Battery based tank circuit (tested) - Page 13

Arathranar · 10-19-2004, 12:43 AM

Quote: Originally Posted by tna0601

Why cant you use the diode in-between the two batterys, The current will flow into the tank battery and will be blocked when starting the vehicle.

You could. But I want to prevent the PC draining the main battery so using the switched 12V achieves that. And it avoids the voltage spikes that occur during the crank.

Quote: Originally Posted by tna0601

Then use an old UPS to convert the 12v to 120 and use a standard psu for the computer and the perhips. You will also have 120v AC in the car for other various uses. The inverter in the UPS will filter out any noise and would also send windows the shutdown signal to windows.

You can also do that but it's inefficient and not what we're aiming for.

Ricky327 · 10-19-2004, 12:45 AM

Quote: Originally Posted by Arathranar

Why not? The alternator outputs 13.8-14.5V whilst idlng or driving. The tank has to output that for up to 5s during the crank whilst nearly 100% charged

You never get that out of a tank, look at the graph on post #156

Assuming the current is 10-15A then you are draining around 2CA out of your 7.2Ah tank battery.

From the graph we can already say your tank is around 12.1V if it was 100% charged up when draining 10-15A. If you are dropping 1.75V then you are down to around 10.35V, thats well below the limit, your PC my not reboot but dont be to surprised if it crash.

At a 100% charge you are already out of spec.

That applies just as much to your setup as mine.

No, because I dont intend to pump the car 12V into the PC directly...thats something Ill never do. Inverter or DC/DC converter cuts out at around 10.5-11V. PC wont be happy when the voltage goes bellow 11.4V or when you go over 12.6V.

EDIT :

The graph shows a battery in perfect working order, in an ideal temperature, situations (its normal for a company to do so).

Use the battery a few months in a not so ideal environment then it be a different story.

Ricky327 · 10-19-2004, 12:51 AM

Originally Posted by tna0601
Why cant you use the diode in-between the two batterys, The current will flow into the tank battery and will be blocked when starting the vehicle.

You could. But I want to prevent the PC draining the main battery so using the switched 12V achieves that. And it avoids the voltage spikes that occur during the crank.

Isnt that what you been trying to achieve?, the diagram you posted? so do we have a switch now or what?

Update your diagram please you are confusing poeple

Arathranar · 10-19-2004, 01:01 AM

Isnt that what you been trying to achieve?, the diagram you posted? so do we have a switch now or what?
Update your diagram please you are confusing poeple

Now it's my turn to tell you to read my diagram

It says "switched + car". I've also repeatedly said that using the switched +12V was my intent.

Arathranar · 10-19-2004, 01:06 AM

Assuming the current is 10-15A then you are draining around 2CA out of your 7.2Ah tank battery.

I still don't understand what CA means. Makes it hard to interpret those graphs. I'd love an explanation.

No, because I dont intend to pump the car 12V into the PC directly...thats something Ill never do. Inverter or DC/DC converter cuts out at around 10.5-11V.

What DC/DC converter are you using?

Ricky327 · 10-19-2004, 01:14 AM

It says "switched + car". I've also repeatedly said that using the switched +12V was my intent.

Ok sorry my mistake

But from your diagram you said your main battery supply only 11.8V when the car is not running and 13.8-14.5V when running?

In that case the PC is only gonna get a good supply when the car is running? therefore you wont be able to use your PC unless the car is running?

A 1CA current on a 7.2Ah = 7.2A and a 2CA = 2x7.2A = 14.4A

You can say "C" stand for the Ah rating of the battery. If you would have to charge a battery of 7.2Ah safely then you go by 1/10 CA = 0.72A MAX.

Ricky327 · 10-19-2004, 01:16 AM

What DC/DC converter are you using?

Im using a TARGUS car-laptop adaptor...12V > 19 V converter.

Arathranar · 10-19-2004, 01:24 AM

In that case the PC is only gonna get a good supply when the car is running? therefore you wont be able to use your PC unless the car is running?

Yes. But that doesn't bother me. I'll be hooking up an additional circuit to cause the PC to switch of when the car is switched off and on when the car is switched on.

Im using a TARGUS car-laptop adaptor...12V > 19 V converter.

Hmm. Some of the dc-dc psu's accept 19V as input. How expensive/efficient is that guy?

Ricky327 · 10-19-2004, 01:26 AM

Hmm. Some of the dc-dc psu's accept 19V as input. How expensive/efficient is that guy?

Nono, its a 12V to 19V stepup converter.

Im off to bed, its late man

Arathranar · 10-19-2004, 01:30 AM

Quote: Originally Posted by Ricky327

Hmm. Some of the dc-dc psu's accept 19V as input. How expensive/efficient is that guy?
Nono, its a 12V to 19V stepup converter.
Im off to bed, its late man

I know. Some of the dc-dc psu's would then take than 19v and produce 12v regulated output. Not any with a high enough wattage to handle my mATX board but it could be an interesting approach to voltage regulation for people that don't have such heavy power requirements as me.

Arathranar · 10-19-2004, 01:38 AM

A 1CA current on a 7.2Ah = 7.2A and a 2CA = 2x7.2A = 14.4A

Ok, so that means the main battery (about 50Ah I believe?) will have roughly 0.3CA output (15A out of 50Ah). That from the graph means an initial discharge voltage of ~12.8V (although I'm a little disturbed the 0.4CA and 0.2CA lines cross...). My 7.2AH will be outputting 2CA which gives us about 12.2V from the same graph. So if I adjust the number of diodes (I was intending to do this by trial an error), a reasonable number is probably just 2 to give an additional 0.5V drop and a range of 11.7V (tank) to 12.3V (main battery). Ah, except the alternator is the one providing that 13.8-14.5V I see when driving. Hmm.

I know people have been fully successful with this setup, but I'm not sure if anyone's done it with such a power hungry setup. That could be the achilles heel of my plan. Outputting 2.7A to drive a VIA m/b is way different from 15A to drive a full mATX system.

Still, when my DC-DC psu arrives, and I get chance to wire up the new fused circuit I need in the car, we'll see what we'll see. Any suggestions on how to make it so I can easily adjust where in my series of diodes I connect the PC voltage to? I don't want to be repeatedly re-soldering as I gradually remove diodes to up the voltage

Ricky327 · 10-19-2004, 01:42 AM

Yes. But that doesn't bother me. I'll be hooking up an additional circuit to cause the PC to switch of when the car is switched off and on when the car is switched on.

But still how are you able to survive a crank if the tank is only supplying 12.1V at 10-15A load? and 10.35V into the motherboard. The point of the tank is that the PC must be running while the car is trying to start (cranking)

So to wrap it up, you have 10.35V from the tank into the PC.
You have 11.8v-1.75V = 10.05V (car not running) from the main battery into the PC

Then you may have 8V from the main battery as the car cranks.

In any situation you are only gonna get 10.35V into the PC from the tank...unless the car is already running...but again the point of the tank is to survive a crank (car not running yet)

Ricky327 · 10-19-2004, 01:44 AM

Quote: Originally Posted by Arathranar

Still, when my DC-DC psu arrives, and I get chance to wire up the new fused circuit I need in the car, we'll see what we'll see

Yup, you do that, let us know the results with your project

Arathranar · 10-19-2004, 01:44 AM

Quote: Originally Posted by justICE

You can test it easily enough. Buy me .

Note: the picture depicted in that link is NOT the right resistor. You should put 2 of the 10W 1-ohm resistors in series between the terminals.

If I'm trying to imitate an upto 200W load (may be as low as 100W) at ~12V, then I need a resistor of only ~0.8 Ohm don't I? But it needs to be capable of getting rid of up to the 200W. I suspect I'll burn myself if I try and do that a resistor - it'll make a nice 0.2kW bar heater inside my car.

Arathranar · 10-19-2004, 01:51 AM

Quote: Originally Posted by Ricky327

Yup, you do that, let us know the results with your project

Go to bed already!