Following the link in the faq to the battery elimination page i found the bat pac.
On the website it advertises that it works with older honda cb 500, bikes.
Is this true? And if this thing is no option how should i go about making my bike battery free?
That website is either lying to boost sales or doesn't know the bike they list doesn't have a magnet in the alternator. Further, I don't understand why the SOHC4 website has a pointer to that battery eliminator site. The Bat-Pac is only practical with bikes that have a permanent magnet in the alternator/generator.
The SOHC4 alternators work by using magnetism created by an electromagnet (the field coil) that only behaves as a magnet when it is provided electricity needed to make a magnetic field.
Our field coils draw about 1.7 amps whenever the alternator is powered by enabling the key switch. (.7 amps if an installed battery is above 14.5V... not likely without the engine turning).
Each ignition coil draws 2.4 amps (5 ohm primaries) whenever its associated point contact is closed. There are two of them. Also, note that spark voltage diminishes with input voltage loss. When supply voltage falls below about 9 V, spark gap arcs are ify, at best. So, if you can eliminate any additional lighting loads, whenever you turn on the ignition, 4.1 amps at no lower than 9V are needed before the engine or alternator rotor is even turning. If not a battery, where will this current flow come from and how long?
Not the alternator.
It should be obvious that even a powered alternator will make no power output unless it is spinning. I've not seen or measured a power output vs, RPM chart. However, I do note that with lighting circuits enabled, the bike is unable to overcome the system loads and charge the battery, which is draining, at idle speeds of 1000 RPM.
As I understand it, the Bat Pac is simply a capacitor bank. To my knowledge, a perfect capacitor has yet to created. They all have series resistance and leakage resistance due to the materials they are created from and their physical properties. What this means is that they will NOT hold a charge indefinately. Nor will they give up their stored charge without some loss. This later property is probably not important for this application, though. But, the leakage is. More on this later.
Also, since our alternators can only make power when supplied some power. The Bat-Pac will have to be precharged to have any hope of starting the bike. And, there will be a very limited amount of time that the capacitor will have enough charge to start the bike. It's going to be a race between ignition on and kick start. And, if the bike has been sitting awhile, forget it, without some external power source.
So, when you kick start the bike, you're going to have to kick it to about 1500 RPM in order to keep the Bat-Pac charged up to a level that will continue to fire the ignition coils and spark plugs.
Capacitor size.
Let's say we start with a fully charged capacitor at an optomistic14 V. We can use it until it drains to 9V, or about 36% of its total capacity. This is about one half of a standard capacitor charge or discharge rate. So, we must double the result of the standard 63% formula of T / R = C, where T is time in seconds. R is the Resitance of the circuit in ohms and C is the Capacitance in farads.
If we assume 5 seconds between key on to kick start Then a 0.834 FARAD (834,000 microfarads) capacitor is needed that is also able to withstand, say 20 V without breakdown.
A not very thorough search, finds that Digikey has some Panasonic Electrolyic caps in 100,000 microfarads. They are $13.36 each and eight of them ought to do it. They are also 40 D x 80 L in size (mm). These can be wired together in a block about 3x3x6.5 inches.
It's up to you whether this is more attractive on your bike than a battery. However, I couldn't find a leakage spec. So, I can't calculate how long they will stay charged after you turn off the running bike.
On bikes with permanent magnet type alternators or generators, each time you kick the bike the capacitor gets recharged. As long as the power generated from the kick is greater than the draw for the ignition, the bike will start and run. On such bikes, the capacitor requirement is far less than calculated above. Probably one or two caps is all you'd need. Or, a few more smaller, cheaper ones.
So, can we get rid of the battery eliminator reference in the SOHC4 FAQ? Or, should we put this post in the FAQ right next to it?
