DC current detection--relay? 5

[TheTick]

I am looking for a means to detect current flowing to a DC motor. Ideally, I would like to find a relay with nigh-zero resistance that switches when it detects or passes current from 0.5 to 5.0 amps with no voltage drop.

I am about to give up and build my own (coils and reed switch). Still hoping to find an off-the-shelf solution.

 

[matthewm1965]

Crouzet are a long established company that do a good range.

 

[catserveng]

Try Flex core at

http://www.flex-core.com,

they have a couple different kinds of current sensors that should do the trick.

Mike L.

 

[DRWeig]

FW Bell has some candidates too:

http://www.sypris.com/test-and-measurement/magnetics-fw-bell/open-loop-sensors

http://www.sypris.com/test-and-measurement/magnetics-fw-bell/closed-loop-sensors

Good on ya,

Goober Dave

 

[dpc]

http://www.crmagnetics.com/products/CR-5395-P9.aspx

What size and form factor do you need?



David Castor

http://www.cvoes.com

 

[Skogsgurra]

Dirt cheap and simple: a reed switch mounted close to the cable.

Gunnar Englund

http://www.gke.org

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

 

[Compositepro]

Gunnar makes an excellent suggestion. Something else that might work is the start relay from a refrigerator. It should be more sensitive to DC current than than the AC current it is designed for.

 

[jraef]

As elegant as Gunnar's solution is, we don't know how much DC current you are referring to and you would have to make sure the magnetic field it creates is strong enough to actuate the reed switch. Still, there is beauty in simplicity...

If you want a good packaged COTS product however, I like these guys.

http://www.nktechnologies.com/pdfs/DS3 datasheet0510.pdf

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[TheTick]

According to the original post, it's 0.5 to 5.0 amps. I'm inclned to believe that number. It's from a trustworthy source.

 

[Skogsgurra]

I don't know about 'trustworthy' - but I take your word for it.

If current isn't high enough to actuate the reed switch, then a conductor that carries 5 A usually can be formed into a few loops and that usually takes care of that. There are quite sensitive reed elements.



Gunnar Englund

http://www.gke.org

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

 

[itsmoked]

I'd do the reed switch too.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TheTick]

Thanks to all who contributed with off-the-shelf items. This isn't my usual arena, so it's been difficult to track down what I need. Even though I can't afford, I have learned a lot and discovered some great new potential sources.

Due to budget constraints (pay out of pocket and beg for money back), I'll probably be going with reed switch and coils. Nice to see some consensus on this.

More about the application: DC actuators that have limit switch stops. When limit is reached, voltage is still applied but current drops to zero due to open switch. I need to detect shut-off and deactivate actuator before it starts to backdrive.

 

[itsmoked]

A reed switch should work well for that. Remember though that reed switches absolutely hate switching any capacitance. They will weld shut easily if you do. If you don't they will last for an insanely long time.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Yes. They weld very easily. Put a reasonable sized resistor in series to avoid welding. Keeping current in switch below one amp is usually safe.

Gunnar Englund

http://www.gke.org

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

 

[TheTick]

No worry about welding. The reed switch is only connecting signal input to PLC. I suppose a resistor wouldn't hurt, though.