Boat Generators

[Portager]

I’m really not a fan of AC generators on boats. The problem is AC generators must maintain a constant speed to produce the required frequency and, since the generator must be sized to meet the peak power load plus margin, most AC generators operate seriously under loaded the majority of the time. This under-loaded condition shortens engine life and makes a lot of unnecessary noise.

I’ve tried to eliminate AC power loads and used inverters to power many AC loads but air conditioning systems remain a significant exception.

My proposed solution is a diesel engine driving a variable displacement hydraulic pump and a hydraulic motor driving an AC generator. The variable displacement pump allows the engine speed to be independent of the generator speed, so engine RPM can vary with loading. A speed controlled hydraulic motor will maintain the AC generator at the required 3600 RPM (60 RPS) and a hydraulic accumulator will dampen out power surges. An additional benefit is that the hydraulic system can directly power other boat systems such as the anchor windlass and davit lifts which typically require very high DC currents.

By making the generator engine and hydraulic pump slightly larger and attaching a hydraulic motor/pump to the main shaft, the generator can double as an auxiliary drive to provide a get home capability and the main engine can power the hydraulics. This eliminates the requirement to run the generator while underway in order to air condition the cabin.

Since the typical battery charger is only 25 amps, using an AC generator to recharge a large battery bank is a very slow process, which contributes to extended periods of generator operation at low loads. To reduce the recharge time, I plan to have a high output alternator such as the Balmar 98-24-220-BL http://www.balmar.net/98dimensions.htm which will produce 200 amps at 3600 RPM and shortens the bulk charge time by a factor of 8. If you wanted to shorten the recharge time further and/or provide an online spare, you could add a second alternator and combine them with the Balmar “Centerfielder” http://www.balmar.net/PDF/Centerfielder.pdf .

Regards;
Mike Schooley

[CDBarry]

The variableinput generator is an off-the-shelf item that has been used in small commercial and military craft.

[Portager]

Thanks for the input CDBarry.

I think your referring to "variable speed generators". To the best of my knowledge, they come in three flavors.

The smaller devices use an alternator to produce DC and an Inverter to change the DC to AC. These systems are usually 1 to 2 kW and too small to run boat AC systems.

The middle size units use continuously variable transmission to allow the engine speed to vary but keep the generator speed constant. All on these units that I aware of are gasoline driven.

The larger units use a hydrostatic transmission to allow the engine speed to vary but keep the generator speed constant. All on these units that I know of are too large for a boat.

The variable speed generator only solves part of the problem. I would still like to combine the generator and auxiliary functions into a single engine and I would like high DC output to recharge the battery bank faster. The hydraulic system provides great flexibility and allows me to meet multiple requirements with a single engine. It also allows me to power all my electrical systems from the main engine while underway without running the generator.

Regards;
Mike Schooley

Airconditioning units are not frequency sensative nor are the sensitive to wave form. Running the generator at constant RPM for the airconditioner is not necessary.
Charge rates on batteries are a function of the voltage of the charger. You can get an AC driven charger that will charge the batteries just as fast as any alternator. Don't get me wrong, a high output alternator is a great thing to have and a necessity on many boats, but don't let the sales men BS you into believing that there alternator is some how doing something no other charger can do.

[Portager]

Please show me where I can get a 200 or 400 amp, 24 volt battery charger. I've been looking for one.

Regards;
Mike Schooley

[yipster]

thats an interesting setup but almost custom. got a four stroke honda X1000. it works fine but figger its not an efficiency sample. hook it into the boats 220 current while using AC but for keeping the battery's loaded i need shorepower, maybe a windmill or solar cells?

still thinking... yipster

Here is a link to a site that sells industrial chargers.
http://www.macmc.com/chargers_industrial.htm
Many units are availible with up to 1000 amp capacity but I really don't think they will do you any good. Just having 1000 amp capacity doen't mean that you will charge the batteries at that rate. All batteries have an internal resistance that cause a voltage drop when ever the battery is charged or discharged. To fully charge a 12 volt battery you will have to use a power supply with a voltage greater than 12 volts. If you check you car battery when the car is running you will find that it charges at about 14 volts. If you increase the voltage of the charging system you can increase the current draw and charge the battery faster but at the expence of battery life. For your 24 volt system you will find that it charges at about 28 volts. If you put an amp meter on you system you will find the amp being drawn by the batteries while charging is a function of the batteries capacity and its charge state. If you have a 1000 amphour battery bank that is halfway discharged you will probably draw between 60 and 120 amps at 28 volts. Having an alternator that has a max amperage of more than 120 amps wont charge the batteries any faster. Your 200 amp alternator won't charge the batteries 8 times faster than a 25 amp charger because your batteries won't draw 200 amp while charging unless you have a several thousand amphour battery bank that is deeply discharged.

[Portager]

Thanks deseely;

I really appreciate the link. Those are very impressive chargers. I was unaware there were chargers that large. Unfortunately I think they are too large for by boat.

Originally Posted by deseely

Many units are availible with up to 1000 amp capacity but I really don't think they will do you any good. Just having 1000 amp capacity doen't mean that you will charge the batteries at that rate.

Actually if you use absorbent glass matt (AGM) batteries, they have much lower internal resistance than flooded lead acid batteries. Flooded lead acid batteries shouldn’t be recharged in less than 4 hours, but AGM batteries can be recharged in under 1 hour. So if I have a 1,000 amp-hour battery bank I could put a 1,000 amp charger to good use, provided it has an AGM battery charging profile.

Regards;
Mike Schooley

http://www.zena.net/htdocs/alternato..._alt.shtml#Top

[Victor Möller]

Hi!


A way to make sure that your AC genset runs at optimal load is to use Victron Energy's Phoenix MultiPlus inverter/charger. Take a look at:

http://www.victronenergy.com/product.php?productid=147

Worth reading is the "Electricity on Board" pdf found on the same page.

Regards, Victor

[MattZ]

A lot of sound deadening insulation can be purchased for the cost of the hydraulic system you are proposing to keep the noise of the diesel engine down. Also consider the windage noise of a generator, especially a 2 pole 3600 RPM model. You may want to use a 4 pole 1800 RPM generator head.

[terabika]

far to complex! run a compressor off an engine and use an autostart function with thermostat. much parasitic lose through converting mechanical to electrical and back. I drive 18 wheelers and the refrgerator units are diesel engines running compressors and these things run almost 24/7 for years! little failure....I have found that it is best to look to an area (outside the marine industry)that has the most need for a given technology and explore it for answers for that is where the most efficient permutation shalll be found. except for local farmers markets, everything you get which is cold you get via a refer truck. think about it! For a while when I was in a borgoues comma, I wanted AC in my Catamaran and this was by far the best bet....I got over it though, even in florida.

[buckknekkid]

nice lead, truckers and rv parts are much cheaper and will work in a marine environment.

[joefaber]

perhaps solar photo voltaic panels.
if you can see, you got electricity.
i've several small panels that generate 12v@0.375A sqft. (20amp capability would be about 55sqft)

[cyclops]

Deseely . You are dangerously wrong that AC powered air conditioners are not frequency sensitive. The size of the motor and the amount of iron in it determine the frequency it will safely run at. If you ment DC air conditioners, say so.