Thread: Ignition power that doesn't stop whilst starting

I thought it was just 'accessory' that dropped out while starting.

Not from the starting battery that I know of, the voltage drop of even a good battery is often enough to turn things off for a second or so, but if you have an aux battery that is not connected to the starter at start up it will keep charging

Originally Posted by Shakey

Are their any ignition switched power supplies under the dash that don't fluctuate/turn off for a second when you start the car?

Have something I want to charge that I don't want to power cycle when you turn over the engine.

Or splice in the yellow wire of connector C028 pin 5 or normally on a Td5 the relay pointed with red should not be there as it's the ignition relay for V8 engines and you have powerfull continuous ignition live where terminal 85 of the relay must fit, as said there will be a certain drop while cranking but with a good battery it must not drop under 11V but deffinitely not below 10V cos then there's a big chance to just crank and not start.

be aware to not use something else than small charger or low consumer there on the relay pin cos if it blows fuse F24 the engine will stop running....but if the engine and the charger are stopping together at least you'll know which fuse to check

Hi Shakey, where have you got your second battery located?

My second battery is next to the turbo and I have run a cable from that to under the steering wheel.

For clarification this is a little WiFi hotspot that I only want running when the car is on. The problem is it takes a little while to start so that blip whilst the engine starts means my tablet/etc. that use the WiFi to alert them to the fact they are in the car and to start the music take a while longer to register. First World Problem I know, but I'd like to try to fix it!

Depending on the current draw of the wifi thingy you may get away with a supercapacitor of the type used in high power car audio systems. Feed the capacitor from an ignition circuit with a diode and run the wifi off it.

It only pulls 1A over USB so that would work. I did wonder if a capacitor would work. Out of interest why would you need a diode too? Do capacitors feedback both ways?

Originally Posted by Shakey

Out of interest why would you need a diode too? Do capacitors feedback both ways?

You don't want the capacitor discharging straight back into the reduced voltage ignition circuit its connected to, do you? The diode only allows charge to flow from the ignition into the capacitor.