Trying to add an Illuminated 12v DC Switch but it's shorting out - Page 1
Forum section: electronics / projects

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 01:38:48 pm
content: 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 ]

author: inse
author_rank: Super Contributor
timestamp: March 26, 2022, 02:07:40 pm
content: 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 illuminatedP.S. sorry, missed that in the diagram...

author: bdunham7
author_rank: Super Contributor
timestamp: March 26, 2022, 02:24:15 pm
content: 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?

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 02:30:14 pm
content: Quote from: bdunham7 on March 26, 2022, 02:24:15 pmHello 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 02:34:16 pm
content: Quote from: bdunham7 on March 26, 2022, 02:24:15 pmHello 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.

author: wraper
author_rank: Unknown
timestamp: March 26, 2022, 02:37:50 pm
content: Quote from: bdunham7 on March 26, 2022, 02:24:15 pmWhy 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 02:52:43 pm
content: Quote from: wraper on March 26, 2022, 02:37:50 pmHello,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.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 26, 2022, 03:08:36 pm
content: Try connecting a resistor in series with the ground to the switch?

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 04:20:13 pm
content: Quote from: NiHaoMike on March 26, 2022, 03:08:36 pmHello,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

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 04:35:22 pm
content: 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?

author: fuzzoli
author_rank: Regular Contributor
timestamp: March 26, 2022, 04:53:16 pm
content: 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 thesuppliedoriginal 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.

author: bdunham7
author_rank: Super Contributor
timestamp: March 26, 2022, 05:03:56 pm
content: 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 05:15:23 pm
content: Quote from: bdunham7 on March 26, 2022, 05:03:56 pmThe 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

author: bdunham7
author_rank: Super Contributor
timestamp: March 26, 2022, 05:27:44 pm
content: 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 05:31:02 pm
content: 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 05:35:09 pm
content: Quote from: bdunham7 on March 26, 2022, 05:27:44 pmIt'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 expected3). 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)

author: bdunham7
author_rank: Super Contributor
timestamp: March 26, 2022, 05:45:43 pm
content: 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 05:51:00 pm
content: Quote from: bdunham7 on March 26, 2022, 05:45:43 pmOk 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 06:03:45 pm
content: 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 cool1K 1/2 watt resistor - No LED - Fuse OK - Resistor cool270R 1/2 watt Resistor - Dim LED - Fuse Ok - Resistor quite HotFrom this is at least seems that maybe a 100ohm, 1 watt resistor might do the trick ?

author: bdunham7
author_rank: Super Contributor
timestamp: March 26, 2022, 06:32:56 pm
content: Quote from: ThermallyFrigid on March 26, 2022, 06:03:45 pmWhat 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?

author: CaptDon
author_rank: Super Contributor
timestamp: March 26, 2022, 06:57:01 pm
content: 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 07:22:47 pm
content: Here are the raw switch continuity test results (no wires connected to switch)SWITCH OFF PositionGround to Load - ConnectedGround to Power - Not ConnectedPower to Load - Not ConnectedSWITCH ON PositionGround to Load - ConnectedGround to Power - ConnectedPower to Load - Connected

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 07:24:54 pm
content: Quote from: bdunham7 on March 26, 2022, 06:32:56 pmSorry 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 backthanks

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 07:26:17 pm
content: Quote from: CaptDon on March 26, 2022, 06:57:01 pmThe maximum charge current is 10AOk thanks I will try that.

author: bdunham7
author_rank: Super Contributor
timestamp: March 26, 2022, 09:30:31 pm
content: Quote from: ThermallyFrigid on March 26, 2022, 07:22:47 pmCan 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!

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 10:51:50 pm
content: Quote from: bdunham7 on March 26, 2022, 09:30:31 pmI 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 26, 2022, 10:55:13 pm
content: Quote from: CaptDon on March 26, 2022, 06:57:01 pmWhat 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

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 27, 2022, 12:02:26 am
content: 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 27, 2022, 02:27:19 am
content: Quote from: NiHaoMike on March 27, 2022, 12:02:26 amI 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 27, 2022, 03:17:09 am
content: Here's a photo of the actual device I'm working on......

author: bdunham7
author_rank: Super Contributor
timestamp: March 27, 2022, 03:23:51 am
content: Quote from: ThermallyFrigid on March 26, 2022, 10:51:50 pm.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 bulbthat 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.

author: inse
author_rank: Super Contributor
timestamp: March 27, 2022, 06:37:29 am
content: 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.

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 27, 2022, 10:39:19 am
content: This is probably why, you might shorting the battery to gnd.Check 2-3 resistance when off.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 27, 2022, 02:59:20 pm
content: Quote from: bdunham7 on March 27, 2022, 03:23:51 amYou 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 27, 2022, 03:04:22 pm
content: Quote from: inse on March 27, 2022, 06:37:29 amThanks 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 27, 2022, 03:05:29 pm
content: Quote from: DavidAlfa on March 27, 2022, 10:39:19 amMakes sense.I'll check that and thanks.

author: bdunham7
author_rank: Super Contributor
timestamp: March 27, 2022, 03:07:39 pm
content: Quote from: ThermallyFrigid on March 27, 2022, 02:59:20 pmIt 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.QuoteIt 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.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: March 27, 2022, 08:22:18 pm
content: Is the fuse the proper rating for what a discharged battery might draw? Like a dead short at start up.JeffFor 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 thecurrent to charge RV batteries.Jeff

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 27, 2022, 08:44:36 pm
content: Quote from: Jeff eelcr on March 27, 2022, 08:22:18 pmThe 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.

author: IanB
author_rank: Super Contributor
timestamp: March 27, 2022, 09:12:57 pm
content: 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-GNDEach 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) OFFWith 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, ClosedPower-ACC, OFF, OpenPower-GND, ON, LampPower-GND, OFF, Openetc.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.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: March 27, 2022, 09:30:20 pm
content: Are we dealing with an RV charger charging vehicle batteries, 14V to start and or run a mobile home/camper/RV?Jeff

author: CaptDon
author_rank: Super Contributor
timestamp: March 27, 2022, 11:09:53 pm
content: 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!!

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: March 27, 2022, 11:49:36 pm
content: If the switch was wrong or faulty then it would not work properly without the extra battery.Jeff

author: CaptDon
author_rank: Super Contributor
timestamp: March 28, 2022, 01:50:00 am
content: 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 28, 2022, 01:50:38 am
content: Quote from: IanB on March 27, 2022, 09:12:57 pmHello,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 STATEPower-ACC, OFF, OpenPower-ACC, ON, Lamp, Closed (shorted)Power-GND, OFF, OpenPower-GND, ON, Lamp, Closed (shorted)GND-ACC, OFF, Closed (shorted)GND-ACC, ON, Lamp, Closed (shorted)

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 28, 2022, 01:55:32 am
content: Quote from: Jeff eelcr on March 27, 2022, 09:30:20 pmIt 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 28, 2022, 02:07:38 am
content: Quote from: CaptDon on March 27, 2022, 11:09:53 pmHi 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 ohmsPower-GND, ON, 21.6 ohmsPower-GND, OFF, OFGND-ACC, ON, 21.8 ohmsGND-ACC, OFF, 1.0 ohms

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 28, 2022, 02:12:59 am
content: This appears to be the switch in question.It says it's SPST

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2022, 02:26:32 am
content: Quote from: ThermallyFrigid on March 28, 2022, 02:07:38 amSurely 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!

author: IanB
author_rank: Super Contributor
timestamp: March 28, 2022, 04:23:21 am
content: Quote from: ThermallyFrigid on March 28, 2022, 01:50:38 amWell, no, not exactly.QuoteIt 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).

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 28, 2022, 01:04:05 pm
content: 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, OLPower-GND, ON, 31 ohmsPower-GND, OFF, OLGND-ACC, ON, 31 ohmsGND-ACC, OFF, 1 ohm

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 28, 2022, 01:22:39 pm
content: Quote from: IanB on March 28, 2022, 04:23:21 amThe 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 positionPower-ACC, ON, 24-50 ohmsPower-ACC, OFF, OLPower-GND, ON, 52 ohmsPower-GND, OFF, OLACC-GND, ON, 21 ohmsACC-GND, OFF, 1 ohm

author: IanB
author_rank: Super Contributor
timestamp: March 28, 2022, 08:30:35 pm
content: Quote from: ThermallyFrigid on March 28, 2022, 01:22:39 pmWell, 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.QuoteSo, 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?

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 28, 2022, 08:54:17 pm
content: Quote from: IanB on March 28, 2022, 08:30:35 pmNoQuote from: IanB on March 28, 2022, 08:30:35 pmI'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.Quote from: IanB on March 28, 2022, 08:30:35 pmWhen the switch is ON.....GND-ACCGND-PowerPS......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.

author: IanB
author_rank: Super Contributor
timestamp: March 28, 2022, 09:11:37 pm
content: Quote from: ThermallyFrigid on March 28, 2022, 08:54:17 pmWell, 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?

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 28, 2022, 09:47:20 pm
content: Quote from: IanB on March 28, 2022, 09:11:37 pmYes, 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 28, 2022, 11:11:46 pm
content: 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.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: March 29, 2022, 01:05:03 am
content: 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

author: IanB
author_rank: Super Contributor
timestamp: March 29, 2022, 05:18:00 am
content: Quote from: ThermallyFrigid on March 28, 2022, 11:11:46 pmWell, 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).QuoteAs mentioned, that's not an LED, that's a bulb.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: March 29, 2022, 12:51:12 pm
content: 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

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 29, 2022, 01:59:29 pm
content: Quote from: IanB on March 29, 2022, 05:18:00 amYou'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

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 29, 2022, 02:10:17 pm
content: Quote from: Jeff eelcr on March 29, 2022, 12:51:12 pmHi Jeff,I'm connecting it to Negative...not Ground.Good points.Thanks

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 29, 2022, 02:44:11 pm
content: Quote from: IanB on March 29, 2022, 05:18:00 amWhere "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.

author: JDubU
author_rank: Frequent Contributor
timestamp: March 29, 2022, 03:50:00 pm
content: 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/#msg4084489Switch off:onlyACC and GND are connected.Switch on:onlyACC 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 anActiveload (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.

author: inse
author_rank: Super Contributor
timestamp: March 29, 2022, 04:29:47 pm
content: 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 29, 2022, 07:42:43 pm
content: Quote from: JDubU on March 29, 2022, 03:50:00 pmThank 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 bulbI 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 29, 2022, 07:44:48 pm
content: Quote from: inse on March 29, 2022, 04:29:47 pmThat 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 29, 2022, 07:55:00 pm
content: I would really like to thank ALL who responded and offered their advice.It has been very helpful and appreciated.

author: JDubU
author_rank: Frequent Contributor
timestamp: March 29, 2022, 08:19:50 pm
content: 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

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 29, 2022, 09:06:07 pm
content: Quote from: JDubU on March 29, 2022, 08:19:50 pmThank 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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 29, 2022, 10:07:20 pm
content: 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?

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 29, 2022, 11:05:21 pm
content: 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

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: March 30, 2022, 10:09:44 am
content: 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 adesign that used 47K for indicator LED's on 12V very low current and red against black can be seen indaylight. Most LED's I tried would not turn on.Jeff

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 30, 2022, 01:14:57 pm
content: Quote from: Jeff eelcr on March 30, 2022, 10:09:44 amJeff,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.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: April 04, 2022, 02:51:56 am
content: 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 thinkfuzzoliwas 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.