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Old 08-05-2017, 02:35   #1
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2nd Start Solenoid on negative.

My boat is steel, it has normal start solenoid arrangement, (any boat with bonded thru hulls similar). Have been thinking that I don't like the idea of Negative of Battery connected to hull thru the starter on a permanent basis.

My reasoning there may be insulation less than 1Mohm somewhere on the positive side, creating a small current that could exacerbate anode wear or worse, hull corrosion.

I anticipate putting a second solenoid so that negative return current is insulated from hull except for the brief moment of Engine start.

Throwing my idea out there to C&S people, any downside, thoughts, do others do it.
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Old 08-05-2017, 03:39   #2
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Re: 2nd Start Solenoid on negative.

I see your point... to a point; I think that trying to eliminate all electrical current is like dividing a sum by half again and again. You get to a very small number rather fast, but NEVER reach zero. There is electrical charge in just about everything, isolated or not.
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Old 08-05-2017, 04:12   #3
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Re: 2nd Start Solenoid on negative.

Yes, the solenoid is a sensible inclusion.

However, it needs to be part of a complete electrical system. On the engine you also need an isolated alternator and senders, otherwise the negative is still conected. Also, ideally you need dual pole circuit breakers on the domestic side.
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Old 08-05-2017, 04:26   #4
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Re: 2nd Start Solenoid on negative.

I'm also faced with similar problem on my aluminum boat with Perkins 4108
I have everything isolated apart from starter.

Woud a big relay work for negative?
Anyone have ideas how much amps is going thru the starter?
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Old 08-05-2017, 04:51   #5
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Re: 2nd Start Solenoid on negative.

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Originally Posted by xslim View Post
I'm also faced with similar problem on my aluminum boat with Perkins 4108
I have everything isolated apart from starter.

Woud a big relay work for negative?
Anyone have ideas how much amps is going thru the starter?
Yes.

Depends on the starter motor but I would reckon about 200 amps is a safe number for a 4108 however I would be looking for a 300 amp relay (solenoid) as a conservative figure.
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Old 08-05-2017, 05:23   #6
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Re: 2nd Start Solenoid on negative.

Two pole electrical systems are very common in larger engines. Starter motors and alternators have both positive and negative terminals and all senders on the block are two pole. Almost all larger Volvo engines are built this way.

Some of the smaller Volvo engines were also built with two pole systems in the past. Because the smaller engine starter motors didn't have two poles, relays were used to momentarily ground the engine block for starting and stopping with electric stop solenoids. This was done at the time to lower the possibility of corrosion on saildrive packages.

Today saildrives are electrically isolated from the engine with nonconducting gaskets and washers. It achieves the same goals without the electrical complexity.

Your idea has lots of merit and should be fairly easy to achieve.

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Old 08-05-2017, 08:48   #7
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Re: 2nd Start Solenoid on negative.

Sound doable. However I doubt your sending units are two pole and would lose their ground. Might cost you buying an alternator if the current one. is using the engine for neg.. I am not sure it will solve the problem? Good luck.
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Old 08-05-2017, 15:40   #8
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Re: 2nd Start Solenoid on negative.

If the senders are single wire, or alternator is grounded, then I would think that the switching of the Negative connection, would have to stay closed while the Engine is running, not sure if I could get a solenoid that big and continuously rated (or a switch maybe), will check the senders when I get back. Thanks.
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Old 08-05-2017, 18:28   #9
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Re: 2nd Start Solenoid on negative.

Maintaining ground on everything is done to prevent galvanic corrosion.
By connecting as much as possible together electrically, the electric potential is reduced . If you unground your various parts, you will increase the likelihood of corrosion.
That's why it is done the way it is. Add a negative side solenoid will allow corrosion in places you might not like.
With the present setup, with a miniscule current leakage on the heavy solenoid contacts, the only point of galvanic corrosion is the contacts. Because the rest is held to the same potential.
If you add a neg side solenoid, the entire starter will be "floating" voltage.
Very likely to increase corrosion inside the starter. . If you unground the entire ENGINE you will likely eat that up also.
Don't.
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Old 08-05-2017, 19:01   #10
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Re: 2nd Start Solenoid on negative.

We are going through the same fun on our 2006 Yanmar. We already have the floating alternator, but each of the senders are single pole and get their ground through the block.

Based on a lot of internet hunting, I found VDO double pole senders in Europe. I'm able to get these for around $400 shipped to the US. Unfortunately, the money isn't in the bank, so we'll just rely on using a Bluesea 6010 switch to connect the ground to the engine block when we're using the engine. I hope that semi-short use won't cause corrosion issues down the road.

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Old 08-05-2017, 20:16   #11
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Re: 2nd Start Solenoid on negative.

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Originally Posted by Redpcx View Post
Maintaining ground on everything is done to prevent galvanic corrosion.
By connecting as much as possible together electrically, the electric potential is reduced . If you unground your various parts, you will increase the likelihood of corrosion.
That's why it is done the way it is. Add a negative side solenoid will allow corrosion in places you might not like.
With the present setup, with a miniscule current leakage on the heavy solenoid contacts, the only point of galvanic corrosion is the contacts. Because the rest is held to the same potential.
If you add a neg side solenoid, the entire starter will be "floating" voltage.
Very likely to increase corrosion inside the starter. . If you unground the entire ENGINE you will likely eat that up also.
Don't.
I disagree. On a metal boat isolation is the best solution.

A simple solution to this is to put a battery switch in the negative line and that way the engine is only connected when it is running. This is a solution that Steve Dashew used on Sundeer and Deerfoot boats built in aluminum.
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Old 08-05-2017, 21:22   #12
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Re: 2nd Start Solenoid on negative.

Yes Mitiempo has the answer I have used this system of isolation switch on both Positive and Negative for years now and have the same setup on my Anchor winch.

I also use a simple check to see if anything on board has gone to ground by having a small pilot light on my power panel connected to the positive side of the power supply and negative side to the hull if any connection in the power supply goes to ground it will ( and does ) light up giving me warning in an instance. When the motor or winch is in use this light is on so it also works as a reminder to turn things off.
Simple but very effective Cheers
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Old 09-05-2017, 02:57   #13
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Re: 2nd Start Solenoid on negative.

Quote:
Originally Posted by Oceanride007 View Post
If the senders are single wire, or alternator is grounded, then I would think that the switching of the Negative connection, would have to stay closed while the Engine is running, not sure if I could get a solenoid that big and continuously rated (or a switch maybe), will check the senders when I get back. Thanks.
There are plenty of 24V solenoids that are big enough and continually rated so I expect there are some 12V ones also.
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Old 09-05-2017, 03:12   #14
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Re: 2nd Start Solenoid on negative.

Yes, Jacko, using earth lamps will discover plenty. Red you got it wrong all shipping uses isolated hull, this way any shorts to hull can be discovered using meters or lamps, the point is without it, shorts to hull are not discoverable.
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Old 09-05-2017, 03:49   #15
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Re: 2nd Start Solenoid on negative.

Quote:
Originally Posted by Jacko View Post
I also use a simple check to see if anything on board has gone to ground by having a small pilot light on my power panel connected to the positive side of the power supply and negative side to the hull if any connection in the power supply goes to ground it will ( and does ) light up giving me warning in an instance. When the motor or winch is in use this light is on so it also works as a reminder to turn things off.
Simple but very effective Cheers
I would be wary of doing this, at least with a conventional incandescent globe.

You are connecting the positive supply to your hull via a resistor. If there is only a small current flowing there is very little voltage drop over the globe and your hull is now at a voltage above ground. Not good if you are leaving this connected for any length of time.
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