What exactly is the battery for?

geezerbiker · Full Member Joined: Sep 15, 2007 Posts: 49

This is a question I’ve posed in other forums, and after considerable debating by some very knowledgeable people, I’ve come to the conclusion that there really is no answer, but here goes anyway. What exactly is the function of the battery, after it has been used to start the bike? This turns out to be a much more complicated issue than I would have thought. It seems there is no one answer that applies to all bikes.
When you first start the bike, power is of course, being drawn away from the battery to operate the starter motor and provide power to the ignition system. But, at some point, the battery must be receiving power from the alternator so that it recharges. Now, looking at the schematic, it seems obvious that this is an either/or situation, as there is only one hot wire leaving the battery. It can’t be delivering power to the ignition system and receiving power at the same time, at least not on these bikes. I rewired a Kawasaki that did have two hot wires leaving the battery, so I could see how that would be possible in that case. Since there is only one hot wire, I must assume that at some point, when the engine reaches a certain rpm, the flow of current in that hot wire reverses so that the battery is charging. That being the case, the battery couldn’t be supplying power to the ignition system to make the bike run. Yet, the Hayn’es manual clearly states that ignition is dependent on the battery being in good shape, as the battery is supplying power to the ignition system. Do they mean only during start up, or all the time? If all power from the alternator had to pass through the battery before going to the ignition system, that battery would never receive a charge, as there is only one wire. I find this very confusing.

tacoswild

I'm no bike expert but I do work in electronics, so I think I can give you a general answer. In a basic power supply like this you have current pulses coming from the rectifier either once or twice per revolution of the engine (or generator at the power station for regular gadgets). These pulses look like short, steep spikes on a scope. They're no good for running anything so they're sent to a big pool, in this case a battery. You can picture it like a big pond that has a constant leak, but a bucket brigade occasionally dumps water in to keep the average level from dropping. When a charging pulse is coming from the rectifier everything can draw power from that, but most of the time that's not happening and the battery holds the voltage up during that time. So the short answer is yes, current pulses do flow both directions in the battery lead. Hope that helps.

geezerbiker · Full Member Joined: Sep 15, 2007 Posts: 49

So then does the direction of the flow in the battery lead change with every cycle of the alternator?

jayel

science we do not understand is magic

tacoswild

I don't have the schematic in front of me and it's possible they use a big capacitor as the pool rather than the battery, so I'll say "probably". I'll look at the schematic later to be sure.

xsleo

on these 650's you need the battery to get the alternator to charge. the alternator does not have a permanet magnet in it like a generator or some alternators have. the magnet in these alternators use the electricity from the battery to magnatize the rotor so there is a magnetic field. as the rotor spins there is a current created in the stator. then through the rectifier to the battery. the rate of charge is controled by the amount of power sent to the rotor. the regulator is set up so that when the engine is not running a full shot of electricity from the battery. once the engine starts the regulator controls the amount of electricity to the rotor to control the strength of the magnetic field. strong field more charge, less strength less charge.

tacoswild

Everything xsleo said is right on. I had a look at the diagram and it's a three phase alternator which means there are three times more pulses than the single phase type I described before (single phase is what we get from most wall sockets in north america, three phase is more efficient). So instead of the rectifier putting out 1 or 2 pulses per second you can get 3 or 6, and with the rectifier they used it's 6. So 6 times per revolution you should get a shot of current topping up the battery and the rest of the time current flowing out.

It might seem weird to think of the current doing all this changing (maybe 300 times a second at decent rpm) but other than something like a flash light most electronics aren't doing anything unless currents are changing. The current in a regular speaker flips direction more than 10,000 times a second for example.

geezerbiker · Full Member Joined: Sep 15, 2007 Posts: 49

jayel wrote:

science we do not understand is magic

or religion.

geezerbiker · Full Member Joined: Sep 15, 2007 Posts: 49

tacoswild wrote:

Everything xsleo said is right on. I had a look at the diagram and it's a three phase alternator which means there are three times more pulses than the single phase type I described before (single phase is what we get from most wall sockets in north america, three phase is more efficient). So instead of the rectifier putting out 1 or 2 pulses per second you can get 3 or 6, and with the rectifier they used it's 6. So 6 times per revolution you should get a shot of current topping up the battery and the rest of the time current flowing out.

It might seem weird to think of the current doing all this changing (maybe 300 times a second at decent rpm) but other than something like a flash light most electronics aren't doing anything unless currents are changing. The current in a regular speaker flips direction more than 10,000 times a second for example.

It's my understanding that the rectifier converts AC, which is what the alternator is producing, to DC which is what the battery needs to be charged with. So is it going from the alternator, through the rectifier to be converted, then to the regulator, then on to the battery? What about a magneto type system, like on a lawnmower, that has no battery? There must be a permanent magnet to produce electricity when you pull the starter cord. I think there have been bikes made with magneto systems, though I can't name any offhand.

pumps

There must be a permanent magnet to produce electricity when you pull the starter cord.

On a small engine such as a mower..a Briggs and Stratton for instance, has a permanent magnet in the flywheel. As the magnet passes the magneto it create the juice to fire the plug by electromagnetic induction. It has to be gapped just so for max effect.

xsleo

guite a few two stroke motorcycles used a magneto ignition. off road bikes that didn't use lights didn't have batteries. the mag just ran ignition. some dual use bikes had a lighting coil to run lights, but the lights would dim at low rpm's, be bright at high rpm's. sometimes blowing bulbs. a battery and charging system was added to keep the lights at a steady output. some states reguire your lights to stay lit for a reguired time without the engine running. some people have adapted the system off of the rd series of yamaha's to the 650's so they don't need a battery, mostly for racing, less wieght-faster bike. others do it to simplify the electric's, do away with starter, turn signals, to have a cleaner chopper/bobber.

tacoswild

Quote::

It's my understanding that the rectifier converts AC, which is what the alternator is producing, to DC which is what the battery needs to be charged with. So is it going from the alternator, through the rectifier to be converted, then to the regulator, then on to the battery?

That's pretty much the idea, there are a few refinements you could make to that picture, like the role of the regulator. If everything went through the regulator before the battery that would be a common type called a series pass regulator, but this one works a little differently. The battery is connected directly to the output of the rectifier. So is the regulator but the only thing the regulator passes is the current going through the brushes to the electromagnet in the rotor. You could say the regulator keeps an eye on the voltage coming off the alternator and adjusts the strength of the rotor to make that voltage stay in the right range.

A rectifier can't convert AC to a stable DC voltage by itself, it produces a pulsing positive voltage that's only DC in the sense that the pulses are all in the same direction. It always needs something like a capacitor or battery after to build up a stable voltage.

geezerbiker · Full Member Joined: Sep 15, 2007 Posts: 49

xsleo wrote:

others do it to simplify the electric's, do away with starter, turn signals, to have a cleaner chopper/bobber.

I've decided to keep the starter, since it's already there and working. But, I do want to simplify the electrical system somewhat. All of these relays and safety switches to prevent you from doing something unless you've done something else first, I could do without. I know they are meant to serve a purpose, but I don't care and just want to get the bike up and running with as few complications as possible. The last bike I did, I didn't bother with the engine kill switch, and no one seemed to care. I'm wondering if it's possible to just get around relays and switches that I don't want. Can I just bunch all the leads together, so the bike will run as though the switch is already closed? What I want to do right now is just get power to all the places it needs to be to get the bike to run. I'll worry about the lights, horn, and other things later.

tacoswild

I have a 71 that never had a starter or safety relays. I'll attach the wiring diagram for it in case it helps.

geezerbiker · Full Member Joined: Sep 15, 2007 Posts: 49

tacoswild wrote:

I have a 71 that never had a starter or safety relays. I'll attach the wiring diagram for it in case it helps.

any thanks. It might be helpful to be able to see how the wiring was done before they added all that stuff that I don't really want.

xsleo

depending on the year of your bike, the safey relay is there to keep the starter from engaging with the kill switch off and to keep it from engaging when the engine is running, not good for the starter gears. later models added a switch to the side stand so you can't start the bike with the stand down. i'm not sure but they my have linked the neutral light switch in so itwon't start in gear either. i'm not sure about the newer models, i have had two 75's.

pumps

xsleo wrote:

depending on the year of your bike, the safey relay is there to keep the starter from engaging with the kill switch off and to keep it from engaging when the engine is running, not good for the starter gears. later models added a switch to the side stand so you can't start the bike with the stand down. i'm not sure but they my have linked the neutral light switch in so it won't start in gear

I think what you mean is the side stand switch won't let you put it in gear. You can start it, idle in neutral etc. But when you try to engage first gear , it just dies UNTIL the bike knows the side stand is up.

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

OK - after the start - the battery acts like a big capacitor supply and even voltage of higher amperage than the alternator and voltage regulator alone can produce through the entire RPM range.

It supplies voltage to "activate" the coils in the alternator to start charging - and voltage to the TCI box for spark at lowr rpms.

geezerbiker · Full Member Joined: Sep 15, 2007 Posts: 49

What I'm getting from all of this is that the battery is indeed receiving and sending voltage at the same time, well not exactly at the same time, but in a pattern of constantly reversing flow, with hopefully more flowing in than out if the battery is to hold a charge. As the alternator cycles, it is receiving voltage from the battery to activate the magnetic fields to produce more voltage which then goes back to the battery.
Another question I'll ask here. What is the purpose of the pick-up coil and where is it located?

duluthmuffler

On a visit to my local motorcycle junkyard. I learned that a Suzuki TM250 or TM400 magneto setup fits perfectly on the taper of the XS shaft. I guess the TM250/400 part is sometimes easier to get than the DT or MX part....

royfisk

batteries hold electricity and with such a low output chargeing system the battery helps keep voltage constant . In other words your headlights dont go dim at street lights, or engine die because the chargeing system cannot keep up. Think I am kidding you just add one high beam ligt to your useual lights and let me know how long before your battery is dead at an idle. The chargeing system is not that big. This is why some people report chargeing problams and bad batteries. If you only ride your bike 2 miles down the road and shut it off and 2 miles back everyday your battery is going to go dead, because the chargeing system cannot keep up. Same bike ride 7 miles down the road every day and back say after work, never has a problam. This chargeing system is very marginal at best.

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