# Power from one or both of 2 sources

• doowruc
In summary, to add a new interior light to your car, you need to use 2 power sources, one of which is +12v and the other is -ve. Make sure the 2 power sources do not affect each other and that the new light draws the same amount of current it requires.
doowruc
Hi all,

Apologies if this is the wrong place to post this but I can see lots of similar questions on this forum which aren't a 100% match for my question.

I want to add a new interior light to my car.

I want it to be on either when the headlights are on (power from the illumination circuit of the radio) or when the existing interior lights are on. It is possible that both could be on at the same time.

Both sources are (I assume) +12v

The new light will be grounded to the car chassis via the cig lighter -ve.

Is this possible? How do I ensure that the 2 power sources do not affect each other? (i.e. I don't want the existing interior light coming on when I switch the headlights on!)

TIA

Hi doowruc! http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

One power diode in series with each lead from each source should work.

Last edited by a moderator:
Thanks for the welcome!

So, would it be 2 of these that I need?

http://www.maplin.co.uk/1500w-unidirectional-transient-voltage-suppressor-diodes-46416

And is this the basic circuit?

What would happen if both were live? would the new light then get too much current or voltage?

Yes, that looks like the arrangement. How many watts or amps is the bulb?

Probably use these: http://www.maplin.co.uk/3a-silicon-rectifiers-46405

doowruc said:
What would happen if both were live? would the new light then get too much current or voltage?

No, it will draw just as much current it requires. Nothing wrong will happen.

(As a side note: Calculating the current shares of the lines, when both line is live, is a difficult and quite unpredictable thing. Depends upon Diode Imperfection and Line resistances.)

You might check something on the interior light before getting too far along.
In old days they worked by completing a circuit to chassis, on side of bulb opposite the battery. The little buttom in doorjamb made that connection.
On those automobiles your interior light would have 12V on both sides when OFF and on one side only when ON.

Nowadays they are controlled by the computer and i don't know which wire the computer switches, could be either the "hot" or the "return".
The button in doorjamb apprises computer there's a door open and computer decides whether to light light and for how long.

So get your meter and check that interior light socket to see which side changes state when it comes "on".

old jim

jim hardy said:
You might check something on the interior light before getting too far along.
In old days they worked by completing a circuit to chassis, on side of bulb opposite the battery. The little buttom in doorjamb made that connection.
On those automobiles your interior light would have 12V on both sides when OFF and on one side only when ON.

Nowadays they are controlled by the computer and i don't know which wire the computer switches, could be either the "hot" or the "return".
The button in doorjamb apprises computer there's a door open and computer decides whether to light light and for how long.

So get your meter and check that interior light socket to see which side changes state when it comes "on".

old jim

Thanks Jim. The kit I am buying comes with specific instructions for my car and wiring into the interior light circuit so I hope that this will be covered!

## 1. What is "Power from one or both of 2 sources"?

"Power from one or both of 2 sources" refers to the concept of combining and utilizing energy from two different sources to generate power. This can include using renewable energy sources such as solar and wind power, or using a combination of traditional and alternative sources for more efficient and sustainable power generation.

## 2. Why is it important to have power from multiple sources?

Having power from multiple sources provides a more reliable and resilient energy system. If one source experiences a disruption or outage, the other source can continue to provide power. Additionally, using a combination of sources can help reduce dependence on non-renewable resources and decrease the impact on the environment.

## 3. How is power from two sources combined?

The process of combining power from two sources depends on the specific sources being used. In some cases, multiple sources can be connected to a power grid and their energy output is combined. In other cases, specialized equipment such as inverters may be used to merge the energy from different sources into a single output.

## 4. What are the benefits of using power from one or both of 2 sources?

The benefits of using power from one or both of 2 sources include increased reliability, reduced environmental impact, and potentially lower energy costs. Additionally, by diversifying energy sources, we can decrease our dependence on a single source and mitigate the risks associated with it.

## 5. What are some examples of power generation using multiple sources?

Examples of power generation using multiple sources include hybrid power systems, where solar and wind energy are combined, or bioenergy plants that use a combination of biomass and fossil fuels. Another example is a microgrid, which can incorporate multiple energy sources, including renewable and traditional sources, to provide power to a smaller area or community.

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