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#77533 - 02/24/05 5:30 pm RM24 Alternator.  
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dave jones Offline
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Following on from my non starting bike thread, I was wondering if the RM24 alternator is a straight swop, size wise, for the RM21 fitted at the moment. Can I use the original rotor? I guess I can keep a positive earth if I buy a whizz bang electronic box. I notice that the bikes fitted with these three phase items were negative earth and I don't want to re wire the whole bike.
Dave

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#77534 - 02/24/05 6:43 pm Re: RM24 Alternator.  
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Tom Sanders Online content
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I've got a 3 phase Sparx alternator fitted on my '72 C-do and kept it positive ground.


LONG LIVE LOCKTITE

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#77535 - 02/24/05 9:20 pm Re: RM24 Alternator.  
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dave:

Alternators on Brit bikes produce AC which has no polarity and is in fact isolated from the ground of the bike. When the AC passes through a rectifier and DC is made, the choice can be made as to whether to ground the postive terminal or the negative terminal of the rectifier. The original Lucas rectifier is so made that mounting it to the frame connects the positive terminal to ground That is why the device has two AC terminals and one DC terminal (negative DC). The mounting stud is actually the positive terminal of the rectifier.

The after market rectifier/regulator boxes like the Tympanium and the Boyer Power Box have four terminals: two for AC input, one positive DC and one negative DC. The box itself is isolated from all the terminals. Mounting the box does not determine the polarity of the system. You determine it by which DC output you connect to ground.

The stock alternator is sufficient for any stock bike and the big three phase Lucas alternator is not really necessary. Add a landing light for a headlight and that is not probably true. Keep stock wattage bulbs or close enough to stock and there is no problem with the original 105 watt alternator system. You can determine if your system is in trouble by adding up all the bulb's wattages and allowing about 36 to 40 watts for the ignition. The sum must not exceed 105 watts for the stock alternator.

LDBennett

#77536 - 02/24/05 10:41 pm Re: RM24 Alternator.  
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Thanks for the replies. I will check my system out carefully before making any big changes.
Dave

#77537 - 02/25/05 2:01 am Re: RM24 Alternator.  
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Hi Dave,

Quote:
Originally posted by dave jones:
I was wondering if the RM24 alternator is a straight swop, size wise, for the RM21
Lucas intended it to be so and it is, ime.

Quote:
Originally posted by dave jones:
Can I use the original rotor?
It isn't recommended. All rotors gradually lose their magnetism, any original rotor is now several *decades* old and the amount of magnetism is directly related to the amount of electricity generated in the stator.

The earthing question has been dealt with: however, you should be aware that there are, in fact, two RM24 alternators (stators):-

1. The best-known is the 14.5 Amp (colloquially converted to '180 Watt') one. If you don't use a 'whizz bang electronic box' with this one, you have to replace the original zener diode with a matched pair (and a second heatsink) but this is all available as a complete bolt-on kit either direct, or via a dealer, from the ultimate world-wide supplier of all Lucas alternators, Mistral Engineering in GB.

2. There's also a 10.5 Amp (same as the RM21) RM24: it needs a 3-phase rectifier but can use the original single zener.

Contrary to LD's assertion, I couldn't praise or recommend the RM24 conversion enough. beerchug I've had high-power (14.5A) RM24's on both my T160's for over 20 years and, yes, while each bike runs things like 100-watt main beam headlights (so car drivers dip their headlights *before* they round the corner wink ), the alternators were simply the end of electric-starting and other low-battery-charge woes.

My experience of single-phase alternators like the RM21 is contrary to LD's. Ime, they aren't capable of maintaining battery charge even if you just fit a normal 60/55w QH headlight, unless you rev. the t*ts of the engine all the time. frown

Another unstated advantage, of all 3-phase alternators over single-phase ones is more power at low revs.: Lucas claimed (and supplied wink ) 85% of maximum at 2,800rpm.

Finally, if you consider a Sparkz 3-phase alternator, you should be aware of one thing - it doesn't produce any more Amps than the high-power RM24.

You'll note that I've quoted alternator outputs in Amps: these are absolute figures - that's the maximum output of the alternator, no argument and they're what *Lucas* use. Otoh, Watts are obtained by mutiplying the Amps by Volts: Lucas wattages (120W or 180W) are obtained by multiplying 10.5A or 14.5A by roughly 12V.

The Sparkz alternator is an exact copy of the 14.5A RM24. Sparkx supply it with copy of a Tympanium-type electronic regulator, which switches at around 15V. Multiply 14.5A by 15V and you get around the 220W claimed in Sparkz's adverts. wink However, if 15V is flowing around your bike's wiring, all the 'consumers' (ignition, bulbs, etc.) are *using* more Watts too. wink

Like I said, you don't get any more power from a Sparkz alternator than you do from the high-power RM24. wink

Hth.

Regards,

#77538 - 02/25/05 4:00 pm Re: RM24 Alternator.  
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Stuart Online content
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Hi Hack,

Quote:
Originally posted by HackAsaw:
matched zeners are pricey and a PITA
Uh-uh, don't get me wrong ...

Firstly, I'm advising using a new rotor with a new RM24 stator (same as the Sparkx).

Secondly, I've always had the twin matched zeners on both T160's and none have given me any trouble. Nevertheless, I'm well-aware that the cost and availability of Lucas bits differs significantly depending where you are on the planet. I'm in GB so, say, were a zener to give me trouble, I'm a 'phone call and overnight post from another matched pair. However, I appreciate that, in the US, a Podtronics or Tympanium is cheaper than a Lucas 3-phase rectifier and twin matched zeners, so I wouldn't advise against using either of those with an RM24.

Quote:
Originally posted by HackAsaw:
the Sparx unit is a bargain at around a buck an advertised watt....
Ummm - my point exactly: looking at the Watts is misleading, because Watts are a product of two other variables (Amps 'n' Volts). Both the RM24 and the Sparkx both produce exactly the same maximum Amps (14.5): if the Sparkx regulator is allowing 15 Volts into the wiring, yes, the alternator is 'producing' more Watts, but the consumers are using more too, so there isn't anything extra from a Sparkx.

Alternatively, perhaps I can be clearer with a couple of examples:-

1. Coil 'n' points or electronic ignition at tickover both consume around 3 Amps: at 12 Volts, that's 36 Watts; at 15 Volts, that's 45 Watts.

2. A standard quartz-halogen main beam is usually quoted as 60 Watts, but that's 5 Amps at 12 Volts. If you raise the Volts to 15, the light's now consuming 75 Watts.

That said, and returning to the economics of the various options, if the Sparkx and its Chinese reg./rect. is cheaper where you are than an RM24 and Podtronics/Tympanium, you'd probably only pay the extra if you wanted good ole British engineering (although I think the Lucas stuff's made in India wink ).

Hth.

Regards,

#77539 - 02/26/05 9:56 am Re: RM24 Alternator.  
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Yeah, but what's the max. Amps?

In GB, Sparkx is advertising 220 Watts: 14.5 Amps and 13.8 Volts do not 220 Watts make (at least not according to the MS Calculator wink ).

As an aside, it's perhaps worth noting that, certainly in GB, the electrical industry doesn't use Watts, preferring VA (Volts-Amps), not only because of the difficulties with Watts outlined in this thread but also because temperature can be another variable that affects the number of Watts you're getting at any given time.

Regards,

#77540 - 02/26/05 11:57 am Re: RM24 Alternator.  
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The readily available Zeners are 10% tolerance parts. Even the new units use a zener (albeit not 50 watts) to control the regulated voltage. So that means a 14.5 volt marked zener (if that voltage zener was available) could regulate at 13.05 to 15.95 volts DC. The key is that the regulated Alternator/rectifier output voltage that is suppose to charge the battery be higher than the batteries terminal voltage when fully charged. Without that voltage difference the battery will not take in current. The higher the applied voltage the faster the battery charges (up to a limit where the battery overheats due to too much current flowing into it).

The internal zener sets the voltage that is applied to the system. The amount of current available is a function of the internal alternator windings resistance. I suspect that the Sparx system suffers a little advertising hype and/or at the lower output voltage it can deliver more current. A true test of the system is running the engine at say 5000 RPM and adding external load resistance monitored with a series current meter and a voltage meter across the system. Anything else is conjecture. The simple fact that the Sparx is rated at more than twice the Lucas system assures that unless you are powering a "landing light" and miscellaneous appliances from the kitchen you have more than enough "watts" to do the job.

When I went to school many years ago, watts was used to describe the power in a DC circuit and Volt-Amps was used to describe the power in an AC circuit which included phase angle between the voltage and current wave forms (commonly called power factor). There is no "temperture" dependence in the calculations that I recall. Maybe it is new math?

LDBennett

#77541 - 02/26/05 5:50 pm Re: RM24 Alternator.  
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I have been looking at three phase regulators to go with the RM24. The podtronics three phase item doesn't seem to handle as many watts as this alternator kicks out. Is that right?
Dave

#77542 - 02/27/05 12:17 pm Re: RM24 Alternator.  
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dave jones:

For the 3 phase alternator buy the package deal: alternator with rectifier/regulator. That is the only way all will be matched for capacity (watts). If that choice is not available contact Podronics and get their recomendation. It is not wise to design your system from a catalog; get help from the manufacturer.

That being said, the capacity of the system is only used up when you add that load to it. If your total load is only 100 watts and the alternator has a capacity of 240 watts you are not using its full capacity and have wasted your money. The rectifier/regulator only has to match the load the bike will put on it. So you could have a 100 watt load, a 150 watt Podronics, and a 240 watt alternator. The trouble would start if you developed a system short that was not protected by a fuse as the alternator would try to supply its full load capacity (240 watts in this example) and the rectifier/regulator could only handle 150 watts (again in this example). The rectifier/regulator would fail by an internal melt down. It is best to get a matched system: load to alternator to rectifeir/regulator. Excess capacity is a waste (it may allow the battery to be charged at a lower engine RPM but that is not a given and would have to be proven by tests).

LDBennett

#77543 - 02/27/05 2:20 pm Re: RM24 Alternator.  
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I've been running a new sigle phase Lucas alternator with podtronics and RITA ignition for just over a year. head light is 55/100w. no problems, first kick starter.
i wouldn't spend unnecessarily and dave, i think you've done enough of that in the past. all you probably need is a new rotor.


my 2 bobs worth
#77544 - 02/28/05 1:12 am Re: RM24 Alternator.  
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Hi,

Quote:
Originally posted by LDBennett:
The readily available Zeners are 10% tolerance parts.
'Matched zeners' are just that, matched by Lucas for switching voltage and power conversion, sold under a different part number to ordinary single zeners.

Quote:
Originally posted by LDBennett:
For the 3 phase alternator buy the package deal: alternator with rectifier/regulator. That is the only way all will be matched for capacity (watts).
It is not wise to design your system from a catalog; get help from the manufacturer.
The RM24, 3-phase rectifier, matched zeners and upgraded wiring loom to link 'em altogether are a package deal from Mistral Engineering: however, they'll also sell individual bits if that's what you want. Aiui, Mistral are the ultimate world-wide supplier of all Lucas motorcycle alternators - certainly they're the nearest Joe Bloggs get to the manufacturer.

Quote:
Originally posted by mike750triton:
I've been running a new sigle phase lucas alternator with podtronics and RITA ignition for just over a year. head light is 55/100w. no problems,
Interesting ... single-phase RM20 or RM21 (but not RM23) produces a maximum of 10.5 Amps (126 Watts @ 12 Volts). Rita consumes 3 Amps (36 Watts @ 12 Volts) at tickover and low revs., slightly less at high revs.; 100W main beam is 8.33 Amps @ 12 Volts ... where's that extra 10W coming from and what's keeping the rest of the bike's electrics going? confused

Quote:
Originally posted by HackAsaw:
do you think two Zeners at 10% tolerance are adequate for the three phase? I don't.... one will do all the work
Nope. Note the comment at the top: matched zeners are not the same as two zeners; moreover, matched zeners are wired in parallel, and you also take care to get the the two cables from the rectifier to the zeners as close to the same length as possible. As I said, I've been running the arrangement for over 20 years on two bikes without any problems.

Quote:
Originally posted by HackAsaw:
the Rita sure seems more tolerant to low voltages
Don't bank on it: the thinking should always be "I have a 12V electronic ignition, it needs 12V". Think any other way and, sooner or later, you'll be walking, ime.

Hth.

Regards,

#77545 - 02/28/05 2:15 pm Re: RM24 Alternator.  
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I'll make several comments to all above:

Buy the amount of power you need. If you must run lights 24/7 go for big (I don't even know if the lights on any of my bikes works as I NEVER run the lights-105 watts is fine for me).

Once three phase is rectified it is no different than single phase except that the available 3 phase units can put out a lot more power. Running two "matched" zener in parallel for voltage control on any high output rectifed alternator setup is no better than running one on a low power stock system. It is shunt regulation that sucks current out of the alternator and relies on the series resistance of the alternator to drop the voltage to the regulated level. It dumps energy to regulate. Modern units like the Podrontic, Tympanium, and the Boyer Power Box and others use series regulation where the regulator part of the device only delivers the energy that the system needs, no more. Doesn't that sound better than throwing away energy (that the motor had to generate). It is more relaible, too, as the regulator unit is not always working at full current and max heat output.

As an aside the sharing of the current by the two zeners in parallel is no better than the matching of the zeners. "Real" electronic circuit designs rarely use such approaches and almost always build in circuitry that assuse equal sharing and rarely rely on component "matching".

As power Zeners are only avialable, as far as I know, up to about 50 watts, and the system should be designed so as to be able to sink the entire output minus the 36 to 48 watts that the ignition needs. I think two zeners in parallel is an inadequate design. Modern series regulators can use very much larger power handling transistors and a smaller zener for regulation and their power handling capacity can be much greater than two "matched" zeners. I find it hard to install an inadequate system rectifier/regulator (know to be questionable in power handling capacity) when better options are readily available. You see I hate to walk when the system fails. Your experience may be different! This is just my opinion based on my engineering background. Take it as you will.

LDBennett

#77546 - 02/28/05 3:34 pm Re: RM24 Alternator.  
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Quote:
Interesting ... single-phase RM20 or RM21 (but not RM23) produces a maximum of 10.5 Amps (126 Watts @ 12 Volts). Rita consumes 3 Amps (36 Watts @ 12 Volts) at tickover and low revs., slightly less at high revs.; 100W main beam is 8.33 Amps @ 12 Volts ... where's that extra 10W coming from and what's keeping the rest of the bike's electrics going?
5W rear light. 100W main beam, 3W igntion = 108W. with occasional brake light at 15W it's still 123W no indicators needed or wanted. may be getting away by the skin of my teeth but it works. so 12v X 12A = 144W. 123W / 12V = 10.25. i have it right here in black & white the RM21 is 12A direct from the current Lucas supplier.


my 2 bobs worth
#77547 - 03/01/05 9:18 am Re: RM24 Alternator.  
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This has certainly got people talking! It sounds like there is still hope (just!) for my single phase system.

Dave

#77548 - 03/01/05 10:36 am Re: RM24 Alternator.  
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Hi Mike,

Quote:
Originally posted by mike750triton:
5W rear light. 100W main beam, 3W igntion = 108W.
No, you've misread/misquoted my post.

Quote:
Originally posted by Stuart:
Rita consumes 3 Amps (36 Watts @ 12 Volts) at tickover and low revs., slightly less at high revs.;
This is true also for points and Boyer-Bransden e.i.

I doubt there's even a secret military ignition that can generate tens of thousands of HT volts from 0.25 Amps (3 *Watts* @ 12 volts) (awaiting incoming :rolleyes: ).

Quote:
Originally posted by mike750triton:
i have it right here in black & white the RM21 is 12A direct from the current lucas supplier.
Who's claiming that?

I've always understood that Mistral Engineering in GB are the sole world-wide outlet for Rita and motorcyle alternators from what remains of 'Lucas' manufacturing - Mistral and Lucas have a relationship stretching back at least to the original development of Rita in the late 1960's. I've just spoken with John Carpenter (boss of Mistral Engineeering) and he's confirmed that, while advising that 'Lucas' has a Chinese partner that manufactures the RM24 copies marketed by Sparkx.

Moreover, John confirmed that *Lucas* rated (and still rates) the RM21 as 10.5 Amps, and that no further development took place after the RM24 was launched (in 1978 or '79).

Finally, depending how old your rotor is depends how much current it can generate - the original magnetism decays - so, if your rotor is original to the bike, it's unlikely even to be generating the rated 10.5 Amps.

Hth.

Regards,

#530565 - 02/26/14 10:57 pm Re: RM24 Alternator. [Re: dave jones]  
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Zombie thread alert! laughing

Be nice if somebody made (or could make) a rare earth magnet rotor for these old things! whistle

#530759 - 02/28/14 2:51 am Re: RM24 Alternator. [Re: dave jones]  
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Back to the original question.
I recently bought an RM24 off fleaBay. I also found a Yamaha rectifier/regulator, rated at 200W, and with a compatible circuit for a permanent-magnet alternator.
Lazy sot that I am, I first installed the stator over my existing rotor. Clearance was to spec, and it worked properly. The real advantage is at low rpm, this thing puts out 13V idling. laugh
I just did my clutch. My original rotor was indeed original to the bike, date 03/71 stamped in the rotor. The 'new' one was stamped 79 and a bit stronger, so I swapped rotors.
That Yamaha regulator is a brick wall at 14.5V. That should keep the Pazon happy, EI's do NOT like over voltage.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
#531349 - 03/04/14 1:45 pm Re: RM24 Alternator. [Re: dave jones]  
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That "voltage reference," is a zener diode. But, as a reference, it does not pass large amounts of current it only controls the turn-on voltage for the SCR.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
#531659 - 03/06/14 12:31 pm Re: RM24 Alternator. [Re: mike750triton]  
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Originally Posted By: mike750triton
. I have it right here in black & white the RM21 is 12A direct from the current lucas supplier.

Interesting. Lucas don't make the RM21 or RM24 Alternators anymore, despite claims to the contrary. The same applies to the rotor. I would guess the unit you have is aftermarket.
All Genuine Lucas product is supplied with standard anti-counterfeit labelling, as set out on their own website here :-

http://www.lucas.info/index.php?p1=5&p2=9

Without this labelling, any 'new' production isn't genuine.

#531668 - 03/06/14 1:10 pm Re: RM24 Alternator. [Re: dave jones]  
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I got my Genuine Lucas from LP Williams in 2007 - been a good unit.

LP Williams


beerchug
#531670 - 03/06/14 1:22 pm Re: RM24 Alternator. [Re: TripleTown]  
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Hi Mike,

Originally Posted By: TripleTown
Originally Posted By: mike750triton
. I have it right here in black & white the RM21 is 12A direct from the current lucas supplier.

Lucas don't make the RM21 or RM24 Alternators anymore,
The same applies to the rotor.

Afaik:-

. Lucas stopped making the single-phase stators (RM21 and RM23) in 1978, when they started making the low- and high-output versions of the RM24 3-phase.

. Not sure when they stopped making the rotors and 3-phase stators, but they're still available, as are RM23 (single-phase high-output) stators (all at a price considerably higher than the much more widely available patterns).

. Once they stopped producing single-phase stators, Lucas did not do any more development of them - e.g. "12A" RM21's, 16A "RM27", etc.

. Nevertheless, it's entirely possible to get an RM21 or pattern to generate 12A ... you just have to spin it at about 8,000 rpm ... at the 5,000 rpm Lucas used to rate stators, chances are it still generates 10.5A, same as they did when Lucas made 'em ... whistle

Hth.

Regards,

#531806 - 03/07/14 1:15 pm Re: RM24 Alternator. [Re: Stuart]  
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Originally Posted By: Stuart
Hi Mike,

Originally Posted By: TripleTown
Originally Posted By: mike750triton
. I have it right here in black & white the RM21 is 12A direct from the current lucas supplier.

Lucas don't make the RM21 or RM24 Alternators anymore,
The same applies to the rotor.

Afaik:-

. Lucas stopped making the single-phase stators (RM21 and RM23) in 1978, when they started making the low- and high-output versions of the RM24 3-phase.

. Not sure when they stopped making the rotors and 3-phase stators, but they're still available, as are RM23 (single-phase high-output) stators (all at a price considerably higher than the much more widely available patterns).



Yes and No really.
From John Healy in this thread :-
http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=286216#Post286216

"LAP will make a lot of the old Lucas parts if the quantity is sufficient, and that quantity is usually beyond the pocket book of most. The one person who has stepped up and placed some pretty hefty orders for Lucas parts from LAP is David Holder of Velocette Motorcycles. The directionals, stator and rotors, switches, zener diodes are a few of the items he has had LAP make."

LAP Electrical in Birmingham have made the RM21 and RM24 stators for many years now, and imo they are very good quality.
LAP (Lucas Aftermarket Products) also make the short and long Stem indicators, but they are now having to rebrand their products LAP rather than Lucas, because they are.... well aftermarket.
See this UK seller's description :-
http://www.ebay.co.uk/itm/GENUINE-LUCAS-...0-/161207002061

I have no idea why they just don't pay a license to Lucas TRW to use the Lucas brand, just as good company's like Andover Norton have a license to manufacture Norton parts from Norton Motorcycles UK.

So, yes you can still obtain 'branded' RM21 and RM24 stators, which are superb, but Lucas haven't made them for a long time, and probably never will again.

#531812 - 03/07/14 2:23 pm Re: RM24 Alternator. [Re: TripleTown]  
Joined: Jun 2002
Posts: 9,297
Stuart Online content
BritBike Forum member
Stuart  Online Content
BritBike Forum member

Joined: Jun 2002
Posts: 9,297
Scotland
Thanks for the additional information.

Regards,


Moderated by  John Healy 


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