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Reply With Quoteno mather what you do you aint gonna get away with that voltage drop.
True. But I'm still far from convinced the resistor is better than just a diode.
Here's the circuit I'm going to try:
Look at the top diode, its connected to the main battery and its supplying to the PC...is that correct?
Look at the bottom diode, its connected to the tank battery and also supplying to the PC...is that correct also?
So now tell me when is the time there will be ZERO volt into the PC? The answer is when both battery are dead.
Havent you noticed its exactly the same circuit as post #1 only with a relay added in...
Argg Im going around in the circle, this remind me of the CAP vs BAT
no mather what you do you aint gonna get away with that voltage drop.
True. But I'm still far from convinced the resistor is better than just a diode.
Here's the circuit I'm going to try:
Progress: 80% - Permanent install left.
Motion LS800 Tablet PC and dock.
Vista, Bu-535 GPS, RoadRunner, MPT2006.
you are right. I repeatedly viewed the "box" around the relay as just that. It's too similar to standard notation.Originally Posted by Ricky327
Progress: 80% - Permanent install left.
Motion LS800 Tablet PC and dock.
Vista, Bu-535 GPS, RoadRunner, MPT2006.
By all means try it and let us know how it goes
Thank you and goodnite
No. This is a crank survival circuit, not intended to run the PC for any significant length of time. So the output of a 5.1Ah tank should be pretty stable for that short time as it won't discharge much in the 5 seconds it supplies power (hence my different emphasis on charging requirements). In addition, I want to avoid over voltage into the PC. ~14V into the +12V line is way out of spec. So I need someway to drop the car alternator voltage down a few notches. I'll be driving an AMD micro Atx m/b so getting that +12V Near spec is a requirement. The 13.8-14.5V fluctuation I see when driving could be too much even if I drop it to 11.8-12.5V. I'm hoping the diode and tank battery combo will also help reduce that fluctuation a little but I suspect not.However, I'm considering adding a number of diodes to drop the tank battery voltage to nearer 12V as all the DC-DC psu's do not regulate this (bar the Opus).
Are you kidding?
Progress: 80% - Permanent install left.
Motion LS800 Tablet PC and dock.
Vista, Bu-535 GPS, RoadRunner, MPT2006.
Dangerous circuit
A few more details would be nice. Why is it dangerous?
Progress: 80% - Permanent install left.
Motion LS800 Tablet PC and dock.
Vista, Bu-535 GPS, RoadRunner, MPT2006.
Maybe dangerous is an innapropriate word. It will be risky for your components assuming you are not going to regulate that power, which I believe is your intention. Either side of the 0.7V swing of your "regulated" alternator is going to cause 1 problem or another. On the low side you will starve your tank. On the high side you will destroy your components.
Spikes could be a problem
I'll be either using the switched 12V (off during crank) or using a relay to achieve the same effect using the switched & unswitched 12V. So spikes during crank will not be an issue.
I'll actually have a bunch of diodes between the tank and the PC psu to drop the voltage closed to the +12V it needs. I found a schottky diode last night with a typical voltage drop of only 0.25V at 20A. I'll be using one of those before the tank and 6 to 7 after the tank. That should take the voltage down from the 13.8-14.5V I see when driving down to 11.8-12.5V which should be close enough to spec for my AMD mAtx m/b to cope with (we'll see - it's a cheap m/b!). There'll also be an in-line fuse between the tank and the PC for obvious reasons.
Are there spikes during driving? If so, then there is indeed risk to my PC but I'm still game to try it. Hmm. Maybe I could hook up a suitable zener diode to limit the voltage my psu will see.
Progress: 80% - Permanent install left.
Motion LS800 Tablet PC and dock.
Vista, Bu-535 GPS, RoadRunner, MPT2006.
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