WHAT IS A GOOD GENERATOR ??

[a64pilot]

If your curious, horsepower and torque are actually the same thing, just quoted differently.
I know we have all been taught that there are high torque low RPM engines and high horsepower high RPM motors, but that is incorrect.
If fact look at any dynosheet, if it’s not been doctored the HP and torques curves will corps at 5252 RPM

[Captain Bill]

Originally Posted by Catmandu

Phasor marine.

Best deal under the sun

Phasor Marine Generators

That may be so, but I've contacted three sites that claim to be dealers including the office in Ft Lauderdale and none will call me back or send me a quote. If this is an example of their customer service then there is an explanation of why there are so many people talking about nextgen rather than Phasor. Nextgen called me back right away and I got quotes immediately from a couple of dealers. Phasor and two Phasor dealers took my information and I never heard from them again.

[Pizzazz]

Here is a link to a paper that describes alternator efficiency in detail. The heart of the matter is that low voltage (12V) and high current losses (in the stator windings) lead to very inefficient power generation. While it is possible to operate a school bus alternator at 70% efficiency (24V helps), this only happens in a narrow rpm band. At higher speeds, the generated current increases and the efficiency drops down to 40%. So, the average could be 55%, see the paper if you want more details.

The inverter generators are very efficient because they use high voltage ac generators (to minimize the losses) which is then rectified, converted and then inverted to 110V AC.

The bottom line for our application is that the Honda 2000i is as efficient as it gets. If you want a 12V DC generator, then you need to look for an inverter generator or an optimized alternator that runs at a specific speed, reaching the 70% quoted above.

If we take the energy content of fuel, lose 60% in the diesel combustion, another 30-40% in the power generation, add mechanical losses and solar becomes really attractive. It also means that using electricity for heating water or the boat is highly inefficient but we all knew this already. Off I go with my diesel heater install...

http://www.delcoremy.com/documents/h...ite-paper.aspx

[john61ct]

> Some had an md6 so about 12-15 horse stock. I'm installing an md2b at 23-25 hp.

10 extra horses may well come in handy in certain kinds of emergencies, and a big Alt will eat up more than that.

Personally I'd want to have that switch.

[john61ct]

Originally Posted by a64pilot

If your curious, horsepower and torque are actually the same thing

Not at all. Yes they are related, but not the same, a quick google will explain.

And the fact that for a given engine, both measures scale per rpm along parallel curves, is nothing to do with the comparing their measures between different engines.

A gasoline pressure washer engine, as opposed to a diesel weighing 20x more, may have the same HP rating.

Do you really think they will both have the same limitations on watts-output-from-alts ?

The reason not, is torque.

[newhaul]

Originally Posted by john61ct

> Some had an md6 so about 12-15 horse stock. I'm installing an md2b at 23-25 hp.

10 extra horses may well come in handy in certain kinds of emergencies, and a big Alt will eat up more than that.

Personally I'd want to have that switch.

john I plan on installing with a pto similar to the one on a riding lawnmower belt pto unit so can totally disengage the alternator if needed .

[missourisailor]

Originally Posted by a64pilot

If your curious, horsepower and torque are actually the same thing, just quoted differently.
I know we have all been taught that there are high torque low RPM engines and high horsepower high RPM motors, but that is incorrect.
If fact look at any dynosheet, if it’s not been doctored the HP and torques curves will corps at 5252 RPM

Although you are technically correct, even I had to do a double take on your wording.

Horsepower is the amount of work and torque is the amount of rotational force (given in lb/ft not ft/lb).

Horsepower and torque are mathematically derived from each other.
But as most Dyno's measure torque, most often Hp is computed.

The formula's are:

Hp= (Tq * RPM) / 5252
Tq = (Hp * 5252) / RPM

Not to get too much into the weeds...5252 is a constant from 1 ft circle divided by 33,000 (1 Hp = 33,000 ft-lb's of work per min.).

As 5252 is a constant, computed Tq and computed Hp curves will always cross at 5252 RPM.

[a64pilot]

Originally Posted by missourisailor

Although you are technically correct, even I had to do a double take on your wording.

Horsepower is the amount of work and torque is the amount of rotational force (given in lb/ft not ft/lb).

Horsepower and torque are mathematically derived from each other.
But as most Dyno's measure torque, most often Hp is computed.

The formula's are:

Hp= (Tq * RPM) / 5252
Tq = (Hp * 5252) / RPM

Not to get too much into the weeds...5252 is a constant from 1 ft circle divided by 33,000 (1 Hp = 33,000 ft-lb's of work per min.).

As 5252 is a constant, computed Tq and computed Hp curves will always cross at 5252 RPM.

This is the correct answer, worded much more correctly than my simplistic statement.

[a64pilot]

However back to the generator question.
I’d buy something that is correctly sized for what my need was, and intended use would dictate whether or not I wanted a low RPM continuous duty type or a light weight less expensive intermittent use one.
Further more my decision would be based on prior experience of users and availability of parts world wide and customer service and ease of maintenance, how well the enclosure is designed, ease of removal etc.
I’ve seen more than one really excellent generator shoe horned into a space with no regards as to servicing, most good engine designs have one side that almost everything needed to service is located on, and I have seen that one side being the one facing a bulkhead, fault of the installer of course, but is another thing to consider if your doing the install.
My opinion is whether it’s a DC or an AC machine is far down the points to consider. Now maybe 20 years ago it was much more important, but now it’s so easy to convert large amount of power back and forth from AC to DC and the reverse, it’s just not as big a deal as it used to be.
AC machines seem to be the mainstream, most likely to find parts and expertise on repair, and due to the sheer number of them, more likely to find a good deal.
Product support to me is huge, it can’t be overstated, being able to make a phone call and knowing you will speak to a knowledgeable person is priceless, I value that over most anything else.

[john61ct]

Originally Posted by kenbo

I'm not a slave to the 50% DOD cutoff. I don't find it has as much bad effects as not fully charging them after every discharge cycle.

Actually as long as you do get to true 100% Full the majority of cycles you don't lose much lifetime.

But regularly going well below 50% can lose hundreds of cycles off the back end, especially if they sit there more than a few minutes.

Look at the lifetime cycles vs DoD charts from the top mfg and you can see. Keeping in mind lab conditions are way optimistic compared to real world usage.

[john61ct]

Originally Posted by newhaul

john I plan on installing with a pto similar to the one on a riding lawnmower belt pto unit so can totally disengage the alternator if needed .

As long as you can do so instantly without leaving the helm, or at least that's what I'd want.

Just disconnecting the field current properly removes 99.9% of the alt's load without any mechanical issues.

Same on a land vehicle hauling a heavy trailer in the mountains, if you've modded it to effectively charge a big House bank.

[Dockhead]

Originally Posted by Pizzazz

Here is a link to a paper that describes alternator efficiency in detail. The heart of the matter is that low voltage (12V) and high current losses (in the stator windings) lead to very inefficient power generation. While it is possible to operate a school bus alternator at 70% efficiency (24V helps), this only happens in a narrow rpm band. At higher speeds, the generated current increases and the efficiency drops down to 40%. So, the average could be 55%, see the paper if you want more details.

The inverter generators are very efficient because they use high voltage ac generators (to minimize the losses) which is then rectified, converted and then inverted to 110V AC.

The bottom line for our application is that the Honda 2000i is as efficient as it gets. If you want a 12V DC generator, then you need to look for an inverter generator or an optimized alternator that runs at a specific speed, reaching the 70% quoted above.

If we take the energy content of fuel, lose 60% in the diesel combustion, another 30-40% in the power generation, add mechanical losses and solar becomes really attractive. It also means that using electricity for heating water or the boat is highly inefficient but we all knew this already. Off I go with my diesel heater install...

http://www.delcoremy.com/documents/h...ite-paper.aspx

This is great information -- I learned a lot from it. Thanks for sharing it.

However, shouldn't we look at the bigger picture?

First of all, ordinary car-type alternators are not good for producing bulk power in any case. They're fine for capturing a bit of energy incidentally to propulsion, but not for running the house systems on an energy intensive boat. And efficiency is not the main issue.

So if we're serious about producing bulk power, we're going to have a school bus alternator anyway. And if it's on the main engine, what difference is +/- 10% or even 30% in the conversion efficiency, anyway? If we're charging with the main engine not doing propulsion, then that inefficiency will be lost in the big inefficiency of running a big diesel engine at a small fraction of its appropriate load. That's on the one hand. On the other hand, if we are producing power while the main IS doing propulsion, then the power is almost free, so who cares if you lose an extra 10% or 30% of it?

So if an alternator on the main engine is all you've got, then a Honda generator does make sense to use instead of running the main at anchor. And the efficiency of the Honda's electrical side is not the first or even second reason why you would do that -- the health of the main engine is by far the most important reason why you would prefer to have another way to do it.

A real DC generator run with an appropriately sized engine will be far more efficient than a Honda -- and far more long lasting -- just because it's a diesel engine. It will have a really good alternator on it -- why would you choose anything else? -- so the electrical efficiency won't be worse than the Honda, but again, that is not at all the main factor.

In my opinion, priorities for mechanical power generation should be something like this:

1. Reliable, long lasting, easy and cheap to repair.

2. Quiet.

3. Inexpensive to acquire and install.

4. Convenient to operate.

I think the cost of fuel doesn't even make the list, it's so minor compared to the other factors. Whether the power produced is AC or DC is EVEN LESS important.


Honda scores high on 3, is OK on 2, but poor for 4 (you have to store it and set it up every time you use it). On 1 -- good for reliability, but poor for long-lasting (compared to diesel). Very good for being easy to just take down to a repair shop or even replace if needed.

Heavy duty AC generator (like mine) scores very high on 4 and 2, very poor on 3, and again mixed on 1 -- very long lasting, very reliable, but expensive and difficult to repair if it breaks.

Simple DC generator like Noelex's scores high on everything except 3, where it is medium. Scores exceptionally high on 1 for being extremely easy and cheap to repair if it breaks. In fact, you can carry an entire spare alternator and regulator at modest cost and weight.


So according to these priorities, the case for a simple DC generator is pretty compelling, in my opinion.

As far as operating costs are concerned --

As I said, I don't think operating costs even belong on the list. But for what it's worth:

1. Fuel cost on the Honda will be not less than for other methods, and will be much more if large quantities of power are generated. Issue is the small gasoline/petrol issue versus diesel. Honda is cheap to acquire but has a much shorter useful life, so amortization per hour should be roughly the same.

2. Cost of maintenance is going to be close to the cost of fuel, and is a function of hours. A bit more or less of incremental load on the engine is not going to change this -- yet another reason why you don't care so much about alternator efficiency.



P.S. -- I had a Honda generator on board my boat, which I used mostly for putting a long finishing charge on my batteries in order to save running the diesel generator for hours without a load. But I also played around with it running the boat on it. So I'm speaking from experience. If you generated a lot of power with it, it used a lot of fuel, and it was a PITA to keep it fueled, not to mention paying for the fuel. For generating small amounts of power, it was great. And you didn't have to worry about its health running very small loads (gas engines don't care), so it was great for the finishing charge.

I finally got rid of it -- not for any of these reasons, but because it was really hard to store. You can't keep it inside the main hull volume because of the dangers of gasoline/petrol vapors.

[CatNewBee]

If you are thinking about topping off your batteries only, use solar panels.

A generator only makes sense if you frequently have heavy loads like air conditioner, water heater, diving compressor, water maker, household appliances, washer / dryer and your battery bank + inverter are nor capable to do the job alone.

For just topping up the batteries to compensate light / navionics, a solar set up of the right size maybe combined by a wind generator can do the job easily.

[Pizzazz]

Dockhead,

I agree with most of what you said and I think you are approaching it the right way. The only issue for me is cost (specifically, the opportunity cost of a diesel generator install vs. other things we spend money on).

On a smaller boat (<35 ft), the diesel generator engine is similar to the main propulsion engine (typically a 2-3 cyl. yanmar or equivalent). There is just no point in carrying two similarly sized engines, one for propulsion, another for generation. I typically use my propulsion engine for power generation and if I have to replace it, it can be done for $2-3K which is cheaper than most diesel generators. Then the efficiency comes into play. If you are marina hopping, it is no problem. But if you are cruising, using diesel for heat, eventually you run out of fuel. It just adds up. So, we do need a smaller generator for our boats and currently, the Honda has the sweet spot. On larger boats (>40 ft), the diesel generator becomes a lot more reasonable.

Pizzazz

[CatNewBee]

I would not put a gas engine / generator on board if there is a diesel propulsion engine. I would always prefer to use the same fuel, so I am more flexible in the usage and need less storage capacity. Also gas is more dangerous at sea.

Alternatively you can add a second alternator to your engine to increase the efficiency.