Guest Posted May 19, 2014 Share Posted May 19, 2014 Hello all, Sorry to trouble you but was wondering whether someone might have some ideas for me. I've just tried wiring in a 12v socket which I thought would be a walk in the park but..... It's not charging anything! If I plug a Tom Tom or mobile phone male plug into it that has an led on it, that will light up but the socket won't charge a device plugged into the cable. It's defo not the lead either as they work fine in our other car. I'm a bit lost as to what I could be missing. Have I done something stupid with the wiring? It's wired negative to negative of battery and positive to positive of battery. There is an inline fuse that I soldered into the positive cable to the battery but other than that, it's just a simple series circuit. The socket is a Sutars 12v socket. I think designed for marine applications but that wouldn't make a difference would it? Any ideas would be welcomed, I could really do with getting it up and running for this weekend if I can. Tom Link to comment Share on other sites More sharing options...
Guest Posted May 19, 2014 Share Posted May 19, 2014 The socket I'm using is this type here Thanks Tom Link to comment Share on other sites More sharing options...
Roadsport06 Posted May 19, 2014 Share Posted May 19, 2014 Put a multimeter in at the charger end and see if you have voltage. Assuming you don't then test the continuity of your wires. Could be your fuse is blown. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 19, 2014 Member Share Posted May 19, 2014 The LED test shows you have some voltage at the socket. I'd put my money on bad contact with the plug on the device that won't charge but good enough contact with the plug on the device used for testing. Could you confirm that those are actually different plugs, and tell us what all the devices and adaptors are? Jonathan Edited by - Jonathan Kay on 19 May 2014 21:16:56 Link to comment Share on other sites More sharing options...
Roger Ford Posted May 19, 2014 Share Posted May 19, 2014 Voltage won't tell you much. If it lights LEDs on a charger then there must be voltage getting through, and in a "no load" scenario it's going to show 12V (or in fact around 13V typically and a bit more if the engine is running). What's most likely is that there is some resistance between the socket terminals and the battery. That will cause the voltage to sag as soon as you put a load on it. You should be able to check that easily enough. The fuse is probably rated for 10A. At that current, a resistance of just 0.1 ohm will drop the voltage by 1 volt (from the standard equation V=IR or volts = amps x ohms). So if you're seeing anything like one ohm of resistance between socket terminals and battery, that's your problem. Link to comment Share on other sites More sharing options...
evotell Posted May 19, 2014 Share Posted May 19, 2014 some times the length of the socket is longer than what we are plugging in so the contact point on the end doesn't touch the power source Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 19, 2014 Member Share Posted May 19, 2014 For the differential diagnosis between those theories: can you get the multimeter probes directly onto the socket terminals (not the wire connected to it) while the different things are plugged in? Poor contact between the plug and socket will give you the same voltage as at the battery. Resistance in one of the joints or contacts between the battery and the socket while the device is connected will give you a lower voltage. Jonathan Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 19, 2014 Member Share Posted May 19, 2014 Quoting evotell: some times the length of the socket is longer than what we are plugging in so the contact point on the end doesn't touch the power sourceAgreed. A good wiggle and push might make contact. Jonathan Link to comment Share on other sites More sharing options...
Guest Posted May 19, 2014 Share Posted May 19, 2014 Thanks for all the responses. Went out with the voltmeter to have a check and yup, you guessed it, that's dead as well. I'll have to go and get another tomorrow. To answer some questions in the meantime. The testing I did was with 2 separate charging leads for 2 different devices. One was a phone charger and the other was a lead for a Tom Tom. As you surmise, the fact that the LED is coming on with both leads suggests I have voltage at the plug, it's got to be a case of not being able to draw the load through for some reason I think. 12v socket was rated to 16A so have stuck a 15A fuse in the circuit for now. Again the fact that the lights are coming on suggests the contacts are connecting properly. Given I've done some soldering within the circuit (inline fuse, ring terminals for battery and a bit on the spade connectors to make sure wires don't slip out) could I have inadvertently produced a circuit with very high resistance and thus I can't draw the current I need? I'm wondering if I should just temporarily make a very primitive circuit direct to the battery with no soldered wires and no fuse to check and see whether that solves it. If resistance is the issue, how do I use the multimeter to work it out, what ohm setting do you go for and what would a high Reading be? Do I simply need to take the ends off the battery and put my multimeter onto the ring connectors thus checking the whole circuit including the socket? Sorry for all the questions, the help is much appreciated. Link to comment Share on other sites More sharing options...
Roadsport06 Posted May 19, 2014 Share Posted May 19, 2014 I didn't read your first post properly and missed the bit that you have an LED lit. It points to having a high resistance somewhere. Put multimeter to its lowest resistance setting and put it across (parallel) each wire. The resistance should be tiny, a fraction of an ohm. It is likely it is an issue on a connection that just needs cleaning up. Link to comment Share on other sites More sharing options...
Ian B Posted May 19, 2014 Share Posted May 19, 2014 Quoting TomWoodis: Given I've done some soldering within the circuit (inline fuse, ring terminals for battery and a bit on the spade connectors to make sure wires don't slip out) could I have inadvertently produced a circuit with very high resistance and thus I can't draw the current I need? I suspect you have created a "dry joint" somewhere when soldering. If you're using decent size wire then you need a big soldering iron to get the wire and terminal hot enough before applying the solder. To test if it's a bad joint take a length of wire and bypass the jointed sections if you can, to see if that helps. If you have a working multimeter then set it to Ohms (lowest range possible if it's not auto-ranging). Join the two meter probes together and you should get zero ohms (or very close). Disconnect the wires from the battery. Connect one (either) meter lead to the positive wire removed from the battery and connect the other meter lead to the centre of the 12v socket; it should read almost zero (up to 1 ohm say). Repeat with the negative wire removed from the battery, and the outer contact of the 12v socket; should be the same reading. If either are high then you have a bad joint somewhere in that wire/link. Link to comment Share on other sites More sharing options...
Ian B Posted May 19, 2014 Share Posted May 19, 2014 Oh, and the fuse rating should be no more than the rating of the wire, or the socket, whichever is the lowest (probably the wire). 10 amp is usually fine (assuming you have used wire rated at greater than 10 amps!). Link to comment Share on other sites More sharing options...
Guest Posted May 20, 2014 Share Posted May 20, 2014 Thanks chaps that all makes complete sense and I bet its one of the wires I've joined that's the issue, probably the live wire. I'll get a multimeter on it today and check out the resistance of both parts of the circuit. As for fuse, wire is rated to 16A as is socket hence the 15A fuse but as you say that's perhaps overkill so I might but something smaller in there. Thanks again for the assistance, will update once I've taken some readings. Tom Link to comment Share on other sites More sharing options...
Guest Posted May 21, 2014 Share Posted May 21, 2014 Once again, my thanks for the help on this. Luckily it's now sorted but I must admit, the fault was not one I'd seen coming. I checked out the resistance of various parts of the circuit and got very low resistance for most of it. What I couldn't understand was why I could get no reading at all with the inline fuse included in the circuit. Looking again at the fuse, I could see that it had blown. This must have been like this from day one, even before I'd plugged in my first device into the socket. The reason I never checked the fuse of course was because LEDs were lighting up on both chargers. Turns out that even though the fuse was supposedly blown, a tiny tiny part of the metal inside was still making Contact. Enough to power the LED but nothing else. A test of the circuit with old fuse still in revealed I was getting just 5V and 0.64mA at the socket. Tom Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 21, 2014 Member Share Posted May 21, 2014 Thanks for the update. Did you measure the resistance of the bad fuse? Jonathan Link to comment Share on other sites More sharing options...
Guest Posted May 21, 2014 Share Posted May 21, 2014 Hi Jonathan, No I haven't done but will do so tonight for interests sake and report back. Tom Link to comment Share on other sites More sharing options...
Roger Ford Posted May 21, 2014 Share Posted May 21, 2014 Should have been around 125 ohms from those figures. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 21, 2014 Member Share Posted May 21, 2014 Can anyone do resistor colours in their head? Jonathan Link to comment Share on other sites More sharing options...
BigCol Posted May 21, 2014 Share Posted May 21, 2014 Quoting Jonathan Kay: Can anyone do resistor colours in their head? used to be able to... here goes... first 3(?) bands: 0 black, 1 brown, 2-7 rainbow (red, orange, yellow, green, blue, violet), 8 grey, 9 white... can't remember multiplier or tolerance though Who says my degree was wasted? (Electrical Engineering & Electronics 1985) Link to comment Share on other sites More sharing options...
John Vine Posted May 21, 2014 Share Posted May 21, 2014 Quoting Roger Ford: Should have been around 125 ohms from those figures.Hmm...I make it over 7800 ohms. Have I missed something? JV Link to comment Share on other sites More sharing options...
Roger Ford Posted May 21, 2014 Share Posted May 21, 2014 Oops, I read it as 64mA. 640 microamps would be extremely low for an LED and any controlling circuitry. If correct, he's dropping 8V over the resistance (13V minus the 5V he's seeing at the socket) at a current of 0.00064A. From R = V/I we get 12500 ohms. Your 7800 is the effective resistance of the load - whatever's plugged into it - rather than the resistance of the faulty fuse. Link to comment Share on other sites More sharing options...
John Vine Posted May 21, 2014 Share Posted May 21, 2014 Yes, I was looking at the wrong voltage, so 12500 sounds much more like it. JV Link to comment Share on other sites More sharing options...
tbird Posted May 21, 2014 Share Posted May 21, 2014 Quoting Jonathan Kay: Can anyone do resistor colours in their head? Jonathan yep Buy british resistors or you get big values going wonky (Black Brown Red Orange Yellow Green Blue Violet Grey White) thats the polite one, the original mnemonic I was taught, while better, contains references to the foreign children of un married mothers, pre pubescent girls and sexual violence, so would no longer be considered PC Tim Link to comment Share on other sites More sharing options...
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