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Topic: OK to start car with alternator disconnected? (Read 890 times) |
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johndyork
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OK to start car with alternator disconnected?
« on: Dec 3rd, 2006, 9:17pm » |
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Hi guys - any help appreciated:
Orig Prob: Battery going flat rapidly. Found large leakage at battery, suspected alternator – which was also whining a litttle.
Solution: Renewed Alternator (Ford part) and battery (which was 5 yrs old) – replaced with larger capacity one. Starting now no problem and battery charging/holding charge no problem.
New Problems after replacements: a) All lights flicker continuously b) Ignition light on very faintly
Asked Ford to check it out – they disconnected blue ignition light wire – light remained on & they also said was charging OK – so said no problem with alternator. (cost £25) Still not convinced.
Observations:
When under full load (front + rear screen + fan + lights the charge voltage drops to from 13.8 to 12v at battery but flickering stops – as items switched off flickering gradually comes back?
Flickering occurs regardless of revs. Belt tension ok & no evidence of slipping
Question: To try and prove alternator related would it be OK to disconnect alternator-to-battery lead and start the car & then test lights – if no flicker then alternator involved somewhere?
Many thanks, johndyork
Below is a list of things tried and other ideas:Solutions tried:
No-load voltage across battery engine off = 12v
No-Load voltage across battery posts engine on = 13.8v (14.4 when just started) (3000rpm)
Full-load voltage across battery posts engine on (front/rear screens, fan, lights) = 12v
Used jump lead from alternator case to battery –ve, no difference & no voltage drop
Used jump lead from alternator +ve to battery +ve, no difference & no voltage drop
Cleaned/sanded battery terminals and all leads at battery. no voltage drop –ve batt to body.
Cleaned both earth points near battery bulkhead (one from battery, one to engine)
Renewed engine earth strap and cleaned all connections
Fan belt is tight
Other ideas:
Any other obvious connections to check? Where is main harness earthed?
Fuses dirty? Lights seem to go through diff fuses?
Are there any relays which could be involved?
Check all earth connections – is there a particular one for lights?
Alternator brushes?
Regulator: Can voltage regulator be renewed at alternator (is it external?)
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N Reg 2.9 12v Silver Saloon
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TiberiuS
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Ex. 1996 2.3 Ultima - RIP P789 KHJ
Posts: 2257
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Re: OK to start car with alternator disconnected?
« Reply #1 on: Dec 3rd, 2006, 10:29pm » |
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Hi John.
What is flickering exactly? dash lights? headlamps??
It seems that the battery is charging ok, around 14v with no load is normal, dropping with heavy load...
When I replaced the battery on my 2.3 Ford had trouble finding the correct rating, they said too large a battery can kill the alternator and vice versa with too small a battery; I'm not certain myself, alternators aren't my area  . I wouldn't recommend disconnecting it and running the engine, alternators can get funny about open circuits - your risk I'm afraid.
I'm thinking either a module fault or (less likely) a fusebox/loom fault, dirty fuses could cause intermittent faults but flickering with a heavy 12v current going through is unlikely. Ignition lamp could just be a bad contact, other lights flickering is more of a worry.
Hope this helps some.
Regards, Bruce.
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johndyork
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Posts: 73
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Re: OK to start car with alternator disconnected?
« Reply #2 on: Dec 3rd, 2006, 10:59pm » |
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Thanks Bruce - all lights flicker all the time (dash, interior etc) - probably everything is flickering but only lights show what is happening. Gen web search view is down to poor connections but coincidence started when alternator switched.
Have access to an oscilloscope - wondered if worth putting it across the alternator - link below gives example of diagnosis waves:
http://www.mztech.fsnet.co.uk/electrics/alt_osc.html
Must admin I am hesitant to disconnect alternator to battery lead and start car as with belt still driving alternator not sure if it would do any damage.
Still have problem how to eliminate alternator before looking elsewhere for a needle in a haystack!
Cheers, johndyork.
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twinturbo
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Re: OK to start car with alternator disconnected?
« Reply #3 on: Dec 3rd, 2006, 11:20pm » |
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12V Static?
Should be 12.7V.
TT
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Dave
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Tourmallard 24v (ex-owner)
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Re: OK to start car with alternator disconnected?
« Reply #4 on: Dec 4th, 2006, 8:10am » |
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Which earth point have you checked? There are a few  Assume the alternator is correct for this engine?
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Snoopy
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Re: OK to start car with alternator disconnected?
« Reply #5 on: Dec 4th, 2006, 8:28am » |
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Yes it is safe to run the car with the alternator disconnected but do not try going very far you will only have battery for ignition and other ancilleries.
If it is just for testing then should be OK .
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mr._floppy
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Re: OK to start car with alternator disconnected?
« Reply #6 on: Dec 4th, 2006, 11:21am » |
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£25 for a replacement alternator, 
tell me the supplier please !
New, re-conditioned or a scrappy one ?
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TiberiuS
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Ex. 1996 2.3 Ultima - RIP P789 KHJ
Posts: 2257
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Re: OK to start car with alternator disconnected?
« Reply #7 on: Dec 4th, 2006, 1:23pm » |
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Disconnect it then, I wasn't sure myself
With the ignition on but without the engine running surely this is the same as disconnecting it, do all the lights work ok then?
It wouldn't hurt putting a scope on, I've got no idea though what the waveform would look like with the alternator running, surely with a good battery the voltage couldn't sag below the cell voltage, mabye spikes are upsetting it all
Regards, Bruce.
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johndyork
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Re: OK to start car with alternator disconnected?
« Reply #8 on: Dec 5th, 2006, 12:20am » |
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Thanks for contributions guys- replies itemised:
Twinturbo – will recheck static volts across battery – my meter has 0-50v scale so not too sure about exact accuracy.
Dave – replacement alternator was from Ford (part exchange) looked up on their system etc so hopefully correct one.
Snoopy – was not thinking of driving anywhere – just starting engine with alternator to +ve battery lead disconnected to see if lights flicker – if no flicker then assume alternator involved somewhere!
Mr Floppy – alternator was about £125 after part exchange with Ford – the £25 was for them to diagnose their alternator was OK! This is the real problem – proving the alternator is at fault has a cost and it is only redeemable if they admit there is a fault which is why I need to prove it!
Tiberius – the alternator is effectively just across the battery terminals, as the main red lead goes from the alternator to the battery, and all devices are across the battery terminals so if the alternator is not connected there is no running charge and any devices will just take their juice from the battery instead. Hopefully no flicker would indicate alternator involved somewhere. Would only run long enough to turn lights on (no other devices) to see if any flicker and then turn off.
Am also going to borrow a ‘scope which I understand is treated like a voltmeter and put across the +ve and –ve on the alternator. Link in previous post shows the images expected for normal or other faults etc.
Jobs for Tuesday night – thanks again for contributions - will report back any useful info.
Regards, johndyork.
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harry.m1byt
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Re: OK to start car with alternator disconnected?
« Reply #9 on: Dec 5th, 2006, 10:03pm » |
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Connect the scope as per a volt meter. DC coupling will offset and cramp the trace above the the 0v line. AC coupling will disregard the DC, so the trace will be on the 0v line enabling the actual ripple on the trace to be amplified for easier measurement/display of the waveform.
BTW... You really need something better than a 0-50v meter for accuracy. You can buy suitable digital meters for around £5 these days.
You may be able to get a rough idea of the (AC) ripple on the DC, by switching the meter to the AC range.
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johndyork
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Re: OK to start car with alternator disconnected?
« Reply #10 on: Dec 5th, 2006, 11:36pm » |
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Cheers Harry for scope hints - must admin the panel scared me a little as hadn't used one for over 30 years! Found the following:
- disconnected alternator & started engine, no light flicker at all - then reconnected alternator for scope tests
- engine off image (to get basic trace): http://i16.tinypic.com/43mtsa9.jpg
- engine on - were up to 4 simultaneous lines at times: http://i13.tinypic.com/3zaodgi.jpg
- engine on - shows frequently broken line: http://i14.tinypic.com/2s6x2bp.jpg
- Trace of other car, Focus, for comparison of health with same settings on scope: http://i13.tinypic.com/2j5l7bo.jpg
Think there is enough evidence here. So will contact local FMD where bought alternator and ask them for a 'free' recheck.
Regards, johndyork.
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TiberiuS
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Ex. 1996 2.3 Ultima - RIP P789 KHJ
Posts: 2257
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Re: OK to start car with alternator disconnected?
« Reply #11 on: Dec 6th, 2006, 8:13pm » |
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Hi John, what's the ripple on the voltages?
I can put a scope on my 2.3 tomorrow if it would help you.
Regards, Bruce.
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Bruce - '07 Jaguar XKR coupe, '95 Jaguar XJ Sport 4.0, '82 Ford Capri 2.0 Ghia, '15 Honda Civic (sloooooww..)
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johndyork
Junior Member
There's a hole in my pocket!
Posts: 73
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Re: OK to start car with alternator disconnected?
« Reply #12 on: Dec 6th, 2006, 8:42pm » |
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Hi Bruce - not sure what the 'ripple' is - I was just looking for patterns rather than actual voltages etc, had measured basic voltages with multimeter. Not too familiar with the theory of the scope waves. From scope images in previous post hopfully the multiple image (pic 2) and broken wave image (Pic 3) is enough evidence - compared to the healthy Ford Focus image (pic 4).
Cheers, john
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johndyork
Junior Member
There's a hole in my pocket!
Posts: 73
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Re: OK to start car with alternator disconnected?
« Reply #13 on: Jan 19th, 2007, 11:06pm » |
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Hi Guys - just to report back on final result:
Following scope tests FMD rexamined the alternator for free - said charging voltage ok & may or may not be contributing to light flicker and faint ignition light being on - basically they did not have equipt/procedures etc to test test an alternator thoroughly.
Bought a 2nd hand one from Motor Spares UK (£35 + £12pp + vat) - put it in and all problems immediately disappeared (ie no light flicker & not ignition light on) - brill!
Wrote back to FMD and they have agreed to refund the £126 for alternator and the £25 I had to pay for them to 'inspect' it - lol!
Thanks to all members for comments and encouragement to see problem through. Regards, johndyork.
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Dave
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Tourmallard 24v (ex-owner)
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Re: OK to start car with alternator disconnected?
« Reply #14 on: Jan 20th, 2007, 8:19am » |
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Nice one John 
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Simmo
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Re: OK to start car with alternator disconnected?
« Reply #15 on: Jan 20th, 2007, 8:29am » |
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Good result... well done.
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