Detect continuity with possible voltage potential?

[nelsonhoover]

Hi, I'm needing some sort of circuit to detect continuity between 2 wires for under $100. The two wires, when open circuited, can have anything from 240vAC to 0v. This circuit will operate a relay when continuity is detected. Any ideas?

 

[itsmoked]

A relay with a 240Vac coil sounds about right.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

A single relay might be confused by the 0v case.

You might need another relay to detect the 240Vac voltage (relative to a suitable neutral return) and change the detection approach. This may be difficult if the AC voltage can be any value between 0 and 240.

 

[nelsonhoover]

Actually, what I've got is a standby generator placed a considerable distance from the utility entrance. The automatic transfer switch at the utility automatically senses whether the utility or auxiliary are powered and switches accordingly. However there where no control wires run from it to the generator.
The generator has a small battery charging circuit that starts the generator when the power goes out on it (seperate power line from the load side of the ATS). But once the transfer switch flips to aux the generator sees its own power coming back and shuts down, only to start again as the wire dies. So if I could detect, from the generator, when the ATS is actually routing the generated power back down to the generator or using utility power, and run a relay to keep the charging circuit disconnected when the ATS is on aux, it'd save having to run a control circuit that far. The ATS automatically goes back to utility when it comes back on.
So, when the ATS is on aux, the output side of the generator would have continuity to the power wire coming back down from the ATS. When the ATS flips to utility, we could have anything from 240V to 0V from generator output to the return power line, depending on the utility phase compared to the generator output (right?).
Thanks.

 

[IRstuff]

I think you're basically going to need a "controller" just to figure out what that line is doing.

At what point as the voltage goes up do you stop caring about the actual voltage? Seems to me that anything above, say, 50V is goog enough? If so, a 10-bit A/D with the appropriate isolation, would get you down to about 50mV.

Anything below that, you'd need to do something active to the line, like a transformer-isolated pulse, but you'd be trying to sense whether the pulse is driving a low impedance, so it'll be more complicated.

This all needs to be adjudicated by some sort of controller, which would then drive the relay.

TTFN

FAQ731-376

 

[VEBill]

Either wire up the generator's 'too clever by half' battery charging (and generator shutdown) circuit to the utility side of the ATS, or find the internal wire (relay?) in the generator that is too smart for its own good and cut it or bypass it.

 

[itsmoked]

Do you have utility power to the generator?
Do you have any wires coming from the ATS to the generator?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

What VE1BLL said. reconnect the battery charger source to the utility side of the ATS. Don't forget to install a breaker or fuses.
You may want to add a time delay so that the gen-set doesn't drop out and then try to restart while it is still turning if the utility returns for a few seconds only.(Common in rural areas on re-closer protected lines.)
You could easily use a relay powered by the generator to disconnect the charger feed and leave the generator running. But then how do you turn it off?
The best solution is to do what the rest of us do and run two control wires.
You can probably ditch the remote feed for the battery charger and reconnect the wires to the proper gen start terminals at each end. If the gen-set does not have a battery charging alternator, feed the battery charger directly from the generator output and charge the battery only when the gen-set is running.
From personal experience with quite a few small sets, all with automotive type alternators to charge the battery:
With a mains powered battery charger, the battery may last six months to a year longer before it fails completely and must be replaced.
BUT, with a mains powered battery charger, the battery often dies explosively rather than dieing quietly.
A couple of boxes of baking soda mixed with water does a fairly good job of cleaning up the spilled acid after the battery explodes, if you decide to continue with the battery charger on the utility supply.
I wouldn't hesitate. The battery charger would be gone and the wires used to control starting and stopping the gen set.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[nelsonhoover]

I believe VE1BLL and waross pretty much summed it up. I guess I'll just run the wires and be done with it. Just thought if there'd be some fairly simple solution it'd save me the bother.
The ATS has a fused terminal block to connect into and the generator has a time delay built in so I'm good to go I guess. Thanks.