Switching 230v 12 amps.

[banda]

Up until now I've experimented only with PICAXE VSM.
Now however I'm going to take the next step, and get my hands dirty.
I am beginning to breadboard.

I want to switch 230v 12amps on for say 2 hours every 12hours.
I see there's an opto-isolator arrangement (SSR-25DA 25A Solid State Relay -- Google? )
that appears able to do the trick.

I am too wimpy to connect it up myself, so I'll get an electrician in. Besides, it would be illegal.
I do intend to do the picaxe, low voltage, switching part myself, however.

Here's my question:
Does this arrangement give off much heat for the time the 230v, 12amp is connected?
Will it need a heat sink or whatever?
Are there better ways to switch than others?

Has anyone knowledge of such a setup?
Thanks anyone for advice.

 

[Circuit]

Have a look at a datasheet for a typical solid state relay of the type you mention; http://www.rapidonline.com/pdf/505111_da_en_01.pdf
You will see the reference to cooling; 10 amps with convection cooling, anything over requires a fan. You can see the colour image on the datasheet shows a built-in heatsink.
You need to check out the datasheet for the actual unit you are choosing; there are quite a few out there. If you are switching mains then I would suggest purchasing from one of the main supply houses to ensure a genuine product to a guaranteed specification - flames are unwelcome in such circuitry!

 

[Goeytex]

The Fotek Relays look like a bargain, but buyer beware. As with many Chinese products, they may or may not work as advertised. If you get one of these be sure to get one that includes the heatsink.

Respected brands include Gordos, Crouzett, Teledyne, Continental, Watlow, Crydom & OPTO. If purchasing from EBAY, I would probably prefer a used/surplus of one of these, than a Fotek. (Until I did extensive testing on the Fotek).

Several years ago I got a surplus lot of 25 Crydom 40 AMP SSRS for < $50. Everyone of them tested perfect.

 

[SAborn]

I purchased some of these a while back, http://www.ebay.com.au/itm/390567702267?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
and so far have not had a problem with any of them.

I do suggest you go for a far over rated amp version, like the 40 amp or 60 amp ones, as they will not run as hot at 12 amp compared to the 25 amp SSR.
The mounting base is a isolated heatsink and it would be advised to mount it on a larger heatsink like a metal enclosure with heatsink compound between the SSR and heatsink.

The hocky puck SSR (as above) has a led built in on the DC side so you can test your circuit to see if the SSR is working without the need for mains power connected.

 

[techElder]

Be sure to wire in a Mains Receptacle in an insulated junction box for your high voltage connection.

 

[matherp]

I've given up on cheap SSRs as I've had too many problems with failures, leakage even when off, huge heat production and overheating even when well within spec, etc.

These though are cheap and work great: http://www.rapidonline.com/Electronic-Components/16a-PCB-Form-A-Power-Relay-5v-60-5030. Just use a 2n2222 with a 680ohm base resistor.

 

[Dippy]

Why do you want to use an SSR rather than mechanical relay?
Is it simply because it is 'solid state'?
What are you switching?

Yes, they can get hot. As mentioned many need forced cooling (e.g. fan).
You can get a good idea from the Volt drop specs.
Get the data sheet and read it and note any de-rating curves too.
Personally, I would only go for the big brands - it's a 'trust' thing

There are advantages to SSR but heat can be a pain which isn't so much of an issue with a suitable mechanical relay.
And, if you go for a mechanical relay, don't skimp on cheapies - again, for me, a trust issue. I like my house.

 

[the old fart]

I've found the cheap chinese imports are dangerous.

I had one that leaked mains voltage into the low voltage side. Less than 1Kohm between primary and secondary side.

Nearly lost me my stock of Koi fish.

 

[banda]

I am ever amazed at who is reading my nooby questions.
people from places around the globe. Thanks to you all.

To Circuit: Thanks for your information. It has been helpful.

To goeytex: I've googled some of the places you've mentioned, but I'll have to read them again to try to understand.

To SAborn: I think I can see that the base of the gadget is metal, so is that where
I'd stick the heatsink to? Does that mean that it would be sitting on the heat sink fins?
Would it get VERY hot over 2 hours?
I can't find any 60amp ones.

To texasclodhopper: I presume the exorbitantly expensive electrician will see to that. I'll check over his shoulder.

To matherp: Thanks for the new possibility. I'll have to try to understand how it works. Have you used one?


I can't hide the fact that I'm quite ignorant in things electronic. But I'm learning!

 

[premelec]

As Dippy suggests a mechanical type might work fine - I like the "clack" noise and you can see if the contacts are good [or welded together / burned!]- and you can push them on with a plastic rod by hand. The down side it higher drive current to the coil and slower operation - they are more forgiving to transient voltages which may pop the solid state ones into shorting and such. Good over rated SSRs work well when used properly [heat sink etc]. Dust and bugs can get into the mechanical contacts as well.

 

[matherp]

To matherp: Thanks for the new possibility. I'll have to try to understand how it works. Have you used one?

The link I gave you is to a simple mechanical relay which I have used successfully. The advantage of it is that it works off 5V and has a 16A contact rating. I'm not sure if Dippy considers it a "cheapie". The non-cheapie version is:
http://uk.rs-online.com/web/p/non-latching-relays/7181796/

Also depending on the power supply available you can use a different coil voltage - there is even more choice when you move to a 12V coil.

See manual no.3 for the circuit wiring - don't forget the diode

 

[DaveC166]

Hi banda,3 years ago i purchased an Omron 20 amp SSR from Active Components in Auckland. it was 1/2 the price local electricial wholesalers were trying to charge. Even with a 5.6 amp load it still requires a heatsink

 

[BeanieBots]

Would it get VERY hot over 2 hours?

That depends on many things, in particular, your choice of heatsink and possibly to a greater extent how/where you mount it.
Put it inside a nice enclosed box and will probably melt very quickly. Lets face it, a small peice of wire in a nicley insulated glass envelope glows white hot with just a couple of batteries as power (a torch bulb).
As Dippy has mentioned, get the specs and do some sums. Most datasheets for SSRs give derating curves to take into account where it is mounted.

 

[banda]

Well now. You've scared me. Some say this, some say that,
and I certainly don't want to burn my house down, or to lose my koi fish!

One thing I have learned from you is that I must work carefully, and decide carefully, so that's what I will do.
Thanks very much to all of you for your help.

 

[tony_g]

im going to be using a couple of SSR's in the process of converting my toaster oven to an automated reflow system.

as well as using the heatsinks im also looking to add some good quality thermal paste between the heatsink and ssr (probably the expensive arctic silver stuff you would use with a pc's cpu) and adding some pc case fans,no doubt the noisy ones that put out some good airflow just to try and make sure i keep on top of heat dissipation as much as i can seeing as its going to be drawing around 12.5 amps !!

http://www.fotek.com.tw/pdf/etc_34.pdf

this is the only info i could find that mentions any sort of thermal curve with regards to the ssr case temp and current draw, presumably those numbers are for use with a heatsink.


tony

 

[Circuit]

Well now. You've scared me. Some say this, some say that,
and I certainly don't want to burn my house down, or to lose my koi fish!

One thing I have learned from you is that I must work carefully, and decide carefully, so that's what I will do.
Thanks very much to all of you for your help.

A very wise reply. Overall, you may wish to look at how major manufacturers of household appliances switch high power mains loads. Most dishwashers, washing machines etc. still tend towards the good old-fashioned and stalwart relay to switch motors and heaters. - I think, that in view of your relative inexperience in these matters, you might want to look again at the solution given by Matherp in post 11 above. The use of such a device needs no calculation of loading vs. heat-sinking etc., but you must merely check that the rating for the relay is greater than the load (in amps) that you wish to switch. The only possible pitfall is that relay contacts have different ratings for AC and DC loads but these are normally stated clearly in the datasheet or on the body of the relay itself.

 

[BeanieBots]

I dont' think the subject of what the actual load is has come up yet.
This could have a large influence on the choice of switching method.
Is it a motor and hence very inductive in which case SSR will be difficult and relay contacts would require suppression.
Is it incandescent lamps in which case VERY large inrush currents can be expected so soft-start or high over-rating is required.
Just a little more to consider.

 

[Circuit]

I dont' think the subject of what the actual load is has come up yet.
This could have a large influence on the choice of switching method.
Is it a motor and hence very inductive in which case SSR will be difficult and relay contacts would require suppression.
Is it incandescent lamps in which case VERY large inrush currents can be expected so soft-start or high over-rating is required.
Just a little more to consider.

Ah, Beanie, it is in the first posting - 230 volts, 12 amps heater element therefore (effectively) non-inductive. The chap is probably best off with Matherp's suggestion given all factors considered.

 

[BeanieBots]

...230 volts, 12 amps heater element ....

I'm sure you're right but I still haven't seen "heater element" mentioned.
I do however agree that if that is the case then Matherp's suggestion is sound.

 

[Circuit]

I'm sure you're right but I still haven't seen "heater element" mentioned.
I do however agree that if that is the case then Matherp's suggestion is sound.

Its amazing how we read what we think we read - or not! You are absolutely right, there is no mention of a heater element - I read the mention that it was to be used with Koi Carp and given the specification I had just assumed that it was a heater. I couldn't think of anything else that would some three kilowatts in this regard. Anyway, it would be one hell of air pump!

Banda, am I thinking in the right direction?

 

[banda]

Good heavens! I thought I'd released you all from feeling you had to help an absolute beginner.
Circuit has diagnosed my problem successfully. I shouldn't have delivered such a narrow brief.
What I'm going to say now will probably start another interesting discussion. I'd like that.
I've asked electricians and they have plumped for one or the other of my possibilities, but without any evidence.

My main electric hot water cylinder gets used for probably less than 2 hours a day.
The 180 gallon cylinder would usually be maintained at maximum allowed temperature.
I imagine that only the top few inches of water is used/day.

Possible answers:
1. Leave as is, leaving the thermostat to maintain the allowed temperature,
including bolstering any heat escaping from the cylinder.

2. Developing what might be a cheap Picaxe project that turns the heater on/off for arranged time(s)/day.
That would keep only the upper few inches hot enough to use, with the rest of the cylinder cold.

I have some doubts as to how to proceed with my experiment:
I want the project to sleep for the bulk of the rest of the day, to minimize battery use over long periods.
Helpful people have already told me the difficulties with switching 230v AC and 12(?) Amps.
I must pay an electrician to set up the high voltage area.
I want the whole setup to have a switch that will revert the whole setup to what it is now, for whatever reason.

I remind people that I am a beginner, and that I am initially using PICAXE VSM.
I think I'm pretty OK with a DS3232 rtc and the switching, but I need to learn about setting the 'sleep' input.

So, that's the reason I started the whole thing. It's to save money.

 

[srnet]

2. Developing what might be a cheap Picaxe project that turns the heater on/off for arranged time(s)/day.
That would keep only the upper few inches hot enough to use, with the rest of the cylinder cold.

I must be missing something obvious.

Over here in the UK, you can buy plug in mains timers that will switch the load you want, they cost from around £3.

Dont they have them in New Zealand ?

 

[banda]

Omigod. Nothing electronic down here seems to cost only 3 pounds.
Can you give me a webpage that illustrates them?

 

[banda]

I've just checked on mains timers.
Unfortunately my hot water cylinder is hard wired.

 

[premelec]

I don't know the NZ situation however various power companies in the USA will give you better rates if you allow them to install timers or controllers on high power loads like DHW - have you checked with your local power provider? You can control it by hand flipping the breaker switch to the DHW unit.

 

[srnet]

Omigod. Nothing electronic down here seems to cost only 3 pounds.
Can you give me a webpage that illustrates them?

Do a eBay search on mains timers, should be plenty to choose from, mechanical and electronic.

If the cylinder is hard wired, then you cant control it without making some changes to the wiring, so modification of the wiring of some sort is inevitable.

230V & 12Amp is within range of a plug and socket arrangement, assuming the correct heat resistant flex is used. Electricians should be able to advise on any local restrictions.

 

[SAborn]

As far as i am aware NZ works on a off peak power system for hot water, so check your power meter board and you would likely find a time clock there that controls your hot water heater.

The next problem with your idea is health and saftey, a hot water cylinder needs to be heated high enough to kill off parasites in the water, which requires above 50-60C i think.

Otherwise you will breed dangerous parasites like salmonella, and many more other nasties, by partial heating of the water stored in a cylinder.

Your best option is to try and find a smaller hotwater system so you dont heat a larger amount of water than required, or add some solar HW panels to your system to reduce the amount of energy required to heat the water.

 

[Circuit]

As far as i am aware NZ works on a off peak power system for hot water, so check your power meter board and you would likely find a time clock there that controls your hot water heater.

The next problem with your idea is health and saftey, a hot water cylinder needs to be heated high enough to kill off parasites in the water, which requires above 50-60C i think.

Otherwise you will breed dangerous parasites like salmonella, and many more other nasties, by partial heating of the water stored in a cylinder.

Your best option is to try and find a smaller hotwater system so you dont heat a larger amount of water than required, or add some solar HW panels to your system to reduce the amount of energy required to heat the water.

My thoughts are along the same lines - although salmonella is not a parasite and is not likely to be found breeding in your water cylinder! The principle is, however, absolutely correct. In fact, the recommended temperature for hot water supplies for public places in this country is 70C - that is why we now have signs over every publicly-accessed washbasin declaring "Danger - hot water". It is not as stupid as it at first appears because the danger of bacterial growth in such systems and the establishment of biofilms within the tanks and pipes has only relatively recently been recognised, leading to the increase in thermostat settings in a lot of places that previously poured "hand-hot" water at the basin.

The recognition of the growth of legionella bacteria (causing legionnaires disease, a sometimes fatal respiratory illness) within domestic and public water systems is one of the major factors involved, but the range of bacteria that can propagate is quite wide-ranging. So the message from SAborn is correct; keep the top of your tank only warm at your peril!

A much better solution is to set your thermostat at 70C and then insulate the tank really well - that will give you the energy savings and the nicely-insulated piping hot water in the tank will not allow growth of most pathogenic micro-organisms. Modern insulation techniques will keep your tank like a thermos flask. In fact, you will probably save more by having a well-insulated hot tank than by having a poorly-insulated one with a two-hour a day timer. So save some money on the electrician's bill and get yourself a shed-load of insulation blanketing for half the money.