Resistor question

[MAC3382]

Hello, All:

I would appreciate any help that you may offer.

1) I have an electromagnet application (large inductive load) and in order to ensure a positive release of the work-piece we apply a reversing pulse. (This accelerates the decay of the residual orientation of teh dipoles in the electromagnet's yoke and the work-piece). In our new deisgn we are using a momentary switch (spring loaded) to develop the opposit polarity pulse. The pulse is applied at about 1/4 the normal "on" voltage. Up till now the voltage it has been reduced by a ceramic power resistor.

Does anyone see why a wire wound resitor would not work?
(Fears- Reverse EMF and the wire wound resistor / wire wound resistor acting as an inductor / ?
(I would like to not have to put a reversing diode)

2) Same application, but this is an indicator question. Can I use a 120VAC Neon indicator on rectified AC as though it was on regular AC? (The DC is has only been rectified by a Bridge Rectifier and it has all of the ripple.)

I really appreciate your help.

All the best ,

Mac

 

[roydm]

1/ I don't see why not, you could also use a small transformer to lower the voltage or a choke to reduce the current.
2/ Yes, a neon indicator will operate on DC but you will see that it only glows at one element,
Regards
Roy

 

[Skogsgurra]

Ceramic resistors are high frequency/microwave devices. There, the inductance of a wound resistor is an important problem parameter.

In an application like yours, reducing inductive kick-back in DC coils, you can use any resistor you find suitable. Wirewound is very common parallel to excitation windings of all kinds.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MAC3382]

Thank you Roy & Gunnar!

This new device is for our mannual power supply and it is very cost sensative. Our PLC driven power supplies do use a step down transformer and a timed pulse for the the reversing. These auotmatic power supplies are performance based and allow for a higher number and higher end components.

Can you make a sugegstion for an indicator which will be wired in parallel to the electromagnet and will operate on the rectified AC. I would like to use as few compoenents as necessary and I have to give an indication that the magnet has power applied. This is in liue of puting an inidcatior on the AC side.

Thanks again!

Mac

 

[roydm]

As I said, the neon will work but may not be quite as bright because only one half will glow, mind you if it's full wave it will glow for twice the time.
Roy

 

[OperaHouse]

A bi color LED would be nice. This would indicate the polarity of the voltage for diagnostic purposes. An additional diode and resistor in the voltage drop circuit will compensate for lower voltage of one polarity.