Large transformers have a huge current demand when they are initially turned on. This is because, until the magnetic field and inductive resistance builds, they are essentially short circuits. For example, you may have turned on some large tool or appliance and heard an initial large "HUMMMMMMM". That is the transformer say "Ow". The circuit breaker for that outlet might also go "Whoa, what are you doing!"
The transformer above (Avel Y236907 800VA 45V+45V Toroidal Transformer), for example, will try to draw over 100 Amps on the first cycle of 60 Hz Power.
To keep a large transformer from being damaged at turn-on (and to keep it from saying "ow"), or to keep a breaker from popping, you put in an inrush current limiter circuit. This Instructable will detail how to do that.
The transformer above (Avel Y236907 800VA 45V+45V Toroidal Transformer), for example, will try to draw over 100 Amps on the first cycle of 60 Hz Power.
To keep a large transformer from being damaged at turn-on (and to keep it from saying "ow"), or to keep a breaker from popping, you put in an inrush current limiter circuit. This Instructable will detail how to do that.
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The thing we are after is a way to limit the current initially at turn on, and then to not limit current afterwards at all.
The circuit I use contains a thermistor, a relay, and some resistors, a capacitor and a couple transistors.
The circuit I use contains a thermistor, a relay, and some resistors, a capacitor and a couple transistors.
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could it not be that you just wait till the zero crossing of the AC line, then switch it full on, considering that because it's an AC wave, it will ramp up the voltage in a sine wave pattern from 0? Or does the ramp have to be relatively slow?
-Thanks. Most transformers i work with are air core resonant.
Now I'm wondering if one couldn't build a circuit of cascading chokes to start a big coil. Kind of like fighting fire with fire? Or would that just aggravate the problem? Inductance is one of my weaker points of understanding. I just never seem to get the stuff.
Most of the books I have read said to give the transformer limited inrush current for 1-2 seconds. I may have gone overboard with 2-5.
I googled "motor inrush current" and got many sites that seemed to have thoughts on it though.
I ask that because some time ago I bought a generator, and the vendor said that for using it to feed the fridge and/or the freezer, I need 7 times more power than the nominal intake of the motors, due to initial pulse. I think the case is like that you show, of tranformers.
Really, it is amazing electric motors run at all. Motors and transformers have coils in common, but after that the similarities end.
In order to reduce starting current with electric motors I think they have to be designed differently before they're built. I've heard of large industrial motors with special coil arrangements to bring them up to speed and limit the current they need in order to start.
To sum up, your vendor was right, and I do not know about anything you can do to reduce the current draw of an electric motor from what it is. Well, maybe if you hooked up a pull starter off a lawnmower ... it is the initial pulse that is the problem, once motors get moving they go within their rating.
I asked advice from a manufacturer of generators, and they said that maybe I could use a small generator if I change my refrigerator and my freezer for a new ones, because currently there are not made with the motor fixed to the compressor but through a centrifugal or electric clutch to prevent the inrush pulse is so high. Clever, isn't?
You´re using a thermistor or NTC.
thyristors usually have three terminals.
The "resistance varying with temperature" fits a thermistor better.