3 ms·

What was unsuccessful? I did this in a 2012 Miata with a pioneer head unit (capacitor on the Acc line so it discharges while cranking, which keeps the head unit

by lukevp 3y ago

What was unsuccessful? I did this in a 2012 Miata with a pioneer head unit (capacitor on the Acc line so it discharges while cranking, which keeps the head unit from turning off). Has a fused line directly to the battery for power. It’s not a huge capacitor either… like a 1500 uF or so? Just tried a couple diff cap values until it had around 5 secs of charge to hold the line open. It also makes it so the music doesn’t cut off immediately when the car is turned off as well… it gives it a few seconds to shut down. Feels more premium.

jakear 3y ago
Well if I knew for sure why it didn't work I'd fix it ;) I think it works better now than before, but it's hard to be sure because I neglected to measure the downtime before/after the modifications. Essentially I had a cap/diode to keep the acc line high during startup for the head unit, but it would still cut off due to the power supply voltage dropping to ~10-11V on the engine turning over (4.8L V8). So then I added a cap/diode to the power supply line, and it works "better...ish...maybe..." now: there are some times when it will stay on across startup, but not always. Perhaps with a larger cap on the PS line (I'm using ~2500uF), but it seemed to be discharging much faster than I'd expect, as if the diode wasn't doing it's thing and the line was effectively just at the system's general "+12V". I wondered if there was perhaps some way the power was escaping the diode/cap isolation and making it back into the main system, but I didn't have a good way to test or fix that (I previously diagnosed a similar issue to a bad diode, but this one seemed to measure fine). And besides all that, the amp is on a separate line in the way back of the car that I didn't bother to tear into because the head unit turns off in the critical stage anyways. So the head unit does stay on for a couple seconds after I turn if off completely, but since the amp is off it doesn't matter.

by lukevp 3y ago

jakear 3y ago

Well if I knew for sure why it didn't work I'd fix it ;) I think it works better now than before, but it's hard to be sure because I neglected to measure the downtime before/after the modifications. Essentially I had a cap/diode to keep the acc line high during startup for the head unit, but it would still cut off due to the power supply voltage dropping to ~10-11V on the engine turning over (4.8L V8). So then I added a cap/diode to the power supply line, and it works "better...ish...maybe..." now: there are some times when it will stay on across startup, but not always. Perhaps with a larger cap on the PS line (I'm using ~2500uF), but it seemed to be discharging much faster than I'd expect, as if the diode wasn't doing it's thing and the line was effectively just at the system's general "+12V". I wondered if there was perhaps some way the power was escaping the diode/cap isolation and making it back into the main system, but I didn't have a good way to test or fix that (I previously diagnosed a similar issue to a bad diode, but this one seemed to measure fine). And besides all that, the amp is on a separate line in the way back of the car that I didn't bother to tear into because the head unit turns off in the critical stage anyways. So the head unit does stay on for a couple seconds after I turn if off completely, but since the amp is off it doesn't matter.