Alternator - Why and when case ground or isolated ground versions?

[Dirk01]

Hi folks,

can someone explain to me which alternator version (case ground or isolated ground) is the best to use on boats and why?
I'm also reffering to the stray current trouble the Wynns have with her HH44.

Cheers
Dirk

[noelex 77]

Isolated ground.

With an isolated ground alternator, the negative pole is not connected to the engine and therefore to seawater. However, this is of minimal value in preventing stray current corrosion if the engine is not isolated. You can easily ground an isolated alternator, but converting a case ground alternator to an isolated design is often difficult to do in a long-term reliable way.

[Pandor]

What modern boat engines are not grounded? I’d be surprised if any are isolated.

[noelex 77]

Originally Posted by Pandor

What modern boat engines are not grounded? I’d be surprised if any are isolated.

The vast majority of aluminum boats are designed to have the engine isolated (disconnected from ground) when running to avoid stray current problems. This is not difficult to achieve with traditional diesel engines.

Regrettably, boats with carbon hulls appear to overlook these and other crucial steps, possibly due to the widespread adoption of conventions that are suitable for non-conductive (fiberglass) hulls. This oversight is unfortunate. The principles for avoiding stray current corrosion problems with electrically conductive hulls are well-established.

For instance, HH’s recent announcement regarding the installation of a stray current meter to measure and alert owners of such issues is commendable. However, it is perplexing why these measures were not already standard on these carbon hulls. These meters are standard on almost all aluminum hulled yachts and the technology is not expensive.

There are additional, more extensive, and costly issues that need to be addressed, such as the adoption by HH of single-pole circuit breakers that do not isolate the negative side. This will significantly contribute to the risk of stray current problems (if my understanding of their electrical system is accurate from the brief details provided).

I am confident that HH will address these concerns. Their vessels appear to be exceptional in many ways.

[FPNC]

Originally Posted by Pandor

What modern boat engines are not grounded? I’d be surprised if any are isolated.

Beta Marine offers insulated ground engines as an option. They always have.

[SailingHarmonie]

Isolated ground engines should be standard in the marine world. Only the cost of converting engines designed for land vehicles prevents this.

[Dirk01]

Okay, let me put the infos together and please correct me if I'm wrong.

Isolated engines makes sense in a boat because it lives in a conductive environment. This isolation includes everything that "goes out" or "comes in". Including the heat exchanger and the prop system as well as every electric connection to the outside (i.e. engine controls). This also includes the NMEA-network (hence the data has to be opto-coupled (does such a thing exists?) or send over the air. In my mind isolated means isolated. Totally.

If it is isolated as described, an isolated alternator makes not really sense. Especially if the energy transfer to the outside (i.e. house bank) is also done by isolated DC2DC.

Am I correct?

[Bowdrie]

Originally Posted by noelex 77

The vast majority of aluminum boats are designed to have the engine isolated (disconnected from ground) when running to avoid stray current problems. This is not difficult to achieve with traditional diesel engines.

True enough, it just takes a little more expense and some forethought.
Even though my boat has a non-conductive hull the engine is 100% isolated from anything/everything electrical that has anything to do with the "ships service" electrical system or the water.
Simply changing from a case ground to an isolated ground on the alternator just removes the engine block/bracketry/bolts from being used as the alternators return path, (although that may decrease voltage drop a half a tenth>one tenth volt, situations vary).
The first third of the equation is using two alternators and disconnecting the engine from the water with a "Drivesaver", as well as any connections to a bonding system or any metallic objects in the boat.
The second third is two completely 100% isolated battery systems, one for starting the engine only, one for the house only.
The stock alternator only charges its starting batts, the other alternator, (isolated ground or off engine mounted,) only charges the house batts.
Zero/nada/none/no connections between them, no excuses no exceptions.
The engine and its gauges live in their own little world, untouched by the outside world of miles of wires strung thru the boat or any bonding.
The last third is two separate battery chargers for shore power usage, each dedicated to its own bank, each adjusted to meet the regimen of the bank it feeds.

[noelex 77]

In many marine engines, the engine block serves as the negative conductor usually electrically connected to seawater. This configuration constitutes an unisolated engine.

In contrast, an isolated engine operates differently. For instance, temperature and oil sensors necessitate two wires (positive and negative) instead of a single positive wire with the negative supply originating from the engine block.

An isolated engine is not possible without an isolated alternator.

It is noteworthy that most isolated marine engines lack an isolated start motor. Consequently, during the initial seconds of startup the engine is briefly not isolated.

[Bowdrie]

One can also use mechanical gauges for oil/temp/tach.
And if wanting to push pedantry to the limits, a manually pumped-up hydraulic or compressed air starter, they even made wind-up spring starters.

[SailingHarmonie]

Originally Posted by Dirk01

Okay, let me put the infos together and please correct me if I'm wrong.

Isolated engines makes sense in a boat because it lives in a conductive environment. This isolation includes everything that "goes out" or "comes in". Including the heat exchanger and the prop system as well as every electric connection to the outside (i.e. engine controls). This also includes the NMEA-network (hence the data has to be opto-coupled (does such a thing exists?) or send over the air. In my mind isolated means isolated. Totally.

If it is isolated as described, an isolated alternator makes not really sense. Especially if the energy transfer to the outside (i.e. house bank) is also done by isolated DC2DC.

Am I correct?

No.

An unisolated alternator uses the engine block as its path back to battery negative.

An isolated alternator has a separate connection to battery negative and there is no electrical connection to the engine block.

An isolated engine has no connection between the block and battery negative.

An unisolated alternator installed on an isolated engine would have no connection to the battery negative, and not function.

SOME unisolated alternators do have a place you can connect a battery negative cable to. If you used one of those on an isolated engine, you would destroy the engine’s isolation.

[noelex 77]

Originally Posted by Bowdrie

One can also use mechanical gauges for oil/temp/tach.
And if wanting to push pedantry to the limits, a manually pumped-up hydraulic or compressed air starter, they even made wind-up spring starters.

It is possible to completely isolate the engine even during the few seconds of start-up. Isolated electric starting motors are available for some engines. However, the few seconds of start-up have no risk of causing stray current corrosion to any practical degree, so using an easier-to-replace standard starter is the more popular pragmatic solution.

[Dirk01]

Okay, then let me sum it up again and give it a fine tuning.

Following Bowdrie the engine should live in their own isolated world. Including both alternators and any kind of sensors, switches, gauges, etc. etc. etc..
Makes totally sense to me! @ SailingHarmonie & noelex 77 - why didn't I see that this has to include the alternators as well?
I'll order an isolated engine from Beta Marine (which is already foreseen) and will check that there is (Citation) "Zero/nada/none/no connections between them, no excuses no exceptions." Including the NMEA-network (which might be oftenu overseen?). BTW, does anybody know if there exists an opto-coupler as a simpel solution instead of going over the air (which is possible, but takes a lot more effort.)

Thanks to all of you!

Cheers
Dirk

P.S.: @ Bowdrie: Can you explain the "Drivesaver"?

[skipperpete]

Quite a few engines are supplied as above ground, Perkins Prima, Lister ST, Volvo MD22 some perkins 4-108’s, yes, Betamarine have the option as do Nanni. Notably Yanmar don’t but some dealerships will modify the engine to insulated earth upon request, it’s not that difficult but the starter motor is the problem. Lister use 2 solenoids for their starter,.. a +ve ….and one for the negative so there’s a momentary ground for startup and I’ve yet to see an insulated negative starter for a Yanmar… any Yanmar! Oddly, some Yanmar alternators are insulated. Its relatively easy to physically isolate an alternator by putting non conductive bushings and washers on the pivot and adjusting arm. Pressure gauge senders and alarm switches can be remotely mounted and connected by a non wire reinforced hose or on an insulated bracket if you want aeroquip but temp senders need to be replaced with compatible double pole senders. The engine is fairly simple to isolate but often the boat itself is difficult, engine cables, vhf antennas etc can all light up the ground warning panel.
Common rail engines might already be above ground but if not, it might be very difficult to insulate one.

[Bowdrie]

Originally Posted by Dirk01

P.S.: @ Bowdrie: Can you explain the "Drivesaver"?

It's basically just a non-conductive disc with offset bolt patterns; it goes between the output flange of the transmission and the prop shaft flange.

In reality a carbon fiber hull is so far positive that everything else that's metallic on the boat can become a sacrificial anode and just "go away".
An aluminum hull is opposite, it's already a good anode that's more than willing to give itself away.
In either case, (all cases really,) it's quite important to keep all the electrons in their place, we don't want any of them getting off the proscribed path.