24Volt Adjustable Time Delay Circuit Needed

[Mad Professor]

Good Day All.

I think this might be over kill for a pic, as I am sure a timer like the 555 would be able to do what I am after, but it's been well over 10 years since I last used 555 chips.

I have posted over on allaboutcircuits.

I am trying to build a power shutdown circuit for a friend.

This circuit is going to be used in a vehicle, but it not going to be connected to anything important.

The problem he is having is that audio/video system does not always fully shutdown (turnoff), when it gets stuck like this it pulls aprox 1.5amps.

If the vehicle is used eveyday it is not a problem, but if the vehicle is sat still 2 or 3 days, the battery is to flat to start.

When the system does shutdown (turnoff) it only pulls aprox 0.10-0.15amps.

The vehicle in question runs on a 24volt system, compaired to a 12volt system.

The vehicle is fitted with a master battery kill box that will remove all power from the vehicle apart from the alarm system, it has a remote kill wire that just needs to be grounded to trigger the system.

So I need a way to kill all the power to the audio/video system, after a preset time, once the vehicle has been turned off.

I am now thinking if I should stick with somthing like a 555 timer, or use a Picaxe 08.

I know when anyone say anything regarding using a Picaxe ect in a vehicle, all hell brakes lose.

I would like your thoughts and sugestions

Thanks for your time.

Best Regards.

 

[BeanieBots]

This circuit is going to be used in a vehicle, but it not going to be connected to anything important.

So, the electrical system isn't important then?
(you knew it was comming).

Robustness and immuity is key, so avoid a micro if possible.
If it's a simple time delay circuit, then probably a few trannys and caps is all that's required, maybe a relay as well.

555's are VERY sensitive to spikes on their power rails. Especially the sort of spikes found in vehicals, so you would need the same precautions as if you were to use a PICAXE.

 

[Dippy]

As BB says, robustness and immunity.
Plus; fail-safe and also not affecting the vehicles electrics or systems.

So, basically; a 24V load-detecting timed circuit-breaker??

IMHO, if you are careful and don't penny-pinch and select the best components and use a good design and sensible/safe construction, then this is a stroll in the park.
It's not 5 minutes work, but design-wise, easy.

(Remember, the breaking loose of hell, and general doom & gloom is because no-one knows exactly what someone will do or try. Skill/experience/competence levels are also unknown - and if it goes wrong then there can be a variety of consequences. In areas like this - and mains leccy- those bodgers should go and watch TV instead.)

 

[hippy]

The vehicle is fitted with a master battery kill box that will remove all power from the vehicle apart from the alarm system, it has a remote kill wire that just needs to be grounded to trigger the system.

Are you suggesting connecting your circuit to that ?

I'd strongly advise against that even if using a 555 or anything else. I'd want to know a lot more about the system and what this kill mechanism did before giving other advice.

I'd tend to think in terms of a relay which is only powered when the ignition switch is any position other than off and feed the A/V system through that, then it's guaranteed to be switched off when the ignition is.

If going for a timed turn-off, what would trigger that to start ?

 

[RexLan]

Wire it through the switch and condition it for your needed voltage .. that is what we did in the heavy equipment. If it is CAT with the weird ground just buy the little 24-12Vdc converter box.