Can It Be this SIMPLE?

[Melanie]

OK guys... I'm replicating this thread in Off-Topic...

We can continue posting on-topic about the technicalities of Mikes Barbie Dragster here...

Did you ever pencil together a circuit with a Time-Delay Relay Mike?

[Mike_Lynch]

Did you ever pencil together a circuit with a Time-Delay Relay Mike?

No, not yet Mel, other higher priorities took over, had to get some dental work done,
then the Water Heater in the house decided to start acting up so I had to attend to that.
I haven’t forgot about it though,

[peterdeco1]

Hi Everybody. Attached is a schematic of a 555 controlled PWM that drives a child's 12V ride on car. This isn't exactly the answer to this thread but maybe can give some ideas. The circuit limits the speed of a 100 RPM motor on the axle to about 25 RPM to keep the car slow. The 1uF cap on pin 5 gives a slight ramp-up delay for smooth starting. Making this cap smaller will eliminate the delay. It's important to use the FR602 fast recovery rectifier across the motor. A standard 6A rectifier will get hot but can be used on the B+ feed from the battery. I used a logic level FET to drive the motor but I'm sure a standard FET would work the same. The heatsink on the FET doesn't have to be big either - it's rated at about 40 amps with a very low on resistance. Hope this helps.

[Mike_Lynch]

Something like this perhaps? Shaded areas show what is new to the circuit.

[Melanie]

Yes that's good...

Very clever that you've ensured you can't go TURBO in Reverse - I had to think for a moment what you'd done there!

One observation, R3 isn't needed where you've drawn it, but it IS needed in series with R1, to ensure you don't ever apply full 12v non-current limited to the base of Q1, and that will also ensure a minimum time period regardless what position R1 is in.

You're going to get considerable sparking on the TURBO Relay contacts, so consider (a) a chunky Relay, and (b) some kind of surpression across the contacts (that's also a good idea on the GO Relay contacts) as the extra energy should be dissipated somewhere other than in wearing away the contacts.

Whoa No... there's a problem...

The Time-Delay Power for it's Relay (via the Parental Control Switch) is OK to be wired where it is (permanent 12v), but the Feed for R1 should be connected to Pin 1 of the GO Relay, so timing commences only AFTER the vehicle is already in motion. You're going to have to adjust your Zener and component values accordingly as that part is being fed from a 6v Supply.