1. Jul 23, 2008

trulka

Hey guys,

I am building an electric racecar for university and I'm stuck!. It has to be run on car batteries and it can only use one at a time... many people are just using an excellent battery with a great amp-hour rating... but I'd like to switch batteries halfway through...

I want to disconnect a car battery when it reaches 11.8V and possibly using an adjustable voltmeter/detector?

Thank you!
-Tom

2. Jul 23, 2008

chroot

Staff Emeritus
You're not going to build much of a race car with only one 12V battery at a time. A single 12V battery, even at 100 amperes of current, is only providing 1,200 watts of power. This is about the same amount of power generated by a lawnmower engine.

- Warren

3. Jul 24, 2008

zeitghost

There are plenty of battery voltage detector chips about.

Combined with suitably zonky Power mosfets, then bob's yer uncle.

4. Jul 24, 2008

Staff: Mentor

You Brits sure talk funny :rofl:

5. Jul 25, 2008

zeitghost

Zonky, by the by, means "large" as in >100A Id(on).

6. Jul 25, 2008

Bolts

One way for a warning system would be to setup a diode with a resistor (or trim pot) combination that switches at 11.8V.

7. Jul 25, 2008

stewartcs

What the heck does "then bob's your uncle" mean?

CS

8. Jul 25, 2008

mgb_phys

It means you're problems are solved

Historical note:
Robert Gascoyne-Cecil,was prime minister in the 1890 and was a big fan of nepotism - appointing his nephew as minister, so if Robert (bob) was your uncle you didn't have any problems getting a job.

Interestingly neptosim is from the Italian for nephew and comes from Pope's giving appointments to their (cough) nephews (cough)

9. Jul 25, 2008

stewartcs

Ah...Thanks.

CS

10. Jul 25, 2008

Staff: Mentor

11. Jul 25, 2008

Redbelly98

Staff Emeritus
Do I understand that both batteries will be in the car at all times, and you want a circuit that electrically switches over to battery #2 when battery #1 reaches 11.8V?

If this is for a contest, how will you convince the judges that only one battery is being used at a time?