DC Engine Bond point

trickdhat

Member III
Blogs Author
While installing a new battery charger, I noticed our new to us 35-3 does not have a main DC bus. The battery negative, charger negative and panel negative are all brought back to one of the studs for the exhaust elbow. I would like to install a negative bus near the engine with a single connection to the engine. I've heard any solid place on the block without paint will work, but the exhaust elbow doesn't seem like a good spot. The cables look OK, but I'm thinking that is a potential week point given the high heat of the elbow. I'm wondering where everyone else is bonding their DC negative cable on the engine.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
EY brought several big neg. cables to a bolt head on our bell housing. I did remove, clean, and re-torque those a couple of time over 20 years as a precaution.
There is a Grounding point on our new Beta - same idea. This time around I added a DC buss bar in the engine compartment and have one cable over to the engine. Easier to monitor, and that's at least two less cables to be vibrating from the engine movements.

(There is also a DC Neg. buss terminal behind the breaker panel, but sounds like you are referencing the high-current cables in the engine compartment.)
 

Christian Williams

E381 - Los Angeles
Moderator
Blogs Author
When I cleaned up my grounds I installed a negative buss on an engine stringer with a single connection to the ear of the starter motor. At least it's neater, and the multiple grounds on the engine block were in bad shape.

 

trickdhat

Member III
Blogs Author
I should know better by now. I should always search Christian's blog first. Of course there's an answer in there.

I like the idea of a single ground point run to a bus bar, I'm just wondering where that point should be. The starter is really difficult to access without removing the cabinet around the engine. Is this a difficult task? Does it involve removing staples for the quarter birth hull liner. I always come up with these questions while I'm sitting at work instead of being on the boat.

If I can get access, is this the "ear" of the starter?

1581353306090.png
 

trickdhat

Member III
Blogs Author
Loren,

A dedicated grounding point sounds like a great idea. I wonder why more engine manufacturers don't have one. If the boat hadn't had a newer engine installed, I would seriously be looking at (or at least pining after) a new Beta. It seems like they really listen to users and solved a lot of those annoying little issues all boat owner complain about.
 

Christian Williams

E381 - Los Angeles
Moderator
Blogs Author
Trickd,

The "ears" hold the machine screws to hold the starter motor to the engine block. (I had to search for an hour to figure out what"ear" meant back when I was doing this job.

Does the attachment point matter? I don't know -- but somebody here will.
 

Tom Metzger

Sustaining Partner
My take on it is that car makers don't run the battery negative to the starter ear so why should we? That big V8 draws multiples of what our little engines draw when starting. The engine block is an awfully large conductor.
 

trickdhat

Member III
Blogs Author
Tom,

Where not to run it is useful, but that's what got me thinking about the proper point in the first place. If the ear of the starter isn't appropriate, where should it go? Access aside, the starter seems like a great place. It's close to the bell housing which is closer to ground (water) and doesn't rely on the engine block to return the starter load. Not saying it's perfect, just wondering where a better option is.

Nick
 

wynkoop

Member II
I have a fairly good background in electronics and electrics.

The best point to ground on your engine for efficient charging is a bolt for the generator. The generator is what is making the energy that will charge the battery. You want the least resistance possible to have the most effective transfer of energy with the least losses and least heat generated. High currents, through resistance cause heat. So for most efficient charging you want a wire directly from your negative battery bank terminal to your generator. The iron of the engine with the bolted connections are higher resistance than the copper wire back to the battery bank.

To lower losses on starting you want to run another heavy ground from your negative battery terminals to a bolt that holds the starter.

I am not a fan of the idea of a single ground from the battery negative bus to the engine. In my diesel conversion I have one wire from the DC bus for the boat's 12 volt system that connects to the same point on the generator as the battery negative wire. This gives the least resistance for loads on the boat's DC bus. I have a second wire from the battery negative to the starter.

Yes you can run the battery negative to a heavy bus where then run a single wire from there to the engine and use that point as the connection of the boat's negative bus, but it will be less efficient.

A positive effect of having a second wire from the battery negative to the engine is you have 1/2 the resistance.

A second good point is you have an automatic fail safe for the negative path should one cable fail.
 

debonAir

Member III
+1 on the second wire to battery negative

+1 on being leery of lots of little ground connections to the manifold and wanting to add a ground bus bar.

One thing to keep in mind is if you might upgrade to a high output alternator in the future. The Balmar I just installed has an IG terminal, i.e. "Insulated Ground" which means the alternator case is NOT the ground (but probably is connected?), and the alternator is also completely painted white. I am adding a ground from the IG post to the main engine ground which is the port bolt on the front-center engine mount bracket on mine. You do want a good ground on the block and a good ground on the alternator.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Not mentioned so far is the battery connection. I would advise *not* leading a flock of current-carrying cables to a traffic jam under the negative post nut and washer on your battery, either.
Other than the main cables, I have only the small Blue Seas fused terminal block there for sensing wires, at the positive terminal.
(I have seen a lot of pix over the years of battery banks with a mixture of wires leading to both posts. Yikes.)
 
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trickdhat

Member III
Blogs Author
I really like the idea of a cable to the starter and a cable to the alternator. I never thought of it because my background is in telecommunications where multiple ground connections is not desirable due to ground loop induced noise (although I'm not sure how important it is now with digital radios replacing most analog microwave equipment).

Although it isn't a Balmar 100+ amp alternator, the engine does have a slightly upgraded 80 amp alternator from Yanmar. I'll have to take a look to see if there is a good ground point. I'm leaning toward a negative bus bar in the battery compartment connected with a large cable to a ground bus bar near the engine. From there I'll take a large cable to the alternator and a large cable to the starter ear. I still need to look at the system to size the cable, but this gets my head spinning in the right direction.

Simply replacing the battery charger is quickly turning into rewiring my battery compartment and DC ground system, replacing the exhaust elbow and removing miles of old unused cable (the old engine wire harness was left in place just clipped at both ends). Funny how that happens so quickly.

Thanks for the great advise and discussion.
 

Tom Metzger

Sustaining Partner
Where not to run it is useful, but that's what got me thinking about the proper point in the first place. If the ear of the starter isn't appropriate, where should it go? Access aside, the starter seems like a great place. It's close to the bell housing which is closer to ground (water) and doesn't rely on the engine block to return the starter load. Not saying it's perfect, just wondering where a better option is.
From ABYC electrical standard:

11.5.4.7.2
The negative terminal of the battery, and the negative side of the DC system, shall be connected to the engine negative terminal or its bus. On boats with outboard motors, the load return lines shall be connected to the battery negative terminal or its bus, unless specific provision is made by the outboard motor manufacturer for connection to the engine negative terminal.

Excerpted from Figure 18

DC negative diag E-11.jpg


On Universal engines there is a convenient(?) hole in the rear engine mounts. A bolt, nut and washers eliminates removing engine component mounting bolts. I have a copper bus bar mounted with the two battery bank connections with that bolt and other ground wires connected to the bar.

Large alternators should be connected to this ground point to avoid the possible resistance caused by the multiple painted mounting brackets usually involved in installing alternators, not because the engine block has high resistance. It is actually extremely low.

Most Balmar alternators are not internally grounded. It is done that way for applications where the engine is not grounded, per their manual.

Multiple connections to negative battery posts defeats a battery monitor.
 

Kenneth K

Sustaining Member
Blogs Author
Wanted to post this yesterday but never got around to it. Tom mentioned two posts above about rear engine-mount holes for the ground point. There are also unused threaded holes in the block (possibly for other types of engine mounts) in this same vicinity. That is what I used for my engine ground point. Just scrape off any excess paint and clean out any grease/grime with q-tips and mineral spirits so you get a good connection. This way the DC ground is always connected no matter what state of disassembly the rest of the engine is in.

Gnd Bus.jpg
 
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wynkoop

Member II
Ken -

You would have lower resistance and less voltage drop if those multiple large negative cables were connected to the engine and only the smaller negative wires were hanging off of that bus bar. Since the three wires look roughly the same size and the same size as the wire to the engine block you would have about 1/3 the resistance that you have now.

Getting the least resistance may not matter in every case, but I try for that in all my installations no matter the vessel.
 

Kenneth K

Sustaining Member
Blogs Author
Probably so. But the highest drawing circuit on my boat is the 20 A glow plug circuit. Does a lower resistance in the battery grounds really make any difference then (1/3 of zero is still zero, right?). Or is there another reason to have each battery bank (and perhaps the DC panel itself) independently grounded to the block? Charging perhaps? I still have the original 50A alternator and the original Newmar 25A Battery Charger.
 
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wynkoop

Member II
trickdhat -

With power circuits the multiple grounds is actually the better practice and having multiple ground points will not have any negative effect on your radios.

Yes audio equipment like mixer boards, recording decks and the like prefer a single common ground point, but when it comes to power more is better. If you have audio equipment in your boat just make sure there is only one ground lead from the audio equipment to boat ground and you will be fine.

The ground system on Silver Maiden looks a bit like this:

Lower portion of back stay below my insulator for the SSB is tied by a heavy wire to the engine.

The engine is tied in two places as described back to the battery bank.

The engine is tied to the raw water intake and the sink through hulls.

Heavy wire from the connection point of the battery cable at the alternator to the negative DC bus that everything else ties into.

This gives me both an effective DC ground with lowest possible IR (current through resistance) losses and a very effective RF (radio frequency) ground for my SSB. It also keeps the SSB from getting into any of the other electronics like broadcast radio, depth finder, LORAN (now retired), or GPS.
 

wynkoop

Member II
Ken -

Your resistance is not zero, just your instrument is not sensitive enough to measure low enough. From a practical point of view there is only a small difference, but if you have a low battery and need to get started, which is the time of your greatest draw, 20A for glow plug, plus starter draw then that lower resistance might make a difference.

For my own part I try to plan for the worst. In addition to noodling about in small boats I am a professional mariner who has gone the world over on the big iron boats and some of the things I have seen and had to deal with as a ships officer inform my operation of my little boat.
 
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