02 S60 Need extra power from alternator only running engine

sergio · Post by **sergio** » 07 Aug 2014, 12:10

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I need an extra +- 50Amp 12 V. I don't want to use the cigarette lighter etc.
It has to be on, ONLY when engine is running aka from the alternator.
It should not draw from the battery, Key on II.
It is needed in the engine compartment.

Where shall I connect my wire?

Thanks

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Post by **regent** » 07 Aug 2014, 14:20

Both +12V sockets in the cabin are fused at 30Amps.

The right way to go is from an open branch on the main distribution bus # 30 (the B+ in the engine fusebox); you have to get in past the fusible link in order to be protected and add a relay that closes with the ignition ON (pos. II).
A suitable candidate would be the 60 Amp fusible link # 1 (11A/1), which is reserved for the glow plug circuit on diesel engines. Make sure you use 4 AWG wire.

If you want to inhibit any draw from the battery, then you will need a bit more complicated control circuit that will drop the relay as soon as the bus voltage gets below certain threshold, say 12.8 VDC

sergio · Post by **sergio** » 07 Aug 2014, 21:27

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Regent

The idea of using a relay to cut off the juice on pos II is great I didn't think of that one. Thanks.
Then again I have to find out the source of power from pos II to activate the relay!

Now, where are those terminals 11A/1~7. Underneath the raw of fuses in the engine compartment?
How do you open it? Do I need to unscrew the fuse holder or just pull it up?

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Post by **regent** » 08 Aug 2014, 06:11

You can splice from anywhere past the Engine Management Relay which is picked up with IGN Pos. II; you barely need just a couple dozen milliamps to energize a relay coil.
It looks like there are a few snap-on catches that you need to undo to get to the main fusible links; I have never opened that one but I can comb through VIDA for a step-by-step.

As usual, the very first step would be disconnecting the battery.

Post by **regent** » 08 Aug 2014, 10:44

Once you’ve disconnected the battery, unscrew the four T15 bolts in the fuse box. You need to remove the positive red cable stud beside the fuse box as well (13mm) - the fuse board is supported with the stud - and then lift out the red positive cable following with earth terminal and finally you'll see the fuse board support on bottom. Carefully lift it up sliding past the two clips opposite and you have access to the internal fusible links.

VIDA has some insight - to a certain extent - see attached.
Hope this helps