Are Marine Diesel Generators Pure Sinewave?

[chala]

Originally Posted by botanybay

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)

Really 24 000 VA that would give a power factor of 12/24000 = 0.0005
Maybe that should have read 24 VA. 12/24 = 0.5, a poor power factor but very common these days.

[botanybay]

Originally Posted by chala

Really 24 000 VA that would give a power factor of 12/24000 = 0.0005
Maybe that should have read 24 VA. 12/24 = 0.5, a poor power factor but very common these days.

Oops... Fingers added the "k" to the "va".

Wow, a power factor of 0.0005 would be pretty terrible!

Thanks for pointing that out!

[colemj]

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 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.

Pretty. What that? 0.1, 1, 2 Hz

The power factor on the charger is 1 according to Victron's published specs.

The scope measurements on the air conditioner where taken when the motor was fully loaded shortly after starting up and the fan on full.

The generator keeps a constant frequency at any specific load (+/- 0.15hz), but that frequency will change with load. At no load it is 62-63hz, but at full load it is 60hz. I don't think this is unusual for generators.

There really isn't any "tuning" ability of this Markon generator head. Frequency is set with engine speed. Engine speed marginally effects voltage, but not by much.

Mark

[botanybay]

Originally Posted by colemj

The power factor on the charger is 1 according to Victron's published specs.

The scope measurements on the air conditioner where taken when the motor was fully loaded shortly after starting up and the fan on full.

The generator keeps a constant frequency at any specific load (+/- 0.15hz), but that frequency will change with load. At no load it is 62-63hz, but at full load it is 60hz. I don't think this is unusual for generators.

There really isn't any "tuning" ability of this Markon generator head. Frequency is set with engine speed. Engine speed marginally effects voltage, but not by much.

Mark

The manual for my Westerbeake 6kva 230v 50hz generator which is mechanically governed for engine speed (and thus frequency) varies with load by about 4hz over the range. At no load the output frequency is about 52hz and at full load it is about 48hz.

It turns out that the generator is easily modified to run 60hz and the power output increases to 8kva. However, some anecdotal data suggests that these generators run nearly forever at 50hz (1500 rpm) but have a somewhat shorter life (very acceptable but shorter) when running at 60hz (1800 rpm).

I suspect that the generator head may also last longer when not pushed quite so hard but I can't convince myself if there is an advantage either way. (i.e. running at 5kva at 50hz vs lets say 7kva at 60hz)

At the moment I am using flooded lead acid batteries and the maximum acceptance is about 90 amps (at 24V) for the bank and so the extra output is not especially useful.

However, the charger can output 200A which would consume the higher output fairly easily if I were to go with LIFEPO4 or some similar high charge rate technology.

Choices, Choices, Choices...

For now, it is happy and I am leaving well enough alone!

[St. Elsewhere]

Originally Posted by botanybay

It turns out that the generator is easily modified to run 60hz and the power output increases to 8kva. However, some anecdotal data suggests that these generators run nearly forever at 50hz (1500 rpm) but have a somewhat shorter life (very acceptable but shorter) when running at 60hz (1800 rpm).

I suspect that the generator head may also last longer when not pushed quite so hard but I can't convince myself if there is an advantage either way. (i.e. running at 5kva at 50hz vs lets say 7kva at 60hz)

Choices, Choices, Choices...

For now, it is happy and I am leaving well enough alone!

If you have frequency sensitive equipment such as motors, transformers, etc. on the boat are they rated at 50 or 60 HZ? It looks like you are in locations for 60 HZ shore power. Is anything getting hot when plugged into shore power?

[botanybay]

Originally Posted by St. Elsewhere

If you have frequency sensitive equipment such as motors, transformers, etc. on the boat are they rated at 50 or 60 HZ? It looks like you are in locations for 60 HZ shore power. Is anything getting hot when plugged into shore power?

The boat is English and was originally setup for 230v 50hz polarized with neutral close to ground.

Most of the equipment onboard is designed for 50hz and 60hz and 208V to 240V.

The washing machine is not happy on 60hz and the microwave does not like 208V which is what my dock is.

The air conditioners are happier on and the holding plate compressor is somewhat quieter on 50hz.

In the end I upgraded the power system for worldwide cruising as follows:
Victron automatic input adjusting isolation transformer
Victron 100A 24V charger
Victron 8kva Quattro inverter/charger 230v 50hz (or 60hz) w/200A 24V charger
Victron 1.2kva Pheonix inverter 120v 60hz
Victron 0.3kva Pheonix inverter 120v 60hz

I can either run the output of the isolation transformer into the battery charger (which can consume the entire transformer) OR into the Quattro 8KVA inverter using shore assist. (so 12kva available so long as batteries last, loads that large don't last long)

The generator also goes through the Quattro and automatically switches between shore and generator.

I prefer running in make DC and then make all the power I want in the forms I want but can run the other way when desired. Still experimenting with how to use the system most effectively but extremely happy.

Installed the Victron Color Control GX and Victron battery monitors so it is an all Victron system at this point other than some old dc to dc converters on the boat which will get upgraded eventually.

[malbert73]

Originally Posted by colemj

The power factor on the charger is 1 according to Victron's published specs.

The scope measurements on the air conditioner where taken when the motor was fully loaded shortly after starting up and the fan on full.

The generator keeps a constant frequency at any specific load (+/- 0.15hz), but that frequency will change with load. At no load it is 62-63hz, but at full load it is 60hz. I don't think this is unusual for generators.

There really isn't any "tuning" ability of this Markon generator head. Frequency is set with engine speed. Engine speed marginally effects voltage, but not by much.

Mark

How many hours do you have on your next gen? I am purchasing a boat with a 5.5 kw next gen with 250 hours, which was chosen mainly due to size limitations. I assume the kubota will run forever-ish, but the Markon head may eventually wear out. I wonder if anyone has replaced that with a better quality generator head. Just before survey, the generator capacitor failed, and was replaced by PO. Part only $75 but water pump has to be removed for it to be replaced. Prior to that PO reports flawless running for past 2 years, obviously light intermittent duty.

Just curious how much quality use I'll get out of the next gen. It wasnt a major factor in my purchase, but is a nice bonus since runs quietly in lazarette for charging, AC, etc.

Mike

[colemj]

We have 661hrs on our NextGen 5.5kw (just changed the oil is the reason I know that number with precision!).

You could in theory replace the generator head, but in practice, it would need to have a pulley machined/fitted for it, be aligned just right, etc. A new Markon head only costs $700. These are intermittent duty units, but run well in that capacity. The Kubota is a standard 12hp used in lots of industrial generators. Like all of these small Kubotas, it will run forever. The generator head is not as rugged as others, but relatively inexpensive to replace - I would guess they are good for 2-3,000hrs based on the ages of several others I know of that failed.

It is a trade-off. These units are light and small. The equivalent Northern Lights (for example) is 150lbs heavier and wouldn't fit in the space we have our current NextGen.

I don't understand the problem or cost replacing the capacitor on the boat you are purchasing. First, those capacitors are just bog-standard run capacitors used around the world on heating and AC systems, etc. I have never paid more than $15 for one and can buy them on the street in every small village in every out of the way place we have ever been. Second, it isn't located anywhere near the water pump and replacing it is as easy as undoing a screw, pulling off the old wires and replacing.

Mark

[malbert73]

Thanks Mark-
This is all good to know. I have not looked carefully at the cost or mode of capacitor repair as this was hired out by PO as part of pre-purchase conditions.
I suspect the water pump issue may have to do with installation constraints, but perhaps it's just a matter of crawling in the other side of the locker where the next gen is housed. It's on a Tartan 40 in lazarette so perhaps less space than on your at. $15 capacitors- I can stock up on. The Markon generator certainly is cheap compared to the cost of installation, entire package, etc. So if that goes after 2000 hours, no big deal in grand scheme. Like you said, the Kubota should run indefinitely if maintained.Nwill be nice to have redundancy of charging modes, all the more if I add solar.

[chala]

Originally Posted by colemj

The power factor on the charger is 1 according to Victron's published specs.

So it looks like the alternator work the best (tuning at design) with a 15A load at a power factor of 1. The power factor can always be checked by comparing the kW with the kVA.

Now if a Victron charger as a power factor of 1 the following may be taken into consideration.
It is common practice to build a generator with a power factor of 0.8. A load with a higher power factor is unusual and a load with a lower power factor is detrimental for the transmission and use of electricity.

According to the above a genset rated at 5.5kW at operating rpm, the alternator would be rated at 5.5/0.8 = 6.875 kVA. The maximum current that this alternator can carry at 240 V is 6875 VA / 240 V = 28.65A and this is the most important point. Now if you were to load this genset with a 5kW load with a 0.5 power factor the motor would not be overloaded but the current would be 41.66 A (5000 / 240 / 0.5 = 41.667) and the alternator would be damaged. At 5kW the power factor should not be less than 5000/ (28.65*240) = 0.73. Also the maximum load at unity power factor that the genset can carry is the output rating of the motor in kW at operating rpm. The maximum current at 240V will be 5500/240 = 22.92A

Originally Posted by colemj

The generator keeps a constant frequency at any specific load (+/- 0.15hz), but that frequency will change with load. At no load it is 62-63hz, but at full load it is 60hz. I don't think this is unusual for generators.

2 Hz difference from rated full to no load is fair for a mechanical governor.
Some engine manufacturers, Perkins Electropak, provide a more suited mechanical governor for use in a genset.
What is also important is at what rpm is the peak torque of the motor. For a Perkins 103-10 it is at 2100 rpm. Far away from 1500 rpm, closer to 1800 rpm, far away from 3000 rpm and very distant from 3600rpm.
Torque is important to recover rapidly from an intermittent heavy load like the switching of a 2000+ watts stove element. For this reason an indirect drive, using gear or belts, may allow the tunning at test time of the genset for best torque and a more tolerable noise.

[chala]

Originally Posted by botanybay

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.

Does your “Kill-a-Watt” let you know if the power factor is leading or lagging?

[transmitterdan]

Originally Posted by chala

Now if you were to load this genset with a 5kW load with a 0.5 power factor the motor would not be overloaded but the current would be 41.66 A (5000 / 240 / 0.5 = 41.667) and the alternator would be damaged.

It is not likely that the alternator would be damaged. Most gensets have a circuit breaker that would trip in this circumstance. Even if the breaker did not trip the field excitation likely would not support this current and thus the voltage would drop to a very low value thus self protecting.

As a practical matter there are not going to be 0.5 power factor loads on a cruising boat. The worst power factor is likely to be A/C, refrigeration or water maker. None of these should have a 0.5 power factor.

[transmitterdan]

Originally Posted by chala

Does your “Kill-a-Watt” let you know if the power factor is leading or lagging?

The Kill-a-Watt device displays Volt-Amperes or Watts. It does not measure the "angle" of the power factor. This is not a big deal because very few devices in the typical home (or cruising boat) have a leading power factor (current leads voltage).

[colemj]

Originally Posted by chala

So it looks like the alternator work the best (tuning at design) with a 15A load at a power factor of 1. The power factor can always be checked by comparing the kW with the kVA.

Now if a Victron charger as a power factor of 1 the following may be taken into consideration.
It is common practice to build a generator with a power factor of 0.8. A load with a higher power factor is unusual and a load with a lower power factor is detrimental for the transmission and use of electricity.

According to the above a genset rated at 5.5kW at operating rpm, the alternator would be rated at 5.5/0.8 = 6.875 kVA. The maximum current that this alternator can carry at 240 V is 6875 VA / 240 V = 28.65A and this is the most important point. Now if you were to load this genset with a 5kW load with a 0.5 power factor the motor would not be overloaded but the current would be 41.66 A (5000 / 240 / 0.5 = 41.667) and the alternator would be damaged. At 5kW the power factor should not be less than 5000/ (28.65*240) = 0.73. Also the maximum load at unity power factor that the genset can carry is the output rating of the motor in kW at operating rpm. The maximum current at 240V will be 5500/240 = 22.92A




2 Hz difference from rated full to no load is fair for a mechanical governor.
Some engine manufacturers, Perkins Electropak, provide a more suited mechanical governor for use in a genset.
What is also important is at what rpm is the peak torque of the motor. For a Perkins 103-10 it is at 2100 rpm. Far away from 1500 rpm, closer to 1800 rpm, far away from 3000 rpm and very distant from 3600rpm.
Torque is important to recover rapidly from an intermittent heavy load like the switching of a 2000+ watts stove element. For this reason an indirect drive, using gear or belts, may allow the tunning at test time of the genset for best torque and a more tolerable noise.

The Kubota engine is a 3600rpm engine operated at 2800rpm. The maximum point on its torque curve is reached at 2700rpm, so it is operating very close to that point. It connects to the Markon alternator with a belt.

The capacitor-regulated Markon generator head on ours is designed for loads at or near a power factor of 1. The AVR regulated version is capable of operating at 0.8 power factor, but is designed for 1.0. The multiphase version of it is designed for power factors between 0.8-1.0.

This specific generator is a trade-off, for sure. It is light and small, but not designed for continuous heavy loads. Our typical use of it is running it for 1-2hrs at ~70% of capacity 3 times/week. This would not be the generator for routine running of AC for multiple hours/day.

Mark

[a64pilot]

Since this has drifted a little already do you guys mind a little further drift?
Why not use a DC Gen., one that could be used to charge a rather large house bank, and an Inverter for AC loads? I think it would even be easy to have it start automatically at a pre-set voltage?
What DC generators are currently available?
Only real need I see for an AC generator is if one wants to run a high power AC device pretty continuously, like an airconditioner, what am I missing, why no DC generators?