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Old 14-11-2016, 15:22   #1
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Why a generator?

I've been reading about electric generation and storage and there's a lot of info here. I haven't formed any opinions yet about a beefed up alternator vs. a gas suitcase generator vs a big diesel generator but that's not what this really about.

Maybe this answer is obvious to everyone here, but I'm wondering why no one uses a PTO off the diesel engine to run a generator.

Alternators seem to have their drawbacks, gas generators require a separate, less stable fuel, and the big diesels are pricey.

I'm really talking about for charging batteries, not running all night for AC. Just seems like you've got a power source not being used.
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Old 14-11-2016, 15:31   #2
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Re: Why a generator?

Alternators are generators. Not all generators are alternators.... not really sure what you're proposing.
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Old 14-11-2016, 15:42   #3
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Re: Why a generator?

Alternators produce 14 or so VDC to charge your bank at a wide range of RPMs. Coupled with a "smart" voltage regulator they can take very good care of your battery bank. If you need just a bit of AC, the bank can be run through an invertor. Gensets run at a fixed RPM to produce 120V AC 60 cycle. They can also be run through a battery charger to take care of your battery bank. So, what are you trying to achieve that would be better served by some sort of generating device off the front end of the engine that isn't already being done by other means?
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Old 14-11-2016, 16:15   #4
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Re: Why a generator?

Diesel engines are designed PRIMARILY, and thats the key word, to handle heavily loads. And a diesel gen set runs at high speed because it needs the inertia/torque to overcome the load of the electrical motor (alternator) which is connected to the crankshaft.
The boats main engine, irrespective of make or rated output, is designed to run at speed under maximum designed output.
Clearly you don't motor up the ICW at idle speed, you need revs, say 1500 or whatever, to do boat speed....yes I know, very simple.
Understand this...if a diesel engine is running at any speed ie, just above idle or say at 30% revs but is not loaded by the prop via the gearbox then you run great risk of glazing the cylinder wall because of incomplete combustion.
Diesel engines are designed to run, forever, on the governor fully loaded at maximum rated output.
If you run a boats diesel engine at say 1000 rpm so that your whiz bang Balmar alternator is dumping heaps of juice into your batteries, AND THE PROP IS NOT pushing the boat at the same time...then you are risking cylinder glazing. And if you end up with glazed cylinders you'd better have a real deep wallet.
The boats main engine is too big to run a generator off the PTO because the pto load is
n o t h i n g compared to prop load and usually glazing will occur.
Many charge their batteries from the main engine on a stationary boat without adverse effect. Many pay a high price
Diesels must be loaded and alternators d o n o t l o a d diesel engines
El Pinguino is just one of many long distance cruisers who have no problems with cyl glazing.
There are many others who regret abusing their unloaded motors.
Free to you from a 70 year old ex mechanic.
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Old 14-11-2016, 16:16   #5
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Re: Why a generator?

Quote:
Originally Posted by SV DestinyAscen View Post
Alternators are generators. Not all generators are alternators.... not really sure what you're proposing.
Understood. I have no proposals yet, just an attempt at understanding. My current (Get it? Current? ) understanding of electric is weak so I've been doing quite a bit of reading to get up to speed.

I read a rather spirited thread about generating and storing electric, primarily around the use of a watermaker and how to charge batteries on cloudy days. The alternators seemed to have limiters for both time and heat which hurt charging ability. Their design isn't optimal for charging banks of batteries.

I like my Yamaha 2000w generator but adding another fuel on board doesn't thrill me.

And I can't ever see myself spending $5K+ for a diesel generator.

They all have drawbacks and I'm trying to figure out the drawbacks to the PTO. You already have the power source and the fuel. You'd get a lot more out of it than an alternator.

I'm just not seeing what the drawback is.
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Old 14-11-2016, 16:38   #6
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Re: Why a generator?

Quote:
Originally Posted by Crazy Talk View Post
Understood. I have no proposals yet, just an attempt at understanding. My current (Get it? Current? ) understanding of electric is weak so I've been doing quite a bit of reading to get up to speed.

I read a rather spirited thread about generating and storing electric, primarily around the use of a watermaker and how to charge batteries on cloudy days. The alternators seemed to have limiters for both time and heat which hurt charging ability. Their design isn't optimal for charging banks of batteries.

I like my Yamaha 2000w generator but adding another fuel on board doesn't thrill me.

And I can't ever see myself spending $5K+ for a diesel generator.

They all have drawbacks and I'm trying to figure out the drawbacks to the PTO. You already have the power source and the fuel. You'd get a lot more out of it than an alternator.

I'm just not seeing what the drawback is.
What part of my post, which I wrote just for you, was as clear as mud.
Anyway, do what I do, DON'T get thrilled about tha Yamaha....but use it anyway.
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Old 14-11-2016, 16:49   #7
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Re: Why a generator?

A lot of commercial boats have a pto driven generator, but use it when operating the main for propulsion. Also there use to be a hydraulic driven generator that many used. But as already said, If you are going to run your main at speed and just drive your pto generator, you will glaze the cylinders/sleeves. The solution for glazing is almost always an overhaul. There goes your $5 grand you saved on the diesel generator.
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Old 14-11-2016, 16:54   #8
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Re: Why a generator?

Quote:
The boats main engine is too big to run a generator off the PTO because the pto load is
n o t h i n g compared to prop load and usually glazing will occur.
Many charge their batteries from the main engine on a stationary boat without adverse effect. Many pay a high price
Diesels must be loaded and alternators d o n o t l o a d diesel engines
El Pinguino is just one of many long distance cruisers who have no problems with cyl glazing.
There are many others who regret abusing their unloaded motors.
Free to you from a 70 year old ex mechanic.
I've wondered about this on charter boats....."run the engine at least 2 hours a day to charge the batteries" policy.

If not motoring that means the engine(s) are running unloaded A LOT. I'm not sure what most private owners do, but this is an issue i am concerned with in regard to my next boat purchase.
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Old 14-11-2016, 16:55   #9
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Why a generator?

I'd love to have a PTO that could drive say a 5 kw gen, that would not glaze my cylinders and my Autoprop would I believe reduce pitch to keep me from overloading my engine when I used it.
But, I don't have a PTO, so that is the end of that
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Old 14-11-2016, 16:59   #10
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Re: Why a generator?

Quote:
Originally Posted by brianlara 3 View Post
What part of my post, which I wrote just for you, was as clear as mud.
Anyway, do what I do, DON'T get thrilled about tha Yamaha....but use it anyway.
Ha! Your first post wasn't up there when i typed mine.

But I did just read it and that makes sense. I thought it might have something to do with the loads being different. I haven't looked but I suspect the HP rating on the diesel generators is significantly less than 30ish HP like the engine. I 'm suprised though that running a generator would not require similar output as running the prop though.

Interesting story about that Yamaha. Hurricane Sandy is roaring up the coast a.few years ago. I'm just outside of Philadelphia and it's sounding bad. Not a generator to be found, I just want something to run a sump pump. I go on Amazon and there's one in Arizona. Prime Overnight used to be cheap so I got it shipped overnight across the country for $4.
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Old 14-11-2016, 17:06   #11
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Re: Why a generator?

Quote:
Originally Posted by brianlara 3 View Post
What part of my post, which I wrote just for you, was as clear as mud.
Anyway, do what I do, DON'T get thrilled about tha Yamaha....but use it anyway.
And I forgot to say thank you for writing it just for me.

I hope someone else can use the info too!
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Old 14-11-2016, 17:10   #12
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Re: Why a generator?

Quote:
Originally Posted by tkeithlu View Post
Alternators produce 14 or so VDC to charge your bank at a wide range of RPMs. Coupled with a "smart" voltage regulator they can take very good care of your battery bank. If you need just a bit of AC, the bank can be run through an invertor. Gensets run at a fixed RPM to produce 120V AC 60 cycle. They can also be run through a battery charger to take care of your battery bank. So, what are you trying to achieve that would be better served by some sort of generating device off the front end of the engine that isn't already being done by other means?
Brian did a good job of explaining the drawbacks of the PTO but in case you didn't see the post below I mentioned I had read that alternators have limiters which can hamper their ability to charge batteries. Not that they can't do it, but there are issues. I was trying to think of an alternate.
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Old 14-11-2016, 17:30   #13
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Re: Why a generator?

Quote:
Originally Posted by Crazy Talk View Post
And I forgot to say thank you for writing it just for me.

I hope someone else can use the info too!
You are welcome Crazy. And to be honest, I felt a little bad after my last (caustic) post, thinking that possibly the posts might have not talked to each other in the ether.
Glad you can see the reasons Crazy.
Re: your shopping....I'm Sydney Oz and your needs were double dutch to this old guy.
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Old 14-11-2016, 17:36   #14
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Re: Why a generator?

Quote:
Originally Posted by Crazy Talk View Post
Ha! Your first post wasn't up there when i typed mine.

But I did just read it and that makes sense. I thought it might have something to do with the loads being different. I haven't looked but I suspect the HP rating on the diesel generators is significantly less than 30ish HP like the engine. I 'm suprised though that running a generator would not require similar output as running the prop though.

Interesting story about that Yamaha. Hurricane Sandy is roaring up the coast a.few years ago. I'm just outside of Philadelphia and it's sounding bad. Not a generator to be found, I just want something to run a sump pump. I go on Amazon and there's one in Arizona. Prime Overnight used to be cheap so I got it shipped overnight across the country for $4.
Crazy, re the generator not requiring similar as the prop.
On this proposed generator, could you imagine this generator pushing the boat into a 10knot wind at hull speed ?
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Old 14-11-2016, 17:59   #15
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Re: Why a generator?

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You are welcome Crazy. And to be honest, I felt a little bad after my last (caustic) post, thinking that possibly the posts might have not talked to each other in the ether.
Glad you can see the reasons Crazy.
Re: your shopping....I'm Sydney Oz and your needs were double dutch to this old guy.
No harm done. At least you didn't call my name stupid. That would have hurt my feelings.
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