# Thread: Tank circuit design + help needed.

1. I'm always open to using linear regulators but so far they look expensive and I'd need to have several in use to get the current. The best I've heard of is a 7.5A one with max voltage drop of only 0.7V but I'd still need two and I have no idea of the cost of that baby. But currently I'm exploring whether it's actually needed for my car.

So far all the components in my plan are very cheap. The most expensive is the \$10 battery I've got. Of course each new gotcha I try and address will start pushing it up. I suspect the battery may end up being the achilles heel - I'll be drawing so much current from it that the voltage may drop too low. If I were using a VIA board, then all of this would be a lot easier (and a lot less risky since the VIA boards barely use the 12V).

I could just build a Mastero (and probably cheaply if I managed to get lots of 'samples') but then I haven't learnt anything. Where's the fun in that...?

Yes, I know I shouldn't really be using the accessory line but it's rated for 20A in my car and it's convenient - I don't have to put in a load of new wiring and relays to get the same effect. My original plan was to do that, but hell, if I don't need to...

2. ## Everythink In This Thread Is Relly Crazy!

dont catch anythink

3. I'm always open to using linear regulators but so far they look expensive and I'd need to have several in use to get the current. The best I've heard of is a 7.5A one with max voltage drop of only 0.7V but I'd still need two and I have no idea of the cost of that baby
The LM1084 (approx 8A capable) is available at digikey for 1.92 in single quantities or free as a sample from national

4. I'd read that as a 5A regulator. So I'd need 3 with that. However, it does say that at it will give a min of 5.5A at Vin = 17V but typical values of 8A.

I'm struggling to see what effect a Vin of 13.3V will have on it. It looks like the dropout voltage is about 1.2V at 5A and I'm estimating (not on the graph) 1.4V at 8A.

What happens if I get the 12V regulator version and it sees (say) 13V on the input - does it output ~11.6V assuming a 1.4V dropout voltage at 8A?

At 3 x \$1.92 a pop, I'm certainly prepared to switch from my diode chain to the linear regulators .

5. So how does 'requesting samples' work anyhow? Do you just request one a day until you have all you need and use a work email/address to receive them?

6. you can usually get up to 5 at a time...I never tried to abuse the system so I don't know how often you can request them.

7. Originally Posted by MrPerfectionest
It sits there because of a lot of other reasons and I don't expect to have a working version until sometime after Christmas (if by then).
I hope you get it done for us...we just gonna have to wait

8. Just an update. I got this mostly put together, but used an LM311 instead. It's smaller and has a built in power transistor so fewer parts. I also used these relays but I'll be messing with MOSFETs soon. Anyway, it works great! Just having it at some unknown setting it switches the relay on at 12.40 and off at 12.38 which is really close like I was hoping for. If you use a different relay, you may need a resistor between the LM311 output and ground. It seem to put out a few volts in the low state but hasn't been a problem. woot!

9. Well, screw this. It was a bad idea. When the battery voltage hits that threshold the relay goes off and the voltage goes back up, so the relay starts buzzing! I guess some hysteresis really would be a good thing. Or maybe I'll just replace that whole right side with a big diode. heh. I'm still happy with the auto-power on/SDC part of it though.

Edit: A 500k resistor between pin 1 & 2 gives it about .5V hysteresis!

10. Originally Posted by Curiosity
I guess some hysteresis really would be a good thing.
The simple resistor on the relay coil mentioned before may do the job if you hit the upper and lower trigger at the right spots

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