Hot water

[Treehouse]

Ok I know this has been talked about to death.... But here goes..

The problem, My friend has a nice RE system 2kW solar 1.5kw turbine and fresh new battery's 1100Ah and 2000 Watt trace inverter,  all equipment in a nice outbuilding about 50 feet from his house. The A/C line from there to his house, much cheaper and safer for insurance. Also in the outbuilding is two c-60's for dump load control, one was not enough!(I wish)  Most day's by noon he is dumping lots of power. What he would like to do is use that power for domestic water heating.

 Solution?
 1 -  Using both c-60's he would need 200 feet or more of very expensive big wire and two custom 24V water heating elements  140$? ea. I don't think this would work RF noise, inductance, line loss would be horrific!

 2 - Then there is putting the hot water tank in the outbuilding and burring the water lines.. I think this would waste a lot of water. In my house 15 feet from hot water tank to my bathroom takes a bit of time to get hot. I can't imagine 50-60 feet.. Then there is the freezing thing in the winter.

I have been playing around with some ideas, A/C relay on inverter output, but as talked about in other posts is not a viable solution, due to poor output transformer loading. Also talked about is how the batteries like PWM vs. bang-bang  type control, so I would like to remain on this path. 

So what to do?  Has or does anyone here do this? How? I'm sure if such a solution existed a lot of people like my self, only on a much smaller scale would like to see it.

 

[OperaHouse]

This would be a good project for that UNO you have.  Water heaters generally have two elements.  You can select which one the dump goes to.   Backup main power can be set at a much lower temp.  Extra tanks and other loads can be switched on.  Decisions can be made on battery voltage and daily conventional dump history.  Then a seperate dump inverter can be turned on for a timed period.  None of this infinite control baloney.

I would never touch the conventional dump load.  I wouldn't want someone looking at me after a blade went through his car.  I would use the GHURDism, Know thy battery.  A micro could easily kjow the state of the battery and if there was a history of conventional dumping.  A seperate dump inverter of only 1,000w would be more than sufficient.  At camp I hav only a small tank and 50W dump gets me a shower that night.  At home years ago my gas water heater went out. I did a tempory replacement with an electric only running on 120V.  That is about 700W.  Havent felt the need to upgrade yet.  So, the inverter solves that long run problem.  Trouble is that you will soon find there is more power than dump.

Control can come in many forms.  I thought about a non computer method.  A resistor is tied to the conventional dump load.  That resistor is mounted to an aluminum plate.  On that plate is mounted a clixon thermal switch.  When batteries are near charged and excess power is dumping, the aluminum plate heats up.  That closes the thermal switch and turns on the dump inverter.  When excess is gone, plate cools off and inverter turns off.  Monitoring and timed dump.  Perfect. 

[Treehouse]

  Finally got a hold of a DC solid state relay to play with and have been having fun playing with it   Grabbed a cheap square wave 800W inverter connected to a bridge rectifier then out to the ssr. I Altered the program of my home made dc dumpload controller and connected it to the ssr. I started with a 100W flood light, it took me several attempts of hardware and software changes but I think I have working!   Then I moved to a larger load, a 400W quarts heater.  All seems to be working ok but I'm a little concerned about the ssr temperature.. Is it normal for them to get rather hot?  From the rather large heatsink it came with this may be ok but does anyone have any experience with them and have some guide lines on what is ok or not ok?

[madlabs]

My rule O thumb is that you should be able to keep a finger on it for at least a slow count of 5 or so. Hotter than that and it may not last too long.

Jonathan

[Treehouse]

Well it seems to be working like a champ! I added a very small fan controlled by my dump controller and the ssr only sits a few degrees above ambient. I came home today and it was dumping 150W, amazing how that little amounts to heat! All was running nice and cool nothing, but the heater was even remotely warm. Now I have to get more solar to test it to my full 400Watts I don't think my wife will go for it, lol If not I will mock up a second unit and take to my friends house.. I will limit it to 400Watts and slowly bump it up, getting him to take measurements along the way..  As always having to much fun!!

[SparWeb]

...Most day's by noon he is dumping lots of power. What he would like to do is use that power for domestic water heating...

I do this already.
Ghurd designed it, I built it, and still use it.

I have a controller that has a "sniffer" wire on the CC's dump load.  When it detects that the dump load is active, it flips on its own (separate) AC or DC circuit.  You set that up to control whatever you want it to control.  I use it to flip on an AC relay which activates a water heater.  Ghurd set up the controller so that the AC will only stay on for a minute or two.  The RE solar/wind supply provides several hundred watts when it's really going, and the AC heater can take out >1200W when it's on, so the cycle is beneficial for not deeply discharching the batteries.   I come home every day to see full batteries, even when this thing has been dumping heat to the water all day.

You're on a similar track with the SSR, but watch out for the heat dissipation.

[Treehouse]

I did that as well but found that in between state of the relay the battery would sometimes over shoot before the c40 could catch it. That's why I wanted a faster PWM option. Also I figure 50 to 150 for a few hours is better than 500W every so often. My system is small.. 100Ah battery 1000W inverter and what I would call a 200W wind turbine and 200W solar.  It's set to 14.4V bulk for an hour then float at 13.8V.  For 3 days now it's been working flawlessly, rock solid at 14.4V.  I still have my c40 connected but moved it up to 14.8V bulk so if things go bad it will still catch things. I have not seen it do anything for the last 3 day's. The other thing I like is my controller is much faster than the c40. As stated before there are many times with the turbine I have seen it way over shoot before it turns on. I'm lucky my inverter just shuts off, on an over volt condition. But still a pain in the butt resetting it on a regular basis.. 

[SparWeb]

I did that as well but found that in between state of the relay the battery would sometimes over shoot before the c40 could catch it. That's why I wanted a faster PWM option.

Misunderstood?  It happens...

I still have the Tristar C60 and the diversion load, and the Xantrex C40 PWM regulating the solar panels.  Absolutely no way that part of the system is going to be removed.  But I think you misunderstood me as saying that, in your reply about the "overshoot" that I might be trying to do without them.

Unless your own C40 doesn't have a dump load?  Or an under-sized dump?  And that's why your battery voltage is/was rising too high? 

Furthermore you can't use a relay for switching the diversion load that regulates the battery voltage.  That's not permitted in the C40 installation manual so I'm surprised anyone would try it.

A relay can be used to switch loads that are powered by the battery- or inverter- side of the system, but only if a control device is used to manage when the relay switches on or off.  That's where the auxiliary heater that you want belongs.  Not among the battery-regulating systems. 

It sounds to me like you've added a circuit to your micro-controller-based battery charge / dump load controller that sends a signal to activate the SSR.  Then the SSR flips on a battery-powered or inverter-powered load.  Which is fine.  Provided you haven't discarded your diversion load for this one in its stead.

[OperaHouse]

Treehouse,  I have been waiting for someone to use one of those DC solid state relays.  Chriss said he ordered one but hasn't reported yet.  These are designed for general industrial use where they are turned on for a major fraction of a second or longer.  I have doubts about the use of them at several hunbdred Hz.  Most have no published spec.  One major brand wasn't too bad, another was about ten times slower.  It would be interesting to see some scope pictures of rise and fall times.  Slow response would resullt in heating.  Even driving a fet directly I avoid duty cycles under 5 or over 95% to prevent heating.

[Treehouse]

  Here is a quick pic. of the output. It's not a perfect square wave and no doubt is probably where the heat is coming from. But for a cheap SSR I don't think there is anything I can do to clean it up. With a very small fan running all after noon, there was no more than 6 deg rise in temp. My min pw is 12% and max is set to 56% I found running it below 12% resulted in a half turn on, due to the slow response time of this relay.  This pic was just shortly after it turned on, I didn't have my netbook connected to my controller so I couldn't tell you exactly what the PW% was. 

[ghurd]

Unless your own C40 doesn't have a dump load?  Or an under-sized dump?  And that's why your battery voltage is/was rising too high? 

Actually, the Xantrex C40/60's are sort of known for reacting slowly.
I have sold quite a few kits to guys who set them about the max they want the battery to be able to overshoot (below when their inverter goes into over-voltage shut-down).
The C60 does most of the regulation, with the ghurd controller used more like a "safety valve".

TreeHouse,
Might consider doing it like SparWeb did, mostly.
Set the timer circuit for 1 minute(?), use it to switch on a deticated inverter, and send the AC to a 2nd water heater (pre-heater)with a lower power element, or to the lower power element in the existing water heater.
2000W of solar and dumping by noon?  Usually a 500W element is not going to put much of a dent in the battery regulation?
Plus whatever the turbine puts out.

It gets around some of the issues of DC, hot SSRs, PWM noise, etc.

http://www.fieldlines.com/index.php/topic,145256.0.html

G-

[Treehouse]

  Now that I know this setup works I am going to order a proper SSR that's rated for 12Khz and intended for PWM motor driving applications. With that relay he will be able to use a 1500W element and have the 2 C60's as a back up. My controller will be in his out building with a cat5 cable into the house to his hot water tank. Then be connected to the SSR, bridge and capacitors. He is then going to run a 120V line from his inverter to the SSR. This way there is no need for multiple inverters. As the load on his inverter increases the PWM to the SSR will back off accordingly. I think this idea simplifies the whole set up. RF noise will be very low seeing how the heating element is in a steel tank of water, so that should not be an issue. As it is, my so called smart charger puts out 10X more RF noise than my SSR does.

 On a side note don't try this setup on an existing controller! The switching freq. is way to high you fry the SSR!

[ghurd]

Let us know how that works out.
I have a bad feeling about it.
G-

[Treehouse]

I have a bad feeling about it.
G-

  Why is that?

[Treehouse]

  Never mind I think I know where your headed So a second cheap inverter will be needed. I shall have to ponder this...

[SparWeb]

...So a second cheap inverter will be needed. I shall have to ponder this...

Nope




Is this anything like what you need?

In my system, that relay's contacts switch over about 20 times on an average day.  With no wind of course the timer doesn't do anything because the dump load doesn't either, nor is there an excess of electric power generated.  There have been some days where I marked 3 hours of total "on" time (really windy and sunny).  With the timer set to stay on for 2 minutes at a time, that would mean that the relay cycled on and off up to 90 times.

So I don't think you need a SSR to do the job.  If you were to focus on detecting the excess (by monitoring the dump load or being more subtle by tracking actual kWhr), and connecting the suitable load to use power most efficiently, then the SSR is all disadvantages with none of the advantages.

I hope this also illustrates that you don't need a separate inverter either.  My inverter is wired to a circuit breaker panel, and from there a pretty typical bunch of branch circuits.  One of the branch circuits just needs to be switched on by that relay and voilà, a load that turns on to shed extra power only when I have some to be shed.

[ghurd]

What I meant about a second inverter was related to the first inverter.
Lets say the heater element is 750W (only about half of the peak available solar).  That only leaves 1250W of 2000W inverter rating left to use.  1250W is not very much inverter left to work with.

My bad feeling is about running a heavy PWM load from an inverter.  I just have a feeling the inverter is not going to like that very much.  It is more of a gut feeling than something I can explain.

I am not clear on your thinking about the 12KHz SSR and existing controller PWM frequencies.
C60 runs at only 100Hz.  TS-60 runs at 360Hz (not what it says in the data sheets, but every model of MorningStar I tested ran at about 360Hz).
I have 0 experience PWM-ing AC or SSRs.
G-