DC wiring on my GB42

[Nick F]

I recently bought this 1974 GB42 and am tracing out the DC wiring. The boat has what I would call a "cross-connected" charging system which I am thinking of "un-crossing". I would like to know if anyone has a good reason for keeping this cross-connected arrangement.

I attach a simplified diagram of the present arrangement.

Comments welcome!

Nick

 

[Comodave]

It looks pretty reasonable to me. The large alternator charges the house bank. The smaller alternator charges the start bank. I might move both starters to the start bank and have an emergency connection from the house bank if the start bank goes dead.

 

[Choices]

It's my understanding that two standard control alt will try to cancel one out.

By separating the loads each alt works equally, maybe.

You should have the ability to connect the batteries.

Maybe an undervoltage relay, or combiner switch.

 

[C lectric]

It's my understanding that two standard control alt will try to cancel one out.

That will only be the case when the batteries are closely approaching the full charge point. Up to that point both alternators will produce whatever current they can produce.

What you see when one alter. shuts down is the result of one regulator being a bit more sensitive , a slightly lower voltage setting, for shutdown or backing off leaving the other to carry on untill its regulator is happy.

But untill that point is reached they will both produce current speeding the Battery recharge.

 

[C lectric]

I was going to suggest last night that there is nothing wrong with the setup you currently have except for sense of order, which is fine.
Just be sure to label the leads appropriately so there is no ambiguity about which is which.

Personally I would have swapped alternators so the large one is nearest the house load which almost always needs the most current. THen the smaller alt. would be mounted on the engine nearest the starting batteries.

Unless of course there is a physical problem to do that.

I am going to guess the two battery sets are where they are due to space constraints.

As long as it is clear which alt. charges which battery either connection pattern will work fine as long as the wiring is up to snuff.

 

[Nick F]

C lectic - thanks for your post. I have yet to receive a convincing argument in favour of the cross-connection, so I do not feel bound to maintain it.

The simplified sketch I posted does not accurately reflect the physical layout. At present the house batteries are split port and starboard, and the rest is not very "cable run" efficient. In fact there are 10 cables of 2/0 and 4/0 running from port to starboard (photo).

I am in the planning stage of cleaning up the DC system and propose the attached schematic. I expect to reduce the 10 athwartship cable runs to two.

Comments welcome!

P.S. I liked Commodave´s suggestion of starting both engines from the start battery, but I ended up preferring the attached arrangement because it makes each engine have starter/alternator/Instruments all from its "own" battery. This also reduces cable runs.

 

[rgano]

Why the cut-out switch at the start battery?

 

[DennisB1]

I have a similar set up on my GB 49. Difference is that start battery starts both engines. The house bank then does not see the electrical tansients when cranking the engine/ On line electronics are not subjected to the starter transients minimizing potential damage. When I couple the house bank to the starter bank you see noticable diming of lights during starter operation so I avoid using the house bank except in an emergency for starting.
In the schematic, the 135 amp alternator would couple directly to the house bank. The engine starter cable would couple directly to the starter bank. My two cents worth

 

[ranger58sb]

I recently bought this 1974 GB42 and am tracing out the DC wiring. The boat has what I would call a "cross-connected" charging system which I am thinking of "un-crossing". I would like to know if anyone has a good reason for keeping this cross-connected arrangement.

Are they "crossed" (in your initial simple diagram) because of physical location, batteries relative to engines?

If so, and if that's not what you want... maybe just swap alternators?

And not specifically related to your question, but maybe then add a parallel switch at the helm so you can combine battery banks in a pinch?

-Chris

 

[C lectric]

If it is a mess of cables going everywhich way because the batteries are not all located together then I would change it. But if possible I would also then group the house batteries together.
The shorter any paralleling jumpers are the better.

As far as the convincing arguement about a cross connection then you won't get one, at least not from me.

 

[Nick F]

Why the cut-out switch at the start battery?

Should not every battery have a disconnect switch?

 

[Shrew]

C lectic - thanks for your post. I have yet to receive a convincing argument in favour of the cross-connection, so I do not feel bound to maintain it.

I honestly feel like you received a decent argument, it may simply have been very subtle. This allows you to charge the house bank and the starting battery while underway. Otherwise you'll rely on far more on the generator and battery charger while cruising.

With the heat exchanger heating the water heater and an alternator pushing amps to the house battery it's nice when you stop and there is no need to run the generator that night, and likely even the next morning, if you plan on travelling again that day.

It's more common now to use an Automatic Charging Relay (ACR). An ACR makes it feasible to charge the house and start banks with a single engine. However this is still a perfectly fine set-up for a twin engine vessel.

I'd turn it the other way.

1) By deleting this set-up..what do you gain??

2) What problem are you solving by deleting this set-up?

 

[Nick F]

1) By deleting this set-up..what do you gain??

2) What problem are you solving by deleting this set-up?

Answer 1 I would have each engine A starting from battery A and charging battery A, with instruments fed from battery A. This seems more logical to me. It also reduces cable runs.

Answer 2 Too many cable runs. Complicated, illogical system. (I like simple)

 

[Nick F]

I have a similar set up on my GB 49. Difference is that start battery starts both engines. The house bank then does not see the electrical transients when cranking the engine/ On line electronics are not subjected to the starter transients minimizing potential damage.

Thanks Dennis - this is a really good reason to have the start battery do the cranking for both engines. At present the plotter always reboots when I crank using the house battery.

Now I have to rethink which battery to use for the instruments ("ignition"). I think I will run all the instruments from the house battery. (No risk of an accidental long term drain on the start battery)

Regards,
Nick

 

[Nick F]

Thanks for your comments. Revised proposed schematic attached.

 

[twistedtree]

Thanks for your comments. Revised proposed schematic attached.

I think that's much better. The point about starting both engines from the start bank is an important one, otherwise every time you start an engine you are likely to have some gadget somewhere rebooting itself.

 

[Scottoz]

You will have to run the ground from the start battery to both engines as well as the house ground to the port engine to have the alternator charge the house.

 

[Comodave]

You should add some type of over current protection on the top leg coming off the house bank that serves the house panel, etc.

 

[Nick F]

You should add some type of over current protection on the top leg coming off the house bank that serves the house panel, etc.

Commodave - thanks for your feedback - I wondered about this. I decided to have the very short run to the positive buss bar unprotected and then the 3 feeds off the buss bar protected close to the buss bar. If I put a fuse between the battery and the buss bar it would probably be physically close to the buss bar and hence would only protect an extremely short amount of cabling.

Right now, the feed all the way to the house panel is totally unprotected, so anything is an improvement.

Regards,
Nick

 

[Comodave]

What is the distance? I think the recommendation is 7” per ABYC.

 

[Bmarler]

What is the distance? I think the recommendation is 7” per ABYC.

Correct. There needs to be overcurrent protection at the battery. And if the house bank is over (I can’t remember the amp hour size) the fuse type can change too. ANL for lower amp hour banks, class t for bigger. It’s a good idea to get the abyc document and try to follow those rules as close as possible.

 

[Nick F]

Thanks Commodave and Bmarler. I have 2008 ABYC electrical guidelines. Do you know if these are still current?

 

[Bmarler]

Thanks Commodave and Bmarler. I have 2008 ABYC electrical guidelines. Do you know if these are still current?

i believe so. that's the copy i use.

 

[Comodave]

There may have some changes but they are probably still fine.

 

[Nick F]

I have now read the ABYC standard and adjusted the schematic as attached.

The bold lines indicate the unfused starter wiring.

To comply with ABYC, the fuses would have to be within 7 inches of the battery terminal, or the cable must be inside conduit. I will have to investigate the practicality of using conduit in order to place the fuses somewhere "tidier".

 

[Comodave]

Looks good to me.

 

[koliver]

Nick
You are getting very close to what I have. The major difference is that my Port Starter has a relatively short run from my Starboard starter, which has the long run from the battery. Your diagram shows both engines coming directly from the battery.

Having nothing else on the start battery seems like a good idea. I have recently disconnected the cross connection between House and start, and I wonder whether reconnecting will ever seem like a good idea.

 

[SteveK]

I like proposal #3.
A thought for you. I have my anchor winch and davit from the start battery. My reason is not to draw off house when I already have the engine that charges the start battery running. I also start the engine first that charges the start battery.

 

[Helmsman]

I have now read the ABYC standard and adjusted the schematic as attached.

The bold lines indicate the unfused starter wiring.

To comply with ABYC, the fuses would have to be within 7 inches of the battery terminal, or the cable must be inside conduit. I will have to investigate the practicality of using conduit in order to place the fuses somewhere "tidier".

In the latest drawing you have 5 wires attached to the positive side of the house battery. ABYC guidelines state a maximum of four. I would suggest a buss bar that the battery feeds, which then feeds all other circuits. The same should be considered with the negative feed.

 

[Bmarler]

In the latest drawing you have 5 wires attached to the positive side of the house battery. ABYC guidelines state a maximum of four. I would suggest a buss bar that the battery feeds, which then feeds all other circuits. The same should be considered with the negative feed.

Totally agree with this. I had an insurance company make me do a wiring change to remove all but one connection to the batteries. This was quite some time ago, and I could probably show them the abyc standard and get around it now, but I like the uncluttered battery connection and stuck with that mentality. I use nice big buss bars for all the connections. It’s easier to get close to the 7 inch rule, and easier to route all the cables and wires to a buss instead of a single post.