DC Amp Question

Critt · Jun 4, 2007

Hello..

I was wondering if anyone knows of a DC current sensor I could use to monitor the amps I have going to a motor. Example is I have a 12VDC motor (running @ 1Amp) I am energizing it by 24 VDC solid state relay controlled by a PLC. I want to monitor the current so if the motor amps change (Motor is driving a door and door jams or hits something) I can stop the motor and go in reverse.

Thanks

Tom Jenkins · Jun 4, 2007

Here are a couple of sources:

http://www.veris.com/

http://www.nktechnologies.com/

Jiri Toman · Jun 4, 2007

I like http://www.crmagnetics.com

I have been using extensively this product:

http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=Remote_Current_Indicator

It's a current transformer with an LED, this is a very inexpensive way to monitor that your heater bands on an injection molding machine are getting power. In many applications all you really need to know is that the current is flowing, but you don't necessarily need to know how much.
Apart from that the Company has a large product selection and in addition they will do specials if you need.

For your application they have relay/CT combo that can be set to a specific current level and also they have CTs with analog output.

panic mode · Jun 5, 2007

we do 12VDC motors all the time, (automotive, assembly and testing...).
we used to do CT style devices as posted before. the only drawback is that they are
so slow (70% change may take anywhere from 0.5-3 seconds depending on used product)
which might not be much of a problem in your case since lag for increase in current
is smaller and the door will have some inertia anyway.

in our case, i've decided that this just doesn't cut it for most of our applications
(specially when doing data collection) so usually we use shunt and DC/DC convertor.
this gives us response of <1ms.

TConnolly · Jun 5, 2007

To measure DC current you will need a shunt or a hall effect sensor.

Try www.ohiosemitronics.com

Critt · Jun 5, 2007

Thanks for all the help so far...

I was thinking of using a current sensor like this one http://www.gavazzionline.com/pdf/DIB01CB.pdf
which is a carlo Gavazzi Current monitor. The idea is that I wouldn't need an analog card since I could use the relays off the sensor. Problem is the unit is expensive and was looking for something a little more cost effect since I will need 12 of them.

TConnolly · Jun 5, 2007

I used one of these magnecraft current sensing relays from Newark Electronics once. This particular unit is intended for AC applicaitons, but I imagine the manufacturer has other models that might meet your needs.

milldrone · Jun 5, 2007

Critt said:
The idea is that I wouldn't need an analog card since I could use the relays off the sensor. Problem is the unit is expensive and was looking for something a little more cost effect since I will need 12 of them.

Hmmmmmm. a digital output is preferred.

How about a shunt and a solid state relay with a 3 volt turn on? It would take some playing arround with the shunt value to get it right.

elevmike · Jun 6, 2007

There are a number of motor controllers out there specifically designed for this type of applicaiton, with an intergrated current sensor.

However, if your not using a door control, to make it simple for you by code a commerical door actuator cannot provide more then 30 lbs of force, (measured at the leading edge of the door) & should not be closing at the rate of more then 1 ft. per second. Presuming that you have a closed limit. (actual closing speeds depend on kenetic energy). Example: If the door travel is 3ft., then if the door hasnt reached the limit in 3 seconds, then obiviously it hit an obstruction and should be re-opened.

JTE · Jun 6, 2007

Tom Jenkins said:
Here are a couple of sources:

http://www.veris.com/

http://www.nktechnologies.com/

Hi Mike,
How do you order from Veris? I need NEED a humidity sensor with either 4-20ma or 0-10V. They got something!!

Jim

elevmike · Jun 6, 2007

http://www.veris.com/ord1.asp

Tom Jenkins · Jun 7, 2007

I just saw an add that shows AutomationDirect.com has added AC current switches and sensors. You may want to check and see if they have DC as well.

rsdoran · Jun 7, 2007

Jiri offered a company that should have what you want, an example: http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR5395

JTE · Jun 7, 2007

Tom Jenkins said:
I just saw an add that shows AutomationDirect.com has added AC current switches and sensors. You may want to check and see if they have DC as well.

I saw those also, I orderd four and will let you guys know how they work out.

I want to measure AC current but also detect what direction the flow is. IE from the utility company to me (I'm buying power) or from me to the grid (I'm selling power).

Tom Jenkins · Jun 7, 2007

JTE said:
I saw those also, I orderd four and will let you guys know how they work out.

Please let us know. I wouldn't worry too much, though. They look like brand labeled units from a manufacturer that we've used for years with excellent success. The only problem I recall was when they were mounted immediately adjacent (as in almost touching) a conventional C/T supplied by others. Apparently the magnetic field from that big chunk of iron threw off the transmitter circuitry. Moving them about a foot or so away corrected the problem.

DC Amp Question

Critt

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Jiri Toman

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panic mode

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Critt

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