# How can I use a sensor output (0-5VDC) to actuate power disconnecting to another device?

#### nfrank12

Feb 28, 2017
5
I have a sensor device that has 3 outputs: 0.5VDC (warm up), 1.0VDC (normal), 2.0VDC (alarm state).

I want to electrically isolate or disconnect power to a device when the sensor has reached the 2.0VDC alarm state.

What type of equipment is necessary to perform this action?

#### davenn

Moderator
Sep 5, 2009
14,260
I want to electrically isolate or disconnect power to a device when the sensor has reached the 2.0VDC alarm state.

What type of equipment is necessary to perform this action?

what is the sensor ... link ??

What type of equipment is necessary to perform this action?

what is the device to be switched off and what voltage/ current is it using ?

#### nfrank12

Feb 28, 2017
5
what is the sensor ... link ??

what is the device to be switched off and what voltage/ current is it using ?

The sensor is a solid state electrochemical gas sensor and is currently under development so I can't provide you with a link or anything. If you have any specific questions about it, please let me know and I will do my best to answer them. It runs on 12-24VDC and runs on about 0.125A @ 12V.

The device which is being disconnected is a lithium ion battery that runs at 48V and will draw no more than 120A.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
120A? Really? Is the load purely resistive?

And about those voltage levels. What do you want to happen when the voltage is very near a limit, so what happens when the voltage is randomly varying between 1.999 and 2.001 volts?

#### BobK

Jan 5, 2010
7,682
I have a sensor device that has 3 outputs: 0.5VDC (warm up), 1.0VDC (normal), 2.0VDC (alarm state).
How are we to interpret this sentence? If it take it literally, the sensor will output only one of the those three voltages, with nothing in between. But I suspect that it actually can output anything within the range and probably outside the range of 0.5 to 2V. Which is correct?

Bob

#### nfrank12

Feb 28, 2017
5
How are we to interpret this sentence? If it take it literally, the sensor will output only one of the those three voltages, with nothing in between. But I suspect that it actually can output anything within the range and probably outside the range of 0.5 to 2V. Which is correct?

Bob
You should take the sentence literally. The sensor device has a dedicated circuit board with embedded signal processing algorithm. The output from the circuit board is arranged so that the voltage is delivered as a step-wise function (0.5V, 1.0V, 2.0V)

#### nfrank12

Feb 28, 2017
5
120A? Really? Is the load purely resistive?

And about those voltage levels. What do you want to happen when the voltage is very near a limit, so what happens when the voltage is randomly varying between 1.999 and 2.001 volts?

At most 120A. The load is going to be a power supply for a robotics device. The battery is a lithium ion battery pack with 12 batteries in series and 6 batteries in parallel. The batteries maximum discharge current is 10A. So yes, 120A, really.

I would obviously like the electronics arrangement I've inquired about to account for noise. Indeed there will be sometimes when the voltage is randomly varying between 1.999V and 2.001V and I would not like to disconnect power in this case. I would only like to disconnect power when the voltage has a large jump from 1.0V to 2.0V.

#### BobK

Jan 5, 2010
7,682
6 batteries in parallel each providing 10A is 60A, not 120A.

So, if the sensor is outputting these discrete levels, you simply need a comparator set at somewhere between 1V and 2V (1.5V seems reasonable). To do the logic. You need one or more robust MOSFETs to switch 60A.

Your last paragraph confuses me though. You say you do not want to disconnect when it varies from 1.99V to 2.01V, but should it not already be disconnected at that point? Surely 1.99V must be interpreted as the alarm state. I presume that when you see a voltage near 2V you want to disconnect and keep it disconnected until you see a voltage close to 1V (normal state). Is this correct?

Bob

#### nfrank12

Feb 28, 2017
5
Bob you're right, my mistake. I have learned a bit about the batteries since I wrote my previous response. The max discharge current of the batteries is 40A.

And about my previous response regarding alarm state. You're absolutely right, 1.99V (or 2.00V, or 2.01V) would be interpreted as an alarm state and it should be disconnected at that point. Your last paragraph is entirely correct!

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