switching ON an high inductive Load (MOT) - Page 1
Forum section: electronics / projects

author: anishkgt
author_rank: Frequent Contributor
timestamp: September 13, 2016, 10:58:14 am
content: Hi All,what would be best way to control a High inductive load such as the MOT ?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 13, 2016, 11:31:14 am
content: Turning on a highly inductive load is not that critical. Due to the inductance the current only slowly goes up. With larger ring type transformers one has to be careful to avoid saturation, which is rather likely when turning on at zero voltage. But with a motor saturation should not be such a big problem.A motor often takes initially a high current as the motor is still standing and it takes some time to spin up. So initial current can be high.The difficult with an inductive load is turning the current of. Here the voltage can rise and cause quite some sparks in mechanical switches.

author: anishkgt
author_rank: Frequent Contributor
timestamp: September 13, 2016, 11:48:03 am
content: Well i was planning on to use the arduino here to switch on the transformer via a triac or a thyristor? The arduino would detect the zero cross via H11AA1 opto from the secondary of another transforer.Just need to know what would be best way to control the MOT ?

author: danadak
author_rank: Super Contributor
timestamp: September 13, 2016, 11:53:53 am
content: There are a number of integrated motor drivers that sense over voltage,current, power, thermals, and protect from the potential damaging trans-ients and currents involved with motor driving.TI, ON, Fairchild, Vishay, IR.....SAll these vendors have extensive motor driving application notes, greatbackground material to make informed design choices.Regards, Dana.

author: anishkgt
author_rank: Frequent Contributor
timestamp: September 13, 2016, 11:58:24 am
content: My idea to use the transformer is to spot weld 18650 cells. Does any anyone have a link or maybe a sample circuit to drive one usung a TRIAC or two thyristors in parallel.

author: Delta
author_rank: Super Contributor
timestamp: September 13, 2016, 12:04:09 pm
content: Do NOT switch on inductive loads at zero crossing! They should be switched at the peak of the waveform.

author: anishkgt
author_rank: Frequent Contributor
timestamp: September 13, 2016, 02:12:31 pm
content: Well obviously, not at zero. At the peak actually for 100 to 450ms. A little browsing about commutation has lead me to choose theBTA26-800BWRG. These are said to have very HIGH Commutation for inductive Load.

author: TurboTom
author_rank: Super Contributor
timestamp: September 13, 2016, 07:53:29 pm
content: Switching off an inductive load with a SCR / Triac type of device isn´t an issue at all since the switch will only open when the current is (close to) zero and this means the energy stored in the inductor is also at its minimum (E=1/2*L*I²). So no danger of high inductive spikes. A snubber across the switch may still be a good idea.Cheers,Thomas

author: tautech
author_rank: Super Contributor
timestamp: September 13, 2016, 08:00:36 pm
content: Quote from: anishkgt on September 13, 2016, 11:58:24 amThere's quite a few threads on this subject, do a forum search for"battery tab welder".

author: anishkgt
author_rank: Frequent Contributor
timestamp: September 14, 2016, 05:42:44 am
content: This forum does have a lot of threads mentioning about tab welder but did not have anything about a custom build spot welder controller.