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Catalina/Capri 25/250 Sailor's Forums

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Electrical issues

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pfduffy
Captain

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USA
317 Posts

Initially Posted - 07/08/2013 : 07:05:31

I finally installed my battery and took my inaugural sail of the season this past weekend (which is another story altogether!)

I am experiencing a weird electrical issue. My tohatsu 9.8 electric start is blowing the fuse in the ignition circuit when I press the start button. Since I had rewired the plug, I assumed that I had wired it incorrectly so I reversed. When I reversed it, the fuse blew immediately when inserted, so I assume that the plug was wired correctly initially.

The motor is effectively wired directly to the battery using a trolling motor plug. (The red wire to the battery switch and the black directly to the negative post on the battery.) I confirmed that I am getting about 12.9v with the correct polarity to the plug.

To add to the electrical intrigue, when turned on the switch on the panel to fire up the depth sounder (small hummingbird model) the display showed some garbled nonsense and then went blank and appears dead. I confirmed correct polarity to this device with my meter, so I am mystified as to the cause of this problem - but it seems like the device got "fried" when I first powered it up.

My running lights are working properly and I really don't have anything else hooked up to the electrical system.

So I am not sure if I have separate problems with my motor and my depth finder or if I have a common problem with my electrical system. All advice is welcome!!

Thanks!

Pat Duffy
1984 SK/SR #4113
Slàinte

Edited by - on

Ape-X
Admiral

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USA
662 Posts

Response Posted - 07/08/2013 : 09:18:17

sounds like one issue may have caused the other electronics to get blown: likely a bad alternator on the motor? Running lights are simply resistors in a circuit, so less likely to come to harm from a resultant short or overload in the system. Wish I could be of more help, but charging systems aren't my special.

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binky
Navigator

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USA
115 Posts

Response Posted - 07/08/2013 : 19:32:06

How many batteries do you have?

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pfduffy
Captain

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USA
317 Posts

Response Posted - 07/09/2013 : 05:32:09

I have a single battery but I do have a battery switch that would allow me to have 2 should the need arise.

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Voyager
Master Marine Consultant

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USA
5371 Posts

Response Posted - 07/09/2013 : 18:09:09

What amp rating is the fuse that's blowing? You could need up to 60A inrush current when you first hit the button. Does the starter take a 1/2 a crank then stop or does it blow right away with only the sound of the first engagement of the starter.
Starters have three important parts:
1. The starter solenoid - it converts a small current from the starter button into the high current from the battery.
2. Starter throw out bearing - another magnet that pushes the geared spline onto the flywheel teeth to engage the starter turning the engine over. When you release the button the starter disengages by means of a spring pushing the gear back out of the way.
3. The starter motor itself. This is a powerful DC motor that has enough oomph to crank the engine.
Any of these three parts could have a short, thus blowing the fuse.
They're also hard to ohm out using a digital multi-meter, since they have near zero resistance.

Lastly, the depth meter, if connected to the starter incident at all could have blown if there were a large voltage spike from the starter, or you could have gotten hit by lightning.
Any other gear like FM radios, iPads, GPSs on board? Lights, unless they're LED, are pretty impervious.
Wow! Mystery

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Tim M
1st Mate

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60 Posts

Response Posted - 07/10/2013 : 13:32:55

It sounds like you simply have too much current draw when attempting to start. I have the same engine and the service manual says it has a 20A internal fuse so there's no need to go higher than that. For a simple test of the motor, haul the battery into the cockpit and connect the cables from the motor directly to the battery and see what happens. When you install a battery - hopefully in the battery compartment under the starboard settee - the wire every step of the way to the battery must be at least as heavy or heavier than the cables on the motor. If there will be a circuit breaker or fuse in the circuit it must be at least 20A. In a simple 'old-school' battery system, one without built-in chargers, battery controllers, etc., it's a good idea to put a fuse or breaker right on the battery (you can find some that mount right on the connecting post) to protect the wiring from a dead short.
The motor has magneto ignition with an alternator coil added to supply the charging circuit and possibly could have had a voltage surge but it's highly unlikely. I have fried a number of electronic devices over the years with wrong polarity. Color coded wiring helps to increase likelihood of assumptions being right. Good luck.

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.