After the motorshow, got in to the 504 which had been parked in Birmingham for 5 days to find a flat battery. A jump start and 120 miles later down the motorway and all is well. Seeing as the battery had done it 3 weeks ago as well I bought a new one. I had a new alternator, dare I say an ebay bargain. It is the same fitting for 504 diesel but a slightly different model.
The one on the car was a Paris Rhone 40amp and the new one Hugo Germany/Paris Rhrone 50amp, but with identical fittment/pully. It works fine when connected up, but if I leave the spade connector plugged on to the new one, the engine will keep running when I switch off the ignition and remove the keys. With the wire disconnected it works just fine, charging at the correct 14v rate.
Any suggestions why the old one needed 3 wires and the new just 2? What is the differences to cause this?
Thanks
Mat
Paris Rhone Alternators
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Paris Rhone Alternators
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1978 504 GL Diesel Saloon (daily drive !)
1978 104 GL 954cc (only 73 - 104s left in the UK).
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fastandfurryous
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This sounds like the old "measured charging" system.
Older alternators used to have 3 wires, as they used the 3rd wire to measure the voltage at the battery (rather than at the alternator) to regulate their voltage. This was especially necessary on low output alternators, as otherwise the output would have been even lower. It also allowed thinner cables to be used from the alternator to the battery, which made a fair difference 40 years ago, when fat cables were expensive.
If you look on most modern lucas alternators, the "output" connector, and the "sensor" connector still exist, but have been bridged together to negate this historic system.
Some older cars used to be a bit clever with this system, and insted of providing a "voltage sense" cable that came from the battery, it came from the ignition, thus meaning that when the ignition was turned off, even if the engine ran on, the alternator was effectively switched off.
it sounds to me like your car has this system, and that the new alternator is a 2-wire type, thus the "sense" and "output" connectors are bridged. This means that your ignition is being hard-wired to the battery via this bridge.
The fix, as you've found out, is to disconnect the "sense" cable from the alternator. A shame really, as the 3-wire alternator system is more elegant, and ensures that losses in the cables are taken into account, and means your battery is charged to a slightly higher voltage. However, short of taking the new alternator apart and modifying it to be a 3-wire, you have no option but to allow the alternator to regulate it'self from it's own voltage, and to ensure the output cable from the alternator to battery is good and hefty.
I would leave the "sense" cable in place though, as it will allow you to use the (better) 3-wire system again in the future, if you decided to.
Older alternators used to have 3 wires, as they used the 3rd wire to measure the voltage at the battery (rather than at the alternator) to regulate their voltage. This was especially necessary on low output alternators, as otherwise the output would have been even lower. It also allowed thinner cables to be used from the alternator to the battery, which made a fair difference 40 years ago, when fat cables were expensive.
If you look on most modern lucas alternators, the "output" connector, and the "sensor" connector still exist, but have been bridged together to negate this historic system.
Some older cars used to be a bit clever with this system, and insted of providing a "voltage sense" cable that came from the battery, it came from the ignition, thus meaning that when the ignition was turned off, even if the engine ran on, the alternator was effectively switched off.
it sounds to me like your car has this system, and that the new alternator is a 2-wire type, thus the "sense" and "output" connectors are bridged. This means that your ignition is being hard-wired to the battery via this bridge.
The fix, as you've found out, is to disconnect the "sense" cable from the alternator. A shame really, as the 3-wire alternator system is more elegant, and ensures that losses in the cables are taken into account, and means your battery is charged to a slightly higher voltage. However, short of taking the new alternator apart and modifying it to be a 3-wire, you have no option but to allow the alternator to regulate it'self from it's own voltage, and to ensure the output cable from the alternator to battery is good and hefty.
I would leave the "sense" cable in place though, as it will allow you to use the (better) 3-wire system again in the future, if you decided to.
This is not a signature.
I have done just that, taped it up out of the way. Kept the old one, if need be can get it overhalled. The new one does have 3 wire connection though, but the engine continues to run when connected, but off!
Events Co-ordinator for :
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1978 504 GL Diesel Saloon (daily drive !)
1978 104 GL 954cc (only 73 - 104s left in the UK).
-
fastandfurryous
- Posts: 1388
- Joined: 07 Jul 2004, 17:57
- Location: On the road, travelling at high speed. Meep Meep.
- My Cars:
- x 4