i need help building a circuit

[jimbarbwe]

hello,
i hope some one can help me.
at the moment on my motorbike i have a variable voltage output of between 9 volts and 22 volts i need this voltage to be limited to a steady 8-12 volts HOW can i do this. i would rather ues some thing that is INLINE. can some one please help me.

 

[bigkim100]

Ok...I dont understand...how the hell are voltages that vary between 8-12 be considered steady, thats kinda variable in my book. Just tell us waht you want to run with your voltage.

 

[jimbarbwe]

sorry i should of given a bit more info. the voltage out put from the bike is between 9v and 22v depending on RPM i would like the voltage to be caped at 12 volts. i want to run a HID lighting kit and it can run on voltage between 8-16 volts. so when i was saying a steady i ment like a steady 9v 10v 11v or 12v. i am a eejit and need help

 

[jimbarbwe]

**broken link removed**
Partlist
1 x LM7805
2 x 100nF condensators
1 x 100uF condensator
1 x 10uF condensator
1 x N4002 diode
1 x LED (optional)
1 x 470 Ohm resistor (optional)

could this work if modded

 

[bassnut]

No modding needed, would work nicley, just change the LM7805 for an LM7808 or LM7812 as required. The LM7812 output will droop if the input drops below 13 or so volts though, but Im assuming that wont be a problem if it only occurs during startup cranking. If you want rock solid 12v at all times, then you will need a switch mode buck-boost regulator, which is a whole different world of pain which might be advisable to purchase, rather than build your own.

 

[lucifer sam]

Ok, wow this might be exactly what i need.
Rather than creating another noob thread which im sure everyone around here hates,
So heres what im doing i bought a digital volt reader off ebay 0.00v- 9.99v readout i think? And im trying to wire it to my O2 sensor off my truck to get some idea of the air to fuel ratio..so it needs a steady 5 volt source which i can assume i can make using the diagram above? Ive seen a few diagrams like it around on google but i couldnt really ask the dumb questions that i am.
The LED is just to show power is going to it correct? and i can just find all this at radio shack right?

 

[flat5]

yes,yes. The caps on the left should have a voltage rating of at least 25v. Those on the right might as well be the same.
Please include an inline fuse at the far left.

 

[bassnut]

Yep, I guess yr truck is 24v, so the LM7805 is fine, you might fit a heatsink to the LM7805 tho. You should be able to find a kit that has all these parts included, easy as.

 

[jimbarbwe]

would i not need to change the 100uf and 10uf due to the diffrent regulator and diffrent voltage input??????

 

[ericgibbs]

would i not need to change the 100uf and 10uf due to the diffrent regulator and diffrent voltage input??????

hi,
Those values are OK, just make sure working voltage of the caps is 25Vdc or higher.

 

[jimbarbwe]

0.33uF and 0.1uF capacitors but what one replaces the 10uf & what one replaces the 100uf???

 

[ericgibbs]

0.33uF and 0.1uF capacitors but what one replaces the 10uf & what one replaces the 100uf???

The circuit you posted is OK as it is.!

If you wanted 8Vout change the 7805 to a 7808.

Or a 7809 or 7810, for 9V or 10V

 

[jimbarbwe]

I did build the above circuit and when I ran 12V thru it the output would be 22v do you no why this would be. I spoke to the guy who gave me the above circuit diergram and he said I would need to change the two caps. Any help is good thanks guys

 

[ericgibbs]

I did build the above circuit and when I ran 12V thru it the output would be 22v do you no why this would be. I spoke to the guy who gave me the above circuit diergram and he said I would need to change the two caps. Any help is good thanks guys

hi,
There is no 0V common line to the input of the circuit.? [I have added it]

Look at this image.

Show me how you have it connected to the 12Vdc.?

BTW: have you got the 470R and LED connected.?

 

[jimbarbwe]

No didn't bother with the 470r or the led. The com line would that the negitive feed? I'm sorry about this I'm learning as I go. Thanks for the help

 

[ericgibbs]

No didn't bother with the 470r or the led. The com line would that the negitive feed? I'm sorry about this I'm learning as I go. Thanks for the help

hi,
No need to be sorry, weve all been there.

Is the motor bike a negative chassis?

If YES, then the 0V common for the voltage regulator is the chassis, also the small 'triangle' on the circuit is also the chassis 0V and must be connected.

I would add a 470R across the +5V output in order to load the 7805 a little.
[include the LED if you have one]

 

[jimbarbwe]

Thank you massive help. Will check to see is the bike is a negative chassism if not then where does the 0v feed come from.
This has been driving me mad and had got to the point of giving up massive help thank you

 

[ericgibbs]

Thank you massive help. Will check to see is the bike is a negative chassism if not then where does the 0v feed come from.
This has been driving me mad and had got to the point of giving up massive help thank you

Let me know what you measure.. we'll take it from there.

 

[jimbarbwe]

Where to get the 0v com from???

 

[ericgibbs]

Where to get the 0v com from???

hi,

The 0V common is the small 'triangle' on the circuit, which must be connected to the chassis of the bike,, assuming the bike chassis is negative.[which I believe it will be]

Does the bike have a battery at all.???