[artuc]

Okay, at the moment I'm finding sometimes I have to charge my phone or laptop with the inverter or something while working, so I don't want to leave keys in the car to keep it charging while I'm away doing things. I'd rather just leave it in the glove box, under the seat or whatever plugged in and charging away with no keys attracting thieves.

I'm installing a few extra cigarette sockets and I was considering having them go through a relay.

Now in my head the setup I have is a switch on the dash or wherever, 2 positions ACC and TIMER.

In acc it acts normally, switches the relay on and off as it would with switching the key.

When flicked to timer if the acc is still on it will wait until it turn offs and continue charging for the time set.

If the acc was off anyway it will turn on for the set time and then turn back off.

Now a few other ideas adding to this was a potentiometer or rotary switch to dial in a time... a switch on style pot where the far left is off then you twist if right and it clicks on maybe. Only issue being showing what time is where otherwise it would be guesswork.

Anyway, I plan on just doing this with a small microcontroller like a picaxe or stamp, just wondering if anyone has done something similar before or there is such a thing as it doesn't seem that strange to me. Just don't want to sink a lot of time on something where I can get it off the shelf for a lot less.

I know I could just have a switch, switch it on when I leave the car and off when I get back, but I was thinking that if for some reason I can't get back to my car, am busy or sidetracked I wouldn't like to come back and have a flat battery. It happens pretty often where I'll go with another workmate and pick my car up later, so I thought a timer would be the best way to go.

Thoughts ?

This post has been edited by artuc: 29 July 2010 - 09:44 PM

[mdlr]

Hi. You could try to rat a timer from an old microwave or possibly try to get a low voltage cut out from a 4wd or auto parts or camping store. these cut outs are normally used for fridges and turn off at about 11.5 volts which is still enough to start a car. Cheers MD

[Big_Valven]

It would seem you wanted a monostable type timer - either digital or analogue, whatever floats your boat.

The monostable engages a relay from a fused battery run as long as the timer is running.

Then you have:

Attached File(s)

•  diag1.GIF (3.42K)
  Number of downloads: 2

[samhouston]

I just ran an extra couple of sockets of my second battery, charging a phone or something is never going to send it flat.

[artuc]

Big_Valven, on 29 July 2010 - 11:25 PM, said:

It would seem you wanted a monostable type timer - either digital or analogue, whatever floats your boat.

The monostable engages a relay from a fused battery run as long as the timer is running.

Then you have:

Cheers, that's sort of what I was thinking with a microcontroller, might see If I can find a decent timer. Used one recently at work and wasn't that impressed with it.

samhouston, on 30 July 2010 - 10:22 AM, said:

I just ran an extra couple of sockets of my second battery, charging a phone or something is never going to send it flat.

Don't have a 2nd battery and as an example we were recently running 2km range wireless routers off an inverter and they flattened the battery pretty well, in that case though we were borrowing an old UPS battery from the client and the inverter low voltage kicked in before they got too lfat. But that's why I'm thinking a timer or possible a low voltage cutout, a 2nd battery is ideally where I want to go in future but not right now as I can't afford it.

[chipa]

I would adapt Big_Valven's circuit to make it a bit more advanced. Use something like this timer kit along with the voltage switch both controlling some auto relay's in series - with the timer closer to the power source. This will allow the timer to trigger power when you want and the voltage switch to only allow it to take the battery down to a set voltage so you don't drain it.

Timer kit: http://www.jaycar.co...w.asp?ID=KA1732
Voltage switch: http://www.jaycar.co...w.asp?ID=KC5377

You could then use a relay to power the circuit from the standard lighter power when ACC/ON position is selected, or when no keys are in it can use direct power.

The timer kit uses a 555 timer so is easy to calculate how long it will run for. From memory the build notes with the timer kit comes with the details for the timing settings/values, you could then use a pot, measure certain points in the pot's rotation to have some 'known' times maked.

[ben1990]

find an old ford econovan, rip the glovebox out, and there is a small flasher relay looking thing that will have timer printed on it, its there to control the little green illumination light above the ignition switch, havnt cracked it open yet but no doubt its adjustable in some way. anyway it has 2 negative inputs from the front doors and rear doors, constant power, earth, and negative output to the light.....im sure you could rig it up to control a relay via negative switching or something....