Prototype water heater - direct DC and AC using Classic PWM

[ClassicCrazy]

I have been tinkering with heating hot water for awhile . My goal was to make only as much hot water as I needed so I had to have a way to vary the amount of water being heated. I also needed to make this system able to drain out since it is in unheated shed. So far this is what my prototyping came up with . I made the video to describe this since it is a bit convoluted. I also gave a brief look at the rest of my PV system. 
Here is the video on Youtube if you are interested
https://youtu.be/Non3H88UzPs

Larry

[Vic]

Hi Larry,

Thank you very much for showing all of your work on water heating.

Looks to be a very comprehensive system.   A good demonstration for the rest of us,  who have yet to take that next step.

Had always thought that we would use excess PV power,   and PWM  from a Classic to do the same.  Being lazy,   we just added some additional PVs,   and  heat water as a Opportunity load on 240 VAC from the inverters.   You approach is more elegant,   and more automatic !

Thanks,  73   Vic

[boB]

Larry, I did NOT know it was you in that video until just now !

Or, maybe I just didn't remember ?

Anyhow, great stuff !

[ClassicCrazy]

Hi Larry,

Thank you very much for showing all of your work on water heating.

Looks to be a very comprehensive system.   A good demonstration for the rest of us,  who have yet to take that next step.

Had always thought that we would use excess PV power,   and PWM  from a Classic to do the same.  Being lazy,   we just added some additional PVs,   and  heat water as a Opportunity load on 240 VAC from the inverters.   You approach is more elegant,   and more automatic !

Thanks,  73   Vic

It will be more automatic again when I get the IGBT figured out and installed. I  keep forgetting to turn off the DC direct in time and over heating the water. But at least I can just add some more cold water and bring the temperature down pretty easily.
The PWM on the AC side sounds so complicated when reading and thinking about it but turns out to be pretty easy to do it in real life.
My approach is functional but not so pretty eh ?
My first prototype experimental controls was working pretty well but it was all mounted on wood and in some plastic container holders . When working on the direct DC rack I disconnected the temp PV install and put all the heating on AC. But  I was kind of dumb and was using cords with plugs from the heating coils to an outlet - and I overloaded the outlet or it had high resistance from the plugs or both. I came back one day to find the whole thing melted and burned up. It did not instill confidence in me using those plastic outlet boxes when I see how they just melt and burn. So at least I sort of got my act together on this newer one and added two AC circuits, hardwired the heating coils, and have everything in metal boxes now.

Larry

[ClassicCrazy]

Larry, I did NOT know it was you in that video until just now !

Or, maybe I just didn't remember ?

Anyhow, great stuff !

Thanks Bob !
I just hope my setups can be of help to others who are more of novices like me and accelerate their learning curve.

Larry

[boB]

Thanks Bob !
I just hope my setups can be of help to others who are more of novices like me and accelerate their learning curve.

Larry

That is what I was thinking...  Helping others.

I don't think you are as "novice" as you are eluding to though 

But you work with what is available very well.

[ClassicCrazy]

Edit - got  the off problem figured out by putting 20k resistor between control pins .
( thanks to Roy Rak )

I was experimenting with the IGBT block I have.
I need to figure out pull down resistor ? since it doesn't shut off .
This is video of my experiment with that if anyone has 7 minutes and some free advice .
https://youtu.be/pFsO8_1QbKY
I had wrong data sheet in video - correct one attached - but it was almost the same.
Thanks
Larry

[boB]

If you want even a faster pulldown, to help the IGBT's or FET's gate, you can do something like this quick LTspice simulation...

You don't want the gate turning off too slowly otherwise it can get hot from staying in that linear region too long.

[ClassicCrazy]

Thanks Bob for the circuit.
I guess that would be needed if I want to start PWM'ing it  ?
For now I am going to just use it for switching off with thermostat.
Roy has told  me about some ways of control schemes  using PWM to get better matching ( mppt ?) from the direct PV array .
But it is a bit too technical for me now - takes me awhile to understand some of that.
But I am going to study the circuit you drew so I can understand how it works . It looks simple enough to solder that together too.
I saw a used IGBT that had some kind of control board on the pins - it may have been something like you just suggested .
Tomorrow I am going to put the IGBT on a heatsink and then hook it up and see if it works for just on off by thermostat.

Larry

[boB]

Oh, OK.  Just turning off once in a while is fine using a resistor.  A lower value resistor will turn the IGBT off faster but then you will have to drive more current.  20K is a good compromise.  This is all a compromise you know    That's engineering.


How this circuit works is that the transistor (PNP here) uses its gain to make the resistor look smaller but only when the driving output turns off so you don't have to drive that low resistance when it is on.  Well, the resistor you see in the diagram is being driven but not the real low equivalent value.

When the driving voltage goes away, (off), a 10K resistor might look like a 100 Ohm resistor but the PWM or driving circuit doesn't have to drive 100 Ohms (higher current) when the output is on.

The diode isn't needed really, it is here to simulate the output from PWM or thermometer that only goes high and does not pull the voltage low on its own.

A Classic Aux output is like this as well.  Actually, I think there is some resistance on the output but I forget !  Could look... 

Say hi to Roy !  One of the three Roys in this industry.  There was an evil Roy and a good Roy and another but can't remember the other Roy "type".

Roy Dyngen, Roy Butler and Roy Rak(ovich).  I like all 3 myself 

[ClassicCrazy]

Thanks for explain of how that circuit works.
Yes it is good to have Roy Rako living close by and encouraging me on and answering my questions.
Darn cold here tonight - down to 12 F at midnight already . Coldest night here yet this winter.
I drain the water heater after use and bring the pump inside . Doesn't take me too long to clip it in and out .
Tomorrow I fill it up again when the sun is out and get the water heating - kind of fun to transform energy like that from PV to heat.
It works !

[boB]

Heat is wonderful especially this time of year !  So you live near Roy !  WoW !  NO wonder it's cold there.

I really want to go to my place near Phoenix, AZ !  I have a lab down there AND the sun works down there.

Maybe during Christmas time.

Stay warm ! 

Brrrrrr....

[ClassicCrazy]

I lived in Phoenix one winter - back in 70's . So I know what the weather is like there  - kind of nice compared to here in Wisconsin !
I stayed at the hostel which was the old Sears Roebuck mansion near South Mountain . It was at that time surrounded by citrus orchards and you could go walk around and glean oranges that got skipped. There was a very elderly woman who still lived in what must have been a family homestead house in the area near there - there was a small orchard of pecan trees of every variety - round , long , hard shell , soft shell, etc. We could go pick up nuts from the ground there for some small amount of money.  And there was a carrot packing house where you could get a whole gunnysack of reject carrots for a dollar or two . They were really super sweet and good for making into juice.  I went with some Australian gals one day to try and make some money harvesting green onions. You had to grab a handful, sort them into a bunch , but a rubber band on them, and then make a whole stack of those bunches. We earned like 50 cents an hour. The Mexicans who did it were super fast at it. Anyway we didn't go back. The worst part of it was we worked all morning and you harvested  this little area , then looked up and saw a huge field of acres of green onions in front of you !

Maybe you can build or get a magnetic loop antenna when you are there in Phoenix so we can try to talk to  you on the ham radio. I know I was able to make plenty of contacts to Arizona last winter when I was playing around on FT8 - although many of those contacts are so down in the noise you probably couldn't even make contact via CW.  I guess there is FT8 Call that allows for some chatting instead of regular FT8 that is just quick contact.  Always fun to play on the ham radio in the winter. I have put up a full 160 meter loop here - not too high above the ground but it works pretty good , tunes up on all bands , and makes lots of contacts on FT8 all over the world - even some far away stuff on 160 meters. Fun catching those fleeting puffs of propagation that wisp in and out.

[boB]

One reason I got a place down there, besides being warmer, was so I might find a neighborhood with lower background EMI noise than I have up here in Everett, WA.

It is awful here.  On good propagation and contest days I can listen to CW while I work but I cannot just turn the radio on at any time and expect to hear anything, much less, work anyone.  S8 to S9+ here.  In Sun City, AZ, my background noise is more like S6 or S7 on 40 meters.  Not great but better than here and I was actually able to make a SSB 20 meter contact last February.  Mobile is my only other option here.

We had a local power outage during the summer and so I took that advantage to turn on my radio here using batteries.  Background of S0 !  It was great !

When the power came back on I turned off my main house breaker and the noise was still S9-ish so I know it's not me making the noise.

All of this is one reason I want to try and make sure the B17 emits low as possible EMI on HF and conducted emissions.

We'll see about putting up a longer antenna for 80 meters or possibly even 160 meters but I kind of doubt that will happen in Arizona.

[ClassicCrazy]

Good thing you got to hear the ham radio when the city power was out - that is amazing difference !
So many new devices are bad . I have two friends who had LED light bulbs that made trouble. One knocked out an over the air TV station on VHF ( the only one left on VHF here )
The other friend it wiped out a local community FM radio station. Turning off lights fixed both . But I know there are better LED light bulbs that don't do that.
But I also have a Morningstar Sun Saver Mppt - small one maybe 20 amps ?  I  had it on a mobile solar cart I made out by the driveway - and when I parked my car near it - wiped out FM station on the car radio. True all these stations that got wiped out were weaker signals but they all did work  before.
The Morningstar makes a very very high pitched squeal that I can hear. I always ask friends who are over if they can hear it and most can't. So at least I know I have good hearing !

Larry