Star delta starting for AC motor with PICAXE
- Thread starter paste
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The PICAXE runs at 5V so a very high power, high voltage driver is required. What is the voltage of your (presumably 3-phase) motor?What I get in the output voltage of the microprocessor?
Paste, you'll need almost the same components as if done with the classic contactors. Ie for the classic way: 2 x contactors and one timer. Picaxe way: 2x contactors and replace timer with picaxe. You still have to do the interlocking.
The second option implies some more relays [or other methods of switching contactors coils], a good power supply for Picaxe [because of harmonics induced by motor] and extra safety measures. I'd go for the first option, there are ready made boxes, just hook your motor and set the timer.
The second option implies some more relays [or other methods of switching contactors coils], a good power supply for Picaxe [because of harmonics induced by motor] and extra safety measures. I'd go for the first option, there are ready made boxes, just hook your motor and set the timer.
The star/delta starter is one method used to reduce starting current on large motors, and uses 3 contactors (main, star, and delta), and a timer, with some auxiliary contacts on the contactors to prevent the wrong sequence of contactors energising.
A rough guide to the sequence would be:
star energises fractionally before the main
timer times out (set to when motor is at least 60% speed)
star drops out then main energises fractionally after.
Realistically, the only thing that the picaxe is going to replace is the timer...I wouldn't have thought it was worth the trouble for a real life application...but I have been wrong before
A rough guide to the sequence would be:
star energises fractionally before the main
timer times out (set to when motor is at least 60% speed)
star drops out then main energises fractionally after.
Realistically, the only thing that the picaxe is going to replace is the timer...I wouldn't have thought it was worth the trouble for a real life application...but I have been wrong before
I would just be using 3 contactors and a timer, one for the main supply, 1 for delta and 1 for the star contact, the star contact just shorts the windings so does not need to be FLC rated, the only need for a Picaxe is for the timing and possibly operating the contactors, but a timer is really all that is needed as you use the contacts of the timer, one thing that is essential is that the Delta contactor and Star contactor are interlocked so that they cannot both be on at the same time, there are mechanical interlocks available with contactors and you must also electrically interlock them too.
I don't know what 18hp is and I'm not going to google it either, but for anybody to do this sort of wiring, you really need to have a license to do this type of work, fortunately I do....
I don't know what 18hp is and I'm not going to google it either, but for anybody to do this sort of wiring, you really need to have a license to do this type of work, fortunately I do....
westaust55
Moderator
There are contactors out there (eg Sprecher & Schuh CA6 range) where the coil can be controled by a relatively low voltage like 24Vdc and the rest of the circuit is a classis start delta starter with maybe 110Vac control including the supply to the contactor electronic coil. The 24V is just an enable gate in effect.
That you are having to ask however does raise the question of your experience in working with these voltages such as 110Vac to 415Vac that the motor will use.
As already mentioned, in virtually all countires you need a license to do electrical work at these voltage levels.
That you are having to ask however does raise the question of your experience in working with these voltages such as 110Vac to 415Vac that the motor will use.
As already mentioned, in virtually all countires you need a license to do electrical work at these voltage levels.
^ Yes, the S&S range of contactors are very good, very reliable and I would be using the 24vdc coils.
I spent many years in mining here in Qld, and was also the Person in Control of Electrical Work, you will find that 24vdc control is the norm now, where I work now (not in Mining, Qld Health!), we get new equipment with 240v control wiring!!!! I hate it and will be more proactive in the purchasing of equipment to elimate those types of control voltages.....
13.5kw, I would be using a main contactor of around 25Amps
I spent many years in mining here in Qld, and was also the Person in Control of Electrical Work, you will find that 24vdc control is the norm now, where I work now (not in Mining, Qld Health!), we get new equipment with 240v control wiring!!!! I hate it and will be more proactive in the purchasing of equipment to elimate those types of control voltages.....
13.5kw, I would be using a main contactor of around 25Amps