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Almost-always-on 12v sockets
Published by alexwhittemore
05-17-2013
Almost-always-on 12v sockets

I have a fairly convoluted phone setup. The details are at the bottom of the post, but long story short, I want my cigarette lighter 12v outlets to turn on when I unlock the car, rather than when I turn the car ON.

The culprit is the Terminal system in the car. 'Terminal' roughly means 'voltage node.' Here's the list of those that matter here:

Terminal 30:
Effectively always on. Terminal 30 is the actual battery cable coming from the trunk (the one protected by the explosive disconnect). If the battery is attached and the car hasn't had an accident, terminal 30 is on.
Terminal 30g:
On when the car is "awake." This is controlled by a relay in the Junction Box. It turns on when the car is 'woken up' by a number of events, such as unlocking, CA fob becoming present, opening a door (if the car is unlocked but asleep), etc. It turns off when the car "goes to sleep," which is code-able but by default 30m after last waking action (so 30m after you lock the car, 30m after you close the door and walk away, etc). On euro-spec cars with a TCU, it's 60 minutes. On US-spec cars with a TCU, the TCU is actually attached straight to Terminal 30 (always on), so the timeout is still 30m.
Terminal 15:
This is on when the car is on. If you've clicked your start button and the gauge cluster is lit up. Note that it doesn't necessarily matter if your ENGINE is running. The car can be 'on' with or without that.
Typically, this is what the cigarette lighter sockets are running from.
Bonus: Terminal 30g-f:
Not really relevant to this mod, but this is basically a version of Terminal 30 that's always on UNLESS there's a fault condition. Namely, the fault condition is "if the IBS says there's just barely enough power to start the engine."
Basically, Terminal 30 is stuff that's CRITICAL for functionality. For example, your gauge cluster and the CAS have to work for you to get in the car and turn it on. On the other hand, comfort access isn't REQUIRED to get in the car, but it drains a fair amount of power. It's on 30g-f - if the battery is so low that any more drain would stop the car from starting, CA gets turned off, along with the other stuff on 30g-f.

For more on the terminals and which drive what components, I attached a PDF that contains most of this info.

So the challenge is: power the outlets from Terminal 30g instead of from Terminal 15. Challenge accepted!

The plan: Open up the fuse box. Splice the accessory-side of the outlet fuse into some empty socket connected to 30g.

Initially, I just cut up a donor fuse and soldered the leads of an external fuse holder to the two legs. This worked ideally, but was too loose - I felt like a hard turn or speed bump might pop it out. Loose electrical leads aren't good. Pictures below.



The solution was to get a pair of fuse taps. The internal construction is such that the output lead is fused to the far-side terminal via the top fuse slot. This is great - I'd just connect the two taps together, put 20A fuses in the top (the socket circuit is fused for 20A stock), and wire them in such that the live side of one is plugged into the socket circuit output, and the live side of the other is plugged into the terminal side of some unpopulated accessory running from T30g. Warning. These fuse taps are only rated for 10A, and I intend to fuse them at 20. I'm not too worried, but if you regularly use your sockets at full-capacity, I'd be careful about this. Also, in this configuration, I'm diverting ALL of the potential 20A OFF the T15 relay and ONTO the T30g relay - it'd be smarter to use T30g to drive a relay that supplies power to the sockets from T30 or something, but again, screw it, it's probably fine. But if you blow a T30g relay, this is probably why (luckily, it's replaceable).

Note in the picture there's one 20A fuse and one 15A - unfortunately, I don't happen to have a 20A fuse handy (the one in there is the original), so the sockets are fused at 15A for now. Note that ALL sockets (well, at least the armrest and under-dash) are on this one fuse, so the 20A is total across all sockets.


Well, I don't have a CD changer and don't plan to get one, and that accessory happens to be on terminal 30g, so that's a perfect donor slot. Initially, I tried to use the empty TCU fuse slot. Well, this is when I found out that US-spec TCUs are always on (connected to T30). Something good to keep in mind if you ever want to hard wire an always-on accessory. Although I'd probably use T30g-f if I were going to wire something always-on (like maybe a dash cam). Reason being, any accessory that's always-on is going to significantly impact the 22mA constant draw the car expects. And the car throws a parasitic draw code at 80mA draw in sleep, which is a really easy limit to hit. At least connected to 30g-f, you won't ever drain the battery to the point the car won't start.


Note that, in all the fuse slots, one side is the gray plastic housing, and one side is a colored insert. The gray housing is the terminal side (so always live), and the colored side is the accessory side (unpowered with no fuse present or if a fuse is broken).

And the final setup!


Next mod is to switch my trunk outlet based on the 30g signal, which is present on the amplifier remote wire.


The phone setup:
As many are aware, the stock USB port doesn't supply enough power to charge a modern phone. I'm actually not sure if the MULF CAN supply enough power, but the resistance across the 3-4m of cable is bad enough that it doesn't matter, phones can't pull the power.

My solution to this problem is that I've got a cable which injects 5V off a normal USB cigarette lighter adapter. This handles the majority of the current load of a charging phone and pulls the line voltage up. Unfortunately, the overall charging current is still limited by the USB negotiation with the MULF (since I'm injecting only power and the USB data lines are still going to the MULF, the phone can only draw 500mA without explicitly asking the MULF for 1A, and the MULF doesn't respond that it can support such a request. No way around that without a software change in the MULF.) So I'm limited at 500mA, but that'll still charge the phone and support continuous usage of all phone features, so I'm happy.

The problem that arises, and that is solved by this mod, is that the cigarette lighter adapter is powered from Terminal 15, and the MULF is powered by Terminal 30g. The mulf turns on when I wake the car up (unlock or open the door or etc etc), which means as soon as I get in, it's on. So I plug in my phone, and it starts talking to the MULF. But at this point, since I haven't turned the car on, there's no extra power from the cigarette lighter adapter, so the phone says it can't charge (and is drawing very little current). Even once I turn the car on and the extra power comes on, the phone doesn't know that it's now available, so without unplugging and replugging it, it'll just charge slowly so as to drain.

With this mod, the lighter sockets come up at the same time as the MULF - as soon as I plug the phone in, car on or not, there's plenty of power. No more 'not charging,' and it's totally reversible.
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  #1  
By jwzimm on 07-25-2013, 10:36 AM
I know this is a little old but I am thinking of doing this for my dash cam. I am trying to figure out how these add-a-circuit taps work. I am concerned that your method will make the entire Terminal 15 bus hot with the power from the tap on the Terminal 30g bus. Your first method seems like the right way to do this properly and ensure that you don't energize the entire Terminal 15 bus with the tap.
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  #2  
By alexwhittemore on 07-25-2013, 11:34 AM
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The taps only tap ONE SIDE of the connection, with a fuse between the tapped pin and the wire. The first and second methods are electrically equivalent in that T30 is supplied to the ACCESSORY side of the lighter socket fuse, BUT NOT the T15 side.
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  #3  
By jwzimm on 07-25-2013, 04:12 PM
I get it now. So it does become important which direction you put the add-a-circuit plug in as well. This could be quite useful. I will have to experiment. I have been looking for a way to extend the length of time my dash cam stays on while I am parked.
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  #4  
By alexwhittemore on 07-25-2013, 05:56 PM
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Yep! And actually, they don't really make it clear, but orientation of the tap sort of always matters: if you have the tap in backwards, current for the accessory flows first through the original accessory fuse (bottom of the tap) THEN through the new accessory fuse, then out the wire. It's easy enough to get right: the bus side of the fuse tap is opposite the wire (so current flows through the top fuse), and the bus side in the fuse holder will be powered, while the accessory side won't be. In the BMW fuse box, where fuses are ganged up in two rows, the bus side is the outside of the row and the accessory side is inside. Note above, the outside of the CD changer is connected to the inside of the lighter socket fuse.
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  #5  
By jwzimm on 07-26-2013, 10:14 PM
well I did the mod just now. I got an error on the dash though. When I put the key in the check control comes out fine though. I did manage to get it to show up in the check control briefly and it said something about an electrical error but then cleared. I am letting the car go to sleep and see if it comes back now.
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  #6  
By alexwhittemore on 07-26-2013, 10:17 PM
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This will often cause a current draw error: basically the IBS senses that there's more current draw than should exist given the current power state. But that shouldn't ever come up in CC.
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  #7  
By jwzimm on 07-26-2013, 11:17 PM
Oh well. I let the car go to sleep and it seems to be working as expected now. I haven't seen the error since. I think the system needed to recalibrate to the new draw. At least I hope that is the case. If it throws more errors I will just undo it.

Thanks again for the help.
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  #8  
By maxhole on 12-10-2013, 04:39 PM
This post was an absolute life saver, I had spent ages trying to work out how to get a proper remote turn on for my amp, and didn't want to take the headunit out again. At first I was annoyed that it didn't work but after reading over it again i realised it mattered which way round the fuse tap goes!! Now I have awesome 30g remote turn on for my amp, thanks!
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  #9  
By alexwhittemore on 12-10-2013, 04:44 PM
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Quote:
Originally Posted by maxhole View Post
This post was an absolute life saver, I had spent ages trying to work out how to get a proper remote turn on for my amp, and didn't want to take the headunit out again. At first I was annoyed that it didn't work but after reading over it again i realised it mattered which way round the fuse tap goes!! Now I have awesome 30g remote turn on for my amp, thanks!
Hehe, 'welcome!

re: remote turn on: what's the deal with the remote out from the head unit, and why didn't you use it? I noticed the timing doesn't seem to line up precisely with when the head unit is visibly 'on' or 'off', but what's the deal?
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  #10  
By maxhole on 12-11-2013, 03:10 AM
Quote:
Originally Posted by alexwhittemore View Post
Hehe, 'welcome!

re: remote turn on: what's the deal with the remote out from the head unit, and why didn't you use it? I noticed the timing doesn't seem to line up precisely with when the head unit is visibly 'on' or 'off', but what's the deal?
Basically my amp has auto sensing turn on, so initially I tested with that and seemed to work so I didn't bother looking into how to get a remote signal. Then I coded to hifi so speaker outs became line level, and the auto sensing just didn't work well at all. So I never tested using the connection from the headunit, I think I read it was for powering the antenna so I assumed it would work but I didn't want the hassle of taking the headunit out again so I tried this way using 30g terminal which seems to be just what I need, ideally it would turn off when locking the car rather than 30 mins after, but there doesn't seem to be a terminal that does that? I could code the time delay I imagine? But this is fine as it is really
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  #11  
By alexwhittemore on 12-11-2013, 03:16 AM
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Ahh gotcha. I don't think you CAN code the delay, no (though I haven't looked into it extensively). The reason I ask is that I'm going to need an on-with-head unit-only remote line soon, and I'd really like to avoid having to mod one into the HU.
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  #12  
By maxhole on 12-11-2013, 06:26 AM
Yeah sorry I never looked into that much, why don't you want to just use terminal 30g?
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  #13  
By alexwhittemore on 12-11-2013, 03:27 PM
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The idea is that I'm working on a Nexus 7 install. The USB rom on there has provisions for a sort of hardwired setup, whereby the Nexus will be in host mode but still draw power. One config option is, if you remove power, the Nexus will go into deep sleep based on the assumption that this corresponds to you turning the car off. This way, the Nexus doesn't drain the car's battery, and in deep sleep it'll last a solid 5-10 days before its own charge is out.

The problem is terminal 30G turns off a full half hour after the car shuts down. There are many reasons that coding this differently, even if possible, would be non-ideal.

What ends up happening is, you unlock the car, 30G comes up, nexus turns on, got your nav/music/whatever, all is happy. Get to your destination, turn off the car and walk away: the nexus is still on, glowing like a neon "steal me" sign, and if nothing else it's draining both batteries unnecessarily. Ideally, it'd enter deep sleep as soon as the radio shuts off.

Listening to when my sub amp pops in and out of power, though, I think that the remote line from the headunit doesn't EXACTLY follow its own power state, for whatever reason.

If that's the case, I'm going to have to do something very silly like open the headunit and MAKE a remote signal sourced from maybe the panel LEDs or something. That'd be really non-ideal.
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