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tom1263 · 30-08-2013, 14:13

Yes, why not, but the system uses a three-phase generator in which the output is unregulated. Monitoring is recommended.

pbiJim · 30-08-2013, 15:13

Quote:

Originally Posted by goboatingnow

Ive seen small ones in Lidl or Aldi for about 300 quid.!

Would you mind pointing me towards those perspective sources?

Thanks,
Jim

**Lepke** · 30-08-2013, 15:52

These guys sell a 1 cylinder Kobota diesel with high amp alternators and other custom setups. i.e. watermaker pump, hydraulic pump, etc.

Aquamarine, Inc - Home

Lepke

**Dockhead** · 30-08-2013, 15:59

Quote:

Originally Posted by pbiJim

Would you mind pointing me towards those perspective sources?

Thanks,
Jim

Prospective.

Here's one source:

IG 1000 Suitcase Generator Kipor IG1000 Pure Sinewave Digital Generator. | eBay

Kipor is what you want if you go El-Cheapo. The best of the cheap ones, but not nearly as good as Yamaha or Honda.

But if it were me, and the choice was between a home-built, and a Kipor, I'd definitely go with the Kipor.

RaymondR · 30-08-2013, 23:32

Quote:

The motor that I'm looking at develops full HP in the 6,000-7,000 rpm range. I don't really have a feel for how fast an alternator is going to want to spin. I'm not sure where to look for data on how fast they want to be spun either. Do you have any suggestions where I might look?

Page 22 of the Balmar product guide gives a set of useful data. 6000rpm is the maximum they list for all of their alternators and one could assume that this is their recommended maximum speed.

Have a look at the attached spreadsheet. I have taken the Balmer figures for rpm versus amps and converted to watts then horsepower. The first thing to note is that after the alternator reaches a certain speed the allowable amps flattens out. This is good because it tells us that whilst we can rev the alternator up to 6000 revs, we don't have to to get almost the full rated power from the alternator - according to Balmer we can get the full 120 amps out of the alternator at 4500rpm and would require a minimum of 2.33hp to do so.

Since I am a very skeptical sort of sole I would go for at least a 4hp motor and as I intend to use a Honda 4 stroke would probably use the 5.5hp model.

RaymondR · 30-08-2013, 23:46

That's "soul" sorry and the spreadsheet did not attach.

I converted the amps to hp by amps x 12/1000 to get kilowatts then divided by 0.7457 to get horsepower required at 4500rpm for a direct coupled motor/alternator.

Delfin · 31-08-2013, 20:32

Hope this technology works out. LiquidPiston unveils its ultra efficient, small diesel engine — Tech News and Analysis

pbiJim · 01-09-2013, 18:06

The Aquamarine option is way out of my price range as well as too big. The suitcase generator on e-bay only puts out 5 amps at 12vdc. The liquid piston motor looks interesting, but I don't see pricing & it doesn't look like it is available yet.

So far it looks like I am still going to try a weed whacker motor with a moderate size alternator & see what happens.

Thanks again for all the plausible suggestions. And Dave, if you can point me to the 300 quid option that you spoke of, I would still like to look into that.

Regards,
Jim

Opie91 · 01-09-2013, 19:10

Keep us posted, I have often thought about a mid sized DC generator. If only I could find a small reasonably priced reliable diesel engine.

tom1263 · 01-09-2013, 23:26

Quote:

Originally Posted by Opie91

Keep us posted, I have often thought about a mid sized DC generator. If only I could find a small reasonably priced reliable diesel engine.

Cheap diesel engines are only air cooled and noisy, the only one i know is the Farymann 15/18w. A good choice is to buy a second hand.....

**Dockhead** · 01-09-2013, 23:29

Quote:

Originally Posted by pbiJim

The Aquamarine option is way out of my price range as well as too big. The suitcase generator on e-bay only puts out 5 amps at 12vdc. The liquid piston motor looks interesting, but I don't see pricing & it doesn't look like it is available yet.

So far it looks like I am still going to try a weed whacker motor with a moderate size alternator & see what happens.

Thanks again for all the plausible suggestions. And Dave, if you can point me to the 300 quid option that you spoke of, I would still like to look into that.

Regards,
Jim

Keep in mind that most ready-made generator options output AC and presume you will be using a battery charger. I imagine Dave's 300 quid option was a Kipor like the one I steered you towards. You have a battery charger, a multi-stage one? Unless you are simply never near shore power, you'll need one anyway.

And by the way, with a DC generator, you will need an external regulator for the alternator, which is not cheaper than a decent small battery charger. Without external regulation, charging a deep-cycled battery from an automotive-type alternator will be slow and incomplete.

**Dockhead** · 02-09-2013, 01:12

So, to summarize this advice:

1. If you are going to home-build a generator, then it should be a DC generator, since small home-built AC generators are not really practical. For reasonable battery charging performance, you will need an external regulator for the alternator, like this: Balmar Multi-Stage Voltage Regulator. Adverc is another good maker of these. Here's yet another way to do it: Sterling Power ProAlt C Alternator to Battery Charger

2. If you are going to home-build a generator, take a little time and engineer it properly. You will be wasting your time and money if you don't design it for sustainable demands on both engine and alternator. You don't need to pee on the electric fence yourself, so to speak -- others have gone before you and the data is available. The engineering is not rocket science.

3. If you go with a cheap store-bought generator (which I recommend if your own time is worth more than $1 per hour), it should be an AC generator. It should be AC because (a) there are no mass-produced cheap small DC generators, since 99% of buyers need AC power; and (b) store-bought DC generators, unless they are very expensive, do not usually have proper regulation for charging deep-cycle batteries. So if you don't already have a battery charger, you will need a small multi-stage battery charger like this: Victron Blue Power 12V 17A 230v Battery Charger. Bigger or smaller depending on the battery capacity (amps of charger should be 15% to 20% of nominal amp/hour capacity of the batt).

It is important to keep in mind that car-type alternators will not do the job without external regulation. They are made to run a car's electrical loads while the engine is running, and to replace -- very inefficiently, but efficiency is not required -- the very small amount of battery power used up in starting. They do not produce enough voltage to recharge a battery which has been deep cycled -- that is, a battery which has been used as a power source without an engine running. As a result, if you attempt to recharge a deep-cycled battery with an unregulated car alternator, it will stop putting much power into the battery long before the battery is well charged, leaving it chronically undercharged while requiring unnecessarily long generator runs. This is especially important in your application, where you will be hauling the generator in the dinghy on board in order to charge, and will not want to charge longer or more often than you possibly can.

If you are severely budget limited, then I would go with a Kipor suitcase gen and something like a small Victron multistage charger. That is probably about as cheap a solution as you will find; the parts for a home-brew DC gen, once you figure in a regulator for the alternator, will probably cost more, not even getting to the value of your own time. However, if you want to built your own genset just for the fun of it, and not because it will be cheaper -- that will work perfectly well if you engineer it correctly.

I forget whether or why you rejected solar; this might be better than any of the above solutions, without really being more expensive. You would need only a pretty small panel.

**Dockhead** · 02-09-2013, 01:30

Quote:

Originally Posted by Opie91

Keep us posted, I have often thought about a mid sized DC generator. If only I could find a small reasonably priced reliable diesel engine.

Here's one: Hatz Diesel Engine — 4.6 HP, 3/4in. x 2 7/16in. Shaft, Model# 1B20X-9901 | Diesel Engines| Northern Tool + Equipment

I think the Subaru-Robin ones are better, but I don't know where you can buy them.

Small diesel engines will be 4x or 5x as expensive as small gasoline (petrol) engines, which is the nature of the beast. They are more expensive because they are more expensive to make (injection pump versus carb, plus must be much stronger internally), plus, they are made in much smaller quantities.

RaymondR · 02-09-2013, 01:51

I initially went the diesel engine design route until I found out what Dockhead has posted, they are very expensive and I could wear out four or five petrol engines for the price of one diesel of the same horsepower. Since I have to carry petrol for the outboard fuel and safety wise I am no worse off.

Since the 12V units are primarily used for bulk charging or emergency starting or boosting the auto regulator is not a problem and they are cheap to replace if you blow them up.

The internal regulators on the Bosch alternators I have standardized on have a voltage sensing terminal which normally is wired to the battery terminal so that the regulator is not fooled by the voltage drop through the charging wiring. If you want to boost the charging voltage and current wire put forward biased diodes in series in the voltage sensing conductor you get roughly .6 volts drop for each conductor and this fools the regulator into a higher output.

Just go ahead pbiJim and build your gadget with the weed whacker and try it out, if you don't get enough power output put a bigger engine on it. The best way of learning about a lot of things is just to make a start and do it.