Car alternator OK for my boat?

[roland stockham]

You will have problems getting a 60a alternator these days and probably find something between 85 and 100a is cheaper. As others have said there is no problem if you match the terminals and mountings. Take the old one in so you can check the fit!
Check where that neg lead goes to, as Matt Paulin said it could be an earth lead for the alternator frame but it is possible it is a batt sense lead for the internal regulator
I would suggest now would also be a good time to upgrade the system to an external regulator. It will cut charging time very significantly if you do ever need to charge from it. This particularly effects the area from 70% - 100% full charge. Generally you will not get much above 85% charge without an external regulator (which is OK if you regularly hook up to a dockside charger. If you do upgrade it is important to also upgrade the wiring and take out any switches. An external regulator senses the voltage at the battery not the alternator so if you have to much resistance in the circuit you can get problems with hight voltages at the alternator that register as a fault.

[Thumbs Up]

I have car alternators on my twin volvo md2030s. I also keep a spare at hand. The originals would have had a "stator tap" wire as a sensor for the tachometer. You can take the alternator apart and add a stator tap or use a different type of tach. I don't recommend adding external regulation to these alternators. The internal regulators are usually temperature sensing and will prevent overload. Maintain your batteries with a good solar or shore based charging system and use your motors for bulk charging.

[wcapman]

Just to clarify a few points, a car alternator SHOULD be suitable for a marine diesel, but maybe not a marine gasoline engine.

Most marine alternators are painted to reduce corrosion on the aluminum body while automotive alternators have no finish. With that said I have run automotive alternators for 30+ years on sailboats in salt water and besides just looking dirty, they still work.

If you have a quick charge regulator an auto-electric shop can bypass the internal regulator so you can connect the FIELD wire directly to the alternator.

If you specify a heavy duty alternator (i.e. police or ambulance service) you will get an alternator capable of running high amp loads for bulk charging. You can also ask the auto-electric shop to install the largest diode pack that will fit. I use Delco alternators with 150 amp diodes, and limit the charge rate to 100 amps max. They last almost forever.

The biggest issue is finding the correct frame/foot size to fit your engine mounts. It is essential that the pulleys line up as close as possible. Even a slight offset can cause excess belt wear. Washers as spacers can be used to adjust the alternator in or out slightly.

Lastly, Auto-alternators are so cheap that for the price of a typical marine alternator, you can buiy a second one for a spare and have change left over.

[Geoff54]

Maybe this will help. I don't remember where it came from so hopefully I'm not treading on anyone copyright.

[georgeg305]

If you go with a new alternator, be sure you get one with an AC tap. Used to drive the tachometer. Easily installed by any alternator shop if you already have bought.
I vote for rebuild as it is easy

[leftbrainstuff]

No airflow in a boat engine room so expect thermal issues to reduce the life or result in failure of insulation earlier than on a vehicle.

That being said the test conditions for vehicle alternators is as bad as you'll ever see in the engine room.

There is no difference in wiring or components other than your choice of regulator.

Your alternator is still earthed to your engine which will have its circuit completed at the negative bus bar rather than the chassis.

High output marine alternators are more rugged and therefore more expensive. Over 100A output expect dual belts or a serpentine belt.

[rwidman]

Originally Posted by taxwizz

Add the word "Marine" to any product and double the price.
.

Not the same product. It may look the same but it's not. Don't be fooled.

[rwidman]

If you go on eBay and do a search on your Volvo part number you will find aftermarket alternators that will be a direct replacement for your alternator. Possibly not the same quality as the original but they should work.

Having yours repaired would be my first choice.

[Cheechako]

Dont worry about painted or not. Aluminum is just fine, actually better, unpainted. Especially inside. It's just window dressing to justify what they charge for it. Early Balmar's were unpainted.

[Lepke]

If you have a gas engine or use propane inside the hull, you need an explosion proof alternator. I don't so I use stock GM CS-144s, 140 amps, one wire hookup.

[Elie]

Remember: Volvo do not built alternators. It uses Paris Rhone for its MD22. And many differents compagnies make this kind of alternator, based on a standard frame, very common. It is cheap, and can be made in many different power settings. Don't even try to buy a Volvo branded alternator: Horribly expensive and not better.

[Dockhead]

Originally Posted by Geoff54

Maybe this will help. I don't remember where it came from so hopefully I'm not treading on anyone copyright.

Thank you for posting this! That is exactly what I meant when I advised to pay attention to the wiring scheme.

[wholybee]

Originally Posted by Cromarty

The alternator of my Volvo MD22 engine gave up after 26 years. A new one from Volvo costs a fortune, but I've been told that a car alternator will do just fine.

I've noticed, however, that a automotive alternator has fewer electrical contacts than the one on my Volvo (Perkins) engine. Apparently, there's a separate negative lead to the battery on the boat that is not there on a car.

Can I just go and buy a car alternator of the same capacity (60 Ah) and install it on my Volvo (Perkins) boat engine?

I have this same engine. No, a car alternator is not ok. This engine is isolated, and has no ground connections to it. So any alternator you use must have the frame isolated from the ground connection. If not, then you ground the engine through the alternator.

If you ground the engine, you will create electrolysis in the engine, and cause damage, likely to the heat exchanger.

I recently replaced my alternator with one from partsplayer.com. Part number PP12411N, $129. It was the cheapest I could find, and not much more than the non-isolated version.

[Dockhead]

Originally Posted by leftbrainstuff

No airflow in a boat engine room so . .
.

Speak for yourself! All my boats have had blowers. If yours doesn't, I highly recommend you install one!

I monitor temperature at the top of my engine room, and it never reaches 40C. it's typically less than 10C above ambient temperature. If you want any of the equipment in your engine room to last, then your temps should be similar.

[Cromarty]

Thank you all for this load of very useful information! The alternator that Nigel1 used seems the most suitable, as I have exactly the same engine. The only difference would be the 70 instead of 60 Ah, but I guess that is not a big problem, rather on the contrary.

This is the one: https://www.dfjauto.com/DFJ010261?gc...SABEgLrAfD_BwE