The Offshore Voyaging Reference Site

Do You Need A Generator?

As a voyager who has had a generator for the past 20 years, it suddenly struck me that for most usage profiles, the decision, generator or not, is an amazingly simple one.


Login to continue reading (scroll down)

More Articles From Online Book: Electrical Systems For Cruising Boats:

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options
  22. Replacing Diesel-Generated Electricity With Renewables, Part 2—Case Studies
  23. Efficient Generator-Based Electrical Systems For Yachts
  24. Battery Bank Size and Generator Run Time, A Case Study
  25. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  26. Eight Steps to Get Ready For Lithium Batteries
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Black Outs
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Batteries Buyer’s Guide—Part 1, BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Part 2, Balancing and Monitoring
  32. Lithium Batteries Buyer’s Guide—Part 3, Current (Amps) Requirements and Optimal Voltage
  33. 11 Steps To Better Lead Acid Battery Life
  34. How Hard Can We Charge Our Lead-Acid Batteries?
  35. How Lead Acid Batteries Get Wrecked and What To Do About It
  36. Equalizing Batteries, The Reality
  37. Renewable Power
  38. Wind Generators
  39. Solar Power
  40. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  41. Battery Monitors, Part 1—Which Type Is Right For You?
  42. Battery Monitors, Part 2—Recommended Unit
  43. Battery Monitors, Part 3—Calibration and Use
  44. Battery Containment—Part 1
71 Comments
Oldest
Newest
Inline Feedbacks
View all comments
Patrick Genovese

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

Patrick Genovese

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

Laurent

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.

Laurent

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.

Matt Marsh

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.

RDE (Richard Elder)

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

Laurent

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…

RDE (Richard Elder)

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?

Matt Marsh

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.)

David

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.