Author Topic: How safe is it to use a SSR to control power to a spa? Or use a relay?  (Read 10225 times)

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Online langwadt

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California law is if the fire happens after the earthquake you are covered by fire insurance. If the fire happens before the earthquake you are not covered.

Really?  Can you tell me where I find that law?

Why would you think fire insurance would not be valid after and earthquake.
Why yes I can.  Goes back to the San Francisco earthquake and fire in 1906.  And was again re-affirmed with the 1989 earthquake and fires.

then no one is ever covered by fire insurance because it'll always be before what ever earthquake comes next



 

Offline DougSpindlerTopic starter

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I wouldn't buy any electronic part that matters from Amazon.  Heck, I recently received Energizer CR2032 lithium cells from them that measured 2.7-2.9V across the board, pack of 20!  I discovered this after they went dead within a month when they should last 6-8 months.  Garbage.  Ordered Panasonic ones from Mouser; a touch over 3.2V across the board, priced $.23 per cell, qty 1. The Energizers were probably counterfit since any legit lithium cell should have a shelf life well over 10 years.  My best guess is they were really alkalines.  Just avoid.

You are entitled to your opinion.  I have excellent success electronic components from Amazon and pretty good with Banggood.  eBay is hit or miss.  In my mind it all depends on the application.  If I were building a pacemaker I would use high quality components.  But to control power to a spa that's protected with a GFCI a $10 high current relay is fine.  What's the worst that would happen?  The contact fuse creating a short?  Burn out causing an open?  Heat up and melt?  The GFCI would trip and the water in the spa would put the fire out.

No need to spend $100 at Digikey/Mouser when a $10 part would probably work just as well.


 

Offline bdunham7

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Why would you think fire insurance would not be valid after and earthquake.

I didn't say that.  I'm wondering why you think fire insurance would not be valid before an earthquake. :-//
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline DougSpindlerTopic starter

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My error and I see a typo  The and should have been "an".

Fire insurance would be valid before and after an earthquake.  But if there is an earthquake and no fire and you don't have earthquake insurance then you are screwed.  But if you have earthquake damage followed by fire then you are covered with by the fire insurance.
 

Offline bdunham7

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My error and I see a typo  The and should have been "an".

Fire insurance would be valid before and after an earthquake.  But if there is an earthquake and no fire and you don't have earthquake insurance then you are screwed.  But if you have earthquake damage followed by fire then you are covered with by the fire insurance.

Well, perhaps, unless you have announced your intent to commit arson in a public forum.  :-DD
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline DougSpindlerTopic starter

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My error and I see a typo  The and should have been "an".

Fire insurance would be valid before and after an earthquake.  But if there is an earthquake and no fire and you don't have earthquake insurance then you are screwed.  But if you have earthquake damage followed by fire then you are covered with by the fire insurance.

Well, perhaps, unless you have announced your intent to commit arson in a public forum.  :-DD

I'll leave that to the protesters.  Have you seen the video of the looter who broke into a Dodge dealership and stole 80 brand new cars under BLM protesting?  These people are videoing themselves.  If my glass jar of gas falls and breaks as a result of an earthquake that's the way things go.  But now way, like these protesters, would I film it and put it on YouTube.  Total value of the new cars the protesters played bumper cars with and stole is about $5,000,000.







 
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Offline Bassman59

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You are upset because I'm not buying from one of the two vendors you suggested?  My post was for advice on using an SSR vs a relay.  Did you even answer that question?   

For what it's worth -- my previous house had a hot tub and it had SSRs for the heater and pump controls. I only know this because one of them failed and I replaced it with the exact model, which was sold by one of the local spa supply stores.
 

Offline james_s

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My hot tub has mechanical contactors for everything. I'd say it depends on the frequency at which you want to switch it. SSRs will typically have higher losses and are more likely to fail shorted (closed) however they have the advantage of being immune to contact wear which can be an issue for frequent cycling.
 

Offline NiHaoMike

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My hot tub has mechanical contactors for everything. I'd say it depends on the frequency at which you want to switch it. SSRs will typically have higher losses and are more likely to fail shorted (closed) however they have the advantage of being immune to contact wear which can be an issue for frequent cycling.
SSRs excel at controlling heating elements although with the high thermal mass of the water, probably not going to make a huge difference. For heating air or small volumes of water, the difference is very substantial.
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Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline DougSpindlerTopic starter

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Take a look at my application.  I am on a Time of Use rate plan with my power company.  (Very common now in California.)  The cost I pay per kWhr changes 5 times in one day.  Depending on the time of day I might be paying as little as $0.13 kWhr and as much as $0.54 kWhr.  My goal is to not have the heater or pumps (cleaning cycle) run during the periods when I am paying more than $0.13 kWhr.

I was thinking of interrupting power to the heater and pump motors.  But then I thought it would be much easier just to place a high current relay or SSR to interrupt the mains to the hot tub.  To control the times relay or SSR would be energized I would use a smartplug.  In one year this would save me about $1,000 in electricity.  Total cost for parts?  Cost for parts...  around $80.00.

Or does someone have a better solution.  My questions is should I use a relay or SSR?
 

Offline sokoloff

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For once or twice daily cycling and no need for anything more than bang-bang control, I’d use a relay.
 

Offline DougSpindlerTopic starter

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That's what I'm going to do.

For educational purposes..  Could I use an SSR?   Can you explain the advantages and disadvantages?

Thanks
 

Offline themadhippy

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ssr's tend to have a bleed current,if theirs something that can sink that current its going to cost you money,even 5ma  comes in at about 4kw over a year.Another issue is some ssr's dont like inductive loads.stick a proper contactor in,not an elcheapo relay.
« Last Edit: July 22, 2020, 02:49:47 am by themadhippy »
 
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Offline floobydust

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What is the spa load? Assuming it's two-phase and there's a circ pump, heater and jets?

An SSR does not wear out like a contactor or relay, but they make a lot of heat. About 1W per amp in a one-pole SSR. So you need a heatsink and good cooling for two SSR's. A decent manufacturer of SSRs like Crydom is expensive then add on the heatsink costs and a place to put them. Cheapola Fotek SSR's and the knock offs are just a hassle as they fail easily, due to the fake specs and bad thermal design.

The highest cost is switching high current. If you can instead find a way to cause the spa controller to shut off the spa, it would be much easier. Like tapping into the run/stop switch or falsely trip a safety limit switch such as low water. The spa should already have some control logic.
 

Offline james_s

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1W per amp is pretty substantial at the currents involved here. My hot tub is on a 50A 240V circuit and with everything going on high it draws more than 40A.
 

Offline DougSpindlerTopic starter

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1W per amp is pretty substantial at the currents involved here. My hot tub is on a 50A 240V circuit and with everything going on high it draws more than 40A.

What size hot tub do you have?  That thing is drawing 8,800 watts.  If it is like most high end hot tubs it would have 2 - 1.5 hp pumps.  That would be 2237 watts.  That would leave 6,563 watts for the heater and the electronics.  Can't imagine a hot tub having over a 6,000 watt heater.  I think the heater in my tub it at most 1,500 watts. 

Imagine if you were a PG&E customer having to pay $0.54 kWhr. any idea what it would cost to power your hot tub?

 

Offline DougSpindlerTopic starter

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ssr's tend to have a bleed current,if theirs something that can sink that current its going to cost you money,even 5ma  comes in at about 4kw over a year.Another issue is some ssr's dont like inductive loads.stick a proper contactor in,not an elcheapo relay.

Thanks - Is there a difference between a contractor and a relay?  Isn't a contactor just a high current relay?  Or is there more to it?
 

Offline james_s

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What size hot tub do you have?  That thing is drawing 8,800 watts.  If it is like most high end hot tubs it would have 2 - 1.5 hp pumps.  That would be 2237 watts.  That would leave 6,563 watts for the heater and the electronics.  Can't imagine a hot tub having over a 6,000 watt heater.  I think the heater in my tub it at most 1,500 watts. 

Imagine if you were a PG&E customer having to pay $0.54 kWhr. any idea what it would cost to power your hot tub?

It's about 6' square, made by Apollo Spas, I believe it's a 1997 model. There are two 2.5HP jet pumps that the labels say each draw 12A on high speed, a 1.5HP air pump and a 5.5kW heater. I haven't actually measured what the pumps draw but I suspect it may be less than labeled, otherwise we're already up to 46A before you even add the air pump, and the controls and light draw something too.

I pay around 8.2c/kWh from PSE, at least that's what it was last I checked. If I have the tub going it doubles my utility bill, adding $30-$40/mo depending on how much I use it.

« Last Edit: July 22, 2020, 05:37:36 am by james_s »
 

Offline james_s

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Thanks - Is there a difference between a contractor and a relay?  Isn't a contactor just a high current relay?  Or is there more to it?

A contactor is just a relay. Usually the term refers specifically to an open frame relay with a mounting base and screw terminals to attach wires, as opposed to a relay which is usually enclosed and solders to a PCB or plugs into a socket.
 
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Offline DougSpindlerTopic starter

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Thanks - Is there a difference between a contractor and a relay?  Isn't a contactor just a high current relay?  Or is there more to it?

A contactor is just a relay. Usually the term refers specifically to an open frame relay with a mounting base and screw terminals to attach wires, as opposed to a relay which is usually enclosed and solders to a PCB or plugs into a socket.

Thanks
 

Offline DougSpindlerTopic starter

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What size hot tub do you have?  That thing is drawing 8,800 watts.  If it is like most high end hot tubs it would have 2 - 1.5 hp pumps.  That would be 2237 watts.  That would leave 6,563 watts for the heater and the electronics.  Can't imagine a hot tub having over a 6,000 watt heater.  I think the heater in my tub it at most 1,500 watts. 

Imagine if you were a PG&E customer having to pay $0.54 kWhr. any idea what it would cost to power your hot tub?

It's about 6' square, made by Apollo Spas, I believe it's a 1997 model. There are two 2.5HP jet pumps that the labels say each draw 12A on high speed, a 1.5HP air pump and a 5.5kW heater. I haven't actually measured what the pumps draw but I suspect it may be less than labeled, otherwise we're already up to 46A before you even add the air pump, and the controls and light draw something too.

I pay around 8.2c/kWh from PSE, at least that's what it was last I checked. If I have the tub going it doubles my utility bill, adding $30-$40/mo depending on how much I use it.

I'm going to have to dig out my amp meter tomorrow to see what the draw is.  I could probably do it from my solar panel monitoring system  I looked at hot tub heaters and it turns out they can be in the 6 kW range.  So with 2.5 hp motors 40 - 50 amp draw is not that out of line.

Be lucky you are paying 8.2c/kWh.  PG&E's TOU rate has us paying $0.14 to $0.54. 

 

Offline james_s

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I thought 5.5kW was pretty standard for spa heaters, at least some models of the little 120V tubs use the same heater but it's only around 1.4kW on 120V. It's a lot of power, but on the plus side, most of the time when the pump runs it's on low speed and the heater only comes on when it needs to. It's rare for everything to be going all at once for more than 15-20 minutes. Normally when I use it I go for a dip in the evening for 10-15 minutes and then shower and go to bed.

If I were paying a lot more for power I'd either get a gas fired heater or just get rid of the thing.
 


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