Alternator and Starter Isolation

[GordMay]

Originally Posted by moneypop

I really wonder how to isolate case ground parts(alternator/starter..) in marine engine
I need to get information or sites substancially.
would you give me tips?

You don't convert case gnd appliances to isolated gnd. You replace case gnd with new isolated gnd devices.

[CharlieJ]

Alan-I know you were tired when you wrote:

but the Neutral is tied to Earth(green/green-yellow)back at the switchboard.

In fact, neutral (white/blue) and safety ground (green/green w/yellow) are only tied together at sources; generators, inverters, and shore power at the mains transformer. NEVER at the switchboard.

Gord-

The new ABYC standards require a “Status Monitor” feature, requiring additional circuitry.

There is another option, not requiring a status monitor, that was developed in ABYC A-28 a few years ago.

A bit of history. While GIs, when made of quality components, did their job well, there was a concern within the ABYC that placing a semi-conductor based device in the critical safety ground wire could lead to loss of the safety ground path if the semi-conductors failed open, their normal mode of failure. Thus the well intentioned requirement for a monitoring system was developed.

Several manufactures (Professional Mariner, among others) brought some sophisticated monitoring systems to market. These monitoring systems checked the ground path at least once every 24 hours and alarmed for a couple of faults, the most critical being for loss of continuity in the safety ground path. If an alarm condition occurred, the alarm sounded and could not be silenced for more than five minute. Unfortunately, these monitoring systems did a fine job of verifying the condition of the shore side portion of the safety ground system...and found that this side of the system was in bad shape!

So, the law of unintended consequences had reared its head.

Enter the fail safe GI. These have been around in the dairy and pipeline protection industry for years. They are constructed of extremely robust components and, unlike their less robust nephews, will fail closed if subjected to an otherwise incapacitating surge so there is no need for the monitoring system. The extremly rigorous testing requirements for candidate fail safe GIs was developed (A-28) and each candidate must be certified by an independent laboratory (UL, AMMANA, etc.)

The fail safe units have been on the marine market for some time and are the only ones that I will install.

Hope this helps,
Charlie

[noelex 77]

Originally Posted by moneypop

I really wonder how to isolate case ground parts(alternator/starter..) in marine engine
I need to get information or sites substancially.
would you give me tips?

It is usually achieved in practice by using:

1) An isolated ground alternator, many marine engines have this as standard anyway.
2) Changing the senders (water temp oil pressure and alarms) to isolated (2 wire units)
3) Leaving the starter motor as is grounded. To start the engine the block must be grounded which is done with a large relay. Once started the relay is released and the engine is ungrounded. The few seconds of grounding, during starting, have little impact on corrosion and this is more reliable and easier than trying to get an isolated starter motor.

Hope that helps

[GordMay]

Originally Posted by noelex 77

It is usually achieved in practice by using:

1) An isolated ground alternator, many marine engines have this as standard anyway.
2) Changing the senders (water temp oil pressure and alarms) to isolated (2 wire units)
3) Leaving the starter motor as is grounded. To start the engine the block must be grounded which is done with a large relay. Once started the relay is released and the engine is ungrounded. The few seconds of grounding, during starting, have little impact on corrosion and this is more reliable and easier than trying to get an isolated starter motor.

Hope that helps

Indeed; concise, yet complete & accurate!

[Tashtego]

Originally Posted by noelex 77

It is usually achieved in practice by using:

1) An isolated ground alternator, many marine engines have this as standard anyway.
2) Changing the senders (water temp oil pressure and alarms) to isolated (2 wire units)
3) Leaving the starter motor as is grounded. To start the engine the block must be grounded which is done with a large relay. Once started the relay is released and the engine is ungrounded. The few seconds of grounding, during starting, have little impact on corrosion and this is more reliable and easier than trying to get an isolated starter motor.

Hope that helps

Nolex (and/or Gord) could the ground relay be another starter solenoid? Then I would have a spare if the primary start solenoid failed.

[Tashtego]

I still haven't seen any recommendation of a US supplier of high current (~200 Amps) isolated ground alternators. Where can I get one?

[foolishsailor]

Originally Posted by Tashtego

I still haven't seen any recommendation of a US supplier of high current (~200 Amps) isolated ground alternators. Where can I get one?

http://www.amplepower.com/products/a...ors/index.html

Their large case alternators all come isolated as standard. They are the best in the biz, and their external smart regulators are the gold standard. See models 4060 4300 on above page. I can't drive an alternator this size but I have purchase on of their isolated small case 100amp models.

Thanks for the solenoid tip!