Help with powering AC motor using SSRs

Discussion in 'The Projects Forum' started by saiello`, Jul 31, 2015.

  1. saiello`

    Thread Starter New Member

    Jul 31, 2015
    1
    0
    Hello,

    I would like to use SSRs to control ( forward/reverse ) an AC motor in a new machine I am building for work. Motor specs:

    TEC 0.18kW (0.25HP) Single Phase 240V Capacitor Run 4 Pole.
    Full Load Current - 1.5A.
    Starting Current is 4A.
    https://www.inverterdrive.com/group...EC-Single-Phase-Motor-180W-1400RPM-LST-63F-B3
    https://www.inverterdrive.com/file/Motor-Connections-TEC-TPC

    I have used the same motor in a previous project which was controlled manually using standard electrical mini-contactor blocks but this caused large voltage spikes and was causing emf havoc with the micro-controller I was using to control the rest of the machine. I installed standard plug-in emf suppressor modules on the contactors and spent a lot of time trying to shield against emf but all this only partly cured the problem.

    In the new machine I would like to use SSRs to eliminate emf problems and also to allow me to control the AC motor via the micro-controller. As far as I understand SSRs are generally not recommended for AC motor control, standard contactors being the preferred option ( comments? ). Having said that I found an SSR solution ( http://www.jelsystem.co.jp/en/product/ssr/ssr_oyo.html, application circuit N.o 4 ) that apparently works. Unfortunately the diagram is not self explanatory and I don't know enough about electrics to be able to:

    1) Fully determine suitable SSR specs for the motor I am using
    2) How to relate the motor connections in the SSR schematic to that of the motor I am using
    3) What components the two black 'bow-tie' symbols are referring to and why they are there... ;)

    The above would be the best solution in terms of EMF elimination and control and also keep component count to a minimum, otherwise there are two other less preferred ( but for me more understandable ) options:

    1) Use a couple of standard contactors and have them operated using SSRs to power the contactor coils ( with contactor emf suppressors installed ). I will still get some EMF but able to use M/C for control.
    2) Use two separate banks of SSRs wired raw into the motor so that each bank would independently power the motor in forward and reverse mode (effectively swapping out the original contactors and replacing with SSRs ).

    These are the SSRs I am thinking of using for 1) and 2) above:
    http://www.rapidonline.com/Electron...lid-State-Relay-Din-Module-5A-3-15VDC-50-9509

    Suitable? Issues..?

    Long post I know, but I wanted to get as much relevant info in as I could... ;)

    Anyone able to help/point me in the right direction..?

    Thanks! :)
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
    2,375
    The jelsystem.co link is only suitable circuit for a 1ph motor that swaps the two winding's for each direction, IOW the winding's have to be equal and not suitable for a dedicated start winding ver etc.
    The two bowtie symbols are VDR's or similar suppressors.
    I would use the opto's to pick up a suitable contactor with coil suppression, Rectifier for DC coil, R/C snubber for AC.
    Max.
     
  3. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,039
    1,667
    I dont see any problem with using a SSR based control system for your motor being I have seen it done in countless applications and have used it myself many times.

    If it was me I would go with SSR's rated for considerably more amp capacity than the motor draws on start up which in this case if its ~4 amps staring I would use 10 - 15 amp rated SSR's.

    As for voltage rating higher is better so I would be looking at using something about 50% over your line voltage and have good quality surge suppression MOV's or similar components in place across the SSR's and the motor windings.

    Given the motor wiring diagram I believe you would need 5 SSR's to make everything work correctly. One for the main start and stop and 4 to make the connections for the forward and backwards control.
     
  4. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    Wouldn't those same 4 used for directional control also control on/off? Two on for forward, different two on for reverse, none on for off, like in DC H bridges. I don't see the need for a fifth, unless it's just an added layer of protection against ssr malfunction.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
    2,375
    A simple 3phase reversing contactor with preferably a N.C. aux interlock contact on each to lock out the opposite coil is all that is needed, a pair of small SSR's could be used for the coils if necessary, the 3ph contactors have a mechanical interlock also.
    This is the customary way to do it with a PLC etc.
    Max.
     
    Last edited: Jul 31, 2015
  6. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,039
    1,667
    Well don't you have to turn the main run winding on and off too? o_O
     
  7. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    Hmmm, just took another look at the motor hookup diagram and it's not clicking for me. I'm sure my idea was wrong, but now I don't even see how to do it with 5. Must be missing something. This isn't my strong suit, so I'll just back away slowly now...
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
    2,375
    CNC machines and PLC's are 5v logic based control and operate in an environment with the likes of multiple relays/contactors with no adverse affects.
    These systems include proper grounding and bonding and suppression on inductive devices.
    Max.
     
  9. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,039
    1,667
    Four of them do the job of the jumpers to set the starting direction and the fifth one is the main power switch that turns the whole motor on and off. Does that make sense now?
     
  10. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    Ok, now I see it. Thanks!
     
Loading...