herodotus
Posts: 4
Joined: Sun Feb 07, 2021 12:09 pm

Advice on relays/mosfets/optotriacs etc

Thu Jun 17, 2021 8:22 pm

Hi,

I'm attempting to control (amongst many other things) a 100w 12V pump and a 230v AC solenoid valve with my RPI 3B. I'm not exactly sure what the power rating of the solenoid valve is, I have no documentation for it; I can't imagine it's a lot (it's small) but there are probably some fun spikes when it turns off. Initially I was using an opto-isolated relay module (rated 10A/250V) with a separate 5v power supply, and switching both the solenoid and the PSU for the 12V supply for the pump with a single relay. I went through 3 relays before I realised I was welding the contacts - presumably thanks to some hefty transients during switching. I should probably get a TVS diode or some other snubber whatever else I do. I moved to switching the 12V to the pump and obviously that also entailed switching the two devices with separate relays. This is working (for now) but I don't have much faith in its longevity. I was hoping there might be an off-the-shelf solution that:
  • Draws minimal current from GPIO (2mA or less)
  • Will trigger from 3.3V
  • High cycle rating
  • Suitable for AC or DC
  • Can switch DC loads of 12V 15A (to give some headroom on the pump current)
  • Can switch AC loads up to 240V 1A
  • Isn't crazy money
  • Has some sort of snubber built-in
So far I've had no luck finding anything that fits the bill.

Alternatively I was thinking about a mosfet SSR (for minimal power drain and 3.3V triggering) switching my 5v supply which would in turn power a couple of ordinary panel-mount SSRs (for current handling/robustness) + some TVS diodes across the loads to help with the transients. Very much open to completely different suggestions!

Thanks,
Lucian

LTolledo
Posts: 5563
Joined: Sat Mar 17, 2018 7:29 am
Location: Anime Heartland

Re: Advice on relays/mosfets/optotriacs etc

Thu Jun 17, 2021 9:21 pm

for the pump, use automotive relays with contacts rated 20A, like the HELLA 933766111 MICRO Relay 12V 20A SPST RES
for the solenoid valve, use industrial relays, like Omron MY2N DC12
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

Some people be like:
"Help me! Am drowning! But dont you dare touch me nor come near me!"

herodotus
Posts: 4
Joined: Sun Feb 07, 2021 12:09 pm

Re: Advice on relays/mosfets/optotriacs etc

Fri Jun 18, 2021 6:29 am

LTolledo wrote:
Thu Jun 17, 2021 9:21 pm
for the pump, use automotive relays with contacts rated 20A, like the HELLA 933766111 MICRO Relay 12V 20A SPST RES
for the solenoid valve, use industrial relays, like Omron MY2N DC12
And would you use mosfets to drive the relays? Obviously i can't drive them direct from the PI.

LTolledo
Posts: 5563
Joined: Sat Mar 17, 2018 7:29 am
Location: Anime Heartland

Re: Advice on relays/mosfets/optotriacs etc

Fri Jun 18, 2021 10:17 am

yes, MOSFETs, or BJTs, depending on your preference and budget...
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

Some people be like:
"Help me! Am drowning! But dont you dare touch me nor come near me!"

Return to “Automation, sensing and robotics”