Topic: Permanent Magnet Alternator for CB750?

[Ricky_Racer]

Okay, guys, I'm out here in Never-Never Land again trying to find an answer in an area where I'm completely clueless..

Question: If it's externally driven, is there any reason why this Permanent Magnet Alternator when properly wired couldn't service a CB750?

Alternator: 12 Volt, 14 AMP, CW, PMA (I have no idea what most of this means!)
Regulator: E/R (or this!)

Thanks in advance to anyone who can help!  RR

[OldSchool_IsCool]

The regulator of a stock charging system manipulates the strength/duration of the field coil to keep the output voltage at battery-friendly levels.  With a permanent magnet setup, there is no way to change the field strength.  A shunt or dump load would need to be added to keep from cooking your battery and other sensitive components such as light bulb filaments.

[Ricky_Racer]

Thanks for the quick response. Okay, makes sense to this point. How would one incorporate a "shunt or dump load" (I assume to ground) or would an external regulator not do the job? RR

[OldSchool_IsCool]

A direct short to ground wouldn't work as it would cause your alternator to freeze up (grounding a wind turbine is a method used to stop the blades during maintenance).  Most dump loads I've read about are heater coils in a fluid of some sort (generally applicable to terrestrial systems).  I'm not sure what would make a good dump on a bike.

[Ricky_Racer]

Thanks. Before I posted I did a search under "permanent alternator" and found several discussions involving non-CB750 Hondas that have permanent magnet alternators. I wonder how they do it?

This alternator is from a Kubota tractor, so I'm not sure what type of voltage regulator they use or how they're wired. I'll inquire further. 14 amp output is about right, isn't it?

You've been very helpful, Oldschool. Thanks. Anything else you can add would be great.

Anyone else out there wanna take on this thorney application? TT, how about you? RR

[OldSchool_IsCool]

Well, if they can do it on other bikes and tractors, then there must be a way.  I'm familiar with magneto systems, but those are generally single cylinder and don't have other electrical systems other than an ignition coil.

12v x 14a = 168 watts.  I don't know the stock 750 output, but I don't think 168 watts is that much of a gain.

[kmb69]

Ricky, Prior to the SOHC 750's, Honda twins and older models have permanent magnet altenators. Most are 3 phase but some are 2 phase. The rectifier is used to convert AC from the altenator to DC for the battery and other components. I don't think any of them used a regulator. The output of the altenator was "matched" to the average consumption of the components plus a little extra to charge the battery. The batteries were properly sized to act as a "buffer" in the system to prevent overload. That Kubota unit is probably designed for diesel tractor kind of RPM's. It would probably work if you get the drive ratio right. It appears to have only 2 wires indicating it is a 2 phase system. You can actually use it on a 3 phase rectifier by just connecting to 2 of the rectifier inputs. Some guy in Europe was selling a CR replica altenator housing using a 2 phase Ducati altenator. Not sure about his rectifier but I know a guy in Florida that is using one with a battery. You can also use a 2 phase system sans the battery. The OEM CR750 altenator is a 2 phase permanent magnet unit that was "normally" (I think) used without a battery. More info may be available from Ken at Cycle-X. Their website says to contact them for information on using their altenator in that manner. Their unit is advertised to have a higher output than the stock system.

Keith

[Don R]

I ran one of those on my dragster for a while. It worked but didn't provide evough power to run an MSD water and fuel pumps etc. Mine also fit a john deere lawn tractor and a miller welder. I went to a 70 amp mini from East coast auto electric. There is a super mini that would run anything you could hang on a 750.

[Ricky_Racer]

Thanks, guys. Don, I'd looked at the East Coast Electric 55 amp mini, but at $249 it appears to be similar in size and design to a different Kubota (Denso) 40 amp with internal regulator for $79. I stumbled on the permanent magnet form trying to reduce the size even more although the Denso is only about the size of a coffee mug. The alternator needs to be able to sit underneath a blower and plenum on a stock-framed CB750K.

Denso:
Replaces Part Numbers:
POWERMASTER 8162
OEM(s):    Powermaster
Voltage:     12 Volts
Amps:     40 Amps
Regulator Position:     9:00
Polarity:     Negative
Output Stud Dimensions:     M6-1.0
Approximate Weight:     6.93 lbs / 3.15 kg
Notes:Internally Regulated/Internal Fan, Includes 3 Prong Self Energizing 1 wire Regulator

I can give Kenny a call tomorrow to see his take on all this; good suggestion. KMB, thanks for the 2-3 wire info; it helps a lot. RR

[TwoTired]

Alternators produce no power when not spinning, be they excited or permanent magnet types.
The output generally increases with RPM, to a point.

So, the first thing with any alternator is to determine its output power curve relative to RPM.  If it has a maximum RPM rating (the point above which centrifugal forces tear it apart), you have to make sure the driven ratios won't ever exceed that RPM.  Then you have to find out at what speed the alternator no longer makes enough power to drive the host system loads.
Don't forget, the SOHC4 spins much higher, has a much larger RPM range than most diesel engines.

None of the specs posted so far are complete enough to make a selection, w.r.t. output power vs RPM.

Next is needed the power requirements for the bike.  This is simply a tally of all the system loads.  If you are going to the trouble of changing the alternator, I assume their other electrical changes being made to the bike, no?  You need to chose an alternator that will exceed the expected loads, in at least one regime of bike operation.

Is the plan to drive the alternator with a belt?  Just curious.

I note a two wire alternator output is either one phase, or rectified DC output.

Some PM regulators only control one phase of the output.  Lights off and two phases are enough to power the bike and provide a slight charge for the battery.  The third phase is either shunted or switched on and off to provide extra power for recharging and, lighting loads.
But, there are many schemes for alternator output regulation.  Best to examine the circuit where the desired alternator came from, in order to determine suitability for a transplant.

Sorry, I can't help more without needed specifications.

Cheers,

[Spanner 1]

NO.

[bryanj]

High current Zener Diode is what Triumph and Norton used to regulate the permanent magnet alternators

[Ricky_Racer]

Thanks, TT... Okay, so...

1) Research/determine candidate Alternator RPM capabilities and output curve. Determine ratio.

2) Determine power requirements of bike: fully stock electrical system + small electric fuel pump.

3) Find a capable EE/motorcyclist in SoCal who can participate in the electrical portion of this project, 'cause I clearly am out of my depth!

Question: TT, if you were trying to find a solution, what type of alternator/regulator/rectifier would you choose? And thanks for your expertise!

BTW TT, the plan is to v-belt drive the alternator and, in all probability, the blower as well. Gilmer will be a pricey (but sexy) second choice, and cost containment is paramount.     RR

[TwoTired]

2) Determine power requirements of bike: fully stock electrical system + small electric fuel pump.

What does the fuel pump draw?

Question: TT, if you were trying to find a solution, what type of alternator/regulator/rectifier would you choose? And thanks for your expertise!

I think I'd try to adapt the Cb700SC or a CBX Alternator and Vreg.  It is located behind the cylinders.  I don't know what the drive ratio is between crank and alternator.  But, if you spin the donor engine crank and count the turns on the alternator shaft, you could learn the ratio.  The 700Sc will spin the crank over 10K RPM.  So, the alternator will survive if you use a similar ratio on the Cb750.

You would still have to fabricate a mount, and change the alternator drive type to your specs.

Cheers,

[Ricky_Racer]

Thanks, TT. The small fuel pump will draw 3-5 amps, and will only be necessary if the Mikuni HSR needs more than gravity feed.

I'll check into the Cb700SC and CBX alternators to see how best to adapt them. I appreciate your help; I'll keep you apprised of my progress. RR

[bryanj]

Mead and Tomkinson on their 24 hour endurance racer, "Nessie", used a bog standard Citroen car(2CV i think) alternator, belt driven from the end of the Kawasaki 900 crank.

As the car alternator had an internal reg and rectifier all you needed was the main lead from alternator to battery, plus a wire via a warning light to alt if you wanted it to start charging at low revs, without that it will only start charging after it "self exites" to over 13 volts which takes some revs.

I know this cos i worked for them way back when

[kpier883]

I think I'd try to adapt the Cb700SC or a CBX Alternator and Vreg.  It is located behind the cylinders.  I don't know what the drive ratio is between crank and alternator.  But, if you spin the donor engine crank and count the turns on the alternator shaft, you could learn the ratio.  The 700Sc will spin the crank over 10K RPM.  So, the alternator will survive if you use a similar ratio on the Cb750.

You would still have to fabricate a mount, and change the alternator drive type to your specs.

Cheers,

Currently the hot ticket over on CBXWORLD.com seems to be using a Kawasaki alternator and a conversion kit to replace the sometimes unreliable CBX unit.  The following is excerpted from the following thread:
http://www.cbxworld.com/modules.php?name=Forums&file=viewtopic&t=10744
(I don't recall whether one is able to read posts on cbxworld as a guest or if signup is required.)

or the technically savvy CBX owner that has the ability to obtain a Denso Alternator commonly found on Kawasaki's, ...
You need an alternator from a ZX-750 Ninja or ZX-1100 (as examples). Their part numbers are 21001-1115 and 21001-1104 or 21001-1134 respectively.

[754]

RR I took an alt off a Nighthawk, think it the same as CBX.. was going to belt drive it.. but have not started on that. My pipes are in the way unless I go forward. I asked a member to check rotation gearing and it was around 1:1, but looking at it I suspect, it may run fasyer.

 Belts, try multi rib, easy to make the pulleys once you have ground the tool,, pitch is a strange number.  These belts run an Eatin blower at 2.5x over on a Tbird.

 Gilmer, I think the pulleys are actually reasonable , and belts are cheap are they not?

 Part of the reasin I wanted to run a beltdrive alt was,  to be able to disconnect it in about a minute for racing..& quoickly reconnect.

[Ricky_Racer]

Thanks for the info, Kpier. I took a look at the Mitsubishi A7T20199 used by the Kawasaki as well as the CBX and GL1500 alternators. Looks like any could be adapted to a pulley drive, but they appear to be 50% heavier than the inexpensive 40W Geo/Denso that already has a v-belt pulley. I will, though, try to find some of the bike alternators so I can compare their width to see if they're thinner than the Denso. I want the most clearance that I can get without breaking the bank.

Frank, my blower engineer has suggested a multi-rib serpentine belt, but we're not quite to that point yet.

Have you got any referrrals for a Gilmer pulley maker? Thanks. RR

[754]

I think they are off the shelf parts. I think they are just called timimg belt pulleys, and places like Browning or other sprocket/coupler type manfacturers offer them. Of couse you will want aluminum.

 I recall making a windshield wiper drive, using tooth belts. And building a drive for a logging machine that used 4 inch wide and pulleys were just ordered in

[Ricky_Racer]

Thanks, Frank. I'll check it out. Have a good one, and stay warm!  RR

[Bodi]

Pulleys and belts are readily available. These guys http://www.sdp-si.com/ have a lot of stuff, even if you don't buy from them the catalog is pretty useful in selecting parts.
You don't need a huge belt: 40 amps at 14v is 560W, less than one horsepower. Use a rounded tooth belt and pulleys, the square tooth ones howl and seem to wear out belts faster although the horsepower rating for a given width/pitch is slightly lower.
If you're driving a blower you will be handling more horsepower, so try and calculate it and get a belt to handle the load. I have heard that top fuel dragster blowers take upwards of 500hp to run, but increase engine power by about 800hp so they're worth it for the net 300hp gain.

[Skunk Stripe]

It might not work in rr's situation but I thought cyclex made a perm mag setup?

[Ricky_Racer]

Interesting stuff, Bodi. Thanks!

Skunk, I can't use anything driven off the stator side of the motor; that's where the blower drive pulley will go. RR

[Skunk Stripe]

Well thats what you get for putting all that stuff on your engine!