Lucas 15TR voltage regulator

[KKson]

Gents, the 390SE charging has started playing up. For ages it wont charge and the battery voltage drops and drops and then eventually it kicks in and charges quite happily for a few minutes at full chat then just stops charging again. I've checked/cleaned all connections and earths and they are all good. Measuring the voltages, when it's not charging it sits at the 12v battery voltage. When it does decide to charge it kicks in around the 14.8 volt range. I'm suspecting it's the actual voltage regulator that's the issue. Stripped it out and it's a Lucas 15TR unit. Struggling to find one on-line. =has anyone bought one previously and if so where are they available? Thanks.

[eesbad]

https://www.johnrichardssurplus.co.uk/alternator-r...

Like this?

[KKson]

I saw that one but no, mine's got four wires coming off it, red, black, yellow and white. Thanks.

[Penelope Stoppedit]

A 2 wire regulator will work without causing any problems, the red and white wires are for battery sensing and are not important to have, battery sensing regulators are not as reliable as the standard 2 wire regulators
Connect the yellow and black wires in the same way as your 4 wire regulator yellow and black wires were connected

[KKson]

Okay, brilliant. I assumed they were different animals. Cheers.

Just ordered a two wire unit for £8 so at that price it's worth a try.

Edited by KKson on Saturday 30th December 17:45

[Penelope Stoppedit]

You could check the brushes while waiting for the delivery

[KKson]

There's certainly some play in the front bearing.........

[KKson]

So two wire voltage regulator fitted instead of the faulty 4 wire unit and all is healthy. Only difference I notice is that the old 4 wire battery sensing unit used to charge at 14 to 15 volts when the car first started and then came down to around 13.5 volts. The new unit appears to charge at 13.5 volts all the time. If I do put all lights, heater fan, rear lights etc etc on then voltage on the gauge does drop to around the 12 volt mark.

[adam quantrill]

Where are you measuring that? Alternator or battery end?

[KKson]

Hi Adam, measured at the battery.

[adam quantrill]

13.5V is a little low you really need 14V to put a decent amount of current into the battery, try measuring the voltage with the engine running, between:

+ post and + clamp
+ clamp and alternator battery post
alternator casing and engine block
engine block and - clamp
- clamp and - post

You can get small voltages in any of the above depending on cleanliness of contacts etc. Anything above 0.1V needs looking at.

The 4-point regulator will have increased the output voltage to compensate.

[KKson]

adam quantrill said:

13.5V is a little low you really need 14V to put a decent amount of current into the battery, try measuring the voltage with the engine running, between:

+ post and + clamp
+ clamp and alternator battery post
alternator casing and engine block
engine block and - clamp
- clamp and - post

You can get small voltages in any of the above depending on cleanliness of contacts etc. Anything above 0.1V needs looking at.

The 4-point regulator will have increased the output voltage to compensate.

Hi Adam, checked the various locations and the one issue is earthing of the alternator itself. It's 13.5 volts at the battery, same from alternator output to battery earth and same from alternator output to engine block. If I measure alternator output to alternator casing then output is 13.8 volts so the earthing of the alternator to the engine block seems to be not ideal. I'll clean all connections, use new new bolts and see if this improves things. Cheers.

[Penelope Stoppedit]

KKson said:

adam quantrill said:

13.5V is a little low you really need 14V to put a decent amount of current into the battery, try measuring the voltage with the engine running, between:

+ post and + clamp
+ clamp and alternator battery post
alternator casing and engine block
engine block and - clamp
- clamp and - post

You can get small voltages in any of the above depending on cleanliness of contacts etc. Anything above 0.1V needs looking at.

The 4-point regulator will have increased the output voltage to compensate.

Hi Adam, checked the various locations and the one issue is earthing of the alternator itself. It's 13.5 volts at the battery, same from alternator output to battery earth and same from alternator output to engine block. If I measure alternator output to alternator casing then output is 13.8 volts so the earthing of the alternator to the engine block seems to be not ideal. I'll clean all connections, use new new bolts and see if this improves things. Cheers.

As mentioned above, measure the voltage drop between the alternator body and engine block, but also measure the voltage drop between the alternator body and the battery negative terminal. Although the starter is cranking the engine fast enough to start it there could be a bad engine earth, it would be good if you were able to get someone to crank the engine while you measured the voltage drop between the engine block and the battery negative terminal as that will show up a bad engine earth/cable, disconnect fuel pump, coil or HT king lead to stop the engine from starting while you're testing - 0.25 Volts Voltage Drop is the acceptable maximum drop on the earth side when cranking the starter motor

[KKson]

I've not measured voltage drop on my multi-meter but according to the dashboard gauge when I crank the engine to start volts drop from 12v down to 8v. I've measured resistance from engine block to battery earth and it's bugger all. The alternator to engine mounts are heavily oxidising so that certainly can't be helping the charging voltage!

[Penelope Stoppedit]

Ok.
You can also measure the battery voltage at the battery when cranking, the 8 volts that you are seeing on the gauge may not be true. 9.6 Volts minimum at the battery when cranking is what you should be looking for - Thats if you're interested

[KKson]

Gents, removed and cleaned the alternator securing points, fitted new shiny bolts and removed, cleaned and refitted the engine earth strap. I'm now getting 13.8 volts at the alternator and also at the battery, so at least no losses. Concern/issue however is if I turn on the headlights and fan then voltage shown on the dash board ammeter drops from just below the 14v mark down to 12 volts. If I turn on the driving lamps and rear fogs then it still sits on the 12 v mark which seems a little low. Is this normal for a non-battery sensing regulator? I've found a battery sensing one for £23 so thinking of replacing the £8 non-sensing one just for piece of mind.

Of course I didn't measure the actual voltage across the battery with my multimeter when all the lights etc are on. Maybe I should check that before parting for some more money?

Edited by KKson on Sunday 14th January 19:27

[phillpot]

KKson said:

voltage shown on the dash board ammeter drops from just below the 14v mark down to 12 volts.

It's a Voltmeter ......... and about as much use as a chocolate teapot

[KKson]

phillpot said:

KKson said:

voltage shown on the dash board ammeter drops from just below the 14v mark down to 12 volts.

It's a Voltmeter ......... and about as much use as a chocolate teapot

Oops sorry - voltmeter it is! I'll measure actual battery voltage with my somewhat more accurate calibrated multimeter and see what that says.

[KKson]

phillpot said:

It's a Voltmeter ......... and about as much use as a chocolate teapot

Hi Mike you were right. With all lights on the dashboard voltmeter showed 12 volts. Actual voltage at battery is 13.5 volts. Even if I turn every single electrical circuit on, the battery voltage doesn't drop below 13.2 volts. So seems to be good enough.