I had just edited the upper post, while you anwsered.... I'm worried about the current spike while charging the caps...
Try RC filters- something like 10-100 ohms between each capacitor positive. Bypass the big caps with a 100nF ceramic or film each.
91 camaro huh? I was thinking of android head for the stereo in my 73 VW Super Beetle once the impending death of the Pioneer stereo comes. I just don't want to go away from something in the single DIN form factor.
About 8khz to 12khz.... connecting amplifier without ground loop isolator produces modem like beeps.
Ok will do.
In my case the factory radio was 1.5DIN.
I cannot tell you how much I regret going this path. This project caused million of tiny problems. I should had went for retro looking modern radio and call it a day.
True that, but still I cannot aford more than 100mA of sandby current, I'm at 60mA right now.
Capacitors seems to filter alot of the noise. Tommorow I will hit the store for 10x 4700uF 6.3v caps and see if noise will be reduced enough.
Yep... but this is way too much noise... I cant feed that back to ECU or even listen to it.
Look what other automotive devices do. They typically use DC-DC converters to generate lower rails. Power management ICs etc. Automotive power is also prone to dodgy stuff like shorts, voltage spikes, voltage drop outs, the ground getting hit by lightening or discharging static to the road/person etc. So some power management/protection and not just a janky linear regulator either may be needed.
The tablet battery should be your saving grace here, bizarre you would remove it. Using the USB port for powering it should provide some protection. Wire it directly to the automotive 12V via a linear regulator even with input and out stabilising caps ... I give the table about a month.
On stopping noise going in either direction, with or without capacitors or chokes you will need impedance. Some resistance. Of course the more resistance you use the more voltage you drop. How much current does the tablet need? You can use an RC filter capacitance multiplier and a pass transistor, but YMMV.
The tablet battery should be your saving grace here, bizarre you would remove it. Using the USB port for powering it should provide some protection. Wire it directly to the automotive 12V via a linear regulator even with input and out stabilising caps ... I give the table about a month.
On stopping noise going in either direction, with or without capacitors or chokes you will need impedance. Some resistance. Of course the more resistance you use the more voltage you drop. How much current does the tablet need? You can use an RC filter capacitance multiplier and a pass transistor, but YMMV.
On standby power and the battery.
I went down this route for the dashcam. I was using the car about 2.5 hours a day, and tried to work out how many additional batteries I needed to add to the glove box and what charge rate did I need to maintain the 100mA for the dashcam 24/7. It turned out to be too many or too high.
You can obviously get a battery minder circuit that will power it down when the battery voltage drops below 12V, but that will start to nucianse trip as you battery ages... and during cranking the engine.
The "modern" way to do this is with power management. Determine the conditions that exist which tell you it's not in use and power it down. Use a signal wire to have the other devices power down.
Literally the board Im working with, as soon as I stop playing music through it, the power consumption drops from 80mA to 1mA.
Also I'm sure you know if you are going to run your battery stuff 24/7 that the starter battery you have in it will NOT do that. It's not designed for it and will fail rapidly. You need to replace it with a deep cycle starter battery like a "marine start" battery designed to handle both long term drain and high cranking amps.
I went down this route for the dashcam. I was using the car about 2.5 hours a day, and tried to work out how many additional batteries I needed to add to the glove box and what charge rate did I need to maintain the 100mA for the dashcam 24/7. It turned out to be too many or too high.
You can obviously get a battery minder circuit that will power it down when the battery voltage drops below 12V, but that will start to nucianse trip as you battery ages... and during cranking the engine.
The "modern" way to do this is with power management. Determine the conditions that exist which tell you it's not in use and power it down. Use a signal wire to have the other devices power down.
Literally the board Im working with, as soon as I stop playing music through it, the power consumption drops from 80mA to 1mA.
Also I'm sure you know if you are going to run your battery stuff 24/7 that the starter battery you have in it will NOT do that. It's not designed for it and will fail rapidly. You need to replace it with a deep cycle starter battery like a "marine start" battery designed to handle both long term drain and high cranking amps.
I had removed battery for two reasons:
1. I don't want my car catch on fire because of chinesse battery on a hot day,
2. I cannot use usb for power as I'm using usb host mode.
The tablet needs up to 1.5A of current.
I want to keep the tablet on -screen off, because of the boot time and car is my second car "the oldie", it won't be used every day, I will probably disconnect the battery in winter, when it wont be driven at all.
Right now I have 60mA drain in standby, when I was working as a car electrician we had a rule of thumb up to 150mA was ok, I'm not concerned...
The alterative is to place a small connector in the wheel arch and slap a small solar panel on it when you park up.
A 100Ah brand new starter battery is good for about 20Ah before you start to damage it. It's Ah rating is more for it's current output requirements than it's capacity.
20Ah / 100mA = 200 hours.
As they get older they tend to provide less and less before they won't crank anymore. Once they won't crank and they die during cranking.... goes in the bin.
A 100Ah brand new starter battery is good for about 20Ah before you start to damage it. It's Ah rating is more for it's current output requirements than it's capacity.
20Ah / 100mA = 200 hours.
As they get older they tend to provide less and less before they won't crank anymore. Once they won't crank and they die during cranking.... goes in the bin.
I won't lie, I was thinking of some type of device you had mentioned before... something that would shut it off when voltage gets to lets say 12.30V...
I don't mind waiting for tablet to boot if I start the car after a few days... I just don't want it to turn off every time I leave the car.... like go from home (boot) > stop for cigarettes (boot) > go for coffe (boot again)... and so on.
I could also set this in the android.... lets say turn off after X hours of inactivity, this would leave only SMPS running.
You think 10x 4700uF 6.3v caps in parallel after smps would not provide enought filtering for tablet to last?
I don't mind waiting for tablet to boot if I start the car after a few days... I just don't want it to turn off every time I leave the car.... like go from home (boot) > stop for cigarettes (boot) > go for coffe (boot again)... and so on.
I could also set this in the android.... lets say turn off after X hours of inactivity, this would leave only SMPS running.
You think 10x 4700uF 6.3v caps in parallel after smps would not provide enought filtering for tablet to last?
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I would leave the battery in the tablet. Buy a cigarette lighter charger. Switch it with the engine (as they are by default). Enable power saving on the tablet such that if it's 5V is available it will power on automatically and stayed powered on. If it's 5V is not available it will power down when it's battery hit 50%.... if inactive.
The only noise you'll need to content with is that which comes from the USB charger. Maybe you already tried that.
The only noise you'll need to content with is that which comes from the USB charger. Maybe you already tried that.
When I worked out the DC Backup power box requirements the issue I had was the car could sit all weekend, pulling 100mA. If I was to charge it back up, I needed to at least add the 9 hours it would be outside work... in the 1 hour it took me to drive to work. That started to look like lithium cells and high charge rates.... in the glove box... no thanks.
This is the branded item for my dash cam. The price is a little sour, you could look for alternatives if that bothers you.
https://blackvueuk.co.uk/product/blackvue-power-magic-pro/
This is the branded item for my dash cam. The price is a little sour, you could look for alternatives if that bothers you.
https://blackvueuk.co.uk/product/blackvue-power-magic-pro/
I cannot charge the tablet thru usb, I'm using usb host mode for dab+ and flash drive. It cannot take charge while in host mode.
Also a really don't want a battery due to fire hazard on hot summer days.
Thrust me, I would do it otherwise, I know that battery is as cleanest power source as it can get.
This is good, might consider it. Must check what will be the draw with tablet of / just smps on first... can solve this with software if just the smps wont draw too much.
Are you powering straight in the battery terminals or through the USB port?
If the later you can choose by setting the resistors on D+D- lines to tell the tablet it's a meer 100mA USB port with no power delivery.
If the former, the only thing you can do is limit it's current, drop its voltage and force it into thinking the battery is running low. I wouldn't recommend that though 🙂 One does not play with lithium ion charge circuits or batterys.
If the later you can choose by setting the resistors on D+D- lines to tell the tablet it's a meer 100mA USB port with no power delivery.
If the former, the only thing you can do is limit it's current, drop its voltage and force it into thinking the battery is running low. I wouldn't recommend that though 🙂 One does not play with lithium ion charge circuits or batterys.