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Cranking Voltage Drop
Posted: January 8th, 2010, 4:18 pm
by pillowmeto
Does anyone know what the voltage drop of the battery is during starter operation (engine cranking)? I want to build a circuit for power regulation of some electronics and need to know my low end voltage. I use a Gel Cell battery, 16-22 amp hours, like most other drivers.
My car, engine, and just about everything else is apart at the moment so I can not test it myself.
Re: Cranking Voltage Drop
Posted: January 10th, 2010, 5:01 pm
by Martinracing98
That is a hard question. Among other things at work we build electronics that are used on diesel generators. We design the power supplies to ride through a momentary drop to 0 volts for about 20 milliseconds. Then a return to 6 volts, before slowly increasing to 24 volts. We design the power supply to be able to ride through a long duration if not continuous at 6 volts. We do not require the power supply to initially power up until 10 volts.
Re: Cranking Voltage Drop
Posted: January 11th, 2010, 10:10 am
by FV80
Matt,
I don't know the exact voltage drop, but I can guess that it might go as low as 1 or 2 volts under "less than ideal" situations. I would also guess that the 'normal' drop would be to something around 6-7 volts - good, charged battery, good no drag starter, etc. I had a similar problem in my car with the video voltage source. My solution was to simply put a set of AA batteries in the circuit isolated by diodes such that the AA's provided 12 volts to the subject circuits if the car 12V wasn't available. When the car battery is at 12v or higher, then IT provides the operating current. It's worked for me for a couple of years. I just change out the AA's about once a year.
Steve
Re: Cranking Voltage Drop
Posted: January 11th, 2010, 2:24 pm
by brian
Steve, your such a smarty. I use a separate circuit for the data acq. and turn it on after the engine is started. I know some systems reboot if the voltage varies, my Racepak does not.
Re: Cranking Voltage Drop
Posted: January 11th, 2010, 5:24 pm
by FV80
Yeah - but I can turn mine on either before OR after the engine is started
. Comes in handy when I end up sitting on the grid for 20 minutes past the 'five'.
I run my data acq, radio, and video off of it.
Steve
Re: Cranking Voltage Drop
Posted: January 11th, 2010, 9:41 pm
by pillowmeto
I need a bit more time to boot up as I am planning to run a PC in the car (a very small one with no moving parts). It should boot up and go straight to dash mode with no user input but it could take a minute or two. I would prefer that my dash turns on before the green flag.
This set up costs less than a normal dash and allows me to do a whole lot more.