High speed switching using reed switches.
High speed switching using reed switches.
(OP)
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.
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.





RE: High speed switching using reed switches.
Switch fails closed? I make the assumption that the switch remains closed once the supply has been removed?
RE: High speed switching using reed switches.
RE: High speed switching using reed switches.
Of course they fail. They have a speed limit.
Inductive loads promptly weld them shut.
Use a magnet on the wheel and coils on the periphery.
Keith Cress
kcress - http://www.flaminsystems.com
RE: High speed switching using reed switches.
3 amp output... nuf sed...
TTFN
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RE: High speed switching using reed switches.
I don't know if there is any snap action in a reed switch. My guess is that at high speeds the contacts are releasing at too slow a speed and are being welded together. You could try arc suppression across the contacts. Or, use the switches to drive a higher power amplifier like IRstuff suggested.
RE: High speed switching using reed switches.
No sweat for Hall switches.
Mike Halloran
Pembroke Pines, FL, USA
RE: High speed switching using reed switches.
RE: High speed switching using reed switches.
I have been trying to understand why anyone would try to switch 1 A at 1 V, but couldn't find any reason. The commutator replacement is closest so far.
Small reed switches have switching times down to 50 microseconds. So, theoretically, they can switch signals at 200 Hz, perhaps.
But the current capacity of the switch is usually given for AC and resistive load. Switching DC and inductive load normally reduces possible load to 5 or 10 percent of resistive load. So, don't even think about 1 A and inductive load. Not even at 1 Hz.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: High speed switching using reed switches.
I watched my daughter build all of the following motors:
http://www.simplemotor.com/howitworks.htm
Keith Cress
kcress - http://www.flaminsystems.com
RE: High speed switching using reed switches.
No I am not trying to make a motor. It is a scientific experiment to measure magnetic interactions. It just looks like a motor.
I am limited to 1 V and cant use other voltage sources.
I talked with some reed switch manufacturers and they didn't seem too phased by speed.
If it is due to current surges would a diode across switch to take the surge help?
RE: High speed switching using reed switches.
I would heed the advice of the previous posters and dispose of the reed switch completely and try some of their solutions.
RE: High speed switching using reed switches.
What is the alternative?
Hall, optic, inductive etc all would require voltage supply above 1V or require extra circuitry that would use too much power.
Mechanical would add extra friction.
RE: High speed switching using reed switches.
Why did my magnet and coils <sub 1V> solution not fly?
Keith Cress
kcress - http://www.flaminsystems.com
RE: High speed switching using reed switches.
You will have to explain the magnet and coils to me. How is current switched?
1 volt is all we can use at the moment.
RE: High speed switching using reed switches.
RE: High speed switching using reed switches.
The Hall effect itself, in raw form, doesn't require "high" voltages. V(H) is proportional to I and B. So a raw sensor might be made to work within the PS limits you have given.
But a simple magnet and coil as suggested by Mr. Smoked might be arranged to provide an accurate zero crossing signal.
Why the 1.0v limit? In my entire career I don't think I've ever seen a "1.00 volt" fixed power supply, and common batteries are at least 1.2 volts.
RE: High speed switching using reed switches.
Have the induced voltage in the coil switch on a FET of sufficient capacity to handle your loads.
RE: High speed switching using reed switches.
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Use it to switch another transistor of some sort.
A hall effect switch eliminates having to try to build coils and parts to get the required switching action yourself. The downside is that at least 3V is required.
RE: High speed switching using reed switches.
Are you switching DC? There's several contact protection schemes that can be used for DC.
RE: High speed switching using reed switches.
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
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RE: High speed switching using reed switches.
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.
RE: High speed switching using reed switches.
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
RE: High speed switching using reed switches.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: High speed switching using reed switches.
Biggest difference for using, is that Hall needs sensor supply and reed is just a contact.
RE: High speed switching using reed switches.
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
--www.calibrator.com--
RE: High speed switching using reed switches.
When the magnet moves by the coil it will induce a voltage/current pulse. Think of it as a generator.
John D