Dedicated DC generator

[owly]

A number of years ago I built up a battery charging generator for a agricultural customer. His equipment would sit for months in a corner of a field, and he was always having to use jumper cables to start it. Impatience was causing problems.... who wants to sit around for half an hour while your pickup charges up your tractor battery? So he would impatiently try to start it before it was fully charged. Starters do not like cranking from a low battery. Amperage is much higher and brushes and commentators die an early death.
This very simple unit used a single cylinder Briggs & Stratton with an ordinary automotive generator and regulator. Put some gas in the tank, pull the rope, and go off and do something else while it's charging... half an hour later, 4 hours later, the next day, etc... come back and it's ready to start....... he loves it!! Very light weight & simple.


It only makes sense to have a tiny diesel with a small DC generator or alternator to charge boat batteries instead of running a general purpose AC generator unit like a Honda driving a battery charger to do the job. An inefficient setup at best. The problem of course is finding a light weight diesel. You will find Lister Petter diesels on a regular basis, and can also find Yanmar, Kohler, Onan, etc. Briggs and Stratton was selling a diesel made by Dihatsu. In terms of weight a gas engine makes the most sense.


Marine diesel mechanics will tell you that running your boat engine just to charge batteries results in a lot of maintenance issues. A fairly large engine under a very light load is a bad idea in many respects. There is also the issue of the charge profile of FLA batteries to consider, where they charge rapidly at first, and the final topping charge calls for higher voltage than your charging system is designed to put out.



Lithium batteries are an improvement on this allowing both a much deeper discharge rate, and a much faster charge rate and more efficient charging profile. Some automotive type generators and alternators have regulators that can be adjusted. That means that you could for example set the regulator for say 16 volts, and feed into a charge controller. Ideally a charge controller would control field voltage... it would be the regulator. This is completely doable. Modern vehicles regulate the alternator from the main computer that controls the fuel injection instead of having an independent stand alone voltage regulator. This is a significant improvement in reliability and battery life.


Due to the extra weight of a generator, it would seem to make sense to charge from the boat engine if you could resolve the issues with that. My idea of an ideal set up would be a boat engine where you could hold intake valves open on all but one cylinder, and shut off the fuel to those cylinders. Again this is doable. They've put compression releases on diesel engines since the early days of diesels which do exactly that. Most injector pumps are piston type, and all you have to do to stop fuel pumping is to prevent the plungers from returning. They are generally cam driven plungers depending on spring return.
If you knock out 3 cylinders on a 4 cylinder engine, the remaining cylinder will work 4 times as hard under the same load... or more due to drag. The result of this will be greater efficiency, because one of the main factors in diesel efficiency is fuel droplet size. The higher the flow through a given nozzle size, the greater the efficiency. As someone who has worked with diesels for well over 30 years, both doing rebuilds, and building up stationary power units for pumping (self employed), I can tell you this really does make a significant difference.



The challenge would be bringing it all together into a system. It would call for an engine manufacturer to specifically design for this, including installing a high output alternator, as well as someone manufacturing a charge controller / regulator that was microprocessor controlled and could be configured to the battery charge profile, and ideally the owner would run Lithium batteries to allow a high charge rate for a short charging time and good load on the engine. The ONLY reason it doesn't exist is that nobody has put it all together yet..... as far as I know.

[sailormed]

".........The ONLY reason it doesn't exist is that nobody has put it all together yet..... as far as I know."

The OTHER reason for me is the ever decreasing price and the convenience of solar.

[Lepke]

These guys sell a small diesel Kubota that can be configured several ways. With watermaker pump, alternator, etc.
http://www.aquamarineinc.net/

[chowdan]

Aren't all alternators AC generators at the heart of the component?

[owly]

Originally Posted by chowdan

Aren't all alternators AC generators at the heart of the component?

The built in alternator on small engines is pathetic... nowhere near what would be ideal. It is designed only to charge starting batteries. Generally a fixed stator coil behind the flywheel which is excited by permanent magnets inside the flywheel. It cannot even be truly "regulated" as a "real" alternator can. Belt driven automotive type alternators are readily available up to around 200 amp, and are fully controllable by an external regulator which would allow a charge controller to ramp up voltage (or down) per the charge profile of the battery you are using.

[owly]

Originally Posted by sailormed

".........The ONLY reason it doesn't exist is that nobody has put it all together yet..... as far as I know."

The OTHER reason for me is the ever decreasing price and the convenience of solar.

Solar is becoming "dirt cheap", but on a boat there are lots of things to interfere with achieving optimal output. Just the shadow of a rope across a panel will greatly reduce output, and of course in some seasons and places the cloud cover really compromises output. That means a lot of solar capacity is needed, and the best way to have it set up is so you can move the panels to where they get full sun. Solar deficit is the ONLY reason for running a generator as far as I'm concerned.

[owly]

Originally Posted by Lepke

These guys sell a small diesel Kubota that can be configured several ways. With watermaker pump, alternator, etc.
http://www.aquamarineinc.net/

This is exactly what I had in mind.... Now all that is needed is a charge controller / regulator combination. It makes no sense to regulate at a fixed voltage and then use a PWM charge controller (chopper) to control charge rate. Interestingly the pumps are as I expected merely ordinary pressure washer pumps... brass head, I wonder what the internals (valves, sleeves, and plungers) are.... Hopefully stainless and brass.


It's been obvious to me for a long time that one could build a cheap watermaker out of an inexpensive pressure washer.... Northern Tool, Harbor Freight, etc.

[a64pilot]

Originally Posted by chowdan

Aren't all alternators AC generators at the heart of the component?

Yes and as they use diodes to recitify the DC into pulsating DC, they are much less efficient than say a Honda running a good shorepower charger.

A good shorepower charger is more precise and way more efficient than any alternator, for example my Magnum MS2812 can be set to drop to float voltage at a precise battery acceptance point, for my 660 AH AGM bank, that is 3.3 amps.
Then the Honda will do other things, like run out vacuum cleaner, or my compressor so I can dive the boat and clean it’s bottom, or if I wanted it to it could run an Airconditioner, or power the TV, or the ice maker, and in my case run the watermaker.
Plus they are available everywhere and you get 2200 Watts for $1,000.

If you search you will find all kinds of threads about DC generators and many think they are more efficient than an AC generator, but they aren’t, and to a great extent it doesn’t really matter a few percent here or there efficiency for a generator is just irrelevant.
But the real killer is that there are only a very few factory machines available, and they cost significantly more due to their low production rates.
AC generators are everywhere and AC power doesn’t require huge cabling like DC does either.
It’s a tough case to try to make to replace a $1,000 suitcase generator with a DC home brew.

Everything you guys want to do is readily available with a Honda running AC appliances. Unless we are talking about energy recovery watermakers, there is just no good reason to run them off of DC and run a DC generator to do it with, whether you have a battery bank in there or not.

It took me awhile to figure out that even with kitchen appliances like blenders and toasters or whatever device it made far more sense to buy AC ones and run them from the inverter or the generator if it was running. The AC appliances are much higher quality and much less money than the hard to find DC ones

DC is converted to AC so easily and efficiently and back the other way with modern inverters and chargers it really doesn’t matter a whole lot which one you have available and a good inverter / charger will do both jobs in one box too.

[RaymondR]

I have done it both ways with a portable inverter genset and battery charger and a couple of gas engine driven alternators.

One of the things I have discovered (at fairly high expense) is that portable AC gensets with their electronics are far less suited to operation in the marine environment than auto alternators, which are designed to survive the dirty, nasty wet and hot environment of the auto or truck engine bay of a motor vehicle.

I have had two gas engine/auto alternator contingency chargers both of which survived for years on the decks of my boats.