Low cost 12V relay/30A

Discussion in 'General Electronics Chat' started by Vindhyachal Takniki, Dec 22, 2014.

  1. Vindhyachal Takniki

    Thread Starter Member

    Nov 3, 2014
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  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    I would say $2.38 for that relay is a good price, also Bosch is a quality product.
    E
     
  3. Vindhyachal Takniki

    Thread Starter Member

    Nov 3, 2014
    349
    6
    To Add End application: Will be switching main on or off depending upon some condition.
    Input driving : 12V dc
    Output control : 220V ac , 30A ac , 50Hz
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    380
    hi,
    I would check with the supplier, I do not think the relay contacts are rated at mains voltages at 30Amps.!
    It appears to be designed for automotive switching of 12Volts DC
    E
     
  5. JohnInTX

    Moderator

    Jun 26, 2012
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    1,029
    The Bosch contacts are rated for 14V (automotive application) so you can't use that. Plus, the one referenced is 'Rayex' not real Bosch.

    Take a look at TE Connectivity (formerly Potter and Brumfield) T92 and T9x. They are very reasonably priced for what they can do. There are also cheap Chinese knockoffs of the more popular ones that hardly ever melt in use.
    Schrack is another good source but it looks like they are sourced by TE now - at least in the US.
    Stay away from Hasco.

    Good luck.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Also automotive types do no necessarily have the insulation rating for 230vac use. typically this type of application uses a contactor or other power relay such as P&B PRD series to also handle the current.
    Max.
     
  7. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,043
    1,676
    I have a bucket full of the 5 pin relays with 12 and 24 volt coils. Some are labeled 30 amps at 30 VDC others are rated 30 amps 250 VAC and the parts form one are identical to the other with the matching brands.

    The only difference between them is what is printed on their caps.

    I would bet my bucket of relays that if I took a pair of 30 volt DC rated and a 250 VAC rated units and put them side by side without their caps on and took a picture no one here could tell me which was which based on their internal components. ;)
     
  8. sdowney717

    Member

    Jul 18, 2012
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    The size of the contact points, I think would be bigger with the 30 amp AC version.
    The metal composition of the points also differs between AC and DC.
    I would think using an AC relay on high power DC is more likely to weld the points than the other way around. Due to DC current never passing through 0 volts. DC current is continuous. SO DC contact points have to work with bigger make and break arcs.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    For high current versions there are also methods employed to extinguish the arc, permanent magnetic or coil wound arc blow-out.
    I have seen a plasma arc form across a AC relay contacts when high current DC switching was attempted, the arc sustains enough to retain current to the switched load. :eek:
    Max.
     
  10. sdowney717

    Member

    Jul 18, 2012
    392
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    I recall reading years ago car makers wished to go to 48vdc to save on wiring-copper costs. But the switches and relays kept failing and they could not affordably engineer the change.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Now there is no large conductor bundles, a signal bus system is used and local electronic control is used via OBD-11 etc.
    Things like blower motor and window motors are local PWM.
    Max.
     
  12. Vindhyachal Takniki

    Thread Starter Member

    Nov 3, 2014
    349
    6
    currently i am using 2 relays, didn't find single relay according to my specs
     
  13. Vindhyachal Takniki

    Thread Starter Member

    Nov 3, 2014
    349
    6
    Consider a test room in which household appliances are run (like fan , tubelight , bulb or any other household appliance)
    Have to switch between main & generator depending upon certain input criteria.
     
  14. Vindhyachal Takniki

    Thread Starter Member

    Nov 3, 2014
    349
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    @vn2nan thanks 4 response
     
  15. sdowney717

    Member

    Jul 18, 2012
    392
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    35 amp AC rated, and comes with various voltage ratings on coils.
    http://relays.struthers-dunn.com/Asset/PM_Series_Motor.pdf

    4 poles, so it is 4pole double throw. Accepts 2 different source inputs like gen or main and sends to one output. Each point is good for 35 amp, so you can gang together two and get 70 amps.

    I have one and run the coil on 15vdc off a wal wart. Better pull in of the relay especially if you get a voltage drop, the walwart keeps the volts to the coil up higher.
     
  16. sdowney717

    Member

    Jul 18, 2012
    392
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    Yes, these are nice relays.
    you might get something new or used cheaper off ebay if you want it cheaper.
    http://www.ebay.com/sch/i.html?_fro....m570.l1313.TR0.TRC0.H0&_nkw=PM-17AY&_sacat=0

    Over the years, several companies have made this style relay. I found they are all heavy duty robust construction. Some the screws are inexplicably too short, so may need to get some longer ones. They are same thread as an outlet, but you need to grind the screw ends clean of the swedged ends.
     
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