Using a Classic with a DC heating element

[dgd]

The DC SSR acts as a diode as internally it is essentially a MOSFET.
MOSFET's are essentially a diode with a variable forward voltage. A relay would be a different thing of course.
What is interesting is that a Stud mount power diode exhibits a Forward Drop Voltage of ~1.35vdc. (I unavoidably have to use a 300A/800V one in the +Ve of the UPS in order to effectively disable the onboard VRLA charger circuitry).
Recall from Ohms law that P=I2.R and that R=V/I. So, at a 2kw resistive load into the HWS heating element, diode losses would amount to ~38 watts.

The  purpose of the diode was to ensure no possibility of the Classic trying to feed current to the heating element. However, I cannot see how this could occur as the SSR is controlled by the C150's AUX2. I did notice just over a 1V drop across the diode and it did get warm today when  the Classic was in BULK MPPT.  I only checked it before when I knew diversion to the element was happening. Then the diode was cool. I think I will remove it.

A better option would perhaps be to place a Schottky fast recovery diode in reverse across the outputs of the SSR to protect the SSR from any inductive spikes at 'turn off' and remove the power stud diode.

Did this already..

A DC device such as an SSR shouldn't buzz, unless it is being fed PWM that is. In which case, you can smooth the PWM pulse train from the CC by placing an electrolytic cap of ~>1.3 the circuit DCV(max) across the SSR input rails, sized at about 470uF per amp(load). So, as you have about 30amps flowing at peak to the water heating element, you could put for example either a 100vdc/10,000uF or 100vdc/15,000uF cap in there. They run at about $15.00 on ebay.
Get a large can type with M6 or 1/4" (or even M8, M10) screw terminals.
That should solve the buzzing.

I will  try this...

Thanks for your ideas and suggestions

dgd

[boB]

The  purpose of the diode was to ensure no possibility of the Classic trying to feed current to the heating element. However, I cannot see how this could occur as the SSR is controlled by the C150's AUX2. I did notice just over a 1V drop across the diode and it did get warm today when  the Classic was in BULK MPPT.  I only checked it before when I knew diversion to the element was happening. Then the diode was cool. I think I will remove it.

If you are going to load down the input of the Classic, you may want to leave the diode in place to keep the Classic input
from being loaded down by any load that would make it draw current from the Classic.  It is bidirectional and although
it's protected for reverse current, it is pretty annoying if it turns off all the time because of that.  There is also the
possibility of the protection not working properly if that load is abruptly too much.  A short on the input terminals
while it is operating would be the worst.

But, maybe I'm reading this discussion wrong and all is well ??  Back to our regularly scheduled thread...

boB

[dgd]

If you are going to load down the input of the Classic, you may want to leave the diode in place to keep the Classic input
from being loaded down by any load that would make it draw current from the Classic.  .

ok, I will leave it, the DC water heating is working nicely for now.
With the ever falling cost of Chinese made PVs I will probably eventually just connect several directly to the heating element.

dgd

[NUMNUM]

I have my Classics about 200ft from my water heater. What I did is pull a signal wire (Cat5 Cable) and I used the Classics Aux1 to run a solid state relay at the water heater to turn it on. So my inverters actually power my 3500 watt element.


Ryan

ryan how did you wire the ssr .are you using this as a dump load ? there so many threads on this but cant see how to wire it. do you no of any books on this.hope you can help.

num

[Halfcrazy]

The SSR is driven directly from the Aux 2 output of the Classic. So from the 2 Aux2 Terminals I ran 2 conductors to the Coil or drive of the SSR. Then I have the 240vac going through the switched side of the ssr to the heater