12v +7.5v +5v power supply

**kramdra** · 09-15-2007, 10:47 PM

Hi this is my first post here.

I am puttng a camera/DVR and a lcd in my car and have a few things to work out for the power supply which I am designing myself. For the recorder I am using a sumvision zengo/250gb hdd. LCD screen is from a sony psone using composite.

Firstly it will use about 30W when everything is switched on, though more like 10-20w most of the time. Id like to leave this on 24/7 so obviously I will need a bigger battery - the one I have now is 25A/H and only lasts 3 hours when radio is on/engine off.

Here is my plan so far:

Get another 50-75A/h battery (one big or several in parallel), possibly from the breakers or anywhere cheap.

I need 12v/2A and 2A/5v for the recoder including hdd.
12v/0.5A for the camer
7.5v/1A for the screen.

I would like to use switching regulators to do this but I have not used them before. Any ideas where to start?

If I used linear regulators, then I would have atleast 19.5W of waste, whilst the battery is off. This is a bit too much since Id like to run this 24hours.

12v is also a problem. Whilst there is little wasted when the engine is off, I will have problems if the battery drops low, and also the only low dropout linear ones I can find have a 1A limit.

And for 7.5v I am using a LM317T with a few extra protection components. This will only power the LCD which I doubt will ever be used for short times and not whilst the engine is running (maybe for parking if i get a second camera)

thanks

**2k1Toaster** · 09-16-2007, 12:09 AM

Originally Posted by kramdra

Hi this is my first post here.

I am puttng a camera/DVR and a lcd in my car and have a few things to work out for the power supply which I am designing myself. For the recorder I am using a sumvision zengo/250gb hdd. LCD screen is from a sony psone using composite.

Firstly it will use about 30W when everything is switched on, though more like 10-20w most of the time. Id like to leave this on 24/7 so obviously I will need a bigger battery - the one I have now is 25A/H and only lasts 3 hours when radio is on/engine off.

Here is my plan so far:

Get another 50-75A/h battery (one big or several in parallel), possibly from the breakers or anywhere cheap.

I need 12v/2A and 2A/5v for the recoder including hdd.
12v/0.5A for the camer
7.5v/1A for the screen.

I would like to use switching regulators to do this but I have not used them before. Any ideas where to start?

If I used linear regulators, then I would have atleast 19.5W of waste, whilst the battery is off. This is a bit too much since Id like to run this 24hours.

12v is also a problem. Whilst there is little wasted when the engine is off, I will have problems if the battery drops low, and also the only low dropout linear ones I can find have a 1A limit.

And for 7.5v I am using a LM317T with a few extra protection components. This will only power the LCD which I doubt will ever be used for short times and not whilst the engine is running (maybe for parking if i get a second camera)

thanks

How are you planning on converting the video feed of the camcorder to write to the harddrive?

As for your battery, dont cheap out. Get a deepcell. Optima Yellowtops are ideal for this because it is made for long time power. RedTops are for extra boost while cranking or when needed, yellow's are used for longevity. If you get a regular car battery, it will fail fast. You will be constantly draining it low, and charging then draining low. The thing is every time it drains beyond a certain point, it starts to harm the actual battery plates so when it charges it never gets as full. So then it will get lower the next time you drain it (because it doesnt have as much charge as it did). Then again it will discharge more so get hurt more, and it is sort of an exponential failing. Get a marine battery a.k.a. deep cell.

**kramdra** · 09-16-2007, 06:49 AM

Im not

the zengo enclosure has AV in, so it can record from composite.

For the battery, I was planning to get several larger ones, so the discharge wont be so deep - this must be far cheaper than buying special new batterys -normal new batterys cost enough

So with this on 24hours, 2A on a 50Ah battery it will last one day but if I use 100Ah or 150Ah then it wont get touched, though 150Ah may be a little ott (and maybe need some extra thought as to if the alterntor/charger can handle it).