AC Frequency vs elec motor efficiency

[MikeP]

I've hunted all over the internet but can't find an answer...

For an 60Hz AC motor what is an acceptable frequency variation? I know that low HZ can cause ac motors to overheat but HOW MUCH Lower?

Here's the reason for the question:

Our NL Genny is set to produce 61HZ under no load in order to produce 60 when there is considerable load - several AC units running, etc. But our new dishwasher - which we really like - is very frequency sensitive. It will go into the fault mode at 61 HZ and works perfectly at 60. What this means is that if we want to use it with the Genny running, we have to turn on a couple of AC units.

I'm wondering that if I adjusted the Genny to produce 60 at light loads, would the resulting 59HZ at heavy load cause any problem for the various electric motors/pumps? Obviously the big motors are more important than the dishwasher but if 59 is OK, it would be nice to have everything work!

OTOH, why the dishwasher s so sensitive is a product of our digital age.

 

[bobk]

My dishwasher doesn't have that issue..... she uses a dishpan, sponge and drying rack.

Bobk

 

[krush]

What matters for most AC induction motors is volts/hz (volts per hertz). This is really in VFD (variable frequency drives) though. On my RV, I cranked the generator up to run 62-63 hz no load so when under load the droop keeps it at 60-61hz. I did this because it rattles a lot less at 60-61hz than it does at 59!

You shouldn't hurt anything at all. Low voltage can be much worse.

 

[tonytrakovich]

Are you using a digital multimeter to measure your Hz or reading the analog meter in the boat? I cant believe that a dishwasher is that sensitive to frequency variation. If you are not reading the Hz digitally, could it be that your Hz is actually higher and reading 61 on the analog meter? ie, meter out of calibration?

Motors dont care so much about frequency. Some digital electronics do care. I think they get their clock signal from the AC sine wave?

 

[Boatsb]

My dishwasher doesn't have that issue..... she uses a dishpan, sponge and drying rack.

Bobk

I have a similar model. Best one to own. The only issue I ever had was the user interface is in spanish

 

[SKYCHENEY]

59hz should be just fine for everything.

 

[bobk]

I have a similar model. Best one to own. The only issue I ever had was the user interface is in spanish

Scott, be careful with the word 'own'. 'Cherish' will work much better over the long haul.

Bobk

 

[MikeP]

I checked the frequency meter a couple of years ago and it was correct. I suppose it could have drifted. I'll check it in the next few days.

Assuming the dishwasher really does insist on 60, not 61, based on the advice from Krush/Sky I'll drop the setting by one Hz at no/low load.

 

[Pascal]

Mike, What kind of dishwasher is it?

We have a fisher paykel drawer dishwasher that keeps throwing random errors. I am wondering if it is freq related, never thought of that... We almost always use it on Genset,

 

[SKYCHENEY]

Mike, What kind of dishwasher is it?

We have a fisher paykel drawer dishwasher that keeps throwing random errors. I am wondering if it is freq related, never thought of that... We almost always use it on Genset,

I just replaced the Control Module on my F&P dishdrawer. I don't know what caused it to go out, but I hope it wasn't related to running it on inverter or generator. I kinda doubt it, since it has run for several years without issues. Hopefully it was just a defect.

 

[MikeP]

Mike, What kind of dishwasher is it?

We have a fisher paykel drawer dishwasher that keeps throwing random errors. I am wondering if it is freq related, never thought of that... We almost always use it on Genset,

Same Brand/model! It works perfectly on shore power (or Genny at 60HZ). The frequency is the only difference I can come up with between shore/genny power - indicated 60 vs indicated 61.

The random errors defied any explanation to me until one day on the Genny when it wouldn't operate I asked myself what possible difference there is between the genny-supplied power and shore power. Since I had intentionally adjusted the Genny to run at 61 - 61.5 at no/low load, I then turned on some ac units and when the freq meter showed 60, I tried the DW and it was fine. I turned off the AC units (DW running) and the freq went up to 61 and the DW stopped/flashed red warnings.

So despite the fact that we really like the DW, it may not be the best choice for marine use if it really is that sensitive to AC frequency...unless you are willing to ensure the frequency of the Genny power is within the same accuracy as shore power.

Of course, it's possible that the DW might accept slightly lower than 60 but not more than 60 - but I suspect it wants 60 and will accept no substitutes.

 

[Pascal]

Interesting

I know things have changed with appliances, motors and electronics in the last 20 years but I used to live on st Barth where for some odd reason the power is euro 220 (one 220v hot and one neutral) but running at US freq of 60hz. Euro appliances incl air cons worked fine running at 60hz instead of 50hz except for clocks obviously

You may be on to something with these dishwashers, I m going have to look into it and check freq vs loads on out generators as so far I haven't been able to find a pattern to the dishwasher errors. And in our case with the drawer models, you can't even open it up when it throws an error because the internal lid is down...

 

[REBrueckner]

Seems digital controls ARE very frequency sensitive:

When Bill Allen [of these forums] and I took his Hatteras to Fla several years
ago, we had on board two really classy digitially controlled coffee makers his wife had just purchased. One was a Keurig. I forget why his wife had gotten them for Bill, but we burned both out with the very first use of Bill's genny. Voltage was fine, I don't recall if we checked frequency. So we reverted to the old simple on-off resistive original coffee maker and it continued to work just
fine as it had previously.

At home, during Hurricane Sandy, I ran a 5KW portable generator to power my house essentials. Our washing machine with digital controls would not function...got a error message. Again, I know
voltage was within a volt or so of 120 so I attributed that malfunction to frequency sensitivity as well. Electric motors for the frig and pool ran fine without incident.

 

[MikeP]

"And in our case with the drawer models, you can't even open it up when it throws an error because the internal lid is down..."

Yep! This happened again to us two days ago, anchored in Leeds Creek (Ches Bay). We turned the DW on with two AC units running because I knew it would work but when the AC units got to the selected temps, I forgot that although I had the blowers set to stay on, the compressors, of course, shut down, dropped the load on the penny, freq went up to 61 (per analog OEM panel gauge) and the DW flashed red with the door locked!

 

[krush]

They is usually a less stable voltage on generator....especially cheap 3600 gas generators. That may piss off the dumb "smart" appliances. My sis-inlaw got tired of the digital washer breaking---bought an new speed queen with the mechanical dial!

 

[MikeP]

For some reason - NOT based on any knowledge of the subject, of which I have none - I would have assumed that the digital TV or the microwave would be more sensitive to frequency but they don't miss a beat whether shore/inverter/Genny.

One more interesting thing somewhat related which makes NO sense to me is sort of the opposite problem:

On shore power, the convection oven/microwave will occasionally beep, and flash some message like, "select time and press start" when a light is turned on in the galley. It is not consistent - at least that I can tell - as to when it happens. It has never happened with the generator running OR with the inverter supplying power from the batteries. However, the inverter always provides power to microwave, either via the pass through when shore or Genny or directly via the batteries. So using shore/passthrough, the Micro might beep but using the Genny/pass through, it won't. WTF?

It's not a problem because it will wait for press of the start pad and if none occurs, it just goes back to "off."

 

[krush]

Aliens...

 

[Boatsb]

Aliens...

Mexican 's?

 

[doc g]

Mike , you have an inverter why not run the DW thru that instead directly from the generator . Inverter output is always correct . At least with the set up I have I can have low voltage and low frequency and as long as I run everything thru the inverter ....no problem...................Pat