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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems > Electrical Upgrades
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Thread: Electrical Upgrades Reply to Thread
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Topic Review (Newest First)
09-17-2012 07:12 PM
Maine Sail
Re: Electrical Upgrades

Quote:
Originally Posted by eherlihy View Post
Update: I now have the 150A fuse in use, and here is why.

After anchoring out for a night, and running the fans all night, and the electric gas solenoid all night (the admiral and I discussed that this should not happen again), and the non LED anchor light, and a couple other electric appliances, I hadn't realized that the #2 battery, which I usually use for everything, had been drawn down significantly. When I tried to start the engine the next morning; first I heard the familiar warning beep, then I pressed the glow plug button, then I hit the start button, and the beeping, and all other electrical functions stopped...

"P = V x I "

Since "V" had decreased, and "P" (to turn the starter under load) remained constant, "I" also had to increase to > 90A, and the fuse popped...

Here is an example; Let's say that the starter normally draws 85A for a few seconds at 13V. That means that the starter consumes 1105 Watts of power to spin the engine, and everybody is happy.

But, if the voltage drops to 12V, the starter motor must now draw 92A for a few seconds to get the alternator to spin. However, after the starter motor button is pressed, V and I will rapidly drop to 0 because the fuse will pop...
See post #8 in this thread...
09-17-2012 06:27 PM
eherlihy
Re: Electrical Upgrades

Fortunately, I had a spare 150A fuse and battery #1, the starting battery, in reserve...
09-17-2012 03:56 PM
eherlihy
Re: Electrical Upgrades

Quote:
Originally Posted by eherlihy View Post
You're right. Because I have been able to start my M25 on a 90A MRBF, it does not mean that I am suggesting that it should be done. If I catch that bone-head skipper doing this again, he's fired!

However, I do recall reading somewhere that the starter on an M25 should be able to do it's job with <100A. If it is sucking more juice than 135A, I want to know about it, because it means that the starter is acting up. Also I have a spare 150A fuse that I keep - just in case.

Your second point, I believe, is the theory of fusing a circuit; the fuse protects the wire, not the device. For details see; ABYC Wiring Standards

All good stuff!
Update: I now have the 150A fuse in use, and here is why.

After anchoring out for a night, and running the fans all night, and the electric gas solenoid all night (the admiral and I discussed that this should not happen again), and the non LED anchor light, and a couple other electric appliances, I hadn't realized that the #2 battery, which I usually use for everything, had been drawn down significantly. When I tried to start the engine the next morning; first I heard the familiar warning beep, then I pressed the glow plug button, then I hit the start button, and the beeping, and all other electrical functions stopped...

"P = V x I "

Since "V" had decreased, and "P" (to turn the starter under load) remained constant, "I" also had to increase to > 90A, and the fuse popped...

Here is an example; Let's say that the starter normally draws 85A for a few seconds at 13V. That means that the starter consumes 1105 Watts of power to spin the engine, and everybody is happy.

But, if the voltage drops to 12V, the starter motor must now draw 92A for a few seconds to get the alternator to spin. However, after the starter motor button is pressed, V and I will rapidly drop to 0 because the fuse will pop...
06-22-2012 12:22 PM
mitiempo
Re: Electrical Upgrades

Eric

You don't have to have 2 double main breakers. You need one before the inverter/charger but not after. There are 2 ways to accomplish this. One is for the shorepower to go from the inlet to the double main on a standard panel. Separate the main from the circuits below. From there it goes to the inverter and the output goes back to the breakers on the panel. This means that all AC items are able to be run from the inverter, not always a great idea. The other and best way is to wire shorepower to the main panel and go to the inverter from one breaker. The inverter output goes to a sub-panel with only the items the inverter is expected to power. The sub-panel does not need a double main breaker. This means that you cannot leave the water heater on by mistake when away from the dock which would quickly drain the batteries.

You are not showing the DC grounding connections. ABYC calls for the AC ground (green) to connect to the DC negative bus. This creates the probability of corrosion so a galvanic isolator is needed if you connect to shorepower.
06-22-2012 10:53 AM
efiste
Re: Electrical Upgrades

Thanks once again to everyone's help. I will probably hold off on the galvanic isolator until my use of the boat changes. For posterity, attached is the final diagram of what I am planning to install. If I make any other changes along the way or have other suggestions on how to improve, I will update and post again. I could not have done this without a lot of great help from forums like this.

Eric
06-21-2012 02:05 PM
mitiempo
Re: Electrical Upgrades

Eric

You need the double pole main breaker before the inverter, not after. One way is to go from shorepower inlet to the double main and then to the inverter/charger. The I/C ac out then goes to the AC panel circuits.

I'm not sure what you mean by #10 red on the AC wiring. The wire should be 10/3 color coded black/white/green.
06-21-2012 01:56 PM
efiste
Re: Electrical Upgrades

I appreciate the feedback. I have revised my schematics to incorporate much of the input including the AC side of the C/I. I was thinking that the AC circuit should be controlled from the boat panel, so that I could isolate the C/I. If I wire it like suggested (and shown in my drawing), I have to disconnect the shore power cable or switch the circuit breaker at the shore power station to interrupt power. Is this preferred over placing the C/I downstream of the boat's AC panel and then managing AC circuits on the boat via the C/I's remote control panel?

I have also added a DC disconnect dedicated to the C/I, so that I can interrupt the battery load if needed (i.e., for servicing and perhaps when leaving the boat for extended periods). BTW, the C/I is a Xantrex Freedom HF 1800.

Thanks again,
Eric
05-05-2012 11:49 PM
eherlihy
Re: Electrical Upgrades

[deleted]

The rule is, as I said in my earlier post, select the correct fuse that will protect the wire, not the device.

Per the chart that I link to above that 2/0 wire is capable of handling 280A w/in the engine compartment, so that is OK. I missed the 300A fuse that Maine Sail highlights...

In the hope that it will help you (the rest of you - don't bother critiquing the use of the 90A and 135A MRBF - I have my reasons), here is the diagram that I have for my boat, which also has an M25 & an Echo Charge;
05-05-2012 10:13 PM
btrayfors
Re: Electrical Upgrades

I agree with MaineSail 100% on this: if you're going to put a fuse in the starter circuit -- and I, too, believe this is a very good idea -- don't fool around with 'barely adequate' size fuses. I use a 400A ANL in my start circuit with 2/0 cable on my 4-108, after having blown lesser fuses in the 200A range.

Here's why.

Electric motors, like starter motors, are generally rated in at least two ways:

LRA = Lock Rotor Amps
RLA = Run Load Amps

When a starter is fed current from a dead stop condition, there is very considerable in-rush current, comparable to the LRA rating. This may be 2 times or 3 times the RLA run load amps, or even more. On cold mornings, or if there is sludge in the engine, or if it is hard starting for some reason, these elevated current draws can be much longer than the "normal" in-rush current times.

Example: a starter on a small to medium size diesel may, indeed, only draw 150A or so while it's turning, but the in-rush current can reach 1,000A for a few milliseconds, dropping to 300A to 400A or so for a few more milliseconds before leveling out at 150A when the starter really gets going.

What you most certainly don't want to happen is to have a fuse blow while you're trying to start the engine. Murphy's Law dictates that this might well be at the worst possible time.

The fuse is there to prevent a catastrophic meltdown and fire.

Bill
05-05-2012 06:25 PM
eherlihy
Re: Electrical Upgrades

You're right. Because I have been able to start my M25 on a 90A MRBF, it does not mean that I am suggesting that it should be done. If I catch that bone-head skipper doing this again, he's fired!

However, I do recall reading somewhere that the starter on an M25 should be able to do it's job with <100A. If it is sucking more juice than 135A, I want to know about it, because it means that the starter is acting up. Also I have a spare 150A fuse that I keep - just in case.

Your second point, I believe, is the theory of fusing a circuit; the fuse protects the wire, not the device. For details see; ABYC Wiring Standards

All good stuff!
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