Putting a Smart Switch on my Hot Tub heater

[DangerBoy]

@wayner I am coming into this conversation late and even though I did skim over what was said in many of the previous posts, I admit that I did not read everything so I'm not sure what I'm about to day has any relevance or is redundant or whatever but FWIW, this is what I have to offer.

I had a problem with my old tub in that the heater relays were burning out fairly frequently like maybe 1 - 2 times per year. I attributed this to the fact that the original heater that came with my tub was a 5.5 KW unit running off 30A heater relays and now the new replacement heaters are either 4.5 or 6 KW depending on what option you go with. My tub (240V) has the new 6KW heater in it and I think it's a bit too much for the 30A relays which were probably taxed to their limits by the old 5.5 KW heater and now being overtaxed by the 6KW heater. My challenge was then to find an inexpensive way to get load power to the heater that avoids routing all of the load power through those 30A heater relays. I think your goal of using the Sonoff to control what time of the day the heater circuit is allowed be powered but not running the load power through the Sonoff is a similar goal and problem to what mine was.

With the excellent advice of @RDspaguy, I came up with a low cost and extremely reliable solution that has worked flawlessly for at least 2 years now.

What I did was reroute the load power going through the 30 A relays and on to the heater through inexpensive but decent quality Chinese made 40A contactor relays that I got off AliExpress. Here's a link to the relay that I bought:

https://www.aliexpress.com/item/32239871351.html

As you can see they only cost $11.02 CAD each plus shipping. I needed two of them.

The signal voltage for these relays is 240V. The load voltage going through the 30A relays to the heater is also 240V but now the 240V that goes through the original heater relays is only used as signal voltage for the contactors. That means the current now being handled by the 30A relays is only whatever is needed to flip the contactor relays so maybe 1 - 2 Amps at most. With that low load, they'll last a long, long time compared to when they were handling 25A or more if you also consider onrush current when the heater is first turned on.

So what I'm suggesting is that you look at using your Sonoff to only send signal voltage to one of these contactors and let the contactor do all the heavy lifting in terms of transmitting the load power. This way, your temp control system may be calling for heat by sending a signal voltage to your Sonoff but your Sonoff will only let that signal voltage get through to the contactor during off-peak hours.

Does this help in any way?

 

[Dirk]

So what I'm suggesting is that you look at using your Sonoff to only send signal voltage to one of these contactors and let the contactor do all the heavy lifting in terms of transmitting the load power. This way, your temp control system may be calling for heat by sending a signal voltage to your Sonoff but your Sonoff will only let that signal voltage get through to the contactor during off-peak hours.

What a great idea. I should have thought of that!
#9 #10

Just teasing. My suggestion was hypothetical. You actually did it and have it working and torture tested. Thanks for the data. I think the OP worked it out some other way, but he'll have your idea for reference, as will anyone else that stumbles onto this thread with a similar challenge.

 

[phonedave]

@wayner I am coming into this conversation late and even though I did skim over what was said in many of the previous posts, I admit that I did not read everything so I'm not sure what I'm about to day has any relevance or is redundant or whatever but FWIW, this is what I have to offer.

I had a problem with my old tub in that the heater relays were burning out fairly frequently like maybe 1 - 2 times per year. I attributed this to the fact that the original heater that came with my tub was a 5.5 KW unit running off 30A heater relays and now the new replacement heaters are either 4.5 or 6 KW depending on what option you go with. My tub (240V) has the new 6KW heater in it and I think it's a bit too much for the 30A relays which were probably taxed to their limits by the old 5.5 KW heater and now being overtaxed by the 6KW heater. My challenge was then to find an inexpensive way to get load power to the heater that avoids routing all of the load power through those 30A heater relays. I think your goal of using the Sonoff to control what time of the day the heater circuit is allowed be powered but not running the load power through the Sonoff is a similar goal and problem to what mine was.

With the excellent advice of @RDspaguy, I came up with a low cost and extremely reliable solution that has worked flawlessly for at least 2 years now.

What I did was reroute the load power going through the 30 A relays and on to the heater through inexpensive but decent quality Chinese made 40A contactor relays that I got off AliExpress. Here's a link to the relay that I bought:

https://www.aliexpress.com/item/32239871351.html

As you can see they only cost $11.02 CAD each plus shipping. I needed two of them.

The signal voltage for these relays is 240V. The load voltage going through the 30A relays to the heater is also 240V but now the 240V that goes through the original heater relays is only used as signal voltage for the contactors. That means the current now being handled by the 30A relays is only whatever is needed to flip the contactor relays so maybe 1 - 2 Amps at most. With that low load, they'll last a long, long time compared to when they were handling 25A or more if you also consider onrush current when the heater is first turned on.

So what I'm suggesting is that you look at using your Sonoff to only send signal voltage to one of these contactors and let the contactor do all the heavy lifting in terms of transmitting the load power. This way, your temp control system may be calling for heat by sending a signal voltage to your Sonoff but your Sonoff will only let that signal voltage get through to the contactor during off-peak hours.

Does this help in any way?

I think the OP wanted to use the power monitoring features of the Sonoff to analyze his consumption. Routing the load around the Sonoff defeats that purpose.

 

[DangerBoy]

As long as the Sonoff can handle the current loads that it would be subjected to handling the load current in the heating circuit then fine but if it turns out that the Sonoff cannot reliably handle those loads then the way I've suggested is pretty much how he'll have to do it.

 

[wayner]

I think the OP wanted to use the power monitoring features of the Sonoff to analyze his consumption. Routing the load around the Sonoff defeats that purpose.

Yes, I did want that. But there may be other ways of doing this, and the power monitoring for the heater is pretty simple - while it is on it is using 5kW. So as long as you have some other way of sensing on or off then you should be able to easily calculate power usage as (Hours ON)*5.5kW.

 

[wayner]

My pool is the opposite. While not quite as big as your pool, mine is still on the bigger end of ABGs. But aside from vacuuming, it is pretty much set and forget. The SWCG keeps the FC where it needs to be, and everything else is rock stable.

My hot tub needs fairly constant nursing, year round.

This is me as well. With my pool at opening in May I need to add salt, and CYA. Once those are at desired levels I might have to occasionally add acid, but beyond that it is pretty maintenance free.

With the tub I have to keep more of an eye on things and I can never get TA and pH to both be in the correct zones so I have to live with low TA.

 

[ajw22]

I have to live with low TA.

As long as your pH is stable there is no too low TA.

 

[wayner]

As long as your pH is stable there is no too low TA.

Agreed.