Pump activation with a relay - Page 1
Forum section: electronics / beginners

author: lololo
author_rank: Contributor
timestamp: January 06, 2020, 12:30:05 pm
content: Hello,I would like to know if with these components it is possible to use a relay to activate my pump.I have a rectifier:https://fr.aliexpress.com/item/33016492467.html?spm=a2g0s.9042311.0.0.27426c37DeMcRwand a regulator:https://www.banggood.com/12V-24V-Pulse-Width-PWM-DC-Motor-Speed-Switch-Controller-Regulator-p-916751.html?utm_design=41&utm_source=emarsys&utm_medium=Neworder171109&utm_campaign=trigger-emarsys&utm_content= winna & sc_src email_2675773 = & = sc_eh 444435fd401f66271 & sc_llid = 16283456 & sc_lid = 105229698 = & sc_uid AR1tse7c97 & cur_warehouse CN =and I would like to be able to connect this relay to activate the pump or not :https://www.ebay.ch/itm/113689047965?ViewItem=&item=113689047965I really don't know how to do it and I don't know if it's possible. (should we add a component?)Can you help methank you in advance

author: andy3055
author_rank: Super Contributor
timestamp: January 06, 2020, 10:08:14 pm
content: I could not get to the Ali Express page as it takes me to a login page.You must first consider the motor specifications in your pump to decide on the rest of the parts you need. What you are listing as a regulator is a speed controller. I would not use a speed controller on a pump motor. All you need is a method to switch the motor ON or OFF. The Relay can be used to control this function from a distance by taking the relay supply away from the pump location if necessary. Relay rating depends on the motor specs.

author: lololo
author_rank: Contributor
timestamp: January 07, 2020, 09:26:11 am
content: Hello,Thank you very much for taking the time to answer me.I thought we needed a regulator to control the pump!So I have :- a toroidal power supply VTX-146-160-212 160VA 0-12V Vigortronix.- the Rectifier Input 5V-35V to 5V-45V Regulated Rectifier 3A Peak 5A- a 24v / 42w pumpso I can just put a DC relay after the rectifier?Thank you again for your help

author: andy3055
author_rank: Super Contributor
timestamp: January 07, 2020, 05:48:44 pm
content: It will be helpful if you can first list the pump motor specifications. Then you have to tell us what your scenario/application is. What type of pump is this? Are you trying to control it from a remote location or are you able to do that from just near the pump location? I would not use a relay if it is not some small device. I would use a contactor that can handle heavy starting current of a pump motor.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 07, 2020, 09:08:50 pm
content: So you have 24V 42W motor.DC motors have however a pretty big power spike during startup, especially with a "stiff" power supply (Such as with big elco's).Your motor can easily draw a 10A spike during startup, and that is exactly when the relay is switching. (Contact bounce etc).The 2A relay as shown are mostly used for pretty small signals, and not fit for an application as this.Get a relay that is rated for at least 10A. (They are also cheap) For example the Relay boards from Aliexpress with the blue "songle" relays. (These are not fit for mains voltage, but ok for anything after an transformer).Alternatively you can also use a MOSfet as a switch.

author: andy3055
author_rank: Super Contributor
timestamp: January 07, 2020, 09:48:36 pm
content: OOOPs! I missed the Motor specs in OP's post above. Sorry about that.I think it is a DC motor from your idea of using a DC power supply. Any idea what the starting current of that motor is? On an AC motor the rule of thumb is starting current = 3 x FLC. I believe it is much higher for a DC motor. In the case of an AC motor, just to be on the safe side, I would use a contactor with contact ratings of at least twice the starting current or 6 x FLC. Contacts tend to be subject to much higher arcing on a DC circuit, if I am not mistaken.

author: george.b
author_rank: Frequent Contributor
timestamp: January 08, 2020, 12:00:06 am
content: A DC solid state relay would be best in this application, IMO. Even one of those cheapies from China will probably do. Or then do like Doctorandus_P said and roll your own with a MOSFET.Otherwise, get a conventional relay that is rated for DC. The AC current rating simply doesn't apply.Quote from: andy3055 on January 07, 2020, 09:48:36 pmThat is correct. AC naturally extinguishes the arc (voltage crosses zero periodically), so a DC arc is harder to extinguish. See:That's why it's important to get a relay with a DC current rating if you're using it for DC.Also, am I missing something, or are you trying to power a 24V pump from 12V?

author: lololo
author_rank: Contributor
timestamp: January 08, 2020, 09:42:30 am
content: Great, Thank you all for your responses.I completely understood, i will take a MofsetHave a good week !