Topic: Max and idle amperage of 77-78 750F2 charging system

[Beemer]

Ok, I searched, and searched, and all I found was a reference to a honda SL 175 that could charge at around 2.5 amps and only had 50 watts to spare if the headlight was on.  Nothing about the 750 other than a possible power deficit when using dyna ignitions, coils and 1157 bulbs.

I want to convert over to the dyna OR the transistorized ignition sold by hondaman, but I also want to run a 100 watt H4 headlight as well.

I live in deer country..big ass Iowa corn fed 350 pound deer..and they CHARGE bikes for fun..so I want to see them LONG before I hit them, like long enough to shoot it, or get away from it.

However, I don't want to be in power deficit mode either.  I can convert to LED lights to replace the 1034's that I have now (I replaced all the 1157 bulbs earlier back to the stock type). 

I can't find the amperage in my clymers OR my haynes manuals either, and google just farts..

Need it at idle and at above 4000 rpm, and if anyone knows the full load of a stock bike with headlight, taillight and turn signals and brake light on, that would be great!

thanks
dave

[Tower]

I believe, regardless of how much voltage the field coils can produce, the fuses limit how much current you can draw.  Putting in larger fuses may provide other nasty surprises, which would indicate to me, you have a predefined practical limit by looking at the fuse.

And, because 14.5v x fuse amps = max available watts, you'll be able to calculate bulb wattage.

Also, since this is not a magneto, the max voltage is achieved at just off idle, at around 1500 rpm, and regulated to about max 14.5v.  Thanks to the battery, you get a steady supply - don't know how long the bike could sustain max current draw though, as it might not be able to continually feed that many amps back into the system?

Edit: to calculate current from a generator this might help (its a combo of Mike's and Hans' formulas)

Current = Inductance  x sum of voltage / given time interval

[bryanj]

Sorry Tower you are way wrong, these generators are lucky to charge below 3,000rpm and current depends on both regulator setting AND engine speed.

Whist i havent got the time to go through the manual I have i do know that there is no way to run a 100watt headlamp, even the "standard" 60/55 H4 is considered marginal unless you keep the revs at over 5-6 000

[Tower]

Bryan, I guess you mean I could be wrong about the stator coil output curve over time.  Indeed, I may have exaggerated a bit (but not much  ). 

The generator is rated 13A @ 12v = 0.16 Kw (max 0.21Kw @5k rpm)
Rectified at 15A (I'd say there is a safety margin here) and that the nominal current is probably less than 15A.

From the old Honda CB750 manual:

RPM                          1k      2k      3k     4k-8k
Rectified voltage       12v  12.4v 13.2v   14.5v
No-load current (A)   2.5      1        1         1
w/load current (A)    6.5      0        2.4   1.3 - 0.6
...what this means is you get peak output at about 2k rpm and you get spiked at the lower rpm (at least according to the manual).

I would still use the fuses as a guideline i.e. 8A@12v = 100watt headlight.

[eurban]

Your goal shouldn't be to install a 100 watt headlight; it isn't realistic.    It should be to dramatically improve headlight performance.  How can this be acheived?  Using a relay system will dramatically reduce the voltage drop to the headlight from the stock wiring, connectors and switches.  It would also allow you to use whatever size fuse/wire necessary for the headlight you choose.  Using a good quality H4 reflector and the 65/55 bulb with a relayed power source will give you loads more light than the stock sealed beam / wiring configuration.  If your charging system is healthy, you should be OK with this setup. . .A HID lighting setup might also give you the results you want without over taxing the charging system, but a well engineered system will cost a bunch.  Very few are DOT approved and they really require advanced optics on the reflector so as to not blind on coming drivers. This one is DOT approved:  http://www.jwspeaker.com/catalog/forward_lighting/model_8100.htm

[speedy gonzalais]

I would start at the altenator as this is where the powers coming from, A 30 year old altenator aint gonna perform as well as the manual says unless its been well maintained, upgrade it if possible then u will have no probs with high wattage bulbs.

[Tower]

OK, here's my opinion then (for what its worth  ) ....Putting in a headlight that could draw 100watts, would really be pushing not only the generator, but also the entire electrical system to its limits or maybe even slightly beyond its limits. 

You would probably need to use a 9A - 10A headlight fuse
You would probably need to put your battery on a trickle charger on a daily basis

I wouldn't recommend it.

Here's another way of looking at it....
At high idle, say 1500 rpm  the generator is putting out about 158 watts.  If 100watts is going to the bulb, 10watts to wiring harness, then 48 watts is going to the coils (since coils need more than 48 watts, it means the battery is supplying the rest).  Flip on any other electrical device, such as turn signals and corresponding idiot lights at about 25watts, and the battery is now supplying about 60watts
At 3000 rpm (bowing to bryanj) the generator is putting out 188watts. Are those 30 extra watts enough to replenish the battery?  Nope - short at least 5 watts - 30watts (with signals) or more.
At 3500+ rpm? Probably OK, but could still be short a few watts (depending on how efficient the harness and connectors, signals etc.)

Again, not recommended.

[bryanj]

Tower I think you will find that that table has a misprint and it is -6.5 (negative charge) at 1k

[Tower]

yup, hence I mentioned you will be "spiked" at the lower rpms - I should have been more clear.

[bryanj]

To be honest the best upgrade i can think of is an electronic regulator which will mean that the battery charging voltage/current stays relatively stable as against the original mechanical which has only 3 levels
(1) Off

(2) Not enough

(3) fry everything


and it just varies between the 3 depending on battery voltage

[jonbuoy]

Brian is spot on, there is a single 3 pin alternator excitation control  chip I have been wanting to try it will fit directly in place of the relay.  I'm away from my bike at the moment so I haven't had chance to try it, chips are obsolete now but you can still get them from surpluss suppliers:

L9448VB

[Tower]

Yes electronics would stabilize the output, which is good.  Unfortunately it wouldn't increase the output - not the regulators job anyway.

I find the mechanical regulators to be hugely robust.  They can go out of calibration easily, but also be put back easily, whereas electronic versions may be more reliable and steady, but I fear they may be more prone to fatigue and ultimate failure. - so I'm undecided on this issue.

I believe the real problem is that current is absent when its needed the most - at idle and near idle.  Since increasing the generator's output would be hard to do, that leaves trying to reduce the draw, as the most beneficial upgrade.  Unfortunately scrounging a few watts here and there is about the best that can be done.  Wiring harness and connectors 5watts, electronic regulator 1watt, LED lights tail lights and turn signals would be big - maybe 20 watts. However, the deficit would still be rather large (maybe 3-4 amps at idle with all the improvements instead of the 6.5 normally drawn)  Might be good enough, or maybe not.

So back to improving the generator - Maybe boost the field coil charge at idle (jonbuoy's suggestion)?  Sorry, now I'm just rambling.

[Tower]

had a look at the specs for the L9448VB one-chip regulator.  @jonbuoy, don't forget to ground the input through a 0.5 µF (or larger) capacitor.  Also consider the current spike at start-up, so maybe have two in parallel instead of just one?

Edit: Another thought...the chip being the size of a man's thumbnail, that could be a lot of heat to dissipate from such a small device.  Mounting to a grounded heat sink might be advisable also - but probably unnecessary.

[Beemer]

Ok, here's another thought, and I REALLY appreciate all the comments and advice so far!

I've seen K models with fairings, lights, radio, CB, trunk lights, side lights on the hard bags, and heater plug ins for a heated riding suit/gloves and probably a coffee pot stashed somewhere!  So where do these guys get all that power from?

That's what doesn't make any sense!  I have been investigating LED lights as well to free up some wattage too.

However, to get a bright enough bulb to be legal, you're using multiple 7 watt LED's, and from what I've seen, you need a few of them to actually have a brake light that's brighter than the running light..same with the turn signals.  Now I can drop back to the 1034 bulbs from the 1157's, or go with LED's, as I haven't determined what the stock OR 1157 bulbs actually draw, but I'm sure it's more than I think it is. I'm also going thru the bike and installing new ground wires (ten guage at least) and also I'm cleaning all the electrical connections and packing them with dielectric grease to keep them from corroding (all my stuff works, but so far I've found quite a few connections that were sub par.)

So if these K series guys (and I know this for a fact when they were new, as my best friend's dad had a full dress 78 K model while my buddy had his dad's "OLD" 75 super sport) could run all these lights and NOT be carrying a deep cycle battery in the trunk, then I'm wondering what happens here?

I can always replace the alternator wiring running to and from the battery/regulator..that isn't a problem.  Plus, 14 guage wire can handle 15 amps..but that's about all.  I'm honestly tempted to find a way to run a very small automotive alternator off the drive chain, and have it sitting on the front center section of the swingarm or somewhere else where it could be driven.  Now here's an idea, use the REAR HUB as an alternator! 

While I can't use a comstar wheel for that, if you had a disc brake rear, and used a hub from a drum brake, I'd be the stator from our bikes could be wrestled in there, but the stator would be turning while the rotor would be stationary.  I'm big into wind power as well, as I'm trying to run my shop off 30 cell phone tower backup batteries (that are $450 apiece when new, but I get them for 25 apiece when they swap them out every four years, and the batteries have a 20 year design life) and a bunch of inverters.  The shop stays pretty electric neutral with that system unless I"m out there a LOT on windless days, but at night the wind picks up and recharges everything again)

Too bad we couldn't design an "add on" small ass alternator that put out something like 30 amps while dumping that huge iron lump hanging off the ends of our crankshafts.  Or, better yet, use the starter as a generator, since DC motors WILL produce power when spun by something else!

Too bad they don't make those magneto kits for our bikes anymore.  I saw one go on ebay this week for 500 bucks or so..and about choked.

With a magneto running the ignition, that would free up some power as well.

Still, I can't see people using a dyna ignition and coils and still being able to keep their battery charged either, but they do.  There HAS to be a way to do this.

Now you CAN increase the power of the existing alternator by reducing the wire size in the stator..more windings=more power, I think anyway.

Maybe using oxygen free copper might help too?  Works for speaker wire anyway!

I'm guessing that newer bikes have a gear driven separate alternator, right?  I mean, they're using fuel injection with a pretty sophisticated ECU for spark and injector timing, a heated oxygen sensor and lots of other electronics and THEY don't just die at a stoplight either.  I know someone had this problem ages ago and found an answer..we just have to find the person who did it.  As heavy as that alternator setup we have is, I can't see it being so damned limited in power output.  I had an old alternator out of my chevy sprint, and it literally was nearly the same size as the components sitting on the end of my crank and surrounding it (rotor/stator) and it would put out 15 amps at idle and 35 amps at 2500-3k rpm.  I wonder if we could run a toothed belt off the rotor (replace it with a sprocket like the one that mitsubishi uses on their balance shaft setup on the 4g63 turbo motors that I race) and have that setup run a regular small alternator or generator sitting where the starter cover is?  Just throwing ideas around here, but it seems that the only solution is to make MORE power somehow, and finding a place to both house the alternator and a way to spin it.  I did sorta invent a mini alternator with "free" power using a fairly small squirrel cage fan with a scoop on the roof of my old travel trailer.  As we were running down the road we had enough wind hitting that duct to spin the alternator quite fast..at the limit the squirrel cage fans would spin.

I know toyota camry's use waste hydraulic pressure from the power steering pump to power the cooling fans mounted on the radiator..I wonder if something like that would work? 

Post your ideas and feel free to shoot mine to pieces..  With enough people brainstorming we might just actually invent something here that people will want to buy!

Dave

[754]

Beemer if it was you that was talking about an 1170cc stroker, can you give us more info.. any pics ..??

[bryanj]

Only way i can seen they cope is cruise all day on the freeway at 3,000rpm + and dont drive in town

[Tower]

The design limits of the generator are pretty clear.  It produces between 155 - 210 watts optimized at around 185 watts at 2000 rpm.  The problem is really only below 2000 rpm, notably at idle (say, 1000 rpm), where only 155 watts are being produced.

So, the discussion has always centred around the two dimensions of the design problem i.e. 1) improve the output curve, and 2) reduce the load.

There is also a third, indirect dimension attached to ease or difficulty of any particular change.  The gamut of ease/difficulty runs from the "low hanging fruit", such as cleaning up connectors to the difficult chores of rewinding armatures, and many in between.

Ultimately, the problem is not difficult to remedy, except when we start to add constraints...i.e.without having to pay exorbitant amounts of money, without altering the basic generator, without replacing parts, etc.

[jonbuoy]

Most modern bikes use a permanent magnet generator, makes decent power at lower engine speeds.  A lot of  cars are only just breaking even at idle with all the electronics they run.  I think cycle X make a permanent magnet kit for the CB750?