Saturday, March 2, 2013

Water Heater and Solid State Relays

A few times I mentioned the solar water heater I have.  It works great and keep me in free hot water most of the time.  Yes, it's the desert and during the summer the coldest the water gets is lukewarm, but I get 140F water out of the heater for zero continuing expense except for the few days where it is overcast.

Those overcast days present a problem.  A couple of times I turned the power on to the water heater and used the helper coil to heat the water because the sun just didn't come out.  Once, it pushed my power bill up because an X10 controller didn't react to the turn off command.  This prompted me to hook the water heater power to the garage controller I have.  This worked fine.  I'm able to send an XBee signal and turn on the water heater.  I also have code in the garage controller that shuts the heater down during peak periods. It's working really great except...

The contactor I have started to buzz.  It works fine, but there is a constant 60Hz buzz coming from it any time it's on.  The first time I heard it, I had to hunt for a while to figure out what it was.  Then, as the days went by, it got more and more annoying.  For those of you that have no idea what a contactor is, here's a picture of the one I have.

They're really nothing much more than a really big relay.  They have specially built contacts to survive high current switching and lots of places to hook wires.  They are probably all over your house and you don't know it.  Appliances have them, some fireplaces, environmental heating, etc.  Most of them run on a 24V coil and last a really long time.  In my particular case, I used a 110V coil because I was originally switching it with an X10 appliance module.  Unfortunately, the 110V units tend to make noise as they age.  They're not wearing out, they just start to rattle at 60Hz and drive you nuts.  There is a solution, use a solid state relay instead.

So, I got online and started looking for an SSR that could handle 25A at 240VAC.  There's a lot of them out there, but I need two of them, one for each leg of the power.  That made converting expensive, but I kept looking and found a SSR for 240 VAC three phase.  This gives me three of them in a package and I only have to use two of them.  I don't know if I'll ever need the spare, but it's there if I need it.  Here's the device I bought:

Notice that is has inputs for three circuits and one control for all of them.  This is exactly what I wanted.  So, when it came in, I took the entire control assembly off the wall and rebuilt it essentially from scratch.  Here's what it looks like on the wall:

Simple isn't it?  Just one device with the control signal coming in the top and hooking up on the left side.  It only takes a little over 4VDC to turn it on and it doesn't make any noise at all.  Since there are no contacts, it should last forever just sitting there working it's little heart out.  

I probably should have used one of these to begin with, but I didn't have a clue XBees even existed when I started out on these projects.  I was convinced by the advertising and various articles on the web that X10 would do the job.  

It's sad that I was that naive.

The followup to this posting is here <link>.


  1. What is the Brand of these devices? I found many hits on a single-phase device. Do you have a north american source, or did you order from China?

    1. I don't know what is the exact brand of this but when you search on the internet, "CRYDOM" is the best brand. Made in Mexico.

  2. There are North American sources, but they are incredibly expensive; way beyond what (to me) is a reasonable amount. I ordered from China and received it in about 10 days. If you want to find the various sources, google for "3 phase ssr".

  3. Do you find that your SSR gets warm during operation ? I've noticed that they
    recommend a heat-sink. I just received mine and will be installing it on my
    water heater soon.

  4. Yes it does. What I did was to put the device in a metal box with the heat sink side of the SSR to the metal box. I put a little silicon grease on the bottom and screwed it down. This way the metal box protected the wiring, kept it from being dangerous, added fire protection, and sucked the heat away from the SSR.

    The box gets just a little warm to the touch, nothing worth worrying about. You should do what I did though, I hooked it all up and fired up the water heater, then kept feeling of it to be sure there wasn't a heat buildup.

  5. Thanks Dave .. I contacted the seller to see if they have a heatsink. Depending on the cost I may or may not use it. From what I've read, the temperature is about 1.2 C / Amp, so a 40A SSR could generate 48W of heat ! Apparently the main cause of failure with these things is heat.

  6. Ever since you asked about this I've been checking the SSR for heat buildup. Mine is mounted indoors with plenty of room around the box, but no direct ventilation such as a fan or blower vent. It's out in the garage where there's no direct or indirect sunlight to add to the ambient heat. The box gets just barely warm to the touch. I haven't actually measured the temperature inside the box while it's on, but there sure doesn't seem to be a problem.

    I'm going to keep checking it over the next couple of months though to be sure. As the heat here in Arizona goes up, I may need to think about a heat sink, but from the results so far, the metal box is doing a great job of getting rid of any heat problem.

    Frankly, unless you stumble across a good deal, the heatsinks for these things seem to cost as much or more than the device itself. If you have heat problems, take a look at using a metal mounting plate to conduct the heat away, a piece of sheet metal could save you a lot of money.

  7. Replies
    1. I looked into tankless water heaters and they are really nice. They won't work for me because they take a huge surge of electricity to heat water as demanded and that would drive my electric demand number up to the 7KW area and cost a hundred dollars or more on the demand alone.

      If I use a gas one, it has to have a 1 inch feed pipe from the propane tanks and a special regulator to allow enough gas to run the thing. That would mean some serious expense for pipe and plumbing, not to mention a huge expense for gas (propane) at almost 4 dollars a gallon. I'd probably be taking a 20 gallon tank to the refill station a month.

      Nope, solar water heating is the way to go. I don't pay a cent for hot water all summer (8 months out of the year) and a minimal amount for cloudy days during the winter. Especially since I turn the entire heater off during peak demand periods.

  8. How did you connect the water heater to the relay? I noticed there is A1 A2, which side is HOT or does it matter?

  9. These are 220, so there are two 'Hot' wires, not a hot and a neutral like the outlets around the house. These things use triacs, so it doesn't really matter which side is what, so I hooked the wires from the distribution panel to A1 and B1, then the wires to the water heater on A2 and B2. The grounds were tied together and hooked to the metal box to protect things if something came loose by blowing the breaker. The C1 and C2 terminals weren't used and could be a spare if something dies later.

    Is this clear? Sometimes describing something like this can be confusing.

  10. Dave,
    Yea, that's clear... By HOT I was referring to the A/C side vs the LOAD side. Like you, I connected the A/C side (A1 B1) to the breaker box and the water heater to the LOAD (A2 B2). I've used SCR's before but they had a datasheet. I just didn't want to hook it up after this long and have it malfunction.

    I did get a heatsink from China. $15 shipped and it took forever to get here. The relay does get warm when the water heater is on but not hot, I'm guessing it was overkill, but better safe than sorry.

    Here is the link to the heatsink.

  11. That's actually a nice heat sink. The ones I've seen around cost more and are huge. Thanks for the link, I may need it someday for some other project. I have a water well contactor that goes out every couple of years and costs $75 each time. It's out in the weather and sun, so a heat sink would be necessary for that job.