Boyer Bransden Power Box

Previously maurice_cloud wrote:

Hi

I was thinking of fitting a Boyer or the like of a power box but know very little about them and how and where they go and what exactly what they replace, I have a commando 850 Mk 3 1977 for one thing how do you tell if you have a three phase or single phase by the way I have two wires coming out from the Alternator so I would think it is a single phase but how do I be sure it is,

if anyone has fitted one to a MK 3 have they got any pictures or fitting insructions they could show me please.

Hi Mo, I fitted mine (Boyer)to my 750 roadster 30 yrs ago not being an electric (it replaces the points)

person, I was surprised how easy it was, just followed instructions which

enables you to ride andtake it to a suitable dealer as it requires strobing

at 3000 rpm which detaches all the tooling off the dealers wall lol.

took it

Cheers Mo

1 Stay away from the Boyer powerbox, the capacitor in it to give the battery less running just like the 2mc it replaces, if you are lucky the rest will still function as a rectifier/regulator but not always, and in a starter equipped bike it's not needed. So just go for a combined rectifier/regulator.

Having a MK3 on the ignition side then either MK4 Boyer or the Pazon will cope with the startier induced voltage drop, do not fit a MK3 Boyer.

Yes, but as you have the high powered alternator the rect/reg needs to be able to handle the power so needs to be rated 200W or more.

Double post courtesy of useless forum.

Standard 180 watt alternator has two wires. A three phase has three wires.

Al Osborn is the man to ask if you need to ask. He is listed in NOC Technical Advise Team.

Al Osborn has + and - earth units in 6 and 12V (also 3 phase) that do the job. The boyer powerbox works fine on my norton and bsa.

My Boyer Power Box has been fine for over 10 years. Dommie with Lucas RITA.

If the battery is flat, you disconnect the battery terminals and kick start it. Then reconnect the battery. If you don't do that, the alternator currentis wasted by feedingthe low voltage battery.

The Power Box is a rectifier (to turn the AC from the alternator to DC) plus a voltage regulator (to provide a steady voltage suitable for battery charging from the otherwise big voltage variations created by the alternator as its speed changes). The regulator function means it does not need a zenor diode to limit the voltage to the battery by dumping waste current.

I have no idea what the Power Box does with excess voltage! I assume it switches its ownalternator input on and off rather than dumping current into something that gets very hot?

Two wires go in (either way round) from the alternator, and two go out to the battery. DON'T accidentally reverse the + and - or you will blow the box!

Previously maurice_cloud wrote:

Hi

I was thinking of fitting a Boyer or the like of a power box but know very little about them and how and where they go and what exactly what they replace, I have a commando 850 Mk 3 1977 for one thing how do you tell if you have a three phase or single phase by the way I have two wires coming out from the Alternator so I would think it is a single phase but how do I be sure it is,

if anyone has fitted one to a MK 3 have they got any pictures or fitting insructions they could show me please.

Cheers Mo

Hi Mo,

On the Commando 850 MkIII you will have a single phase alternator.

The Power Box will replace the the 2MC capacitor (The Blue Thing). The Rectifier (the round black thing next to the starter solenoid with the fins ) and the two Zener Diodes, one on each footrest plate.

It is easiest to simply remove the wires from the devices and insulate, but do not cut anything yet.

The Alternator wires go to the two yellow wires from the Power Box.

The Red wire from the Power Box goes to a solid earth. Or it can go to the + on the battery.

The Black wires can go directly to the - on the battery but if you have a fuse (which you should) then it goes to the fused side. (wire from battery to fuse then from the fuse to the rest of the wiring and the black from the Boyer).

You will need to disconnect the wiring from the Charge Warning Light Assimilator. This is the little black box just in front of the battery underneath the black air box. Again just fold back and insulate.

The mounting is anywhere that it will fit, I have a single carb on mine so no black air filter. Thus I fitted on a plate where the black air filter used to be.

Assuming it all works you can then look at removing unused wires if you wish. But at least if you have problems you can put it back as it was.

Regards

Tony

Previously David Cooper wrote:

I have no idea what the Power Box does with excess voltage! I assume it switches its ownalternator input on and off rather than dumping current into something that gets very hot?

Hi Dave,

If it switched the alternator input off, so that there isno load on the alternator, the alternator volts would shoot up which would cause problems when switched back on again.

I think that itprobably uses zero crossing clamping (not sure if that is the correct term) the box detects the charge voltage is too high, it waits until the AC crosses the zero volts line, it then clamps the alternator voltage at zero volts (effectively shorting the alternator), as it is at zero volts and Watts = Volts x Amps, then there is very little Watts and therefore little heating.

Once the charge voltage has dropped, the short is removed.

If any electronic whizzes out there would wish to correct / expand, please do so.

Regards

Tony

Thanks tony

What happens to the red Charge light on the dash if you disconnect the Assimilator wire dose that not make that redundent or is there still a way of connecting that so it do the same job as it was meant to be ?

I also have the old look air filter and not the big black boxbut still have the twin Carb`s

Oh I hope that it would all work as what a waist of time and Money if it don`t I was only thinking of doing this Mod to make itmore reliable

Regards

Mo

Hi Mo,

The only reason it would not work is if you have done something wrong. I am a great believer in only changing one thing at a time if possible. If you hack all the unused wires out and it does not work, you have no idea what the real issue is. If you remove the absolute minimum and it all works and then you 'tidy' and it doesn't then you know where to start looking.

I am also a great believer in'if it ain't broke, don't fix it' I changed to the power box when one of the zeners died but if it had not I would still be using the old setup.

I only say to not use the Assimilator as that is stated in the Boyer instructions. I have replaced the charge LED with the indicator from Al Oz (http://www.aoservices.co.uk/data/bsm.htm). The wiring is simple and short for this.

Another advantage of doing the Power box and Assimilator mod is that (if you are careful), there is a lot fewer wires and therefore joints required.

Regards

Tony