Charging System Capacity -- Power for Accessories

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wiseguydave
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Re: Charging System Capacity -- Power for Accessories

Postby wiseguydave » March 22nd, 2008, 6:07 pm

Me thinks you guys have WAY too much time on your hands... :lol:
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Re: Charging System Capacity -- Power for Accessories

Postby Quigg » March 22nd, 2008, 6:37 pm

wavydavy wrote:Me thinks you guys have WAY too much time on your hands... :lol:

hey, they laughed at Frank Hudak too!

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lyd
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Re: Charging System Capacity -- Power for Accessories

Postby lyd » March 22nd, 2008, 6:49 pm

Quigg wrote:Couple things; Think of the gen/regulator first as a 14 V battery with infinite capacity connected in parallel with your battery. What that means is that it can deliver enough current to the system to develop 14 V no matter the load. (Max load is a dead short and that can happen.) You have a constant voltage system.

The battery (generator) sees the bike battery as a load. It has resistance. The electrolyte resistance, the terminal resistance, and the battery terminal voltage appear to the charging system as a simple resistor. The battery voltage subtracts from the applied voltage and the charging current is determined by that difference voltage divided by the total internal resistance of the battery. Example: 14V applied and say 12.5 V battery voltage = 1.5V across , say, 1.5 ohms internal resistance results in 1A charging current. As the battery comes up in charge that difference voltage is reduced and so the charging current is reduced.

Now think of the gen/regulator as a normal 14 V battery with a limit on the amount of current it can supply. When total current demand exceeds that limit the system voltage will drop. If applied voltage drops to 13V, the difference voltage is now .5V and the resulting charging current is about 300 ma. So in effect the battery doesn’t hurt the system that much when the system voltage falls to 13V. If system voltage falls below battery voltage the battery will help the system by discharging. You can determine the amount of discharge current the same way you did the charging current. Round numbers. Available power = 25A @ 14V. = Max load of 2.8 ohms. Call that load 2.0 ohms because we are in trouble, overloaded. Just for shits and giggles I’ll say that drops the gen output voltage to 12 V. The difference is .5V across 2 ohms or 250ma discharge current.

Again think of the gen/regulator as a battery. If that battery has an internal resistance of, say 1 ohm and a terminal voltage of 14 volts open ckt, a current of 10 amps will develop a cemf in the battery of 10 Volts!!! This results in the available system driving voltage dropping to only 4V. I’m pulling these numbers out of my ass but you get the idea. Is a poor analogy, generators don’t work exactly like that but it’s close enough.


I'm think I am following you on this, but from everything I can find out, batteries like we're discussing here have an internal resistance at SoC of only a few to a few tens of milliohms. So, sure, I know I was just fudging with that brazen infinity symbol there, but it ain't all that far away either, as far as we're concerned.

If the generator was truly like a 14 V battery with infinite capacity that could develop 14 V no matter the load, I wouldn't have anything to worry about. But it can't, and as soon as the current ceiling @ SoC voltage (+ the extra needed to overcome CEMF and stuff a full charge in as resistance rises close to SoC) is reached then voltage is gonna start to drop. Then the battery is going to take up some slack by discharging, but the current won't be there to charge it, so both its voltage and resistance will continue to drop. So the voltage continues to drop, the generator is running at 100%, death spiral results.

This is a blood from a stone thing. Maybe we are saying the same thing at this point. I was just trying to illustrate, with that revised table, that it is of little use to do much figuring below 14v, because anything less than 13.5v is either a transient drop following an intermittent heavy load (or intermittent drop in generator output, like idling at an intersection) that discharged the battery, and will shortly it will shortly come back, or a totally unsupportable condition indicating too much steady load, and the system is gonna crash in just the way all this calculating was intended to avoid. And I guess I was further saying that whenever voltage is < 13.5 for any reason, there is effectively no surplus during that time, as all available current not being used by the rest of the load will be going to charge the battery. If there were surplus, then the voltage wouldn't be < 13.5v, it would be 14+v, because that's what the regulator will cause the generator to produce if it can.

Sound right?
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lyd
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Re: Charging System Capacity -- Power for Accessories

Postby lyd » March 22nd, 2008, 6:58 pm

annieh wrote:All that just to figger out how to keep your GeePeeESs working? :roll:

Yer killin' me here, Annie.

Why don't you get mister annie to chime in here? He knows his way around an electron, not to mention an automotive charging system. Or is he too busy drinking beer and laughing at my assumptions? ;-)
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Re: Charging System Capacity -- Power for Accessories

Postby Quigg » March 22nd, 2008, 7:28 pm

lyd wrote:
I'm think I am following you on this, but from everything I can find out, batteries like we're discussing here have an internal resistance at SoC of only a few to a few tens of milliohms. So, sure, I know I was just fudging with that brazen infinity symbol there, but it ain't all that far away either, as far as we're concerned.

If the generator was truly like a 14 V battery with infinite capacity that could develop 14 V no matter the load, I wouldn't have anything to worry about. But it can't, and as soon as the current ceiling @ SoC voltage (+ the extra needed to overcome CEMF and stuff a full charge in as resistance rises close to SoC) is reached then voltage is gonna start to drop. Then the battery is going to take up some slack by discharging, but the current won't be there to charge it, so both its voltage and resistance will continue to drop. So the voltage continues to drop, the generator is running at 100%, death spiral results.

This is a blood from a stone thing. Maybe we are saying the same thing at this point. I was just trying to illustrate, with that revised table, that it is of little use to do much figuring below 14v, because anything less than 13.5v is either a transient drop following an intermittent heavy load (or intermittent drop in generator output, like idling at an intersection) that discharged the battery, and will shortly it will shortly come back, or a totally unsupportable condition indicating too much steady load, and the system is gonna crash in just the way all this calculating was intended to avoid. And I guess I was further saying that whenever voltage is < 13.5 for any reason, there is effectively no surplus during that time, as all available current not being used by the rest of the load will be going to charge the battery. If there were surplus, then the voltage wouldn't be < 13.5v, it would be 14+v, because that's what the regulator will cause the generator to produce if it can.

Sound right?

Yes, once the system is in overload the battery will continue to discharge until it cannot help the gen any longer and the lights go out. When the system voltage falls much below 13V and nothing is done to reduce the load, it is only a matter of how fast the system will fail that is in question.

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Re: Charging System Capacity -- Power for Accessories

Postby annieh » March 22nd, 2008, 7:49 pm

lyd wrote:
annieh wrote:All that just to figger out how to keep your GeePeeESs working? :roll:

Yer killin' me here, Annie.

Why don't you get mister annie to chime in here? He knows his way around an electron, not to mention an automotive charging system. Or is he too busy drinking beer and laughing at my assumptions? ;-)

to be honest with ya - I don't think he has the patience to read all that. But yeah - I think he'd be laughing his ass off at your assumptions. Basically - what he said was too much load kills your system. As in buy batteries for your GPS. :roll:
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Re: Charging System Capacity -- Power for Accessories

Postby whipporfukkinwill » March 22nd, 2008, 7:58 pm

Ok now that I'm done laughing at you you skinny so and so ............

You can and will overload the system on those volusia's - Annie did.

My solution for you is a) get a solar helmet and plug yourself into the bike thereby putting more power into your system to run your doodads

or b) buy stock in energizer.

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lyd
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Re: Charging System Capacity -- Power for Accessories

Postby lyd » March 22nd, 2008, 8:30 pm

Well, there's no question that you can overload it. This has all been an exercise in determining exactly how much capacity there is before that point is reached. I don't think we've entirely determined that yet, although we may be close.

I have enough test gear on the way, in addition to what I already have, that I should be able to check empirically soon. Too bad I can't think of a good reason to get the scope down there as well, just for the spectacle of it all...

lyd
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Re: Charging System Capacity -- Power for Accessories

Postby qjohnson50 » July 5th, 2009, 2:51 am

So, any resolution on how much extra wattage we can add before the charging system gets overloaded?
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Yaatri
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Re: Charging System Capacity -- Power for Accessories

Postby Yaatri » January 20th, 2013, 8:40 pm

lyd wrote:Well, there's no question that you can overload it. This has all been an exercise in determining exactly how much capacity there is before that point is reached. I don't think we've entirely determined that yet, although we may be close.

I have enough test gear on the way, in addition to what I already have, that I should be able to check empirically soon. Too bad I can't think of a good reason to get the scope down there as well, just for the spectacle of it all...

lyd

Sorry to revive "This Old Thread". I have been mulling about this issue myself, which is how I came across this thread. People want to add all kinds of gear, heated jackets, gloves, etc without thinking about whether the bike's alternator can support the gear. Trying to reduce this question to the "need" to run your GPS of the bike is missing the point. Actually, I was looking for a high output alternator.
Thank you very much lyd and Quigg, for an excellent discussion. I too had trouble calculating the real operating load of the bike, especially since important parameters such as inductance of the coil are not given.
I have a couple of comments regarding this.
The missing inductance term actually helps us by increasing the impedance and hence reducing the current.
A minor missing load is the horn. It's intermittent, but might not be a small current, depending the type of horn you have installed.
One should not think of the alternator as a voltage source (a battery) with unlimited supply, but as a current source in a specified voltage range. It's like your mains electric supply system, that delivers power at one or more specified voltages. It might seem unlimited to the end user, except in the summer when the demand is high, but it really is not unlimited. The supply system is capable of delivering xxx amperes of current (energy in MWhrs) No more. I hope this discussion can be revived.


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