Electrical Problemo

[kbj149]

The initial message was deleted from this topic on 15 December 2011 at 14:40

[kbj149]

The initial message was deleted from this topic on 15 December 2011 at 14:40

[Bassfiend]

Hmmm ... very limited practical knowledge of TVR electrics but do you have a multimeter?

When you start the car does the voltage across the battery terminals go up to 13.8v or more once it is running? (This will at least tell you whether the alternator is getting a charge to the battery.)

If not then check the main 100a fuse. (Tucked on the chassis rail where it's easy to get to and is protected from all the road crud - not!)

If it is then load up the electrical circuits of the car (heater blower, lights, wipers etc.) and see if you continue to get the same voltage across the battery terminals - I have had alternators in the past that have been able to hold their charging voltage when only a little current was being drawn but have collapsed when asked to supply a decent load.

Phil

[Goaty Bill]

Bassfiend said:

If not then check the main 100a fuse. (Tucked on the chassis rail where it's easy to get to and is protected from all the road crud - not!)

Phil

+1
Would say always the place to start given the symptoms leading to the result. Link makes it easy to recognise;
100 amp fuse

[plushuit]

kbj149 said:

Ok,
I've done a few tests a moment ago with a voltmeter, gave it a quick run and ....
12.3 - off
12.0 - off, radiator fans active
13.8 - driving, NO lights/blowers/wipers active
12.8 - stationary, held at 2K revs
12.1 - stationary, WITH lights/blowers/wipers active, held at 1K revs

Try testing the battery voltage AS you engage the starter.

P.

[Bassfiend]

I would have said that as the terminal voltage goes up when the car is running then the 100A fuse is intact but given that the voltage drops considerably when under load (I wouldn't expect it to sag as far as 12.1v) then my thoughts would be *EITHER*:

1) Alternator regulator fried and not holding voltage when there's a decent current draw.

• OR*

2) High resistance connection somewhere between alternator and battery ... most likely to be the infamous 100A fuse.

Now, if it's the fuse that's gone high resistance then that may well mean that it has been generating significant heat (passing current through a resistance generates heat of course) and that could have damaged the fuseholder so possibly best to change it in that case?

Phil

[Doc Toad]

Sounds like the same problem I had - bought the car with this as a known problem, seller had just fitted a new alternator in an attempt to cure it - no luck.

I managed to get it within 20 miles of home when it conked out (already had my shiny new RAC card though..)

RAC guy said he was 99% sure it was alternator, but of course I'd spent months lurking around various forums and thought I knew better!

Started working through the usual stuff (100A fuse, chassis ground connections etc etc).

Guess what - in the end it needed a new alternator!

Sometimes TVRs fail in a normal way, sometimes they don't. Get hold of a new alternator, it'll take 5 minutes to fit. If it sorts the problem get the old one repaired and keep as a spare. If it doesn't take the new one back and pay the restocking fee.

[Bassfiend]

Have to say I like to try to start with the cheap stuff first and then work up ... as has become almost TVR "lore" the 100A fuse is a bad design choice and a poor installation choice. It's a strip fuse that in itself becomes fatigued with vibration over time and it isn't very well protected from the environment - replacing it costs about a fiver for a new fuseholder and fuse and is a very sensible thing to do.

If you're going to get a new Alternator then be careful - I found the part number for what is supposedly the Chim Alternator and when I ordered a replacement rectifier / regulator pack for that part number it was some 65A unit for a Land Rover (which doesn't actually fit) whereas the one that is fitted to my Chim is apparently a 100A unit so just make sure you get the right part...

Phil

[Ribol]

Bassfiend said:

... as has become almost TVR "lore" the 100A fuse is a bad design choice and a poor installation choice. It's a strip fuse that in itself becomes fatigued with vibration over time and it isn't very well protected from the environment - replacing it costs about a fiver for a new fuseholder and fuse and is a very sensible thing to do.

Indeed, awful design, mine blew today for no reason at all after 11 years of use ................. another 20p spent, these cars ain't cheap to run are they

[kbj149]

plushuit said:

Try testing the battery voltage AS you engage the starter.

P.

Hmmmm ..... it slumps to 10.3 as I engage the starter :-/

[spend]

Clean battery terminals and where the cables connect to the chassis & starter, as well as the engine-chassis earth cable.

[MikeTVR]

kbj149 said:

Hmmmm ..... it slumps to 10.3 as I engage the starter :-/

That's what I would expect as it's probably drawing about 300 Amps when the starter is engaged.

The battery voltage should be in the region of 13.3 - 14.2 with headlights and heater fan on, and with the engine above about 1500RPM.

The voltage measured at the alternator output should be between 13.95 and 14.45V at the same engine speeds. I can be sure of this because I developed the test spec for the Lucas A127 and all ACR range of alternators in about 1982 (Yes I'm quite long in the tooth, but still enjoy my Chim)

The difference between readings will be down to volt drops on the resistive cables and of course increases with load.

Good luck

Mike