Newbie here with next project. I'd like to control when a circulation pump comes on when the temperature drops to a certain level. I'm estimating the pump draws about 10A while it's running. And a bit more on start up.
I'm planning on using a DHT22, Nano and an SSR (25A, 3-32vDC / 24-380vAC). I know there are issues with inductive loads. Reverse EMF, right? Does this approach seems correct? If not, any help with a list of components that can handle the operating conditions would be appreciated.
The SSRs take care of inductive load effects, within reasonable limits. The startup current for motors is high, that might be a problem. You just have to compare the SSR and motor specifications to see if they match. The Arduino logic input side needs no special precautions, but you do need to supply the right voltage and current.
Reverse EMF doesn't apply to AC circuits, as there is no "reverse". There can be inductive voltage surges, but they can't be clamped with diode in the same way because they are bipolar.
I would be cautious of some the relays on Amazon and eBay ... the plastic enclosure looks identical to this.
Here's a good reference for proper relay selection for control of an AC motor.
From the table and info, a 50A rated SSR (random turn-on type) would be recommended for your motor.
EDIT: Also consider connecting an MOV across the output and proper heatsinking.
I run a 2000W AC industrial hoover motor via one of those SSRs; controlled by an IR sensor and a ProMini. The pin on the ProMini is directly connected to the 4-32V terminal on the SSR, with a pull down resistor; and that's it.
The motor draws around 4-8 amps when running, and considerably more on start up.
The base of the SSR gets quite hot. I have mounted the SSR on a 100mmx100mmx6mm steel plate, to draw some of the heat away.
The hoover is never on for more than 30 minutes. It's been working fine for over a year now.
It might be best to go for a 40amp SSR, to give yourself plenty of leeway and not have the device running near to its limits (particularly if you buy a cheap version, that may have 'built to a price' electronic components inside it).
dlloyd:
I would be cautious of some the relays on Amazon and eBay ... the plastic enclosure looks identical to this.
Here's a good reference for proper relay selection for control of an AC motor.
From the table and info, a 50A rated SSR (random turn-on type) would be recommended for your motor.
EDIT: Also consider connecting an MOV across the output and proper heatsinking.
Thanks for the link to the plastic cased SSR. I've got a few of them just because they were cheap.
Chinese Amps are likely 40% of Metric and Imperial Amps....
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That's a good one. The top review for this 100A version on Amazon rates his at 25%, well 0% now. He should've read the seller's details:
Cooling Condition:10-30A With Radiator; 40-300A Add The Fan Strong ColdEdit: Yeah, it's DC type, but I'd like to know where to get that fan that can up its rating to 300A DC.
