# Car Battery Circuit.

Discussion in 'General Electronics Chat' started by AgentSmithers, Jan 15, 2011.

1. ### AgentSmithers Thread Starter Active Member

Jan 14, 2011
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Hey Guys, Thankyou for making me feel welcome to the forum, Right now I am a newbie at circuits and I plan to change that very soon.

This Post question is, what is the best way to emulate a car battery on my circuit?

I know that a Car battery is 12V, so does that mean I should take a Dbattery (9v) and use a Parallel Circuit with 2 TrippleA(1.5V) batterys to make the 12 volts, am I missing something, Does AMPERAGE effect the circuits if they are just LED's? DO I need a Bigger Voltage Regulator?

2. ### PatM Active Member

Dec 31, 2010
81
72
You would need a Series circuit NOT Parallel.
A 9v battery is nothing but a bunch of little 1.5v batteries (smaller than Triple A) in series, in a case.
Current draw will affect the life of the battery.
Better to use 8 1.5v cells that are all the same size.
If you are just trying to light LED's you can do that with just the 9v battery.

Last edited: Jan 15, 2011
3. ### AgentSmithers Thread Starter Active Member

Jan 14, 2011
52
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Ah Great! Well If I run my whole model off a breadboard of basing it off of a 9V battery once I hook it up to a car battery done I need to change out certain parts like resisters and voltage regulators?

4. ### tom66 Senior Member

May 9, 2009
2,613
214
A car battery is *rarely* 12V.

Instead, during normal operation it usually runs from about 12.5V to 14V. A car battery reading 12V would actually be flat.

The best way to emulate a car battery is with... a car battery.

But these are expensive, so you can get a small 12V ~3Ah SLA battery and test your circuit with it.

Also, be aware if you plan to use this in a car to make sure your project can withstand the imperfect 12V supply. Not only is it variable over a large range, it can be subject to large voltage spikes of up to 60V due to load dumps. For example, when turning off the headlamps, the alternator can't get rid of all its excess energy immediately, so it appears in the form of a large spike in voltage.

5. ### AgentSmithers Thread Starter Active Member

Jan 14, 2011
52
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Awesome! thanks for the Info, Ummmm So what do I need to keep the Voltage steady.. like a Nice 3pin Voltage Regulator?

6. ### tom66 Senior Member

May 9, 2009
2,613
214
An LM7805 wouldn't be advisable due to the limited input range of up to 40V but a MIC2940-5.0 in a TO220 case would be fine (it can handle a 60V surge.) Also include a fuse in-line with the power connector.

7. ### Jaguarjoe Active Member

Apr 7, 2010
770
90
What are the LED's indicating?
A not so good car battery can dip to 6 volts as it turns the starter motor.
Reverse polarity protection with a diode is an easy and cheap thing to add too.

8. ### AgentSmithers Thread Starter Active Member

Jan 14, 2011
52
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Where can I buy that combo(MIC2940-5.0 & TO220)?

9. ### Jaguarjoe Active Member

Apr 7, 2010
770
90
TO-220 defines the standardized package that a part comes in, like AAA or D define the package that a battery comes in. It is not an actual part.
Regulators need a little bit of overhead to work with. Most need about 2 volts above the voltage they put out. LDO (Low Drop Out) regulators do it at about 1 volt or maybe less. If you are powering a 12 volt circuit with a 12 volt regulator, you'll need more than a 12 volt supply.
The LM2940 family of 3 terminal regulators are tailored for automotive applications. They withstand spikes, reverse power, and, like Tom said, 60 volt load dumps. Search the National Semiconductor website for that part and it should lead you to all of its variants, like the LM2937-5 etc.
If your circuit draws any great amount of current, figure out the regulator's power dissipation to see if you need a heatsink.
Practically every part you'll ever need is available at Digikey, Newark, Mouser, or Allied Radio. There are numerous discount shops around where you can get stuff really cheap. I like All Electronics, BGMicro, Electronix Express, Electronics Goldmine, and MP Jones. They're all on the web.