The Offshore Voyaging Reference Site

10 Tips To Install An Alternator

JHH5_102204-2

Alternators For Live-aboards Are Different

Before we start, the key thing to understand is that an alternator that is adequate for a boat that is used for weekending and occasional cruises of a few weeks’ duration most likely won’t be able to handle the demands placed on it by full-time live-aboard offshore cruising.

So let’s look at what a real cruiser’s alternator is, and how to install it.


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
179 Comments
Oldest
Newest
Inline Feedbacks
View all comments
Nicolas

I think Nanni and Yanmar solved most of the very well presented in your article alternator issues. Nanni offers water cooled intercaled generators on their engines: 300 A at 14 V DC, 160 at 28 V DC, and 175 A at 230 AC. These are mechanicaly coupled with the crankshaft between bell housing and reduction gear. It is technology developed with Iskra electronics Slovenia. Yanmar offers similar 4KW AC intercaled generators but only on the 55 hp engine. Although this concept seems to really make sense I think feedback is needed from cruisers actually using it.

I would also like to add on your article that when sizing a suitable alternator for the engine the side loading of the front engine bearing should be taken into account. Sometimes it makes sense to place two alternators on opposite sides of the pulley as to cancel out each other’s side loading on the bearing.

Nicolas

An issue with the two alternators configuration is that even when placed on opposite sides of the pulley the second always imposes greater torque on the front bearing due to greater distance from the bearing. ( Torque = Force x distance). Thus twin opposite alternators will never quite equate each other’s side loading on the front bearing. The engine manufacturer can be consulted for max permitted side loading on the front bearing which should be taken into account in single generator configurations as well.

Carl Stevens

I think that while the distance from the engine bearing to second sheave would be greater than the primary alternator sheave, the sum of the opposite torque vectors, if you want to think of it as such would be sum less then either one, If both alternators are applying the same load on the engine shaft, but in opposite directions and different distances from the fulcrum (the engine bearing) the loads of each neutralize the other, in this simplified example.

Matt

Crank shaft bearing:
Most engines have a specified limit for the power that can be drawn from the front shaft, and/or the radial load on that shaft. It’s partly a shaft deflection issue, partly a vibration risk issue, I would hope it’s not a bearing wear issue as that would raise concerns about the longevity of the (much more heavily loaded) crank journal bearings. In any case, if you’re coming anywhere close to that limit, whatever you’re driving belongs on the other end of the engine in a proper rigid mount.

Big generator between engine and gearbox:
Why not? If they’re built well, electrical machines last virtually forever. There is no shortage of motors and generators in industrial use that have hundreds of thousands of continuous full-power hours on them since their last rebuild.
Today’s boat alternators might tend to die after 2000 hours, but there’s no reason why we can’t do much, much better. The bearings in a bell-housing-mounted unit, for example, would see much smaller radial loads than those in a belt-drive alternator, and they could also be four times larger and much better cooled. The thing could be sealed against dust and crud, and since space constraints are now relaxed, the windings could be much thicker (and therefore run cooler) for the same output current.

Eric Klem

Just chiming in to agree with Matt on the crankshaft loading. The moment arm tends to be quite small for the front pulley and the loads are relatively low so most of the loads ends up being reacted as a radial force in the nearest bearing. The loads placed on the crankshaft by the rods are quite large. Care should be taken to minimize vibrations, that is just good practice. As to their effect, it really depends on the specific type of bearings in there although most are plain.

Synchronous belts really are superior including from a loading standpoint. Overall, they last longer, have lower loads, less vibration and are much more efficient (you will burn less fuel). I would never intentionally install a V belt these days. For people who are space constrained, there are now some synchronous belts from people like Gates with really high power transmission density.

Regarding in line generators, I don’t see anything wrong with the concept, the actual execution of it is what matters. As Matt mentioned, properly designed motors are some of the most reliable things out there. The things that seem to go bad are the brushes and bearings. The loading on the bearings should be relatively light provided that proper coupling and alignment is done between the different components. If this is not the case, you could go through a lot of bearings quickly. Also, bearing lubrication is key. Most smaller motors use sealed bearings which don’t give the best life. Really, you should either have an oil system (more complexity) or a system to allow you to periodically grease them. For me, I don’t have a big enough battery bank to have one of these make sense so I will stick to my alternator for now.

David Branyon

I don’t think torsional vibrations are an issue for belt driven alternators off of the crank nose, especially since alternator load is relatively constant as opposed to e.g. camshaft or diesel fuel pump loads. It is very hard to transmit strong torsional activity through a belt (as opposed to say, through a geartrain). I think it is primarily a cantilevered issue on the leverage over the front main bearing.

I am more familiar with larger engines, but typically there is one or more bolted joints on the crank nose that attach the torsional damper and front pulley. The diameter of the nose of the crank is generally limited to main bearing diameter and that bolted joint is often a challenge, especially for applications with high loads off the front of the crank, so that may be another limitation.

I know it would be much more challenging, but do people ever drive a large alternator directly off the nose of the crank, through a coupling that allows minor misalignment? I know they sometimes do this for large hydraulic loads off of large off-highway engines and those engines are often spec’d to be capable of driving 50% of their output power off the front of the crank (if you can also do it within side load restrictions).

Thanks in advance.

Svein Lamark

Hi John, I agree with your conclusion. In my sailboat I have much the same experience as you have had. A standard car generator will not last much more than 2000 h. However I have two remarks that will improve charging very much: Proper alignment of generator is very important. Belts and bearings will last much more. Second and the professional solution: Buy a professional generator for maritime use. I use Transmotor generator. The lifetime of a Transmotor kept well is 30 years in a professional ship. A Transmotor cost some more than a car generator, but it is worth it. Maritime gear costs often more than gear from the car industry, but in this case it is easy not to pick the car gear.

Marc Dacey

When I spec’d my Beta 60 repower, I went for a double PTO so I could run two smaller (90-100 amp) alternators, the output of which would be combined and would be sent to a large house bank (about 1,000-1,100 Ah in the form of six 320 Ah 6-volt flooded L16 format batteries). The start battery would be fed via echo charger, as would the manual/electric windlass battery forward (smaller wire gauges would be required).

In that sense, the spare is already working.

Are you suggesting that a 180 amp (say) is better, and I should carry a second 180 amp alternator? I suppose the second PTO wheel could be used for emergency bilge pumping!

I would add that I have solar, wind and (if necessary) genset options. My ideal is to run the engine less than most, and never, if possible, just to make amps. That said, if I need to motor, I want to make plenty of amps and would use “motoring intervals” to make ice cubes, water and generally light up the joint!

Anyway, your guidance in this would be heeded. The only investment so far is that second PTO wheel. The rest of the gear has yet to be bought and installed while I think these ideas through for suitability to offshore conditions and shoreside electrical independence.

By the way, I have used the serpentine belts and they are indeed a better choice. So far, I like Greenlines.

Dick Stevenson

A tip for microwave users (and other heavy amperage equipment): install a field wire dis-connect switch. This way, when motoring and wish to use the microwave through your inverter you do not hammer the alternator, belts, brackets etc. with amperage demand as the microwave kicks in. If you dis-connect, then, when done, re-connect the switch, the amperage is quickly returned to the battery bank, but done gently through the smoothing of the battery bank’s spontaneous recovery and the regulator’s soft start program.
The above disconnect can also give you full engine power in a fire drill of some sort if you are a bit under-powered. The bigger alternators can demand 6-10 hp or more and one often wants full power at night when the batteries may be down draining hp away from the prop where you might want it.
Also consider the connection to the engine. We de-tuned our alternator not to give it longer life, but because I considered our alternator bracket on our engine to not be robust enough to tolerate high output alternators. As a side consequence, I have considered alternators to just last forever as we have almost 5000 hours on the two I swap every few years.

Eric Klem

People tend to think about power in boats as if they have some form of gearing such as a transmission or torque converter that decouples load and shaft rpm which is of course not the case. In boats, the load on the engine is determined by the load on the propeller for a given rpm. Of course, this load depends on many factors like propeller geometry, slip, boat speed, etc. Another way to think about it is that if you give the engine more fuel while you are motoring, its power will increase and you will have an imbalance of forces which results in an acceleration and the shaft speed will increase until the power output and load balance (this is actually a little unfair because the governor for mechanical engines and electronics for the new HPCR engines don’t work strictly on power but it is still generally fair). If you are overpropped, what happens is that you reach a certain rpm where you can’t increase the engines output power above the load from the prop and you get stuck at that rpm.

This can be both good and bad for boaters. The bad news is that a giant alternator can pull enough power that you won’t be able to actually reach full rpm when charging hard. This could potentially be a problem in an emergency situation. On the other hand, if you have the ability to turn the charging off, it lets you have a very large alternator without having to regear or repitch. The reason that this works is that the engine power output curve and propeller load usually diverge a bit at cruising rpm so you have extra power there.

I hope that this makes sense. It just bugs me when people get worried that they are loosing power to something like an alternator when they can still get to full rpm which means that they have plenty of power.

Eric

Marc Dacey

Thanks, Eric, for the clarification. I can’t speak for Dick’s setup, but my power output curve/propeller load will be variable as I have a four-blade feathering Variprop that is capable of in-water pitch adjustments.

I will have to empirically fine-tune the prop pitch from a baseline pitch to chart my own fuel consumption, my own “best economy cruise speed” and the interplay between RPM and the potential for lugging. Only at that point will I see the effect of a big alternator and whether or not I am “robbing” thrust in quest of amps. The reality is that the alternator load, all else being equal, is a pretty minor concern once I find my sweet spot of pitch and thrust. I selected the Variprop precisely for this ability to be adjusted (carefully) in-water, the reduction in drag of a feathering prop, and the ability to have separate pitching to achieve a “flatter” pitch in forward and loads of torque in reverse, which is desirable if one has a steel full keeler with plenty of windage. That said, I still think an ability to disconnect alternator output might be worth the slight addition of complexity, even as I hew more closely to John’s “KISS” mantra.

Once again, the deep experience of the members here has impressed me favourably.

Eric Klem

Marc,

If both John and I are correct in believing that the Variprop is a variable pitch propeller and not a controllable pitch one, then John’s statement is correct that even with a correctly pitched propeller, there will be a single rpm where the propeller can put a load on the engine that is equal to the engines maximum output at that rpm and the rpm will also be the maximum rpm that the engine can achieve.

In steady state (no acceleration but constant velocity), the net force on something must be equal to 0. On a boat, this means balancing your propulsive forces (from sails or the propeller) with the drag of your hull. In the drivetrain, it means balancing the force output of the engine with the drag force of the prop. The propeller will have a certain drag force for a given rpm so the engine will be matching this force. Obviously, if the engine can’t output enough power at that rpm, you are not at steady state and the engine will decelerate until it either stalls or reaches a point where its power output is equal to the load. You can also have a situation with a seriously underpitched prop where you can’t use very much of the engine’s power because the propeller load is too low.

The solution to this is to make the load and the rpm independent. A controllable pitch propeller lets you put a wide range of loads on the engine for a given rpm. A transmission would also let you do this as we discussed in one of the hybrid threads. If you think about your car, having only a single gear would be really limiting. You would have to gear it so that you could make it up the steepest hill possible but then your top end speed would be really compromised because it would be like driving in too low of a gear the whole time. Boats have it much better than cars but there is still somewhat of a mismatch.

Choosing the right propeller pitch is really tricky and there is no such thing as perfect. If you wanted to be really conservative, you would wait until your prop was fouled, discharge your batteries and then make sure that you could just reach full rpm while tied in your slip. Unfortunately, this makes for generally slow motoring and high fuel consumption so most people put more pitch than that in.

I hope that I haven’t gone too far off topic here. The takeaway message is that a big alternator could mean that you either need a way to shut it off or take a bit of pitch out of the prop.

Eric

Laurent

If a diesel engine is driven at say, 70% max rpm with a load torque that is say only 70% of max torque (and power…) at that rpm., its thermal efficiency (diesel liters per kilowat*hours) will not be as good as the same engine at the same rpm. with a load torque that is 100% of max torque at that rpm. (let us say 99%…). But diesel consumption in case 1 will be distinctly lower than in case 2. In fact you can estimate thermal efficiency should improve about 5% in case 2, which means that the extra 30% load torque (and power…) will cost about 25% more diesel, so “marginal efficiency” for those 30% should be about 13% better than case 1 efficiency (30/25 * 100…), and about 8% better than this engine max thermal efficiency.
Those maths suppose that engine has not been sized for max rated engine RPM & torque + full genset load at WOT, otherwise 70% of max rpm. plus max alternator load should not give more than #70% of max possible load torque at that rpm, unless you have à CPP or equivalent. In that case, global thermal efficiency of the whole system can not be better than same without alternator.

David Branyon

Concepts are good but the actual numbers are significantly different. I took the Yanmar 4JH45 (their smallest 4 cyl) rated 45 hp @ 3000 rpm (lowest rated speed I found). I took their fuel consumption (only available on the prop curve) and did a bunch of calculations. At 70% speed (2100 rpm), a standard 0.3 exponent prop curve consumes only 41% of the engine torque available at that speed, not 70%, so you can see how low of load you end up by backing down speed when motoring.

I used your estimate of full load at this speed being 5% improved brake specific fuel consumption (BSFC, in g/kW-hr, inverse of thermal efficiency) from the prop curve’s 262 to a full load value of 249 g/kW-hr. So, if we go from the prop curve to 95% load at this speed, we get an increase of 133% power with a fuel flow increase of 120%, so about 11% of the power increase for electrical generation (133/120) comes for free. Not earth-changing, but not bad. And way better than generating that power at 2000 rpm in neutral with the electrical as the only load.

Other considerations are that this implies a power generation power of 15 kW on this example setup. If we assume (from the video presented) a generator efficiency of 50%, that’s 7.5 kW electrical generation or 576 Amps @ 13 V. So we’re going to need a heck of an alternator, cabling, BMS, battery bank, etc. to accept that.

And per another comment on this article, this would require an alternator cutout if you wanted to reach 3000 rpm with this prop sized for the full 45 hp @ 3000 rpm. So, reality intrudes and demands one of the loads be controllable vs. engine speed, so either a controllable pitch prop, or some kind of programmable voltage regulator. Without that, if both are fixed, you’d need to limit to well below this generation power or else you could never exceed 2100 rpm or put more than 15 hp into the propeller. It’s a tangled web.

Also need SERIOUS cooling to load up an alternator to anywhere near full output at lower speeds, as I also learned form the posted video. So definitely some caveats.

Dangerous talking about parameters that have units of %. There is “delta points”, as in 15 vs. 20% is 5 points of efficiency. And then there’s “delta percent” as in 20% is a 33% increase over 15%. Have to be VERY careful in this area to avoid errors.

Yanmar_4JH45_engine_power_curve2
Eric Klem

Hi John,

You are correct that there is usually power to spare at cruise rpm although the actual power available will vary depending on the specific application. For the size boats that most people go long distance cruising in these days, the draw of the alternator is usually a relatively small fraction of the total power output.

Unfortunately, there is no free lunch and the power to run your alternator comes at the expense of burning more fuel in the engine. The real question then is, what is the most efficient way to charge so that you burn the least fuel. Engines have relatively low efficiencies thanks to a host of losses that all give off heat in the end. Your mechanical losses are typically fairly constant for a given rpm regardless of load. Therefore, if you increase the load, you don’t have much extra mechanical loss so you are dividing a larger overall power output by the same mechanical losses. How the other efficiencies such as combustion track is much more engine specific. Some engines try to be really power dense and end up with inefficient combustion and high valve losses. Other engines are effectively loafing along and a small increase in power will be quite efficient. In the absolute best case where your incremental power output was produced at 100% incremental efficiency, you would still have to make up that amount of energy in fuel. In practice, everything is below 100% efficiency and in engines, it is much lower. For engines like your Perkins, I suspect that the incremental efficiency for charging at cruising rpm is actually quite good. If your engine actually had the extra power to spare without having to increase the throttle, it would accelerate and go to a higher rpm.

I don’t want to make it sound like this is a bad time to charge your batteries, it is usually an excellent time. Running the engine just to charge the batteries is terribly inefficient because your power output is overwhelmed by all of your power losses. In the extreme case, with no load on a running engine, its overall efficiency is 0%.

Along the lines of engine efficiency, it is no coincidence that at WOT, the most efficient operating speed of an engine is very close to its torque peak. Engines are typically designed around a maximum cylinder pressure and the rpm associated with the torque peak is the rpm where there is the best balance of all the factors that make up the overall efficiency.

Eric

Svein Lamark

I will explain my short comment given above a little: A car alternator will normally last around 5000 hours in a car with a small load. In a boat with 80% load it will last 1000-2000 h. A marine alternator like a Transmotor can last 30 years. Alignment should be done with laser tools. Laser tools is uncommon on boatyards in North America, but the price of this tools are falling fast, so just demand it to be used. When the lifetime of the alternator is 30 years, it is important to keep the engine room clean. Otherwise the alternator will be filled with dirt that can cause damage.

Svein Lamark

Many commercial alternators are too big in a small boat, but Transmotor has small alternators. They can be found on scrap yards in Scandinavia, but a new one is worth its price and will usually fit on a small boat. I have one 40 years old at 100 amp that still works good.