Requirment to Connect To Common DC Ground

[Edward1960]

First post after reading this forum for a long time. Can anyone with experience installing DC equipment help with this question? A while back, I had a "professional" install a bow thruster on my sailboat (38' custom boat... centre cockpit...86 vintage) and he did not connect the DC negative to the boat DC ground system. My question is, "Is this DC negative connection to the boat DC ground system truly required?". The boat and bow thruster has operated seemingly with no problem, with no connection to the boat common DC ground, but I am in progress putting right several things this professional had not properly installed and am left wondering if I need to do the work to make this connection. Anybody? Thanks.

[billknny]

When you say the "DC ground system" are you actually talking about the bonding circuit?

This whole area is tangled with imprecise language.

Where does the negative return wire from the bow thruster connect? Obviously electrons are flowing back to the battery negative SOMEHOW.

[Edward1960]

Hi and thank you for your reply. I tried to keep it brief, but went overboard. I was not referring to the bonding circuit.


I had a bow thruster and windlass installed by a well known local boat yard in my area. They did a good job on the physical install. Both devices look good and function properly. Most of the electrical install was also adequate too (correct circuit protection devices are present, isolating switch is present), but the new batteries are undersized and the power cables for the thruster are too small (1/0 installed where 2/0) as specified by manufacturer.


My question is about the joining of this new DC "sub" system to the common negative bus and eventually to ground via the engine/prop shaft. The preexisting DC system's negative side is connected to a common DC grounding bus and then grounded to the lake (sea) by the engine/prop shaft. The new DC subsystem for the windlass and thruster was not connected on the negative side to this common DC grounding bus. It's electrically floating on it's own. It operates correctly, thrusting the boat port and starboard, and the windlass brings in and lets out the anchor as it should, but the negative leads connect only to the battery and not to any ground (the sea via the engine/prop shaft or any other method).


I am wondering whether this negative subsystem needs to be grounded (like the rest of the boat's DC system). I think the answer is yes, but I'm not sure. Does this clarify?

[smac999]

So it has its own bow battery? How is it charged?

Yes the ground of the bow battery should be connected to the ground of the main batteries.

That would Also allow you to run say an echo charger to charge it from the main batts (And therefor the alternator )

[Fair_Skies]

I don't know but am very interested in the answer... I hope someone has the answer. I have shipyard electrician install all new chargers and with my new GEL batteries. I found a year later the charges set on lead acid not GEL charging profile..... always check the yards work.... it your money and boat.

[GordMay]

Greetings and welcome aboard the CF, Edward.

[slug]

Originally Posted by Edward1960

First post after reading this forum for a long time. Can anyone with experience installing DC equipment help with this question? A while back, I had a "professional" install a bow thruster on my sailboat (38' custom boat... centre cockpit...86 vintage) and he did not connect the DC negative to the boat DC ground system. My question is, "Is this DC negative connection to the boat DC ground system truly required?". The boat and bow thruster has operated seemingly with no problem, with no connection to the boat common DC ground, but I am in progress putting right several things this professional had not properly installed and am left wondering if I need to do the work to make this connection. Anybody? Thanks.

The ground plane . The copper wire connecting all thru hulls and metal components together , is not part of your electric system

Marine electrics are a two pole system

Two wires ...Separate + and - conductors . To each user

Auto electrics are a one pole system , One wire system ...the chassis is -
And all control wires are +

[Edward1960]

smac999, thank you. Yes, separate battery was installed to power the thruster and windlass. Currently, they have only an AC charger (another thing done wrong or not completed as there is no way to charge the thruster battery while underway unless I run the generator. I will look into the echo charger you mentioned.

[Cadence]

JMHO! I would leave it isolated.

[markcouz]

Is the house bank and the bow bank the same voltage? That info would be required before opinions of any value can be offered of how best to move forward (which may be many and varied!)

[Shrew]

Originally Posted by Edward1960

A while back, I had a "professional" install a bow thruster on my sailboat (38' custom boat... centre cockpit...86 vintage) and he did not connect the DC negative to the boat DC ground system.

You need a round trip to complete a DC circuit (technically ANY circuit). If the DC motor on the bow thruster didn't have a return path to the battery (open circuit), it would not work.

[markcouz]

The OP did say that he has a separate battery bank with an AC charger in the bow so...nope.

It could be used like that but PITA to have to use A.C. to charge, I would suggest DC to DC charger in the bow which would allow thin (6mm) pos+neg connection back to the main bank.

The actual charger used would depend on the voltages involved, hence my previous post.

[FPNC]

There is scant information to provide a concrete answer.

Everything is working correctly right now. That's good and if you lost +12v power to the bow thruster from your dedicated DC bank it would simply fail to operate.

If you lost the -12v ground to your dedicated DC bank, the thruster would not operate as it should however the +12v power will try to seek a path back to ground. If there is no path to ground to be had, all is good. You have a completely isolated system.

If that power finds a path available that is not designed to take the amperage of the system, that's when trouble happens. This path could be hardware, electronic controls or maybe the AC battery charging system. Without looking at the wiring or schematic its hard to tell.

Example: I was called aboard a boat with starting issues. Found this twin engine vessel did not have the two battery bank grounds connected together. When the switches were set a certain way, the only path to ground one of the engines would have was through the steel Morse control cables. This caused intermittent starting issues and hot control cables.

Consult a marine electrician.

[Nord Sal]

I'm not sure if it's the same charger for the windlass battery as the other bank(s), but if so, it could be sharing the same ground through the charger.

[copaco]

When you say common bus bar ground, can this be near the negatif battery post or near the ground on the motor?