Rectifier / Regulator and cooking your alternator

 That the regulators went open circuit and therefore there was no load and it was the Zener system that 'shorted' the alternator and dumped the excess as heat, but you learn something every day. I suggest that you need to talk to Al Osborn and enquire about his reg/rect units?

For what its worth,  my 650 has a 3-phase alternator and it is happily controlled by a reg/rect from a Kawasaki 1100.

Regards, George 

I thought that they are pulse width modulated at a constant frequency, with an on/off ratio depending on feedback of output voltage. So heat dissipation from the unit are a combination of diode forward voltage drop, typically about one volt, some other internal resistance and switching losses when changing between on and off state. This guess is based on the fact that TriSpark recommend a filter to suppress RFI (radio frequency interference) if you have a Podtronics unit. They also have put a high power MOSFET reg/rec on the market. Probably because MOSFETs have shorter transition time between on and off.

I don't understand why a shunt type reg/rec should cook the alternator more than the original rec/zener, some of them have been working for decades.

Hopefully, Al will explain and lift the clouds.

I am keen to stop things from getting too confusing here.

You should refer to a ‘short-type’ regulator/rectifier instead of using the term ‘shunt’

...this is because all regulators (including your original zener) shunts excess power some where in some way.

So with that in mind, talking about shunting can confuse people.

The behaviour of ‘short-type’ regulator/rectifiers shorting out the AC input side is not specific to three phase units.

The single phase units do this too.

The most common examples are Podtronics, Boyer Bransden Power Box and Tympanium, and they all work this way.

And don’t be too concerned - they have been doing this for years with no issues at all.

But do bear this in mind - we are all under the impression that bigger is better - and have been conditioned to think that way.

To that end, many of us have fitted higher output alternators to our bikes thinking that it's going to be a big improvement and all of our problems are going to go away.
Actually it just introduces a new set of challenges.

The original charging system on an old brit bike was designed to charge at around the same rate as the electrical loads on a bike draws - look at it as kind of a balanced system.

A Commando will be typically drawing around 10 amps when it’s up and running (with headlight on)

So when you are upgrading to a super duper charging system, maybe ask yourself as you are bolting up that high power single phase 200 watt, 16 amp RM27 (LU47239) or three phase 180 watt, 14.5 amp RM24 (LU47244) what is going to happen to all that extra power you’re now making!?!?

And if you don’t ride with your headlight on, or are fitting LED lamps as part of your upgrades, then once again think twice about your upgrade!

The ‘series-type’ regulator/rectifiers by Shindengen are the models SH775 and SH847 NOT SH755 as stated by the OP.

This type of unit is also referred to by some manufacturers as ‘open-type’

The components used to make these are no more expensive or exquisite than anything else available in the market, but they haven’t been widely implemented yet, which means production numbers are low (hence the higher cost)

Now Yamaha are rolling this technology across their range, as are Polaris on their ATVs, jetskis and snowmobiles hopefully the price will start to come down.

They are also catching on with the Harley boys too.

You say that your 750 works well with an RM24 and a reg/rec. Most people seems to have no problem with that setup.

Then the 850 came with a faulty alternator (RM24?). Why had it failed?

You fitted a new RM24, which melted.

Two obvious questions. Could a faulty reg/rec have caused death to both alternators? Was the new RM24 faulty from start?

Be careful here as confusingly Lucas list two types of RM24 alternator stator:

• RM24 10.5 amp stator (LU47252)
• RM24 14.5 amp stator (LU47244)

I would suggest that the 10.5 amp unit is a great fit for the Pre-MK3 Commando.

The high power unit should only be considered if you have an electric start and your charging system is continually recharging a depleted battery.

I run a RM23 single phase, a Tri Spark mosfet rectifier and a BSM from Al. On the MK3 even with full beam on the BSM still indicates green. This suggests that the RM23 output is more than adequate once you have a system that can effeciently use what it generates. 

The podtronic fitted prior to the Tri Spark rectifier was not as efficient as the BSM used to glow orange red at night when the revs dropped and that was with just dipped beam on. 

Unless you are going to tap and use the extra a 3 phase stator will give you, then it seems pointless heating the atmosphere. 

Alan osborn is correct in what he said

the norton alternator is a permanent magnet type what you seem to be thinking about is the princaples of a standard car alternator which is very different

they will charge if the roter is spinning if you short it out it cant develop volts 

i x v = watts so no volts no power to dissipate 

the problems of melted stators is usaly faulty rectifier packs 

google it 

Hi Robert,

I agree with what you are saying about shorting out will not cause a problem, in which case  what IS the mechanism that causes overheating?

Tried searching for anything relevant without success.

Tony

http://www.zefox.net/~bob/mc/vfr/alternator.html

read it towards the bottom of the article

the other problem is rubbing stators on the magnet (overheating)

Just as an aside to all this, the zener on my '72 Commando failed open circuit, the voltage rose to heaven knows what and cooked the battery. This resulted in my show-winning bike being sprayed with sulphuric acid over the silencer, rear (aluminium) wheel, aluminium hub etc.

Made my day.

The Zener going O/C as you say gave the battery excess voltage (won't happen if your lights are on, but we don't all do that) I have an answer, I sell a BSM LED that changes colour with battery voltage hence you would have seen this problem very early on the warning on the BSM. The advantage over an Ammeter is that very often one does not look at the Ammeter but a changing colour on a lamp will catch your eye.

Hi Alan,

Does your LED fit directly in the headlight shell?

Or is surgery required?

Richard,

Have a look at http://www.aoservices.co.uk/data/bsm.htm

It will tell you all you need.

Tony

Brilliant bit of kit, just buy one and fit it, ether on the handle bar, headlamp shell or console.

Just to add my two pennys worth. I agree that the rectifier/regulators are not the best design in some cases.

I do quite a lot of work on Nortons and can cite 2 cases on Mk3s which have had failed stators. Both of them had the higher output stators and boyer power boxes. So it could have been a failure of the boyers or the stators. Both stators got cooked and in one case it de-magnetised the rotor. On both machines the whole charging system was replaced, but with podtronics 200w regulator.

I am very interested in these Shindegen open type regulators. They look like the way forward. Especially with the new lithium type batteries that are finding favour now and electric starter demand.

I do see the stators on some bikes do look more overheated than others. I shall have to see if there is any correlation between reg/rect equipped bikes and those on zeners.

Cheers 

Paul

Paul, 

The latest lithium type batteries don't need special chargers, just a DC voltage of the correct specified range. There are only two batteries on the market at the moment that are like this and would fit motorcycles. Not cheap though. 

Things move on rapidly these days. 

As a simple old ‘erbert who barely knows his **se from his volts, I think Grant has a very valid point in saying we have been conditioned into believing bigger is better. This really does call for some back to basics thinking: what is my riding style (ie am I an every day, all-weather rider or a weekend/summertime leisure rider), plus what are the demands of my bike- more ie electric start, powerful/daytime lights etc or less: low demand, LEDs etc.

Having determined that, the range of suitable alternator setups (outputs) can be ascertained, and then determine which of the RR units available are compatible- and in our price range.

Perhaps Lucas got it right first time round, with a 3-wire setup controlling the alternator output directly through the lighting switch and its position…although I would hate to go back to that huge doughnut of a switch in the headlamp shell like my old Tiger Cubs had!

.. the 3 wire alternator was ideal. But I was very happy with the 2 wire alternator, full wave rectifier (using a modern silicon type) and Zener diode on my Commando. Simple and relatively bulletproof.