Start/Stop + Aftermarket head unit = Hair Loss

Wuffles

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This was originally posted on another MB forum (I'm new to the marque and didn't know where best to ask this) but it didn't get much traffic - thought I'd give this forum a go - so apologies if you've read it before.

Hi, new person here, will try and convey all the info required but please bear with me.

Paid to have the head unit from my last vehicle fitted to my new (to me) estate w204. It’s a CarPlay and DAB unit and since I had it hanging about after I sold my last car, and I missed the functionality, I thought why not.

Looks great fitted, no problem there. First problem was the day after it was fitted I went out to the car and it had lost all the settings, took it back to the installers who informed me there’s a timed live in these cars and that’s why that was happening, goes off after 4 or 5 hours. No problem, they’ll run a permanent live from the battery to get around that.

Next problem, head unit isn't losing the settings any more, but does restart after every stop/start cycle in economy mode. Which as you can imagine, is pretty frustrating.

Harness adaptor company (Autoleads) recommend an in-line adaptor to force the head unit to ignore the drop in voltage during the engine crank.

Bought that, fitted it, makes no difference. Spoke to another person at Autoleads who basically said “why did you buy that adaptor, that’ll never work”. Consistency issues with the technical staff there.

Next up, a very much more expensive adaptor to hide the 12v drop during the engine crank, fitted that, makes no difference.

So to clarify, in the original configuration the headunit would stay live during the day even with ignition off keeping the settings, was even happy during the start/top eco mode cycle, but it would lose settings overnight (or after a good few hours of non use). So a permanent live solution was to run a live from the battery. Only then did the start (of the start/stop eco cycle) affect the head unit.

My question, and I can’t be the first person to ask it. Is there a permanent live in that head unit loom that doesn’t go to sleep, and also not affected by the engine start? It wasn’t affected when it was connected to the sleepy live you see.

My options.

- Find a real live that doesn't time out and is unaffected by the start/stop.
- Have the vehicle modified to alter the start/stop - some reading of this forum seems to suggest that's either possible or completely impossible, I've yet to make my mind up.
- The adaptor lead is supposed to mask drops up to 7v, and the Sony head unit is particularly sensitive to the voltage drop. Perhaps I have basically fitted a very expensive battery tester that is pointing out my battery is on the way out :)

Thanks for reading, hope that all makes sense.
 

wongl

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From your description, it seems that a permanent live have been taken directly from the battery, is this correct? If so, the installer has by-passed the complex circuitry involving the Aux Battery/Voltage Converter (in later models) provided by MB to combat the voltage drop during the ECO re-Start. A relay is used to switch to the Aux Battery during the ECO restart to avoid the electronics from suffering from a voltage drop.

If your head unit worked perfectly fine with the timed live, then it would suggest that your main battery is not the problem? You can always get your main battery tested for free to eliminate this from your troubleshooting list?
 
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Wuffles

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Exactly that. I’d much rather it was wired utilising the correct method... it’s just finding pointers for the correct method seem to be difficult.

Assuming there’s no non-timed live that can be had from the original wiring?

Really appreciate the interaction on this.
 
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Wuffles

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Thinking this through, should the permanent live not have been run from the auxiliary battery rather than the main, if the engine crank will force a head unit to restart?
 

wongl

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I suppose you could draw a permanent live from the Aux Battery, but I don't think this is necessary as there should be plenty of permanent live feeds from the fusebox. I would use a piggy-back fuse to tap into the fusebox for a webcam.
 
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Wuffles

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Right, I’m with you now.

Perhaps I should instruct the fitters to move the wire from the battery to a suitable live from the fuse box then. If anyone has a suitable recommended “start/stop” protected, non-timed live then that would actually be the ideal solution all round.
 

bob6600

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I wonder if they actually ran it from the battery directly or from another connection that comes from the battery? The battery will always give out 12v permanently, so not sure why it should drop during start/stop?
 
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Wuffles

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I wonder if they actually ran it from the battery directly or from another connection that comes from the battery? The battery will always give out 12v permanently, so not sure why it should drop during start/stop?

They certainly charged me for that. I’ve no reason to suspect they didn’t as that’s when this new problem occurred. Everyone I’ve spoken to seems to agree that the battery will drop its output during the crank so therefore expensive extras are required to mask that. Except they don’t, and may not even be required after all.
 

m80

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An after market HU requires 2 +ve 12v feeds.
One is the load feed, usually yellow at the HU and a heavier gauge wire. This will keep memory of settings and run the main current to the HU.
If this was being affected significantly so as to cause the HU to shut down I would expect you to also lose your settings.

T'other is signal to start, usually red at the HU. I will often pick this up from the front ciggy lighter.

From what I see of Carplay they are Chinese and the Chinese stuff is often fairly generic.
First to look for in the settings is an 'over run' option. This will cause the HU to continue playing even after the signal feed is interupted. Mine is set for 10 seconds I think.
So I turn off the ignition and the unit keeps playing.

All batteries will experience a dip in voltage while the starter is spinning. That could feasibly affect the red signal feed, to understand that measuring the voltage on that wire at engine start would be useful. But the above suggestion should overcome that effect.

The yellow load wire will experience a volt drop at all times as the HU can draw a significant current and cause that drop, a dip of battery voltage during start can only exaggerate that. Hence the thinking to pickup the supply from an independant(ish) aux battery.
I've no experience of aux batteries and their charging but would have concerns around the aux battery possibly being discharged faster than it may charge when the HU is under heavier load (hi volume).
 
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Wuffles

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It’s a Sony head unit, no such setting. It’s not a confusion with the ignition and permanent live unfortunately, I wish it were.
 

bob6600

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I wonder if a capacitor of some sort between the battery and the HU on the permanent feed will solve it? They used to be used on larger audio set ups where amplifiers/subwoofers would require a sustained voltage supply and would prevent voltage drops (HU dimming etc)
 
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Wuffles

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I wonder if a capacitor of some sort between the battery and the HU on the permanent feed will solve it? They used to be used on larger audio set ups where amplifiers/subwoofers would require a sustained voltage supply and would prevent voltage drops (HU dimming etc)

Two different brands of start/stop specific adaptors have been tried inline with this already, my guess is they are just posh capacitors in a nice package, neither have worked. One “protects” down to 7v, such is what made me think initially it could be the battery on its way out, dropping below that.

I still prefer the idea of a start/stop protected permanent live from the fuse box as a solution though.
 

wongl

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I wonder if they actually ran it from the battery directly or from another connection that comes from the battery? The battery will always give out 12v permanently, so not sure why it should drop during start/stop?
This may be a silly question to ask, but why run a wire to the battery instead of running a wire to the wiring loom of the factory fitted audio system? There will be a permanent live and switched live there and presumably would have been much closer and a lot less routing of the wire required.
 
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Wuffles

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This may be a silly question to ask, but why run a wire to the battery instead of running a wire to the wiring loom of the factory fitted audio system? There will be a permanent live and switched live there and presumably would have been much closer and a lot less routing of the wire required.

That’s how it was wired initially, but the permanent live in the original loom is actually a timed live. Doesn’t appear to affect the factory fit head unit but anything else resets when left for longer than 4 hours.
 

moodi

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This doesn't read right. Are you confident your fitters know what they are doing? It should be a simple as 1) using a perm live from the OEM headunit loom, 2) tapping (piggy back fuse) into a permanent live from the fuse box. Any car audio fitter should be able to find one in less than 10 minutes and only charge you once for a job done properly or 3) Wiring straight to the main boot battery should do it too but not my ideal choice given the effort in wiring and need to use an inline fuse.

1,2,3 in order of preference.
 
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Wuffles

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This doesn't read right. Are you confident your fitters know what they are doing? It should be a simple as 1) using a perm live from the OEM headunit loom, 2) tapping (piggy back fuse) into a permanent live from the fuse box. Any car audio fitter should be able to find one in less than 10 minutes and only charge you once for a job done properly or 3) Wiring straight to the main boot battery should do it too but not my ideal choice given the effort in wiring and need to use an inline fuse.

1,2,3 in order of preference.

This will be my fourth trip back to them, no, I’m not remotely confident they know what they’re doing.

Is 1 an option in this car? The live they thought they’d found on the first visit was a timed live (I’d never even heard of that as a thing). I would agree that 2 or 3 would be the best solution, but I don’t think they’re aware of the aux battery and the other clever stuff. They will be when I explain it to them. Is it my place to do that? Not really.

I’m gutted as I only paid a company to do this because I felt it was way beyond my pay grade. And here I am investigating the issue for them.
 

moodi

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Not too sure, but 2 or 3 should not be impacted by any of the other "clever stuff".

Live (12v) is live. You simply need the right source. If the live source is fine then it may be an issue with the headunit itself. But, again, simple to diagnose with only basic skills and a multimeter.

I would be asking for my money back and going elsewhere.
 
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Wuffles

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It’s definitely not the head unit. That’s acting exactly as it should be.

I feel like I’ll have to leave it with them to find a live that isn’t timed. By the time I’ve driven up there, it needs another few hours to show it’s not a permanent live. I suspect their knee jerk reaction was to give it a permanent live they knew they could trust, unaware of the relay and auxiliary battery.
 

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