How to install a second marine alternator on any engine

How to add a second marine alternator to just about any engine


Modern cruising vessels have high electrical demands, where refrigeration, radar, laptop computers and even plasma TVs are the norm. Keeping batteries charged is a challenge, and fitting a second alternator, says Scott Fratcher, is an easy solution

Marine alternator installation

Want more charge amps? Less time running the engine to keep the batteries up?

More amps often means either a bigger alternator, or better yet, a second alternator which adds significantly more potential to the boat than only increasing the amperage of the original alternator...


The rest of the free report with photos is available here-

http://www.tongacharter.com/report-alternator.htm

 

this is the second tonga charter article I have read and I am comming to the conclusion that what they say should be treated with scepticism..

Two alternators yes BUT if you have starting and house batteries you need 25A of output per 100 ah of house battery .....you will not charge a battery at over 25a ( and that current will be falling ) with an alternator ....ever seen a battery charged at 100A ...needs about 20v and it gets very hot and gasses a lot .
Also it it common to have one alternator for the starting battery and one for the house battery ....When the starting battery is fully charged the starting alternator is switched in ( automatic ) to assist the house battery alternator .
If the house alternator is rated at 25a for every 100ah of house battery then you dont need to do this .....If anyone interested can provide diagrams


Why stop at 2 alternators ???

Perhaps Scot Fratcher can answer these points ....

 

Triple alts

Pistenbroke- Thank you for the thoughtful questions. The article link is about mounting a PTO device to most any engine. Thus the article is about methods of mechanical attachments. How to add a pulley to the front of a crankshaft and such. This article is much of what I learned after building hundreds of second alternator kits over the last 20+ years.

To be clear I no longer build second alternator kits. I did the designs for the Yanmar second alternator kits that fit the JH4 series exported from New Zealand. I still answer the tech questions but the Yanmar alt mounts are built, sold and exported by Seaquip in Auckland

Your questions seemed more about regulators. I have put out some information on regulators that can be seen here-

http://www.tongacharter.com/report-alternator-ideas.htm


This link is a series of questions that I answered about high output alternators when this article first appeared in print a couple years ago. You have to scroll down about half way to get to the q&a section.

You ask why stop at two alternators? That's a good question. Steve D was building the Sundeers. In correspondence he mentioned that in order to balance the load on the crank Yanmar wanted him to use two alts plus the original. I have worked on a few of these systems over the years and it's a lot of extra wires and regulators for not a lot of extra gain. I understand why the third alternator was added (manufacturer warranty requirement), but the bang for the buck is quickly lost.

Consider a second alternator kit from Yachtwork.com costs about 600USD and a Delco 160 amp alternator costs 150USD. Add in the cables, belts and extras and that means for less than 1000USD a yacht with a JH4 series Yanmar can produce about 240 amps. That is a lot of grunt for the buck and worth the effort/cost to many yachts.

A triple alternator mount is not commercially produced anywhere so it would cost upward of 2K to have built. The crank pulley would extend another belt width and thus the crank leverage loads would increase. Most engines limit the amount of hp allowed from the front of the crank. Seven hp at max rpm's is a common figure. Seven hp can be adsorbed from a single large frame alt.

So, why not use a triple alt setup?

• Cost,
• low gain from the third alternator
• no gain in redundancy
• Warranty hp issues

Thanks again for asking and keeping the discussion going.

Regards
Scott

 

Putting in the photo of 4 alternators was a joke ...

Well i dont find anything practical in your link to help people wire up two alternators in a starter battery priority arrangement ....Think I will give tonga charters a technical miss ...

 

I have to agree Piston.

If you run electrical motors maybe, or have that many battery banks, maybe,

One should also keep in mind that turning those alternators takes power, and fuel.

As you rightfully pointed out, a battery requires only so much current initially, after that the current will fall back to whatever is required.

A small 800W 230V power generator can supply 80A if stepped down through a 230 - 10V transformer. You need a suitable rectifier and smoothing caps to bring the output to 14V. The advantage is a small motor running using less fuel.

 

the point often missed is that its fine to have one alternator for the starting battery and one for the house battery BUT if you combine the two outputs to charge the house faster then you must arrange so that the starter battery is not drained into the house battery .....and its not just a diode or a big switch if you want it automatic.

MY experience is with canal boats ( UK style ) with about 400 ah in the house system ..

Your 800w generator into a "battery charger" is only good for 200Ah ( 800 div by 14.4 is 55A ...thats one heavy transformer ....

 

Thank you for asking abut how to charge two battery banks from two alternators and then automatically divert the surplus charge from one alternator into the second bank.

The standard system we tend to use on yachts is a VSR or voltage sensitive relay. One can be seen here-

http://www.bepautomotive.com/showproduct.cfm?productid=1023

The VSR has replaced the diode splitters from the 80's and have a dependable track record in the field.

Thanks for keeping the discussion flowing.

Scott

 

like I said you dont understand the problem ..if you have a fully charged starting battery and connect it to a 400AH discharged house battery using a simple VSR then the start battery discharges into the house battery until they equalise ...then the whole lot comes up together ...not what we want .....the start battery should stay fully charged and the two alternators charge the house battery ......

 

Pistn
The relay is volt and current sensing so it stops the drain.
I think they are on the balmar or victron web site,
to prevent exactly what you describe
cheers