So im working on a project that controlles 2 water pumps ( 1.1 hp and 1.5 hp ). I am going to control them with an arduino nano, based on 6 float switches.
The problem im facing is while choosing the relay. The motors are lets say 8 amp( actually a bit less, but rounded up for simplicities sake) each.
I first up thought about buying solid state relays, but some forum posts online states that they are prone to failure in this specific case.
What amp rating does the relay need to be? 30amp? 63 amp? xx amp? 63 amp costs a lot more than the 30 amp one obviously. I would like not to go too overboard with the costs.
Is there anything special/exceptional that needs to be noted about? I do know about the lra, and how a motor needs much higher starting current. Is there anything im mising?
So im working on a project that controlles 2 water pumps ( 1.1 hp and 1.5 hp ). I am going to control them with an arduino nano, based on 6 float switches.
The problem im facing is while choosing the relay. The motors are lets say 8 amp( actually a bit less, but rounded up for simplicities sake) each.
I first up thought about buying solid state relays, but some forum posts online states that they are prone to failure in this specific case.
What amp rating does the relay need to be? 30amp? 63 amp? xx amp? 63 amp costs a lot more than the 30 amp one obviously. I would like not to go too overboard with the costs.
Is there anything special/exceptional that needs to be noted about? I do know about the lra, and how a motor needs much higher starting current. Is there anything im mising?
The relays need to be rated for your motors. You gave the HP, but such ratings are given for commercial control relays and your question seems be indicate you are looking at hobby grade relays. If the project is fairly critical, go with the commercial relays, either SSR or regular motor control relays.
Again, if this project is for an important operation, you need to consider the power source to power all this also needs to be rugged, commercial units.
Motor Starting Currents
When an AC motor is energized, a high inrush current occurs. Typically, during
the initial half cycle, the inrush current is often higher than 20 times the normal full load current. After the first half-cycle the motor begins to rotate and the
starting current subsides to 4 to 8 times the normal current for several seconds. As a motor reaches running speed, the current subsides to its normal
running level.
I first up thought about buying solid state relays, but some forum posts online states that they are prone to failure in this specific case.
Regular electro-mechanical relays tend to be more "electrically rugged". You can (usually) over-voltage or over-current them briefly/occasionally without damage, although that will probably shorten their life.
A 10A solid state relay (probably) won't fry immediately at 10.1A but solid state electronics can die quickly when electrically (and thermally) stressed.
When used within it's limits a solid state relay can virtually "last forever".
Electro-mechanical relays eventually wear out, but normally they last for years-and-years.
I'd guess that you can get-way with a relay rated for 5 times the motor running current. The resistance in the electrical wiring will probably limit the current so you probably won't get 20-times the running current, and even if you do it's for a very-short time and even a solid-state relay can probably handle it.
You can't directly drive a relay coil from the Arduino. You need a driver circuit or you can get a relay board with a relay and driver built in.
There are solid state relays that can be directly driven by the Arduino, and the inductrial type are super-easy to wire-up and mount.
Paul_KD7HB:
The relays need to be rated for your motors. You gave the HP, but such ratings are given for commercial control relays and your question seems be indicate you are looking at hobby grade relays. If the project is fairly critical, go with the commercial relays, either SSR or regular motor control relays.
Again, if this project is for an important operation, you need to consider the power source to power all this also needs to be rugged, commercial units.
Paul
Im having a hard time finding 2hp rated relays locally and online, specefically mechanical relays.
DVDdoug:
When used within it's limits a solid state relay can virtually "last forever".
Paul_KD7HB:
Not pricey at all if you consider a 50 year service.
Paul
I do want reliability, but I dont feel so comfortable when this comes to contactors, plus most of them that i found are 3 phase, my motors are single phase.
do contactors work the same way as relays? i mean while setting them up with arduinos.
I didnt think of this before, but the Circuit board has to withstand a lot of current. Im not at all comfortable with such high current circuits, but using th ssr's, i would straight up screw my motor wire through them.
Can someone please check this and this and help me know if any one of these would fit my purpose or not?
If I am to use them, would they need heat sinks? given the motors have below 8A Full Load Rating
Solid State Relays (SSR) are rated for a maximum current for a range of voltages, so you need to calculate the current required for the application.
First determine how much current the motors will require, do this using the relationship between voltage, current and power. The equation for electrical power is given by
P = I V
where damaged is the the power in Watts, I is the current in Amps and V is the voltage in Volts. Solving the above for current you get
I = P / V.
You gave the power in horsepower so you need to convert hp to Watts, 1 hp = 747 Watts, many just use 750 Watts. So you have one motor at 1 hp or 750 Watts, the other is 1.5 * 750 Watts, = 1125 Watts. Use this in the equation for current, using the voltage of the system, which I don't know. You can use your voltage to determine the current.
When you calculate the current I think you will find it is much less than 60 Amps, the SSR you linked to has a rating of 60 A, so yes that will work for the application but will probably overkill.
Yes heatsinks are required for SSR the most common failure mode is thermal breakdown due to inadequate heatsink and/or inadequate airflow.
You asked the question: "do contactors work the same way as relays? i mean while setting them up with arduinos.". And the answer is they are relays, but are usually much more. They may have thermal switches to open the primary coil circuit when the current they are switching is more than the contactor is designed for. They may also have smaller secondary contacts for an indicator light. And they may also have a push button switch to manually open the relay coil circuit.
The contact points are usually silver and may be replaceable if they are prone to erode away over time due to arcing when the circuit is opened.
I have a Nano running one of my water wells and recording/transmitting data. The data is: tank depth, water pressure in pressure tank, and accumulated flow. The control is water tank depth turns on and off downhole well pump(2HP), and the water tank pressure is controlled by a booster pump(1HP).
The Nano outputs are all connected to relay drivers such as a TI ULN200X with surge protection. Control of the pumps is done by solid state relays (SSR's). I use Crydom SSR's, and in fact swear by them. Ratings: start up current for my 2 HP pump is 27 Amps and for the 1HP it's 16 Amps. The Name Plate running currents for the motors are 13 Amps and 7 Amps respectively. I always use double the running current as inrush current for sizing purposes. HP ratings are for power available before motor stall, not the start/run current requirements.
Instead of SSR's you can also use contactors for higher currents and single phase, SPST ones are available through Amazon for about $10 USD each.
Some of my SSR's have been operational for 20 years and probably switch several hundred times a day. I hope this helps.
AJLindfors:
I have a Nano running one of my water wells and recording/transmitting data. The data is: tank depth, water pressure in pressure tank, and accumulated flow. The control is water tank depth turns on and off downhole well pump(2HP), and the water tank pressure is controlled by a booster pump(1HP).
The Nano outputs are all connected to relay drivers such as a TI ULN200X with surge protection. Control of the pumps is done by solid state relays (SSR's). I use Crydom SSR's, and in fact swear by them. Ratings: start up current for my 2 HP pump is 27 Amps and for the 1HP it's 16 Amps. The Name Plate running currents for the motors are 13 Amps and 7 Amps respectively. I always use double the running current as inrush current for sizing purposes. HP ratings are for power available before motor stall, not the start/run current requirements.
Instead of SSR's you can also use contactors for higher currents and single phase, SPST ones are available through Amazon for about $10 USD each.
Some of my SSR's have been operational for 20 years and probably switch several hundred times a day. I hope this helps.
AJLindfors:
I have a Nano running one of my water wells and recording/transmitting data. The data is: tank depth, water pressure in pressure tank, and accumulated flow. The control is water tank depth turns on and off downhole well pump(2HP), and the water tank pressure is controlled by a booster pump(1HP).
The Nano outputs are all connected to relay drivers such as a TI ULN200X with surge protection. Control of the pumps is done by solid state relays (SSR's). I use Crydom SSR's, and in fact swear by them. Ratings: start up current for my 2 HP pump is 27 Amps and for the 1HP it's 16 Amps. The Name Plate running currents for the motors are 13 Amps and 7 Amps respectively. I always use double the running current as inrush current for sizing purposes. HP ratings are for power available before motor stall, not the start/run current requirements.
Instead of SSR's you can also use contactors for higher currents and single phase, SPST ones are available through Amazon for about $10 USD each.
Some of my SSR's have been operational for 20 years and probably switch several hundred times a day. I hope this helps.
THANKS!! I saw a forum post else where that motors might have even 1200%++ FLA, that got me worried. Now i think those were for other motors, not water pumps.. The motors I have are single phase, capacitor start and the voltage here is 220V
And one last thing, What is the difference between a sealed ssr and a non sealed ssr. I am extremely confused on which one i should buy cause they are of the same price.
Please help me out a bit more,again.
kaseftamjid:
Can someone please check this and this
I also recently found a contactor... But it seems both the input and outputs are marked live and neutral.
Is this a better choice?
Can i run the input coil with dc voltage? Like 12v?
Does it need additional protection circuit?
Anything else i need to know about? I dont have any experience with contactors, this is actually my first time hearing about them...
And one last thing, What is the difference between a sealed ssr and a non sealed ssr. I am extremely confused on which one i should buy cause they are of the same price.
Please help me out a bit more,again.
kaseftamjid:
Can someone please check this and this
I also recently found a contactor... But it seems both the input and outputs are marked live and neutral.
Is this a better choice? While keeping in mind the complexity of the circuit?
Can i run the input coil with dc voltage? Like 12v?
Does it need additional protection circuit?
Anything else i need to know about? I dont have any experience with contactors, this is actually my first time hearing about them...
I saw online that ssr's require rc snubber network for optimal working while using with high inductive load such as motors. But i cant find any clear indications to calculate the resistor and capacitor values.
Moreover, i found that "Fotek" doesnt have any 60A ssr. So the one i was looking at is most likely a relabeled 40A ssr. And worse than that, the brm(?) one has no information on it online.
Just when i thought i had everything figured out, i find myself more confused than ever