[paulgato]

Update...

Work has been super-busy lately and I haven't had a chance to do much on this. I've researched various options, and made a few preparatory purchases, but not actually done much. Also, nights are getting longer and I've not had much daylight for working on the car.

I have managed to replace all interior bulbs with LED's. Small potatoes, but just about worthwhile I guess. That cost £25. Well, frankly, if I'd known how much hassle it was going to be I probably wouldn't have bothered. But now it's done I guess it's kind of worthwhile.

I replaced the two front sidelight bulbs with Osram LED's and fitted those Phillips EcoVision H7 dipped headlight bulbs. That saves me 20w. I'll get some LED's for the tail and brake lights, which will save me another 15w. It doesn't sound much but that's probably adding at least 1mpg.

These little electrical savings will save me fuel now and will extend my alternator-free range once I start plugging the car in every night.

I did get a battery to replace my standard starter battery. In the end I went with a 90Ahr AGM battery which was slightly smaller than the 110Ah flooded leisure battery I was originally looking at. The 90Ah AGM is heavier than the original but fits straight into the existing battery box without modification, and it seems AGM batteries are a good choice for this 50% daily discharge regime. It cost £90 delivered and has a four-year warranty. They claim it will be good for 1000 discharge cycles to 50%.

I've just ordered a 10A charger to install in the engine bay and a remote (keyfob activated) relay switch to turn on the engine heater from indoors in the mornings. So the battery charger (and possibly a small, 100w sump heater?) will be active all the time the 230VAC lead is plugged into the car's inlet socket, and the coolant pre-heater (3kw?) will be switched on a half hour before drive-time.


Two further thoughts...

1. Having discovered how much electrical power the heater blower motor uses, I've been experimenting with using windows instead. Once the car is warm I can just about keep the screen clear using the windows, but as the weather has got colder I'm finding I can't heat the car properly without the blower.

I've done some calculations and realised that the blower at lower speeds is incredibly inefficient due to the use of resistors to slow it down (That's Stone Age technology VW!) If I could fit a Pulse Width Modulation speed controller in place of those pesky resistors (resistance is useless!) then I'd save a HUGE amount of power...

At present, the blower motor uses...

Full speed... 217w (including 0w wasted in resistor)
Speed 3/4... 154w (including 46w wasted in resistor)
Speed 2/4... 106w (including 53w wasted in resistor)
Speed 1/4... 75w (including 50w wasted in resistor)

...so on the lowest speed I could cut the power consumption from 76w to about 25w using a PWM controller. In fact, on any speed but the maximum speed (which I almost never use) I would save a similar amount of power: about 50w. That's 4A (!) and will improve gas mileage by almost 2mpg in my car. Given that in the winter I really do need that blower motor, and tend to also use it all year round, this would be a real saving. I can't believe that no one is making after-market PWM modules to replace the resistor pack modules in these cars. (Maybe no one realises just how much fuel is being wasted by these stupid resistors?!) The resistor packs are pretty unreliable too, as they rely for cooling on the motor blowing cold air over them.

(Perhaps an easy, though slightly inelegant solution is to leave the existing set-up as it is and add the PWM in between the blower motor and the max speed contact of the blower speed selector switch, mounting the potentiometer knob of the PWM on the dash somewhere. I can then leave the original switch on the max setting and control the speed with the new potentiometer knob.)

I can't believe VW are forcing me to make this blower motor mod by their continued use of 19th Century technology, but I stand to make more gains by doing this than by all the lightbulb LED replacements combined. A blower motor PWM controller should save me about 50w under nearly all driving conditions, whereas the LED's will only be saving me fuel when it's dark.


2. Now what was that other thought...? Oh yes, a slight problem. If I drive with the alternator field wire (IGnition wire) disconnected from the alternator, then after about ten minutes a warning light comes on. It's actually the 'ESP' warning light (yellow triangle) that normally indicates that I have switched off traction control, but reading up on it reveals that it will also come on if there is a break in the field wire from the ignition switch.

I haven't tried yet but I think I can stop that warning light coming on if I connect a 12v +ve supply to the disconnected Ignition wire so the ECU sees a proper voltage on that wire and 'assumes' the alternator is working and is supplying '12v' to its own rotor field. I'll experiment, but I don't like having warning lights on the dash, even if I know they don't mean anything. I guess if the experiment 'works' then my alternator ON/OFF switch will have to be a changeover switch that disconnects the IGnition wire from the alternator field and connects it to a 12v +ve supply.

(I'd thought about including an 'alternator kill switch' which drains the field current down to ground in an already excited alternator, but it's also very easy to momentarily stop the engine if I ever need to kill the alternator while driving, so I won't bother with that one.)

So that's the update. Mostly thoughts rather than actions, but it's all coming together gradually.