Relay for arduino

Hi all,

i tried to control my water heater with a 5V 1 Channel Relay Board Module for Arduino but the voltage was 2000w and it stopped working after a while! Can you point me to a "heavy duty" relay for my arduino?

Thanks

Firstly the power was 2000W or 2kW, not 2000w. upper and lower case always matters
for scientific units and prefixes.

You need a mains relay rated for enough current - that depends on your
mains voltage, which you haven’t stated. If its 240V, then 2kW is over 8A,
so a 10A or 16A mains relay would do.

For 110V its about 18A, or for dual phase 220V, 9A per phase, a 16A relay
is indicated for that (dual pole).

Since heaters are resistive, no snubber circuit is needed.

Any relay board will need to be opto isolated for safety, and thus require a separate, isolated, 5V
supply for the relay driver transistors. Most relay boards have a link that must be removed for
full opto-isolation - this needs checking.

Many people choose to use an SSR for mains switching as these are UL-rated.

Thank you for your reply it is a 220v/2000W. I used a 10a relay but it "failed"! I wil try a 16a

When i say failed...i mean...smoke coming out and....

Perhaps something like this:5V, 12V or 24V 1-2-4-8-16 Channel Relay Module Arduino PI ARM AVR DSP PIC | eBay

Only 10A rated, but if this is US 220V, that's actually two 110V phases that need switching so two
relay poles are needed at 9A?

There seems to be very few 16A relay modules spefically for Ardiuno, probably because such
relays are larger and more expensive. I would err on the side of caution with ratings if you don't
want a repeat of the smoking relay incident...

What about this one:

https://www.ebay.com/itm/1-2-4-8-16-Channel-20A-Relay-Control-Module-for-Arduino-UNO-R3-Raspberry-Pi/182294622448?hash=item2a719b30f0:m:mPWaHlnC4ectbDg-e7_ZJcw

MarkT:
Perhaps something like this:5V, 12V or 24V 1-2-4-8-16 Channel Relay Module Arduino PI ARM AVR DSP PIC | eBay

Only 10A rated, but if this is US 220V, that’s actually two 110V phases that need switching so two
relay poles are needed at 9A?

There seems to be very few 16A relay modules spefically for Ardiuno, probably because such
relays are larger and more expensive. I would err on the side of caution with ratings if you don’t
want a repeat of the smoking relay incident…

I think this one is exactly as the one that i used.

Perhaps you need to be more specific as to what part of the relay the "smoke" came from. IF it came from the coil, then you have not powered the coil properly.

Paul

Paul_KD7HB:
Perhaps you need to be more specific as to what part of the relay the “smoke” came from. IF it came from the coil, then you have not powered the coil properly.

Paul

I did not see the exact location from where smoke came out, by the time i figured it out it was too late, but there was a black burned “spot” on the relay (see image). The powering was ok;after the “burnout” i bridged the wires used in the relay and the water heater worked perfectly.

Anyway i ordered this:

https://www.ebay.com/itm/152820014868 AC 100-250V 30A. I think it is more than enough!

blackTrace.JPG

Hi,
Image of OPs relay in post #8 from ebay.
5a79e77ac4d3d81299251.jpg

Tom… :slight_smile:

You could buy a solid state optically coupled relay these can driven safely/ directly from your Arduino . Buy from a reputable electronic supply source.

A lot of the cheapo relay modules on eBay do not have sufficient clearance on the PCB to provide safe isolation when used with mains voltages - despite what they say.

Ensure someone compentant wires your heater .

hammy:
You could buy a solid state optically coupled relay these can driven safely/ directly from your Arduino . Buy from a reputable electronic supply source.

A lot of the cheapo relay modules on eBay do not have sufficient clearance on the PCB to provide safe isolation when used with mains voltages - despite what they say.

Ensure someone compentant wires your heater .

Agreed.

If the spider tracks you put on the picture indicate where the smoke came from, it was not from the relay, which are housed in the blue plastic boxes, but from outside the box. So the problem was not the relay but somewhere in the associated electrical components, or the circuit board traces.

Paul

I agree, a SSR is probably the best solution

Looking on my favourite online sellers site I see an SSR rated up to 380volts and 80amps for a mere $9.00

This SSR is "zero crossing" which is not important for a water heater being a resistive load.
The Fotek website specs this SSR input at 7.5mA which is well within spec for direct driving from Arduino.
The SSR should be electrically bonded to your water heater which I assume would be properly earthed.

BanditDave:
This SSR is "zero crossing" which is not important for a water heater being a resistive load.

What makes you say that.
AFAIK zero-crossing could be bad for inductive loads, but it could reduce mains rattle on AM radios with resistive loads.

Take care. I have seen reports of fake Fotek SSRs (Google it).
Leo..

Wawa:
What makes you say that.
AFAIK zero-crossing could be bad for inductive loads, but it could reduce mains rattle on AM radios with resistive loads.

Take care. I have seen reports of fake Fotek SSRs (Google it).
Leo..

You refer to AM (Ancient Modulation) radios. Do that technology still exist?

My main point in responding to the original question was to suggest to Bitaris that mains power is potentially dangerous and should be taken seriously. Any project involving mains power should be done by a suitably experienced person to ensure that equipment is securely bonded to earth and bolting an SSR to the water heater is a minimum for safety. I am of course assuming the water heater is part of a permanently wired structure i.e. a house otherwise it is quite a different situation entirely.
An incorrect implementation could result in more then a "blackened" relay

BanditDave:
You refer to AM (Ancient Modulation) radios. Do that technology still exist?

Yes AM VHF is used in the Aviation industry.

Tom... :slight_smile:

Yes there are fake SSR’s about - Spend the money and buy one from a good source as I said .

Google fake SSR’s ...

So, I used a SLA-05VDC-SL-A 5V 30A Relay Module. It works ok for the past two months!

TomGeorge:
Hi,
Image of OPs relay in post #8 from ebay.
5a79e77ac4d3d81299251.jpg

Tom… :slight_smile:

I ordered that from ebay. The seller sent it to me with no protection (he put it on an envelope) and I`m guessing it got damaged during transfer. So i bought this SLA-05VDC-SL-A 5V 30A Relay Module from a Greek e-shop which works ok (but it only has 1 relay).