Lotus Elan

Dynamo and Control Box problem after rebuild

PostPost by: Craven » Fri Jun 28, 2024 4:03 pm

FWIW.
Seems unlikely to me the output from the dynamo could provided that level of current, probably the battery is being connected, somehow, incorrectly into the circuit. When the dynamo output voltage gets to a set level the battery is connected up via the cutout contacts, try a thin insulating material between the cutout contacts and see if there is a difference
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PostPost by: 2cams70 » Fri Jun 28, 2024 11:45 pm

To understand the problem in the absence of anything obvious you should reverse the steps you went through to get to where you are now. Assuming things were working before you took them apart the reversal process may include reinstalling the old armature and observing what happens.
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PostPost by: johnradrr » Sun Jun 30, 2024 9:42 am

Another update - I did the test of the Dynamo output using the jumper method and a voltmeter (see img).

Image

The dynamo is putting our plenty of voltage-- at 1000 rpm it is putting out 12.54 V and if I rev it just a bit to 2500 the output is climbing to 40 V. My question is, is this normal or it is just putting out so much voltage it is frying my control box? I at read that the voltage will climb as you increase the rpm if you do this and this is part of the voltage regulator purpose. But just want to see if anyone can confirm that this is normal. I really do not want to pull out the dynamo and replace it, if it is actually working.

Then the only next step I can think to do is get a 3rd new control box and be extremely careful when wiring it in, unless anyone sees something I am missing.
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PostPost by: johnradrr » Sun Jun 30, 2024 10:43 am

A bit more research here and I think the problem is the control boxes I sourced here are for tractors and it seems that they are actually not compatible with the Lotus :-( So perhaps this is the entire problem.

I have now found a RB340 Regulator which should be a direct and uprated replacement for the RB106/2 and am ordering this, unless someone here now confirms that this will also cause problems :-(

The others were FO 81824174 / DB looks exactly the same with all the same connectors but AI tells me it is not suitable for cars. "Industrial Use: The FO 81824174 and DB K900136 are meant for tractors and other machinery, which have different electrical demands."
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PostPost by: Craven » Sun Jun 30, 2024 11:09 am

Output voltage from your dynamo is what you would expect from an uncontrolled dynamo, output is controlled by the feedback to the ‘F’ terminal from the control box. Monitor this voltage as you run up the speed. Simple test is cross check, with ‘F’ connected / disconnected.
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PostPost by: 2cams70 » Sun Jun 30, 2024 2:24 pm

johnradrr wrote:A bit more research here and I think the problem is the control boxes I sourced here are for tractors and it seems that they are actually not compatible with the Lotus :-( So perhaps this is the entire problem.

I have now found a RB340 Regulator which should be a direct and uprated replacement for the RB106/2 and am ordering this, unless someone here now confirms that this will also cause problems :-(

The others were FO 81824174 / DB looks exactly the same with all the same connectors but AI tells me it is not suitable for cars. "Industrial Use: The FO 81824174 and DB K900136 are meant for tractors and other machinery, which have different electrical demands."


You could even reinstall your original regulator and see how it goes - heaven forbid!
Perhaps you've already chucked it in the bin though. That's another golden rule. Never chuck anything in the bin until the job is done; or if you have a problem personality like me it becomes somewhat simpler - i.e never chuck anything in the bin.
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PostPost by: johnradrr » Sun Jul 07, 2024 9:39 am

OK problem solved with the correct voltage regulator. Just posting this for anyone that has a similar problem in the future because this cost me 10X the amount to fix and months of trouble.

Not all Lucas C40 control boxes are the same. The 3 bobbin control boxes all look the same and there is no technical data that I could find in any of the places selling them that would say there is any difference, but there is. Those made for agricultural machinery will not work. As soon as I plugged one of these into the dynamo within minutes it burned the points.

How did I figure this out? I asked AI (openai https://chatgpt.com/). For anyone having problems with classic cars this is a godsend. It instantly told me the differences between control boxes and why the agricultural one will not work. Here is what it said:

Key Differences
Application:

FO 81824174 / DB K900136: Primarily for agricultural and industrial machinery.
RB340: Specifically designed for classic automotive use.
Design and Fit:

FO 81824174 / DB K900136: May have a different physical design and mounting configuration, which could make them unsuitable for direct use in a car.
RB340: Designed to fit the standard automotive electrical systems and mounting points.
Compatibility:

FO 81824174 / DB K900136: May not be compatible with the automotive electrical system of the Lotus Elan +2.
RB340: Direct replacement for the RB106/2, ensuring compatibility with the Lotus Elan +2.

Conclusion
For a 1970 Lotus Elan +2, the Lucas RB340 is a suitable and direct replacement for the RB106/2, ensuring proper fit and functionality. The FO 81824174 / DB K900136 regulators, while potentially similar in electrical specifications, are designed for different applications and may not be suitable for use in your car.

The Lucas RB340 and RB106/2 are both voltage regulators used in classic British cars, but they have some differences in their design and applications. Here’s a detailed comparison:

Lucas RB106/2
Voltage: 12V
Current Rating: Typically handles up to 22 amps.
Design: Mechanical voltage regulator with a straightforward design, suitable for the electrical systems of classic cars.
Applications: Commonly used in a wide range of classic British cars, including various models of the Lotus Elan.
Terminals: Usually includes terminals for E (Earth), D (Dynamo), WL (Warning Light), F (Field), and B (Battery).
Lucas RB340
Voltage: 12V
Current Rating: Generally similar to the RB106/2, often handling up to 22 amps, but can vary slightly depending on the specific variant.
Design: Improved and more robust design compared to the RB106/2. It includes a more sophisticated regulation mechanism for better voltage control and stability.
Applications: Also used in classic British cars but often found in slightly later models or as an upgrade for systems originally using the RB106/2.
Terminals: Similar terminal configuration, making it compatible with systems designed for the RB106/2. It typically includes E (Earth), D (Dynamo), WL (Warning Light), F (Field), and B (Battery).
Key Differences
Design and Robustness:

RB106/2: Older design, simpler mechanism, generally sufficient for the electrical loads of classic cars of its era.
RB340: Newer design, more robust, providing better voltage regulation and stability, which can be beneficial for more modern electrical loads or higher-performance setups.
Applications:

RB106/2: Widely used in a variety of classic cars from the 1950s to the 1970s.
RB340: Often used in later models or as an upgrade for vehicles initially fitted with the RB106/2.
Performance:

RB106/2: Suitable for standard electrical loads of classic cars.
RB340: Improved performance for better handling of varying electrical loads and more consistent voltage regulation.
Conclusion
Both the Lucas RB106/2 and RB340 can be used in the 1970 Lotus Elan +2, but the RB340 offers improved performance and stability due to its more advanced design. If maintaining originality is important, the RB106/2 is appropriate. If better voltage regulation and a more robust solution are desired, the RB340 is a suitable upgrade.
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PostPost by: 2cams70 » Sun Jul 07, 2024 12:09 pm

Great that you got there in the end and reported your findings. Interesting way of getting there though I must say!
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