Trying to add an Illuminated 12v DC Switch but it's shorting out

[ThermallyFrigid]

Hello,

I am trying to add a simple 3 pin illuminated 12v DC switch to a 12v battery charger but I'm doing something wrong and can't figure out what that is.
There is the PC board on the charger which has the Positive Output solder point going through a fuse, then to the battery charger output alligator clips, and the Negative output.

What I did was added the switch in between the Positive Output line as shown below.
It works without the negative LED connection.   As soon as I connect the negative wire it blows the fuse.

How can I get this switch to work WITH the indicator LED also working properly?

Thanks

[ Specified attachment is not available ]

[inse]

Did you verify the pinout of the switch with a multimeter or continuity tester?
Is the fuse blown in on or off position?
On position: LED shorted ()
Off position: toggle switch, not illuminated
P.S. sorry, missed that in the diagram...

[bdunham7]

Something is not connected properly or as indicated in the drawing.  If your switch is causing a short to the ground wire, it wouldn't blow the fuse in the drawing but would be an unfused short so something else would have to give.  Try disconnecting the battery and see what works--if the switch is internally misconnected or doesn't work the way you think, it might short the battery to ground in one position.  What is the p/n of the switch?

[ThermallyFrigid]

Something is not connected properly or as indicated in the drawing.  If your switch is causing a short to the ground wire, it wouldn't blow the fuse in the drawing but would be an unfused short so something else would have to give.  Try disconnecting the battery and see what works--if the switch is internally misconnected or doesn't work the way you think, it might short the battery to ground in one position.  What is the p/n of the switch?

Hello and thanks for your help,
I tried testing the switch before connecting it and it works properly.
What I did was create a simple circuit independent of the charger using a 12v battery, a small 12v motor and some alligator clip jumper wires.
In that circuit it performed exactly as expected and the LED came on when the circuit was switched on and the motor ran.
So I ruled out the switch as the problem.

[ThermallyFrigid]

Something is not connected properly or as indicated in the drawing.  If your switch is causing a short to the ground wire, it wouldn't blow the fuse in the drawing but would be an unfused short so something else would have to give.  Try disconnecting the battery and see what works--if the switch is internally misconnected or doesn't work the way you think, it might short the battery to ground in one position.  What is the p/n of the switch?

Hello and thanks for the assist.
When I disconnect the battery the fuse does not blow.  It's only when I connect the battery to be charged that it blows.
As long as it is not connected to a battery to be charged it seems to work fine.  But of course, the goal is to charge the battery.

It's as if the connected battery is backfeeding the circuit and causing the fuse to blow.
I tested the switch in a different circuit and it worked as expected so I ruled out the switch as the problem.

[wraper]

If your switch is causing a short to the ground wire, it wouldn't blow the fuse in the drawing but would be an unfused short so something else would have to give.

Why wouldn't it blow the fuse? The switch in this case can short a power supply or a battery. As fuse is blown, it should be shorting the battery. IMHO the switch is either connected backwards or a wrong type of switch is used. Probably it's a SPDT switch instead of SPST illuminated switch.

[ThermallyFrigid]

If your switch is causing a short to the ground wire, it wouldn't blow the fuse in the drawing but would be an unfused short so something else would have to give.

Why wouldn't it blow the fuse? The switch in this case can short a power supply or a battery. As fuse is blown, it should be shorting the battery. IMHO the switch is either connected backwards or a wrong type of switch is used. Probably it's a SPDT switch instead of SPST illuminated switch.

Hello,
The switch has no model numbers or any other identification on it other than an indication of the Power, Load and Ground terminals.
I bought this switch years ago and it has been sitting in a tool box, sealed in an airtight package.

[NiHaoMike]

Try connecting a resistor in series with the ground to the switch?

[ThermallyFrigid]

Try connecting a resistor in series with the ground to the switch?

Hello,
Ok, I could try that.
May I ask what your thoughts are for doing this?

I was also wondering if a diode in series with the switch ground might work.

Thank you for your help

[ThermallyFrigid]

With the circuit diagram as shown, the circuit (including the LED) works perfectly and as expected UNTIL the alligator clips are connected to a battery for charging.
As long as there is not a battery to be charged connected, it works perfectly.

The black wire from the switch only serves to power the LED.  It has no other purpose.

Would a diode in the GND wire with the cathode facing the switch solve this issue?

[fuzzoli]

I'm going to guess that the switch is a DPST (not a typo), with the LED/bulb between the 2-3 circuit.  So 1-3 is a heavy-duty switch, and 2-3 is a switched, low-current circuit for the bulb.

In the supplied original diagram, the illumination would work as long as it's a bulb and not an LED, but it's actually getting power from both the charger and battery (so be careful not to blow it).

Try hooking it up like the attachment.

The switch looks either like the one in the drawing, or the LED/Resistor is an ordinary bulb.

In this circuit, the light will be on when the switch is on and either the battery or charger is on.  If you want the light to be on only when the charger is on, then connect a suitably rated diode (pointy end to the right) where the arrow is on the positive side of the battery.  That will prevent the battery from backfeeding to the bulb.

[bdunham7]

A couple of good close-up photos of the switch might help us understand.  Clearly the switch is not wired the way you think it is internally.  You can also remove it and check continuity between the terminals in both (assuming there are only two) switch positions. 

[ThermallyFrigid]

A couple of good close-up photos of the switch might help us understand.  Clearly the switch is not wired the way you think it is internally.  You can also remove it and check continuity between the terminals in both (assuming there are only two) switch positions.

The switch is marked and I did connect it in an independent circuit as outlined in a post above and it worked perfectly as expected.
That leads me to believe I have it connected correctly and it is marked correctly.

It works perfectly in the power supply circuit until I connect the alligator clips to a battery for charging.  Then the fuse blows when I switch it on.
So I'm thinking it has to do with the power feedback from the battery?

I tried a diode and that did not work.  Next I'm going to try a resistor as suggested above.  I'll have to guess the values.  Trial and error.

Thanks again

[bdunham7]

Do you know that it is an LED for illumination?  It looks to me like you maybe have an incandescent bulb (or something that doesn't care about polarity) and you have the POWER and GROUND connections reversed.

[ThermallyFrigid]

It has just now occurred to me that it is possible.....when the external battery is connected for charging, the Load and Power sources will swap relative to their positions on the switch when no external battery is connected.

The voltage of the charger "pushing" against the lower charge state of the battery.

So, I'm pulling power for the switch from the PC board before the external battery is connected, then once an external battery is connected for charging, perhaps the "LOAD" and "SOURCE" swap places?

However, the battery to be charged will ALWAYS be at a lower state of voltage than the charger right up to the moment the battery reaches full charge equilibrium with the charger.
So electronically, I'm not sure that is how it would work.

[ThermallyFrigid]

Do you know that it is an LED for illumination?  It looks to me like you maybe have an incandescent bulb (or something that doesn't care about polarity) and you have the POWER and GROUND connections reversed.

It's possible.
I'm not certain if the bulb is LED or not.  I assumed it is LED because it works fine on 12v DC and usually other type bulbs in these illuminated rocker switches require much higher voltage like (AC).

If it is connected incorrectly, how does one explain that it works perfectly fine until I connect the external battery?

When no external battery is connected......
1). The rocker switch correctly turns the circuit On and Off and I can read 14.4v at the alligator clips (NOT attached to a battery)
2). The LED comes on as expected
3). Placing the rocker in the OFF position, the LED turns off and the circuit powers down.

It is ONLY when I connect an external battery to be charged that problems develop.

It may also be significant that if I do not connect the black wire that powers the LED, I can then connect the alligator clips to the external battery to be charged and it turns the circuit on and off normally and as expected (just without any LED)

[bdunham7]

Just draw it reversed and it should be obvious.  The circuit isn't "working perfectly", it is simply turning the light on, which it will do either way.  Unfortunately, in the reversed position, it is connecting the center terminal to GROUND instead of POWER.

[ThermallyFrigid]

Just draw it reversed and it should be obvious.  The circuit isn't "working perfectly", it is simply turning the light on, which it will do either way.  Unfortunately, in the reversed position, it is connecting the center terminal to GROUND instead of POWER.

Ok thanks.
I'm going to think about what you said for a bit.  I'm sure you're correct.  My light bulb moment is lagging :-)

Thanks again for your help.

[ThermallyFrigid]

For the fun of it.....as suggested by NiHaoMike above.....

I just tried an experiment with resistors inline in the ground wire between the switch and the PC board.

Here are the results....

56K 1/2 watt resistor - No LED - Fuse OK - Resistor cool
1K 1/2 watt resistor - No LED - Fuse OK - Resistor cool
270R 1/2 watt  Resistor - Dim LED - Fuse Ok - Resistor quite Hot

From this is at least seems that maybe a 100ohm, 1 watt resistor might do the trick ?

[bdunham7]

From this is at least seems that maybe a 100ohm, 1 watt resistor might do the trick ?

 

What trick?  Can you test the voltages at each point with a multimeter and see if you think that resistor results in a working circuit--one that charges the battery?

[CaptDon]

As one poster suggested, with battery connected to charger and switch wired correctly the light won't go out with the battery connected. The bulb is between ACC and GND. The switch was intended to be used with fog lamps and such. Connect BAT to Battery, ACC to the fog lamps and GND to ground. The switch will light when the fog lamps come on. In your case, Connect BAT to the charger +, ACC to battery + and tie Switch GND / charger - and battery - together. The light will not go out because the battery will backfeed it unless you use a diode in series with the wire going to the battery + and that diode must be capable of handling the charge current. Also the fuse must be capable of handling the charge current.

[ThermallyFrigid]

Here are the raw switch continuity test results (no wires connected to switch)

SWITCH OFF Position

Ground to Load - Connected
Ground to Power - Not Connected
Power to Load - Not Connected


SWITCH ON Position

Ground to Load - Connected
Ground to Power - Connected
Power to Load -  Connected

[ThermallyFrigid]

From this is at least seems that maybe a 100ohm, 1 watt resistor might do the trick ?

 

What trick?  Can you test the voltages at each point with a multimeter and see if you think that resistor results in a working circuit--one that charges the battery?

Sorry if I seem confused.  I am.
I don't claim any awards for brilliance or knowledge.  Just trying.

Ok I will test that and report back
thanks

[ThermallyFrigid]

As one poster suggested, with battery connected to charger and switch wired correctly the light won't go out with the battery connected. The bulb is between ACC and GND. The switch was intended to be used with fog lamps and such. Connect BAT to Battery, ACC to the fog lamps and GND to ground. The switch will light when the fog lamps come on. In your case, Connect BAT to the charger +, ACC to battery + and tie Switch GND / charger - and battery - together. The light will not go out because the battery will backfeed it unless you use a diode in series with the wire going to the battery + and that diode must be capable of handling the charge current. Also the fuse must be capable of handling the charge current.

The maximum charge current is 10A
Ok thanks I will try that.

[bdunham7]

Here are the raw switch continuity test results (no wires connected to switch)

SWITCH OFF Position

Ground to Load - Connected
Ground to Power - Not Connected
Power to Load - Not Connected


SWITCH ON Position

Ground to Load - Connected
Ground to Power - Connected
Power to Load -  Connected

Can you distinguish between the terminals that are connected via switch contacts vs through what I presume is a light bulb?  It should be at least a few ohms, I would think.  The switch contacts should be well under an ohm, so you'll get close to whatever reading your DMM gives you with shorted terminals.  Assuming the Ground to Load connection is through the light bulb and you have it connected as in your diagram, I don't see where the problem is.  But I'm sure it is there!