24 12volt invertor and power/fuse ratings

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chatterbox

Member - Posts: 1

Joined: August 27, 2007

Location: Australia

Posted: August 27, 2007 at 6:06 AM / IP Logged

Hi,

I have a coach which is 24volt. I am putting a 24 to 12volt convertor in to run various items.

Some items ie dvd player/screen etc have the power consumption on them, but the sub woofer and radio only say what the fuse is rated at...

1. how do I work out the power requirements?

So far I have VIDEO SCREEN - 3AMP

DVD PLAYER - 1.5A

HEADPHONE AMP - 180 mamp

RADIO - FUSED AT 10A (4 x 50W)

SUBWOOFER - 20AMP FUSE. wattage not known

I am looking at (hopefully) a 15w - 20 w invertor to run all of these...

2. would this be ok?

Any advice -

3. is this the best way to go to run these...or any other ideas etc....??

and

4. should the invertor be powered from the bus accessory circuit or directly from the batteries ?

Thanks

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i am an idiot

Platinum - Posts: 13,667

This member consistently provides reliable information

Joined: September 21, 2006

Location: Louisiana, United States

Posted: August 27, 2007 at 6:35 AM / IP Logged

Does your vehicle have 2 12 volt batteries? Or 3 8 volt batteries? Is it a Negative Ground System?

If you have 2 12 volt batteries you do not need a converter. All you need to do is determine which battery is connected to ground. Then connect to the positive terminal of that battery. But of course use a meter to verify that you have only 12 volts on that wire before connecting any hardware. This will do for your constant power feeds. You will need a switched 12 volt for your radio. If there is a switched 24 volt feed on your vehicle, let us know we can get that for you simply by using 2 relays.

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haemphyst

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Joined: January 19, 2003

Location: Michigan, Bouvet Island

Posted: August 27, 2007 at 10:31 AM / IP Logged

First of all, a 15 to 20 watt invertor (which is technically a device for converting DC to AC - you need a DC to DC CONverter) will not be REMOTELY large enough. The way you figure it out is by multiplying the input voltage by the current rating of the device (the fuse value is generally speaking, a maximum SAFE rating, but a good way to decide, in this case...)

3A + 1.5A + 180mA (.18A) + 10A + 20A = 34.68A

34.68A X 12V = 416.16W

You will need a 500 watt DC-DC converter to run all of those devices simultaneously.

However, as i am an idiot mentioned, you can tap the battery jumper - the one between the two 12v batteries (if equipped as such) if you have four 6 volt batteries, you simply tap the middle jumper - easy peasy. Again, confirm 12 volts to the chassis of the vehicle!

This will work, however it is NOT the best way, as one of your two batteries will always be less charged than the other - making the OTHER one live in an overcharged contition, perpetually. This will cause it to fail, by boiling off all of the electrolyte first. The converter is the best option, certainly!

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

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24 12volt invertor and power/fuse ratings

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