Alternator bypass & engine preheater mod

[paulgato]

26w wastage isn't too bad. That's less than half of what mine wastes. What wattage is your motor at full speed?

At 12.4v mine wastes around 50w (50w, 53w or 46w) at all speeds apart from full speed. (At 14.4v it wastes 66w, 74w or 62w at speeds 1, 2 and 3 respectively.)

To be honest, I don't really know what these PWM's look like. I only know what I've read online myself. I think the one you linked to is probably the kind of thing to use. PWM motor controllers I've seen online look similar and cost a similar amount. However, a 15A rating would not be enough for my blower motor, and even if yours is significantly smaller I still don't think a 15A rating would be enough. Motors can sometimes take a surge of power when they first start which is much higher than their sustained current draw. This isn't normally an issue with simple resistors, as they would take a while to overheat anyway, but I think you'd need to over-specify an electronic controller by quite a wide margin to avoid problems. In theory, a nice big capacitor across the windings of the motor would supply the start-up current boost required but it's better to get a controller you are sure is big enough to start with. But I don't really know any of this from first hand experience. Maybe these controllers have large enough output capacitors built in to them anyway. Doesn't look like, but maybe.

One thing (as far as I have read) that you need to be aware of is the frequency at which the PWM switches. If that frequency is within the audio range then the motor can end up audibly humming. 20+KHz should apparently be OK unless you've got ears like a bat. ;-)

But do your own research and don't rely on what I say. I've only recently looked into these things since I realised how much power those resistors are wasting.

If you fit a PWM before I do let us know how well it works.

[echo-francis]

my blower motor use
1, 39w
2, 55.5w
3, 98w
4, 146w 11.7a
I like the PWM idea because I allways use my heater at speed 1 or 2
and at those speeds 50%or more of the watts are wasted.

[paulgato]

I'm looking at this one...

12V 30A 360W DC Motor Speed Controller with Enclosure | eBay

...more expensive but it ticks all the right boxes for me. Right current rating, right frequency (ultrasonic), comes with a case and can be controlled using a simple 0-5v signal, which can be fed directly from the existing speed selector switch (with judicious addition of a few voltage-dropping diodes) without running any new wiring or requiring the addition of an extra control knob on the dash. Also, the listing shows that the seller understands what he's selling.

But your blower motor is almost exactly half the power of mine so maybe you don't need such a high-rated controller. The lower-powered ones are MUCH easier to get hold of. Also, if you wire it up clever then for the highest speed the current doesn't have to go through the controller at all but can bypass it. That way, the maximum current you put through the controller is going to be for your second-highest blower speed, whatever you decide that will be.

It is entirely permissible to rig it so that the three controlled speeds are slower than the existing three controlled speeds and then there's a jump up to the maximum, uncontrolled speed. That way, the maximum current you ever put through the controller need only be about 5A. (Or for me, 10A.) I myself very rarely use speed 3/4. I sometimes use speed 1/4 but mostly use speed 2/4 for everyday use, ...and then very occasionally, when I need all the power I can get for a brief period, I'll use speed 4/4. I'd probably be happy with just two speeds but that would make the speed selector a bit weird. Just thinking aloud here but in fact I could use a much lower-rated controller (say 15A, which is readily available in the UK) and have in effect, speed 1, 1.5, 2.5 and 4.

[paulgato]

...

Aha...!

http://www.amazon.co.uk/6V-90V-Pulse...pr_product_top

...only 15kHz, so not strictly ultrasonic, but I personally can no longer hear 15kHz at all (snif) so it should be OK. One of the Amazon reviewers there had good luck using this unit to control the blower motor on his Landrover so I have a good chance of success with it. I do like the fact I can control the output with a 0-5v signal rather than having to use a potentiometer.

By the way echo-francis, I just noticed what mpg you're getting there. Impressive. In theory you should be able to squeeze a couple more mpg out with the blower motor PWM mod.

Another test I can recommend is to measure mpg at various electrical load levels. (Do you have a real-time mpg meter of some kind in the car?) That will give an idea of the mpg gains you get by reducing the load on the alternator. I would imagine that a small, petrol-driven car (?) which already gets high mpg would get the most mpg gains from reducing electrical load because the alternator is using a higher proportion of the engine's output. Also because petrol engines tend to be less efficient than diesels in absolute terms of power produced per gramme of fuel burned, so all that electrical power is going to cost more fuel than in a diesel.

...

Ha ha - i just found your thread. Loads of good stuff there. I'll be back for a good long read soon. Also I just realised the 'perfect' PWM I just found is the exact same one you found. Looks good to me.

[paulgato]

Quick update. Workload has prevented me from doing much. I've replaced the last few light bulbs with LED's, but not much else... (I had trouble with the combined stop/tail bulbs and had to modify them to get them to work.)

...but I have finally at least purchased all the kit I need for this alternator delete mod. A 2KW Kenlowe engine coolant pre-heater kit and a CTEK 10A temperature compensated battery charger. Now i just have to find the time - and a gap in the weather! - to install it all. I might crack and get my mechanic to do it for me, ...at least to install the heater and pump into the coolant system. That part will probably have to be done from below, and I'm not keen on crawling around under cars outdoors in this cold wet weather.

I also bought a PWM motor speed controller to fit to the blower motor, but it looks like that's not as straightforward as I thought it would be. It turns out the first controller I bought (from China) does not use a common negative for input and output (it uses a common positive) so I can't just ground the negatives of the input and the output. It can still be done, but it will need a bit more thought. I have bought another one which might be easier to install. Anyway, I think I'll put that one on hold and concentrate on the alternator delete and pre-heater for now...

But yeah, looking forward to having a slightly hybridised car in a little while! And one that starts each morning at 80 degrees Celcius!

[Occasionally6]

One comment on the blower motor speed control. While the OEM uses discrete speeds for the blower motor, with a PWM controller there's little reason to keep that. The fan speed can be varied continuously if you contrive a variable input.

[paulgato]

Agreed Occasionally6, ...in fact these PWM's come with potentiometers and control knobs, so that's probably the easiest way to use them: just mount the supplied control knob and pot' on the dash, extending the wires if necessary. I would want to be careful not to run so low a voltage to the motor that it won't turn though - in case that damages the motor. I'd probably want a 'bypass' resistor for the lowest speed.

Actually I prefer, when driving, to have a tactile indication of what level I've set things to. I kind of know, under given driving conditions and at a given vehicle speed, that blower speed 1 will be enough, or that I'll need blower speed 3 for a while and then can drop down to blower speed 2 once the windscreen is clear for example. I also quite like the idea of not having an extra control knob on the dash if it's not needed. Ideally, I'd have four trimmer potentiometers back in the guts of the wiring connected to the PWM and switch between them using the stock VW control switch on the dash. That way I could infinitely adjust each blower speed to my own requirements and then when I have them right, leave them alone and use the stock control switch.

But I'm not clear about how these things work. (E.g. why do potentiometers need three wires?) I know some of these PWM's can have a 'control voltage' input between two contacts (0v - 5v for some PWM's) to control the output power voltage, but I don't know if the one I bought can accept that. (I guess I should ask the guy in China I bought it from.) That would make life really easy as I could then simply solder resistors between the output terminals of the stock VW speed selector switch.

But that's for another time. I've been puzzling over the installation instructions of this Kenlowe coolant pre-heater, trying to decide where it will fit best in my engine bay. The unit looks well designed and well made.

[paulgato]

It's been a busy winter so far - and a really, really, record-breakingly wet winter. The wettest January in the UK since records began 250 years ago. It has rained virtually every day and I have not felt like working under a car on my driveway, so all this was put on hold. Also, during one of the many storms we have had a tile fell off my roof onto my driveway so have not felt too comfortable about parking my car there by the house where I can plug it in to the mains power supply, in case another tile falls on it.

However, I did manage to fit a waterproof outdoor power socket on the wall of my house by my driveway, and also, crucially, I got around to getting rid of an old van that had been permanently parked on that driveway for the past 5 years and had been used as a storage shed. So now I have a space to park the car and a means of plugging it in to the mains overnight.

I still haven't got that engine pre-heater installed, but today I did fit the battery charger in the engine bay and sorted out a temporary way of plugging it in overnight. I disconnected the alternator field wire, so from tomorrow onwards I shall be running without the alternator for all normal daily driving, only switching the alternator back on for longer trips of more than about 150 miles.

I'm kind of regretting buying that expensive and rather complicated coolant heater. Monitoring more closely the mpg meter in the car, it seems the mpg is only significantly higher for the first few minutes of driving, and yet it takes nearly 30 minutes to get the engine up to full temperature in the winter. After 5 minutes the engine temperature is probably less than 50 degrees. My guess is that a simple, cheap, silent and reliable oil sump contact heater, of the self-adhesive type, and of perhaps 125 watts power, would be enough to warm the engine to a point where the fuel economy is reasonable from the time the engine is started. I would need to switch it on a few hours before drive-time, but at only 125w I could probably justify leaving it on all night along with the battery charger. I have a 100% grille block and a good engine undertray, so the engine would probably stay fairly warm even with a mild breeze blowing. I could also insulate the oil sump with PU spray-on foam, which would increase the effectiveness of the heater, and would also help to keep the oil warm for longer when the car is parked up away from home during the day.

So, I'm not sure what, if anything, I shall be doing about the pre-heater in the short-term, but I am looking forward to seeing what gains I get now with the alternator switched off.

[paulgato]

OK, so I'm in the process of installing an engine preheater which I bought back in October/November when the MET Office were predicting a long, cold winter. In fact we've had a rather warm and extremely wet winter and i haven't got around to installing the heater unit until now.

It's a 2Kw Kenlowe coolant heater and pump that is supposed to heat the engine to 85 degrees Centigrade.

I've got as far as plumbing the thing in to the heater hose and now I'm struggling with the electrics. Currently struggling to install the mains connector on the front grille without it sticking out forwards in a potentially pedestrian-injuring way.

It has taken MANY HOURS to install this heater thing but I'm getting there. And I am enjoying the process.

By the way, my initial impressions on running without using the alternator are encouraging. So far on my daily driving routes for work and social use, I have had no cause to worry about the voltage getting too low. It starts about 12.5 under load and it seems I can take it down to 11.5 under load with no problem at all. That represents about 4 or 5 hours driving with no lights or windscreen wipers, etc, or about 2 hours with all that stuff on. My overall running mpg average seems to be up by about 10% and the test runs I've done show that indicated mpg at 30mph is up from about 87mpg to 99.9mpg. (The gauge only goes up to 99.9mpg). 50mph test runs show a somewhat smaller inprovement of about 5%.

I have a CTEK waterproof, temperature compensated 10A intelligent charger sitting in the engine bay, connected up to the 90Ahr AGM battery, and I plug that in to the mains when I park up on my driveway. I have a 4-digit illuminated volt meter mounted on the dash that I can also read through the rear window if I'm not in the car, so I can get an idea of the state of charge while it's plugged in. The 10A charger seems to fully charge the battery overnight with no problem at all, although I haven't got in there with a current meter to confirm that.

More later...

[NachtRitter]

I would be interested in seeing a pic or two of how you have it all arranged in the engine bay... charger & battery & coolant heater with pump.

Would you be able to do a timer on the coolant heater, so that it switches on automatically 2 hours (or whatever) before you have to leave?