Do You Need A Generator?
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How about DC Generators?
I have not crunched any numbers but converting down from AC back to DC is fraught with losses in efficiency. Why not just use DC ? For ac loads an appropriately sized inverter should do the trick. Although I personally would try to avoid having 220v AC anywhere on my boat.
Food for thought…
Rgds
Patrick
Hi Patrick,
A very good point that we have discussed at some length in the comments to other posts. The bottom line seems to be that while DC generators are undoubtable more efficient than making AC and then converting to DC, the problem is reliability. AC generators are made in large volume for commercial purposes and are extremely reliable. DC generators are made in small volume, mainly for yacht use and we have had a large number of reports of problems with these units.
I see your point regarding the production volumes. On the other hand it baffles me a bit to hear of lots of problems with them, what sort of problems ? . I have never actually used/maintained one so I have no first hand experience with DC generators but … DC generation is not an exotic science …. your are still looking at an alternator and a some regulation circuitry. Or am I completely off base here ?
Regards
Patrick
Hi Patrick,
You are right, the technology is not complex. However, never underestimate the combination of low production volume, no proper prototype testing and no proper quality control to produce products with very high fail rates. Come to think of it, much of the yacht gear market is living proof of that! That’s why Phyllis and I use commercial gear whenever we can fit it in, even when it is substantially more expensive than the yacht equivalent.
For example, our Northern Lights generator—designed and built for commercial use, on and off the water—has run reliably for 22 years with only one failure—an oil pressure sensor. Contrast that with the yacht DC generators that, from what I’m hearing, have a hard time running for more that 20 months without problems. Alternator alinement, overheating, regulator problems, burned bearings, and on it goes.
I understand that existing “yachts DC generators” are in fact home hobbyist equipment sold to yachtsmen, and are much lower quality than typical “yacht AC generators”, because the yachts DC generator market is not big enough to justify specialized fabrications (better than home-hobbyist and not as good as professional equipment..).
Being a electrical engineer by training, I think it is pretty easy, and not very expensive, to assemble yacht-AC-generator type diesel-engines and alternators to build very decent yacht DC generators, but that is my opinion and you won’t find them today on the market.
Technically speaking, it looks very easy to assemble a small genset diesel engine with a marine-grade DC alternator+regulator and associated paraphernalia.
The diesel engine could be the same as Fisher-Panda’s gensets (Farymann brand, made in Germany, looks like all Fisher-Panda engine paraphernalia are stock farymann parts….). The alternator should be a 2500 rpm, 4KW heavy-duty or marine type, directly coupled to the engine.
As an added bonus, diesel-engine regulator might be coupled with alternator-regulator and perhaps batteries management system to slow-down the engine when operating at limited power.
This solution seems technically obvious and should not be very expensive. Point is that today’s market for this kind of equipment seems too limited to allow the development of commercial/industrial offerings in that field, but I guess many good mechanics can assemble that using standard components.
The DC generator situation basically boils down to there being a lot of options that are light duty, low production volume, and aimed at markets where gear failure is more easily tolerated.
If you’re on a tight budget and want a DC generator for battery charging only, you could do far worse than to mount a 150 amp truck/bus alternator to one of the small industrial diesel engines that are normally used for refrigerated trucks, mini excavators, etc. Assuming you make sufficiently beefy mounts and brackets, such a setup is quite reliable and can be easily repaired in the field with common parts.
If you want an off-the-shelf unit, and you want it to be long-lived and reliable, then a conventional AC generator (the kind with big heavy coils and no fancy electronics) is probably the way to go.
And for something entirely different: An engine driven variable speed AC generator that is not a DC alternator plus an inverter.
http://www.marine-surveyor.com/newsletters/9711.html
It looks very much like a DC alternator plus a regulator, an inverter and a switch in the same box.
The main point is that you don’t need an intermediate battery when using this system, because the power regulation logic of the inverter seems to regulate directly the alternator’s excitation circuit. Plus you may hope that a regulator plus an inverter in the same box are more efficient than a regulator and an inverter in 2 separate boxes (?…).
Last, this system can generate up to 3.5kw (30A. * 115V) from a 150hp engine (about 110KW), that is at most 3.2% of the engine output. I think it is not a good idea to keep that engine running at idle just to use the microwave or the curling iron with this device. Corresponding diesel-fuel costs and diesel-engine amortization/repairs costs might well be prohibitive…
Hi Laurent,
No idea whether this is a useful system or not.
Looks like a DC alternator plus an inverter/controller to me as well, even though they imply otherwise.
It does come in sizes up to 18 kVAwhich would have an input power requirement of 34.2 hp. Certainly enough to load the typical propulsion engine in a 40′ sailboat. Of course, would you have the capacity to use or store that much output?
For a boat with an autopilot but no freezer or air conditioner, I usually lean towards specifying no generator. Instead, I’ll often call for a larger battery bank and larger main alternator than might ordinarily be expected. The autopilot can then run from the batteries alone for at least a day, ideally more, along with all other on-passage loads. And the bigger the battery bank, the greater the charging current it can accept.
With perhaps 300 Ah (@ 12V) more battery and 50 amps more main alternator than would be typical, you can come closer to properly loading the main engine when running it for charging purposes. A big alternator drawing 5 hp from a 30 hp engine is a big enough load to get the engine into a comfortable (although admittedly not optimal) region of its fuel map. The extra batteries take up a fair bit less space than the generator would.
If you want air conditioning or a big freezer, you need a generator. (But I do think it’s easier, and an awful lot cheaper, to simply decrease clothing and/or increase latitude if you find the weather too hot.)
I think that the charging profile of new battery technology could change the analysis. While I am not rushing out to buy lithium ion batteries for my offshore boat today, hopefully the EV industry will be pushing the limits and the reliability factors for us in the near future (very near?). Almost all new battery technology is focused on aggressive (fast) charing profiles which will ultimately eliminate the need for a generator and allow sailors to use main engine charing more efficiently.