Thread: Anyone want to help me with the tank battery

I hate using big *** diodes because of the heat and voltage drop. What would be the drawbacks of this idea? Just use a relay that only switches from car batt to tank batt during crank, then have a diode and resistor from ignition to tank for charging only when running, and maybe a cap before the PSU so it survives the relay switching? I sure I'm missing something important, but what is it?

I wish I could come up with some sort of answers too. I guess I am holding off until i get my optima wired in the trunk. Right now i just have it in there for when my main battery dies (diehard...yeah right). It has come in handy a few times, actually quite a few times.

Anyhow I have a batter from and APC UPS that i want to use as my tank battery. It is small and would fit in my glove box next to the PSU so.

If you all figure out this tank thing please post a how to so i can be cool like you all

Curiosity

Your idea can work if I picture it correctly from your descriptions. Basically the relay will switch over from main to backup battery when you crank?

As you are already aware the relay switching from main to backup can have problem. That split second the relay switching over may cause your PC to reboot or crash. True a capacitor will help the situations but then thats just making things complicated...a big capacitor is not cheap thought, they are quite bulky. I cant see it not working but the solutions is not cheap.



UPDATE :

I do agree with the zero voltage drop concept, as you said it is ideal. I have posted a zero voltage drop circuit before...basically its based on diodes as well as relay switching over from main to battery as you crank.

The diodes are there so the PSU doesnt loose the supply completely as the relay switches over. The diodes keep the voltage into the PSU at full amount at any time (less the 0.3-0.7V drop of course). Once the relay switches over then thats when theres no voltage drop at all since it shorts the diode.

As you can see the diodes are only at work for split second...so hardly any heat is generated. The resistor is placed that way so full amount of charging voltage always enter the tank battery...as well as it serve as a current limit.

I have to post all over again as I couldnt find the zero voltage drop tank circuit I posted months and months ago.

Ricky I don't want to run two batteries and I'm willing to try your set up and test it out on my carputer.

Im not too sure what you meant but you do still need an extra battery...well a tank battery anyway.


Give me a few minutes Ill be posting some new ideas based on zero drop tank circuit.

Originally Posted by Ricky327

Ricky I don't want to run two batteries and I'm willing to try your set up and test it out on my carputer.

Im not too sure what you meant but you do still need an extra battery...well a tank battery anyway.


Give me a few minutes Ill be posting some new ideas based on zero drop tank circuit.

Well this shows how confused I really am. I thought the design in your other post was without a second battery. I truly need help. Ok based on that I now I figure I need a small battery(tank battery) with a diode and cap in between the starter battery and tank battery. Don't know what sizes or part numbers though and I don't even know if that's right or not.

Hey Ricky if you hit the quote button in the person's post that you want to quote it'll copy and paste for you and also allow you to reply. Don't know if you knew that or not.

Ricky, what ideas? That's perfect!

Originally Posted by falconey

Well this shows how confused I really am. I thought the design in your other post was without a second battery. I truly need help. Ok based on that I now I figure I need a small battery(tank battery) with a diode and cap in between the starter battery and tank battery. Don't know what sizes or part numbers though and I don't even know if that's right or not.

Hey Ricky if you hit the quote button in the person's post that you want to quote it'll copy and paste for you and also allow you to reply. Don't know if you knew that or not.

Yes I did know how to "QUOTE" just too lazy I guess

Anyway...one thing Ill never do is use a capacitor in the circuit. They are just too bulky, expensive and never guaranteed to work...some do claim to work with keypower and sproggy but not on inverters. If you want to use them then go ahead but Ill rather use an SLA battery, they are cheap, small, easy to find, and do work for sure.

Anyway heres some more tank ideas for poeple who want to explore :

The tank battery get disconnected by the relay when you crank. The relay switch is always connecting the main battery to the tank battery. As soon as the starter comes on the main is disconnected and therefore leaving only the tank to supply to the PC.

The problem is that a standard relay may not disconnect the main battery due to heavy load from the starter...the voltage may have gone too low and the relay is not able to disconnect.

But as you can see the main battery is always connected to the tank battery, only when starting it disconnect. This always charge up the tank battery so you can be sure it will survive the crank.


The zero voltage drop tank circuit I posted is probably better to use. Ill see it more being robust than any other ideas I have come up with. I do admit I havent tested it at all but Im sure it should be fine in any configurations.

Up to you what you guys want to use...I think I have gave more than enough info whats good and bad about the design.

If you see I missed something and want to improved on it please do so with a new diagram. After all we are after a reliable design that can work with others.


Robbiew is using a circuit something like that. I think his one work slightly different? it only connect the main battery when the ACC is on? When the starter is on the ACC goes off and therefore disconnecting the main battery?

...I cant remember now as the circuit is now gone. I think robbie is the best person to ask about this.


Argg theres so many ways to do it...just play with it and see what suits you best. Good luck and let us know how it goes

Originally Posted by Superduck

Why can't you just use a solenoid to isolate the second battery?
Run it off a Hot In Run wire from the fuse panel or the radio power wire.

Wouldn't it do everything you need, with a quarter the difficulty?


Kris

Sorry I missed your post...would be nice if you can post a diagram of your idea. I know there lots of poeple with relays idea and have claimed they have worked for them. But it is hard to undertand whats going on without a diagram or some full explanations.

I know for some reason most poeple dont like the idea of a relay, I personally would do anything to avoid them but if relay is the only way then I guess that is the only way. I see most commercial circuit do tend to use diodes and theres reason for it...cost and reliablity I guess. But then we are back to the heat and voltage drop problems.

I still like the first one, but can see the advantages of the second like running it before you start the car or after. I think both would do well with the cheap shutdown controller mentioned about a week ago too. The one with a relay held closed by both ACC and the PCs 12V. Well, or an ITPS. Either one to keep it from draining when not in use.