Ariel Owners Motorcycle Club

I am get a flashing reading of approximately 18 volts at the battery. I suspect the rectifier has developed a fault. (I am assuming the alternator is OK because I am getting the 18 volts at the battery). I have tested, using the diode setting on my multi meter, between the earth (+ve) and each of the three connections. They all read about the same approximately 690. I believe there may also be a zenon incorporated in the rectifier to control the voltage to 6 - 7 volts. Any suggestions for a cure?

On a standard system there isn't a Zenor diode in the system. To check the rectifier you will need to test each connection in both directions using the resistance setting, it should read open circuit one way and low resistance the other, see the diagram in the manual. I assume that you are getting a reading of 18volts with the engine running? Is that AC or DC? The mind does a bit of boggling. Test the alternator when disconnected and engine running, then reconnect and test output at rectifier with output wires removed. Main problems are wiring switches and rectifier.

Thanks Roger for the response. The 18 v at the battery is flashing hence I think it is a.c. Without the Zenor diode what regulates the voltage?

The 6 volt alternator system used on British bikes was less controlled than the earlier dynamo one. There are 2 fixed charging rates, without lights one third of the alternator coils provides a charge and when the lights are on the remainder are switched in. When more powerful 12 volt alternators were fitted the control was by Zener diode that limited the voltage sent to the battery, which was an improvement, but not much. The original system works pretty well but the ideal solution is a modern solid-state regulator and rectifier combined, unfortunately only available in 12 volts that I know of.
A conversion to 12 volts has just been made easier by the availability of a battery carrier to hold 2 6 volt batteries, there isn't a 12 volt battery that will fit the std battery carrier. https://draganfly.co.uk/shop/346353/bat ... #T2167-BAT
regulator https://draganfly.co.uk/shop/82626/12v- ... or/#ELE-30

There are several 6v regulator/rectifiers available. I have used 2 types in my bikes, and A-Reg6 from AO Services and an Electrex 6/12 volt one from Feked. This is the one I have on my Arrow and previously on my Tiger Cub, both at 6V. The standard system simply uses the battery as a crude regulator but the addition of the solid-state reg/rec means that the battery is spared that task and allows the fitting of gel batteries and LED bulbs, both of which prefer a regulated voltage. I fitted mine in exactly the same placed as the standard rectifier using exactly the same wiring. Very easy to do.

From the replies on this thread, there seems to be people who have a better grasp than I do on the subject.
The question I have posed before but failed to secure an answer relates to the circuit operating on both AC and DC simultaneously.
When the engine is at tickover or off, the lights are operating from the DC battery supply but, as engine speed rises, they are then powered by an unrectified AC supply to terminals 4 and 7 on the lighting switch??
I understand that lamps will work equally AC or DC but is this enigma as simple as when the AC RMS exceeds battery voltage it seamlessly takes over or is there something else to it?

The only time that AC should get anywhere after the rectifier is when the emergency start is used. If the battery is too flat to start the bike AC can be fed to the coils which will cause multiple sparks, enough to start the bike although understandably it will run rather roughly. As soon as the engine starts the ignition should be switched from the emergency to the normal position. I suggest the either you have the ignition switch in the emergency position or there is a fault in your wiring.

Thanks for your reply Roger.
But, looking at a 1962 (key ignition) wiring diagram, the two outputs from the alternator to the rectifier ALSO (pre rectifier) are shown go to the lighting switch terminals 4 and 7

Yes, that is to switch in the additional coils from the alternator to the rectifier, they do not connect into the lighting circuit, or at least they shouldn't. Two separate functions of the switch lights and additional charging, mechanically connected but not electrically.

The AC goes through the rectifier first and only DC comes out of it so it should never be AC out of the rectifier onto the rest of the bike system. However, the original rectifier is a crude device, simply bridged diodes that by no means produces smooth DC, so it may well be choppy and bulbs could flash or vary in intensity. It is DC, in that the current is flowing in the same direction, so to speak, but it will vary from 0 volts to high volts in quick succession. It is then up to the battery to act as a voltage regulator of sorts to keep the max voltage to around the nominal voltage. If you fit a solid state rectifier/regulator then not only is the AC from the alternator turned into DC - and potentially much smoother DC than with the original rectifier, but the resultant DC voltage will be controlled by the regulator to around 7 volts to effectively keep the battery charged and without the risk of overcharging and subsequently boiling the electrolyte. If you fit a solid state rec/reg then you can, and should, join the low and high output wires from the alternator together so you are not controlling the output with the light switch.