Engine starter / HU capacitor mod

[CARRisma]

In some cars, such as mine, when I start the engine, ACC power is cut to the HU. So, if I am sitting in the car with the HU on and engine off, when I then start the engine, power is briefly interrupted to the HU. Sometimes this can cause issues with Android. It can also restart the boot sequence if the HU hadn't fully booted. So I have been considering this mod...

Since the ignition wire gives a very weak signal to the HU, using a diode and a capacitor at the ignition entry of the HU should prevent the reset without any Xposed based module.
It works for my mirror with compass.

(the diode has one end connected to the ignition wire; the capacitor has one end connected to ground; the other two ends are connected to the ignition entry of the HU - the red wire(?))
Just use a so called solid/polymer capacitor (not with liquid electrolyte!) which works below freezing temperatures - or otherwise rated up to -40 degrees Celsius.

                   HU IGN 
IGN o-------i>|-------X------i]-------o GND

Any (Sillicium) diode would do, finding the appropriate capacitor value, only by testing. If it's too big, then the normal powering off is delayed objectionably, while if too small, it won't delay enough (to cover for those few seconds while the engine starter is working). You would also need a capacitor that still works at below freezing temperatures (solid, tantalum).
Just connect the diode between your ACC/IGN car (or CAN bus adapter) wire and the HU IGN entry, and the capacitor between the same HU entry and ground.

I reccommend against tantalum caps unless you really know what you are doing as tantalum caps failure mode is flames. :fingers-crossed:

Solid polymer organic caps, though harder to find, or low temp rated electrolytics (they exist) are what i would go with.

Read my lips:

Connect a diode (Si) between the car's ACC wire and the HU's ACC entry. If the HU does not start then reverse the diode.
Connect a capacitor between the HU's ACC entry and ground. Choose a capacitor able to function below freezing temperatures. If capacitance is too big, the HU will remain on too long after stopping the car engine. Conversely, if it's too small, the starter will reset the HU as before. Start with a 100uF capacitor and find the optimal value for your car.

If unhappy with this hardware solution, delve into the Xposed framework based software solutions (mtc... xposed... something).

680uF & 1,000uF capacitors have been suggested.

But then I saw mention of some prebuilt timer PCBs and there were some links to listings on eBay USA. Has anyone got any links to tried and tested devices sold through UK based sellers that are relatively simple for a non-electronics expert to configure?

 

[Gona80]

What are your exact problems with your HU?

I had the same issues with those cheap USB plugs for the cigarette lighter.
5V output is not stable during power on, the connected usb harddrive does a reset.

I took a look at the switched 12V supply. In my case when powering on the switched power supply is pulled down to 0V for about 2seconds.
That's nothing you can solve with a capacitor. Step 1 was to use a diode with resitor capacitor combination to switch a relay.
Step 2 was to use a different 5V supply which is stable down to 6V.

 

[CARRisma]

It's not a major problem. I just don't like power being interrupted when starting the engine. This can interrupt the boot process, causing a slight delay. It can also cause an error message when booted, some sort of system app / service doesn't like it. Also, I don't think it's good for device longevity having its power suddenly cut and reapplied in quick succession. So I wanna fit a capacitor to keep the ACC power live to the HU when starting the engine.

 

[CARRisma]

I'm looking at electrolytic capacitors on eBay and it seems like a mission getting a 12v capacitor. Would a 10v or 16v capacitor work? Which would be best?

 

[solmer]

I'm looking at electrolytic capacitors on eBay and it seems like a mission getting a 12v capacitor. Would a 10v or 16v capacitor work? Which would be best?

Hi CARRisma, just use a capacitor rated above 12v, 16v would be fine, keep in mind that xxV referes to the maximun volta. the capacitor can handle, the other value ( µF, F...) is the "charge" it can hold. Very important, if you use electrolytic capacitor pay attention to the polarity (- to GND and + to POSITIVE), otherwhise it could EXPLODE
A picture (video) is worth a thousand words
https://www.youtube.com/watch?v=-KX5HIE7Ddk

 

[TT_Vert]

I'm going to have to do this too. Every time I start my car w/ the unit already booted up it starts to shut down and it says exchange service has crashed or something similar. Are you just using one cap and without a diode? Could you tell me what you go with?

Dave

 

[CARRisma]

Yes, that's the problem I have, some sort of Google service crashes. I plan to use a diode too.

 

[mike.s]

I'm looking at electrolytic capacitors on eBay and it seems like a mission getting a 12v capacitor. Would a 10v or 16v capacitor work? Which would be best?

You don't want a 12 v one - "12 volts" in a car is actually closer to 13.5 v. I'd get a 25 v one. You can use one which is rated for more voltage within reason (e.g. don't go for a 250 v one), it's just that as the voltage rating increases so does the size and cost.

 

[TT_Vert]

so are you guys going to use a 1 Farad 16v cap? Unless my math is wrong but that is HUGE.

Dave

 

[CARRisma]

Pass, I haven't got that far yet and electronics isn't my strong point.

 

[TT_Vert]

Or based on size constraints i'm thinking maybe wiring three 5.5V 1.5F in series to get me to about 16.5V .5F. That'd give me about a second and a half of capacity down to 10V. You guys think that'd be acceptable for this instance?

 

[pounce]

Maybe try one of these:

http://www.amazon.com/gp/product/B00PD65UGA

http://www.3rdbrakeflasher.com/timer-c-68/multifunctional-3v24v-time-delay-relay-timer-p-192.html

 

[TT_Vert]

That will work for the times when I start the car right away but for the times the accessory is turned on then the car is started it wouldn't. I just need to retain 10-13Vdc for a few seconds while cranking voltage dips.

Dave



For packaging reasons I think I may go with this instead. Three of these will put me at 16.2V and 1.68F and I'd have ~5 seconds of runtime in a manageable package about 1.25" square. Problem is I have to buy 100 of these things although their 100qty is cheaper than most 5qty. Opinions?

Or maybe these as they're a bit cheaper and smaller

 

[pounce]

That will work for the times when I start the car right away but for the times the accessory is turned on then the car is started it wouldn't. I just need to retain 10-13Vdc for a few seconds while cranking voltage dips.

Dave

Is that a response to the timing I posted? If so this timer is programmable so if you want it to smooth out a drop in acc it will do that. You simply set its delay longer that you expect the drop for the cranking. Obviously, you can also use it for longer delays if you want your unit to be powered for a period of time after you turn off the car. Both short and long delays will smooth out your issue.

 

[TT_Vert]

I can't always predect the delay between acc on and crank to be honest. With that I just checked w/ my DVOM and the acc. goes dead on crank so that is my culprit, not so much a minor voltage drop but a complete drop.

 

[mike.s]

The ignition wire is only a signal, power is drawn from a different wire. Maybe a couple of mA? So, a few mF might do.

 

[TT_Vert]

You're right. I thought it was more than a signal. it is only drawing 1ma. Excellent, looks like a 35v 1000μF should do nicely.

 

[pounce]

I can't always predect the delay between acc on and crank to be honest. With that I just checked w/ my DVOM and the acc. goes dead on crank so that is my culprit, not so much a minor voltage drop but a complete drop.

I think perhaps you misunderstand how this works. If you configure the timer delay for 30 seconds it solves your problem. If you configure it for 10 seconds it probably solves your problem. You don't need to know specifically how long because if you set it at something like 30 and your cranking lasts 3 seconds it still works because the cut of acc triggers the timer and the power stays on for 30 seconds. 3 seconds later the power turns on and the timer stops because you have power again.

 

[TT_Vert]

Thanks, I'll look further into this.
Dave

 

[TT_Vert]

Went ahead and used a 470μF cap today w/ a 1A rectifier diode and it works great. W/O the diode i only got about 1/2 a second of capacity. with the diode I get over 7 seconds. It seems the HU will stay on when the acc. is all the way down to ~6.5v which surprised me.