Topic: What ignition when driving without battery ?

[Hummel]

Hello.

I have a cb750 74' and I have stripped it for all stuff I find unnecessary. That includes battery. I have bought a condensator from kedo, but it seems like my electronic ignition needs more power than I can make with the kick starter.

My alternator is from xcycle and should make more power than the original.

My ignition is from Boyer bransden.

So my question is: is there an electronic ignition out there that don't need a lot more power than the original or is the only solution to either get a battery mounted (small one) or go back to the points, by the way how many RPM is the points good for ??

Thanks

Tommy Hummel

[TwoTired]

I couldn't find info for xcycle alternators.  Either give a pointer to specs or state what they are.

But, the SOHC4 doesn't usually have a permanent magnet to generate it's magnetic field.  Instead it has an electromagnet.  To get the magnetic field, it must be electrically excited, as in with a battery.  Once this field is established, the alternator will make more power than it consumes and thus sustain the magnetic field if the RPM is maintained to make more power than the entire bike consumes (lighting, ignition, field coil, etc.).

A capacitor will not hold up to draining power loads long enough to keep the ignition system coils operating during start.   Either switch your alternator to a permanent magnet type, or put a battery on the bike to initialize the charging system.

I don't know what Boyer unit with coils consumes.  I do know that the Dyna-s will almost double the ignition power draw over points.

Points are good for at least 9000 RPM and about 11000 if you double spring them.


You might wish to review what you find unnecessary.

[Bodi]

If you are using the Cycle-X permanent magnetic alternator system, it should be possible to go no-battery. Their web page says "Single phase system allows battery or battery less operation. ( call for details )". I recommend calling them for details if this is what you have.
Electronic ignitions systems vary widely in electrical load.
A magneto is perhaps the best approach to no-battery ignition. None are currently made for the SOHC750 though.

[Hummel]

http://www.cyclexchange.net/Elec%20System%20Comp%20Page.htm

Here is a link to the alternator, I believe it's a magnet kind of alternator, but I also think the Boyer ignition needs a lot of power to give a spark.

Dyna ignition would be nice with rev limiter and all, but if that also needs a lot of power to spark then I have the same problem.

Would hate to buy a expensive light battery just to start the bike, seems like a lot of waste.

I will try to contact Xcycle about his ignition maybe that will work with his alternator, a least it should.


Thanks again for the response.

Tommy

[Hummel]

So xcycle means that my ignition needs to much current and he says that it will help with a bigger capacitor? What do you guys think ? And does anyone know what capacitor I maybe could use ? Is it possible to mount two on the bike and Connect them parallel for more capacity maybe ?

[Bodi]

Please contact cycle exchange and ask them. We don't know the answer. This is a permanent magnet single phase alternator, they make some big claims about output amps - but with a single phase system that allows for a bit of shady marketing hype. The peak current may be quite high but the average current - what produces average actual charging amps - would be a lot less - this is more true with a single phase type than with a 3-phase type, rectified single phase goes from zero to peak amps every cycle. A rectified three phase output never drops to zero amps.
CONTACT CYCLE EXCHANGE! They specifically say to contact them if you want to go batteryless using this alternator!

Possibly more capacitance would help but probably not. If you had extra alternator output power (more than the ignition system is drawing) at kicking speed, the cap you have would charge up. You can't make up for a lack of power with extra storage capacity, and more storage would mean more time required to charge it up to working voltage IF you have a bit of excess to use... a smaller cap might be what you need.

[tomkimberly]

A sealed battery comes in many sizes and can be mounted anywhere, even unside down. IMHO, this would be your best option.


Tom

[Hummel]

As I wrote earlier I've already talked to xcycle. And they said a bigger capacitor would solve the problem. I then asked you guess about a bigger capacitor, I shouldn't.

I probably end up with a small battery

[TwoTired]

One of the problems I have with CycleX is that they have woefully incomplete specifications for nearly all of their product offerings.
In the case of their alternators, they only give a maximum specification.  Whereas ALL alternators have inherent spec behavior regarding power output over a range of RPMs.

Could be they have these specs, but don't publish them.  But, I suspect they simply don't know the full capability of the units they sell.  They only know what "works" when using the full compliment of products they sell.

We can't tell you if a bigger capacitor will help, because we do not have the power output curve of the cycleX alternator(s).

We only know that it will put out zero Amps at Zero RPM and 16 amps at some unspecified RPM.  Who knows what the alternator will put out at kick start RPM?  Such limited published data is woefully inadequate to make any sort of predictive circuit design modification different from the exact configuration of components cycleX offers.

Once you start buying their components, you are a junkie addicted to whatever they tell you to buy from them, and can only hope they got the engineering correct enough to meet your needs.

The SOHC4 was designed to operate with a battery.  If you want to change that design successfully or reliably, you need to be as smart and knowledgeable as the Honda engineers, or be totally reliant on promises from a third party with unknown credentials, besides a price in a catalog.

[AJK]

If your dead set about doing away with the battery, you may be able to assemble a few 'ultra capacitors' from ebay. The boyer will need power from the get go. Not having a battery means you will need another power source to get it underway.
  You will need to experiment 'how many' ultra caps would be needed to start up the bike. Probably not that many i'm guessing.

Here is a clip of a guy starting up a small car with them, albeit he has a few, but still smaller & lighter than a lead-acid.
https://www.youtube.com/watch?v=z3x_kYq3mHM


I can't say this setup is for me, but if your keen to go down this route, it might be worth taking a look. In time, with a bit of experiementation, these might turn out alright in practice.

[TwoTired]

It takes 30 watts per second  to charge up a standard 5Ω SOHC4 ignition coil.  You have two of these.  Or...
It takes 48 watts per second  to charge up a standard 3Ω SOHC4 ignition coil.  You have two of these.

Points will turn on one coil at a time and alternate between the two during one revolution of the crankshaft.

The Dyna-s (and possibly the Boyer) turns on both coils at the same time, only turning them off during an actual brief spark event.

How many seconds will you have the key switch on during start operation?

If you rely on capacitors, they must supply all the power of ignition components AND all other bike loads until the alternator reaches a speed that provides that power, and recharges the capacitor.

This turns out to be a math problem which cannot be solved until the power drains, the capacitance (or stored power), and the power generation numbers or available.

Otherwise, you can try random assemblage of parts until you observe behavior that suits you.