Limiting domestic appliance current draw?

Has anyone tried to limit washing machine, or dishwasher, heating current draw to stay within available PV generation? A quick fix to limit the heater to 1kW or so would do!
Alternatively it might be something that an energy diverter and some logic could be useful for.

You cant limit the energy going into the appliance as it contains electronics to manage the wash/cycle etc.
What I am planning to do is feed hot water from the tank via 9mm plastic pipe during the summer and reduce the water temperature at the appliance with a TMV, that way the water going in will be 40*c and therefore the appliance wont need to heat up water as the energy profile of these type of appliances are very low.
It is worth noting that appliances are not usually designed to have hot water through them but my Melie dishwasher has a feature within the menu to have it fed with hot water that’s heated up via solar and it disables the drying function.
I am open to suggestions thou.


Of course, but at the risk of losing your warranty etc, it should be possible (but undoubtedly difficult) to install the business end of a diverter inside the machine, so that only the heater power was controlled, leaving the control gear and motors to work normally.

I was thinking of just working on the heater circuit (should have mentioned I have an old but reliable Hoover washing machine).

However - I really like Dave’s idea of feeding the machine with 40C water via a TMV. It happens that my water tank is next to the washing machine. Once I have a PV diverter heating the water via an immersion, I’ll effectively have the washing machine running on solar PV.

So maybe a device to valve the hot and cold water under some OEM logic control would do the trick.

I think that’s true of modern appliances, but not older ones. My washing machine can accept both hot & cold, and if that’s the case with yours, Simon, the problem reduces to controlling the solenoid valves inside the machine, or adding a pair externally to mix the water first.

The only argument I’ve seen for not having a hot feed relates to the low volume of water used in modern appliances; and the potentially long pipe runs. So long as the water is at say 40C, I don’t anticipate any issues with a valve and pipework designed for “cold” water.

I’d guess that the real reason for having a cold feed only is half that - as you infer, it might be more economical just to heat the exact amount of water in the machine, unless you have a store of hot water and you’re not generating off your PV. The other half might well be manufacturing cost - it cuts out one valve, its controls and all the associated pipework and assembly time, and trims the price of the appliance in the store.

I take advantage of the long pipe feed to my laundry. My modern washing machine has both a hot and cold inlet, but the only way to convince it to use the hot inlet is to tell it you want a very hot wash. I tell it I want an 80C wash and once it’s filled tell it “nah, only kidding make it 30C”. As luck would have it, due to the long pipe run, that turns into a wash in the low 40s with no local heating.

The dishwasher only has one inlet, but it’s rated for cold or hot and it’s connected to the hot. In that case I run the kitchen sink hot tap to ensure the pipes are pre-heated. That greatly reduces how much heating it has to do, but doesn’t completely eliminate it.

I have a friend who is just about to leave a large house he ran as a B&B. He had similar long pipe to the furthest bathroom, and installed a return loop with a pump so that the guests didn’t have to wait for the hot water to arrive!

That is an option Robert, a pumped secondary loop, but a TMV would still be required to reduce the temperature of the water. For me the best option is to install a plastic 9mm pipe as even a 5m run will only contain 318ml of cold water. The next hurdle comes in how to deal with A) Winter, when the hot water isn’t free and B) Wasting hot water during the rinse cycles. Thinking potentially a momentary push switch that activates a solenoid for a set time period (30mins?) but that then rely on the wife being able to interpret when the waters been heated with free solar rather than gas.


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It has to be user-friendly and that’s where I think some logic from OEM can really help.

Great discussion.

I have often thought this problem could and likely will be solved by manufactures in the future with smart appliances. It could be solved adding some logic into the dishwasher specifying a maximum current draw allowed to keep within the generation capacity of the PV.

I read this post through one day thinking it could be added to with some code to control the heating element. A workable solution might be that openenergymonotor sits at the meter and measures current in/out of the premises (and may or may not divert excess to HW). This data would then be transmitted to inform any listening nodes of the excess power available. The dishwasher and any other appliances that want to know could then have access to this data to decide when and how to operate.

Very rarely am I in a hurry to have my dishes washed. I could see that 2 modes could be programmed, one instant cycle at full power and one solar wash that might take a max of 6 hours or so, using only excess energy to heat unless a pre-defined time is exceeded.

Just my thoughts. I’m not sure I’ll get the approval from my partner to hack a working dishwasher :slight_smile:

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My old washing machine (and dish washer) had a hot fill option. However, I found that for any wash hotter than 30c it would take both hot and cold unless set to a 90c wash. I too fooled it for a while by filling while set to 90c then turning down.

In the end I added a mains relay in series with the cold solenoid wired for normally closed. The coil was across the hot solenoid so if it called for hot or a mixed feed the relay was energised and the cold solenoid was turned off. However for a cold wash (or rinsing) the cold solenoid operated as normal.

I was very disappointed that hot fill machines are almost impossible to find (in my price range). Given many have combi boilers and some have multipoint water heaters often in the kitchen the “long pipe run” argument would seem bogus.