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

[ThermallyFrigid]

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!

I think you are right.
When I remove the switch from any connections then connect a 12v power source to the Power and GND terminals the LED comes on when the switch is turned on.
I could read .001 ohms through those terminals and none through power and Load.

As long as I do not connect the DC output alligator clamps to a battery (for charging) the switch seems to operate exactly as expected.
In that case, the switch correctly turns on the power to the leads and energizes the output alligator clamps to 14.4v as expected, and the LED glows.

It is only when I connect the external battery to be charged that it blows the fuse.
If I never needed to charge a battery I would be satisfied.   However, that defeats the purpose of course.

I am reviewing the suggestion by CaptDon.

Thanks again for any suggestions.
I will continue to explore and pursue this until I get a working solution.

[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.

What connects to Switch Power Pin in your scenario?  I don't see where you specified a connection to the Switch's Power Pin ?
Does your connection scenario intentionally leave that pin not connected?

Below is the schematic modified to your instructions (I think)


Testing the switch, the LED seems to be between Power and GND, not ACC (Load) and GND.
I could be wrong, but when I test the switch outside any circuit, the LED only lights when I connect 12+ to Power and 12- to GND.
No other terminals activate the LED.

Given that, could the LED still be between ACC (Load) and GND ?
Thanks

[NiHaoMike]

I'm thinking the switch is defective and the negative wire going to the LED is touching some part of the switch that's connected to the switched positive when the toggle is in just the right position.

[ThermallyFrigid]

I'm thinking the switch is defective and the negative wire going to the LED is touching some part of the switch that's connected to the switched positive when the toggle is in just the right position.

I would totally agree with you except that......
When I remove the switch from the battery charging circuit and simplify the circuit using a simple 12v battery and a 12v bulb, it works exactly as expected.
In other words, this works perfectly and as expected....so I don't think the switch is bad unless you know something I don't?

The big difference is that instead of connecting negative and positive to a normal load, I'm connecting them to another power source and that is the problem I have to overcome here.




So I'm essentially doing this instead......and it is not working.   I am obviously trying to do something the wrong way and I need to start from scratch and re evaluate this.



And this is essentially the Original Circuit.
I'm simply wanting to add an illuminated Switch to turn on and off the connection to the 2nd battery with an illuminated indication when it is on.
Adding a simple switch is actually very easy.  It's the LED Indicator light that is giving me trouble.
If I didn't care about having an indicator light to indicate when it is On or Off I could have been done with this already.

[ThermallyFrigid]

Here's a photo of the actual device I'm working on......

[bdunham7]

When I remove the switch from any connections then connect a 12v power source to the Power and GND terminals the LED comes on when the switch is turned on.
I could read .001 ohms through those terminals and none through power and Load.

.001 ohms?  Really?  That's going to be tough to measure.

Look, you're just spinning your wheels unless you can resolve with certainty which side of that switch the light is on and nothing so far has actually done that.  If you have a 12V source and a 12V bulb that is much larger than what could conceivably fit within the switch (like a headlight perhaps), make yourself a continuity test light using the 12V source and bulb in series.  Then repeat the continuity test you did earlier and note for each position and set of pins whether the large light or the switch light illuminates.  What you aren't seeing is that when the circuit is just the source and the light (no load) the switch light would appear to work even if the actual connections were reversed.  Or, you could just reverse the two outer wires and the thing will probably work.

[inse]

Honestly, I would skip the illumination idea as it serves no purpose, only leads to confusion and possibly could deep discharge your battery.
If you need a charging indicator, a different approach would be necessary.

[DavidAlfa]

This is probably why, you might shorting the battery to gnd.
Check 2-3 resistance when off.

[ThermallyFrigid]

When I remove the switch from any connections then connect a 12v power source to the Power and GND terminals the LED comes on when the switch is turned on.
I could read .001 ohms through those terminals and none through power and Load.

.001 ohms?  Really?  That's going to be tough to measure.

Look, you're just spinning your wheels unless you can resolve with certainty which side of that switch the light is on and nothing so far has actually done that.  If you have a 12V source and a 12V bulb that is much larger than what could conceivably fit within the switch (like a headlight perhaps), make yourself a continuity test light using the 12V source and bulb in series.  Then repeat the continuity test you did earlier and note for each position and set of pins whether the large light or the switch light illuminates.  What you aren't seeing is that when the circuit is just the source and the light (no load) the switch light would appear to work even if the actual connections were reversed.  Or, you could just reverse the two outer wires and the thing will probably work.

You are right.
I meant 00.1 ohms.  Sry for the typo.  Probably wasn't wearing my glasses at the moment.


I guess the point was there was no resistance on one side and a little on the other.  That coincided with the LED lighting when power was applied as mentioned.
So that seemed to indicate where the LED bulb was connected.  I may not have made that very clear.
For me it's all a learning process and an adventure.  I really don't mean to cause you any grief so I apologize if that's the case and thank you VERY much for your kind assistance.

You know, I thought about reversing the wires like you say. 
After searching the Internet and YouTube, I found that what I'm trying to do is not very common (adding a power switch to a battery charger).
I could find very little if anything that helps with this type project.

To do this properly, I would actually need to address the Mains side as well as the DC output side.
Here, I'm only addressing the DC output side.
I also have a Meanwell Battery charger and it also has no ON/OFF switch so it seems that maybe even for manufacturers and EE's, this is not an easy concept or at least not so easy to implement?
Now that I think of it, NONE of my battery chargers have On/Off switches.  You just unplug them when you're not using them.

I never really thought about it until now.

Thanks again for your patience and insight.
It is appreciated.

[ThermallyFrigid]

Honestly, I would skip the illumination idea as it serves no purpose, only leads to confusion and possibly could deep discharge your battery.
If you need a charging indicator, a different approach would be necessary.

Thanks Inse.
The reason for the illuminated indicator light is because I will have this charger connected to a LiFePO4 battery pack that powers an RV permanently behind a panel.
I don't want to have to connect and disconnect it after every charge cycle.
I wanted a clear visual indication when it is connected because when it is connected it draws a small parasitic current and I do not want that to slowly drain the battery while it is connected.
Thus the desire for a disconnect switch.

That said, you are correct that it is very easy to get a working On/Off switch for this.   The difficult part is getting an indicator light to go with it.

[ThermallyFrigid]

This is probably why, you might shorting the battery to gnd.
Check 2-3 resistance when off.

Makes sense.
I'll check that and thanks.

[bdunham7]

You know, I thought about reversing the wires like you say. 
After searching the Internet and YouTube, I found that what I'm trying to do is not very common (adding a power switch to a battery charger).
I could find very little if anything that helps with this type project.

To do this properly, I would actually need to address the Mains side as well as the DC output side.

It should be very simple and there's no need to address mains or anything else.  You probably are frustrated that such a simple thing is not working--and it is simple and it should work.  The theory is pretty obvious and as far as I can tell you got it right.  You can replicate the function of the illuminated switch easily enough with a few wires to confirm it should all work as you think it should.  The problem is that either you have miswired something or your switch does not do what you think it should.  That's why I suggested the large-bulb continuity tester.

The difficult part is getting an indicator light to go with it.

It just occurred to me that even if it worked as it should, the switch indicator would be on whenever the battery was connected, not just when it was charging.  That probably isn't what you want. 

[Jeff eelcr]

Is the fuse the proper rating for what a discharged battery might draw? Like a dead short at start up.
Jeff

For some reason half or more of this whole post was missed by me.
This does not look like the RV chargers I have worked on  with 3-4  30A ATC fuses in parallel to handle the
current to charge RV batteries.
Jeff 

[ThermallyFrigid]

Is the fuse the proper rating for what a discharged battery might draw? Like a dead short at start up.
Jeff

The fuse is 15A and it doesn't blow when powered on normally without the switch so maybe a bad one, but I assumed the fuse was capable.

[IanB]

This is an interestingly difficult thread. Any one of us reading it could diagnose the problem in moments if we were there and had hands-on access to the switch. We would either determine the correct way to wire up the switch, or would determine the switch to be faulty.

If you could trace out the internal connections of the switch, it would help enormously.

Consider each pair of terminals:

(1) Power-ACC
(2) Power-GND
(3) ACC-GND

Each of these pairs has one of three states:

(a) Open (no circuit)
(b) Closed (short circuit)
(c) Lamp (lamp in circuit)

And the switch has two positions:

(i) ON
(ii) OFF

With the switch on the bench, methodically go through all the permutations of terminal pair and switch position, and for each permutation write down the state.

For instance:

Power-ACC, ON, Closed
Power-ACC, OFF, Open
Power-GND, ON, Lamp
Power-GND, OFF, Open

etc.

Once you have this table, it will be possible to know how to wire up the switch.

Edit: to find out if the lamp is in circuit, you will want to connect a small 9 V battery between the terminals and see if the lamp lights.

[Jeff eelcr]

Are we dealing with an RV charger charging vehicle batteries, 14V to start and or run a mobile home/camper/RV?
Jeff   

[CaptDon]

I have two illuminated switches similar to yours. I measured them. From ACC to GND is 38 ohms, the resistance of the incandescent grain of wheat bulb. The resistance from ACC to GND never changes. From BAT to ACC is open circuit when the switch is OFF and closed circuit when the switch is on exactly as would be expected. Perhaps for some weird reason your switch shorts ACC to GND when in the off position.  This would be strange but perhaps your rocker switch is actually a SPDT which would explain the fuse blowing in the OFF position!! Cheers!!

[Jeff eelcr]

If the switch was wrong or faulty then it would not work properly without the extra battery.
Jeff

[CaptDon]

Sure it would work for its original design purpose and he already proved that by hooking up an external lamp instead of a battery!!! Again, it appears the switch may be a SPDT and shorting the battery out in the OFF position. It wouldn't matter if it 'shorted out' an unpowered device like fog lamps or such in the OFF position, but it would matter if it is shorting out a power source like his battery connected between ACC and GND!!!! The switch may not be faulty, it may just not be the correct configuration for his intended use. My lighted switch here in my junkbox on the other hand would work perfect. Bought several at a car show years ago for fog lights and a bed light on my truck.

[ThermallyFrigid]

This is an interestingly difficult thread. Any one of us reading it could diagnose the problem in moments if we were there and had hands-on access to the switch. We would either determine the correct way to wire up the switch, or would determine the switch to be faulty.

If you could trace out the internal connections of the switch, it would help enormously.

Consider each pair of terminals:

(1) Power-ACC
(2) Power-GND
(3) ACC-GND

Each of these pairs has one of three states:

(a) Open (no circuit)
(b) Closed (short circuit)
(c) Lamp (lamp in circuit)

And the switch has two positions:

(i) ON
(ii) OFF

With the switch on the bench, methodically go through all the permutations of terminal pair and switch position, and for each permutation write down the state.

For instance:

Power-ACC, ON, Closed
Power-ACC, OFF, Open
Power-GND, ON, Lamp
Power-GND, OFF, Open

etc.

Once you have this table, it will be possible to know how to wire up the switch.

Edit: to find out if the lamp is in circuit, you will want to connect a small 9 V battery between the terminals and see if the lamp lights.

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)

[ThermallyFrigid]

Are we dealing with an RV charger charging vehicle batteries, 14V to start and or run a mobile home/camper/RV?
Jeff

It is a 14.6v LiFePO4 charger (10A), charging a 12v - 4 cell LiFePO4 battery pack.   It is never used for starting the vehicle.  Only for USB charging and small inverter use.
However, for these tests, a small 35Ah 12v battery was used on the bench.

[ThermallyFrigid]

I have two illuminated switches similar to yours. I measured them. From ACC to GND is 38 ohms, the resistance of the incandescent grain of wheat bulb. The resistance from ACC to GND never changes. From BAT to ACC is open circuit when the switch is OFF and closed circuit when the switch is on exactly as would be expected. Perhaps for some weird reason your switch shorts ACC to GND when in the off position.  This would be strange but perhaps your rocker switch is actually a SPDT which would explain the fuse blowing in the OFF position!! Cheers!!

Hi CaptDon,
I was admittedly very tired when I posted those readings.
Tonight I tested the switch again across ACC and GND and the resistance is 21.1 ohms when the switch is ON and 0.7ohms when it is off.

Here's a table of values.....

Power-ACC, ON, OF (overflow)
Power-ACC, OFF, 1.0 ohms
Power-GND, ON, 21.6 ohms
Power-GND, OFF, OF

GND-ACC, ON, 21.8 ohms
GND-ACC, OFF, 1.0 ohms

[ThermallyFrigid]

This appears to be the switch in question.
It says it's SPST

[bdunham7]

Power-ACC, ON, OF (overflow)
Power-ACC, OFF, 1.0 ohms
Power-GND, ON, 21.6 ohms
Power-GND, OFF, OF

GND-ACC, ON, 21.8 ohms
GND-ACC, OFF, 1.0 ohms

Surely you have the first two reversed?   And if so, your switch is problematic since it appears to short the lamp when off.  This wouldn't be a problem as long as the accessory connected wasn't a battery, generator or something that holds a charge.  It clearly isn't performing as a SPST switch.  But I'm sure it was a great learning experience! 

[IanB]

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).