Question about mechanical relay

[Megahertz]

I have a requirement to switch an inductive load (Motor) of 30-40Amp (starting current). The enclosure I have is restricting me to use one mechanical relay of 30-40Amp rating (because of the size). I would like to ask if it would be a good idea to switch this load using 6 x 5AMP mechanical relays. I can only use mechanical relays for this and not solid state ones.
I am not sure if by this approach I will risk any one relay getting stuck and burning out.
Thanks

[kellyseye]

Absolutely not - you should not use relay contacts in parallel under any circumstances. Look at getting a small automotive 12V coil relay or even consider using MOSFET(s) for the switching component.

[HenrikOlsson]

Agreed, don't do that. Get the correct part for the job.
Regarding the automotive relays, look out for the voltage rating on the contacts if you're switching anything above "automotive" voltages (12-24V) and their current rating with respect to AC and DC - which ever you're switching. Switching (interrupting) high DC currents is a lot harder than AC-currents.

Is it AC or DC? If AC, single phase or 3-phase? What voltage is it?

[Megahertz]

Thanks. It is an 230VAC single phase motor.

[kellyseye]

Go with an opto-isolated triac then.

[martintorres]

kellyseye, an opto triac to implement as auxiliary firing a triac may be, but this would only much smaller engine ... We are talking about 30-40 amp in starting, and then drop to 10/12 amp rated. To work with a triac, uqe would not only have to be a motor with brushes, but also the inductance you'd have to build a triac to implement, would be quite large and without knowledge of electronics, you will make it impossible.
If I were you, instead of making the circuit with relay, contactor and implement a shot of this, it could be a relay or with a Optotriac

NOTE:
motor a escobillas del tipo universal = motor ac universal brush:
6671

contactor:
6672

(aclaro y menciono por el tema de la traduccion)

[m_flfl]

i was resolved it before by using mixing the triac and relay Paralleled. the triac contacting faster than relay.. so the triac come at the first facing the inductive load .after that the relay come to keep at the current connecting... without burning the small relay ..and without heating the triac..and you must turn off the relay at the first to avoid inductive load .. after that turn off the triac .Interval could be ms ... so you can use bta41 or higher driven by moc3042 or moc3082 and relay 5a ..... you can try..

[martintorres]

Flfl m Sorry, I do not want to contradict your idea, but in my opinion, aside these simple solutions to control inductive loads triac; And you pose, if not understood why my English is half bad, not see obsolete.
The implementation of an auto-inductor in series with the triac and load respectively, is the appropriate solution, but given the size of the engine and do not know what experience does the friend, we recommend you implement contactors to start or stop the engine.
This would be an example of an auto-inductor:

6691




The contactor coil can have 12 to 24-48cc / 110-220AC; For the case of implementing a contactor with AC coil, to my way of seeing things, the right thing would be to implement an opto-triac firing as auxiliary a triac, with the triac, the contactor coil excite ...
I leave as an example a development arm for the company forces (economic heating fuel) two years ago ...
Basically it is a simple fan controller, where the temperature program and then as sensing, turns on the fan to move the hot air on heating ducts.


6693

6694

6695




Notes on the triac, there is a legend that says: "100uH", there, the auto-inductance is housed with their respective toroid
There are other specific integrated circuit solutions and ideal for these applications. For example IR21362, but is discontinued in the market, and has its complexity using this IC.
Years ago I dedicated to teaching and electronic developments, and the solution of the self-inductance was as simple and practical to implement ocurriopara I always control my projects ...

[m_flfl]

my idea simply look like6698