Relays 0/0/4 trip with DC load

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farrokh747
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Relays 0/0/4 trip with DC load

Postby farrokh747 » Fri Feb 22, 2013 5:40 am

HI!

IM noticing something odd with my relay array:

Flight sim/FS2P(alan dyer)/WinXP

Relays controlling 28vdc loads (actuator motors)

At certian points in the flight, several relays have to function together - on touchdown for e.g., we have spoiler deployment, all air/ground systems, etc - all of these control 28vdc power to various devices, each with a load of not more than 2 A DC

I find that at these times, the pidgets cards drop offline/trip off the USB daisy chain.. they sometimes reboot on their own after a few seconds, or don't come back until i restart the PC

Now, If i operate the relay system without the 28vdc supply, they all work fine and stay on the chain... once the 28v is on, and the relays are operated (either by FS2P or the fidget controller) they start dropping off the chain...

I dont see any connection between the usb voltages/signals and the loads that the relay hardware is controlling - (aren't they isolated from each other?) but for some reason, it seems to have an effect on the USB.... not sure what's happening..

The relays are connected to the PC via a powered hub, with more than 2A capacity
Has anyone noticed this?

Cheers!

fc747

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mparadis
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Re: Relays 0/0/4 trip with DC load

Postby mparadis » Fri Feb 22, 2013 9:29 am

Based on your description, it sounds like the instability is being caused by electromagnetic interference. When a mechanical relay switches, current briefly arcs across the switching arm, causing a burst of EMI. It would seem that one of these events is fine, but multiple simultaneous events cause enough interference to affect the stability of the board. You could try using diodes to attempt to suppress the arcs as discussed on this wiki page , or you could use solid-state relays instead.

farrokh747
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Re: Relays 0/0/4 trip with DC load

Postby farrokh747 » Fri Feb 22, 2013 9:39 am

Thanks! will try suppressing the EMI, and also have a look at the SS boards...

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Patrick
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Re: Relays 0/0/4 trip with DC load

Postby Patrick » Fri Feb 22, 2013 9:41 am

Also, make sure you're using 24 AWG USB cables with ferrites.

-Patrick

farrokh747
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Re: Relays 0/0/4 trip with DC load

Postby farrokh747 » Fri Feb 22, 2013 9:50 am

Thanks Patrick....

On testing i also noted that operating just one relay at a time could drop the board out.... without any 28v, all cards are stable...

I have other relay arrays controlling 5vdc power, to the deck panel lighting, which seem to work fine... it's just this one panel with 3 x 0/0/4's with 28vdc power....

odd...

thanks for your inputs

fc747

farrokh747
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Re: Relays 0/0/4 trip with DC load

Postby farrokh747 » Sat Feb 23, 2013 1:03 am

One question:

IS the coil/usb/5v side of the 0/0/4 electrically isolated from the load/28vdc(in this case) side? Im guessing it has to be....


http://www.phidgets.com/docs/Addressing ... h_Phidgets

in this doc, adding a ferrite bead (if not already there) to the usb cable will help: from what i gather the elemental composition of the bead determines the freq of suppression... are there specific types of ferrites for usb cables?


cheers!

farrokh747
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Re: Relays 0/0/4 trip with DC load

Postby farrokh747 » Sun Mar 24, 2013 7:58 am

So after some tests:

Short cables with beads from phidget to hub seem to suppress the interference, cards remain on the usb chain

Relays may need a higher amp-per-port usb hub, like this one -

http://www.amazon.com/4-Port-Industrial ... B0077RM2Z0

also looking at the ground loop and power system, as per http://www.phidgets.com/docs/Electricity_Primer#Ground

will report more


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