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Solar Hot Water ...
#1
Solar Direct or DC that is my next question... or challenge maybe even. 



Really just a first look at how all this will work, now I've kinda got the jist of it I'll need to find somewhere useful to install it. If your keen Patron's already know Smile 

Kudom 100amp DC relay - https://ebay.to/2KIgNGG
DC Element 600w 24v https://ebay.to/2K5aVIk
Clamp Meter -- https://goo.gl/z8b4uJ
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#2
Pete, that SSR is junk, it's a RIP off Crydom/Sensata

There's an RS down under ....

https://uk.rs-online.com/mobile/c/relays...4294530390
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#3
With HWS it's a really good idea to make sure the thermostat's contacts don't weld with the DC. They're only intended for AC.
Fortunately with that low wattage element, the tank pressure valve will cope easily if there's an event where the SSR fails shorted (on) & the thermostat's contacts are stuck.
You've seen the Myth Busters Hot Water Tank episode right?
Running off solar, DIY & electronics fan :-)
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#4
(06-09-2019, 08:10 AM)Redpacket Wrote: With HWS it's a really good idea to make sure the thermostat's contacts don't weld with the DC. They're only intended for AC.  
Fortunately with that low wattage element, the tank pressure valve will cope easily if there's an event where the SSR fails shorted (on) & the thermostat's contacts are stuck.
You've seen the Myth Busters Hot Water Tank episode right?

Pete's sensibly just using the tank stat to make/break the SSR control signal, it'll be fine.
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#5
(06-09-2019, 07:50 AM)Sean Wrote: Pete, that SSR is junk, it's a RIP off Crydom/Sensata

There's an RS down under ....

https://uk.rs-online.com/mobile/c/relays...4294530390
This one is listed on rs but a few bucks cheaper and much cheaper post (and i need cheap lol)  how you go with those trips any luck yet, i'll need one of this project Smile .  I'll pm you a private vid   
(06-09-2019, 08:10 AM)Redpacket Wrote: With HWS it's a really good idea to make sure the thermostat's contacts don't weld with the DC. They're only intended for AC.  
Fortunately with that low wattage element, the tank pressure valve will cope easily if there's an event where the SSR fails shorted (on) & the thermostat's contacts are stuck.
You've seen the Myth Busters Hot Water Tank episode right?

I am worried about that! was thinking of undersizing the cable or just put an inline fuse so if it does weld it'll blow (in theory) Yes, seen MB hws ep they love a good explosion lol
If you'd like to support the forum please feel free to use my affiliate links to purchase all kinds of stuff for your projects 
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#6
(06-09-2019, 08:19 AM)Sean Wrote:
(06-09-2019, 08:10 AM)Redpacket Wrote: With HWS it's a really good idea to make sure the thermostat's contacts don't weld with the DC. They're only intended for AC.  
Fortunately with that low wattage element, the tank pressure valve will cope easily if there's an event where the SSR fails shorted (on) & the thermostat's contacts are stuck.
You've seen the Myth Busters Hot Water Tank episode right?

Pete's sensibly just using the tank stat to make/break the SSR control signal, it'll be fine.

That'll help with the tank stat's contacts but if the SSR goes short...
I guess the batteries being hauled down by a shorted SSR would be noticed before much danger with a 600W element.
If you left the original element in there, things could get interesting! Could become the owner of QLD's biggest steam whistle that isn't a steam train!
Running off solar, DIY & electronics fan :-)
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#7
After a few conversations, I think I'll need to look elsewhere for another solution - I know there are complete elements/thermostats you can buy but they are quite expensive.
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#8
I've been researching this for some time now and about to put one inline. Your SSR setup is fine as long as you have a good SSR. This setup is not any more safe than the original thermostat getting stuck. Your hot water heater should have come with a external relief valve that would release once the pressure build up. If you want added safety, then have another thermostat in series so if one fails open then the other will be the backup.

More importantly, you need to size your panels to the heating element. If you run 120V to a 240V element you will only get about 1/4 the power. So a 3000W element will be no more than 750W.

https://www.youtube.com/watch?v=kVaxAfXQPDU
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#9
(06-09-2019, 09:13 AM)hbpowerwall Wrote: I am worried about that! was thinking of undersizing the cable or just put an inline fuse so if it does weld it'll blow (in theory)
Under sizing the cable (bad idea) &/or fusing it (proper fuse or breaker good idea anyway) doesn't help the over temp issue but like the guys are saying, it should be fine with the regular stat > SSR & yes the over pressure valve is there.

(06-09-2019, 11:15 AM)not2bme Wrote: If you run 120V to a 240V element you will only get about 1/4 the power.
HBPW's down here in Australia so the mains is 230/240VAC but it looks like he might be running it direct off his panels.
Yeah the power matching video is good :-)
Running off solar, DIY & electronics fan :-)
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#10
If your hot water system is a header tank the relief is for the tank to blow back the water into the header tank, which if plastic, then melts...

Pressurised systems without a header tank would have an external vent pipe. From the video I'm not sure if the tanks is 3bar rated (typical header) or 5-10bar.

SSR and DC is the only way to go, just use the thermostat at 12V into the trigger for the SSR. The thermostat will work ok at 30-40V DC for a long while at small load, but not as long as the element. The thermostats are typically current rated for HV, so only a few amps, not 20-50A with LV DC... You could use just a few FET's on an aluminium bar as that is pretty much all that SSR's are internally...

Hot water should really be direct thermal, going DC is way less efficient and then becomes a spill battery in a way.
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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