BlueSea Monitor and Bus Layout

[Neo]

I need help cleaning up the rats nest in my battery compartment.

Is there anything obviously wrong with the schematic below?

If I switch to start battery (#2) and start the engine will the battery monitor shunt detect it as an amp draw? Whoever installed the BlueSea monitor knew less than I do, so it has to be rewired.

Because the fuse box is supplied via the positive cable leading to the starter, if the main battery switch is in the off position the fuse box will be dead and so will the bilge pump and gas detector. I could draw power for the fuse box from the positive cable leading to battery #1 instead, thereby avoiding an accidental shut off of the bilge pump and gas detector. Would that be OK or am I missing something?

Next year I hope to add a second house battery and convert the start battery to a reserve battery, a' la Main Sail.

[Ex-Calif]

If you already have all this gear that's cool but I would not have selected the 7748 with negative bus. I just don't like heavy gauge positive and negative wires going into the same box - chafe concern. 7727 has a couple fewer circuits and no negative bus. Even if I had the 7748 (on hand) I would run all grounds to one separate bus.

Just eyeballing the circuit.

- The shunt should rightfully be attached right at the battery. House if that's what you want to monitor. It won't measure the start battery. This is not a big deal for most people.
- Positive cables of both batteries should be fused within 7 inches of the battery. I'd like to see them fused before the switch - the first piece of equipment that could potentially fail.
- I presume the small unidentified blue box with 3 cables is a fuse block. Fuse at the batteries and eliminate this. Gang the 2 reds off the switch C post - one to starter and one to DC+ bus
- Consider what "always" on circuits you have. If only bilge and detector gang this to the start batt positive post. I would use start batt because it is less likely to drain than an inadvertent drain of the house batt. If you care about these amps being measured however you must gang them to the house batt.

Where is the alternator sense wire attached? You want to make sure that you can't inadvertently shut of alt sense with engine running.


-

[Neo]

I haven't ordered anything yet, just planning and saving.

he 7727 is twice the cost of the 7748, almost $250 (I'm already up to $400 for the fuse box cables and buses), but I like your idea of using the 7748 for the positives and adding a neg bus for the grounds.

That unlabeled bos isn't a fuse, it's just a post I was going to order to gang the cables. If I gang the start and fuse box cables at the battery switch, it will free up room for the neg bus. Thanks.

Add now you want me to spend another $100 on fuses, LOL, of course you're right, but I have been rationalizing that the boat has lasted this long without them. Of course, now that I am messing with the system the danger has increased exponentially. Check, fuses.

I had to google, sense wire. I'll try to find that but I don't think it's in the battery compartment.

At present, there are 9 wires connected to the battery terminals. I'm hoping to reduce that to 2 and consolidate all in line fuses to the safety hub. If one were to blow now, I would have a hell of a time finding it.

Thanks for the help.

[Yeti]

For the battery fusing the Ex-Calif is talking about blue sea 5191 is the way to go.

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

Its under $20 at most places and a 250 amp fuse is around $20 as well.


Here is the relevant Maine Sail info on these.
http://www.pbase.com/mainecruising/battery_fusing

[Ex-Calif]

Originally Posted by Neo

I haven't ordered anything yet, just planning and saving.

he 7727 is twice the cost of the 7748, almost $250 (I'm already up to $400 for the fuse box cables and buses), but I like your idea of using the 7748 for the positives and adding a neg bus for the grounds.

That unlabeled bos isn't a fuse, it's just a post I was going to order to gang the cables. If I gang the start and fuse box cables at the battery switch, it will free up room for the neg bus. Thanks.

Add now you want me to spend another $100 on fuses, LOL, of course you're right, but I have been rationalizing that the boat has lasted this long without them. Of course, now that I am messing with the system the danger has increased exponentially. Check, fuses.

I had to google, sense wire. I'll try to find that but I don't think it's in the battery compartment.

At present, there are 9 wires connected to the battery terminals. I'm hoping to reduce that to 2 and consolidate all in line fuses to the safety hub. If one were to blow now, I would have a hell of a time finding it.

Thanks for the help.

The attached may be useful to you. It is the equipment list for my electrical rewiring.

I have not bought everything yet band am wrestling with some compromises - While I would love to have the Blue Sea fuses the BB Link 2 pack comes with 2 fuse holders and the fuses for $13.

You can also have a look at my choices for DC+ and DC- buses and fuse blocks.

I am not recommending a course of action for you as that is a personal matter but where there are alternatives in my thinking I have those listed and highlighted in yellow.

Oh, this probably makes better sense in context of the schematic so I am including that as well - this is rev 1 and there have been a few changes.
I am not recommending

[Neo]

Very helpful, thanks.

I am about 6 months behind you but will probably be doing the job piece meal. I started with plans to rewire the battery monitor (the pos and neg voltage drop wires on the shunt are reversed and there are loads on both sides of the shunt). This requires a rewiring of the battery compartment, and you know how one wire leads to another, I am now looking at the whole mess.

I just started work on a schematic of the existing. I'm using a free program, yED Graph Editor. I had to cobble together the icons for fuses and switches and such from the internet, but it's not bad and it's free. Your schematic helps me to think about how to organize it. Foir sure, I need to use smaller icons and a larger font so that it fits on one screen (or piece of paper) and is still legible.

[Neo]

If you want a little laugh, take a look at this. It might look pretty but it's impossible to read, and I'm not even half way done.

[skipmac]

If you haven't yet looked at the previous discussions on this it might save you a lot of time and questions. 12V system layout, fusing, switches, etc has been very thoroughly figured out by experts in the field. Check this thread.

http://www.cruisersforum.com/forums/...ml#post1576430

There are links to diagrams and complete analyses of how and for the curious, why everything is done that way.

Neo, I don't see a need for the 7748 at all. Fuse the cables with terminal fuses as they come off the battery. Set up + and - bus bars for multiple connections.

Also, as you will see on the circuits already designed, to be certain that you or a crew member doesn't make a mistake and drain the start battery, that should be on a separate circuit and switch. Everyone says they won't forget but everyone (including me) has forgotten and drained the start battery at least once. You charge the start battery with an voltage controlled relay that links in the start battery anytime you are charging the house battery. Then automatically disconnects the start battery when you aren't.

[exMaggieDrum]

I am a big fan of the automotive blade style fuses for things like bilge pumps that you want on all the time. I put the input to my solar panels to a 6 gang blade fuse block and sized each to the particular circuit. The feed wire from the battery bank has to be sized right and it has to be fused within 7 inches (or so) from the batteries. To turn off all of these circuits I would pull the big fuse. If just one, I would pull it (like the solar panel charge). IMHO you should never run anything off of a start battery except the engine starter and put a parallel switch in so you can either use the start battery to power your VHF or whatever critical circuit you need. Or, you can use the main bank to start the engine if the start battery is dead.

I am rewiring my newly purchased old boat and looked at the fuse blocks you are considering. They are pretty slick and will do what you want to do but they are also pretty expensive. I am going with a new age terminal fuse links on the battery terminals though. They are cheap and handy. Blue Seas sells them - I don't remember the model numbers but they are high amp. Re the battery monitor - wire it up just like the install manual says and you will be OK. And you should never have more than 3-4 wires coming off a battery post or any other big post that you are hanging things off of. Use a big buss (like you show) so you have multiple big posts. Just fuse everything - everything!

[Stu Jackson]

Originally Posted by Ex-Calif

Where is the alternator sense wire attached? You want to make sure that you can't inadvertently shut of alt sense with engine running.


-

Dan, that shouldn't hurt anything, should it? If so, how? All it will do is report incorrect voltage to the regulator. It's the alternator output that should never be interrupted.

[Ex-Calif]

Originally Posted by Stu Jackson

Dan, that shouldn't hurt anything, should it? If so, how? All it will do is report incorrect voltage to the regulator. It's the alternator output that should never be interrupted.

There are several types of alternators. But there are 3 main feeds.

Alternator Output - It is OK to interrupt alternator output. It is like having a big potential (like a battery) with no path. It doesn't' go anywhere. But connection and disconnection can cause spiking which can be an issue to electronics and for big alternators perhaps the alternator/regulator itself

Field Excitation - This is the supply that excites the field coil, creates the magnetism to create the electricity. This is the circuit I would interrupt if I wanted to take an alternator "off-line" - no field excitation = no electricity.

Alternator Sense - This is the circuit that "tells" the regulator the battery voltage. The lower the voltage the higher the voltage the regulator will command the alternator to produce. An "open" sense line will be read as "zero" voltage batteries and the alternator will be driven to max output and this can overload (fail) the rectifying diodes in the alternator.

Most "standard" dual bank setups apply the sense wire downstream of the "C" post on the 3-way switch. In this case as long as the 3-way switch is not "off" sense is available and the alternator will charge bank 1-2 or both depending on switch position. The farther the sense line is wired in from the batteries the greater the error that can be introduced in the sense wire due to voltage drop and resistance in the wiring.

As SkipMac says the first "improvement" to the supply system is to wire the sense and output on the unswitched side of the 3-way switch as close to the house battery as possible. Then the sense and supply can never be disconnected.

Then a paralleling relay (charge relay, DVSR etc) is set up between house and start batteries. When charging voltage is available the batteries are automatically linked and the start batt is charged.

[exMaggieDrum]

Dan - good post. For years I have only heard & read that dropping the output connection from the alternator to the batteries without stopping it by dropping the field first will cause the voltage to spike immediately and fry the diodes.

I have to admit I have not tried it too see though.

[transmitterdan]

Originally Posted by Ex-Calif

There are several types of alternators. But there are 3 main feeds.

Alternator Output - It is OK to interrupt alternator output. It is like having a big potential (like a battery) with no path. It doesn't' go anywhere. But connection and disconnection can cause spiking which can be an issue to electronics and for big alternators perhaps the alternator/regulator itself

Alternators are not voltage sources. They are current sources and nearly all alternators will be damaged by disconnecting the output while it is running. The loss of the battery means current has no where to go which forces the output voltage beyond the diode breakdown voltage thus killing the alternator. Removing field excitation before disconnecting the output may prevent damage. But it's best to just leave the alternator output connected to the battery all the time.

[Ex-Calif]

Originally Posted by transmitterdan

Alternators are not voltage sources. They are current sources and nearly all alternators will be damaged by disconnecting the output while it is running. The loss of the battery means current has no where to go which forces the output voltage beyond the diode breakdown voltage thus killing the alternator. Removing field excitation before disconnecting the output may prevent damage. But it's best to just leave the alternator output connected to the battery all the time.

Thanks for the clarification. For the record I would never personally switch the alternator output. Too many downsides.

When you get to complicated externally regulated, large frame alternators and someone feels a need to take the alternator off line their are strategies for that.

[transmitterdan]

To take an alternator off line just disconnect the field wire. That will shut it down.