Are Marine Diesel Generators Pure Sinewave?

[colemj]

Originally Posted by ksanders

Just so readers do not get confused...

Brushless, AVR regulated generator ends are the industry standard, and have been the industry standard for 30+ years in industrial and fixed marine installations.

There are manufacturers that try to offer lower priced units, and there always have been, and there always will be.

If one wishes to have a smaller, lighter genset for occasional duty, these will be higher-rpm and most likely capacitor-excited regulation. They are not all lower-priced cheap units.

If one wishes to believe that this is not the industry standard, that is OK with me, but the reality is that those generators of this type sold by Phasor, NextGen, MASE, Westerbeake, Mastervolt, and probably others I don't know about, are certainly capacitor-excited and regulated. The Westerbeake may be transformer-regualted.

Mark

[colemj]

Originally Posted by Matt sachs

I recently learned about pure and modified sine wave. Never heard of good and bad electricity until now. This is a great thread.

All non-inverter generators are pure sine wave in the way you are thinking about this. The cleanliness of the power output is a different thing.

Mark

[sy_gilana]

In the context of the OP's question, yes, they are as sinusoidal as standing next to a carousel listening to your daughter's laughter...

[ksanders]

Originally Posted by colemj

If one wishes to have a smaller, lighter genset for occasional duty, these will be higher-rpm and most likely capacitor-excited regulation. They are not all lower-priced cheap units.

If one wishes to believe that this is not the industry standard, that is OK with me, but the reality is that those generators of this type sold by Phasor, NextGen, MASE, Westerbeake, Mastervolt, and probably others I don't know about, are certainly capacitor-excited and regulated. The Westerbeake may be transformer-regualted.

Mark

Westerbeke generators are generally transformer regulated.

Capacitor regulation is only used to make a generator end at a lower price point. There is no benefit to capacitor regulation except that it is cheaper.. It is not necessarily much lighter. A little lighter but not much.

There are allot of good reasons people might want a smaller, lighter generator set. Sometimes there are size constraints. Sometimes there are weight constraints. Sometimes there are budget constraints. The smaller lighter weight high RPM units fill all of those needs.

Some of those are capacitor regulated, and some are not. The power coming from capacitor regulated units is "choppy" or "noisey" That is not arguable, it is a fact. You cannot for example fun a fluorescent light off of many capacitor regulated generator ends.

The frequency regulation of a small lightweight generator is not as good as the large heavy units. Again, that is not arguable, it is a fact.

Inverter generator sets are a solution to those problems. Now, for a reasonable price we can overcome the challenges of small generators. Persoally if I was going to have a small generator on my boat, I'd make it a DC generator. My inverter is pure sine wave, and the DC generator could keep my house bank up.

[deandavis1]

Wow. As the OP I just wanted to say a big thank you to everyone. I understand and appreciate the answers. Very valuable information here.

[Rapanui]

One factor not discussed is the effect of the load itself on the supply. A generator may produce a sinewave output into a resistive load, but into a reactive capacitive or inductive load the generator wave form will be distorted for all users because its source impedance is finite. There are very few resistive loads these days e.g. water heaters, incandescent lamps, electric heaters and far more that are reactive using induction motors, and switch mode power supplies for virtually all electronics. Inverter generators should produce a cleaner waveform on reactive loads but like all things not all inverter generators are equal.

[svinshallah]

Rotating AC generators are supposed to be pure sine wave. But highly inductive loads can have serious effects. My example: a 4.4KW Westerbeke genset trying to drive a very old Heart 25 charger/inverter. It would work fine at the dock, charging at almost 100A. When running on the genset, it would fault and shut off. If I ran a hair dryer at the low power setting along with the charger, it would work but only put out about 65-70 watts. Heart said try a capacitor across the output but that had no effect. I finally junked the Heart and bought an Outback. 100A easily with about 18A AC input.

[chala]

Originally Posted by Rick R

Everything you ever wanted to know about marine diesel generators is here:

Marine Generator Test - Victron Energy

Really? In my view the test is flawed.
The rating of the generators tested is given in kW. It should be given in kVA.
The test load is mainly resistive which is uncommon in a normal application.
No power factors are given for the other appliances. (induction cooker, motor and Multi).
The test is as good than their maths.

“
The main differences:
- Service life of a 1500rpm genset will be longer. 1500rpm gensets have a service life of up to
10.000hrs (2,5 years continuous use), whereas 3000rpm gensets will last up to 5000hrs
(1,5 years continuous use). Small 3000rpm gensets with a one cylinder engine have a
shorter service life. “

If we accept that there are 24 hours in a day so 10 000/24 = 416.67 days.
If we accept that there are 365 days in a year then 416.67/ 365 = 1.14 year.

Originally Posted by svquintana

Any AC electricity made by a rotating "generator", will have a "pure" sign wave.

Lets say a rotating “generator” will try to achieve a sinusoidal-shaped voltage waveform.
Variation of the air gaps across the pole face, setting conductor at an angle to the center line of the pole face, distribution of coil winding in the stator and other proprietary methods may be used to achieve a near perfect sinusoidal-shaped voltage waveform. I doubt that a cheap alternator will have all these features.

[Greg4cocokai]

Originally Posted by svinshallah

Rotating AC generators are supposed to be pure sine wave. But highly inductive loads can have serious effects. My example: a 4.4KW Westerbeke genset trying to drive a very old Heart 25 charger/inverter. It would work fine at the dock, charging at almost 100A. When running on the genset, it would fault and shut off. If I ran a hair dryer at the low power setting along with the charger, it would work but only put out about 65-70 watts. Heart said try a capacitor across the output but that had no effect. I finally junked the Heart and bought an Outback. 100A easily with about 18A AC input.

Great thread guys! I didn't know the differences til now.

I had/have the opposite problems. I installed a Westebeke 7.6kw and kept the old Phasor 3.5kw as I had the room to keep both. We had a Heart 30 at the time, and when our Westerbeke went down on passage, I resorted to the Phasor which ran the Heart at close to it's rated 140a, struggling a bit. When on the next passage our Heart went down I had an Outback VFX2812 shipped out. When I tested the Phasor to run the Outback charger it just cycled off and on. Would start to ramp up the charger then just shut off for several seconds then start over. Didn't like the "dirty" output? I just figured I would have to wire in my backup charger if needed. Any ideas?

Thanks, Greg
Grenada

[colemj]

We used to run an Outback VFX2812 off a Phasor 6kw with no problems, as well as with the NextGen, with the output quality shown above. I suspect that your generator frequency is a bit off and beyond the Outback's parameters, or the charger startup is pulling the voltage down momentarily below the Outback's parameters. Check these first - the parameters can be changed if needed.

Mark

[Greg4cocokai]

Originally Posted by colemj

We used to run an Outback VFX2812 off a Phasor 6kw with no problems, as well as with the NextGen, with the output quality shown above. I suspect that your generator frequency is a bit off and beyond the Outback's parameters, or the charger startup is pulling the voltage down momentarily below the Outback's parameters. Check these first - the parameters can be changed if needed.

Mark

Thanks much for that Mark! I'm sure the voltage does drop a bit as rpm's try and stablize. I will check the parameters. I kind of dislike scrolling menus. Thanks again.

[botanybay]

Originally Posted by Fuss

Yes, thats true, I made up that example.

The real example that I have in mind was around 70 amps on shore power and around 40amps on generator.
Still a big loss. The generator manufacturer suggested that we replace a capacitor.
This changed things only very slightly.
It was not possible to fix it in the 2 days before the boat sailed.

Often a significant part of the problem is older battery chargers... It is rather non-intuitive but there is a difference between a big power plant and a small generator even if both have exactly the same waveform when unloaded.

The effect is called "Power Factor" and basically describes how the consuming device pulls power out of the supplied waveform.

A "Power Factor" or Pf of 1.0 means that the consuming device pulls power out of the waveform exactly like a resistor would (this is called a "non-reactive" load) and this will result in the maximum useable power from any power source (shore power and a generator).

If the consuming device only uses part of the waveform (as some battery chargers do) then the "Power Factor" is smaller than 1.0. Take as a really bad example. If the charger only used the half of the sinewave when the hot lead is higher voltage than the neutral (positive voltage) and when the hot lead was lower voltage than the neutral (negative voltage) the charger did not consume any power then the power factor would be considerably less than 1.0, in fact if I remember correctly this would be Pf = 0.5. This type of thing could occur if the battery charger was using a "full wave rectifier" but one or more of the diodes were bad.

So, let's think about an example. If your generator can run the hot water heater just fine (lets assume a 3kw generator and a 2kw hot water heater). This has a power factor of 1.0 and so the generator still has 1kw of power left to use (assuming you could get 100% out of a generator without overheat etc which it will not).

Now, put a diode in the circuit. The resistor in the hot water heater will only work on half of the cycle, on the other half of the cycle it pulls no power at all. If you measure the heat load of the resistor it is making 1kw of heat. From the generators viewpoint half of the time it sees 2kw of load and the other half of the time it sees 0kw of load.

This does not mean that the generator has 2kw more (3kw of generator - 1kw to the hot water heater = 2kw), it only has 1kw more available (3kw of generator - 2kw of worst case load = 1kw). It is actually worse than that because generators don't like having that kind of varying load.

Normally the issue is far more complicated, this is just a simple worst case example. More common are circuits which in which the sinewave of the current does not follow the sinewave of the voltage. If the amperage and voltage are in phase completely then the power factor is 1.0. If the amperage rises early or late then the load is called "reactive" and is caused by either inductors, capacitors, or other active components (like diodes). If care is taken when designing equipment one can create equipment which approximates a resistor and that is "Power Factor Correction".

Ok, but why does shore power work better. Because the shore power generator is huge and has a lot of inertia and so it can deal with the combination of all of the different bad power factors which average out to near 1.0 . In the case of a small generator and a device which consumes a significant portion of the generators power that is not the case and it limits the generator output.

Another way to look at this is to stop thinking in terms of watts and start thinking in Volts * Amps or VoltAmps. For resistive loads (Power factor = 1.0) it does not matter. For reactive loads (Power factor less than 1.0) the peak volts * amps represents the available peak power.

An interesting example is that my Victron inverter displays Volt Amps on the supplied power, the battery monitor is monitoring consumed DC amps and voltage. For resistive loads (the hot water heater) these are very close to each other. For the refrigerator holding plate compressor they are very different.

Please don't read too much into the above discussion, I came up with some unrealistic examples to demonstrate the possible situations, they may not be quite right but provides a thought process as to what can happen and why they would be different.

The upshot is that the difference in performance might be the generator having trouble producing a clean sinewave when under load OR it could be the battery charger not pulling power off the generator in a clean way. For large loads on small generators it is always important to look for a power factor of near 1.0 (above 0.9 is probably a good rule of thumb)

load KVA = load KW consumed / power factor

So for a 1KW load and a power factor of 0.5 the KVA would be 2KVA

[chala]

Originally Posted by colemj

http://www.cruisersforum.com/forums/...ut-126997.html

Originally Posted by colemj

1. Generator waveform with no loads
2. Waveform with 15A resistive load (waterheater)
3. Generator with 15A inductive load (air conditioner)
4. Generator with the 120A heavy transformer-based battery charger that draws 15A

The battery charger cleans up the waveform the best, which I don't understand because it should be an inductive load with a relatively poor power factor.

I guess that there is no point in achieving a perfect sine curve on a no load situation. Who will run a generator in a no load situation for any length of time?
That type of alternator is cheap and if it requires compromising, it would be normal to tune it for the most common type of load.
4 give the best result. Now if it is for you to find the power factor of that load.
3 air conditioner. It is to be remembered that induction motor power factor is at is best when the motor is fully loaded. For a heat pump it is normally at the start of the cooling cycle and for the fan it is at Full.

Originally Posted by djmarchand

On my 3.5 KW NextGen which I think has the same Markon gen head,
the ammeter needle will bounce an amp or so either side of 12 amps when it is just running the Freedom Charger. It smooths out when I add the water heater load.

The freedom charger may produce a fluctuating load that the water heater smooth out. Also the power factor may move toward unity.

Originally Posted by colemj

The frequency stays pretty constant, though.

Pretty. What that? 0.1, 1, 2 Hz

[chala]

Originally Posted by colemj

http://www.cruisersforum.com/forums/...ut-126997.html

Originally Posted by colemj

1. Generator waveform with no loads
2. Waveform with 15A resistive load (waterheater)
3. Generator with 15A inductive load (air conditioner)
4. Generator with the 120A heavy transformer-based battery charger that draws 15A

The battery charger cleans up the waveform the best, which I don't understand because it should be an inductive load with a relatively poor power factor.

I guess that there is no point in achieving a perfect sine curve on a no load situation. Who will run a generator in a no load situation for any length of time?
That type of alternator is cheap and if it requires compromising, it would be normal to tune it for the most common type of load.
4 give the best result. Now it is for you to find the power factor of that load.
3 air conditioner. It is to be remembered that induction motor power factor is at is best when the motor is fully loaded. For a heat pump it is normally at the start of the cooling cycle and for the fan it is at Full.

Originally Posted by djmarchand

On my 3.5 KW NextGen which I think has the same Markon gen head,
the ammeter needle will bounce an amp or so either side of 12 amps when it is just running the Freedom Charger. It smooths out when I add the water heater load.

The freedom charger may produce a fluctuating load that the water heater smooth out. Also the power factor may move toward unity.

Originally Posted by colemj

The frequency stays pretty constant, though.

Pretty. What that? 0.1, 1, 2 Hz

[botanybay]

Originally Posted by chala

I guess that there is no point in achieving a perfect sine curve on a no load situation. Who will run a generator in a no load situation for any length of time?
That type of alternator is cheap and if it requires compromising, it would be normal to tune it for the most common type of load.
4 give the best result. Now it is for you to find the power factor of that load.
3 air conditioner. It is to be remembered that induction motor power factor is at is best when the motor is fully loaded. For a heat pump it is normally at the start of the cooling cycle and for the fan it is at Full.



The freedom charger may produce a fluctuating load that the water heater smooth out. Also the power factor may move toward unity.



Pretty. What that? 0.1, 1, 2 Hz

Generally the manufacturer can provide the power factor for a device.

On the other hand, I measure it for "small loads" with a "Kill-a-Watt" meter. It is a $20 device which plugs into the wall and then you plug the load (up to 15A) into the meter and it provides KW, KVA, PF, etc. Nice product.

I rarely purchase anything which runs on AC which I have not checked out first. Most modern electronics are pretty good, old computer power supplies were horrible. Laser printers were especially bad.

If I remember correctly the old "Ferro Resonant" chargers were quite bad. Some early regulating chargers which varied the portion of the sinewave they consumed to regulate the output voltage were really bad.

Luckily, a good power factor is necessary for good efficiency and so modern equipment is often pretty good. Although very small monitors and TVs tend to have a bad power factor. Consuming perhaps 12 watts but as much as 24 kva! (19" monitor I have in the nav station, the 22" version has a great power factor)