Power distribution changes - battery fusebox prep

Re-working the power distribution circuit.

There was no massive issue with the original standard setup however - reading through various sites over the years I noticed there was always at least a fusible link somewhere in the setup and on many modern cars a fusebox right on the battery. 

The stock Zero had no such built in weak point - just massive 35mm² cabling, and plenty of it from the positive battery terminal in the engine bay and behind the firewall before any fuse. When everything works, as it has for 4.5 years, its fine, but a failure in any of these cables insulation could be serious.

Power distribution layout changes

The stock Zero cabling is routed: Battery->fusebox binding post->starter->alternator.
The isolation switch is my own addition - helps ensure everything is off when the car isn't actually being driven.

The new arrangement will have physically shorter runs, not via the firewall, not taking the usual alternator->starter route which is significantly longer on a RHD Zero. It also minimises cable joins.

I'm moving my isolation switch to the negative side of the battery at the same time - again safety - less unfused cabling just waiting to find a short.

Downside?

a. If the alternator fuse blows with the engine running, the alternator is likely to cook itself. I'm positing if this fuse goes I've probably got bigger issues to worry about anyway!

b. If the isolator is used with the engine running its also likely to blow the alternator. The switch is only used to disconnect the battery when I'm not driving and/or working on the car. Its an isolator not a kill switch.

Battery mounted fusebox 

The positive battery terminal to be replaced with a fusebox - found on ebay by searching for 'Renault battery terminal' - its perfect for the job, originally used on Renault Scenics so should be up to the task.

   1x CAL 1 Powerfuse for the starter, 

   1x 80A midifuse for the main fusebox (60A pictured)

   1x 80A midifuse for the alternator (60A pictured)

My alternator is 40A output could hit ~50, therefore fusebox should only be drawing ~50A and fuses sized at 80A to run at ~75% of their rating and well under the 16mm² cable rating.

The box required a couple of minor modifications, first picture, the midi line exit holes in the case needed a little adjustment to accept a standard 6mm cable end.

The lid also needed a little of the bottom edge removed to fit around my battery.

Offered up, I think I'm going for this orientation - two cables leaving for the starter and alternator, one the other side toward the fusebox. There's plenty of room under the bonnet at this location.

Update - engine run test, better voltage indicated on the clocks so thumbs up for the wiring change. The significantly shorter runs and fewer joints have given me a good 1/2 a volt perhaps more indicated - I'm now seeing 14.5V on the volt meter instead of the usual 13-13.5.

Update - up-rated 2x midi fuses to 80A for more headroom. Spec on the 40A alternator shows it could hit 52A in normal operation.

Update 2 - I think the extra 1-1.5 volts upset the injection settings - perhaps an over enthusiastic default battery voltage compensation curve in the ECU. I lost slow idle and had to boost the injection values a little so get back in the range where the wideband live adjustments can do their job and not pegging at its set +-15% settings. ECU settings updated to compensate.

Polyswitch bypass

Moving the isolation switch to the negative lines means I need a different approach for a permanent live. My radio and immobiliser flashing LED need a trickle current even if the isolator is turned off, they draw around 10mA total.

Going back to the polyswitch approach, this time a modified blade fuse which can sit in a standard holder. This sits across the isolation switch and will let low currents pass but then open completely if, for example, the ignition is turned on or anything tries to draw more than 100mA. Once the current drops below 50ma it resets itself and everything is back to normal.

All set for final assembly and testing.
(Garage is still to cold to work in for any length of time)

Update - jury is out on the PTC - problem is if I turn on the hazzards (which are live even with ignition off) they trigger/reset the PTC continuously due to drawing the trigger current then immediately turning off, PTC doesn't mind - but the flasher relay will.

Either the PTC goes, or I mod the hazzards switch to have a constant ~50mA load.