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Author Topic: need help with circuit schematic  (Read 1189 times)

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Offline jerryfreak

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need help with circuit schematic
« on: June 22, 2009, 11:59:24 PM »
this isnt an audio project - but i dont know where else to turn.

I'm trying to install a 3-wire start-stop circuit to a variable frequency drive.

Its described as a simple latching circuit, and is the first diagram shown here:

http://support.automationdirect.com/docs/hitachi_threewire.pdf

correct me if im wrong, but the circuit shown describes the following:

1. the circle with 'run' in it is a 24V coil that activates the normally open terminals (that look like a capacitor) and are labeled 'run'

2. diode should probably be a simple 1W basic diode for this basic control circuit? they spec belden 18GA for control wiring

3. manually closing the circuit between 'P24' and 'IN1' causes CM1 to energize the coil, latching the run relay until the stop button breaks it.

thanks so much!


Offline ghellquist

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Re: need help with circuit schematic
« Reply #1 on: June 23, 2009, 10:34:43 AM »
I read the diagram the same way as you do.
Small note, the diod is a standard solution when running relays. It is there to eat up the energy stored in the relay coil when power is removed. This would otherwise create a voltage spike which the electronics do not like.

Gunnar

Offline jerryfreak

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Re: need help with circuit schematic
« Reply #2 on: June 23, 2009, 12:48:11 PM »
thanks gunnar.

i actually tried this last night with a relay i had laying around, but somehow the coil was getting backfed 5V and energizing when it wasnt supposed to. i think the diode would stop this

I read the diagram the same way as you do.
Small note, the diod is a standard solution when running relays. It is there to eat up the energy stored in the relay coil when power is removed. This would otherwise create a voltage spike which the electronics do not like.

Gunnar

Offline JD

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Re: need help with circuit schematic
« Reply #3 on: June 23, 2009, 01:27:51 PM »
thanks gunnar.

i actually tried this last night with a relay i had laying around, but somehow the coil was getting backfed 5V and energizing when it wasnt supposed to. i think the diode would stop this

I read the diagram the same way as you do.
Small note, the diod is a standard solution when running relays. It is there to eat up the energy stored in the relay coil when power is removed. This would otherwise create a voltage spike which the electronics do not like.

Gunnar

The diode shown is parallel with the coil, they would both see the same voltage, thus the diode does not affect the voltage seen at the coil. If it were in series with with the coil it could prevent a stray voltage from backfeeded to the coil.

Gunnar is correct the diode shown is used to suppress a voltage spike when the coil de-energizes. AC coils will use a capacitor to do the same thing.

If wired correctly, the only way you could have 5VDC at the coil would be if there is voltage present from IN1 to CM1 and I would not think there should be. Try disconnecting your circuit and measuring voltage across those two terminals with the inverter powered up.
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