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Author Topic: High Volt, High Current Switching?  (Read 1648 times)
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Hi,

I have a 3000 W, 240 V (AC) water heater element (12.5A-15A) that I'd like to turn on and off with my Arduino.

Obviously, I'll need some sort of heavy duty relay or triac to do this. Can someone please point me in the right direction? I'm not used to dealing with: AC, High Voltage (other than wiring) or high amps (again, other than wiring).

Thanks.

S
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Daniel
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hi

the best and most reliable solution is a solid-state relay. It can be directly connected to the Arduino, as it is optically isolated.
Have a look at this page. The pictures at the bottom right are the style you'll need.
  
D
« Last Edit: July 26, 2007, 08:02:31 pm by Daniel » Logged

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I saw one that looked like this at the electronics shop, tonight, but it wasn't marked (rated). I'll have to go back and ask.

Thanks for the quick response!



S
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Turns out the relay I found can't quite sustain my load.

I found another that says it will do 30 amp. The pins are labeled 1,2 (load) and input: +3.

There's a place for the 4th pin, but the contact isn't there. I measured across the pins and found about 20[ch937] between pins 2 and 3. Do I just use #2 as my ground?

S
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Daniel
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hi

I strongly suggest you  to wire it until you're completely sure of how everything's connected. AC can kill.

What does the relay you bought  look like?

D
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I'll be careful around 110v, certainly. I'm more concerned about frying my Arduino than my fingers, though (-:

(especially since _everyone_ seems to be out of stock until the mysterious new revision ships, today)


Here's a (crappy) photo of the relay:


I don't have my real camera, just the iSight.

Anyway, I expect to connect the low voltage across pins +3 (bottom right) and 4, but 4 is missing (bottom left). Load is pins 1 and 2. As I mentioned, there's 20[ch937] (in both polarities) between pins 3 and 2.

(the relay was in the surplus box at my local electronics shop)

Thanks!

S
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Daniel
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hey

that was fast!

If you can measure anything between the input side (1&2) and the output side (3&4)  that means the relay is fried. That makes sense: technicians will often do something damaging to a broken part ( like break off a contact) so it doesn't get mixed up with the working parts.

What country are you in? You can easily mail order a relay like that. Digikey has several rated at 20A, 260V:
Z178-ND, Z179-ND or Z180-ND; These are all about 25$ each Try and get one that is rated at least 30% over what you actually need.


Be really careful with the connections. 220V 20A will really make a large puff of smoke if you connect things wrong! And, like I said, under the right conditions that voltage and current is easily lethal.

D
« Last Edit: August 03, 2007, 01:38:23 pm by Daniel » Logged

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Hi,

Thanks for the info.

A couple things, now.. (-:

First, I'm using the info above to power something else, now. 110v (which hurts much less (-; ), peak at 25A. The SSR I found works for this load, but it's the compressor of a freezer, so when it peaks out (unlocking the rotor), it draws enough power to drop the voltage of the SSR to ~80v, and then the freezer powers down for some amount of time. Perhaps there's a weird delay or something on the freezer side..

Anyway, the 2nd thing is that there's no short/load between 1&2 or 3&4. Just 20[ch937] between 3 and 2. Also, the 4th contact doesn't APPEAR to be broken off (there's no stub or anything; it's just missing.. like it was never there).

And a 3rd bit of info: there was a whole box of these at the shop. I guess it's possible they're all duds, but it doesn't seem that way. There must have been 50 of them.

S
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Btw, I'm in Canada. I know I can mail-order or buy on eBay, but I was hoping to get my keggerator back up and running today...

S
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Daniel
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hmmmm

if there is any electrical path between the input and output, then they're not optically isolated.
That's bad smiley

D
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Ok; thanks. I'll take it back. Buying surplus sucks (-:

S
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Daniel
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hey

I'm in Vancouver! What city?

D


PS: Digikey is the way to go in Canada. I am just waiting for a shipment from them now. I ordered it 18 hours ago. They ship to Canada for $8 CAD overnight, brokerage included.  
« Last Edit: August 03, 2007, 01:51:37 pm by Daniel » Logged

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Montreal (-:
this guy is just down the street from me, but he's not answering email.. )-:

(plus it's a bit expensive..)

S
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Daniel
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My fellow Canadian:


you must have bought that relay at Addison!

I'd suggest that you order up something form Digikey, with double the specs you need, and it will be there Tuesday morning, as Monday's a holiday. You could also try a an appliance parts supplier, as they sometimes have them, but you will pay dearly.

D

PS: who needs a Keggerator in Montreal, with so many great bars? smiley

« Last Edit: August 03, 2007, 01:57:20 pm by Daniel » Logged

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Home brew. (-:

I got the relay at Acces Electronique, yes, an Addison branch out here in the suburbs. I called Addison, directly, today to ask about SSRs, and they said they didn't have any (not that I really believe them, but it's a 30-min drive each way if they don't... )-: ).

Digikey can really deliver that quickly?

S
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