question

steve-fowler avatar image
steve-fowler asked

Washing machine problems as frequency varies on AC coupled off grid system.

I have a medium size off grid system, consisting of the following:-

20Kw battery bank, 2 Multi plus inverter chargers (in parallel 240Volt 50Hz), 3 PV arrays (1Kw each),

I Venus GX system to control and report what's going on and one 11KVa stand by generator.

This system worked great but due to increasing the load by adding a deep well pump and a large irrigation system with a 1.5kw pressure pump I needed to add extra 240volt power to the system.

As the system also supplies power to another area of the property I decided to add another 4.5Kw of PV panels and a 3Kw grid tie inverter AC coupling it to the 2 Multi plus inverters and providing the whole property with a "mini Grid" which would be beneficial for future expansion.

This all works fine, the multi plus inverters controlling the output of the grid tie inverter and using the GX to limit the battery charging, all good, except!

As the multi plus units push up the frequency (50.5 or more) the washing machine goes into fault mode and stops working.

I have nearly 30 years experience in off grid installation and understand a lot about electronics. I have also travelled a lot around the world in my own yacht, fitted out with Victron inverters etc. When I arrived in South America, where the power is 240Volt but 50Hz many people in the anchorage were reporting problems with their washing machines and starting to ditch them overboard. I mentioned to a few that their problem was Frequency related and if the tried to run their washing machines on their own generators the problems would go away. This proved to be the problem and I managed to save a few people lots of money, unfortunately one German guy had already convinced himself the machine needed new parts and he had ordered them from Germany at a cost of over €1000 plus 40% import duty. He was very red faced when he started his generator and the washing machine work faultlessly!

So I have tried several things to get a steady 50hz but frequency is difficult to convert. I have already tried using a VFD and I can get a steady 50Hz even as the input varies. The VFD will not drive the washing machine though, even with a balance load connected.

At the moment my solution is to use an independent Inverter power supply just for the washing machine.

I could try and find a washing machine that is Frequency tolerant but none of the washing machine manufacturers I have contacted will talk to me the standard answer is " for health and safety reasons

please contact your local dealer". That just brings a blank look on their faces as the problem is beyond their pay grade.

So anyone got any ideas?

AC PV Coupling
5 comments
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Robert avatar image Robert commented ·
Hello, this is very interesting.

I want to run a German made wash machine/dryer in the future as well with my Phoenix Smart Inverter 24/5000.

Did you know why the Mulit goes higher than 50Hz?

Best regards Robert



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steve-fowler avatar image steve-fowler Robert commented ·
Hi Robert.

Yes the Multi goes higher than 50 Hz to control the Grid tie inverter that is connected to the output of the Multi. This is so the Multi does not over charge the batter bank.

This part of the system works very well. We are in southern Portugal and get lots of sun.This morning for instance the PV inverter (Panels pointing SE) was giving out 1890 Watts at 07:20 Portuguese time. Our 2 other Panel banks are pointing S & SW respectively . So they come on line later in the day. The battery bank is charged early in the morning and then we use the solar via the inverters to supply our daytime needs of water pumping, irrigation and workshop. When it get very hot +40*C we cool the house down in the afternoon with AC powered by any excess solar. Everything works extremely well except the washing machine, which gets upset by the very small change of frequency.

I know this frequency problem is fairly common as I described in my post. I will come up with a way round it and will post on here to help people. At the moment we get over the problem by switching out the Grid tie inverter and pulling the frequency back to 50Hz by applying a moderate load to the multis the the washer works fine. I just want to make this all happen automatically.


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Michelle Konzack avatar image Michelle Konzack steve-fowler commented ·
Please can you tell me the BRAND and TYPE of the washing machine please?
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Mike Dorsett avatar image Mike Dorsett commented ·
No problems with old fashioned twin tub....

I think that the best solution here would be a separate inverter for the washer. I've thought about this for driving individual heavy loads that are only occasionally used, but so far have not had the need.


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graham-perry avatar image graham-perry commented ·

I am currently having similar issues with running our UK purchased washing machine off of the generator, but the unit works fine off of the MultiPlus inverters (two 1600/70's in parallel).


Checking the output frequency of the generator, I see 54hz. I have a question into the manufacturer of the generator on the ability to dial the frequency in.


The MultiPlus is putting out a solid 49.9-50.1hz.


We never had any issues with the washing machine until we plugged into the dock in Tahiti and then discovered that Tahiti is 60hz. I suspect that we have damaged the PCB in the washing machine as now it seems to be very sensitive to the voltage frequency.

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4 Answers
JohnC avatar image
JohnC answered ·

Hi @Steve Fowler

I very much doubt this is Frequency related. Gensets usually don't even come close to holding a stable frequency, yet you say they usually cure it.

The trouble with being offgrid is that there's no 'infinite' grid to buffer things, so any feedback from the mongrel 'switching' kit within some appliances gets reflected back from a standalone inverter. And then that appliance baulks at some fault in the power quality that it's actually caused itself. Gensets at least have a little spinning reserve that may help counter this.

You'd need a scope to see what's going on, but then would need to also know what to look for as the culprit. The appliance makers won't help. as they'd have to admit their kit is designed only for a grid buffer, and useless without it.

I came across this many years ago with a (non-Victron) standalone inverter and a washer too. I tried adding a 45metre long power lead to the washer, and that dumbed down the power faults enough to let it work.

This may not help you much, but maybe a broadening of your Hz fixation is warranted.. :)

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Trevor Bird avatar image
Trevor Bird answered ·

Hi @Steve Fowler . I have read your story with great interest because of the detail you have gone into and the apparent reason for the failing washing machines. I completely agree with JohnC that the frequency shift you mention is not the reason for the problem. A mains frequency variation of 0.5 hz is so minimal that it would have practically no impact at all on the operation of equipment. Even a variation of a couple of hz would not be noticed. As mentioned by JohnC, generators can vary that much without concern.

What is of interest may be the nature of the load presented by the washing machine. I am guessing here but it makes sense that a washing machine runs a motor at varying speed. The method of changing the speed of the washing machine may be to vary the amount of the sine wave presented to the motor, in other words change the duty cycle of the power supplied to the motor. This can be achieved with electronic triggering of mosfets to provide a small amount of power (say only 5 degrees of a 360 degree sinewave ) or a lot of power like all of the sine wave. The multiplus is rated to take a crest factor of 3. That means the peak curent drawn can be 3 times the RMS current drawn meaning quite a distorted waveform but beyond a crest value of 3 the specifications don't say.

The start and stop characterisitc of the sine wave may seem inconsequential but in fact provide an enormous amount of distortion of the current waveform to the load. Fourier analysis can show that say, a square wave has a certain series of harmonic components to make up the square wave. It looks like a square wave in the time domain but it looks like a series of sine waves of varying amplitude at harmonic frequencies (odd harmonics for square waves actually) in the frequency domain. This helps relate to the distorion measurement known as Total Harmonic Distortion (THD). A pure sine wave doesnt have any total harmonic distortion because it only consists of the fundamental frequency (50hz).

As metioned by JohnC the grid has virtually infinaitely low impedance so the very distorted current waveform has little impact upon the voltage waveform. Also, but to a lesser extent the impedance of the generator can handle a distorted current waveform and not suffer too much distortion of the voltage waveform.

The inverter may be a different beast however and when presented with a very chopped and distorted currnet waveform may provide a very distorted voltage waveform that the washing machine may not like. You mentioned a dedicated inverter for the washing machine which is interesting becasue if the original inverter doesn't drive the washing machine load, I cannot explain why a dedicated one would unless the loaded inverter has a distorted voltage waveform but the unloaded inverter has a slightly less distorted voltage waveform.

The washing machine retailers will not know anything about this problem because they are not used to dealing with systems that cannot handle the non-linear nature of the load the washing machine presents. Put simply it is not the washing machine fault. It is a supply issue.

The trick may be to provide some damping of those harmonic distortions. If you had a simple, very basic isolation transformer to feed the washing machine, the inductance of the transformer may just be enough to reduce the harmonic distortion for the washing machine to work. I am not suggesting the isolation transformer is being used for its normal purpose but to merely introduce some inductance into the feed to slightly reduce the harmonic distortion. This is only a suggestion of an idea that could be tried if an isolation transformer is conveniently available.

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Michelle Konzack avatar image
Michelle Konzack answered ·

Very interesting topic, because I have a washing machine from Beko and one from AEG and both have no problems running from 45-55Hz on a MultiPlus-II 25/5000...


However, I just I vestigated the topic a little bit and my conclusion is, that ALL in Europe availlable washing machines are frequency tolerant from at least 47Hz to 53Hz because otherwise the washing machines would stop, if Grid Providers shifting the frequency to stop GTIs overloading the Grid...


Also I so not know a singel GenSet between 2kW and 9,5kW which has a stable 50Hz frequency. The are all shifting between 45Hz and 55Hz and I have never heared of someone which sayed, that his washing machine stop working if it is not exact 50Hz.


I assume, that the error must be somewhere else.


MAYBE the GenSet produce higher voltage?


I had this issue with a rental SDMO HX6000 (230V/6kVA/4,8kW) which outputted 252V instead od 240. My MultiPlus-II is setup to 240V and everything is working PERFECT, but if the HX6000 is connected to charge the Batteries, my Panasonic MicroWave stop working... she simply refuse to work with voltages above 250V.


MAYBE you should check this too.


Have a nice evening

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Paul B avatar image
Paul B answered ·

If I understand you correctly the issue is only occur9ing when the batteries are full and the mutli starts to frequency shift upwards to derate the PV inverters you have.

so of cause you could change to DC coupled and this would solve it as then frequency shift is not required anymore.

or if the PV units you have can be controlled by serial or can bus like the Fronius inverters then this is another way to derate them.


Or you could turn off the frequency shift and then setup a assistant to control AC2 out and connect the pv inverters to ac2 out so that when battery voltage raised to say 56v then the ac2 out would open and thus turn the pv units off, this is a heavy handed way of dealing with it though, especially for the pv inverters.


or only do your washing when the batteries are not full


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tilo avatar image tilo commented ·
Or implement a dump load system (water heater, air heater) which acts before the Multiplus starts shifting the frequency.
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