I want to control the voltage from a modified sine wave inverter going into a hot water heater.
I want to use the excess power from my solar panels for the water heater.
I'm doing it now by turning on and of the water heater inverter.
I can get high and low by putting the power thru a diode and getting 600 watts.
Or 1200 watts straight from the Inverter.
I would like to control the voltage in smaller steps say 200 watts or so.
I can use my existing PLC to do the controlling it already monitors the battery voltage.
The PLC is controlling it now but i need smaller steps in the current.

Any Ideas?
I'm asking in advance this time before I make something
and have you guys show me a better way, Again.
I'm thinking of some cheepo dimmer circuit, but will It work with modified sine wave?
At least its a pure resistive load.

 

I'm doing it now by turning on and of the water heater inverter.

Does the water heater have its own dedicated inverter?

 

Does the water heater have its own dedicated inverter?

Yes

 

The way the power to electric on-demand water heaters is controlled around here is by using a triac and changing the firing angle to obtain a suitable power level.

 

Phase angle delay as Dick is implying can work. So can adjusting PWM on time to.

However the bigger question is simply why? What do you think you gain from doing so?

 

Phase angle delay as Dick is implying can work. So can adjusting PWM on time to.

However the bigger question is simply why? What do you think you gain from doing so?

I am trying to keep a constant full load on the solar panels.
600 watts is a bit to large a chunk of power to turn on and off some times.
when you turn it off the voltage goes right back up and the inverter turns on again.
I'm trying to keep the batteries from cycling so much, so basically I'm trying to be nice to the batteries.

 

The way the power to electric on-demand water heaters is controlled around here is by using a triac and changing the firing angle to obtain a suitable power level.

View attachment 128338

This is what I have now. attached.
could I replace the diode with an scr and controls to cut the power to around 300 watts.
Then with another relay from the plc increase the power back to the 600 watts.
Then when The sun is even stronger close the high relay to get 1200 watts.

 

This is what I have now. attached.
could I replace the diode with an scr and controls to cut the power to around 300 watts.
Then with another relay from the plc increase the power back to the 600 watts.
Then when The sun is even stronger close the high relay to get 1200 watts.

It sounds like you need a properly matched battery charge management and MPPT tracking load bank system.

 

It sounds like you need a properly matched battery charge management and MPPT tracking load bank system.

I am way more interested in a $15 SCR controller.
Any one ever used an scr in this fashion. to reduce the time on of one half of the sine wave

All the rest of my system works great, as is just trying to be nice to the batteries is all.
And just trying to use that extra 300 watts without the on off syndrome.

when the controller turns off something 300 watts or less the battery voltage
seems to just slowly drift up about 0.5 volts and it takes 0.8 volts to start it back up.
So it does not turn on and off while the sun is a bit to low to carry the load.

 

Well there's the right way and there's the cheap way. They rarely are the same nor serve the same function and capacity.

As for the .5 volts and .8 volts references without us knowing what voltage you run your battery system at that means nothing of use to us.

That and without us knowing what size of battery system you have and to what limits you cycle it when use most of what you say has no present value.

 

I am way more interested in a $15 SCR controller.
Any one ever used an scr in this fashion. to reduce the time on of one half of the sine wave

All the rest of my system works great, as is just trying to be nice to the batteries is all.
And just trying to use that extra 300 watts without the on off syndrome.

when the controller turns off something 300 watts or less the battery voltage
seems to just slowly drift up about 0.5 volts and it takes 0.8 volts to start it back up.
So it does not turn on and off while the sun is a bit to low to carry the load.

You could do that. I'm not sure what your inverter will think about it. The triac that @DickCappels posted might be a better choice.

 

You could do that. I'm not sure what your inverter will think about it. The triac that @DickCappels posted might be a better choice.

Yes, a half-wave rectifier puts an unbalanced load on the inverter and causes a large DC current in the output transformer which could cause core saturation and overheating.
I would not do that.

 

Or, if you have a strong need or desire to use an SCR put it in a full diode bridge so that while the SCR sees DC the inverter sees an AC load.

 

Well here it is the answer to the hot water 300 Watt $15 fiasco ,
And yes it can be done for $15.
Thank you A.A.C. Schooling and you too Dick.
My Inverter has no output transformer, no over heating, lucky I guess.
100 amps at 1200 Watts 50 at 600 Watts and 25 at 300 Watts.