Solid State water heater control

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Electromatic said:
Well, shoot! Thanks for all the replies even though it sounds like everyone thinks this thing will just burn up in the panel which is not what I wanted to hear.
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When the SSR is on, it has a voltage drop of about 1.6V, so when the water heater is drawing current you will be dissipating about 30W at the SSR. If you mount the SSR on the side of the panel, and use the panel as a heat sink, then it will probably work. Mount a heat sink on the outside of the panel at the SSR location, and it will have an even better chance of working.

Unfortunately this becomes a design exercise rather than a no-brainer 'it will simply work'. Probably not what you want to sell your customer.

Something like https://www.automationdirect.com/ad..._ad-ssr2_-z-_ad-ssr6_series)/ad-ssr645-45-acz

would just barely fit in https://www.hammfg.com/part/1416E

This would handle the current and would not burn up, but now it is getting more expensive and taking up more space

-Jon
 
Look at the Magnecraft 199 -series DPDT relays. They're an open-frame design (so you'll need to place them in an enclosure) with contact ratings up to 50A. Millbank and (I think) Generac use these relays in their load shedding modules.

https://www.serelays.com/library/section6/105A_Section_6_Power_Relays.pdf

Wire the relay to use the N.C. contacts to send power to the water heater, and change the logic in the ATS to energize the load-shed circuit when the water heater needs to be dumped from the generator. The relay will actuate, and cut power to the water heater. Added bonus - the customer isn't paying to keep a relay energized all the time.

If you can't change the logic of the ATS, you can do it with a small interposing relay. Just match the coil voltage to whatever is coming from the ATS.

A few years ago, I used a pair of Magnecraft 199 -series relays to build a 2-load load shedding panel for a home generator install. I selected Magnecraft p/n: W199APX-15. These are 50A DPDT relays with 240VAC coils. Those relays are controlled with interposing relays with 24VDC coils, driven by the ATS. I had to use the interposing relays because the ATS didn't have the current handling capability to drive the Magnecraft relays' coils directly. PM me, and I'll send you the drawing for the panel.



SceneryDriver
 
Thanks again, everyone. I got the Aube heating relay:
https://www.warmlyyours.com/en-US/publications/RC840T-INSTALLATION-GUIDE-A.pdf

It seems like it should fit the bill, is even intended to control heating loads, was available with a couple of days shipping, and about $50. I figure, too, that if people are putting them inside baseboard heaters, they can't be very noisy either. I'll probably install it this week and let the forum know if I run in to any issues.
 
Electromatic said:
Thanks again, everyone. I got the Aube heating relay:
https://www.warmlyyours.com/en-US/pu...ON-GUIDE-A.pdf

It seems like it should fit the bill, is even intended to control heating loads, was available with a couple of days shipping, and about $50. I figure, too, that if people are putting them inside baseboard heaters, they can't be very noisy either. I'll probably install it this week and let the forum know if I run in to any issues.
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Interesting relay. Going to have to keep that one in my pocket for future reference. I'll bet the relay coil is might be DC, and the switched 24VAC signal is rectified internally. DC coils are silent, and don't buzz.


SceneryDriver
 
Jraef said:
There are “quiet” contractors made for this very purpose. I helped on a hotel project in Las Vegas years ago (Wynn) where every room has a contactor in the small sub-panel that’s in the room, same problem. The contactor closes only when the room sensor detects that someone is in there, which means the contactor was buzzing only when the guest was trying to sleep. Not good.

Siemens had one specifically designed to not make noise. We tested them and they were acceptable. Can’t remember the series though, I’ll have to dig around in the half-dead brain cell section. May not have been big enough for a water heater though, as I recall I only needed 20A. I’ll post what I find.

By the way, we investigated SSRs too, wasn’t going to work. Watts loss is 1-1/2 W per running load amp, so even if you use only one pole, it’s like putting a 75W heater element inside of the panel, with no ventilation. It will cook itself.
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Whats the contactor in the hotel room panel for?
 
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