Sunbeam S7 Deluxe Chronometric Speedometer - Temporary Substitute

The speedometer has not worked reliably on my Sunbeam S7 Deluxe in about two years.  It would work on and off, then finally it quit altogether.  It needs to be properly rebuilt.  With stories of other folks overseas shipments being quarantined or lost in customs, I did not think it was a good idea to send it to England for repair.  Sure there are proper aftermarket replacements but they cost over $300 USD plus shipping and they still need a cable and hall-effect pickup to function.

I had been just dealing with the lack of speedometer, and I wasn't actively looking for another solution.  Fortunately here in the USA if we register as an antique there is no safety inspection or MOT.  Sometimes targeted advertising is actually a good thing.  In my news feed of a popular social media up popped an advertisement for a GPS Speedometer.  Brilliant!  Why didn't I think of that!  It needs no cable, just power and a clear view of the sky.  The antenna could be hidden anywhere on the bike or just strapped on with tyraps in plain view.  It would look plain and not unusual unless you really looked hard at it to find the digital display.

Nobody makes a GPS speedometer for an 80mm diameter speedometer bucket.  They are all 65mm or 85mm.  My grandma used to say "Can't is a coward", meaning if you think you can't then you are already defeated.  There must be a way to fit a 85mm speedometer in a hole for an 80mm unit.  I bought the speedometer for the modest asking price and resolved to figure it out.
ELING MPH GPS Speedometer Odometer 140MPH For Auto Motorycle With Backlight 85mm 12V/24V

Upon arrival like any good engineer, I took it apart to see how it worked.  The mechanism was simple.  The bezel pried off easily exposing the bucket with the speedo unit inside.  Two screws in the back removed, and the speedo pushed out of the bucket releasing the power connector inside.  Another connector went to the GPS receiver hot-glued to the bottom of the bucket.

The plan was to cut the speedo bucket so that half was above the headlamp and half was inside.  I would then contrive a way to join them back up.

Luckily there is just enough room around the edge for some stainless steel sheetmetal.  The sheetmetal was fastened carefully to the inside of the bezel and passed along the inside of the speedo bucket.  It could then be re-attached by drilling a hole through both and allowing the sheet metal to self-tap.

All assembled, but there was naturally another challenge to overcome.  My bike is 6 volt positive ground and the speedo needs at least 9 volts.  No problem.  I bought a boost regulator and set it for about 12 volts.  It gets powered from the original speedo backlight and there you have it.
MT3608 DC-DC Boost Power Converter

 One night's worth of work and I have an operational speedometer.  I can take my time getting the original rebuilt and nothing on the bike was done that couldn't be reversed.  A big fat o-ring from a spin-on oil filter covers the bottom of the bezel which had to be thick enough to support putting four screws in it.  The o-ring could be backed with some RTV if I thought the bike was ever going to get wet... which it usually doesn't.

The maximum speed is a bit optimistic.

Sunbeam S7 / S8 permanent magnet alternator conversion (recap)

This is a recap of my alternator build.
(as published in the Sunbeam Owners Fellowship club magazine "On The Beam" issue Nov-Dec 2011)

---

I’ve been frustrated with the original Lucas dynamo on my Sunbeam since I’ve been riding it. Neither the MC45O nor the MC45L (that I later purchased) produced enough electricity in a foolproof fashion. I don’t want to have to worry about if there’s enough charge in the battery to get me home anymore, and I want to run the lights all the time. I also don’t want an after-market alternator conversion that does not look exactly like the original. This is why I was determined to create an alternator conversion by myself for a small price. I submit the following to any interested do-it-yourself owners.

I took suggestion from some Douglas and Vincent motorcycle owners who also have problems with dynamos. A few intrepid owners have taken permanent magnet alternators from modern applications and fit them inside the original dynamo cases. One particular application caught my eye while searching online for a suitable solution. There is a simple alternator from a Kubota tractor that measures only 3-1/2” across and a little over 3” high. I bought model APM0001, which was the smallest available. This came as a self-contained belt driven assembly. I tested it briefly before taking it apart to see how easily it produced enough current being turned by hand to light the tail lamp bulb on my bike. Removing the nut and pushing the bolt out easily disassembled the unit, shown in Figure 1. The back housing was discarded.

Figure1

The magnet cup was surprisingly powerful. It all fit nicely into the original dynamo case. There would be two major challenges. Fit the magnet cup to the crankshaft, and then to fit the case back onto the engine block so it all stayed together. I elected to do the reverse of what the Douglas owners had done, and fit the magnet cup onto the shaft first, so that the stator would be accessible from the front of the bike. It sounded wrong at first, but it eliminated so many problems it was worth the effort, in my mind, to machine all the required parts on the lathe. There would have to be an adapter to fit to the end of the crankshaft, which included pins to fix the magnet from rotating independently from the crankshaft. This I spun out of round stock on the lathe to a relatively high degree of precision. I would use the original left-handed bolt so I didn’t have to machine another one. The outside casing would have to be secured to the engine block by means other than the two long bolts originally used, because they interfered with the outside diameter of the magnet. The wires could easily come out the front and affix to the original terminal block. Below is the solution showing the framework cage that was made to hold the outside casing. I could have welded tabs to the casing, but I didn’t want to modify it.

Figure 2

The whole assembly fits together with a specific procedure, it’s not ideal, but it works. (I later discovered that the magnet was so strong, that I needed to fit two of the sealed bearings inside the stator winding assembly to keep it centered with respect to the crankshaft. That isn’t represented in the photographs.)

The cage, at the left of Figure 2, goes on first. The magnet and center bolt (with spacer) then affix to the crankshaft adapter. The spacer holds the sealed bearings from the original Kubota unit, and another outside press-fit spacer makes up the difference between the stator and the outside bearing race.  The fourth arm of the cage assembly encloses the magnet, before the case is slid onto the cage. The pole shoe screws fasten the case to the cage in such a way that it forces the case into the engine block firmly as the countersunk screws are tightened. The stator coil, at the right side of Figure 2, slides into the magnet which is centered by one of the bearings from the original alternator assembly. This took a brass spacer precisely machined out of an old pipe fitting. The wires tuck neatly up against the casing out of the way of the rotating magnet. The outer plate bolts on with 6 screws and then the cast aluminum cover of the dynamo bolts to the outside of the case.

Figure 3

I’m quite pleased that the mechanics of my alternator conversion work well. The next challenge was to rectify and regulate the alternating current into direct current. Normal people would just have converted to 12 volts and put the Kubota tractor regulator in place of the Lucas MCR2 dynamo regulator. I had purchased a Rooster Booster 6 volt positive ground ignition module, and already had my 6 volt battery and lamps, so I was determined to stay with 6 volts for the present time. I know it’s not ideal, but I knew I could make it work fine. The 6 volt scooter rectifier/regulator that I bought was quickly overwhelmed by the 14 amp capacity (and probably the open circuit voltage capability) of the stator coil, and burned out. I ended up with a commercial shunt regulator from Electrex World LTD.

I spent a lot of time on this project, but it met my goals. It looks original from the outside, it is reliable, and it was less expensive than the alternatives, as long as I don't count my massive investment of time.

Keep Shafting

Voltage Regulation

... or lack of voltage regulation as the case is.  The alternator actually works too well.  I bought this cheap regulator/rectifier intended for scooters.  Its voltage stability is horrendous.  Naturally the Permanent Magnet alternator increases in voltage and frequency as I rev the S7 Deluxe engine.  The regulator should compensate for this and keep the voltage around 6.x volts and not too high such as the 7.x volts that I saw this morning.  At highway revs the ammeter was reading nearly full scale of 8 amps!  "That's WAY TOO much current", I said to myself as I sat beside the road this morning.  The voltage kept going up with the revs... its supposed to be regulated to limit the voltage so that the battery won't get overcharged.  Well, the reason I was sitting beside the road this morning was that the battery WAS being overcharged and had blown the 7.5 Amp fuse that I had installed in series with it.  I was trundling along until I dropped the revs and the alternator wouldn't produce enough voltage to keep the ignition going... at which time the bike stopped running at the intersection.

A quick disconnection of the stator leads and a jumper across the fuse, limped KYL95 back home to the workshop.

So, now I need to replace that cheap scooter regulator.  I imagine its just a simple series pass transistor regulator in there, and its not yielding good results.  The correct solution is to use a switching regulator.  Like this one:

http://www.national.com/pf/LM/LM3150.html#Overview

Oh, and I've purchased a resettable circuit breaker too.  I HATE fuses.