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Topic: controlling a 3 phase induction motor - Relay Suggitions (Read 8925 times) previous topic - next topic

anilkunchalaece

Hi,
 I wanted to control a 25 hp Induction Motor using arduino..
 How can I do it?
 Is it using a Solid State relays?
can anyone suggest me relays to control 3 phase induction motors...
--
Check Arduino  Tutorials here
https://www.youtube.com/playlist?list=PLjzAdjfnefPzBOijmWo9t6-S2x2jye2fs

Kunchala Anil

knut_ny


110v / 220v ??

25hp eq. 18kW
Start current (Y-connected) 18k/110/3 *5 = 250A 
It may be difficult to find that high current SSR..  (up to 100A U'll find several 3-phase SSR)

..so: mechanical contactors. control coils with small SSRs/relays
Ny

anilkunchalaece

--
Check Arduino  Tutorials here
https://www.youtube.com/playlist?list=PLjzAdjfnefPzBOijmWo9t6-S2x2jye2fs

Kunchala Anil

knut_ny

#3
Nov 19, 2014, 02:33 pm Last Edit: Nov 19, 2014, 02:43 pm by knut_ny Reason: add pic
Then 100A will do.
Three pcs of http://www.ebay.com/itm/Electromatic-Three-Phase-AC-Solid-State-Relay-Instant-480V-100A-GJX-3-FHRG-/111419145546?pt=LH_DefaultDomain_0&hash=item19f1193d4a
could do the job.

google: "using SSR to control motors" for more info, as this has to be done correctly!

* Some kind of thermoprotection is needed
* Both SSR should never be on at same time! (use e.g. small relays for interlocking??)
 (not enough with software control)
* At least 30ms delay from Y-connect OFF to D-connect ON
* Detect stall (read RPM)  RPM can also be used when starting to select correct time for Y->D switching.
Ny

knut_ny

Ny

avr_fred

You cannot do this with a solid state relay.

Assuming a best case of having a 480 volt supply and motor, a 25 hp motor will draw about 30 amps at full load (assuming a std nema 4 pole machine). That same motor will draw about 7 times that amount at start which will absolutely kill a 100 amp solid state contactor before the motor ever reaches speed.

Seriously, you do not want to attempt this with solid state contractors, you need a mechanical contactor with a motor thermal protection relay. A three phase contactor with an overload device mounted on it are called motor starters and that's what you really need here - a motor starter for 25 hp.

You can then control the motor starter with the Arduino if you need to. What is this motor controlling that you think you need a Arduino to do this?



avr_fred

110v / 220v ??

25hp eq. 18kW
Start current (Y-connected) 18k/110/3 *5 = 250A 
It may be difficult to find that high current SSR..  (up to 100A U'll find several 3-phase SSR)

..so: mechanical contactors. control coils with small SSRs/relays
knut_ny: not sure what you thought you were calculating there... To get the single phase current from a three phase total, you'd divide by the square root of three, 1.732, not 3. Further, locked rotor current is never as low as 5. It has always been about 7 x full load and today's higher efficiency, low slip motors can approach a 10:1 full load to locked rotor ratio.

dave-in-nj

You cannot do this with a solid state relay.

Assuming a best case of having a 480 volt supply and motor, a 25 hp motor will draw about 30 amps at full load (assuming a std nema 4 pole machine). That same motor will draw about 7 times that amount at start which will absolutely kill a 100 amp solid state contactor before the motor ever reaches speed.

I'm  thinking about 5 times, called locked rotor, but you are spot on, a HUGE spike in real power for enough time to destroy an SSR that is full on.
however, a soft start device would regulate voltage and power to get the motor to start moving.
you can run a 100hp motor on a 10 hp VSD up to the amp load of the VSD.  

the part to create is the volts to hertz ratio and keep this as the goal.

when you think about it, we do not use time as a function, but a motor that gets 60 hz does not care if those 60 pulses come in 1 of our seconds or 100 of our seconds, it only knows that for 60, it rotates so much.  if you feed it those 60 pulses in 10 seconds, it runs 1/10th the speed.  

also, soft start is for centrifugal loads, not conveyors or compressors or such.  

my answer to the poster is to get a VSD and that can take the 5v to control not only on/off but also speed.


dave-in-nj


avr_fred

the data sheet on the link says that a GH15FT  can control a max 20hp motor at 460v/3ph
Oops, forgot motor cosine/pf/whatever you want to call it when trying show why you cannot use solid state contractors on 25 hp motors. Jeesh. Wanna check my spelling too?

Notice I said 30 amps and not 25 horsepower?

TomGeorge

Hi, I agree with Fred and Knut, get a proper starting contactor set, not sure if  your motor is 3wire/4wire or 6 wire.
You usually start motors like that in star/delta as the Knut diagram shows.
There are solid state soft starters but they all have a contactor bypass to switch in when the motor up to speed.
(I helped configure a 110kW soft starter, at that power level quite a unique SCR chopping noise.)

Tom.... :)
Everything runs on smoke, let the smoke out, it stops running....

anilkunchalaece

.

You can then control the motor starter with the Arduino if you need to. What is this motor controlling that you think you need a Arduino to do this?


I just need to pump a water / solution from 5kl tanks...
so On and Off the motor is all i wanted to do.

it is having a star/delta starter with automatic timer to switch between those.

motor starter control circuit uses different power than the motor power circuit which is taken from single line of three phase supply.

i noticed some voltage/current ratings states 230v/6A.
how can i start or stop the motor using arduino?
--
Check Arduino  Tutorials here
https://www.youtube.com/playlist?list=PLjzAdjfnefPzBOijmWo9t6-S2x2jye2fs

Kunchala Anil

MarkT

You have a motor starter?  Perhaps you could say which one or provide
model-number or link to a datasheet for it.  Given full information
is essential to getting useful advice.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

anilkunchalaece

iam afraid i can't have the more information right now...
 please see the link.
http://mahendraelectric.com/wp-content/uploads/2013/08/BCH.pdf

under Star Delta Starter
25 HP NASAMLEN

and Under Three Phase - DOL Starter
5HP NAJLEN
--
Check Arduino  Tutorials here
https://www.youtube.com/playlist?list=PLjzAdjfnefPzBOijmWo9t6-S2x2jye2fs

Kunchala Anil

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