Subject: Re: unreliable DC 12v to regulated DC 12v
Date: Sat, 21 Dec 2002 13:01:14 -0800
X-Mailer: Mozilla 4.78 [en] (Win98; U)
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
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
when cranking I have 11.8v at battery, 9.5v at
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
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?
Sounds like you built a "nice" power supply
what it needs to do. Do a google search for
AN9312.pdf for some
enlightning but scary information.
Building a supply that regulates whether the input
is above or below
the output without a transformer is doable, but
rarely worth the
The best solution is to use a 120V computer and a
12V to 120VAC converter.
You won't like the thought of this initially, but
you'll really appreciate
the flexibility when you want to add/modify the
system in the future...
and you will modify it.
You can get more efficient with one supply. All
you have to do is duplicate
all the functionality of a PC supply, but switch
the primary from 300ish VDC
Unless you need to run the thing for hours and
hours with the engine off, you'll
never miss the efficiency lost by a 12V to 120VAC
converter. You'd gain more
by starting with a laptop that doesn't draw 60W.
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