Alternator sparks

[two2_tango]

New owner of a 41 Formosa with a Perkins 4-108 in it, and I'm an 'advanced beginner' when it comes to working on a gas engine, but this is my first time owning a diesel. This is probably a stupid question, but...

...when I pull the engine compartment covers off while the engine is running, I can see the sparks of the alternator as it turns. I understand how an alternator works and generates electricity so I know that brushes spinning creates spark/energy, but the sparks seem kind of excessive, like lighting a sparkler on the 4th of July.

I'm looking at the *back* of the alternator, NOT the side where the belt attaches. The spark seems excessive at cruising RPM (around 1500), like they extend past the alternator housing and are not contained within.

I'm worried that it could start a fire with such a hot-running engine. Am I over reacting or do I have an issue here?

Any input is appreciated - thank you!

[Sailmonkey]

Well.... I’ll be never seen sparks from my alternator.

I think you’ve got a problem

[AndyEss]

Originally Posted by Sailmonkey

Well.... I’ll be never seen sparks from my alternator.

I think you’ve got a problem

👍🏼👍🏼👍🏼👍🏼👍🏼👍🏼👍🏼

[two2_tango]

Ah - thanks. Turns out the alternator was a little loose. Tightened it up and have run the engine for 15 minutes and all seems normal now.

It's the little things, isn't it? *phew*

[Jim Cate]

^^^^^

This suggests that the ground wire may not be attached to the alternator correctly and that the return is solely through the case's physical connection to the engine block.

Might have a look at that soonish.

Jim

[AndyEss]

Good example of “there are stupid questions (mostly asking about life/money advice from total strangers) but mechanical questions almost never are stupid.
The engine accessories on diesel engines are often identical to those on gasoline engines, sometimes just beefier.
Sparks are never a good sign no matter what. Even welding or grinding, you need to keep track where the sparks are flying so you don’t start fires or damage something.
Good the fix was easy. As Jim says, see if that alternator even has a separate ground cable. If it is only grounded through the case (like many automobiles do) it is easy to add one. Sparks in cars often can just fall to bare ground. Sparks in boats fall into the bilge - where propane, gasoline or other explosive vapors may gather.
Whatever you do, don’t ground the B terminal - that should have a big ole red cable going to your battery positive terminal, sometimes first through a battery selector switch.
Take some time to learn about your boat’s electrical system. I’d say the majority of boat problems are electrical in nature.

[two2_tango]

Thanks for the insights. The brush looks a little old with some corrosion on the outside, so I'm going to replace that tomorrow, and also check the ground cable too.

I hear ya about reviewing the electrical system. That's how I'm spending my weekend. it's an older boat that has had some electrical upgrades, so it's a bit of a maze tracing wires that sometimes lead somewhere, and sometimes don't.

But it's a great way to get to know the boat, that's for sure.

Thanks again, all. These forums are an awesome resource.

[lmxr]

Originally Posted by two2_tango

Ah - thanks. Turns out the alternator was a little loose. Tightened it up and have run the engine for 15 minutes and all seems normal now.

It's the little things, isn't it? *phew*

Happy that you found the issue.

If the alternator is wired such that its ground is only connected to the batteries through its frame to the engine (aka no thick black wire on its B- terminal), then it likely has operated without a good connection to the batteries for some time. Such a bad connection can result in damage to its regulator and/or diodes. A regulator failure usually manifests itself as high battery voltages (16..18 V) once the batteries reach full charge. Evidently this destroys the batteries and possibly some connected equipment. So, to be sure I would check whether the regulator still regulates correctly.