Subject: Re: unreliable DC 12v to regulated DC 12v
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Date: Sat, 21 Dec 2002 13:17:37 GMT
NNTP-Posting-Date: Sat, 21 Dec 2002 13:17:37 GMT
Organization: AT&T Worldnet
Purchase a motorcycle battery and put it closer to the computer.
Then isolate it so it won't discharge when starting the car. You
could use a diode to isolate it, but the .7 voltage drop across the diode
would prevent it from fully charging with the alternator. You could build a
circuit to close a relay when the alternator voltage is above 12.8 or 13.2
or ?. This would keep you motorcycle battery charged but not allow it to
discharge while starting the car.
If I skipped to many details email me and I'll further explain.
"cvt" wrote in message
> The plan is to regulate unreliable 12v input (from the car battery
> directly, wired to the back of the car)
> Currently, I am getting 0.9 volts drop over the distance.
> With the engine running I have 13.6 at battery, and 12.5 at boot
> with engine off, I have 12.6v at battery, 11.5v at boot
> when cranking I have 11.8v at battery, 9.5v at boot
> Now, this is to run a computer.
> I have built a nice 60watt power supply, regulating all the voltages,
> *IF* I have a clean 12v comming in (12v is note regulated, but direct)
> so simply, I am trying to regulate 12v to 12v, which AFAIK can't be done
> without stepping up the voltage, which then comes into a power wasting
> system, which may be necessary, but I was wanting it to be as economic
> as possible.
> having the 12v rail between 11.5 and 12.5 in my books will not hurt, but
> much below 11.4 i feel is too low, and the computer will crash/lock
> up/reboot, or be damaged by the spike to 12.5 when the engine starts.
> I don't think running a 1,000,000 farad car audio cap would be any good,
> because if I am at 11.5v already, its not going to be enough to hold the
> voltage acceptable during the long time cranking.
> If I had a battery switching tecnique, I'd want a SLA 12v in the boot
> with it, bt will it safely handle the power the system is drawing?
> So thats my dilemna... any ideas?
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