Thread: Battery based tank circuit (tested)

Originally Posted by Ricky327

I dont think your setup is bad....Im just trying to avoid the relay

I don't necessarily think it isn't bad. Why would you want to avoid a relay when the car will deal with things for you?

does this help understanding?
drawing not to scale.

You didnt just draw that did you

Anyway, I had thought about this setup before, it will work very well infact as long as your backup battery is big. The problem I thought I might have is when someone put the key on "ignition" position. The PC is now running off the backup battery, if the car is not started within a few minutes in my case (0.8Ah battery) the backup would have drained then. On cranking Ill get a reboot

Yes relay is good but its also bad. Ill try to get away from relay if I can help it.


What make your setup good is theres no voltage loss

I reused the relay diagram from helping out night(hunter?), but yes, MS PAINT ALL THE WAY!

You're going to have to do a lot of work to get away from relays. I count over 30 of them in my car, stock.

I just put another battery in the car. For me the tank is really that- If i want to leave my car comp on while I go into the grocery store and not have to worry about a dead battery, I can. Also, no more of this "ooh ooh look at me I can't survive crank" bull ****

Originally Posted by robiewp

I don't necessarily think it isn't bad. Why would you want to avoid a relay when the car will deal with things for you?

does this help understanding?
drawing not to scale.

Yes I understand.(I think)but the tank battery needs to be charged and the carputer needs current in the milliseconds the relay changes.And where do you put the ITPS?
The second battery cannot deliver to the ITPS,because then the carputer will only see 10,5 volt and the car battery cannot deliver direct to the puter
because then it will see 13,5 -14,2 volt when the car is driving.
So the car's battery must deliver to a ITPS when driving and direct to the puter when idle and heavy consumption,the second must deliver direct to the puter but must get 13,5 volt from the car via a resistor for charging Right

ITPS? whatcha smokin? I didn't spend $40+ on a glorified linear regulator (just joshing! don't bite my head off!). As for where I would put one if i had one? I'd plug the power (not switching) part into the tank. Atleast in my experience, except when pretty close to dead, a car battery gives pretty close to 13.8v (including the one in my tank, as i've tested).

Charging? the battery is charging any time the car is turned on. It's basically in parallel with the regular battery any time the key is in the accessory position.

This is working for me. I don't know if it will work for others, but if you have the space for an additional battery, I think this is a better solution than the big capacitor idea. As for how it compares to ricky's design, I have no idea. All i know is its simple.

robiewp,

Sorry I got alittle confused at first...my brain hurts

I didnt realised you connected the backup battery on the (87) of the relay. Which means your backup is connected to the main only when theres a +12V on the relay?

So your backup only get charged up when the "accessory" is on. The accessory do get cut out when cranking, I dont know if this is the case for all cars. So in turn your backup get disconnected when cranking...It obviously worked for you but I had this fear were the starter motor may have already start draining the battery before it disconnect the second battery. This happen in split second but I kept thinking it may be enough to reboot some setup.

The diode based tank allow the backup to be charged at all time ignition on or off.

Maybe I am wrong but I am afraid to send unregulated 13,5 volt to the screen and the motherboard (the PW-70 does not regulate the 12 volt).
About the "big capacitor" idea,i understand that you needs 50 Fa for it to work,that is a little to expensive and too big for me
I like the PW-70,it is not too expensive and small,it fits on the motherboard;but if you have to add battery(with or without relays and diode and capacitors,it gets bigger)
The sproggy is the same price (with the free parts)but it is not small.
The best would be a Opus but they are expensive and big.

Originally Posted by Ricky327

robiewp,

Sorry I got alittle confused at first...my brain hurts

I didnt realised you connected the backup battery on the (87) of the relay. Which means your backup is connected to the main only when theres a +12V on the relay?

So your backup only get charged up when the "accessory" is on. The accessory do get cut out when cranking, I dont know if this is the case for all cars. So in turn your backup get disconnected when cranking...It obviously worked for you but I had this fear were the starter motor may have already start draining the battery before it disconnect the second battery. This happen in split second but I kept thinking it may be enough to reboot some setup.

The diode based tank allow the backup to be charged at all time ignition on or off.

The diode design sounds cool. My concern would have been if i had substantially discharged my tank, I'd suck the juice required to bring the batteries to equilibrium out of the main battery, and not be able to crank. This obviously isn't a problem with a small battery.

My accessory does indeed cut out while cranking. I had another solution devised before I realized this: quite simply, conect the tank to pin 87a, and 86 to the starter wire. This might eleviate some concerns about the relay not switching quickly enough- the relay for the starter is probably just as slow

One thing i had been considering was some means to only have the tank connected to the main battery when the car is running. The accessory method can't guarentee this. I don't know enough about the ignition harness, but it seems to me, that connecting 86 on the relay to ignition 1 or 2 (and the tank to 87) might accomplish this.... but then you'd need a seccond relay to kill the bridge durring crank.

I might later throw in something to bridge the circuit durring crank if my computer equiptment is hard switched off (by relay)... that way if my main battery is too low to start I could use the tank.

Sproggy is a good design if it is really true it can survive the crank. The 1F is very expensive and bulky. I dont know if the sproggy has been redesigned or not, but I just looked at a modified sproggy and I beleive it can survive a crank.

Surving a crank solution doesnt have to be that big. On the experiment I just tried im using a 12V 0.8Ah...its probably the smallest lead acid you can buy, its about the size of a big match box. Some even use a full car battery...no where I can put that.

I dont know what robiewp is using but I cant use OPUS, SPROGGY, ITPS or something like that as my setup is based on a laptop motherboard.