Have I cooked my alternator?

[bodgy]

Last week I stupidly turned the battery selector to off whilst the motor was running.

I have just had the exhaust elbow replaced and when I started up I noticed there was no alternator current nor was the warning light glowing. I checked to see if there were any loose leads, couldn't see any. I also checked voltage at alternator positive post - same as battery.

I doubt the elbow replacement had any impact here, but somethings happened.

Engine will start as normal but she no charge

The engine is the green anchor MD 2003, 28 HP. The alternator is a 50 amp model.

Before I remove the alternator and take to a shop, any ideas? How can I test the diodes etc?

Thanks, I did search but couldn't see any similar posts.

Jon

[Pete7]

Jon,

That's not sounding good. However, if it needs replacing rather than fix the existing alternator there are 100A models available. I have one of these waiting to be fitted for the same sort of money a 50/60A alternator costs. Mine also came with the field wire already fitted if I want to install an external regulator controller.

https://www.startermotor-alternator-...1m-11862-p.asp

Appreciate you are on the other side of the planet but worth looking locally or even importing one.

Pete

[Wotname]

Originally Posted by bodgy

Last week I stupidly turned the battery selector to off whilst the motor was running.

I have just had the exhaust elbow replaced and when I started up I noticed there was no alternator current nor was the warning light glowing. I checked to see if there were any loose leads, couldn't see any. I also checked voltage at alternator positive post - same as battery.

I doubt the elbow replacement had any impact here, but somethings happened.

Engine will start as normal but she no charge

The engine is the green anchor MD 2003, 28 HP. The alternator is a 50 amp model.

Before I remove the alternator and take to a shop, any ideas? How can I test the diodes etc?

Thanks, I did search but couldn't see any similar posts.

Jon

Hi Jon,

Turning the battery selector off while the engine was running can kill the alternator however you haven't given us enough information.

You say the warning light isn't glowing (assuming while engine running), this is normally a good thing. Likewise the voltage at the alternator positive post is meant to be the same as the battery voltage.

But what was the actual voltage? It should be over 13.6V and usually around 14.2 or a bit more if the alternator is charging.

[Dockhead]

Normally you just blow the diodes, and these are usually replaceable. Don't panic.


Just take it to an auto-electric shop and let them deal with it. Normally not too expensive. Or if the alternator is old, see this as a sign from Neptune to upgrade it to a better one.


And battery selector switch? Those things are from the devil. Maybe it's time to reconfigure the system so that you don't need it?

[bluenoser613]

Originally Posted by Pete7

Jon,

That's not sounding good. However, if it needs replacing rather than fix the existing alternator there are 100A models available. I have one of these waiting to be fitted for the same sort of money a 50/60A alternator costs. Mine also came with the field wire already fitted if I want to install an external regulator controller.

https://www.startermotor-alternator-...1m-11862-p.asp

Appreciate you are on the other side of the planet but worth looking locally or even importing one.

Pete

You can cook your engine if you put an alternator that’s too big on the engine. Make sure you check that out first.

[Flatswing]

Originally Posted by Dockhead

Normally you just blow the diodes, and these are usually replaceable. Don't panic.


Just take it to an auto-electric shop and let them deal with it. Normally not too expensive. Or if the alternator is old, see this as a sign from Neptune to upgrade it to a better one.

This: diodes, bearings, brushes, whatever - they usually come back like new for 1/3 to 1/2 the price. My local shop turns mine around in 24-48hrs.

[philcun50]

Had better check your charge light. If the lamp is blown the alternator doesn’t get any power to initiate the charge.
The charge light should illuminate when the engine is switched on but not running. Brushes can give this result too. Any break in this circuit will stop the charging. If it is a LED lamp then a different circuit gives the alternator it’s initiating power.
Make sure you get the same wattage lamp if this is the problem.

[Wotname]

Philcum makes a very good point about the charge light.

It must illuminate as soon as the engine key is switched on and then should extinguish once the engine has started and the generator is providing an output. To repeat, if the lamp is blown, the alternator will not self excite (usually).

Originally Posted by philcun50

Had better check your charge light. If the lamp is blown the alternator doesn’t get any power to initiate the charge.
The charge light should illuminate when the engine is switched on but not running. Brushes can give this result too. Any break in this circuit will stop the charging. If it is a LED lamp then a different circuit gives the alternator it’s initiating power.
Make sure you get the same wattage lamp if this is the problem.

[JimsCAL]

Most likely you cooked the diodes. As has been said, a shop should have no trouble relacing them. A voltmeter on the battery will confirm charging. Voltage at the battery should quickly rise above 13 volts and keep climbing after the engine starts.

[bodgy]

Thanks to all who responded, in retrospect the lack of any warning light once ignition was on was important.

Happy, happy days!

When checking out the bolts etc prior to removal, I saw (hidden behind a clump of wiring) a stray lead waving in the breeze. I then found a lonely stud on the back of the alternator. Plugged it back on and woo hoo, all back in action.

I should have focused on the concurrency of the exhaust elbow replacement and the alternator failure. Mechanic had knocked this wire off.

I feel I have used up my quotient of good fortune, I await the next disaster.

Jon

[Wotname]

Great outcome and thanks for the update Jon

[Pete7]

Originally Posted by bluenoser613

You can cook your engine if you put an alternator that’s too big on the engine. Make sure you check that out first.

How do I do that?

It's a change from 60A to 100A on a 28hp 3 cylinder diesel. What do you think will be the problem?


Pete

[GordMay]

Originally Posted by Pete7

How do I do that?
It's a change from 60A to 100A on a 28hp 3 cylinder diesel. What do you think will be the problem?
Pete

The alternator is a side load, which can become very hard on your crankshaft bearings. The simplest solution is to use two smaller alternators, installed so they oppose each other, and cancel out the side loads from each other.
An alternator typically takes about 1 HP (horse power) for every 25 amps of nominal 12VDC power generated, including belt losses. Hence, a larger alternator [or 2] reduces your motive power, more than does a smaller alternator.

[Nicholson58]

I have had alternators inspected and repaired several times, usually for less than $80 US. Look for a dedicated starter - alternator shop catering to truckers. Several times I have done a swap at one of these places.

[Pete7]

Originally Posted by GordMay

The alternator is a side load, which can become very hard on your crankshaft bearings. The simplest solution is to use two smaller alternators, installed so they oppose each other, and cancel out the side loads from each other.

Indeed. The problem is the engineering to achieve that in a small space is so tricky its not worth the gain. Since the uprated alternator is still single belt and only likely to be producing 60A as a best guess, it isn't in the same league as fitting a big Balmar alternator were concern would be warranted.

Pete