WEIRD electrical problem - help, please!

[JayeM]

I don't normally get flummoxed by an electrical problem, but this one's got me stumped!
I've been helping diagnose ignition problems on a friend's SP, which has led to changing every single item on the ignition except the battery.
The car now starts and runs fine in standard setup - points, coil etc,all electronic modules removed, BUT the charging voltage is ridiculously high (30v+ at one point).

Assuming we simply had a blown alternator regulator, we changed the alternator for a brand new one, only to find exactly the same symptoms!

Thinking a bit deeper, I thought there might be an internal connection between the LT and HT windings in the coil, allowing some direct high volts back into the LT wiring. We changed the coil for a new one, and the symptoms stayed the same!

Now deciding we may have just been unlucky with the new alternator, we disconnected the alternator and fan belt, to just run the car from the battery.

Now the WEIRD bit - the symptoms still stayed the same!
No electrical generator of any kind in circuit, and the battery volts rising above 15V!
Even with a simple piece of wire bypassing all the car wiring loom and connecting the coil to the battery direct produced the same effect!

Now doubting my meter (a mid-price DVM) I plugged my "quick check" gizmo with LED readout into the cigar lighter - engine off it read about 12.7V, immediately the engine starts it overranges!
I tried the same thing with my AVO8, and it promptly blew the cutout on the 30V range!
Also, when the engine is stopped, the battery volts will continue to read about 16V for some time before coming back to 13v or so.

All my meters work as expected on other cars, so far as I can tell all earths etc are good on the car, and the effect seems to be independent of ignition hookup, contactless or contact ignition, coil used etc. The only thought I'm left with is that this is some kind of RF pickup that needs a snubber to be fitted to the coil. (My DVM does behave oddly if the leads aren't connected around this engine bay.)

The real problem is that the car is "frying" coils, and I'm really concerned that it will overvolt lamp bulbs/wiper motor/fuel pump, but I'M STUMPED!

Have I missed something? Has anyone any ideas for something I can check/try?

All help from Forumites is always appreciated, but this time I could REALLY do with some!

 

Cheers,

John

[Rod1883]

Voltage regulator problem?

Or is that a silly comment on an alternator system?

Edited August 3, 2014 by Rod1883

[boxofbits]

Hi john

 

Out of interest have you tried another battery. Just wondered if there is a short developing inside the battery. Even though it still starts the car, maybe it is drawing a lot of current from the alternator?

[JayeM]

Thanks guys,

 

trying a(nother) new battery tomorrow!

 

(Everything on this car is less than 2500 miles old!)

 

John

[RobH]

The symptoms as described make no sense at all. A good battery will have a pretty low impedance so you would need a fearsome charging source to really get that sort of voltage - and you would destroy the battery no time or at the very least blow a fuse. I assume the battery turns the starter over normally which would indicate that it is OK ?

 

Can you tell us please:

 

1/ where and how are you measuring the voltage ? Is it straight across the battery ? (I would trust your AVO measuring there but not the digital things which have ridiculously high impedance for this kind of work.)

2/ how many batteries does the car have ? I don't know much about SPs but is it possible it has two in parallel ?

3/ I think an SP has a plastic body - how are the earths connected - through the chassis?

 

I guess it is possible this is all a red herring caused by odd effects on the meters, while the car is really frying coils because it should have a ballast resistor fitted in the coil feed ?

[JayeM]

I agree with what you're saying, RobH - it doesn't seem to make sense, hence the cry for help!

 

In answer to some of your questions;

a/ the battery turns the engine over normally (the car has a high-torque starter fitted so it doesn't have to work hard)

b/ I've been taking readings across the battery and between the coil feed terminal to earth.

c/ single 12v battery only

d/ earths are all connected via chassis, primary earth is to a bellhousing bolt. Earth continuity checks good throughout the engine bay.

 

e/ the coil(s!) are 12v 3ohm and no ballast resistor is fitted.

 

This car was wired up by me and is close to identical to the wiring on my own car which doesn't show these symptoms. Also, it was running fine for 2500 miles, then abruptly stopped with an ignition fault. From that point on these weird symptoms have been showing.

 

Take the point on high impedance DVM, but don't understand why my AVO cutout would trip if it was a red herring, and my plug-in voltmeter works perfectly on other cars, including mine, but I'm happy to try again with another moving-coil meter when I can lay my hands on one.

 

I'll be very happy if it is just a meter effect - I just don't want to risk the car's electrics until I'm sure!

 

Thanks for your help - let me know if these answers suggest anything to you.

 

Cheers,

John

[AlanT]

I should think that the alternator earth-return does not connect to the battery earth.

[Paul Down]

Its a bit far fetched but assuming that the alternator is functioning normally the only other potential generator with the engine running is your starter motor. But it would have to remain engaged and the wiring be incorrect to cause the problem. A remote possibility but you are running out of options. The coil even if faulty would not increase the volts it would just fail. 30 volts would certainly burn out your coil, and possibly other 12v items such as lamp bulbs and or wiper and heater motors and fuel pump.

[RobH]

OK John - understood.

 

You shouldn't get any spurious readings directly on the battery terminals as it should be effectively fractions of an ohm, though the coil feed terminal is downstream of numerous switch, fuse and other connections which could be putting resistance in the circuit so you might get something odd happening there. If you do get odd readings directly across the battery it might indeed be failing in some way.

 

I guess trying another battery can't hurt, though the fact that the battery starts the engine OK seems to indicate there might be nothing wrong with it - even a geared starter needs a fair bit of current.

Is there an ammeter which confirms a large charging current (which there would have to be) or have you tried a clip-on ammeter ?

 

Paul - you beat me to it suggesting the starter - exactly what I was going to say. Its a very long shot though and would need multiple failures. However if the AVO popped with a bare engine it might point to something like that.

 

Final thought on the coil failures - is the points capacitor OK - if it shorts there might be current on the coil all the time.....

 

 

Rob

[BlueTR3A-5EKT]

Long shot - you have a 24v Alternator?

 

Cheers

Peter W

 

PS Sorry - Just reread - you had high voltage even with the alternator disconnected. Now that is curious. If it were a canal barge I'd say you had a dynamotor fitted.

 

 

Now the jokey bit - Should you now contact the big car makers as you have the possibility of 'perpetual motion' ?

Edited August 3, 2014 by BlueTR3A-5EKT

[RobH]

John - a simple check. The starter solenoid obviously pulls in OK, but does it let go again while the ignition is on ? Measure the volts on the main cable to the starter motor downstream of the solenoid - should be nothing once the button or key has been released and the engine has started.

 

Rob

[Rodbr]

Clutching at straws here, real foxy problem.

Do you still have original starter solonoid connected?

Is there a solonoid on the hi torque starter? my WOSP one has and there are two methods of connection.

Any unusual noises from starter?

If so does one release and other engage and so it spins when running?

 

Link to fitting instructions

http://www.wosperformance.co.uk/products/starter-motors/fitting-instructions/

Edited August 4, 2014 by Rodbr

[AlanT]

Is the voltage related to engine speed?

[JayeM]

Thanks guys - some good thoughts there, I'll get back to you when I've run the checks.

 

(and Peter, if it does turn out to be perpetual motion, you can do the presentation to "Dragon's Den" !)

 

John

[Lebro]

Having read all of above, I think the starter motor being still engauged theory is the only one which could explain the high voltage with no alternator.

The starter will crank the engine over quite slowly with 12V applied, but once started it would be spinning much faster, & so would generate a "back EMF" much higher than 12V. Just a thought - has the motor got the right No. of teeth for the flywheel / ring gear - I know that early TR's needed a 9 tooth gear where as later cars (TR3A's, 4's etc need a 10 tooth gear. I don't know what a "SP" is but may be worth checking.

 

Bob.

[peejay4A]

Wouldn't it make one hell of a noise if still engaged though?

[Lebro]

Yes, I would have thought so. The idea is very unlikely, but 30Volts ? where else can it come from ??

 

Bob.

[MikeF]

Am I right in saying that you only get the over volts
1) after running the engine but
2) not if you just walk up take a meter reading.
3) The over volts decline in a few minutes after switching off (and only re-occur if you re run the engine.)
4) the over votes occur even with alternator completely out of circuit?

Here is a bunch of ideas to try, pretty well in the order I thought of them, so not entirely logical process steps.
Likely you will be in for a long plod of try this and that till you get an insight.
The question is in a DC system how are you getting higher volts than the ~12V of the battery? There has to be some sort of intermittent current going through an inductance somewhere and this only intermittency can only be coming from a make and break somewhere. The higher volts don't necessarily mean a lot of power, just higher volts.
So you are looking for coils on the car, anything with a motor and likely multi earth points in their associated circuitry, probably one will have a higher impedance than the other.. It sounds mad but just disconnect the wiper motor, car radio, electric aerial and anything like that, one item at a time and take your readings,

What happens if you "measure" the over volts with a bulb, does it light very brightly and then decline to normal?
What happens if you start the engine with all the lights on to give a load, what does your meter show.
Do you get over volts if you bump start the car?
What happens if you rig a new loose wire circuit from battery to ignition and back to battery, and then disconnect the wiring loom engine running (alternator already out of circuit) so engine can run just off the new loose wire loop..
Could it be.... that there is a misrouted wire in the loom, or an additional one you don't know about? (In my own car the wires went in one (the right) colour and came out another (wrong) colour somewhere else, a PO had done this, but the next PO didn't realise so he wired something else up to the (wrong) wires and lo and behold when you turned the engine off, the lights came on for a second or two. I still don't understand how that worked. Just accepted that in a fairly complex network strange things will happen.

 

MIke

[Paul Down]

Mike,

 

As the over voltage is burning out ignition coils the source has to come from something capable of sustaining AMPS so something substantial such as the alternator or possibly the starter motor running as a generator. I cannot imagine anything else that would supply enough current.

[Clarkey]

Mike,

 

As the over voltage is burning out ignition coils the source has to come from something capable of sustaining AMPS so something substantial such as the alternator or possibly the starter motor running as a generator. I cannot imagine anything else that would supply enough current.

Not sure wether this could happen but is the starter motor solenoid keeping the starter pinion engaged on the flywheel.after the starter has been released

Straw clutching but could this be possible

Edited August 4, 2014 by Clarkey

[Guest ntc]

Not sure wether this could happen but is the starter motor solenoid keeping the starter pinion engaged on the flywheel.after the starter has been released

Straw clutching but could this be possible

Yep

Disconnect one wire at a time and you will find it.

[peejay4A]

I don't buy the starter remaining engaged theory. It would make one hell of a racket and there'd be a good chance it would fall apart if you revved the engine. I lean toward's Al's theory. Has the car had any attention to it's wiring before this started? New loom maybe? Here's another theory. The alternator is somehow appearing in series with the battery, not in parallel as it should be. This would give normal battery voltage across its terminals, or indeed from wherever else you expect to see 12v, when the engine is off. With the engine running and measuring from one of the "earths" to the ignition supply you could see up to 14V from the battery plus whatever the alternator could produce and I would think that could exceed 30v. As Neil says, pare the wiring back to bare minimum and go from there.

Edited August 4, 2014 by peejay4A

[Rodbr]

Peejay,

The guy said in his first post

Quote

Now deciding we may have just been unlucky with the new alternator, we disconnected the alternator and fan belt, to just run the car from the battery.

Now the WEIRD bit - the symptoms still stayed the same!
No electrical generator of any kind in circuit, and the battery volts rising above 15V!
Even with a simple piece of wire bypassing all the car wiring loom and connecting the coil to the battery direct produced the same effect!.

 

What else could potentially generate power with alternator disconnected ?

With perfectly aligned starter dog there may not be loud noises. Things may have worked as intended prior to the problem but possibly a solonoid stuck. It is very much a case of first principles and check off as you go.

 

It is a Daimler v8 after all!!!!!!!!!! Noisy at the best of times LMAO!

[tthomson]

The trouble with using a multimeter on a car is that there are lots of spurious voltage spikes that can lead to false readings.

Intermittent connections in the coil circuit will cause the coil to fry from exactly this kind of situation and it will generate a lot of spurious voltage spikes on any other circuit in the car, which would certainly give erroneous readings on a multimeter. (The AVO fuse blow may be just coincidence.)

 

The only thing in line between the battery and the coil is the ignition switch. I have in my possession a faulty ignition switch that is intermittent, until then I would not have believed it was likely.

 

Any loose connection in the ignition circuit could cause this sort of problem.

 

To really troubleshoot this problem you need an oscilloscope to see what is happening at various places in the circuits of interest.

 

Having said that, I would be checking every connection in the ignition path.

 

Good luck

 

TT

[AlanT]

If this is being generated by the starter, then you are pushing a lot of energy into the battery.

 

A lot of Hydrogen will be released. I once blew up a battery by over-night charging and igniting the Hydrogen in the morning.

 

Be really careful, the battery could explode, split, melt or fail with an internal short.

Edited August 5, 2014 by AlanT