Summer / Winter charge rate.

[Nick Feakes]

Hi All
I am writing a booklet on the electrical system of the pre-war MGs. My question relates to the high / low charge rate on the M type which has a similar (identical?) electrical system as its parent car. Where is the resistor that reduces the field current in the summer position?
Also, it would seem as though at some point the M type changed its electrical components from Rotax to Lucas (not sure if Lucas owned Rotax by then) . Did the Minor change components as well, and if so, do the later cars still have the variable charge rate?

Any info gratefully received
Nick

[Ian Grace]

Hi Nick,

Welcome to the forum.

I think you'll find the half charge resistor inside the vertical dynamo. At least, that is where it is in the Lucas dynamos fitted to the OHC Minors and early M Types. The early (1929) M Types had Lucas electrics and instrument panel - identical to the OHC Minor, and then switched to Rotax. I'm not sure that we know exactly when the changeover occured, and i also believe it was a pit piecemeal - presumably depending on what Lucas stuff was left in stock. The Minor stuck wirth Lucas all the way through - never having any Rotax electrical components.

Hope this helps,

Ian

[Nick Feakes]

Thank you Ian for your swift response.
If the resistance is inside the dynamo, how is it bypassed for full charge? Wouldn't that require a second field wire?
Nick

[Ian Grace]

Nick,

I think you will find the answer on this thread - specifically see Ken Martin's comments in the third post.

http://www.vintageminor.co.uk/Forum1/ph ... stor#p2158

[Nick Feakes]

Hi Ian
I think I see how that could work. The resistor inside the dynamo is connected between the D and F terminals to give a reduced charge rate. The "charge rate" switch shorts out the resistor to give the full output when "summer" is selected. Clever! Some info on the resistor would be useful.
I wonder why they dropped this system? Any sort of variable rate charging didn't re-appear in the MGs until the TA in 1938!
The early M type didn't have any fused circuits at all, was the Minor the same?

Thank you for your help with this.
Nick

[Ian Grace]

Nick,

Here's the wiring diagram for the OHC Minor, with the same Lucas electrics and panel as the early. It shows that the charging fuse is housed in the cut-out. The resistor in the dynamo is a piece of resistance wire, insulated with some sort of period equivalent to insulting tape (spelling mistake intended! )

It's noon here in Seattle - so just off to the English Pub (the Three Lions) for a pie and a pint!

[Nick Feakes]

Hi Ian
Lucky man - no pubs in Florida! Have to go the UK for a decent pint - but not at this time of the year!
Thank you for the diagram and the info on the resistance wire. Whilst it is possible there is a fuse inside the cut-out, the Lucas picture I have of the inside of this unit does not show one and there are no other wires going to the unit.
Also, it could be in the charging circuit i.e. between the output of the dynamo and the ammeter but I think that unlikely.
Anyone have a photograph of the inside of the correct unit?

Thank you as always for all the help
Nick

[Ian Grace]

Nick,

Jaut back after a couple of pints of draft Fuller's ESB and a Stilton burger. Watched a bit of the West Ham/Man United game on their 60" screen - 2 nil to West Ham at half time. Swung by Staples on the weay back for more colour ink for the magazine covers and CD's for the Yearbooks - which will consume the rest of my spare time between now and SDunday night to mcomplete and get ready for shipping - hopefully to be with everybody in time for Christmas.

The OHC cut-out had two terminals in it with a flat piece of resistance sheet metal (for want of a better description - and the best I can do after lunch!), between the two. The cars left Cowley with three or four of these flat fuses secured under one terminal. When the one in use blew, the owner simply strapped the next one across the gap. I must have a pic somewhere, but if anyone else has one, feel free to post it.

[Ian Grace]

Nick,

I can't find a picture right now, but this is the circuit of the Lucas CF, as fitted to the OHC Minors, and showing where the fuse goes:

[Ian Grace]

And here is the cutout, taken from the 1929 Minor Handbook (or Handbuch) - just for fun, in German. I have them in several languages. (Inside the front cover, it says "MOTORING LIBRARY, The Editor, Motoring, Publicity Department, British Motor Corporation Ltd., Longbridge, Birmingham."

You can see the flat fuse, with the spares between the two terminals. Most of the OHC Minors I have owned (probably about a dozen or so) have had regular fuse wire between the terminals, but some have had these original flat fuse tabs (or Ersatztriefen) still in place. A nice tie-decider for concours!

[Nick Feakes]

Hi Ian
I am very envious (about the beer and stilton at least).

I think I have unraveled the answer with your help and some early Lucas catalogues. The early M type MG had the CF cut-out and the SO5/A11 charge rate and lighting switch (two separate knobs). At some point, they changed to the CJF1/DA1 cut out and the SA1/DA1 combined lighting & ignition switch (one knob).
The early setup had a resistance inside the dynamo to give the summer/winter setting and nothing that looks like a conventional fuse (thank you for the picture - that explains the 'fuse'!) but the later setup did not have the internal resistance only having the facility to switch the charge rate off altogether.

Did the OHC Morris make the same change to the electrical system?

I wonder why they changed? Perhaps it was time for a 'proper' fuse?

When the book is finished (if it ever is!) I will send you a copy in pdf format, some of it may be of interest to your members.

Nick

[Ian Grace]

Evening Nick,

And greetings from Seattle to Florida - probably further than Florida to England! If you are over over this way, we'll go out for a pint or two, and some genuine pub grub.

I'd be very interested in the book - I can supply images of the cutout and other electrics - in English - if you need any. The OHC Minor retained this early Lucas arrangement for all short wheelbase Minors with no modifications (except the dynamo - which went from narrow to fat at chassis M15136 - dynamo DEL 24 replaced by DDS5. (Early dynamos DEL 7 and DEL 19 were superseded by the DEL 24). New concave cylinder block and nosepiece to suit). The LWB car (introduced for the 1932 season in July 1931 at chassis M34700) had the later Lucas panel and cut-out, etc.

Let me know if I can provide any other graphics or data for the book. I presume you have the Lucas catalogue pages for the M?

Ian

[Sam Christie]

I think E Sicherungsstreifen is the fuse strip and F Ersatztriefen is a spare fuse strip. By the way Nick, thanks for your diode conversion which is doing a fine job in my M-type and the Rotax F Strommesser is no longer a fire hazard.

[Ian Grace]

I think you are right Sam. Next time, I'll scan the Portugese manual I have!

[Sam Christie]

I thought it was French.