Actual alternator output

[suzukizone]

Does anyone have rock solid wattage/amp output figure on the 81 GS850G? I cannot find this number. My old GT750 was listed as 260 or 280 in many sources. I am going to pop in an Electrex stator & R/R and want to know what the actual gain will be.

Thanks.

DH

[Keith Winter]

Hi,
The formula for calculating output is really simple math, it goes like this:
Wattage = volts x amperage draw
eg) 260 watt AC stator> maybe 9 amp draw with all lights on and bike running at rpm for maximum AC output =
260 / 9 = 28.8 volts AC
Depending on the condition of your magnet and stator, this will be what AC you have BEFORE the regulator with a 9 amp draw on a 260 watt stator. In reality, it's never that easy, but it's close enough for all we need to know on our bike's. It's called Ohms law and you can use it for all sorts of stuff electricaly. Just remember;
Volts x amps = watt's
Volts / amps = resistance
Volts / resistance = amps
You can rearrange the formula's to figure out almost anything. On the bike you just have to remember that as you draw more current, the AC voltage from the stator will drop;
Eg) 260 watt / 14 volts = 18.5 amps. The math would indicate that at 14 volts, a 260 watt stator would give you 18.5 amps! If you could keep the output AT the 260 watt maximum, and not including heat and resistive losses, it may just do that too! We can not keep the stator at maximum output however because we have a fixed magnet system and the output is directly proportional to how fast it spins. The Ohms law formula's do give you a very good idea at what you can expect out of your charging system, AND it makes trouble shooting easy to!
Keith

[suzukizone]

Actual alternator output

Wow Keith. With my math skills it will take me a week to figure that out :-) I gather from your reply that this is not a static number but varies with rpm & a number of factors. I guess I thought that when I see a car or bike rated at X watts that this was fixed but perhaps it is a potential under the best conditions?????? I thought perhaps it was a fixed number or one could put some sort of guage on the bike & take a reading like compression or voltage.
Thanks for your reply I will go over those facts until I get it.

DH

[Keith Winter]

Hey DH,
You have got the idea in one response, top marks go to you!! It would be really easy, charging system wise, if it WAS a static number,, saddly for us it is not. Our stator output does vary with how fast (engine rpm) the magnet spins and I would guess that you would get the full 260 watts at the 5000 rpm. That is why the "book" has a voltage reading for that rpm. As we know, we can't ever keep the rpm that high, so you will never get 260 watts all the time.
We need voltage to get current flow, and as you draw more current from a fixed voltage, the voltage will drop. If you hook up a volt meter to your battery, with only the small current through the meter, it should read something like 12.7 volts, right? Now turn on the headlight, the voltage will drop because of the current draw from the headlight, crank the bike over with the starter, the voltage will drop even more because of the current drawn by the starter. This is with the bike turned off. If the bike is running and we have a good charging system, the positive potential from the rectifier, should be higher than the battery (12.7 volts) and that means we can get the required current from the charging system and NOT the battery.
Any EXTRA from the charging system is used to charge the battery. Extra what you ask? Voltage. If the stator AC is high enough, to supply us with enough DC voltage after the rectifier, to give us the required current for the bike to run with the lights on, ect, ect, the voltage ( even with the drop from all the current drawn) should still be higher than the battery 12.7 voltage.
AND, if you are now thinking that, with a higher positive voltage from the charging system at the battery, than the battery would have WITHOUT the charging system,,, would this not result in current flowing BACKWARDS through the battery??? If you are thinking this way, please GO TO THE HEAD OF THE CLASS, because that's exactly how a battery get's recharged.
The electro-chemical process that goes on, is to complicated to explain in this post, but that's how it work's. That's why, in reality, you really don't need 15 or even 14 volts to charge the battery. As long as the voltage from the charging system is more than "static" battery voltage, the battery will charge. Why do the book's say 14 - 15 volts? The reason is simple. If you read the "NOTE", that all books have it state's that the battery has to be good, fully charged, has WATER in it, ect, ect, before testing the charging system. All battery's have resistance, resistance is to current flow. As the battery is drained, the resistance goes down. Put a good (but drained battery) on a charger with a built in AMP gauge. Also hook up a volt meter. Turn on the charger and watch what happen's. The voltage will be low, but the current will be high. As the battery comes up in charge, the current will go down and the voltage will come up. The resistance to current flow is increasing causing the voltage to rise, YES the opposite to voltage DROP from current draw. THAT is why testing your charging system with a crap battery is not a good way to get accurate reading's.
And that is why the books say 14-15 volts, WITH A GOOD BATTERY. If you have a crap battery in the bike, it may not charge up, the resistance may stay low causing a current draw the whole time, this would result in a low voltage reading all the time, OR, it may have a high resistance all the time and this would give you a high voltage reading.
If any of this has made any sense to you, you are well on your way to being able to fix ANYTHING on your charging system with out any trouble! If you have a twisted craving to know the exact chemical process I spoke of, E-mail me anytime and I will dig it up out of my book's and send it to you.
Keith