Head Unit Cutting Out When 12v Lights Switched On

[Themisto-Adrastea]

Hi,
I just replaced the cheap and nasty no-brand head unit in my van with a Sony MD unit and 10 CD Autochanger that I had lying around from an old car. Everything works fine, except when I turn on either of the two 12v lights directly underneath the cupboard in which I mounted the changer (the head unit is set into the panel directly above this cupboard), at which point the head unit loses power briefly, then reboots. Not the end of the world, but very annoying.
I can turn on any other 12v light in the van without problems, but switching either of these two on causes the problem. Additionally, if more than a few of the 12v lights are on, and one of the two offending lights are then turned on, then head unit will not successfully reboot, resulting in clicking and endless reboots. Turning the light off again lets it boot up.
Any ideas? I realise this question might be better suited to an In-Car Audio forum, but I thought I'd ask here first.
It seems like the head unit is drawing a lot more power than the original, and the 12v lights take too much juice out of the system. Strange that its only the two of them though.

 

[Thingy]

Are they sharing a common live feed, try running a feed direct to the battery, as a temporary thing just to see if it makes any difference.

 

[ProfJohnL]

The symptoms do read as if there is 12v wiring may not be up to carrying the total power needed by the lights and the radio. As thingy suggests a separate 12V feed directly to the radio may cure it but also if the lights at the front of the van are halogen bulbs. Filament bulbs have a characteristic of having a lower electrical resistance when the filament is cold, but as soon as you turn them on and they begin to glow their resistance rises. This effect causes a current spike which depending on the design of the bulb can be two to three times their hot working current. If the wiring feeding the bulbs is not thick enough, the wires own resistance will cause a momentary voltage drop when the light is turned on.

You could try replacing them with warm white LED bulbs. Almost as much light but only a tenth of the power used and don't have the current spike.

The other factor could be the Sony head unit is likely to need more current than the stock fitted radio, especially if it has the associated disc changer, so this may be drawing more current than the wiring installers allowed for. Worth checking the radios specs for minimum wire size etc

 

[Themisto-Adrastea]

Thank you Thingy and Prof.
I agree that running a separate feed from the battery sounds like the solution. Weird how it is only 2 out of 6 lights that cause it, with the other 4 having no effect whatsoever.
Anyway - I'm taking it away tomorrow for the weekend, so it can wait until next week.

 

[ProfJohnL]

When you have studied and worked with electrics and electronics and understand about current resistance and voltage drops, its not surprising.

 

[Thingy]

If you are going to wire straight from the battery, make sure you have a suitable inline fuse fitted. :cheer:

 

[johnandrew70]

Only problem with running a live feed direct from the battery is that you will have to make sure the head unit is switched off when the van is not in use,
I expect you had thought of this though.

 

[Dustydog]

Wire a separate earth for the radio.

The symptoms you describe could well be poor earthing on both radio and lights.

 

[bertieboy1]

What's a "head unit" why don't you say what it actually is instead of using these stupid fancy descriptions that don't really mean anything.

 

[Dustydog]

What's a "head unit" why don't you say what it actually is instead of using these stupid fancy descriptions that don't really mean anything.[/quot

I'm baffled?
So what should he have said?
A head unit is a head unit!

 

[Thingy]

Not sure what else you can call a head unit, except maybe a head unit :cheer:

 

[ProfJohnL]

Control Unit
Dash Unit
Car radio
may be even Head Unit?
Answers on a postcard........

 

[WoodlandsCamper]

Here's Wikipedia's definition.

 

[Thingy]

In my case then, the car very definitely has a head unit, there is a built in music server et al behind it.

which provides a unified hardware interface for the various components of an electronic media system

is a good a definition as I have seen.

 

[Gabsgrandad]

You're not alone Bertieboy I didn't know what a 'head unit' was either. Bet there were others too. (At least this old 'so & so' has learnt something!!)

 

[Themisto-Adrastea]

I got back yesterday from a weekend away at Newlands in Charmouth. Thanks for all the replies here (except Bertie's - if you didn't know what it was, you should have Googled it before mouthing off at me. Are you always that rude to people who use words or phrases you don't understand?).
I will investigate the earthing and 12v feed wiring this week.

 

[ProfJohnL]

Hello TA,
Sadly some people think that because this is a forum that uses nicknames, they can write things they wouldn't dream of saying face to face. Sorry you've been upset.

 

[Themisto-Adrastea]

Hi prof, thanks for that, but no problem here. I'm not upset, I just don't let people get away with speaking to me like that, whether in real life or on the net.
Anyway... I've assumed that when people have said to run a wire from battery, I can actually just go from the 12v fuse box which is much closer and much more convenient. Is that a fair assumption?

 

[Dustydog]

Hi TA
I hope you find the cause of the problem. Please tell us the results. It helps old dogs like me to understand what's gone wrong.

 

[Thingy]

I just don't let people get away with speaking to me like that, whether in real life or on the net.

Not married then I take it

Seriously, dont let little things like that bother you, very often they sound much worse than the context in which they are meant. Like you Im new to this forum, and to be honest, I have found them all to be a very welcoming bunch, much more than some of the other forums.

 

[Themisto-Adrastea]

Not married then I take it

Ha! I used to be!

I have found them all to be a very welcoming bunch, much more than some of the other forums.

I agree with this completely.