How safe is it to use a SSR to control power to a spa?  Or use a relay? - Page 1
Forum section: electronics / projects

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 06:25:34 pm
content: I would like to know how safe and if it would be a good idea to use a SSR to control the power to a spa/hot tub. We are on a Time of Use rate plan with our power company. My plan is to use a TPLink smart-plug to provide the timing. This give me control of a 120 vac circuit. The TP Link would then be used to control a high current SSR to control power to the spa. The SSR would be used to control the mains to the spa. (Placed after the GFCI in the mains power to the SPA.) I'm wondering if this is a good ideas? I read SSRs do not interrupt the circuit like a relay would. The circuit is energized at full voltage be the current is what's being controlled. I'm wondering if an SSR is a good idea? Is it safe? Would it damage and of the electronics or motors?Or should I just purchase a high current relay?

author: bob91343
author_rank: Super Contributor
timestamp: July 19, 2020, 06:42:51 pm
content: Before you spend too much time on this, realize that there are concerns regarding insurance, and that any installation working from the power line must have a permit covering its safety.You may design a perfectly working system but if an insurance claim is made, the company will be ready to deny the claim based on not having a permit.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 06:47:41 pm
content: What concerns should I have about insurance claims? Who would be making the insurance claim?I live in California and a permit is not required for this type of work.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 06:57:02 pm
content: Oh just did the calculation based on our power company's current rates. Using the hot tub during peak hours the cost for electricity is $0.54. Manufacture claims 1,875 kWhr are used per month. Cost to power the hot tub over a year would be $1,275.If limited to off peak it would be $225. Installing an SSR would save me over $1,000 per year. Well worth it.

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2020, 06:58:19 pm
content: It tends to be easier to obtain UL approved high current mechanical relays with decent insulation and contact ratings than SSRs. You'll probably have more choice.An SSR will have a higher thermal dissipation than a relay too.EDIT: For something high power like a hot-tub, you're probably looking at a 'contactor' rather than a relay too.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 07:11:56 pm
content: Quote from: Gyro on July 19, 2020, 06:58:19 pmSo just go with a contactor/relay? Looking on Amazon i'm finding 30a contactor/relay's for $10.

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2020, 07:24:05 pm
content: Quote from: bob91343 on July 19, 2020, 06:42:51 pmWhat is your basis for that statement?

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2020, 07:26:35 pm
content: Quote from: DougSpindler on July 19, 2020, 07:11:56 pmEither will work fine as long as you are adding them to a complete system and not depending on them in any way for safety. The contactor is more conventional, easier to work with, probably more reliable and as a bonus, is usually guaranteed to interrupt both hot legs of the circuit.

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2020, 07:45:25 pm
content: Quote from: DougSpindler on July 19, 2020, 07:11:56 pmWell personally I wouldn't go to Amazon for a guaranteed genuine UL approved contactor these days, I'd use an electrical / electronics distributor, but yes.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 07:54:33 pm
content: Quote from: Gyro on July 19, 2020, 07:45:25 pmWhat difference doest it make where you BUY a product? Shouldn't you really be concered about the product itself and not who sold it?

author: Benta
author_rank: Super Contributor
timestamp: July 19, 2020, 07:59:55 pm
content: Quote from: bdunham7 on July 19, 2020, 07:24:05 pmSomeone gets killed due to DIY electrics in a moist/wet area? A Spa or any safety relevant application is not really the place to use SSRs. You need an installation with 100% safe disconnect, meaning mechanical contacts.Just the idea makes me shudder.

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2020, 08:09:51 pm
content: Quote from: Benta on July 19, 2020, 07:59:55 pmYes, a two-pole contactor seems a safer to me too. However, in this case, the SSR would simply be an additional switch to an already (presumably) safe system. Even if it shorted on, you would be no worse off than before. The OP isn't counting on it as a disconnect or a normal control switch. And these spas are fully GFCI protected at the supply.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:10:28 pm
content: Quote from: Benta on July 19, 2020, 07:59:55 pmDid you read and understand my post? Did you see there is a GFCI in the circuit. In the US, a GFCI is considered a safe disconnect. Not sure how much safer it could be.

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2020, 08:11:10 pm
content: Quote from: DougSpindler on July 19, 2020, 07:54:33 pmYes, absolutely, that's why I stick to places where I'msureI'm not getting cheap knock-off copies, especially when safety critical. However, if it's a genuine brand from a legitimate looking seller...

author: langwadt
author_rank: Super Contributor
timestamp: July 19, 2020, 08:11:18 pm
content: Quote from: DougSpindler on July 19, 2020, 07:54:33 pmthe chances of actually getting an UL approved contactor that meets specification at electrical/electronics distributor is vastly higher

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:16:11 pm
content: Quote from: langwadt on July 19, 2020, 08:11:18 pmAre you sure? Look at all of the "fake" immolation Chinese products that are out there where expert's can't even tell the difference. An electronics distributor is just going to resell what they were sent. Who knows for sure if the item meets specs or not?

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2020, 08:20:38 pm
content: Because they have a fully documented suppy trail from the manufacturer. Amazon is just like all the other 'international marketplaces' these days, with the same cautions.I wouldn't expect to get a genuine semiconductor from Amazon any more than a China seller on ebay for instance. The same applies to other [Edit: much more easily faked] parts.

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2020, 08:24:10 pm
content: Quote from: DougSpindler on July 19, 2020, 08:16:11 pmThat's not really true. Experts usually CAN tell the difference and reputable distributors use appropriate supply chain practices to avoid counterfeits. It still can happen, but getting a fake brand-name contactor from Grainger or even Home Depot is a lot less likely than getting a fake from Lonely Baby Garden Store on AliExpress. And a NOS unit in a worn box from some eBay seller is also very unlikely to be fake.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:25:18 pm
content: Quote from: Gyro on July 19, 2020, 08:20:38 pmTake a look at the fake Cisco products that are on the market. Or the fake chips. Not sure a suppler could even spot the difference.

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2020, 08:29:57 pm
content: You're in the US - Just buy it from Digikey or Mouser, it's not difficult!

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2020, 08:31:07 pm
content: Quote from: DougSpindler on July 19, 2020, 08:25:18 pmLet's say they can't. Does it matter? Do you think Cisco is selling the fake Cisco products??

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:31:51 pm
content: Quote from: Gyro on July 19, 2020, 08:29:57 pmI could, but from Amazon I get it on Tuesday.

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2020, 08:33:57 pm
content: Sigh, don't they offer next day? I'm sure you need to buy other stuff anyway.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:34:26 pm
content: Quote from: bdunham7 on July 19, 2020, 08:31:07 pmHow are fake Cisco products getting into the supply chain? These are not just isolated incidents either.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:36:16 pm
content: Quote from: Gyro on July 19, 2020, 08:33:57 pmThey do, but 2 day shipping is free. I wonder what Digikey and Mouser would charge. Don't they have a minimum order size? I think they would charge more than $10 just for the shipping.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 19, 2020, 08:36:40 pm
content: Check if there's an existing control relay you can tap into. Other than that, a contactor controlled by a smart plug is one very easy way to automate large loads.

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2020, 08:40:06 pm
content: Quote from: DougSpindler on July 19, 2020, 08:36:16 pmI sometimes wonder what the point is of spending my time to give someone technical advice, only to get dragged into this sort of crap.Buy it where you want.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:41:18 pm
content: Quote from: NiHaoMike on July 19, 2020, 08:36:40 pmI have and there is not one relay. There are at least 3. One for each of the two pumps and another for the heater. The electronics have "settings memory" so if power is lost the settings are retained. (My last tub the settings were lost.)

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:43:13 pm
content: Quote from: Gyro on July 19, 2020, 08:40:06 pmYou 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?

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2020, 08:46:40 pm
content: I'm not upset, just pissed off. My only point was that you should buy one with a genuine approval. I'm in the UK, I don't use either.... and yes I did - I said use a contactor not an SSR. Go back and read your own thread!

author: Benta
author_rank: Super Contributor
timestamp: July 19, 2020, 08:48:48 pm
content: Gyro, you have my sympathyA technical thread devolving into "where is it cheapest" and "I don't care if it's genuine" is kind of sad...

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:49:16 pm
content: Quote from: Gyro on July 19, 2020, 08:46:40 pmI am taking your advice and using a contactor. Thank you very much.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:50:31 pm
content: Quote from: Benta on July 19, 2020, 08:48:48 pmNo that's not true. If I wanted cheaper I could have used Banggood.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:51:10 pm
content: Thanks for all of the comments. Decided to go with a $10 relay/contactor I found on Amazon. Others have purchased it saying they have used them of air conditioners, compressor motors, electric hot water heaters etc. Should be fine for my application. What's the worst that would happen? Heat up and the contacts remain closed/shorted? Or burn out and remain open? The GFCI is their to protect the people so no problem there.I guess the worst thing that could happen is the relay overheats and someone causes a fire in a hot tub filled with water. Fine with me, I have insurance.

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2020, 08:51:43 pm
content: Quote from: DougSpindler on July 19, 2020, 08:34:26 pmBecause people are willing to buy from less-reputable distributors to get a deal and those less-reputable distributors are willing to buy stuff out of the back of a stepvan in the middle of the night.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 19, 2020, 08:55:01 pm
content: Quote from: bdunham7 on July 19, 2020, 08:51:43 pmThat's the American way. What made America Great and Proud. I would not call buying something off of Amazon akin to buying stuff out of the back of a stepvan in the middle of the night.

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2020, 09:02:02 pm
content: Quote from: DougSpindler on July 19, 2020, 08:55:01 pmIf it is sold by Amazon directly, then it is likely not fake unless it is an item with inventory commingling. Is this a Packard contactor? Even less likely to be fake because nobody will bother to clone something already at the low end of the price range.However, buying a Cisco router from a third party seller on Amazon is indeed like midnight stepvan shopping. Interestingly, many people like their 'deals' so much they willfully overlook the counterfeit issue, even when it is fairly obvious.

author: Benta
author_rank: Super Contributor
timestamp: July 19, 2020, 09:02:42 pm
content: Quote from: DougSpindler on July 19, 2020, 08:51:10 pmIn that case you don't. Read the fine print.

author: robca
author_rank: Frequent Contributor
timestamp: July 19, 2020, 11:03:33 pm
content: If you are in the USA you very likely might have a Platt close by, and you can get a reliable contactor from Platt (if they don't have it in store, they can get it delivered to the store free for you in a short time, usually)I'm all for saving money and I buy routinely from dodgy Aliexpress/eBay sellers, but for things on mains and higher currents, I prefer to use trusted suppliers.

author: bob91343
author_rank: Super Contributor
timestamp: July 20, 2020, 01:27:32 am
content: Don't overreact to my caution about insurance. I have heard horror stories and think it's wise at least to add that concern to the equation.These guys know how to play hard ball so make sure you know what you are doing.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 20, 2020, 04:21:32 pm
content: Quote from: bob91343 on July 20, 2020, 01:27:32 amI know exactly what I am doing. I live in California where earthquake insurance is very expensive. That's why I keep a gallon of gas on top of my natural gas hot water heater. Should their ever be a large earthquake that would damage my house the fire insurance will cover it.

author: cdev
author_rank: Super Contributor
timestamp: July 20, 2020, 04:40:33 pm
content: Check with your local building and health deparments that your hot tub is code compliant. Better safe than sorry.In my experience, spas always had to be connected to a reliablemechanicaltimer switch with a maximum on time per turn of an hour or less (check local laws) All this means is that you have to give it a twist every hour. (you have to be present and conscious)The reason is that people have lost consciousness in spas and literally have been cooked alive.Also, you are not supposed to bring alcohol into a hot tub and may be required to post a sign to that effect..The temperature should not be allowed to get too hot. The CDC recommends 104°F (40°C) as the maximum temperature.The need for a mechanical timer prevents it from just being left on. My knowlege may be old but in my experience, a mechanical timer tends to be the most reliable kind.(They are also useful for soldering equipment. Its easy to reset a timer and worth it for the peace of mind knowing your soldering iron or preheater cant be left on all day by mistake).

author: james_s
author_rank: Super Contributor
timestamp: July 20, 2020, 04:45:17 pm
content: I would attack this from a different angle. The spa already has a system that controls power to the heater and pump(s). You can intercept the low voltage signals that control those, or you might look at upgrading the control, I'd expect there are models available that can be programmed to run during certain hours. Mine has an "eco mode" that only heats during the scheduled filter cycle and that can be programmed to run at a specific time and it's pushing up on 30 years old so nothing new there.

author: langwadt
author_rank: Super Contributor
timestamp: July 20, 2020, 05:00:09 pm
content: Quote from: DougSpindler on July 20, 2020, 04:21:32 pmmaybe, or the isurance will say the fire was caused by the earthquake and not covered.Louis Rossmann has told several times about his business insurance refusing to covers loss from not having electricity,because they didn't cover flooding and the missing electricity was caused by a flood at the powerstation

author: DougSpindler
author_rank: Super Contributor
timestamp: July 20, 2020, 05:05:01 pm
content: Quote from: cdev on July 20, 2020, 04:40:33 pmYour information is old and out of date. A mechanical timer will not work for this application. The power companies in the US are changing how they charge for electricity. The amount of money we pay for electricity changes 5 times today. Prices will range from $0.12 kWhr to $0.54 depending on the time it is purchased. Then on weekends the times change.With a mechanical timer I would be really screwed when the power company shuts the power to the city during high winds. I would have to reset the timer every time that happens.While I appreciate your suggestion, it's not solving the problem.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 20, 2020, 05:06:38 pm
content: Quote from: langwadt on July 20, 2020, 05:00:09 pmCalifornia 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.

author: bdunham7
author_rank: Super Contributor
timestamp: July 20, 2020, 05:11:53 pm
content: Quote from: DougSpindler on July 20, 2020, 05:06:38 pmReally? Can you tell me where I find that law?

author: DougSpindler
author_rank: Super Contributor
timestamp: July 20, 2020, 05:15:40 pm
content: Quote from: james_s on July 20, 2020, 04:45:17 pmJames_s - Thanks, I gave that some thought. All of the relays are mounted on a circuit board and there are four different clean, heat, filter programs. Just way to complicated. Far easier to just install a high current relay after the GFCI and interrupt the mains power to the spa. The spa's circuits have memory so the temp and other settings will all remain the same. (I had another spa where the settings were not retained on power loss.)In looking at posts in other forums getting others are doing exactly the same thing I am doing for AC units, electric heaters, pool pumps, electric hot water heaters etc.Not sure if you read my other post, but the power company will change the amount of money they charge for a kWhr 5 times today for $0.12 to $0.54.This $10 relay will save me over $1,000 in just 1 year.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 20, 2020, 05:20:27 pm
content: Quote from: bdunham7 on July 20, 2020, 05:11:53 pmWhy 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.

author: bson
author_rank: Unknown
timestamp: July 20, 2020, 05:32:50 pm
content: 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.

author: langwadt
author_rank: Super Contributor
timestamp: July 20, 2020, 05:47:32 pm
content: Quote from: DougSpindler on July 20, 2020, 05:20:27 pmthen no one is ever covered by fire insurance because it'll always be before what ever earthquake comes next

author: DougSpindler
author_rank: Super Contributor
timestamp: July 20, 2020, 05:56:45 pm
content: Quote from: bson on July 20, 2020, 05:32:50 pmYou 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.

author: bdunham7
author_rank: Super Contributor
timestamp: July 20, 2020, 06:00:35 pm
content: Quote from: DougSpindler on July 20, 2020, 05:20:27 pmI didn't say that. I'm wondering why you think fire insurance would not be validbeforean earthquake.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 20, 2020, 06:05:04 pm
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: July 20, 2020, 06:18:03 pm
content: Quote from: DougSpindler on July 20, 2020, 06:05:04 pmWell, perhaps, unless you have announced your intent to commit arson in a public forum.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 20, 2020, 06:30:26 pm
content: Quote from: bdunham7 on July 20, 2020, 06:18:03 pmI'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.

author: Bassman59
author_rank: Super Contributor
timestamp: July 21, 2020, 11:22:07 pm
content: Quote from: DougSpindler on July 19, 2020, 08:43:13 pmFor 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.

author: james_s
author_rank: Super Contributor
timestamp: July 21, 2020, 11:42:23 pm
content: 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.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 22, 2020, 12:40:40 am
content: Quote from: james_s on July 21, 2020, 11:42:23 pmSSRs 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.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 22, 2020, 01:17:31 am
content: 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?

author: sokoloff
author_rank: Super Contributor
timestamp: July 22, 2020, 01:28:28 am
content: For once or twice daily cycling and no need for anything more than bang-bang control, I’d use a relay.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 22, 2020, 01:32:12 am
content: That's what I'm going to do.For educational purposes.. Could I use an SSR? Can you explain the advantages and disadvantages?Thanks

author: themadhippy
author_rank: Super Contributor
timestamp: July 22, 2020, 02:47:23 am
content: 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.

author: floobydust
author_rank: Super Contributor
timestamp: July 22, 2020, 02:48:53 am
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: July 22, 2020, 03:51:15 am
content: 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.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 22, 2020, 05:20:25 am
content: Quote from: james_s on July 22, 2020, 03:51:15 amWhat 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?

author: DougSpindler
author_rank: Super Contributor
timestamp: July 22, 2020, 05:25:18 am
content: Quote from: themadhippy on July 22, 2020, 02:47:23 amThanks - 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?

author: james_s
author_rank: Super Contributor
timestamp: July 22, 2020, 05:34:44 am
content: Quote from: DougSpindler on July 22, 2020, 05:20:25 amIt'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.

author: james_s
author_rank: Super Contributor
timestamp: July 22, 2020, 05:36:12 am
content: Quote from: DougSpindler on July 22, 2020, 05:25:18 amA 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.

author: DougSpindler
author_rank: Super Contributor
timestamp: July 22, 2020, 05:43:04 am
content: Quote from: james_s on July 22, 2020, 05:36:12 amThanks

author: DougSpindler
author_rank: Super Contributor
timestamp: July 22, 2020, 05:48:16 am
content: Quote from: james_s on July 22, 2020, 05:34:44 amI'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.

author: james_s
author_rank: Super Contributor
timestamp: July 22, 2020, 06:10:23 am
content: 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.