how to convert volts into amps

im wiring two devices to my car a voice recording module and a standard ipod/mp3 player docking station and one takes a 9v battery and the other takes 4 aaa batteries. this adds up to 9v and 6 total . which would be the correct amperage to put them at. my guess is 5a fuse . thanks guys1993 sdv

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78nova

5-re audio 5x7 ,10" sub &

Xtx-500.5

"Take the faceplate off get the jumperpack"

The device determines the amp draw, and the fuse is to protect the wiring. Wire gauge determines the fuse size. You can't just wire in a 9v and 6v device to 12v on the car. Do these devices have cigarette adapters or how do you plan to wire them to the car? You may be able to get away with wiring them in series since the total voltage is 13v but I am not sure that is even a good idea.

Ok here's how I was Planning to do it .I got a voice recorder from radio shack and I wanted to amplify it so I got a simple set of mp3 player speakers rated dc 9v. So I was going to wire the speakers into the voice recorder to make it louder. I was going to use 16 guage wire and a inline fuse To the fuse box. No the dont have cig chagers but the speaker set has a 9dc connection and it plugs to a usb so I can plug into the wall or pc. also use a trunk pin so when the trunk opens the recorder would say "trunk open" .now i could use batteries on these items but I rather have it wired to the car so I don't have to replace batteries. Let's say I use batteries would the trunk pin cause a problem being bolted to the car. http://www.radioshack.com/product/index.jsp?productid=2102855 1993 sdv

Alpine 4x6 6x9 5 1/4 swr-10d4

alpine v60

12.5 VGA flip down

Nettop pc w/10" touch screen

78nova

5-re audio 5x7 ,10" sub &

Xtx-500.5

"Take the faceplate off get the jumperpack"

As was mentioned, you cannot safely power a 9 volt device directly from your car's electrical system.  You will need a DC to DC power converter that will generate the 9 volts you require.  Go to Radio Shack and ask if they sell a car power adapter for your recorder

And there is no way to "convert volts into amps."  They are two different things.

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Understood however I wanted to have a trunk pin switch I want to control both of them can I safely do that and use batteries for the device's. The recommended batteries1993 sdv

Alpine 4x6 6x9 5 1/4 swr-10d4

alpine v60

12.5 VGA flip down

Nettop pc w/10" touch screen

78nova

5-re audio 5x7 ,10" sub &

Xtx-500.5

"Take the faceplate off get the jumperpack"

still_walkin - I suggest you draw a diagram showing your plan. If you connect your 6V & 9V devices to 12V, you will probably destroy them (you need a voltage converter). And what is required to make <whatever> announce trunk_open? (Can you trigger it, or you merely power it up?)

I'm going to power the devices with the batteries it was designed for . I'm just going to use a trunk pin to trigger it to come on/off when the trunk opens. Ill post the diagram later1993 sdv

Alpine 4x6 6x9 5 1/4 swr-10d4

alpine v60

12.5 VGA flip down

Nettop pc w/10" touch screen

78nova

5-re audio 5x7 ,10" sub &

Xtx-500.5

"Take the faceplate off get the jumperpack"

Use the trunk pin to complete the device's power circuits. IE - connect each battery -ve to the wire side of the pin and the device "ground" to the vehicle ground. Assuming all devices are -ve ground there should be no issues. The alternative is to have the trunk pin energise a relay that closes the power circuit for the devices - ie, SPST or DPST (DPDT). (Or powers the voltage converters that power the devices, hence they will not need batteries.)

When i read this topic heading, i thought i'm in for a totally sarcastic, critical read! LOL!  Guess i was kinda dissapointed! commit your way to jehovah and he will act in your behalf. psalms 37:5

Yeah - I thought I'd make a fortune selling one of those voltage to current converters. (Cheaper than "smart" battery and voltage sensing isolators, dc-dc battery chargers, etc.)