Contactor coil: 50 Hz vs. 60 Hz
On Aug 29, 7:03*pm, John Fields wrote:
On Mon, 29 Aug 2011 07:28:53 -0700 (PDT), NT
wrote:
On Aug 29, 3:03*pm, John Fields wrote:
On Sun, 28 Aug 2011 23:21:56 -0700, DaveC wrote:
I may be able to obtain a very small 2-pole 240 vac contactor I need rated
for 50 Hz only.
If I install it in N. America, what's the implication? Is the hold-in
magnetism less than if it were 60 Hz? Just noisy?
Please don't ask or suggest other sources. This is a very specific device and
I've not been able to locate other than this.
Not knowing the specifics about the coil makes predicting what will
happen at 60Hz difficult.
However, assuming that the inductive reactance and resistance of the
coil will remain constant at 50 and 60Hz means that the impedance of
the coil at 60Hz will be 1.2 times (60Hz/50Hz) what it is at 50Hz.
no, only the L component of the impedance will be 1.2 times as high.
---
Well, that's true, so let's just see how far off I was, by using a
real-world example.
I have an old P&B MR5A here with a 240V 50/60Hz coil.
The coil has a resistance of 4800 ohms, and an open inductance of 14.5
henrys, so it has an impedance of 6616 ohms at 50 Hz, and 7270 ohms at
60 Hz.
7270 - 6616 = 1.1, so my error was 1 part in 11, or a little less than
10%
I can live with that.
---
Consequently, the current in the coil at 60Hz will be about 83% of
what it is at 50Hz.
If that turns out to be a problem, a higher drive voltage could be
used in order to increase the current, namely 1.2 times 240V; 288V.
That could easily be accomplished using a transformer to boost the
240V mains to 288V, like this: (View with a fixed pitch font.)
240AC-----+--+
* * * * * *| *|
* * * * * oP||S
* * * * * *R||E
* * * * * *I||Co *
* * * * * *| *|
* * * * * *| *+----- \
* * * * * *| * * * * * 288AC TO COIL
240AC-----+-------- /
The transformer would need a 240V primary, a 48V secondary, and a VA
rating greater than or equal to the contactor coil's rating.
these are the kind of 'solutions' that happen when people dont put the
relevant numbers to things.
Well, your tone is certainly insulting,
yes, my apologies.
NT
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