Revd Up

After working on the boat for many hours the other day, I thought I had everything back together and ready to go.

So today I thought I would do a test start up on the hose to make sure all was right.

I turned on my battery switch and tried to lower the engine hatch. Nothing. Looked into the engine compartment and heard the sound of an electrical short. For those that don't know that sound, it is the sound of burning electrical wires. I dove to the battery switch and switched it off as I saw a flame and a poof of smoke.
Switch was on for a total of about 15- 20 seconds.

I immediately noticed my dumb a** had put the battery cables on one of my batteries on the wrong terminals!

I switched the battery cables and did a damage assessment. Reset the 50 amp circuit breaker,. Starter wires looked good. Ground battery cable had burned the heat shrink tape off by the terminal, but otherwise fine. Alternator wires were still in tact with no signs of melting. Alternator had a terrible burnt smell. Everything else I looked at seemed normal with no damage.

Tried to fire it up and to my surprise it started right up.. Voltage gauge on the dash showed 11.5 volts at idle. Let it come up to temperature and things seemed fine. Gave it a little gas and heard a squealing and smoke started coming out of the alternator,.

Pulled the alternator as I am sure it is toast. It is from a Gen 6- 502. Merc Part # 807653. Vender part # AC165617

Is this something I can get at the local auto parts store, or does it have to be a Merc part? Any part numbers would be helpful if not the above mentioned.

What other things should I be looking into for possible damage.

Thanks

BUP

it depends and your app is not stock at all. The depends meaning how is it fused and circuit breakered - does it have a 90 amp fuse at the starter ? does it have a 50 amp red button circuit breaker in a bracket ? does it have a yellow flag 50 amp breaker ? What ignition set up ?

Possible bad items, but depends -- things to look for -- alternator and or possible ignition related items and or fuses and or breakers and or possible wiring and or possible the ECM -

Its not a stock app nor prob not stock fused and breaker protected like a stock app is a guess on my part..

You have a MEFI ecm correct ? and which MEFI 3 or 4 ??

Just had a blown mefi 3 from a boat owner who did the exact same thing with his battery cables. Lucky for him I fixed it. One of the circuits blown across saving the whole ecm. I bridged that circuit and the ecm was good to go. Actually I was shocked and he got lucky that the ecm was not toast.

Revd Up

Thanks John for replying.

It is a MEFI 3.

It does have the red button circuit breaker in a bracket. I pushed on it to see if it was tripped and believe I heard a click stating it had triggered.. I am hoping that saved my ECM

Even though it started right up and idled, I probably won't find out it the ECM is ok until I can get it on the water and test it.

I felt and looked for any damage to the wires to the starter and alternator and they all looked fine. I didn't see any fuses there. I am glad I didn't try to start it or those probably would have been fried.

Something definitely fried in the alternator though. I saw fire and a puff of smoke as I was cutting the power. It smells worse than an old campfire.

Is there anything special about the Merc alternator or can I purchase the same one at a auto parts store?

Revd Up

Sydwayz

You MUST replace it with a marine alternator.
Your best bet may be to take it to a local alternator shop and have it rebuilt.

Revd Up

That's exactly what I did. lol

I dropped it off today at a local reputable shop that specializes (30 years) in electric motor repair. He said he would have it done in a day or two.

At least I know it will be rebuilt with quality parts while still using the original oem part.. Your just asking for trouble with the cheap aftermarket parts.

SB

Lucky you didn't have to change your name to Blown Up.

speicher lane

As a FYI, marine alternators must be used as Sydwayz stated in post #5 as they are designed to be spark proof with internal screens. A GM direct replacement may be identical match in terms of design and output but they are like using a match to find a gas leak (in an enclosed engine compartment no less).

Hopefully you are limited in damage to the alternator and the fuse on the starter after feeding 24v - fingers crossed!

Revd Up

That's good information and got me thinking so I called the guy doing the rebuild.

He said he is aware of that and is SAE certified. Said when doing equipment for boats, mining equipment, or fertilizer plants they must be spark proof. The guy is pretty sharp and knows his stuff.

Should have it back tomorrow. Then do a test fire to see is everything else is ok. No pun intended

Keeping my fingers crossed.

3pointstar

I did the exact same thing a year ago - talk about feeling like an idiot - I was VERY lucky - I didn't turn the key and try to start the engine - I blew out a couple of the circuit breakers on the engine and a solenoid on the starter- but we were on the water in a couple of days.
I feel you pain

all the best

3pointstar