Direct-coupled alternator?

[akio.kanemoto]

Greetings all,

Firstly, a quick introduction - I am a very long time lurker - I read CF religiously, but have never posted... I guess there's a first time for everything.

I'm currently in the middle of a long and painful project (3 years... converting a racer to a cruiser - gutted entire boat, redid bulkheads, redid everything... *groan*) and am roughly entering the final stages where I'm actually starting to close the cabins up and paint the interior (real soon now!) before tackling the outside... which means that once the interior is painted, I won't be able to glass in anything new unless I grind the paint off (yet) again etc etc... so am trying to think as far ahead as possible to avoid rework.

One of the things that I have been studiously procrastinating is the issue of charging, however the engine cover is almost complete...

Anyway - without going into the details of the entire system etc- I want to squeeze in as many amps in a daily ~1 hour charging regimen as possible..

So I've been looking at high output alternators and have done the reading and in effect, installing a 300 A large case alternator on my little Yanmar 3gm30 is not exactly recommended...

As for the reasons - I generally see the "side-loading" issue as the primary argument against.

Now, thinking laterally, I was wondering what would be the problem with direct coupling the alternator to the pulley? I.e. no belt... Engine crankshaft pulley bolted directly to the alternator pulley or a flex coupling or somesuch.

I can think of two options for mounting the alternator itself:

• One is on the engine - i.e. two steel beams bolted to the engine mounts/feet themselves (and maybe a few other places) so the engine/alternator moves as one....
• My preferred option: is to heavily glass a platform into the bilge in front of the engine and mount the alternator on that - and have threaded rods or somesuch bolted to the platform and utilize jacking nuts to adjust height/angle etc..

The biggest problem I can see here is that this system will not have the benefit of different pulley ratios etc - so alternator rpm would be the same as engine rpm.

Looking at various alternator output curves - including the Balmar 98, at 3000 rpm, it puts out ~240A... and 3000 rpm is not much to ask of the engine, and this is with zero side-loading.

Can somebody please tell me whether this is going to work or is there something I've missed?

Thanks muchly!

//ak.

[DeepFrz]

Do you already have and engine? If not you might be interested in checking out the Steyr Hybrid

STEYR-MOTORS.com

[akio.kanemoto]

Yep, I already have the engine (came with the boat)..

[James S]

I would think I you want to charge while sitting still that 3000 RPM is a lot.

There are other ways to deal with side loading like a pto with a pillow block,
Or mount a refer compressor or another alt. apposing.

The reality is your crank almost certainly already have side loads on it...you may just be balancing it with an additional alt.

[MidLandOne]

As James has pointed out you will not want to charge at 3,000rpm while at anchor.

One also has to keep in mind the charge that your batteries will accept when charging - for example, for 300A you will need to be thinking of at least 1,500AHr of batteries if they are lead acid.

In the end you could direct couple the alternator and accept a lower output from it when charging at anchor at low rpm's but that would seem a waste to me. Furthermore, as I understand it your engine is only around 20kW - I suspect you will be letting yourself into all sorts of problems putting a 300A alternator on it among which will include the loss of power you will suffer driving the alternator when motoring especially seeing as, assuming your boat is around 40 foot as in your profile, the boat is already likely quite underpowered if intended for use as a cruising boat.

[George Elliott]

Hi I've got a 20 hp Yanmar 3gm that has for the last 20 yrs run 2 100A alternators, a 508 refrigeration compressor and a Cat 247 pump for a water maker. All belted of the engine which is mounted under the floor, so because of the turn of the bilge the belts are exiting the crank on both sides at approx 60 degrees. Obviously I rarely run everything together, but if I'm running at 1500 at anchor it'll do it. I bring the loads on 1 at a time and ramp them up as slowly as possible. I rebuilt the engine at 4000 hrs and the front main bearing showed a bit of scuffing, but was not through the babbit and the crank miked fine. I've read all the horror stories about side loads, but it hasn't been the case with this application. Good luck George

[akio.kanemoto]

I was thinking of wiring in a field disconnect switch or using something like "Small engine mode" on the regulator (e.g. Next Step etc..) when motoring.

While charging at anchor, there should be no problem with dedicating all of the engine's power to charging (assuming the side-load issue is the only issue to deal with here for pulling power off the front).. and the Yanmar service manual states something along the lines of "up to 3400-3600 rpm" being "cruising rpm" and that this is ok for "90% of engine run time".. so I'm not too worried about the engine or needing to use the power for propulsion as there are simple solutions to those (field disconnect).

The question is whether the direct-coupled mounting off-engine approach is going to work? Will there be any problems with vibration? How well aligned does the setup need to be? How much does the average engine move up and down/side-to-side and will I need to mount the alternator on rubber feet like the engine itself? Is there any other problem with hp load on the engine apart from the side-loading?

//ak.

[akio.kanemoto]

Howdy,

That's fantastic news - I don't suppose you have a photo showing placement/setup?

I've got a mounting for a refer compressor pump at the top of the engine, which I was planning on potentially using in the future for a watermaker, but I can't think of a way to balance the loads etc as well - especially with a second alternator off the starboard side of the engine. I'd love to see your setup if that's easier to build!

So you have a 5 groove pulley or somesuch?

//ak.

Originally Posted by George Elliott

Hi I've got a 20 hp Yanmar 3gm that has for the last 20 yrs run 2 100A alternators, a 508 refrigeration compressor and a Cat 247 pump for a water maker. All belted of the engine which is mounted under the floor, so because of the turn of the bilge the belts are exiting the crank on both sides at approx 60 degrees. Obviously I rarely run everything together, but if I'm running at 1500 at anchor it'll do it. I bring the loads on 1 at a time and ramp them up as slowly as possible. I rebuilt the engine at 4000 hrs and the front main bearing showed a bit of scuffing, but was not through the babbit and the crank miked fine. I've read all the horror stories about side loads, but it hasn't been the case with this application. Good luck George

[Chief Engineer]

In a yard I worked in an owner wanted a 5 groove sheave on the front of his Yanmar 4JH-TE.....we tried to talk him out of it but he went ahead and had the sheave made....The vessel was about 42 feet.....when he had the reefer and alternators on
the boat smoked like a mother...and couldn't get out of its own way.....he was going to travel the world....I think he made it to the other side of the harbor and down to Annapolis a couple times before he sold the boat.

[George Elliott]

hey man you sent me a private message requesting photos of the installation on my Yanmar. Can't help you there until the computer gets fixed, but here's a thumbnail of the installatio. Pulled the Hitachi alternator and replaced it with a 508 compressor for the reefer system, used the 2nd sheeve onb the compressor to drive a 100a lestek alternator. Added a 2nd sheeve to the crank pulley and drove a cat 247 pump, used the 2nd sheeve on the pump to drive a delcoo 10dn alternator. The pump and alternator are on a structure I built onto the motor mount support legs, in both cases the 2nd device is driven across the face of the engine. Very simple system, belts last 2 yrs + and it's been complete since 96, engine now has 6000 hrs. Obviously this is a sizeable hp load when everything is engaged, I need to bring it on 1 device at a time or it'll cradle the engine and I can't do any motoring with all this stuff running, but since it's easy to control fields and clutches... For my money it's simpler than direct coupling and since the yanmar pulley is 5" and a 2-1/2" alternator pulley is about as small as you can go you get twice crank speed and an alternator that's configured for lo frpm will give you about 70 a at 1500 engine rpm. Good luck George Ps you didn't include a return email address hence the 2nd post

[slomotion]

Originally Posted by akio.kanemoto

I.e. no belt... Engine crankshaft pulley bolted directly to the alternator pulley or a flex coupling or somesuch.

No real experience. But, the only PTO installations I have seen have U joints or as you say some sort of flexible coupling. I think the direct bolt idea is asking for trouble.