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Maintaining 12V While Engine Is Starting?

zoomzoom

By zoomzoom,
in Car Audio & Electrical

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zoomzoom Mentor

zoomzoom

Posted
Posted

I have a stepper boost gauge which is powered by an accessory circuit. When starting the engine, the gauge switches off and on again. The problem is I think the gauge has a self zeroing startup procedure, ie it centres the dial to 0 boost/vac. When it turns on the second time I believe its zeroing to about 0.1 bar boost (that is what it ends up on when turning the engine off, back to accessory position without disrupting power to the gauge)

Could a large capacitor be used to keep the gauge running in the short time while cranking the engine?

89CAL Grand Master

89CAL

Posted
Posted

Think you have another problem. It should be designed to get around this.

The fact is that the starter draws alot of current, which drops your voltage. Dont think a Capacitor setup would be efficent or cheap enough for keeping a boot gauge on. Have you sourced power from a strange spot?

If your battery is dropping to much further then 9V during start then you might have another issue. And to me, 9V shoudl keep the gauge on.

89CAL Grand Master

89CAL

Posted
Posted

FYI, I have an electronic boost gauge, electronic oil pressure gauge and an electronic Wideband gauge. All 3 of them dont drop out during engine cranking. I'd say the power source for your gauge is either from a bad spot, there is a problem with the earth, or the car is drawing to much power during cranking.

Like I said the gauges are (or should be) made to get around situations like engine cranking. I'd find it very unusual for the gauge to require a capacitor/reserve power supply to keep it powered during cranking

Sinista32 Grand Master

Sinista32

Posted
Posted (edited)

Maybe a silly question but does it matter?

what is critical or failure if the vehicles voltage to the meters turns off during cranking? especially if it is ancillary (eg: radio)

defi gauges do this in the evo VIII, i'm not sure what the issue or seriousness is

in the evo they power up when the key is turned, then off whilst cranking and then on when running.

so my questions are out of interest

Edited by Sinista32
  • 1 year later...
zoomzoom Mentor

zoomzoom

Posted
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Posted

So just to revisit this, I had further problems with the gauge and voltage drop during cranking. Perhaps my battery is getting close to replacement time (voltage drops to 10 around cranking).

Anyhow I thought I would test out some of these Chinese supercapacitors that have been popping up on ebay at a decent price.

Basically I connected 6x 2.7v 6F caps in series to produce a 16.2v 1F cap bank. These were about the size of AA batteries.

Coupled with a 6 amp diode, I produced a circuit similar to this: http://en.wikipedia.org/wiki/Reservoir_capacitor

Only difference being the source is DC in a car, not AC.

It works a treat, and not only smooths out the voltage supplied to any connected load, it also helps to reduce transient voltage drops.

This is being used to power my innovate wideband controller (3 amp draw on start due to the heater), plus my gauge. I would probably use larger capacitors if I made one again.

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