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Lucas C39 and C40: What are the differences?


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Hello all,

I have a question: What are the differences between Lucas dynamo C39 and C40?

I can get a C39 housing stamped with the correct date for my TR3A (11 58) and I have a good C40 on the bench. Would it be possible to put the internal parts of the C40 into the C39 housing?

Thank you very much!

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 The C40 produces a higher maximum current than the C39 -  approximately 5 amps more -  and the matching regulators are different. Some web sources say it is possible to swap the internals over as the basic casing dimensions are similar. The field coils are the same resistance but the armatures are bit different and have different part numbers. The brushes are different so you may have to use the C40 rear plate and brush carrier to suit the armature so even if the date is right the appearance will be slightly incorrect - the later C40 rear plate has more holes in it for better cooling. 

This lnk has some data and photographs:

https://www.britishcarforum.com/community/threads/generator-configurations.97573/

There is information here on dismantling and rebuilding a C39, albeit one with a tachometer drive, but the basics are the same:

http://midgetandspriteclub.com/wp-content/uploads/2016/06/C39_dynamo.pdf

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With the C40 dynamo. you might benefit from a Lucas RB340 regulator, which has both voltage and current sensing.  The Competition Department fitted RB340 units to the Works' TR4 Rally cars because they used a higher output dynamo.

The RB340 is slightly wider than the usual unit because it as 3 coils inside.  But the connections remain the same.

From Google, I see that RB340 units are available, and the instructions for adjustment can be found, too.

Ian Cornish

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My works 3a has from new had a C40 with an RB310, again current and voltage sensing. This was a common Lucas fitment to works Tr’s and Healeys Of the period to try and cope with more auxiliary equipment.

Iain

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The TR regulator RB106/2 has current loops around the voltage coil and is current sensitive too.

They RB310 and 340 may be better on a discharched battery, but the original RB106/2 on my TR4A works without problems.

Back to Christian's question

FkZH-CQ0BEyUFpPqeZWqGiVGbmnkD_VoSS0wQfVv

This ist from the 1970 brochure "LUCAS, Service Training Center, Part 4, Generators" page 17 from 24

Ciao, Marco

Edited by Z320
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The RB 106 uses a single bobbin for both voltage control and to limit current. There is no adjustment for the current - the overwind acts to limit the maximum but at the cost of poorer voltage regulation particularly at low loads, and is a fixed value so it is a bit of a compromise.  It is described as 'compensated voltage control'. Nonetheless it works perfectly adequately.

The RB 310 and 340 use separate bobbins and so provide better voltage regulation and the ability to adjust the maximum current. The main difference between the 310 and 340 is really the way the adjustment is done. The 310 has screws while the 340 has an eccentric disc wheel arrangement.  Any of these will work with either the C39 or C40 dynamos but really should be adjusted appropriately (not something to be undertaken lightly by non-experts).

We do seem to have strayed from the original question though. 

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Yes, the RB106/2 is not current adjustable but current sensing too.

About the RB310/340 current voltage regulators:

ElCF_ZgoulZ_LW9iaOAO6IwPXTVFczDYxjg5t_gS

This ist from the brochure "LUCAS, Service Training Center, Generator Output Control" page 15 from 28.

Indeed we "overanswered" Christian's question, Christian, sorry for that :rolleyes:

Edited by Z320
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Thank you all! OK, seems to be a bigger prob than I imagined :rolleyes:

I will think over that.

Three alternatives: Putting the the internal parts of another C39 in the correctly stamped C39 housing or use the (incorrect) C40 and benefit from 5 amps more or looking for a C40 with date 58 (and go the racing dep. way), which seems a bit like looking for the Pink Panther diamond :D

Iain, do you perhaps know if there are C40 with screwed connectors on the back?

Rob, thank you for the two links; very helpfull!

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8 hours ago, Black Forest TR3A said:

Thank you all! OK, seems to be a bigger prob than I imagined :rolleyes:

I will think over that.

Three alternatives: Putting the the internal parts of another C39 in the correctly stamped C39 housing or use the (incorrect) C40 and benefit from 5 amps more or looking for a C40 with date 58 (and go the racing dep. way), which seems a bit like looking for the Pink Panther diamond :D

Iain, do you perhaps know if there are C40 with screwed connectors on the back?

Rob, thank you for the two links; very helpfull!

I believe all C40s are Lucar, but I’m sure someone will correct me.

Iain

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          Simple folk at Lucas. A C39 dynamo is 3.9 inches in diameter, a C40 is 4 inches in diameter and a C45 as fitted to Austin Healeys is 4.5 inches. Early C40 dynamos have screw fittings, later are Lucar and dynamos fitted to Ferguson tractors do not have the cooling holes in the end casing.

          Cheers Richard

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