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Old 15-02-2012, 10:12   #1
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Converting Diesel to Floating Ground

One of a couple of projects I am looking to complete on my next visit to the boat is an overdue one to remove the engine from ground.

Currently the previous owner put a set of isolating switches between the alternator and the batteries and engine and the ground so that when the engine is off there is no ground in the boat and when it is on there is. To be fair it seems to have worked well for 30 or so years but who am I to stick with what works?

As I am an aluminum boat with my whole electrical system a two wire floating ground I would like to make the engine a floating ground as well

I know I have to do the following and wanted to know if there is anything else I need to do or any advice or guidance that could be had.

I have an old Volve MD17C and 1000Ahr single bank liquid

from: Alternator and Starter Isolation

1) An isolated ground alternator: I am going to change to the AmplePower 4023I

2) Changing the senders to isolated (2 wire units) - have to order, know a suplier for my engine??

3) Leaving the starter motor as is grounded. To start the engine the block must be grounded which is done with a large relay. - This is a question I have. Relay properties and supplier recommendations?

Anything else I should be looking out for?

Experiences doing this exact changeover?

thanks
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Old 15-02-2012, 12:10   #2
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Re: Converting Diesel to Floating Ground

no bites?
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Old 15-02-2012, 12:32   #3
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Re: Converting Diesel to Floating Ground

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Originally Posted by foolishsailor View Post
no bites?
Well, I don't know anything useful for you but am waiting with anticipation because I have a similar project for my old steel boat
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Old 15-02-2012, 13:04   #4
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Re: Converting Diesel to Floating Ground

"2) Changing the senders to isolated (2 wire units) - "
Why? If the engine is off and ungrounded, anything that grounds via the block, including all conventional senders, will be ungrounded. What would separate grounds on them accomplish?

Same thing for the starter, since the only ground it normally uses IS the engine block, when the block is ungrounded, so is the starter. Matter of fact...that applies to a normal alternator as well.

Unless I'm missing something here, you really need to draw up a complete schematic of the boat and take a good look at where and how the grounds are made. I'm pretty sure you are concerned about ungrounding things that aren't grounded--exept through the engine block, which you're already addressing.

Don't forget to isolate the prop shaft, you'll have to break the engine ground that way as well, and then presumably you already have graphites in the shaft to allow it to be bonded to the hull?

"no bites? " What, in two hours?
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Old 15-02-2012, 13:08   #5
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Re: Converting Diesel to Floating Ground

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Originally Posted by hellosailor View Post
"2) Changing the senders to isolated (2 wire units) - "
Why? If the engine is off and ungrounded, anything that grounds via the block, including all conventional senders, will be ungrounded. What would separate grounds on them accomplish?
By changing the sender to two wire units they will no longer be grounded to the engine. this allows the engine to be disconnected from ground after it is started, eliminating any current flow through it and leaking into the hull.
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Old 15-02-2012, 14:37   #6
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Re: Converting Diesel to Floating Ground

Has the present situation caused a problem? If so, fix it. If not then you may be better off using your time on other things.
Regards,
Richard.
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Old 15-02-2012, 14:38   #7
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Re: Converting Diesel to Floating Ground

And you expect to unground the engine while it is running? With coolant flowing there will be galvanic paths anyhow, won't there?

Don't the two-wire units STILL ground through the engine block as well? I don't think they isolate, I think they just ADD a ground lead.

I hadn't heard of isolating the engine from ground on powerboats.
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Old 15-02-2012, 15:06   #8
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Re: Converting Diesel to Floating Ground

VDO makes 2 wire floating ground senders and supplies Volvo Penta at the OEM level. Should be no problem getting ones to fit. You may have them on the engine already

A "Drivesaver" or other flex coupling should isolate the shaft.
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Old 15-02-2012, 15:11   #9
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Re: Converting Diesel to Floating Ground

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Originally Posted by hellosailor View Post
And you expect to unground the engine while it is running? With coolant flowing there will be galvanic paths anyhow, won't there?

Don't the two-wire units STILL ground through the engine block as well? I don't think they isolate, I think they just ADD a ground lead.

I hadn't heard of isolating the engine from ground on powerboats.

If all of the electrical producing and consuming items are above ground the only items left to create a small electrical charge will be the coolant. This is sop on aluminium vessels.
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Old 15-02-2012, 15:28   #10
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Re: Converting Diesel to Floating Ground

Hellosailor, Sailmonkey --
I do not understand the thing about coolant. Is the goal to electrically isolate the engine from the DC ground, the hull, the ocean, or everything?
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Old 15-02-2012, 15:39   #11
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Quote:
Originally Posted by S/V Antares
VDO makes 2 wire floating ground senders and supplies Volvo Penta at the OEM level. Should be no problem getting ones to fit. You may have them on the engine already

A "Drivesaver" or other flex coupling should isolate the shaft.
Thx for the tips. The shaft is isolated via a Venus bullfrog isolation coupler.

I understand that there needs to be a relay in the starter circuit that temporarily grounds the engine during the starting process and then automatically disengages after the engine starts.

Anyway around this and/or what would be the specs or supplier of this type of relay for a marine application. Also where in the electrical system would this be installed?
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Old 15-02-2012, 15:44   #12
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Re: Converting Diesel to Floating Ground

I don't know if there's an above ground starter available for your engine, but there are for many larger engines.
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Old 15-02-2012, 15:45   #13
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Re: Converting Diesel to Floating Ground

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Originally Posted by msponer View Post
Hellosailor, Sailmonkey --
I do not understand the thing about coolant. Is the thought that the engine is electrically connected to the ocean through the sea water intake?

Is the goal to electrically isolate the engine from the DC ground, the hull, the ocean, or everything?
There's really nothing with the coolant. I just brought it up as Hellosailor already had said something about it.
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Old 15-02-2012, 16:49   #14
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Re: Converting Diesel to Floating Ground

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Originally Posted by foolishsailor View Post
Anyway around this and/or what would be the specs or supplier of this type of relay for a marine application. Also where in the electrical system would this be installed?
In case you haven't seen it, here is a bunch of isolated relays, some of which are OEM parts for big marine diesels. Of course, your 4 cylinder Volvo doesn't need 1500 amps like a Caterpillar, so I am guessing -- 200 amps, intermittent, should be more than enough. Anyone know?

My preference would be to mount it in reach of the engine, so that all of the "engine is not starting, what is wrong?" diagnostics are in one place. It's easier for me to keep my train of thought if I can see and reach everything, to check it with the volt meter, hear if it's clicking, and etc.
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Old 15-02-2012, 17:05   #15
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Quote:
Originally Posted by msponer

In case you haven't seen it, here is a bunch of isolated relays, some of which are OEM parts for big marine diesels. Of course, your 4 cylinder Volvo doesn't need 1500 amps like a Caterpillar, so I am guessing -- 200 amps, intermittent, should be more than enough. Anyone know?

My preference would be to mount it in reach of the engine, so that all of the "engine is not starting, what is wrong?" diagnostics are in one place. It's easier for me to keep my train of thought if I can see and reach everything, to check it with the volt meter, hear if it's clicking, and etc.
I'm not sure that it was I need? But I might just not know what I am looking at.

I am not trying to isolate the batteries from the engine. The engine will be part of the boats dc system and that is not the problem. My understanding is that since my dc is a floating ground, ie not grounded to the hull at any point in the system, that the engine will not start and that on an engine this size I need an external relay to the starter that when I turn the ignition switch creates a temporary ground for the starter and then automatically opens and disconnects the ground once the engine is running.

Not an EE me self so I am sure someone out there is and knows what the name and rating of this type of relay is and some tips on wiring into the starter? Engine ground? And hooking it to my starter panel?
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