Author Topic: Electrical Problem  (Read 2217 times)

Offline rtree

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Electrical Problem
« on: September 19, 2019, 08:45:11 PM »
My friend has a 1959 BSA B31. Finding his 3 original wire 6 volt alternator had died, he decided to change the  electrical system on the bike, to 12V Positive Earth . Most will recall this model had an emergency start, on the occasion of a flat battery.
He began by fitting a  2 wire Lucas RM21 12V  Stator and matching Rotor,  a 200W Regulator, 12V Battery, Lucas 12V DLB 102 Coil, 12 V Ammeter,  and Bulbs.
As one can imagine, this required some changes to the original wiring loom/harness. The new Alternator via the Regulator/ Rectifier, produces a charged, to a full  battery,  of  13.9 volts with the engine running around 3000 rpm. Switching on the ignition only, the Ammeter shows a draw of around 6 amps. Unfortunately, after running a few miles the Ammeter still has not moved from its starting position, of  minus 6 amps. I have checked the Coil primary / secondary, readings, they fall within the Lucas DLB 102 parameters. As the system is positive earth, the coil is wired minus to the switch side and plus to the points side. On the wiring diagram for the 1959 3 wire Alternator system, a wire runs from number 15, of the PRS8 Ignition Switch to the + side   of the Coil. Can anyone explain the purpose of this wire? The bike starts on the first kick. Any contributions regards Amps draw and Switch to Coil wire, would be greatly appreciated.

Offline chaterlea25

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Re: Electrical Problem
« Reply #1 on: September 19, 2019, 10:02:16 PM »
Hi rtree,
That wire has to do with the emergency starting setup,
When converted to 2 wire alternator disconnect this  from the coil and insulate it
I would think the reason that the ammeter is showing minus charge is the way it has been wired up ???
Has the wire from the rectifier regulator been connected directly to the battery?
For the ammeter to read properly the charging wire needs to be connected to the ammeter, (load side)
the battery supply goes to the other side via the loom
One of the wires that used to switch the alternator coils (now spare) can be repurposed to take the charge to the ammeter

John

Offline rtree

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Re: Electrical Problem
« Reply #2 on: September 20, 2019, 10:28:27 AM »
Many thanks John for your reply. In your reply,  think you have nailed the Ammeter problem. I brought up the the Podtronics wiring diagram on the net this morning and it confirms what you suggest. When I go to visit him I will draw this to his attention.

Offline chaterlea25

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Re: Electrical Problem
« Reply #3 on: September 20, 2019, 10:24:00 PM »
Hi rtree,
Thanks for the "Thanks"  ;D

John