Designing a Diversion Water Heater Load For AUX 1 using an SSR - AC or DC?

[Matrix]

Use new or used Crydom ssr from Ebay, D1Dxx are mosfet and can be paralleled (2x D1D40=> 1x D1D80).

So would it be better to a parallel connection with the control wire like this...

[Matrix]

Use new or used Crydom ssr from Ebay, D1Dxx are mosfet and can be paralleled (2x D1D40=> 1x D1D80).

Or would it be better to do a parallel connection with the control wire like this...

[SolarMusher]

...and I think that it's safer to use control and relay to supply your load.

I like the idea of safer.  That is what drove my Off-Grid solar project costs up in the first place.  I started the project  with the idea I could use an Ebay/Amazon  $225 CC and  $300 Inverter ... until I realized neither was UL Listed 1741 (In home wiring grade) and many at that price point had NO certification AT ALL.  Can you say "fire hazard". I ended up with all UL 1741 products including  $560 worth of CC and $1,450 worth of Inverter.

So safety is a HUGE priority for my system.  That and low maintenance.  I don't want to have to continuously be testing and replacing things that burn out in 6 months to a year ... every so often ... if possible.

So when you say "...safer to use control and relay to supply your load." do you mean... that It is safer to control the stat on the low volt side of the SSR Relay?  AND that it is safe to use the existing AC Lower DWH thermostat ? 

Thanks  (I know,  probably dumb questions,  but its not like we are sitting discussing this over coffee face to face)

I mean that it is safer to disconnect your original water heater thermostat with good quality products such Crydom or other ssr/relay/contactors using 12V control than to use directly a cheap made in china thermostat ($15?) to disconnect higher current. You won't have any problems using the AC original thermostat with 12Vdc from aux1.
Try to find 1x Crydom D1d80 first, it will be better/safer than two D1d40 (if one fails, you will have 900W/37A on just one 40A ssr).
Your first picture is ok for ssr parallel connection, you can also find good  diagram in Crydom spec sheets (D1d serie).
Sorry, I know nothing about Kyotto ssr.

[mike90045]

Chris Olson, AFIK, abandoned his wind & solar, in favor of stacked diesel generators, which he found more reliable in his harsh winters.  Perhaps he uses solar in summers.

Another route, is to use an inverter, with a remote Off / Disable control, and feed AC (mod-sine even) to the heating element and control the inverter with the Waste Not.

Contactors are simply Heavy Duty High Current relays

[Matrix]

Cool. Thanks folks.

I saw a 100 amp Crydom on ebay NIP with a best offer. Shot a low ball. Waiting to see what comes back?

[Matrix]

I ordered the 900 Watt 24v Element today.  Am I correct that this will pull 37.5 amps  (900w / 24v = 37.5), and so it will require AWG 8 wire and a 40 amp breaker?

In a DC set up, is it OK to use NMB #8 that is solid copper?

[ClassicCrazy]

You need to do the voltage drop of the wire you would be using also when planning .
Also you will need a very good heat sink on your  SSR . And the diode as it says in spec sheets.
I think the advantage of a contactor may be that it won't heat up so much like SSR since it is mechanical contacts instead of SSR which is solid state and gets warm when passing high amounts of current.

It wouldn't matter if wire is solid as long as it can fit in whatever terminals it is going to - or put a ring terminal on it that will fit the terminal that it is going to .

Larry

[Matrix]

 I plan to use ring connectors so that's not a problem, but what do you suggest for diodes I'm clueless

[ClassicCrazy]

I plan to use ring connectors so that's not a problem, but what do you suggest for diodes I'm clueless

Here is the info on heat sinks - I will try to find the one on diodes
http://www.crydom.com/en/tech/white-papers/hs_wp_hs.pdf
http://www.crydom.com/en/tech/techlab-videos.shtml

Larry

[ClassicCrazy]

I plan to use ring connectors so that's not a problem, but what do you suggest for diodes I'm clueless

Here is the info on heat sinks - I will try to find the one on diodes
http://www.crydom.com/en/tech/white-papers/hs_wp_hs.pdf
http://www.crydom.com/en/tech/techlab-videos.shtml

Larry

Follow all that or else just put a really good sized heatsink on it !

[ClassicCrazy]

Here is the info on diode or resistor protection of coils in SSR . It says resistive loads aren't really a problem but I thought I had read somewhere in past  that the some  wire runs can present some capacitive load .
http://www.crydom.com/en/tech/newsletters/solid%20statements%20-%20coil%20suppression%20&%20dc%20output%20ssrs.pdf

Larry

[Matrix]

Thanks  for all the research assistance Larry.  This is working out great. 

I have a friend who is an electrical circuit and relay type engineer at a large local Natural Gas lift station for the pipe line that runs thru central FL.  He is going to be checking my set up before I go live with it.   But I really wanna understand  what and why I am doing things before that.  I plan to be ordering the pieces bit by bit in the next week.

[mike90045]

even if you use a Contactor, it has a coil like a relay does, and needs a snubbing diode on the coil.

https://electronics.stackexchange.com/questions/100134/why-is-there-a-diode-connected-in-parallel-to-a-relay-coil

[Matrix]

Looking for a diode. I can't find anywhere that suggests exactly which diode I need to purchase and where to purchase it. I can only find that says I need a diode. Where are some links to purchase the diode that I need?

[ClassicCrazy]

even if you use a Contactor, it has a coil like a relay does, and needs a snubbing diode on the coil.

https://electronics.stackexchange.com/questions/100134/why-is-there-a-diode-connected-in-parallel-to-a-relay-coil

Mike - some of the Gigavac contactor models have this note
" Contactors feature internal transorb for coil suppression.  No external
diodes should be added across the coil. "

Larry