VWDiesel.net The IDI, TDI, and mTDI source.
Engine Specific Info and Questions => IDI Engine => Topic started by: dokarex on May 04, 2007, 05:18:52 pm
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The berings are almost gone in my 87 Na Diesel Doka so I removed the alternator today and took it to the local rebuilder.
Holy Cow :o I must have picked up 5 or more hp (remember I only have 52 to start with 1.6l na). what a difference without the alt. I know racers run with no alt for this reason I just never thought it would actually make this much difference, on hills that I usually slow down on we just kept going and on a road I usually only barely hit 80kph we easily maintained 100kph. :D
Since this is a diesel only the fuel solenoid and the guages use power unless driving at night or blasting the radio but how can we disconnect the alt if we want to with out getting out and removing the belt. Until I get a 1.9 TD I'm tempted to run with out the alt and carry a charger. :evil:
87 Doka na
97 Jetta TD (wifes "think she would notice if I swapped engines? :twisted: ")
B2600 Kubota only here cause its diese
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I drove without an alternator in a rabbit for a few months. I just keep a spare battery on the back seat and a set of jumper cables. I used to swap the battery everytime the one died but that got old fast so I would just hook up the battery using the jumper cables, start it and then pack it all up. You'll kill your battery fast though.
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If you removed the alternator,how did the water pump run,its on the same belt? well its the same belt in uk :wink:
Bert
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Full throttle alt/A/C cutout switch? There's a thread kicking around somewhere...
Andrew
It has some good info and ideas. I still havent found a big enough closed state relay to kill the alt.
http://www.vwdiesel.net/phpBB/viewtopic.php?t=7460&start=0
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I should know the explanation to this better, but every book I've ever read about charging systems says "Whatever you do don't run the alternator with the B+ lead disconnected from the battery"... and goes on to talk about ruined diodes, hoards of locusts, global warming, and other evils that will befall you if you do this.
The ideal place to cut out the alternator would be the field windings... much lower current than needing to find a honking big relay on the B+ line, and evidently much safer on the diodes. As a young lad with a 1969 VW van I had a pull-switch bolted to the stickshift that performed this function for the enviable red light races (when all you have is 57 hp every little bit helps) but that was an era of generators with an external regulator and very accessible field windings.
Lots of modern racing cars still have "Alternator ON/OFF" switches so it must be possible... I'll do a little more digging.
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what about a marine battery selecter switch they have batt1 batt2 and off?
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It could certainly handle the current, but you'd be taking your chances on the alternator diode bridge.
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I don't get it. The alternator should present little or no parasitic drag when there is no call the charge the battery or power electric accessories. I thought that was the point of the voltage regulator, high battery voltage means reduced field strength and less charging from the alternator? So, I don't see how a cutout switch would help. Feel free to enlighten me though. :)
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Yup, assuming the battery is in good shape a diesel doesn't present much of a load to the alternator... but it does take power to make power... every 746 watts is a horsepower if the alternator is 100% efficient.
I agree... the gains are likely slight. Disconnecting the A/C would probably have a much higher yield.
Vince
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well having a clutch like on the a/c compressor would be nice... but then again that draws power...
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Yeah ... a clutch that disengaged automatically until battery voltage dropped to a specified level would be ideal.
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Yeah ... a clutch that disengaged automatically until battery voltage dropped to a specified level would be ideal.
I still don't see how this would recover any HP. The alternator is pretty much already disengaged by the voltage regulator until the battery voltage drops.
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the alternator is a rotating mass though... surely you could gain more revvability
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Yup, assuming the battery is in good shape a diesel doesn't present much of a load to the alternator... but it does take power to make power... every 746 watts is a horsepower if the alternator is 100% efficient.
I agree... the gains are likely slight. Disconnecting the A/C would probably have a much higher yield.
Vince
The alt provides all the power needed to run the car. The battery is there to start the engine and assist in case the car needs more current. With diesels having such low current needs, the battery is pretty much doing nothing 95% of the time.
Would putting the switch on the exciter wire work as well? The thing is, if you kill the alt, you kill the tach, which is a no-no when doing a WOT acceleration. I like the idea of a clutched pulley but then again, no tach unless you use a gas tach with a sensor on the IP sproket.
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Yup, assuming the battery is in good shape a diesel doesn't present much of a load to the alternator... but it does take power to make power... every 746 watts is a horsepower if the alternator is 100% efficient.
I agree... the gains are likely slight. Disconnecting the A/C would probably have a much higher yield.
Vince
The alt provides all the power needed to run the car. The battery is there to start the engine and assist in case the car needs more current. With diesels having such low current needs, the battery is pretty much doing nothing 95% of the time.
Would putting the switch on the exciter wire work as well? The thing is, if you kill the alt, you kill the tach, which is a no-no when doing a WOT acceleration. I like the idea of a clutched pulley but then again, no tach unless you use a gas tach with a sensor on the IP sproket.
AHA! that is the first best problem with this mod so far... you're absolutely right... hmmm
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the alternator is a rotating mass though... surely you could gain more revvability
Oh I agree the removing the alternator entirely will gain some HP -- not only the rotating mass, but also the extra friction on the V-belt. But a cutout swich will not do anything about those. You'd have to get a smaller V-belt to go around just the crank and WP and use shims to tension it, which is a pain and wears out the belt faster.
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Once the alternator "self-excites" it's pretty much off to the races, although in the old days of bulbs (before the red LED) a burnt out bulb was often the cause of the battery going flat ie no output from the alt... maybe it would still work.
I'm sticking to the my story... yes the altenator does produce all current when the car is running (that's why your volt meter jumps from 12V (battery voltage) to 14V (alternator) when you start the car) but a diesel during the daylight has very little demand for current.... the gains by turning off the alternator are likely to be slight (unless the headlights are on, the blower is running, or the rad fan is on). My guess is that a large part of the omph you see running without an alternator is not having to spin another shaft with a fan on it.
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Once the alternator "self-excites" it's pretty much off to the races, although in the old days of bulbs (before the red LED) a burnt out bulb was often the cause of the battery going flat ie no output from the alt... maybe it would still work.
I don't think that will work. The LED is tied to the exciter wire. I'm actually driving my car without the exciter wire even hooked up and it's charging fine
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yup that would have been my guess... generators were much more sensitive to that than alternators.
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My guess is that a large part of the omph you see running without an alternator is not having to spin another shaft with a fan on it.
Never thought about the fan. An old alternator with worn bearings will also produce drag. Most MK2s and later vws' have DRL. Albeit working at only 90% or their capacity, it still needs a bit of current.
So killing the alt by interrupting power going to the battery will cause premature death and interrupting the exciter wire won't work.
I was looking at an AC compressor with a magnetic clutch pulley. It's a rather simple design. One two prong electrical connector and the clutch system. Main problem with this is the size of the compressor pulley. Mated to the alt, it would rev a lot less.
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How about using the smallest alt possible (55A as I recall) and grinding down the fan blades a bit? Switching to a serpentine belt should reduce belt friction a lot too. V-belts are very draggy.
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How about using the smallest alt possible (55A as I recall) and grinding down the fan blades a bit? Switching to a serpentine belt should reduce belt friction a lot too. V-belts are very draggy.
I think you'd see better performance with simply going with the serp belt setup. It can't be that hard to switch to a serpentine setup without using a MK3 alt. Simply swap the pulleys for the crank, waterpump and alt. If you got AC and PS, I think you're screwed (but if you're looking for less drag, you probably dumped them anyway :P ).
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well - according to the workings of the regulator and some silly experience, the bosch alternators give no load once the battery voltage climbs up to 14.1
Over here we call them bosch ones easy going alternators, when charging they will load up the engine and when purpose fulfilled they will freewheel, unlike the jap hitachi and denso ones which constantly have a brake applied on the engine - and also tend to overcharge the battery if you only use your car in daytime
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well - according to the workings of the regulator and some silly experience, the bosch alternators give no load once the battery voltage climbs up to 14.1
Over here we call them bosch ones easy going alternators, when charging they will load up the engine and when purpose fulfilled they will freewheel, unlike the jap hitachi and denso ones which constantly have a brake applied on the engine - and also tend to overcharge the battery if you only use your car in daytime
Overcharging the battery? wow that's no good :?
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^^
isnt it, it tends to boil the battery and reduce its service life.