Weird 12v TV, rear socket, extension lead type problem

[Plungetaker]

Hi everyone, I'll try and keep this short.

The rear cigarette lighter socket in my Bongo goes directly to the leisure battery. The 12v TV I've just bought runs fine when plugged into it. However, the power lead isn't long enough to reach the rear of the passenger seat (where I want to put it). To get round this, I bought a 3 metre extension socket but, when I plug this into the Bongo socket and then plug the TV socket into the extension, the TV switches itself off after about 5 seconds. It's almost as if the extra length of the extension is reducing the power that's reaching the TV

As you will probably gather by now, I have no idea when it comes to this kind thing so any ideas would be greatly appreciated.

Thanks

[peanutcrusher]

i might be wrong but in some cases the 12v supply as a delay relay on it which turns off after a set amount of time.
now i don't if this is the case on bongos, but i know it happens on over cars.
does it happen with the engine is running.

[Plungetaker]

No, it's fine when the engine's running.

Not quite sure what a delay relay is tbh? As I said it works fine off the 12v socket when plugged directly in without the extension lead and also without the keys in the ignition.

[peanutcrusher]

sounds to me there is a relay inline with the rear 12v supply to the battery, if it works fine with the engine running while plugged into rear supply.
I'm not total up on the wiring in a bongo but that is what its sounds like from what I've come across in over vehicles.
it more than likely all tired up with the split charger unit.

[rwill19050]

Your TV is switching off because it is getting a reduced voltage, caused by the resistance of the extension lead.
Your problem proved by the fact that with the engine running it stays on, I think

12 volt DC, resistance of cable, current drawn by load, ohms law = voltage drop in circuit.

You need to find an extension lead with 'thicker' cable.

[phedders]

rwill19050 hit the nail on the head.

Basically all wire has some resistance. Fewer, thinner strands and the resistance goes up. Corrosion and the resistance goes up. So on a long piece of thin wire there is quite a high resistance. Now this is ok when there is a very small current draw, but with a device that takes a fair bit of power.. there is a fair bit of power lost in the wire - it's basically acting as a heater. 12v DC is not good over distance.

(Sadly the wiring to most 'fag lighter' sockets is pitiful... First thing I did on Bongo was put some decent wiring round (good for 60A) with Neutrik Speakon connectors (good for 30A per pair of pins) which is supposedly overkill when taking say 5A for a fridge - except that I lose less in the wire... so it's more efficient as well as safer. And Speakons are solid reliable connectors - ciggie sockets were never meant to be used for continuous power supply... and it shows, they suck at it.)

[peanutcrusher]

hi

is this an easy thing to do, because it seems to be well worth doing as I'm looking at running a couple of things off the 12v supply e.g DVD, Nintendo DS. Or do you think i should look at running thing from the front 12v supply, which i don't want to do as it means having wires every where.

[phedders]

No it's not hard. Dont run too much off the front one - the wiring is pathetic. It was designed to heat up a coil for 20 seconds - nothing more.

Just get some flexible nice copper multistrand cable (proper speaker cable works very well) and some decent connectors.

I used speakons just because, well I'm love with them: http://en.wikipedia.org/wiki/Speakon_connector

(You could use the Neutriuk powercon which is very similar but keyed differently for safety - I preffered not to since I want to use powercon for connecting maing t'bongo one day too - a powercon is much neater connector than a 16A.

[Plungetaker]

Your TV is switching off because it is getting a reduced voltage, caused by the resistance of the extension lead.
Your problem proved by the fact that with the engine running it stays on, I think

12 volt DC, resistance of cable, current drawn by load, ohms law = voltage drop in circuit.

You need to find an extension lead with 'thicker' cable.

Yep, that makes total sense. Thanks rwill19050, I guess I should have asked the guy at Maplins as it doesn't look paricularly good quality for £5 .

Cheers for the help.