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2.5 V8 Dynamo, Regulator

sumptners
Posts: 7
Joined: Sat Jun 11, 2016 9:20 pm

2.5 V8 Dynamo, Regulator

Post by sumptners »

After starting and for approximately 30 minutes motoring the charge on my saloon is fine. After say 30 minutes the charge diminishes and the red light glows faintly. this is an ongoing problem. I have replaced the voltage regulator twice and this does seem to cure the problem for a limited time although the regulators are presumably cheap Chinese ****.

It is I suspect a problem which occurs when getting hot under the bonnet. Any ideas would be appreciated.
Many thanks.

classiclife
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Re: 2.5 V8 Dynamo, Regulator

Post by classiclife »

Hello Stewart,

The next time the you are out & about and the red light shows, switch on the headlights and fan motor - if the light goes out then you have an overcharging issue which is not being controlled by the voltage regulator - which I believe should be a Lucas RB340.

There are different amperage regulator units and it's important to ensure that you have a RB340 which easily handles the output - I presume you still have a dynamo and not converted to an alternator using the RB340 as a junction box ??

If a dynamo is fitted, then your regulator must be able to handle at least 25amps.

Out of interest, where have you sourced your regulators from ??

If you have a multimeter or similar, it will be useful to take a voltage reading directly across the battery terminals with the engine running and warmed up - anything above 14.75V is indicating an issue.

When the red light comes on, does the ammeter go to the Discharge section of the gauge ??

Final question, when you switch the engine off either with the red light showing or not........... does the ignition light stay on with the engine off ??

Regards.

Richard.
1968 Daimler V8-250 Saloon
DLOC East Sussex Branch Secretary
DLOC 2.5L V8 & V8-250 Registrar - https://www.dloc.org.uk/v8-250
DLOC 2024 International Rally - https://www.dloc.org.uk/rally-2024

sumptners
Posts: 7
Joined: Sat Jun 11, 2016 9:20 pm

Re: 2.5 V8 Dynamo, Regulator

Post by sumptners »

Hello Richard.

Firstly thank you for your helpful reply.

I have not had a chance to take the car out but I can confirm the regulator is RB340 and I still have the original dynamo fitted. I have fitted a 'dynamo shaped' alternator to 2 of my other classics with mixed but finally satisfactory results and if I cannot fix this issue I will go down this route.

I got an auto electrician to supply and fit the last regulator and seem to remember the supply cost was £25-£30 and therefore I am fairly certain from where the item came from.

When the red light is on when running it is only a faint glimmer with the ammeter possibly showing a slight discharge. I assume if I were to switch the headlights on the red light would glow brighter. It does not glow with the ignition switched off.

Later this week I will remove all of the terminals/connections and clean them to see if the current is breaking down when hot. After this rather than getting the dynamo checked and overhauled I may go down the alternator route.

Regards
Stewart

Christopher Storey
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Re: 2.5 V8 Dynamo, Regulator

Post by Christopher Storey »

I'm not sure that I understand all this. You say in your initial post " after 30 minutes of motoring" but then in your last post you say " I have not had chance to take the car out". If you are just leaving it idling for 30 minutes , is the red light glowing at all engine speeds, or do you mean that it glows faintly at idle, and then goes out if the speed is raised? If the latter, then there is nothing wrong at all

Sydsmith
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Re: 2.5 V8 Dynamo, Regulator

Post by Sydsmith »

I would say this is almost certainly a regulator set up problem not a faulty regulator.

New regulators need properly setting up to suit the car. Auto electricians of today rarely understand how to do the job properly. Can't find it at present but the set up procedure has been discussed here before.

The RB340 is inherently reliable and even the far east rubbish are usually cheaply built but OK in service. But you cannot just slap them in connect them up and expect them to work properly, they have to be fine tuned to suit the particular dynamo/car.

Most problems in the original units are fairly simple to cure and again that has been discussed here before, but there are folks who will refurbish originals, even fit electronic conversions that need no adjustment, for my money I would go that route rather than fit far east rubbish or change to an alternator.

Hope that helps. Syd

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John-B
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Re: 2.5 V8 Dynamo, Regulator

Post by John-B »

I bought a new regulator and also found it impossible to adjust properly. It would charge OK and later discharge a lot. Eventually I gave up and sent it to http://www.dynamoregulatorconversions.com/ for an electronic conversion and it was £200 well spent.
Your wiring and dynamo need to be good.

Ian Hastings
Posts: 163
Joined: Tue Mar 15, 2016 3:00 pm

Re: 2.5 V8 Dynamo, Regulator

Post by Ian Hastings »

It also sounds like you may just need a new set of brushes for the dynamo and the armature cleaned.
With your ammeter check the voltage from the dynamo at the dynamo and not at the battery. Take off the two cables from the dynamo, join the two terminals together and from there measure the output voltage to earth when you start the engine.

johnwager
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Location: Thundersley, Essex

Re: 2.5 V8 Dynamo, Regulator

Post by johnwager »

I agree with Ian, I had the same problem with a flickering ignition light.
A new set of brushes and clean up the armature, a cheap easy fix so check that first.

sumptners
Posts: 7
Joined: Sat Jun 11, 2016 9:20 pm

Re: 2.5 V8 Dynamo, Regulator

Post by sumptners »

Thank you all for your most helpful replies.
An explanation Christopher, what I meant in my second post is that I had not had a chance to take the car out after receiving Richard’s reply. The 30 minutes referred to earlier journeys made over the ‘Summer’. I trust that is now clear.
I will initially check the Dynamo output when the car is hot and the charge disappears. If this indicates a problem then it is a Dynamo overhaul I assume. I am not quite clear on testing the output but assume this can be found on the internet.
Regards
Stewart

classiclife
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Re: 2.5 V8 Dynamo, Regulator

Post by classiclife »

The dynamo voltage test is covered in the Daimler WSM.

Regards.

Richard.
1968 Daimler V8-250 Saloon
DLOC East Sussex Branch Secretary
DLOC 2.5L V8 & V8-250 Registrar - https://www.dloc.org.uk/v8-250
DLOC 2024 International Rally - https://www.dloc.org.uk/rally-2024

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