Retlas "Manchester" Dynamo

[Chipmaster]

Quote from Doncaster Show post (reply 11)  by Alyn Foundry

“The AGB Dynamo....

Andy has a set of castings for the Retlas " Manchester " dynamo, Vincent and I developed this around the early Eighties. Once " fine tuned " we were able to light a 55W car headlamp bulb with no problem........

Cheers Graham”

So here are some pictures of the castings.

This is the base casting Graham gave me, he also gave me the keeper or top, I had them shot blasted and sprayed them with primer straight away. It might be another year before I can start work on this.

image by Andy, on Flickr

Graham also gave me the two brass oil reservoir covers and name plate. At the time he thought the armature would be very expensive.... The two bearing supports were cast by the AJD  Foundry  using patterns I borrowed from Graham.

Building Retlas 1034 by Andy, on Flickr

With the Retlas engine in the background.

Building Retlas 1035 by Andy, on Flickr

Building Retlas 1037 by Andy, on Flickr

Building Retlas 1038 by Andy, on Flickr

Building Retlas 1039 by Andy, on Flickr

Building Retlas 1040 by Andy, on Flickr

Pattern Lucas C40 armature obtained for £27.00 inclusive from a supplier in Warwickshire, England 

Building Retlas 1041 by Andy, on Flickr

Building Retlas 1042 by Andy, on Flickr

Picture of the plan, the 'Keystone effect' is because the plan was large and I was using a hand held camera in Graham's kitchen

Retlas Dynamo 1 (2) by Andy, on Flickr

Andy

[Alyn Foundry]

Hi Andy.

It's nice to see all the parts together in one place!

I was quite shocked by how cheap the armature was but they are probably being mass produced in the far East. There were literally millions in use on cars here in the UK before the alternator became popular. If you're a purist car restorer then the Lucas Dynamo is a must.

As you can see from one of your photos the armature will need some modifications, Vincent " upped " the shaft diameter to 3/4" and lengthened them too.

The final  touch was to " serve " the windings with a thin woven string using super glue dabbed here and there then he used Brown shoe polish to get the desired colour. A final coat of Shellac was given to improve the look and insulation.

I'll be following your progress when you start Andy. Please don't hesitate to ask for advice.

Cheers Graham.

[Jasonb]

Looks interesting Andy

Can I ask what the OD of the armature is, I got one that is a little on the small sid efor the main motor I was going to build at 27.5mm, cheap at under £10 and hiding inside a RS 755 motor. Would really like something about 38-40mm.

Nice to know another expert advocates the use of string

[Chipmaster]

Hi Jason,
The diameter of the armature is  2.376” / 60.34mm.

https://www.autoelectricalspares.co.uk/c40-dynamo-armature-12v-22a-replaces-lucas-227271-3770-p.asp

Andy

[Chipmaster]

Hi Graham,
I’m sure I’ll take up your offer of advice when the time comes.
Cheers
Andy

[Alyn Foundry]

A little history.

A few will know that my background was in electrical engineering and with a passion for vintage machinery.

I had the privilege of both seeing and working on a wide range of " machines " that spanned nearly a century. North Wales has many hydroelectric stations one in particular dated at 1905 was the oldest that I had seen. The turbines and alternators now replaced by a single and highly efficient replacement.

After Vincent had completed his Retlas he found that a load " softened " the rather erratic running nature so we discussed various means towards this end. A dynamo was the obvious choice as you can easily place a given electrical load in the form of lightbulbs.

Vincent's choice was a " Manchester " style as they were of very simple construction. The base becomes one pole, either North or South and the two field coils are wired to provide the electromagnetic influence to the top and bottom. The choice of a Lucas dynamo armature was twofold, they were very common and cheap because nobody wanted them and a low output voltage was safe in the usually wet rally field environment.

The prototype was a very plain affair, a simple cross at the bottom and the top is the only bit that wasn't remodelled. All the other patterns were redone after the Dynamo was proved to work. I've forgotten who wound the coils but I think we scavenged the Copper wire from the donor machine. This ensured that we had the correct resistance.

You will notice that the " brushgear " can be rotated about the axis of the commutator. This was a method used on early DC machines to combat something called " armature reaction " . This effect happens as more load is placed upon the generator, bending the magnetic flux which, in turn moves the best output from the commutator. As a result arcing occurs which, if left unchecked quickly burns the segments. The operator would then rotate the brushgear to find the point of least arcing.

The Retlas Dynamo was also fitted with Brass gauze brushes and ring oilers for that extra look of authenticity. The overall finish was such that Vincent's Dynamo fooled many an expert eye over the years few believing that it was home made.

Cheers Graham.

[Chipmaster]

Here are pictures of two Retlas dynamos that I copied from the Internet some time ago, I don't have any details about them.
Andy

rd2[1] by Andy, on Flickr

rdj2[1] by Andy, on Flickr

[steam guy willy]

Hi , Interesting project..I was also an electrical engineer in the Army and they had quite a few old 'Machines" that the y use to start up.  including one with the handle for adjusting the brush position !!  Also there is a black wire connected to the frame  ? is this part of the electrical circuit ?? and are the  4 middle connections able to reverse the polarity of the output  ?...and on the green one the rotor wire seem to be coloured slightly red and black...havent seen that before ??


willy

[Alyn Foundry]

Good morning Willy.

Like Andy I've seen these pictures before but the builders and their methods are unknown.

With the Black one I surmise that they have only isolated one of the brushes and the frame becomes a return to the terminal block.

I'd never noticed the different colours in the enamel insulation before, well spotted. The armature is however " proprietary " so this is something that the manufacturer might have used to designate the coil termination to the commutator?

Cheers Graham.

[Admiral_dk]

To me it looks like it is a "Bifilar Winding" - means that there are two (or more) parrallel wires, wound together as if there where one. There can be several reasons for this - in this case, to easier to get the coils into place after they are wound.

[Chipmaster]

After a twelve month gap in this thread I have started to build the dynamo. Here are extracts from Grahams drawings that I photographed back in 2017.

Dynamo Base by Andy, on Flickr

Dynamo side view by Andy, on Flickr

Dynamo end view (2) by Andy, on Flickr

Dynamo bearings by Andy, on Flickr

There are a some differences between my castings and the drawings.
1. My two pedestal castings have lugs on each side for bolts or studs whereas the drawings show two bolts 1.1/2" apart coming up form the underside of the base.
2. The base casting isn't quite as long as the drawing.
3. The height of the pedestal castings and the pads they sit on had to be reduced to ensure the keeper or yoke would be a reasonable thickness after machining it to clear the armature and eventually look right.

In this picture I had machined the mild steel field coil cores to a height of exactly three inches then determined the height of the armature shaft.
 
IMG_2116 by Andy, on Flickr

IMG_2103 by Andy, on Flickr

Milling the underside of a pedestal flat.

IMG_2100 by Andy, on Flickr

I spotted through the base into the keeper casting.

 IMG_2118 by Andy, on Flickr

Tapped the base and the field coil cores 1/2" Whitworth and used short studs in the base and short bolts through 1/2"
holes in the keeper to hold it together.

IMG_2119 by Andy, on Flickr

IMG_2121 by Andy, on Flickr

Andy

[Alyn Foundry]

Hi Andy.

As always, excellent workmanship.... 

The Retlas Dynamo evolved, please see my earlier post. It moved from a practical working machine to something, I hope could be considered, nice looking?

As members of the FB group will know we've been discussing the field coils. The Lucas unit has field coils that had, in general around 6 Ohms resistance per coil.

I've been doing a little mathematics and a 1Kg  spool of 22SWG which is approximately 0.75 mm ECW has a resistance of 0.04 Ohms per Metre. This equates to 10.1 Ohms. I'm of the opinion that each bobbin will require 500 grams of wire for a close match to the original machine.

Looking forward to the next instalment Andy.

Cheers Graham.

[Dave Otto]

Interesting project Andy,
I'm looking forward to following along.

Dave

[Chipmaster]

Thank you very much Graham and Dave.

I hope I haven't painted myself into a corner with my sequence of operations, my concern was how to machine the pole pieces and have a minimal air gap between them and the armature. The only way I can machine the pole pieces is to use a between centres boring bar with the dynamo mounted on the lathe cross slide. However, I will need to be able to check the gap with the assembled armature and the dynamo remaining on the cross slide. The outcome will be dependent on how well the armature shafts fit and run in their plain bronze bearings.

I decided to mill the surfaces of the two pedestals so that I could bolt them in turn, directly to an angle plate and faceplate to ensure the centre heights matched. There were differences between the pair of pedestal castings which meant I had to compromise on the thickness of the bearing housings but perhaps JB Weld or Milliput can be used if necessary.

IMG_2127 (2) by Andy, on Flickr

Boring out the pedestals to 1".

 IMG_2140 by Andy, on Flickr

 IMG_2144 by Andy, on Flickr

Being able to rotate a length of 1" diameter ground bar mounted in the pedestals without binding confirmed that the centre heights matched.

IMG_2151 by Andy, on Flickr

In this picture you can see what I meant about compromising on the thickness of the bearing housings.

IMG_2154 by Andy, on Flickr

To reduce the height of the armature I milled away the pads that the pedestals sit on, that gave me about 0.09".

IMG_2156 by Andy, on Flickr

IMG_2158 by Andy, on Flickr

The faces and underside of the base and keeper castings were flat and in the same planes / in line before I started machining them so I assume they had been machined years ago before they acquired the 'special coating'.

image by Andy, on Flickr

Unfortunately the 1" precision ground steel bar isn't long enough to be used to position the dynamo between centres on my lathe so another one has been ordered. However, it was sufficient for keeping the pedestals lined up as they were bolted down to the base.

IMG_2191 by Andy, on Flickr

Andy

 

[Roger B]

Looking good     

I am following along