Battery based tank circuit (tested) - Page 16

Curiosity · 06-14-2006, 09:51 AM

Move the resistor up between the 2 diodes. The little silver band on the diodes should be on the right in that picture too.

kromec · 06-14-2006, 12:50 PM

thanks for the info "Curiosity"

Pandaman72 · 06-19-2006, 07:18 AM

I am confused. Is this safe / sensible / reliable?

Panda

DracoDan · 02-11-2007, 04:34 AM

Ok, This is my first post, so go gentle on me guys.

I've read through a majority of the posts, but I am still not sure if what I picture in my head will work.

I want to set up a tank circuit, do I HAVE to use a deep cycle or other lead based battery? I was hoping to use an old Li-ion laptop battery with ~12v output as my secondary battery, so if I totally turn the car off, the computer will stay running until I tell it to turn off, or possibly have something set up to tell it to initiate a shutdown like 45secs after the power is lost. I don't have anywhere to put an extra lead battery and I want this install (which is still in the pre-pre-pre-planning stages) to be absolutely invisible.

Thanks

edit: LOL, just noticed I'm reviving a very old thread here, just goes to show I *DID* search before asking a question.

Arathranar · 02-11-2007, 01:54 PM

You don't have to use a full car battery as the tank battery. The SLA I use is about 3x4x7" in size - maybe a bit bigger. Still chunky but it fits inside my dash.

You can probably use the Li-ion battery instead but it might end up developing memory over time and stop doing it's job.

My tank circuit and battery are still running just fine. I bought a shutdown controller to automate getting the PC to switch off after the car is turned off.

DracoDan · 02-11-2007, 03:01 PM

Quote: Originally Posted by Arathranar

You don't have to use a full car battery as the tank battery. The SLA I use is about 3x4x7" in size - maybe a bit bigger. Still chunky but it fits inside my dash.

You can probably use the Li-ion battery instead but it might end up developing memory over time and stop doing it's job.

My tank circuit and battery are still running just fine. I bought a shutdown controller to automate getting the PC to switch off after the car is turned off.

Thanks a lot for the tips man. Just a few more questions - How long can you run on your tank battery before the voltage drops below the minimum required for your PSU? I know with SLA batteries, as they go down in charge, they go down in voltage pretty quickly. Inversely, Li-ion batteries can still keep a solid voltage until they get really low. Also, what exactly do you mean by "develop memory" I tried to search on this, but naturally got about a billion false positives.

Thanks again,
Dan

Arathranar · 02-11-2007, 05:32 PM

The small battery I have could run the PC for 15 minutes max when it was new. It'll be less now. Maybe up to 10 minutes max as long as you don't do it regularly since it's slow to recharge.

Li-ion batteries don't like being recharged small amounts - it causes the start remembering a lower max-charge than they were originally. Over time the power they can store gets less and less.

SLA are kind of the opposite. They don't mind small recharges but being fully discharged can damage them.

netman86 · 02-11-2007, 06:10 PM

Quote: Originally Posted by Arathranar

The small battery I have could run the PC for 15 minutes max when it was new. It'll be less now. Maybe up to 10 minutes max as long as you don't do it regularly since it's slow to recharge.

Li-ion batteries don't like being recharged small amounts - it causes the start remembering a lower max-charge than they were originally. Over time the power they can store gets less and less.

SLA are kind of the opposite. They don't mind small recharges but being fully discharged can damage them.

modern li-ion batteries really dont have problems with battery memory anymore. I mean, they do a little- but overall your average li-ion has a useful lifespan of 2-4 years (tops) and frankly you wont find more than a 10% memory effect on the newer ones after that period has passed... The NIMH back in the day, on the other hand, were pretty bad about memory. The early li-ion ones had it, but not nearly as bad as the NIMH, or worse, NI-CAD.
Not familiar with SLA, but li-ion batteries dont like being taken under around 10% or so iether. They will have circuits built in to keep it from going past the point of damaging the battery, but i perferr keeping my li-ions over 20% or so.

vfinterceptor · 02-11-2007, 06:11 PM

Are you sure you'r enot hinking of NiCad?

I don't remember Li-ion having this issue........

Cheers

BJ

Curiosity · 02-11-2007, 07:29 PM

Yeah, MIMH sucked in the beginning. The newer ones still have some memory, but not bad. They drop in capacity just a little each time you cycle them, and need to be cycled once in a while. I like eneloop! :-)

Li-ion cells require a more complex charging circuit. Each cell has a nominal voltage of 3.7 and if it discharges below 3.0, it won't recover well. Other than that, I've never seen any memory issues. They can also balloon after that. If the cell casing splits it will explode, causing an incendiary fire.

solo44 · 06-08-2007, 05:12 PM

I'm running a Optima yellow top 75/25 to a second 75/25. My question is wouldn't it just be easier to make a board with the proper amount of diodes on it to act as a one way path for the current to flow in but not out?

solo44 · 06-08-2007, 05:34 PM

OK...OK I KNOW I SHOULD HAVE READ THE WHOLE POST....I LIKE KYLE'S SET UP...ANYONE HAVE A GOOD LINE ON THE Schottky diode? If this diode is 20A but my alternator puts out 260(i have two) won't this overload the diode?

Curiosity · 06-10-2007, 02:19 PM

The current that you're drawing is what you need to worry about. If your second battery is low from running the PC without the engine running, as soon as you start the car, you'll be drawing quite a bit depending on the resistance of the battery and whatever is connected to it.

Grrrmachine · 10-24-2007, 03:44 PM

Im running an Opus, so don't need a tank for cranking, but all the same I'd like my 7Ah tank isolated until the car starts. Can I use a Bosch relay connected to the alternator that, when engaged, links the two batteries in parallel, and then stick a 20A Schottky diode on that connection too? My current draw is only about 5A for the PC.

drutort · 12-24-2007, 02:16 PM

since i have a m2 and i havent tested but seems that the crank issue with them still exists, my question is, since i want a theoretical max of 10A for the pc or whatever the M2 is rated at max, to be able to work with a tank circuit i must get diodes that support that amount of current from the tank battery and from the car battery?

this is my understanding right? and i need to find a diode that will drop the least amount of voltage correct? and then the resistor is for charging the tank battery

how on earth can i measure fast voltage drop on the car battery without some higher quality gear, i doubt that with a multimeter i would be able to catch the split fraction of the voltage drop on the car battery during cranking?