DC water heater.

[efficientPV]

You can use PWM DC into an immersion heater/s. I'll dig out the approach

View attachment 202986

It is easier than that. Eliminate the inductor and capacitor in the output. Just simple PWM duty cycle with lagger C1. Preset a minimum off time every 10ms and you can use standard mechanical thermostats on the output DC. It is curious that the Polish are one of the main sources of this equipment. You can build your own with only one integrated circuit.

 

[mciholas]

You can use PWM DC into an immersion heater/s. I'll dig out the approach

Thinking about this more, this solution is overly complex. You don't need an inductor.



PV panels feed input cap. MOSFET (or IGBT) connects input cap to water heater. PWM the MOSFET to get the desired voltage on the cap.

That's all you have to do. The inductor is there to provide steady power to the load, but the load doesn't need it.

I'd put a free wheel diode on the MOSFET output just to catch wiring inductance.

The software would monitor the voltage and duty cycle to optimize the panel power delivery. A current sensor would add to the capability if desired.

This would be very efficient, no inductor losses. Since the DC is chopped, the AC thermostat would work.

Depending on size of the capacitor, this can run at slow rates, say 20 Hz. You want to avoid 30 Hz to 20 KHz since that makes audible noise.

(Parts nominated above are notional, not checked)

Edit: I see efficientPV had the same idea...

Mike C.

 

[marksman]

It is easier than that. Eliminate the inductor and capacitor in the output. Just simple PWM duty cycle with lagger C1. Preset a minimum off time every 10ms and you can use standard mechanical thermostats on the output DC. It is curious that the Polish are one of the main sources of this equipment. You can build your own with only one integrated circuit.

View attachment 203014

What kind of Chinese board is that? Is it related to the meter at the right side?

 

[solarsimon]

Thinking about this more, this solution is overly complex. You don't need an inductor.

View attachment 203015

PV panels feed input cap. MOSFET (or IGBT) connects input cap to water heater. PWM the MOSFET to get the desired voltage on the cap.

That's all you have to do. The inductor is there to provide steady power to the load, but the load doesn't need it.

I'd put a free wheel diode on the MOSFET output just to catch wiring inductance.

The software would monitor the voltage and duty cycle to optimize the panel power delivery. A current sensor would add to the capability if desired.

This would be very efficient, no inductor losses. Since the DC is chopped, the AC thermostat would work.

Depending on size of the capacitor, this can run at slow rates, say 20 Hz. You want to avoid 30 Hz to 20 KHz since that makes audible noise.

(Parts nominated above are notional, not checked)

Edit: I see efficientPV had the same idea...

Mike C.

Quote below explains the inductor is for suppression

The Inductor and C2 provide filtering to limit dI/dt and dV/dt on the external cables. D1 is used to catch the back emf spike and energy released by the inductor when the MOSFET switches off. Whilst this arrangement may look like a low side switched buck, it isn't!. This arrangement is sometimes referred to as a Linear Current Booster - it maximises the output current without excessively loading the input. With some tweaks, this circuit could easily be used to maximise the current (i.e torque) delivered to say a DC Solar irrigation pump.

 

[efficientPV]

Yup, its a screamer that will drive radios nuts. I totally discounted that idea as having no real advantage. Sourcing inductors for people around the world is a pain. I got a ton of oil caps I'd like to do something with. But, big electrolytics are much more available. Operating at 50Hz max allows spark interrupt and FET can have slow transition for no noise. This was my first one put together in an hour from scrap in the garage. Note IP57 weather protection.



I guess everything from China is related. That is a searched as a 300W inverter board. You never know what chip you get, they all will work. FET are low voltage and must be changed over 48V. Clearances are poor. This is a later version which is easier to modify with less cuts to board. Looks less home made. It is just a half dozen parts and easier to build from scratch. Stuff from China keeps changing making it hard to give directions.


I just roll my own. This one is pulsing 25A into a 0.7 ohm load. Lets see Loadmaster do that.

 

[sunsurfer]

This thread is getting interesting. These water heating threads always seem to head that way.

I have always wanted to build a heat pump diversion load for water heating using a PLC. This could allow for a VARIABLE output. I would just pull from the batteries at their top voltage and have the PLC ramp up or down a 3 phase AC compressor using a VFD. This could be a regular solar setup vs a dedicated panels just to heat water. I think using an MPPT from the panels is the best option to batteries. It doesn't have to be a big battery, just enough for when a cloud goes over.

Could use a lower voltage compressor if you didn't want the inverter for 120/240v AC to the VFD. I know they have the 12v/24v brushless 3 phase compressors getting more common. I'm not sure if there was a 48v version out there. The inverters they come with should have a control lead that the PLC could feed for output control.

PLCs are cheap to find, reliable, programmable and work well controlling VFDs. They could be tied into a Victron system using their Raspberry Pi software.

Might as well pull some heat from a walk in freezer and dump to the hot water tank while we are at it.

 

[Zwy]

Just use one of these if you want to start a dump load at battery full voltage, I doubt $15 will break the bank. https://www.ebay.com/itm/2849250939...rZbdK9_mQSC&var=&widget_ver=artemis&media=SMS

 

[sunsurfer]

Just use one of these if you want to start a dump load at battery full voltage, I doubt $15 will break the bank. https://www.ebay.com/itm/2849250939...rZbdK9_mQSC&var=&widget_ver=artemis&media=SMS

That is a simple solution. How about more than 1 that is staged so that the diversion can change as solar increases or decrease? Assuming the voltage control is fine enough. Run directly to an AC compressor for a heat pump. The delay is nice for avoiding compressor lock up with to much head pressure

Could use it to simply turn on and off a cheap inverter running a compressor. I like this relay idea. Thanks!

 

[wpns]

I would love to be able to divert to an RO or UF water generator, but I’m not sure how they react to being turned on and off frequently.

 

[Zwy]

That is a simple solution. How about more than 1 that is staged so that the diversion can change as solar increases or decrease? Assuming the voltage control is fine enough. Run directly to an AC compressor for a heat pump. The delay is nice for avoiding compressor lock up with to much head pressure

Could use it to simply turn on and off a cheap inverter running a compressor. I like this relay idea. Thanks!

I'm amazed that a heat pump water heater doesn't have much for load. On average mine uses about 3Kwh per day. Sunday the Official Loads Tester did 3 loads of laundry and ran the dishwasher, the heat pump water heater used 5.8 Kwh for that entire day heating the tank back up. You can program the control using the app to only run certain times of the day and what is used for heat- heat pump or resistance element.

I was originally looking at just a resistance element water heater combined with the relay but decided why not get the hybrid heat pump unit that also has a resistance element? This allows me to dump power at the end of day in large quantity by increasing the tank temp and using the resistance element by using the phone app. I can change it as long as I have cell service with data, even 500 miles away.

 

[sunsurfer]

I'm amazed that a heat pump water heater doesn't have much for load. On average mine uses about 3Kwh per day. Sunday the Official Loads Tester did 3 loads of laundry and ran the dishwasher, the heat pump water heater used 5.8 Kwh for that entire day heating the tank back up. You can program the control using the app to only run certain times of the day and what is used for heat- heat pump or resistance element.

I was originally looking at just a resistance element water heater combined with the relay but decided why not get the hybrid heat pump unit that also has a resistance element? This allows me to dump power at the end of day in large quantity by increasing the tank temp and using the resistance element by using the phone app. I can change it as long as I have cell service with data, even 500 miles away.

Those are some pretty good numbers for water heat. Definitely do able for off-gridders. In the summer time you will get unseen gain from the cooling and drying on the cool side of the heat pump. Nice feature if you live where there is humidity.

I will probably build my own heat pump water heater (I already have a couple of stainless indirect tanks with heat exchangers built it) and have it prefeed into a small 3KW range on demand water heater. The hot water tank will just get excess solar when available (load diversion).

 

[sunsurfer]

I would love to be able to divert to an RO or UF water generator, but I’m not sure how they react to being turned on and off frequently.

I'm trying to figure out what RO or UF stands for. Getting mix results on google. Are you talking about condensing water from the air? If they are compressor driven, they will not do well going off and on frequently.

 

[ksmithaz1]

I'd guess reverse osmosis (RO) Ultra Filter (UF).

 

[wpns]

I'm trying to figure out what RO or UF stands for. Getting mix results on google. Are you talking about condensing water from the air? If they are compressor driven, they will not do well going off and on frequently.

Sorry, Reverse Osmosis and UltraFiltration.

 

[Zwy]

Those are some pretty good numbers for water heat. Definitely do able for off-gridders. In the summer time you will get unseen gain from the cooling and drying on the cool side of the heat pump. Nice feature if you live where there is humidity.

One of the deciding factors was the temp and humidity reduction in the basement. Inverters and SCC's are down there along with the battery bank. Before we installed the system, we cut the floor 12 inches from the wall, jack hammered that out and installed a footing drain and cemented it back up. Ground the floor, parged the basement walls and put down epoxy on the floor and waterproofed the walls. That cut down the humidity in the basement considerably. I noticed last summer with inverters running it would get warm and humidity level was high even with air conditioning upstairs. The HPWH should help not only in the basement but also on the main floor.

I will probably build my own heat pump water heater (I already have a couple of stainless indirect tanks with heat exchangers built it) and have it prefeed into a small 3KW range on demand water heater. The hot water tank will just get excess solar when available (load diversion).

Don't know your location but the Rheem units qualify for the 30% federal tax credit. I purchased from Menards, it was on sale and had an instore 11% rebate to boot. I wanted a load diversion and in some respects it still is when PV is limited. I can turn it off with my phone and run off the propane water heater. I just shut if off now as the sun is going down, ran temp up to max today. Weather looks to be cloudy tomorrow, then snow thru the night and again over the weekend so I'm not expecting much for PV yield over the next 5 to 6 days.

 

[B-Mod]

One of the deciding factors was the temp and humidity reduction in the basement. Inverters and SCC's are down there along with the battery bank. Before we installed the system, we cut the floor 12 inches from the wall, jack hammered that out and installed a footing drain and cemented it back up. Ground the floor, parged the basement walls and put down epoxy on the floor and waterproofed the walls. That cut down the humidity in the basement considerably. I noticed last summer with inverters running it would get warm and humidity level was high even with air conditioning upstairs. The HPWH should help not only in the basement but also on the main floor.


Don't know your location but the Rheem units qualify for the 30% federal tax credit. I purchased from Menards, it was on sale and had an instore 11% rebate to boot. I wanted a load diversion and in some respects it still is when PV is limited. I can turn it off with my phone and run off the propane water heater. I just shut if off now as the sun is going down, ran temp up to max today. Weather looks to be cloudy tomorrow, then snow thru the night and again over the weekend so I'm not expecting much for PV yield over the next 5 to 6 days.

Can you change the water temp remotely also?

 

[Zwy]

Can you change the water temp remotely also?

Yes, you can change mode (heat pump or element), temp, set up a schedule (which can change temp automatically thru the day if desired) and view Kwh used. Very nice app.

When using a phone to set up the water heater with the app, you will see a popup screen where you have to turn off cell data. It won't connect to the wi fi network in your home if you don't, it will just give an error. Took me a few tries to figure that out.

On days where there is limited sun, I can turn down water temp using the phone app, then if batteries get fully charged and I have some excess, I can turn the water temp up anywhere I'm at. The same applies if excess PV is available and cloudy weather is forecast for the next day, I'll run temp up to max, then turn the temp down when evening comes.

 

[efficientPV]

That is a simple solution. How about more than 1 that is staged so that the diversion can change as solar increases or decrease? Assuming the voltage control is fine enough. Run directly to an AC compressor for a heat pump. The delay is nice for avoiding compressor lock up with to much head pressure

Could use it to simply turn on and off a cheap inverter running a compressor. I like this relay idea. Thanks!

HPWH aren't the best dump load because you can only dump about 100W. With a voltage relay you need to add a few smarts. You don't want to have hot starts locking the compressor or running the compressor for just 3 minutes. A timed on period started by a voltage trigger is a must. I run a fridge from a micro that only runs when the battery is near full charge. It has lots of conditions built in like automatic reset. Ideas are great but you learn a lot from experience. Simple ideas usually bite you in the butt.

 

[Zwy]

HPWH aren't the best dump load because you can only dump about 100W. With a voltage relay you need to add a few smarts. You don't want to have hot starts locking the compressor or running the compressor for just 3 minutes. A timed on period started by a voltage trigger is a must. I run a fridge from a micro that only runs when the battery is near full charge. It has lots of conditions built in like automatic reset. Ideas are great but you learn a lot from experience. Simple ideas usually bite you in the butt.

The hybrid I have has both the heat pump and resistive heating element. One can choose the 4500W element as dump load once battery is full, I've done it as I had excess PV. All done with the app on a phone. For days in a row of great PV yield, the heat pump mode can be used and any excess over that can be used for other purposes.

I'm impressed with the options and control of the unit I purchased. Very ideal for a solar system.

 

[efficientPV]

I use resistance heating with my HPWH. That and other modifications are just too exotic for most here.