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

[ThermallyFrigid]

I'm not sure if the switch is changing inside or if I simply make mistakes measuring.  I do believe I am testing it as stated.
I do  see that pressing down slightly on the rocker button can change the test results.

Testing the switch again this morning.....

Power-ACC. ON, 21 ohms (However, putting downward pressure  on the switch button makes these readings change significantly so the switch may be bad?)
Power-ACC, OFF, OL
Power-GND, ON, 31 ohms
Power-GND, OFF, OL

GND-ACC, ON, 31 ohms
GND-ACC, OFF, 1 ohm

[ThermallyFrigid]

Hello,
Thank you much for your assistance.  I also find this a very interesting topic.   And one that can carry over to many other situations.
I tried to do this in post #21 but maybe I didn't do it according to your description so I am trying again.

The switch is on the bench and not connected to anything at all except as noted.  Please let me know if these are the test results you requested.
For the LAMP tests, I connected power and ground to the pins as noted.


PIN-PIN, SWITCH STATE, LAMP ON (where applicable), CIRCUIT STATE

Power-ACC, OFF, Open
Power-ACC, ON, Lamp, Closed (shorted)
Power-GND, OFF, Open
Power-GND, ON, Lamp, Closed (shorted)

GND-ACC, OFF, Closed (shorted)
GND-ACC, ON, Lamp, Closed (shorted)

Well, no, not exactly.

Power-ACC, ON, Lamp, Closed (shorted)

It is not possible for the connection between Power and ACC to be both closed (low resistance direct connection) and also to have the lamp connected between them. It can only be one or the other.

The way you test this is you measure the resistance between the Power and ACC terminals using your meter or a continuity tester, with the switch on or off, and with nothing connected to the GND terminal. If the connection appears to be high resistance, then you can check if the lamp is in circuit by applying power between the terminals and seeing if the lamp lights.

This will give you two results: Power-ACC (ON), and Power-ACC (OFF).

Then repeat the same test with the Power-GND terminal pair, and the ACC-GND terminal pair.

This will give six results in total, and each result will either be (a) open circuit (no connection), (b) closed circuit (low resistance connection), or (c) lamp in circuit (high resistance connection, lamp lights when power applied).

The test results above were Continuity Tests.  Are you meaning you want me to do Resistance tests or Continuity tests?
It sounds now as if you mean Resistance tests.  When you said "On or Off" that sounded to me as if you were requesting continuity tests.  My apologies if I misunderstood.

Ok, re-doing the tests using the meters OHMS position

Power-ACC, ON, 24-50 ohms
Power-ACC, OFF, OL

Power-GND, ON, 52 ohms
Power-GND, OFF, OL

ACC-GND, ON, 21 ohms
ACC-GND, OFF, 1 ohm

[IanB]

The test results above were Continuity Tests.  Are you meaning you want me to do Resistance tests or Continuity tests?

Well, no, I don't want you to do the tests, you want to do the tests for yourself so you can find out how the switch works.

What you want to do is to find out what is connected between each pair of switch terminals with the switch in either position. Is it a closed switch, an open switch, or a lamp? You can do this with a continuity meter, a resistance meter, or a battery (to power the lamp). You probably need to use some combination of these to get the right information. For battery tests, use a small 9 V battery so you don't burn out the switch contacts if there is no lamp there.

It sounds now as if you mean Resistance tests.  When you said "On or Off" that sounded to me as if you were requesting continuity tests.  My apologies if I misunderstood.

Ok, re-doing the tests using the meters OHMS position

Power-ACC, ON, 24-50 ohms
Power-ACC, OFF, OL

Power-GND, ON, 52 ohms
Power-GND, OFF, OL

ACC-GND, ON, 21 ohms
ACC-GND, OFF, 1 ohm

So, OK, the first one does not seem right. When the switch is ON, Power-ACC should be a direct connection, not a high resistance connection. If you connect the 9 V battery between the Power and ACC terminals with the switch ON, does the lamp light?

The last one, on the other hand, seems to explain the fuse blowing. 1 Ohm seems like a closed switch, which would short out the battery.

Have you by any chance got the Power and GND terminals mixed up?

Of the six combinations you listed, which one makes the lamp light up with a small battery?

[ThermallyFrigid]

The test results above were Continuity Tests.  Are you meaning you want me to do Resistance tests or Continuity tests?

Well, no, I don't want you to do the tests, you want to do the tests for yourself so you can find out how the switch works.

What you want to do is to find out what is connected between each pair of switch terminals with the switch in either position. Is it a closed switch, an open switch, or a lamp? You can do this with a continuity meter, a resistance meter, or a battery (to power the lamp). You probably need to use some combination of these to get the right information. For battery tests, use a small 9 V battery so you don't burn out the switch contacts if there is no lamp there.

It sounds now as if you mean Resistance tests.  When you said "On or Off" that sounded to me as if you were requesting continuity tests.  My apologies if I misunderstood.

Ok, re-doing the tests using the meters OHMS position

Power-ACC, ON, 24-50 ohms
Power-ACC, OFF, OL

Power-GND, ON, 52 ohms
Power-GND, OFF, OL

ACC-GND, ON, 21 ohms
ACC-GND, OFF, 1 ohm

So, OK, the first one does not seem right. When the switch is ON, Power-ACC should be a direct connection, not a high resistance connection. If you connect the 9 V battery between the Power and ACC terminals with the switch ON, does the lamp light?

No

The last one, on the other hand, seems to explain the fuse blowing. 1 Ohm seems like a closed switch, which would short out the battery.

Have you by any chance got the Power and GND terminals mixed up?

I'm going by the markings on the switch body.
I believe I am connecting it according to the markings. In this image, the switch is in the OFF position.

Of the six combinations you listed, which one makes the lamp light up with a small battery?

When the switch is ON.....

GND-ACC
GND-Power

PS......
I could be wrong but.....I think it's important to note that as long as I do not connect to the external battery that is to be charged, the whole think works perfectly as expected.   it's ONLY when I try to connect a battery for charging that things go wrong.

[IanB]

I could be wrong but.....I think it's important to note that as long as I do not connect to the external battery that is to be charged, the whole think works perfectly as expected.   it's ONLY when I try to connect a battery for charging that things go wrong.

Well, yes, because according to your measurements, there is a 1 ohm connection between ACC and GND with the switch OFF. But your external battery is connected to ACC and GND. So turning the switch OFF will short the external battery and blow the fuse. (Lucky there is a fuse, otherwise it would blow up the switch, wiring and generally make for a lot of heat and smoke.)

It seems this switch is not really suitable and maybe you need a different switch?

[ThermallyFrigid]

I could be wrong but.....I think it's important to note that as long as I do not connect to the external battery that is to be charged, the whole think works perfectly as expected.   it's ONLY when I try to connect a battery for charging that things go wrong.

Well, yes, because according to your measurements, there is a 1 ohm connection between ACC and GND with the switch OFF. But your external battery is connected to ACC and GND. So turning the switch OFF will short the external battery and blow the fuse. (Lucky there is a fuse, otherwise it would blow up the switch, wiring and generally make for a lot of heat and smoke.)

It seems this switch is not really suitable and maybe you need a different switch?

Yes, that seems to be the case.  Or a different approach to power the indicator light that is not connected to the battery being charged.
I will eventually come up with a working layout.
I will explore different switches and configurations.  Maybe I will find schematics for battery chargers that already have illuminated ON/OFF switches and go from there.

I sincerely appreciate everyone's input on this.

[ThermallyFrigid]

For anyone interested......

I opened the switch (ever curious) to see what was inside.
It looks to me as though the ACC tab comes up to the copper plate in the middle and electrically touches and holds the copper plate.
The GND and POWER tabs come up through the housing and are touched by the center copper plate as it rocks back and forth depending on the ON or OFF position of the plastic Red Rocker button.
The LED appears directly connected to GND AND ACC from the photo.

[Jeff eelcr]

Not an LED, LED's require being connected correctly + and _ or they do not turn on.
This incandesent lamp will work as long as one side is + and the other is _ either way.
So this all works (including the lighted switch) until the extra battery is added?
If so then the wiring is wrong or the battery draws to much.
Jeff

[IanB]

I opened the switch (ever curious) to see what was inside.
It looks to me as though the ACC tab comes up to the copper plate in the middle and electrically touches and holds the copper plate.
The GND and POWER tabs come up through the housing and are touched by the center copper plate as it rocks back and forth depending on the ON or OFF position of the plastic Red Rocker button.

Well, that all seems clear. When the switch is ON, then ACC is connected to Power. When the switch is OFF, ACC is connected to GND (which is the cause of your problems).

The LED appears directly connected to GND AND ACC from the photo.

As mentioned, that's not an LED, that's a bulb.

[Jeff eelcr]

Ian, one thing I think we both missed the switch mode power supply _ and his refering to it as ground.
Hopefully it was connected to _ and not to ground?
The switch does look suspect though the wire leads of the lamp?
Or the switch was marked backwards?
Jeff   

[ThermallyFrigid]

I opened the switch (ever curious) to see what was inside.
It looks to me as though the ACC tab comes up to the copper plate in the middle and electrically touches and holds the copper plate.
The GND and POWER tabs come up through the housing and are touched by the center copper plate as it rocks back and forth depending on the ON or OFF position of the plastic Red Rocker button.

Well, that all seems clear. When the switch is ON, then ACC is connected to Power. When the switch is OFF, ACC is connected to GND (which is the cause of your problems).

The LED appears directly connected to GND AND ACC from the photo.

As mentioned, that's not an LED, that's a bulb.

You're right.  I'm not sure why I keep calling it an LED.  Bad habit maybe.  I should just call it "The Light".
I'll stop.
Thanks

[ThermallyFrigid]

Ian, one thing I think we both missed the switch mode power supply _ and his refering to it as ground.
Hopefully it was connected to _ and not to ground?
The switch does look suspect though the wire leads of the lamp?
Or the switch was marked backwards?
Jeff

Hi Jeff,
I'm connecting it to Negative...not Ground.
Good points.
Thanks

[ThermallyFrigid]

I opened the switch (ever curious) to see what was inside.
It looks to me as though the ACC tab comes up to the copper plate in the middle and electrically touches and holds the copper plate.
The GND and POWER tabs come up through the housing and are touched by the center copper plate as it rocks back and forth depending on the ON or OFF position of the plastic Red Rocker button.

Well, that all seems clear. When the switch is ON, then ACC is connected to Power. When the switch is OFF, ACC is connected to GND (which is the cause of your problems).

The LED appears directly connected to GND AND ACC from the photo.

As mentioned, that's not an LED, that's a bulb.

Where "should" the bulb get's it's power ?
The only other choice is if it was connected directly to the Power Pin....but then it would be illuminated at all times.

[JDubU]

OK, here is the answer to your problem:

When you took apart the switch, you confirmed its operation as depicted by DavidAlfa in:
https://www.eevblog.com/forum/projects/trying-to-add-an-illuminated-12v-dc-switch-but-its-shorting-out/msg4084489/#msg4084489
 
Switch off:  only ACC and GND are connected.
Switch on:  only ACC and Power are connected.
The switch's internal incandescent lamp is connected between ACC and GND.

So, when the switch is off, the lamp is shorted.   When the switch is on, the lamp is connected between Power and GND.

The problem that you are having is that you are trying to control power to an Active load (a battery) with the switch.  The battery can both draw power (charging) or supply power (discharging).  That means that when the switch is in the off position, it directly shorts the battery/fuse between ACC and GND.  If you were trying to control a passive load (like a light bulb or motor), that cannot source any significant power, it would work fine.

In your circuit, using this SPDT lighted switch, you would need to add a high power diode in series with the battery to prevent discharge current from flowing to GND when the switch is off.  The trouble is that the charging circuit would not be able to measure the battery voltage for charge control.  If you are only charging a lead-acid battery it would work since current would stop flowing to the battery when the charge voltage matched the battery voltage (plus the diode voltage drop).  This will not work for most other types of batteries since they usually require a more sophisticated charge profile that needs active battery voltage monitoring.

[inse]

So the switch is a toggle switch (SPDT) with one position bypassed by a lamp.
Let me repeat my proposal to drop the idea of illumination.
The charger seems to have indicators, use them as status display.

[ThermallyFrigid]

OK, here is the answer to your problem:

When you took apart the switch, you confirmed its operation as depicted by DavidAlfa in:
https://www.eevblog.com/forum/projects/trying-to-add-an-illuminated-12v-dc-switch-but-its-shorting-out/msg4084489/#msg4084489
 
Switch off:  only ACC and GND are connected.
Switch on:  only ACC and Power are connected.
The switch's internal incandescent lamp is connected between ACC and GND.

So, when the switch is off, the lamp is shorted.   When the switch is on, the lamp is connected between Power and GND.

The problem that you are having is that you are trying to control power to an Active load (a battery) with the switch.  The battery can both draw power (charging) or supply power (discharging).  That means that when the switch is in the off position, it directly shorts the battery/fuse between ACC and GND.  If you were trying to control a passive load (like a light bulb or motor), that cannot source any significant power, it would work fine.

In your circuit, using this SPDT lighted switch, you would need to add a high power diode in series with the battery to prevent discharge current from flowing to GND when the switch is off.  The trouble is that the charging circuit would not be able to measure the battery voltage for charge control.  If you are only charging a lead-acid battery it would work since current would stop flowing to the battery when the charge voltage matched the battery voltage (plus the diode voltage drop).  This will not work for most other types of batteries since they usually require a more sophisticated charge profile that needs active battery voltage monitoring.

Thank you!
This summarizes well what I suspected but couldn't quite piece together.

It may be why none of my Lead Acid or LiFePO4 battery chargers come with ON/OFF switches that are illuminated.  It is not an easy problem to solve.
Adding a simple NON-illuminated switch works fine.  I think I can still add an LED or some other lighted bulb to indicate if it on but I need to come up with an alternative source of ground for the bulb

I have reservations about adding diodes since as you point out, it may affect the feedback loop for the charging system or could decrease the current or voltage to the battery being charged.

I will continue to look for that solution.

[ThermallyFrigid]

So the switch is a toggle switch (SPDT) with one position bypassed by a lamp.
Let me repeat my proposal to drop the idea of illumination.
The charger seems to have indicators, use them as status display.

That is still an option.
It's just that some sort of illuminated indicator would be really the ideal situation.

The purpose of the illumination is to be an active reminder to shut off the charger since when the charger is not plugged in on the AC input side, but still connected to a battery to be charged, it has a small parasitic drain on the battery and I don't want that.  I could easily forget and not notice without an indicator light of some sort.

Maybe a separate LED powered by a 12v source on the PC board not going through the switch, but only powered when there is 12v to the output side of the charger.
If it is not going through the switch, it should work.   I have to look at the board and do some tests to find that point that wont interfere with anything else.

[ThermallyFrigid]

I would really like to thank ALL who responded and offered their advice.
It has been very helpful and appreciated.

[JDubU]

There are lots of illuminated switch options.
For example, here is a latching push button switch with separate illumination circuit and both normally open and normally closed contacts:

https://www.amazon.com/API-ELE-Warranty-Latching-Mounting-Self-Locking/dp/B08L4C6N6M/ref=sr_1_1?crid=2OO9PKMF2E14L&keywords=0746362282424&qid=1648584885&sprefix=0746362282424%2Caps%2C716&sr=8-1&th=1

[ThermallyFrigid]

There are lots of illuminated switch options.
For example, here is a latching push button switch with separate illumination circuit and both normally open and normally closed contacts:

https://www.amazon.com/API-ELE-Warranty-Latching-Mounting-Self-Locking/dp/B08L4C6N6M/ref=sr_1_1?crid=2OO9PKMF2E14L&keywords=0746362282424&qid=1648584885&sprefix=0746362282424%2Caps%2C716&sr=8-1&th=1

Thank you.
Worth looking into.
A couple of problems with this particular one.......

Limited to 5Amps and I'm working with 10A.
I only have 1 inch below the cover to work with so it has to be very shallow in depth into case...and that includes wires etc.
But the concept would probably work if I could find one metting those two requirements.

[ThermallyFrigid]

Most SMPS chargers are divided into an input side that handles the mains 120v input (USA) then rectifies that into DC for the output side, in this case 14.6v to charge LiFePO4 batteries.

On the 14.6v Output side of this charger there is a fan.
It is controlled by a thermister I'm sure.

However, this fan and it's power supply are likely 12v and totally independent of the Output leads that go to the external battery to be charged.
It seems to me I could tap in before the thermistor, to power the LED (or neon) bulb.
Of course it would require a resistor.

Then the switch would not need it's own lighting.

So I would have two 22 Gauge wires coming from before the thermister to power the LED that would only come on on when the unit is switched on, and the other side of the switch would handle the 14.6v that charges the battery.

So how about this as a solution?
Will the LED change the current or voltage going to the thermister enough to change the fan operation?

[ThermallyFrigid]

Or simply this.......

MGI SpeedWare 12vDC Neon Lighted Mini Rocker Switches On-Off DPST 5 Pack (Blue)
https://www.amazon.com/gp/product/B087D9NLNB/ref=ask_ql_qh_dp_hza?th=1

[Jeff eelcr]

Here we go again. Look at your circuit what will happen when you through the switch?
It can not be a good idea to connect + 12V to negitive 12V by way of a switch, even a nice looking switch.
Also resistor value looks a bit high 56K for 12v??? Depends on the diode if it will even light I do have a
design that used 47K for indicator LED's on 12V very low current and red against black can be seen in
daylight. Most LED's I tried would not turn on.
Jeff

[ThermallyFrigid]

Here we go again. Look at your circuit what will happen when you through the switch?
It can not be a good idea to connect + 12V to negitive 12V by way of a switch, even a nice looking switch.
Also resistor value looks a bit high 56K for 12v??? Depends on the diode if it will even light I do have a
design that used 47K for indicator LED's on 12V very low current and red against black can be seen in
daylight. Most LED's I tried would not turn on.
Jeff

Jeff,
The resistor picture was just a screen grab.  Not the actual value I would use.
Besides, the blue rocker switch has it's own resistor built in.

I may not have expressed the idea exactly correct in the illustration, but I'm fairly certain it will work.
The representation is of current going through the switch.  Not actually shorting positive to negative.
Even though the illustration could be interpreted that way from the way I did it..

I'm pretty sure the way I'm going to do it now will work, even if I'm not great as an illustrator.

What I'm doing is tapping the switch into the 12v power that is going to the thermister before the Fan to power the internal switch light only.
So yes, that power will be going through the switch to power the LED.  Completing the circuit.  But not shorting positive to negative.
The other side of the switch will be inline with the wire going to the battery charging output lead.

This should work.

The answer seems to be using a Double Pole switch rather than a single pole switch.

[ThermallyFrigid]

Got the switches and I can see what Jeff meant now.

You can't just wire positive and negative across the switch.  Of course.

Fortunately, this device had sources of 12v on the PCB that were separated from the Battery connection lines.
I will use those to operate an LED since they are both 12v and low current.  No heavy diode necessary. (Only a small one)

The way I was initially trying to do it I think fuzzoli was probably pretty close to a workable suggestion.
But still, messing with the circuit that charges the battery could lead to other troubles.

I see that now.