High speed switching using reed switches.

[alansimpson]

I am switching a 0.9 A current at 1V using reed switches and I am running into problems. Rotating wheel with 4 magnets on circumference

1)At high speeds (over 200 Hz) not switching.
2)Switch fails closed.

The switch is rated for an 1 amp.

Load is inductive so there could be surge current.

Would there be alternative available in semiconductor sensor for instance that could take speed. Must work with 1V supply and must consume minimal power.

Can't find hall switch to work at that voltage and current.

 

[IRstuff]

Is the current unipolar?

If so, you could use an open-collector germanium transistor:

http://www.nteinc.com/specs/10to99/pdf/nte27.pdf

At the spec saturation current of 15A, Vbe is only 0.6V, so there's some head room to play with.

TTFN

FAQ731-376

 

[OperaHouse]

"I talked with some reed switch manufacturers and they didn't seem too phased by speed."

Well there you go, problem solved. I don't put much stock in it. I have a low regard for most tech support people. Duty cycle makes the effective frequency much higher. If you are anywhere serious about this project, that 1V requirement will have to be dropped.

 

[roydm]

Low tech I know but if you are stuck with 1 volt why not use a commutator and brushes?
You could take a multi segment commutator from a small motor and short bars out to get the right number of contacts.
If you only need 1 contact wire from brush to brush with jumpers across commutator to close the circuit as required.

Roy

 

[Skogsgurra]

Low tech and common sense - not a bad option.

Gunnar Englund

http://www.gke.org

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

 

[DYV1973]

We have done also some experiments with both reed and Hall effect sensors. And even a 500 mA rated reed switch got stuck at 7 mA @ 24V due to surge currents. Hall effect sensors worked out fine, even at elevated temperatures. You can check allegromicro.com for some appliciation examples.
Biggest difference for using, is that Hall needs sensor supply and reed is just a contact.

 

[CharlieGill]

I would suggest an OptoMOS relay. Clare make several.

http://www.clare.com/Products/SSR.htm

The LCA715 will handle 1.8A with 0.25 ohms RDSon. Being MOS the 1V signal will not be a problem.
With a 3 ms Ton/Toff it is marginally fast enough. I'm sure a faster device could be found but I'm at the end of my lunch time.
Charlie

Charlie Gill
--

http://www.calibrator.com--

 

[zappedagain]

"You will have to explain the magnet and coils to me. How is current switched?"

When the magnet moves by the coil it will induce a voltage/current pulse. Think of it as a generator.

John D