Motorbike GPS One Way Diode and Capacitor Recomendation Please.

[statesmanjeff]

Not sure to ost this one here or in GPS forums but this is more Electronics.
I have mounted an android auto head unit on my motorbike. It works a treat but does have an annoying issue that appears to be common with a lot of these cheaper chinese models. Every single time I start the bike it looses power and almost always requires me to pull over and reconnect the bluetooth to my phone and intercom. Annoying when you forgot to start the bike when you first get on and even more annoying if you stall your motor while riding. The battery is fine its just the way the bike directs all power to the starter.
Most of these devices just have a Positive and Negative ground wire connection (no accessorie wire) that you connect into your 12v switched ignition that then runs throug an inline transformer reducing it to 5V.
My current draw is apparently 12V 1A then reduced to 5V 2A. Id like to put a one way diode in place and a capacitor that would give me 5 seconds comfortably. A little more would be great but 5 would fix 99%.
Do I put it in the 12v line or the 5v reduced? Then what value diode and capacitor is recomended?

Thank you.

[wotnot]

What model bike?

[statesmanjeff]

BMW F800GS. It does have an accessories timeout feature of about 15 secs after the ignition is off but at motor start, allpower is directed to starter.

[wotnot]

Nice bike....and just what I was hoping for...(same thing in modern cars) ; accessories etc et_al are turned off during cranking, but KEY-ON always provides constant battery voltage to ECU/EFI electronics, even during cranking obviously (or no start possible). In cars, they use an ECU relay... and one can tap into the constant, switched 12v supply there...not sure what bimmer do ..I'd hedge a bet there's 12v on the diag plug =)

Your initial idea basically depends on how much power you need for how long ..you'd have to measure that (current draw of the unit once connected and ready to go) before you can ballpark a capacitor value.

[Uncle Fester]

Not sure to ost this one here or in GPS forums but this is more Electronics.
I have mounted an android auto head unit on my motorbike. It works a treat but does have an annoying issue that appears to be common with a lot of these cheaper chinese models. Every single time I start the bike it looses power and almost always requires me to pull over and reconnect the bluetooth to my phone and intercom. Annoying when you forgot to start the bike when you first get on and even more annoying if you stall your motor while riding. The battery is fine its just the way the bike directs all power to the starter.
Most of these devices just have a Positive and Negative ground wire connection (no accessorie wire) that you connect into your 12v switched ignition that then runs throug an inline transformer reducing it to 5V.
My current draw is apparently 12V 1A then reduced to 5V 2A. Id like to put a one way diode in place and a capacitor that would give me 5 seconds comfortably. A little more would be great but 5 would fix 99%.
Do I put it in the 12v line or the 5v reduced? Then what value diode and capacitor is recomended?

Thank you.

Must be on the 12V side because a capacitor can not hold the 5V constant while it discharges.
The 12V can drop to 7-8V, sometimes lower for the 5V step down regulator to still work but that depends on the design of the 5V regulator.

You would need around 0.5 F (yes Farad, not a typo) and a powerful diode to charge it back up, at least 10A and I would add a 1 Ohm 15W current limiting resistor on the cathode side.


You might not need to go down that path.
The DC is pulsating while it cranks.
Just filtering the '12V' with a smaller cap 4700µF and a 3A diode should keep a steady 7-8V while it cranks.

From this link it appears the diagnostic plug is always connected directly to the battery and like Wotnot says the accessories socket could be disabled by the ECU :


Connecting it directly to the ignition switch (where the cable marked green is) should work as it is a low power device but use an inline fuse with 2A slow blow time lag and you might not even need the filter cap.

[SS Dave]

My BMW K1300s has a 3 pin connector for the GPS navigation option that mounts just forward of the fuel cap that I use for my GPS tracker.
It has an Ignition power, Ground, VSS ( Vehicle Speed Signal)
The Ignition signal is BCM controlled and stays active while cranking and will remain on for around 2 minutes after switching off the bike.
I believe the BMW F800GS has the same connector.

It might be worth looking in to that

[GT250]

It's an old link, but it might help you out if it gives you a different way to look at your issue...