Who knows the most about Full Sign wave vs Modified sign wave inverters?

[Mr_D]

Originally Posted by twinboat

There are 1800 rpm generators. Cost more to build, need more power to turn for same output as 3600 rpm.

I believe there are 900 and 2700 rpm types also.

Yes, the 10K and 12.5K Onan diesels are 1800 rpm units. Onan also makes variable speed units like some 7.5 units.

[nothermark]

The relationship of shaft speed and frequency is determined by the number of magetic poles. A 2 pole (1N, 1S) needs 3600 RPM or 60 RPS. A 4 pole (2N, 2S) runs at half speed or 1800 RPM. I have seen some really big multi pole stuff that ran pretty slow. ;-)

[ladagobago]

Originally Posted by nothermark

This is mostly wrong.

The conversion of mechanical power to electrical power is generally done by moving a conductor through a magnetic field. The field has two polarities so the resulting output voltage is a sine wave due to the changing field strength caused by the relative distance of the conductor to the field pole at a given instant in time. That is your power line generator system with some exceptions. It is also your typical low cost AC generator like the contractors grade or the typical 4000 W Onan in most smaller Motor Homes or the $99 special. They are all pure sine wave allowing for some noise due to dirty contacts in the sliding connection. They all have the same problem of controlling speed to control the frequency of the generated output.

The search for better efficiency combined with the availability of better cheap electronics lead to the development of the Inverter Generator like the Honda line. By changing the mechanical configuration of the generator they get DC out and feed it to an inverter that turns it into AC. That makes frequency independent of motor speed so the motor can slow under light loads using less power and with less noise. Now my $99 special costs $990 and may be a sine wave or something else at the output. I see they are doing the same with "top line" generator sets up to 10 KW or so with equivalent cost differentials.

FWIW I have not looked into it but given the cost spread of MSW vs PSW Inverters that might partly explain the spread in cost of similar rated combination units. If I was buying one I would be looking at how clean the output power was. Personally I have a hard time paying for the combination units because noise does not bother me as much as all the cost and complications needed to lose a few DB.

Nothermark is 100% on target with the info. As for pure sine wave - not all inverters/converters have a pass through shore power transfer switch unless the unit is also a battery charger such as the xantrex etc. In my work truck we run a pure sign wave 2000 watt inverter which powers our computer and laser printers along with the chargers for the power drills. modified sign wave devices and there are various qualities of them just is not trustworthy enough for us. Goodone will power a lot of items but we found they destroyed our sensitive tool charging units

The neat thing with unit like the Honda and other which use electronic sync can be added together for more power. we use them in our not for profit band for power in parades. we have never had any issue even with sensitive electronic instruments or control panels.

Never had any frequency problems with generators even in our boat or MH

Thanks for the question FIreUP. it brought forward a lot of great answers.

[Mr_D]

Originally Posted by nothermark

The relationship of shaft speed and frequency is determined by the number of magetic poles. A 2 pole (1N, 1S) needs 3600 RPM or 60 RPS. A 4 pole (2N, 2S) runs at half speed or 1800 RPM. I have seen some really big multi pole stuff that ran pretty slow. ;-)

Our previous 8.5KW PowerTec and now our Onan 12.5 KW units were both 1800 rpm constant speed units. Both also had/have Kubota 3 cyl diesel engines.

[jerichorick]

Originally Posted by Mr_D

Yes, the 10K and 12.5K Onan diesels are 1800 rpm units. Onan also makes variable speed units like some 7.5 units.

To add a bit to the confusion about Onan... My 8KW diesel has a built in inverter that produced two ~120V feeds (L1 & L2) that are in phase. In other words, this generator is not a 240 to 120/120 to neutral setup. This generator is not a constant speed, governor regulated type like many of the portable types. The alternator in it is 3 phase and the inverter produces the regulated voltage and Hz.
My Magnum MS 2812 is not a hybread as we all know but my system is set up to use it to supplement my power when the pedestal is 30A, if the batteries are ready.

Also, my system, through the inverter and B.I.R.D. solenoid keeps both the house and start battery banks charged... pedestal/generator or engine alternator.

This is a PSW coach.

The MSW inverters can cause havoc on home type electric blankets and motors. The power produced by a microwave/convection oven is also reduced. I know about motors and microwaves first hand.

Happy trails all,
Rick Y

[nothermark]

FWIW car alternators are also multiphase and I suspect generators like the Honda are. The more phases and higher the frequency the easier it is to get decent DC out of the system to feed the inverter. ;-)

[FIRE UP]

Man,
You electrical wizards are something else. I've never trusted electronics 'cause I CAN'T SEE IT. But, I can sure as he.. feel it and have so, over the years. It doesn't FEEL GOOD!

I have one more question for you WIZ KIDS. When we camp with many other D/P buddies, and all of them have either the 7.5QD or, 8QD diesel generators, every single one of those generators seems to run quite a bit quieter and, with what sounds like a lot less RPM for doing the same chores as mine but, mine seems louder due to the fact that it really seems to be running at a much higher RPM than every one elses.

On my panel inside, I'm reading 117-120VAC, all the time it's running. A little history here. When we purchased the coach, I found out one of the magnets on the rotor for the generator had disintegrated and spread magnetic pieces all over the place inside that generator housing.

Well, after a bit of research, I picked up a perfect condition, 8K rotor off ebay and installed it. Now at that time of replacement, I noticed the stator had some damage in multiple places due to the shrapnel from the magnet exploding. But, I kept that damaged stator in there for a year or two.

Well, after a while, I finally decided to replace that stator. Whew!!! That was not cheap!!!! A whopping $1,100 for that darn thing. But, I tore the gen apart again and installed it. Now, as stated, it seems my gen runs at a higher RPM than any other diesel RV gen I've camped with.

Is there a way to "tone down" the RPMs and still get 117-120 out of it?
Scott

[nothermark]

FWIW - my assumption is that your generator is not running as efficiently as the others or you are using more power than they are.

The first idea takes a shop to check out how well everything is performing. You probably did not have the tools to do that when you replaced parts so you also do not know if the parts you used have a problem or if there are problem you missed like an open rectifier on one phase.

The second one only you can judge.

[pasdad1]

Originally Posted by FIRE UP

it seems my gen runs at a higher RPM than any other diesel RV gen I've camped with.



Is there a way to "tone down" the RPMs and still get 117-120 out of it?

Scott

The 7.5 and 8 QD generators you speak of are "inverter" type generators, which allow the engine RPM to go up or down to match the load....the inverter electronics takes care of keeping the electrical output a steady voltage and frequency. I don't know which model you have, but there are the other type of generator (without inverter) that needs to run at a constant RPM.