I am not much of an electrician, more at home with software. What is the easiest device to switch hot tub filter pump on/off? 220V, 280W pump. Shelly mini enough? RC snubber - yay or nay?
That rating is less than 2 amps…
280w / 220v = 1.27 amps...
Because the pump is a motor, you would at least double the rated requirement, so
1.27a * 2 = 2.54 amps
is the minimum sized relay I would recommend.
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There are two key problems with switching inductive loads - motors and relay/contractors - the startup current and the switch off voltage transient.
For single phase AC motors (particularly fans and pumps/compressors with a physically connected initial workload) the inrush current can be 20 to 50 times the eventual running current. Fortunately this falls very quickly as the motor begins to turn, but in general the capacity of the wiring and the switching device should be around double the stated running power. Averaged out over the first few seconds at startup, this is why eg domestic refrigerators have a power lead with double the running need.
Then there is circuit protection. Old wire fuses were great, as they could handle the short term over-current without going pop. MCB devices are more sensitive, and things like my Shelly 1PM switches have overcurrent protection, so recommendations vary but it maybe necessary to overrate by, say, 4 fold to avoid device or circuit protection tripping.
I have a Softub with a rated 1kW pump (950 Watts running when warmed up), and I use a Shelly Plus 1PM. Snubber also fitted.
Startup power peak today was recorded on my HA at 1.7kW, probably instantaneously more but Shelly does not sample sub-second, so personally I work on double the rated load to be safe. My tub instructions also recommend a supply rated to almost 4 kW, so as to avoid the circuit protection tripping. I have my Shelly device overcurrent limit set to maximum too.
Turning off is just as troublesome due to the high voltages generated by the collapsing magnetic field. These can be in the order of kV, and can do a lot of damage. Smart switches invariably use a dinky tiny relay, with small contacts and just-too-small gap separation. Perfect for arcs, and if you know anything about arc welding, it can be a very easy way to permanently join two relay switch contacts together without even trying.
The eg Shelly electronics do not like kV running around either, and with over-voltage protection such devices can either fry (technical term) or shutdown /reboot. Shelly, I noted, recommend a snubber for induction loads, and personally I regard the cost of a snubber as much less than the cost of a burnt out relay contact or device or tripping or rebooting. I did have a period of shutdown issues with the 1PM, but that was due to firmware and over-enthusiastic action with the over-voltage protection. Firmware update last year seems to have fixed the problem. Also I don’t use the switching facility much, just the power monitoring.
A Shelly mini may be OK in your case at, I believe 8 Amp. For myself the power monitoring ability in the 1PM enables me to measure and track hot tub energy use.
This does not constitute formal advice, just relaying my success (lack of issues) with my Shelly and snubber!
First locate a contactor (at least what it’s called in the states) rated for a motor load of that specification - that will let you switch the inductive load safely (as explained by others above) the contactor will work on normal mains voltage so you can switch it on and off easily with your chosen smart relay solution.
Relay enables contactor contactor turns on your pump.
Motor loads like this eat smart switches and relays for lunch.
It’s a 1,2 amp motor… The typical 10-15 amp relay will nave no problem because of the scale.
I agree for motors that draw like 5a or more need a contactor and/or snubber, but not this…
That, of course, is the difficulty with following the manufacturer’s recommendation and using their expensive snubber from the start. Not having experienced an issue, I just don’t know now if it would have been a problem without.
With an expensive Hot Tub, I decided that ÂŁ5 up front was good insurance on a possible ÂŁ5k damage if it went bang (off) during a winter vacation and froze. If my Shelly reboots, my hot tub also drops its settings.
I guess it’s down to personal tolerance of risk.
My Shelly 1/1PM/2.5 is restarting when switching on inductive load – such as fans, motors, roller. What should I do?
To avoid that a RC snubber should be wired between Output and Neutral of the circuit. Еnergy absorbing circuits are used to suppress the voltage spikes caused by the circuit’s inductance when a switch, electrical or mechanical, opens.
I vote snubber yay