Re-wiring plan for old boat

[Rugger8]

Ok, everybody. I finally downloaded Visio and have started my electrical plan for re-wiring my 1947 DCFB Chris Craft. Please let me know if I am on the right track. There are some areas I am a little unclear if I did correctly. In particular, I have 2 starting batteries (1 for each engine) and a house bank of batteries. I tried to wire the switches so that I can switch between any of the three banks if necessary to start either engine. Special thanks to Knotty Buoyz as I relied heavily on his thread. Any thoughts on how to do it better is appreciated as well.

Thanks,

Jeff

[James S]

I'm not clever enough to give much constructive advice on the lay-out, but I deliberately left no connection between my start batteries and the house bank...I figured if I ever did need to use the house to start I would do it with jumper cables...a bit archaic for sure...but I'm really afraid of accidentally depleting all my juice.

[Rugger8]

Thanks for the response James. I am not necessarily sold on doing it this way and would certainly hope others can chime in. This is my first re-wiring project, so I am certain I didn't get it all right, so please everyone let me know what you think.

Thanks,

Jeff

[knottybuoyz]

I thought it looked vaguely familiar for some reason!

Why two shorepower inlets?

I think you'll need another switch on the stbd engine battery feed to starter.

[crashkahuna]

Originally Posted by James S

I'm not clever enough to give much constructive advice on the lay-out, but I deliberately left no connection between my start batteries and the house bank...I figured if I ever did need to use the house to start I would do it with jumper cables...a bit archaic for sure...but I'm really afraid of accidentally depleting all my juice.

I think a lot of boats are this way including mine. Do you have electric or mech fuel pump and which battery is that and engine instruments on?

[Rugger8]

Thanks KnottyBuoyz, hope you don't mind me borrowing from your experience. As for the battery switches, it appears I could do it with just the two switches a (1 + 2) and a on/Off switch, but it sure makes it a lot more complicated. I am wondering if I am not better off just doing 3 on/off switches - 1 for each starting battery and then 1 for the house bank.

The plan is to have all the instruments 1 row of DC circuit breakers with a main 30A breaker. IE, I can shut down the whole flybridge instrument panel with the one breaker. This would be powered by the house battery bank.

As for the fuel pumps, they are mechanical. The engines are the original circa 1950 Hercules gas in-line 6 engines.

Jeff

[Rugger8]

oh missed the one question. The reason for 2 30A inlets was to allow for more power. This is a 46' boat, so maybe not 100% necessary, but figured I would leave room for other items that may come up. I could have gone to 1 50A inlet, but 30A are more common where I am at. I also have to confess, I already hooked up the 110 part, as I found this site after I started work on that. But for some reason, the 12V seems a lot more confusing to me. But if I did something wrong on that, let me know and I can change that as well. So far all of the 110 is working as its supposed to.

Jeff

[gmau]

Lets first discuss how some two engine boats come wired from the manufacture.

With out getting to techinical at this point, this is what I have found.

They use one battery to start both engines. Makes sense as a person would not normall try to start both engines at the same time.

Usually this battery is connected to the port engine. It is usually switched on and off with a simple on/off MBSS. When on it provides all the power that is needed for running the boat. The house circuits are usually tied to this battery if only one battery is used.

If only one battery is shipped with the boat, the boat has the following wiring.

The second engine (usually the starboard) is wired with a sense wire from the alternator to a battery. The charge (output) of the alternator is also wired to this battery.

So if there isn't a second battery the alternator is disable because the sense wire has no volteage.

If a battery is present a simple on/off MBSS is used to provide power to the house circuits. House circuits are any circuits not required when the engine(s) are running.

Some manufactures will provide another on/off MBSS that can connect the two batteries together for emergency starting. The con is if this switch is left on without the engines running or a charger hooked to the batteries, it is possible to drain both batteries with house loads.

The above does work and many boats are wired that way.

Another was is to have both engines wired the same. Makes it easier to trouble shoot.

In this case a 2-4 position (Off,1,2,Both) MBSS is used. Both engines are wired the same. The common is connected to the starter of the port engine. 1 to the first (port) start battery, 2 to the first (port) house battery.

The starboard engine would be wired with the common going to the starter, 1 to the second (starboard) battery, 2 to the second (starboard) house battery. The sense lead has to be connected to the house battery

It's a good practice to add another 4 position MBSS. Common goes to the house loads/battery charger. 1 goes to the port house (at the port switch) and 2 goes to the starboard house (at the starboard switch).

IMHO this gives the best for ballancing the alternator output. Gives you the ability to isolate batteries. If you have two batteries in parallel and you loose a cell, both batteries will go bad if left connected. If you loose an alternator you can use the switches to charge all batteries.

There are ways to use on/off switches and automatic charge relays (ACR) for less switching.

Using a 100 amp alternator to charge two group 27 batteries is way over kill.

Two group 27 100 amphour batteries is not very much. First if you discharge more than 50% you will shorten the life of the battery. The majority shoots for 40% discharge. so that would give you only 80 amphouse of usefull power before having to charge your batteries.

I have a 32 foot bayliner. The biggest drain is the refer. Next would be the water pump. How late you stay up governs your light usage. We end up using about 60 amphouse a day. So the group 27 would last us about a day.

The conses is golf cart batteries give the best bang for the buck. We have 4 golf cart batteries in two banks. Gives us an easy three days until we have to charge the batteries.

The above should give you plenty to ponder.

Ask away if you have any questions.

Gordon

[Rugger8]

Gordon,

Thanks for your reply. I need to sit down and draw up what you wrote, so I can get my head wrapped around it. But to answer some of your questions before I do that, I will start with this.

I have not bought the alternator yet, so I can get a smaller one if necessary. What size do you recommend. My thought was to have each generator charge the starting batteries and then have the alternator, which is only on the port engine, charge the house batteries. I plan to have all the electronics, lighting, etc. run off of the house batteries. I know the house bank of 200 Ah @ 12V is not very big, but I generally just go out on a saturday, spend the night and come back on a Sunday, so don't need to run it much. I figured if the batteries get low, I can either run the engine a bit to recharge or shut off the refrigerator. i don't want anything running off the starting batteries as I want to have the security that I can always start the engine to recharge if necessary. Your reply brings back a question that I have been struggling with, should I just go with 1 starting battery for both engines and then combine 3- 100 Ah batteries for the house bank. Still not as large as others, but for my limited overnighting, should do the trick. Or should I stick with 2 starting batteries and 2 batteries for the house bank. BTW, I am installing LED lights as well to reduce usage, so the refrigerator will be the main draw on the boat.

Jeff

[gmau]

Originally Posted by Rugger8

I have not bought the alternator yet, so I can get a smaller one if necessary. What size do you recommend. My thought was to have each generator charge the starting batteries and then have the alternator, which is only on the port engine, charge the house batteries.

Your battery usage does not sound very large. For starters you could just go with the group 27. If you haven't purchased the group 27, I would not waste my time or money and get one set of golf cart batteries. Sams Club, Costco and others have gold carts for about $85 each. I would not get a third alternator at this time.

The first boat I had was a 28foot carver. The refer drainged one group 27 over night.

The easiest and cheapest way to go is to do the single start battery for both engines and charged by the port engine. I would get a bigger start battery if using only one. Then have the house charged by the starboard engine.

The con on this is the loads of the alternators are not ballanced. The port will charge the start battery(s) for shorter periods of time. The starboard will be loaded longer depending how much you drain the house batteries.

Originally Posted by Rugger8

Your reply brings back a question that I have been struggling with, should I just go with 1 starting battery for both engines and then combine 3- 100 Ah batteries for the house bank. Still not as large as others, but for my limited overnighting, should do the trick. Or should I stick with 2 starting batteries and 2 batteries for the house bank. BTW, I am installing LED lights as well to reduce usage, so the refrigerator will be the main draw on the boat.

Jeff

Since you aren't in a rush, I would start with just one start and one house. If things don't work out, keep adding until you are happy.

The all around light when on is the battery killer. I would change that to a LED as soon as you can.

Gordon

[Rugger8]

What I currently have and figure I would use are 3 Interstate Group 27 batteries ~100 Ah each that are 2 years old, but working fine. I also have 1 Odyssey group 31 battery that is brand new. The Odyssey has over 1050 CCA and in reality should be able to easily start both engines. Obviously, need to keep the Odyssey battery separate from the other 3 due to dissimilar sizes and battery materials.

As for the generators, these are original, but have been rebuilt. But in any case, they only output a trickle charge, 3-5A. Which is why I am going to add a alternator to the port engine to charge the house bank. You indicated that a 100A alternator would be overkill, what size do you think would be appropriate? 60A?

I do have a light load, but am also putting in LED lights in high usage areas to make it even lighter. I am not going back in the water for 2 months here in NY, but want to get all this right before I go back in.

Thanks,

Jeff

[rustypirate]

One quick question for everyone here...

Is it standard practice to combine the ground buss for the AC and DC systems togeather as in the diagram above?

[knottybuoyz]

Originally Posted by rustypirate

One quick question for everyone here...

Is it standard practice to combine the ground buss for the AC and DC systems togeather as in the diagram above?

As far as I can tell they'll invariably have to be connected at some point so I designed it that way..

[gmau]

Originally Posted by knottybuoyz

As far as I can tell they'll invariably have to be connected at some point so I designed it that way..

Plus 1!

As far as I know!

The bonding system and neutral also come into play.

Its how they are connected that counts.

DC Ground - The return path for the 12VDC system. Can carry lots of amps.

Bonding system-galvanic corrosion-different metal things are tied togeter so a metal (zink) is left to be eaten away. Metals are usually in conductive solution (salt water). Should be very low current.

AC ground-A non current conductor. Used for safety. If current is on this conductor circuit breaker/fuse and GFIs should be tripping.

Neutral-The return path for AC. A current carry path.

The AC ground is also tied to the neutral at it's source.

So at least the DC Ground, AC ground and Bonding system are tied together on the boat. They are tied together so current from one is not counducted thru the other. An example is a l2 VDC light. The return (ground) side can be connected to the bonding system and the light will work. The bad thing is the current used by the light is now flowing thru the bonding system. Galvanic corrosion can be greater because of the increase of current.

This is a complex topic and I hope others will comment.

If not done correctly there can be drastic results for your boat and other boats around you. People in the water next to boats can be electrocuted. You could loose any metal under water.

Gordon

[gmau]

Originally Posted by Rugger8

What I currently have and figure I would use are 3 Interstate Group 27 batteries ~100 Ah each that are 2 years old, but working fine. I also have 1 Odyssey group 31 battery that is brand new. The Odyssey has over 1050 CCA and in reality should be able to easily start both engines. Obviously, need to keep the Odyssey battery separate from the other 3 due to dissimilar sizes and battery materials.

From the above. I would use the Odyssey for starting of both engines. The Group 27 are used for the house.

Lets talk about your generatoers and alternators first before wiring.

Originally Posted by Rugger8

As for the generators, these are original, but have been rebuilt. But in any case, they only output a trickle charge, 3-5A. Which is why I am going to add a alternator to the port engine to charge the house bank. You indicated that a 100A alternator would be overkill, what size do you think would be appropriate? 60A?

If you ended up with a start battery and 4 golf cart batteries as house the 100a alternator would be really good as a charging source.
3-5 amps is very little. First, are they generators or alternators? 3-5 amps is very little. Barely enough to power a bildge pump! If they are that small, have you considered replacing them with alternators? I know you can get alternators in the 60 Amp range at a reasinable cost. Having two for reduncany reasons is better than one. When you get over the 100a range you may have to do special things like dual belts. Another topic is regulators. The 3 stage seem to be the recommended choice these days.

Originally Posted by Rugger8

I do have a light load, but am also putting in LED lights in high usage areas to make it even lighter. I am not going back in the water for 2 months here in NY, but want to get all this right before I go back in.

Thanks,

Jeff

What's you short term and long term 12VDC power needs?

LEDs should take care of lighting.
Refrigerator?
galley and head water?
bildge pumps?
electronics for navigation?
Heat? Fans for air circulation.

What are you short term and long term 120VAC needs?

Charger/Inverter?
lights?
Heat?
microwave?

Gordon