanks,
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Old 05-05-2011
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Wow it looks pretty good! You might cosider fuses for the banks though. MRBF's, ANL or class t's all work well. The only thing I have a question on the the shunt in the + line at the panel. They are usually installed on the ground side but I can't tell what it's for..
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Thanks for the reply. I based the system on some of the posts you and some of the other posters here have shared with us. I'm attaching an updated wiring diagram.

The instructions for the AC/DC panel show the shunt between the positive 12v supply and the 100A main breaker (panel) for the DC ammeter. Should it be located somewhere else?

I was thinking of using the MRBF's after seeing your post on them. I think they would work out well for my installation. I was going to use a 250A rated fuse for the house bank (this size was recommended by the inverter instructions). Should the fuse on the reserve bank be rated at 250A too? It seems like the largest normal draw from either bank would be the starter which would draw the same amount from which ever battery was selected. Does 250A seem like a normal fuse size for this type of install?

Also, does the DC neg bus and grounding bus look correct?



Thanks again for the help!
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Old 05-05-2011
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Looks good to me as well. Don't worry too much about the starter's amp draw. The ANL fuses will withstand about 160% of their rating for 500 seconds so starter amperage on your engine isn't an issue. I would also fuse both banks.

The inverter fuse doesn't have to be a Class T fuse - ANL or MRBF fuses would work also.

You don't really need a dc negative bus and a ground bus as they are really the same.

I don't see a good battery monitor like a Victron BMV-600 though.
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Old 05-05-2011
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I agree that it looks pretty good. But I would keep the separate dc neg and ground bus. Some boats have a separate grounding bus and some don't, but the larger the boat is the better it is to separate the functions to keep everything straight.
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I am planning on fusing both banks. Is there a good rule of thumb for determining what rating fuse to use at the batteries? Should I try to calculate max possible draw?

A battery monitor is on the list and will hopefully be added within a few months. It was hard enough to convince my wife that I needed all of the stuff already listed
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Old 05-05-2011
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Quote:
Originally Posted by peikenberry View Post
I agree that it looks pretty good. But I would keep the separate dc neg and ground bus. Some boats have a separate grounding bus and some don't, but the larger the boat is the better it is to separate the functions to keep everything straight.
1. Given that you've got the DC Neg and Ground bus connected together, personally, I'd think you'd make life simpler without it.

A separate Ground bar is really only required on the AC side - and don't, under any circumstance, connect the AC Ground to the DC ground - even through a Galvanic Isolator. You'll kill someone. Actually.. on second look, your grounding system isn't right at all!.. Have another go.

2. Given all that pretty Xantrex gear, I'd have thought you might have added a Xantrex 'LinkPro' battery monitor..
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Last edited by Classic30; 05-05-2011 at 11:26 PM.
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Old 05-05-2011
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The AC ground (green wire) and the Dc negative should be connected. For both safety and to satisfy ABYC.

Green Wire (Controversy) - Resources - Blue Sea Systems
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Old 05-06-2011
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The AC ground (green wire) and the Dc negative should be connected. For both safety and to satisfy ABYC.

Green Wire (Controversy) - Resources - Blue Sea Systems
Hmm... Thanks for the link, Brian. Interesting reading and far be it for me to disagree with BlueSeas. Although I'd still be way too wary myself, the OP has it connected via a galvanic isolator, so.. go right ahead. I'm glad we don't have rules like that over here!

I still think his AC ground system needs re-work - as per the BlueSeas link you posted.
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Last edited by Classic30; 05-06-2011 at 01:02 AM.
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