Any Sparks?

George Elliott · Nov 22, 2008

Perhaps some-one can help me with understanding the operation of a voltage regulator?

Why?

My Dash (I know they are inaccurate) voltmeter is telling me the following:
- when I flash the lights, or switch on the Front Demist switch, the voltmeter indicates about half a volt drop in reading. (as these two are independent I am working on the basis that there is nothing wrong with either circuit. Additionally the ABS pump (which is also a high current device) causes a big deflection on the guage.

- I have an adjustable voltage regulator fitted, came from "ArnnWorx" .com. The benefits are improved electrical performance, and I am convinced better running at the higher end of the boost range (1.2Bar). I believe the boost may have the effect of killing the spark/flame front on combustion at highish rpm (5K+) and therefore I dont want to remove the adjustable regulator - It also took me hours to fit[>:].

The earths are good
The alternator is good
The battery is good
The DME relay is good[

]

Back to the question, & another bit of info - sometimes (following the high current deflection described above) the dash voltmeter will indicate increased voltage (perhaps 1 volt) above the 12.4v indicated in normal running. (The car has13.3v according to my multi-meter at the battery @2000rpm). When this happens, the increase occurs in a linear fashion with engine rev's. I realise there are huge risks from excessive voltage in the circuit, anything over 14.5v being excessive. The most I have seen is 13.8ish volts.

I would like to understand the components and how they work so I can understand the problem. I should have said it is intermittent.
Any explanation appreciated.

George
944T
964

peanut · Nov 22, 2008

I think you may be confusing amps with volts. Volts are no indication of current load or supply. The voltmeters in the Porsche are pretty crude to be honest.
I would suggest you get your car checked at Lucas or Halfords . Sounds like the regulator in your alternator might be faulty or the brushes may be worn giving a flaky output under load.

Clarkes Garage website has some good elec tests and guides and schematics worth a look

rcsalmons · Nov 22, 2008

I cant see that you have a problem.

The regulator simply limits the voltage from the alternator so as not to damage the battery and car components. Typical limit is 14.5V.

When you turn on something that draws current you will have a voltage drop - more when the engine is not running or from a higher current device.

Rich

George Elliott · Jan 23, 2009

Just to close this problem fyi,
The intermittent behaviour continued as described, and developed until two more things happened,
1. when main beam was selected the rev counter jumped say +500rpm
2. Occasionally (one time in 20) but increasing in frequency, the car was totally dead electrically at startup, (once going it never stopped though)
So I fitted a new ignition switch to the barrel on the steering column, bit awkward but as Scott mentioned on another post it can be done.
Tried the new switch, - still the same...........[

]
So, I have the new switch on, the interior light is on, the bonnet open, back hatch open, and I am trying to locate the component which needs a poke to bring on the ignition. I tapped the DME, fuses, fuse box, loom at the ignition, - nothing. Then I touched the Battery earth to body Strap, click - ignition on, Repeated the test 5 times until it "hung" off again, then wiggled the strap, and - on again immediately. Removed the strap, cleaned its ends, the strap securing bolt was "slightly" low on torque.
George
944t
964

sawood12 · Jan 23, 2009

Don't confuse the voltage delivery from the battery with the operation of your voltage regulator. As i'm sure you'll know the main difference between a Dynamo and an Alternator is that a Dynamo delivers voltage relative to engine speed whereas an alternator delivers constant voltage irrespective of engine speed. The key component that achieves this is the voltage regulator. So in short the voltage regulator delivers a constant voltage to the battery - so I don't know why you are seeing the voltage output varying with engine speed.

When you observe changes in voltage when switching on various electrical items you seeing what the battery is delivering which is completely independent and nothing to do with the voltage regulator attached to the alternator.

Again the voltage that is delivered to the spark is boosted by the coil from the 12v or so provided by the battery to circa 20,000 volts. The coil draws electrical energy from the battery and not the alternator/voltage regulator (if you're alternator packs up or your fan belt snaps your car will continue to run until your battery runs flat) so I don't see how your voltage regulator will affect the strength of your spark.

From what you describe I don't see any problem relating to your volt meter dropping as you switch on various electrical items. The thing that does sound strange is that you are seeing an increase in voltage and that it is related to engine revs. The whole point of a voltage regulator is to regulate the voltage at a constant level relative to engine speed.

Hallsy · Jan 24, 2009

I'd agree with the above, a slight drop in voltage on the voltmeter when operating certain circuits is perfectly normal, it's just that, a volt drop as the circuit goes under increased load. The battery will normally recover from this dips very quickly, rpm may increase momentarily to give extra charge to the battery, again this is normal.

When an engine is running at reasonable rpm it is quite normal to see as much as 14.4V being delivered to the battery, and will not be a problem.

I'd also echo the above, if you feel you have a weak spark, or it is being blown out on boost, then this could be the plugs themselves needing replacing, or at least having the gaps checked (too wide will cause the spark to get blown out), failing that it could be a problem with the HT leads or the coil. You can check continuity of the leads with a multi meter, you could also check insulation resistance but as a multimeter is powered by 9V, and the HT leads carry 20KV it probably won't show up any strak arcing, although if it does the leads would be in very poor shape.

HTH.