Easy jump start point Part 3

[Herbie]

Given that our 'boot' is always full and the engine covers are held in place with tiny plastic clips that are easily broken or lost, I decided to put a more convenient socket in the cabin. If I ever do need to use my jump start Battery pack, at least I can do it from the comfort of the driver's seat.

Most of this is covered in an earlier post (Parts 1 & 2) but this final piece covers the protection of the Battery pack. I may as well include the photos that have got us this far and then explain this part when we get down there.

The first photo shows the chosen location for the socket. The RX450h has a two-tier centre console and a panel on the lower tier lends itself to this perfectly.
 

Next photo shows the choice of socket. It's a Neutrik Speakon 2-pole socket. I chose this for a number of reasons (a) I already had one, along with its corresponding plug in my junk box (b) it's keyed and so can only be connected one way, with the correct polarity, and (c) it's rated at 30A, which is higher than we need.

This next photo shows it in situ and connected, indicating that we're getting 12.29V from the car.

How the pack connects:

I decided to run the cables to the jump start connector post in the engine bay fuse box as it was an easier route than trying to get them to the Battery itself under the floor of the boot. I did this by running the cable from the centre console and up behind the glove box, where there's already a big rubber grommet in the bulkhead firewall that takes the existing wiring loom through. It was then easy enough to cut another little hole in the grommet and get my flexible conduit up through there.

From there it was an easy job to find a neat route up into the fuse box. The circuit needed to be fused so I installed an in-line fuse holder with a 25A fuse in it and connected the positive wire to one of the post terminals in the fuse box. It should really have been connected to the one under the red cover but due to the size of the ring terminal it was easier to 'break out' of the other one. It makes no difference as both terminal posts are permanently connected to the Battery anyway.

The negative (black) wire didn't need to go into the fuse box so I dropped it out to a nearby bolt and made the connection there.

And that was as far as I got but one very important thing still needed to be done, hence the reason for this third and final part of the project.

Obviously, the jump start Battery pack will only be used when the 12V Battery is flat, in order to get the car running. However, once the car is running, ie, in READY mode, it will then immediately start to squirt power back up the wires to charge the Battery - great for the car Battery but not necessarily a good thing for the jump start Battery pack!

The way to protect the Battery pack is by way of a diode. This allows current to flow in one direction, ie, from the pack to the car, but will prevent current from flowing in the opposite direction.

Now, I'll be the first to admit that it doesn't exactly look pretty. Yes, it could have been smaller; Yes, it could have been prettier, but I had these things in my 'junk box' so thought I may as well make use of them instead of buying new stuff, especially as the diode pack will not be out on show.

The plastic box is from a Sky wifi connector, made redundant when I changed to a more modern Sky box with built-in wifi. The aluminium heatsink came from the guts of a duff ATX computer power supply, and the diode itself was surplus from some other project.

The diode had two 'legs' and a heatsink tab. One leg of the diode is internally connected to the heatsink tab so I just cut that leg off and thought I'd utilise the heatsink itself as a conductor, which is one reason why the whole thing is inside a plastic box - to avoid the 'live' heatsink shorting to earth on any exposed metal. I also used a dab of thermal paste under the diode to ensure good thermal conductivity.

And here we have the last photo, showing that the diode is indeed doing its job and stopping power from the car backfeeding into the Battery pack.

[Illogan]

Excellent article Herbie!

Should be titled "Boy's Own Guide #1 - Easy Jump Start"

 

[stringbender]

Well done Herbie. That's an amazing job. Just hope you never have to use it !

I seem to remember being told that there was a jump start terminal under the bonnet of the 4th series. Does anyone know if that's true ?

Alan

[ColinBarber]

3 hours ago, stringbender said:

Well done Herbie. That's an amazing job. Just hope you never have to use it !

I seem to remember being told that there was a jump start terminal under the bonnet of the 4th series. Does anyone know if that's true ?

Alan

Yes that is correct. Within the fuse box in the engine bay:

[Gliderask21]

Great install, I would have thought the jump pack was already backcharge protected as it would be receiving charge from whatever engine was "jumped" with it.

 

[Herbie]

45 minutes ago, Gliderask21 said:

Great install, I would have thought the jump pack was already backcharge protected as it would be receiving charge from whatever engine was "jumped" with it.

The Battery packs are protected from a backfeed but, as you'll see below, that protection is a bundle of diodes in the little red box on the positive lead.

I had to make up my own lead so that protection wasn't there on mine.