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ameador1
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Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Fri Mar 29, 2019 12:50 pm

I am trying to control US 240v mains and would like a rating of 8 to 10amps. The wiring is basically two legs of 120v each with a ground wire. So, a DPST or even a DPDT would be optimal. I know I can use SPST/SPDT relays that are easy to find and just control 2 relays for each 240v load, but that creates the risk of only cutting power to one leg if a relay fails for some reason. In my case - this will still allow the equipment to partially run but its state can become flaky - stressing the PSU, possibly trying to pull too much amperage across the single leg, etc... I really need to have a DP solution. But, so far I cannot find these kinds of relays - that are raspberry pi friendly anyway - or getting into relays that would control other relays. I'm ok with the idea of using another PSU to power the coil side of these relays - so long as the signaling can be done via 3.3v to 5v (can use a logic leveler between if needed). I have 16 240v devices I want to be able to control via the RPi - so my goal is obviously a 16 channel relay board or 2 - 8's or even 4 - 4's. If need by 16 individual ones. Price is a concern - I need to keep the costs to a minimum.

Any suggestions or advice would be greatly appreciated! Thanks!
"When money ceases to be the tool by which men deal with one another, then men become the tools of men. Blood, whips and guns–or dollars. Take your choice–there is no other..."
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omegaman477
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Fri Mar 29, 2019 4:18 pm

I find you cant go past either Banggood or AlliExpress. BOth source from China, so its cheap, but quality is always unknown.

As you need 16 relays, I would buy singles from 2-3 vendors and test them out.

You are wise to overrate the relays, as a general rule I always double the relay rating for AC, and triple for DC loads.

Switching both wires on a mains supply is also a good idea, as you never know if they may be reversed, and you switch only the Neutral, so a short to Ground could be lethal.

Just remember that 10 A AC is a fair load, and if the load is inductive, expects some relay arching, consider an AC snubber circuit.

I alway try to use Solid State Relays (SSR's) wherever possible, they are more expensive but provide so many advantages. Their are version for inductive loads as well.

I get 20A SSR's from AlliExpress for about $6 ea.
..the only thing worse than a stupid question is a question not asked.

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ameador1
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Fri Mar 29, 2019 4:56 pm

This is for high power computer equipment - so not inductive load and pretty constant power draw. 240v - constant pull at 5 to 6 amps depending on the unit. They are a pretty good load. I'll look at them. I'm finding more options in the 24v coil side - beginning to think that using the little JBteck 8 or 16 SPDT relays to switch a 24v PSU to the control and coil side of larger relays may be the way to go. You have found 20amp SSRs that are DPST/DPDT that are controlable directly via the RPi - or are you using intermediary relays?

That's a good thought on even then 120v mains - that is a good reason to even run those on DP relays vs SP.
"When money ceases to be the tool by which men deal with one another, then men become the tools of men. Blood, whips and guns–or dollars. Take your choice–there is no other..."
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ptimlin
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Tue Apr 02, 2019 12:53 am

If you shop places like Digi-Key or Grainger and other trust worthy vendors you know you are not buying cheap knock off junk from China. Not sure what you hope to be a "reasonable" price, but you should be able to find DPDT relays that can switch 240V/10A for about $18-ish US each. But as you mentioned typical coil voltages are 12Vdc or ac, 24Vdc or ac, 120Vac, and 240Vac. So nothing that would interface to a RPi directly.

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ameador1
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Wed Apr 03, 2019 1:43 pm

Thanks - that's more or less what I'm finding. My reasonable price would be to stay around $50-$75 for the 16 relays. I mean - when you can get 16 SPDT relays rated for 250V/10A on a PCB with optocouplers, LED indicators, etc... for a total of $15 - $18 per relay seems unreasonable. I mean, It's a small plastic box with a few wires, small coil, and 6/8 metal pins... they are simple devices. Even with good materials - $18 is a rip-off. Now, I get what you are saying too - spend too little and get garbage that will fail is not good either. There must be a middle ground. But at $4 or $5 each is still more than 5 times over the cost of the 'cheap' ones and hits the $50 to $75 range for the batch.
"When money ceases to be the tool by which men deal with one another, then men become the tools of men. Blood, whips and guns–or dollars. Take your choice–there is no other..."
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scruss
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Wed Apr 03, 2019 2:59 pm

ameador1 wrote:
Wed Apr 03, 2019 1:43 pm
… a total of $15 - $18 per relay seems unreasonable. I mean, It's a small plastic box with a few wires, small coil, and 6/8 metal pins …
… that needs to switch reliably 1000s of times and every time fail to melt and burn your house down. That seems a pretty good deal to me.
‘Remember the Golden Rule of Selling: “Do not resort to violence.”’ — McGlashan.

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NGC6543
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Wed Apr 03, 2019 4:34 pm

Do you know the inrush current of the SMPS you are switching? It should be on the specifications from the manufacturer.

Anyway, one thing to consider is how you are going to mount the relays. Are you making a PCB that you can cut slots in for relay tags and mains side isolation distance? Most relays suitable for your needs have tags, not pins. If not then you need to either use a relay socket or a chassis/panel mount relay. A socket is going to be nearly the cost of a relay and is useful in situations where you might need to replace popped relays occasionally. So, that leaves (me, anyway) with a chassis mount solution.

I've used this type before. It's easy to mount, not as expensive as some, has 1/4" spade terminals for easy wiring and is DPDT:

https://www.alliedelec.com/product/te-c ... /70198630/

There are cheaper ones with tagged connections, but like I mentioned above...

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ptimlin
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Wed Apr 03, 2019 6:58 pm

ameador1 wrote:
Wed Apr 03, 2019 1:43 pm
Thanks - that's more or less what I'm finding. My reasonable price would be to stay around $50-$75 for the 16 relays. I mean - when you can get 16 SPDT relays rated for 250V/10A on a PCB with optocouplers, LED indicators, etc... for a total of $15 - $18 per relay seems unreasonable. I mean, It's a small plastic box with a few wires, small coil, and 6/8 metal pins... they are simple devices. Even with good materials - $18 is a rip-off. Now, I get what you are saying too - spend too little and get garbage that will fail is not good either. There must be a middle ground. But at $4 or $5 each is still more than 5 times over the cost of the 'cheap' ones and hits the $50 to $75 range for the batch.
You can get cheaper relays if you don't mind ones designed for printed circuit boards rather that ones that use screw terminals or spade lugs. But then you need to either layout a circuit board or do your own hand wiring on a perf board soldering wires to pins on each relay? Are you able to do that? If so...

Try searching for, as an example, Omron G5LE-14 series. Only a little over a dollar each.They come in a range of coil voltages including 3V and 5V but will require too much current to drive directly off a GPIO pin. I would suggest the 5V coil versions and then use the ULN2003LV and that little adapter board I pointed out in your other thread...
viewtopic.php?f=37&t=237013

You can get 25 pieces of the 5V version for $30us (a buck twenty each).

UPDATE: looking at that relay more closely, I forgot you wanted two poles. Those are only single pole. Also they are 250Vac MAX for switching but really rated for 120Vac operation. So perhaps this one...
https://www.digikey.com/product-detail/ ... ND/1789837

DPDT, 5V coil, 8A, 440Vac max Price does jump up to around $3 for 25 of them but still within your price target.
Last edited by ptimlin on Wed Apr 03, 2019 7:44 pm, edited 1 time in total.

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NGC6543
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Wed Apr 03, 2019 7:38 pm

Those little relays are nice, but (1) are only single pole (we really need two) and (2) will not cope with the inrush current of the big SMPSs it's going to be switching. They can have an inrush measured in tens of amps.

A Dell server I know with a similar power requirement is specified to have not more than 35A inrush current. My Cisco 2800 routers I used to run in my lab had an inrush specification of up to 35A! (I made the power distribution for a rack of them in my study.) I've seen specs for servers up to 50A inrush.

Inrush current is a real thing that needs accounting for, if we want things to be reliable and safe.

A much bigger relay is needed.

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ptimlin
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Wed Apr 03, 2019 7:50 pm

NGC6543 wrote:
Wed Apr 03, 2019 7:38 pm
Those little relays are nice, but (1) are only single pole (we really need two) and (2) will not cope with the inrush current of the big SMPSs it's going to be switching. They can have an inrush measured in tens of amps.

A Dell server I know with a similar power requirement is specified to have not more than 35A inrush current. My Cisco 2800 routers I used to run in my lab had an inrush specification of up to 35A! (I made the power distribution for a rack of them in my study.) I've seen specs for servers up to 50A inrush.

Inrush current is a real thing that needs accounting for, if we want things to be reliable and safe.

A much bigger relay is needed.
Ya I was looking at that while you posted and updated my post to a more suitable relay for his requirements. Unfortunately those little ones have a switch rating about equal to their load rating (8A load = 8A switching). So if his equipment required much higher switching currents they may not be suitable. But as we already discussed above, he doesn't want to pay for the type of relays he needs to do this (those cheap relay board he references are going to be the same issue, if they are 10A then that is likely the switching current as well.

So the solution is buck up and buy the $18+ relays. I bet he hasn't even seen what real "contactors" are that are used to switch large loads that run closer to $100 each.

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ameador1
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Thu Apr 04, 2019 3:35 am

Thanks - I will look into this information. I can solder and if need be can design a PCB for them. The ones I'm looking at so far are socket based for DIN rail mount. I had considered some pin based versions and designing a PCB, but it would be so much easier to change out failed relays I've pretty much dropped that route.

I don't disbelieve the price of electronic parts, I have an issue with the logic of pay a lot so you don't burn your house down as opposed to cost to manufacture and sell at a reasonable price. If you are content to buy them based on the fact that they won't burn your house down - then why not sell them for $100 each or why not $1000 each - wouldn't it be worth it not to burn your house down? It doesn't change the fact that at $18 each or $50 each or $100 each - it's a rip off compared to production costs.

I still have to look into initial power spike levels at startup, but I don't think these units will be bad as they phase in - turning components on, testing, ramping it up, then slacking back off - the adding in another component and doing the same procedure. It has 4 or 5 of these phases based on model. Just watching a wattage meter on them, 7 or maybe 8amps should handle the highs. But, like suggested earlier - I'll test a relay or two before buying into all relays at once.

Ive not suggesting using the cheap little relay board to run these devices. I've considered using them to control the 12v or 24v power that will in turn control the coils of the larger DP relays - as an intermediate step between the RPi. But I'm still getting feedback on options for controlling these DP relays. I like opto isolation. I like fewer components to limit failure points. But I'm taking it all in to try to make best choices.

I appreciate your help and explanations.
"When money ceases to be the tool by which men deal with one another, then men become the tools of men. Blood, whips and guns–or dollars. Take your choice–there is no other..."
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Brandon92
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Thu Apr 04, 2019 2:49 pm

ameador1 wrote:
Thu Apr 04, 2019 3:35 am
I don't disbelieve the price of electronic parts, I have an issue with the logic of pay a lot so you don't burn your house down as opposed to cost to manufacture and sell at a reasonable price. If you are content to buy them based on the fact that they won't burn your house down - then why not sell them for $100 each or why not $1000 each - wouldn't it be worth it not to burn your house down? It doesn't change the fact that at $18 each or $50 each or $100 each - it's a rip off compared to production costs.
The point is also, when you buy from a well known manufacture. You know what you are getting and that the specifics are through and the relay is reliable.

For example this relay. It is rated at 20A and a piek current of maximum 30A. But it can "only switch":
  • 230V incandescent/halogen 1000W
  • 230V LED 200W
And the reason for the big different between a LED an da incandescent lamp is the larger inrush current of a led lamp.

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ameador1
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Thu Apr 04, 2019 4:06 pm

I suppose after 35 years in the IT industry I have found that name buys very little in too many cases. In some cases, it may matter. Motherboards, RAM, hard drives, optical drives, cases, PSUs, cooling fans, switches, routers, tools, etc... I have had good experiences with all of them from no-names to known names. Many times name brands simply take advantage of the fact that people are simply buying their name. I've learned a long time ago not to just buy the name.

My focus is on specifications and customer reviews/recommendations - based on the details of those reviews and the apparent knowledge level of the poster - as well as consistency and looking for trends. I have used top names for critical components and them fail and with miserable support. I've seen trends of being great in both and then going down in quality and their support being crap because of being too big for their own good. I've had small companies provide excellent products and support as well - and everything in between.

Focusing on the name instead of product and service will never allow small companies with high-quality products and services to rise up, and it allows big companies with big names to take advantage and charge exorbitant prices for their mediocre products and services. I feel like that is the case here. For relays that have been around forever - mass produced - and that probably cost them less than $0.50 to produce - $18 is buying a name or the feeling that $18 will save your house but $3 will burn it down. It is completely feasible for a company to produce them with the same materials, standards, and specifications and sell them for a few dollars and still make a profit.

So when I ask if there are people here that have a recommendation of components they have experience with that seem to be of quality without paying a jacked up price due to name - I'm following my typical buying philosophy. If they have suggestions - and then I can research them and see reviews and test them and they seem good - why not use them? Simply because they don't have the right name? No. That's not how I make decisions. Probably in part due to the fact that I, in my own businesses, have strived to provide the best products and quality I can - yet too many times was beaten out by companies like Gateway, Dell, etc - when in their early days (and still now) were/are notorious for using non-standard proprietary components, had/have poor customer service, etc... Better now? Well, Gateway (and any others) went under and Dell? Again - it trends. I've not been happy with their customer service by a long shot. Their products - not when I have to deal with repairs as standard components in many cases goes out the window. Toshiba - I've had such insane run-ins with their products and services that they are one of the few companies that have made my list of companies to NEVER deal with again. I can expand this list quite extensively to show that name is not that important.

Enough rant for now. Let us just leave it at - our purchasing philosophies are different and I have plenty of experience to back up my approach. I do understand your concerns and points - they just aren't my deciding factors.
"When money ceases to be the tool by which men deal with one another, then men become the tools of men. Blood, whips and guns–or dollars. Take your choice–there is no other..."
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ptimlin
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Fri Apr 05, 2019 3:36 pm

A couple of points.

One, relays are much more than simply a coil and some contacts. A lot of R&D goes into developing relays and there is a WIDE range of technologies and materials used in various relays, even if they all just say "DPDT" in the specification. So the better relays are not charging more because they are promising not to burn your house down, they are charging more because they have been designed for high load switching applications where the contact surface area, contact material coating, spring forces uses, ability to withstand arcing, etc. have all been beefed up and tested again and again. So instead you are buying a well designed relay for the purpose it is being used that will give long life in that environment. It just so happens if you buy the right relay for the job, the fringe benefit is you won't burn your house down.

Second, your examples of brand names tend to be more the manufacturers of end equipment. To your point, a no name brand can build just as good a router, switch, computer, etc. as the brand names, *IF* they used the good components. In this case we are not talking about the equipment manufacturers, we are talking about the component make. A good relay is worth the price when put into your equipment just like as an IT guy I bet you wouldn't buy the piece of equipment with the processor from the no name company vs. Intel or AMD, right? You probably got familiar with some of the names of manufactures who made processors, RAM, video chip sets, etc. So ya, the non-Dell company can make a kick ass competing product as Dell but when you open both of them up you are going to find Intel, Samsung, Micron, etc. with the components, so who cares whose name in on the enclosure. But a relay is like those internal components where there is something to be said for the industry leaders in that industry such as Potter & Brumfield, Omron, and a number of others.

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ameador1
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Fri Apr 05, 2019 6:24 pm

Relays in the realm of lower level components are simple. I get R&D - how much R&D needs to be done by a manufacturer that has made n number of relays before? It's not rocket science. Yes, I get that they have many factors to consider - material, thickness, spring strength, etc... Do you think they don't have to do that and more to develop microcomponents that are operating on tiny voltages/amperages where a microvolt could make or break the component? Yet you can get a DIP with multiple subcomponents that also had to go through significant R&D and have changed at a much greater pace than magnetic relays have - yet you can buy those for cents. Those made incorrectly could cause damage to very expensive items as well. Most of the companies producing end-user electronics are doing so via China - yet the Chinese relays can't be trusted?

My analogy with Dell and the like was that - an analogy. It carries up and down the spectrum. Yes, I dealt with the subcomponents of computers - Seagate, Western Digital, Micron, Siemens, etc... Same applied to them - they cycled on good and bad - some individual products were good and some were bad - some transitioned from one way to the other. They are companies dependent on other smaller subcomponents. Manufacturers of transistors, relays, capacitors, resistors, etc... also rely on suppliers of their base materials and components - and so on. You'll not convince me that name is the factor to consider. I've had too much experience in life to tell me otherwise.

I have found products that I liked - and while they were good - I stuck with them - but with VERY few exceptions - I would have to vary onto another source as the quality of the ones I had liked would begin to fall. Then as you said - who cares what the name is on the outside. Very true and somewhat to my point. How many companies simply have another company make their stuff and simply put their brand on it? What if that company is a no-name to the end user - yet they are producing the items for the rest of the market and sticking their names on it? On top of that - when that manufacturer is willing to modify the specifications on the components for particular customers of theirs - so even though it appears nearly identical to other ones they are producing - they are not of the same quality - even though manufactured by the same company. I've seen this in monitors and hard drives for example.

Believe me - I understand your position - I started off in my business that way - And almost every time I thought I finally found a good source for some part - they crapped out and I was off and researching for a replacement source and/or product. Another point in bringing up Dell is that even the big names do it - not just little no-names. You'd think they'd be concerned about damaging their reputations - but at some point, it seems like they get a large enough customer base that they are willing to piss off a batch of them without having any real concern about it. "We have 100M customers - who cares if we loss 100K of them to a crap product so long as they pay for it".

I do give consideration to a company's reputation and experience with them - it's human nature. It buys more leeway when they do have problems as to how far I'll let that go before firing them and finding a replacement - but it is not my primary focus. I'll not ignore no-names just because they are no-names. I've had very good experience with them - maybe because they are hungry and want to impress their customers so they can expand and get larger. I'm sure there are many factors - but to ignore them is anti-competition - which in turn keep prices higher by empowering to big guys to set the rates vs having to compete - or catering to those who buy in name only. Not me.

Also, consider the fact too that my experience has not been at the low-level components - I have no idea who is "supposed" to be good or bad. To me, at this point, they are all no-names. If people on here or other places I'm asking questions at have experience with brands they've had good experience with - I'll definitely consider that. Again, I'll look at the product in question - look at reviews (positive and negative) - I look at prices - I consider the component as to whether it justifies the price. Etc, etc... Some on here have given me model numbers/part number to look at - but when I look them up, it seems like many times there are multiple manufacturers producing the "same" item with a variant of the same model number - so who's better? I don't know. Where are they ACTUALLY made? Here? China? Made in China with their name stamped on it like they ACTUALLY manufactured it, yet a company in China is making them and re-branding them for half a dozen "manufacturers"? I can't tell. If multiple companies are selling nearly identical unit - does that mean patents have run out and now anyone can make them? If so, and Chinese companies are making them for everyone else - why is their cheap Chinese version then inferior? Now, I have other issues about that - but that's another discussion. But it doesn't change the fact that I quite frankly, at this point, don't know the industry well enough to know what I'm really getting, where it came from, or who REALLY manufactured it. So again, I fall back to specific recommendations, reviews, etc... And - will not just simply ignore "no-names"

Sorry - I don't want to argue with you guys, and I can write a book on this, but I'm sure you don't want to read it ;) Just consider that I am considering everything you guys are suggesting and I'm willing to listen to your explanations about design, specs, recommended items, etc... and I appreciate your time in helping me. I'm not angry or trying to sound so - just conversational. :)
"When money ceases to be the tool by which men deal with one another, then men become the tools of men. Blood, whips and guns–or dollars. Take your choice–there is no other..."
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ptimlin
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Sat Apr 06, 2019 6:20 pm

TL;DR past paragraph one. So will only comment on one part of paragraph one. You wrote:

"Most of the companies producing end-user electronics are doing so via China - yet the Chinese relays can't be trusted?"

We are not talking about components manufactured in China for known brands with good designs, process controls, and testing. We are talking about Chinese designed knock off brands where actual components sold may or may not meet the specifications claimed and certainly won't be certified by any sort of safety agency.

If you are building a personal hobby project where the failure of a component isn't a big deal in your robot, RC car, toy, doorbell, etc. than I am all for using the cheapest stuff if it seems to work. We are just warning you that if you are switching mains voltages at significant currents for equipment that sounds like it won't handle one phase not switching correctly or that the no name switcher is not UL or other agency approved and especially if this is not a one off thing but instead will be a product to be sold or provided to customers, well now you are talking Penny Wise & Pound Foolish.

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omegaman477
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Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Tue May 21, 2019 7:27 pm

ameador1 wrote:
Fri Mar 29, 2019 4:56 pm
This is for high power computer equipment - so not inductive load and pretty constant power draw. 240v - constant pull at 5 to 6 amps depending on the unit. They are a pretty good load. I'll look at them. I'm finding more options in the 24v coil side - beginning to think that using the little JBteck 8 or 16 SPDT relays to switch a 24v PSU to the control and coil side of larger relays may be the way to go. You have found 20amp SSRs that are DPST/DPDT that are controlable directly via the RPi - or are you using intermediary relays?

That's a good thought on even then 120v mains - that is a good reason to even run those on DP relays vs SP.
99% of computer equipment is powered by either a traditional transformer (inductive load) or a switch mode power supply (inductive load again, but with substantial inrush currents.

Reading your posts I get the impression you are trying to do this as cheap as you can, and size the load relays accordingly.

Switching mains, with inductive loads, is not an application you should cut corners on. As mentioned by others, when switching a 10A mains load, look to overate you relays by 300-400%, ensure you have snubber circuits. I have yet to see a multi-relay I/O board that is suitably rated for your application. Yes the relays may be rated to say 10-15A, but are the PCB tracks and connectors rated such. The cheap stuff you see on Banggood etc, is usually of Chinese origin, and rarely carries a CE or UL safety mark.

I would use on of these boards as you describe, but then insert a suitably rated, discrete relay or contactor on each channel. Fuse each channel on the hot side of each relay to protect against relay or wiring loom failures. All basic mains wiring design inclusions.

Select SSR's carefully for inductive loads, seeking a version designed for inductive loads. Overrating SSR is critical for longevity as they are very intolerant of high inrush currents.

Have you considered a ready to roll packaged mains switching powerboard, usually USB controlled. Would save you all this trouble and provide a level of safety. Alternatively use cheap Home Automation Wifi controlled appliance switches, https://www.banggood.com/SONOFF-S26-10A ... rehouse=CN
..the only thing worse than a stupid question is a question not asked.

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