Paranormal Battery box

[Jyera]

I have a plastic battery box with an on-off switch.
It can hold 4 AA size 1.5V batteries to give a 6V voltage source.

I placed some batteries in it. These are not new batteries.
When I turn it on and measure it with a digtal multimeter, it shows around 4.4V. When I turn off the switch, it shows 1.46V on the multimeter.

Weird!??!

I would have thought that it should show zero because it is an open circuit.

Why?

 

[PixyMisa]

The switch is what is known in the trade as "stuffed". It's leaking current. There's some crud in there that is conducting electricity even when it is nominally open.

 

[teddygrahams]

The numbers look suspicious to me. Is it possible it's switching between 3 cells in series and the remaining cell ?

Take the batteries out and beep out the connections.

 

[PixyMisa]

Yeah.

If it's a half-way decent multimeter, set it to measure resistance and have a play around with the various contact points.

 

[bruto]

I think teddy has it. If it's a new box, there's a possibility they just wired it wrong. Also make sure the batteries are right way round. Not all battery cases are intuitively arranged. I've seen some, for example, that put three batteries in one direction and the fourth in the other, etc. My cheap wireless keyboard here takes 2 AA's, and uses the coil spring contact you usually see going to the negative end as the positive on one of them, a confusing visual cue.

 

[Jyera]

I had measured each batteries to be around 1.1V to 1.2V.
The 1.46V doesn't seems to be the voltage of a single battery.
If the switch is on, and I measured the voltage progressively, it seems to register the correct voltage of 1.1V, 2.2V, 3.3V, 4.4V. So I think it is not wired wrongly.

Further more I have tried this:
Turn the switch to off. Removing one of the four batteries.
I remove the battery which is furthest from the the switch within the series.
And measure the voltage. Result 0V.
In this case, I have 2 apparent breaking of the circuit; one via the switch and one via the removed batteries.

 

[Jyera]

The switch is what is known in the trade as "stuffed". It's leaking current. There's some crud in there that is conducting electricity even when it is nominally open.

Is it very common to have "stuffed"? Why would it be leaking current ?
It would seems to be against the notion that open circuit do not allow current to flow.

 

[PixyMisa]

Is it very common to have "stuffed"?

Yes.

Why would it be leaking current ?

Because there is something in the switch that is providing a path for the current even when it is nominally off. But that something isn't a very good conductor, so you only get a fraction of the voltage.

It would seems to be against the notion that open circuit do not allow current to flow.

The circuit isn't open. Obviously.

 

[bruto]

I had measured each batteries to be around 1.1V to 1.2V.
The 1.46V doesn't seems to be the voltage of a single battery.
If the switch is on, and I measured the voltage progressively, it seems to register the correct voltage of 1.1V, 2.2V, 3.3V, 4.4V. So I think it is not wired wrongly.

Further more I have tried this:
Turn the switch to off. Removing one of the four batteries.
I remove the battery which is furthest from the the switch within the series.
And measure the voltage. Result 0V.
In this case, I have 2 apparent breaking of the circuit; one via the switch and one via the removed batteries.

If the batteries are correctly inserted, and the case correctly wired, in series, you should get 0 volts if you remove any one of the batteries. If this is not the case, look for a problem in the wiring of the series. If this is the case, then there is some path of resistance parallel to the switch (i.e. the switch is probably stuffed).

 

[Elind]

I had measured each batteries to be around 1.1V to 1.2V.
The 1.46V doesn't seems to be the voltage of a single battery.
If the switch is on, and I measured the voltage progressively, it seems to register the correct voltage of 1.1V, 2.2V, 3.3V, 4.4V. So I think it is not wired wrongly.

Further more I have tried this:
Turn the switch to off. Removing one of the four batteries.
I remove the battery which is furthest from the the switch within the series.
And measure the voltage. Result 0V.
In this case, I have 2 apparent breaking of the circuit; one via the switch and one via the removed batteries.

If you have a multimeter, why have you not checked the resistance across the switch when open?

If that shows open circuit, take out the batteries and with the switch still open check resistance from the suppy side (not the battery side) of the switch to the battery terminal points in turn. There could also be a short in the last three positions closest to the switch (not the first one) direct to the supply lead.

 

[Jyera]

The fact that the voltage changed when I switched it from on to off, created the impression that it is indeed working and "opening the circuit".

It didn't occur to me that the switch might behave like a resistor.
I was a little hung up about the possibility that it might be behaving more like a capacitor.

Will go measure the switch for resistance.
But what is the frequency of a "stuffed" switch behaving like a capacitor.

 

[Elind]

The fact that the voltage changed when I switched it from on to off, created the impression that it is indeed working and "opening the circuit".

It didn't occur to me that the switch might behave like a resistor.
I was a little hung up about the possibility that it might be behaving more like a capacitor.

Will go measure the switch for resistance.
But what is the frequency of a "stuffed" switch behaving like a capacitor.

No capacitance possible from that type of device. If it were you would see the voltage slowly, actually quickly, drop to zero from the start level.

 

[Jyera]

Without the batteries in the battery box, I measured the resistance of the (open/off) switch. I put the multimeter to it's highest resistance measure of 2M Ohm. Result, out of range. This usually means open circuit. But still it could mean very very very high resistance.

What I did next gave me the biggest surprise yet.

I measured the voltage of the switch in the open/off position, without the batteries in the battery box. And to my surprise !!! It shows a voltage, 2 mV.
And the voltage did not go to zero.

No battery and yet there is a voltage ??!!?

 

[Elind]

Without the batteries in the battery box, I measured the resistance of the (open/off) switch. I put the multimeter to it's highest resistance measure of 2M Ohm. Result, out of range. This usually means open circuit. But still it could mean very very very high resistance.

A very very high resistance is equivalent to an open circuit in this case, and would not allow you to measure 1.49 volts even if it were not infinite. The switch is OK.

What I did next gave me the biggest surprise yet.

I measured the voltage of the switch in the open/off position, without the batteries in the battery box. And to my surprise !!! It shows a voltage, 2 mV.
And the voltage did not go to zero.

No battery and yet there is a voltage ??!!?

That's the voltage, 2 thousands of a volt, generated either by the sweat in your socks or the fluorescent lights in your garage. Try sticking one end in your mouth and another somewhere else, and see what you read

Your box appears to have a short that bypasses the switch. Did you measure those paths?

 

[PixyMisa]

Without the batteries in the battery box, I measured the resistance of the (open/off) switch. I put the multimeter to it's highest resistance measure of 2M Ohm. Result, out of range. This usually means open circuit. But still it could mean very very very high resistance.

Okay, bang goes that idea.

If it was conducting but above 2M Ohm, the voltage would be tiny, so we can be comfortable that that's not it.

 

[bruto]

Without the batteries in the battery box, I measured the resistance of the (open/off) switch. I put the multimeter to it's highest resistance measure of 2M Ohm. Result, out of range. This usually means open circuit. But still it could mean very very very high resistance.

What I did next gave me the biggest surprise yet.

I measured the voltage of the switch in the open/off position, without the batteries in the battery box. And to my surprise !!! It shows a voltage, 2 mV.
And the voltage did not go to zero.

No battery and yet there is a voltage ??!!?

If it's a digital meter, a low battery can cause odd readings. Also make sure the voltmeter is set to DC, not AC. An open circuit on AC will often show a stray voltage (of nearly infinitesimal current, not to worry about).

I still think there's something funny about the connections in the box. Did you try removing one battery at a time, to see if there is any combination of 3 batteries that still gives a reading?

 

[Jyera]

A very very high resistance is equivalent to an open circuit in this case, and would not allow you to measure 1.49 volts even if it were not infinite. The switch is OK.

I understand it is equivalent.
But a open circuit (infinity resistance) will not draw any current. When I switch off the battery box, there is no leakage of battery. I

That's the voltage, 2 thousands of a volt, generated either by the sweat in your socks or the fluorescent lights in your garage. Try sticking one end in your mouth and another somewhere else, and see what you read

I understand what you mean. However I have not touched any conducting part of the circuit while doing the measurement. so I cannot say my body contributed to the voltage. Placing my digital multimeter under my fluoresent light yields no readings. It simple puzzles me why a simple on-off switch without battery can provide a voltage.

Your box appears to have a short that bypasses the switch. Did you measure those paths?

Measured those paths, no short.

 

[Jyera]

If it's a digital meter, a low battery can cause odd readings. Also make sure the voltmeter is set to DC, not AC. An open circuit on AC will often show a stray voltage (of nearly infinitesimal current, not to worry about).

Measured a brand new AA battery with the multimeter and it shows 1.57V so I think it is okay. Did set the multimeter to DC mode.

I still think there's something funny about the connections in the box. Did you try removing one battery at a time, to see if there is any combination of 3 batteries that still gives a reading?

Yes. Tried that. Get the result of 0V expected of a an open circuit.

 

[Jyera]

Okay, bang goes that idea.

If it was conducting but above 2M Ohm, the voltage would be tiny, so we can be comfortable that that's not it.

The thing is that, the "Out of range" reading did not happen instantanouesly.

When I measured it, it started as 1.XXX M Ohm . And then very quick change to "out-of-range". So you could still be right that the switch behaved like a resistor when it is at off position.

Would it made a difference if the actual resistance is 1.999M Ohm. compared to if it is 2.00001 M Ohm which would make it out of range?

 

[PixyMisa]

Would it made a difference if the actual resistance is 1.999M Ohm. compared to if it is 2.00001 M Ohm which would make it out of range?

No. For our purposes, either one is close enough to an open circuit.