Great working tank circuit with backup bat.

**NightHunter** · 03-03-2004, 11:12 PM

Originally Posted by LESLIEx317537

The voltage is the same for both batts, so you will not need a voltage regulator.

You should place the diode right before the backup battery so the current doesn't flow backwards and try to crank the engine with the backup battery.

Now this was my great idea I came up with last night after thinking about this tank thingy for 1 week..............................

Since you only want the battery to charge when the PC is on, since we have no way of shutting off the charging cycle, you need the PC on to draw some juice away from the abttery do it doesn't overcharge.

Yo accomplish this, you basically wire a relay and hook it up to a molex so it connects the backup battery only when the PC is powered on and the 12 volt line on the molex is throwing out 12 volts.

Now this solves issues such as the accesory cuttingout during crank, the molex 12 wont cutoff during crank leaving teh relay connecting hte backup battery and wa la. No reboot. Well if I planned it right, I hope.

Does that make sense? I'm suprised no one ran the relay turn-on from the PC PS 12 volt Molex. I love my great ideas.

OK I tried this out and it works awsome, I put a relay on the accessory wire to cut the power from the battery to the inverter when the accessory wire is powered off and I put a second relay switched from the 12volt wire on the hard drive power plug to keep the back up bat from recieving power when the computer is not turned on. This should keep the Back up from not over charging since it only get charged while the computer is pulling volts. And if I forget to turn off the computer it will run off the backup until it is totally drained(which is ok since the backup is a NICd anyway). Should work with a rechargable lead acid battery as well. I found one a rat Shack for $28.00 today. 12v 5ah, great for this use.
Thanks again for the help.

**kreyzig** · 03-25-2004, 02:07 AM

Originally Posted by NightHunter

OK I tried this out and it works awsome, I put a relay on the accessory wire to cut the power from the battery to the inverter when the accessory wire is powered off and I put a second relay switched from the 12volt wire on the hard drive power plug to keep the back up bat from recieving power when the computer is not turned on. This should keep the Back up from not over charging since it only get charged while the computer is pulling volts. And if I forget to turn off the computer it will run off the backup until it is totally drained(which is ok since the backup is a NICd anyway). Should work with a rechargable lead acid battery as well. I found one a rat Shack for $28.00 today. 12v 5ah, great for this use.
Thanks again for the help.

You shouldn't fully discharged lead acid battery. That will kill the battery itself

http://support.radioshack.com/suppor...-ldac-main.htm

KOKO

**migel628** · 04-02-2004, 09:46 PM

Originally Posted by NightHunter

OK I tried this out and it works awsome, I put a relay on the accessory wire to cut the power from the battery to the inverter when the accessory wire is powered off and I put a second relay switched from the 12volt wire on the hard drive power plug to keep the back up bat from recieving power when the computer is not turned on. This should keep the Back up from not over charging since it only get charged while the computer is pulling volts. And if I forget to turn off the computer it will run off the backup until it is totally drained(which is ok since the backup is a NICd anyway). Should work with a rechargable lead acid battery as well. I found one a rat Shack for $28.00 today. 12v 5ah, great for this use.
Thanks again for the help.

Sounds great, but I'm having a hard time visualizing this. You wouldn't happen to have a schematic or something to go by? Thanks

**robiewp** · 04-03-2004, 01:05 AM

kreyzig, you were able to quote his post in your critique, but not able to read it? "(which is ok since the backup is a NICd anyway)"

That said, I have a similar setup with a regular car battery. Yes, if i discharge it all of the way it will harm the battery. Do i intend to discharge it all of the way? no. However, if and when I do forget to throw a switch and a battery ends up dead, better the tanker than the one that gets me home!

**kreyzig** · 04-03-2004, 01:44 AM

sorry, my bad

**Valhalla** · 04-04-2004, 02:23 PM

Originally Posted by migel628

Sounds great, but I'm having a hard time visualizing this. You wouldn't happen to have a schematic or something to go by? Thanks

Yeah, if you have something like that it would be great, I think I understand what you are saying but it would be great to get a visual.

**turbochris** · 04-29-2004, 10:51 PM

I've been thinking about these relay circuits. it seems it's really important to have the relay drop out when the starter engauges. I think I figured out a way to be sure this happens no matter where the relay gets it's power from, whether it's the ACC, IGN or anything else. Instead of connecting the relay coil negative wire to ground, connect it to the wire that goes fron the ignition switch to the starter solenoid.

The relay can't pass enough current to pull the starter solenoid in. The starter solenoid has very low resistance when compaired to the relay so it will be a good enough ground for the relay. Now when you actually start the car, the starter solenoid we're using for ground will jump from like 1 volt to battery voltage. At this point both leads to the relay coil are at battery voltage and the relay drops out.

Connect one relay coil lead to the starter solenoid, connect the other to IGN so the relay would only be on when the engine is normally running. This way the tank battery cannot discharge the main battery when the key is on ACC

Does this make any sense? What made me think of it is GM grounds the pull-in windings on some of their starters to the starter motor windings. When the solenoid pulls all the way in the point where it was grounded jumps upp t battery voltage and the pull-in windings ge no more power.

I know I know, stinkin know it all noobs.....