Yet another stupid electrical question

[benVFR]

Yesterday I rode for about 2hrs with my jacket cranked up to max heat.

Most of the riding was back roads and twisties at a slow pace due to the "Is that water or ice?" factor. In general I was freezing, the jacket didn't seem to put out enough heat.

Then I get on the highway and blast home and warm up which really seems strange.

When I got home I plugged the bike into the battery tender and it charged the battery for about 20 minutes.

One thing I noticed is the tender tries to keep the battery at something like 13.6 volts, whereas the service manual says the battery should be charged to 12.x volts. Could the bike's charging system be letting it drop back down to 12.x volts?

I had tried using a voltmeter on the plug for the jacket while the bike was idling, it was putting out 12.x volts, I forget exactly how much. (This was earlier in the winter)

Should I try idling the bike with the jacket plugged in and on max heat and then check the voltage at the battery? Any other tests I can do to see if it's charging correctly?

When I got home it still cranked the engine to life instantly, so apparently it's not draining the battery heavily... just curious in case I end up using the jacket a lot when I go on a longer trip for several days or a week.

Last time I asked about this Randy had mentioned the wattage of all his accessories and how his bike was charging correctly. If I recall correctly my jacket draws a heavier wattage than all the stuff he mentioned combined. (77watts according to gerbing)

(Wishing I had taken some EE courses)

Ben

[stoinkythepig]

With the engine running, measure voltage across the battery terminals with no added load (like the jacket). You should get no more than 15 volts and no less than 12 volts. The voltage should increase as the engine speed increases from idle until you reach 15 volts or so. Note the RPM at which this happens. Do the same with the jacket turned up to high. Odds are good the RPM will be higher with the jacket turned on. Ride at that RPM or higher to ensure the best heat from the jacket. Any lower and the charging system is not fully working but probably working adequately enough to keep the battery from discharging.

[benVFR]

Thanks for the quick reply, I will do that tonight.

Unfortunately it's hard to ride at higher RPMs when the road is sketchy. I was making an effort to do that yesterday though.

Guess maybe I should get the jetting taken care of to smooth out the throttle, that would make it easier when the road is shitty.

Ben

[ShredHed]

My 12 Volt battery has to be charged at 14.6 V's or better in order for the charge to get through. I noticed the charger goes to near 15 volts when in charge mode, than backs off to mid-13's when on trickle mode.

I dunno the specifics why, batterytender.com has some great info on charging but I never bothered to understand it all. I got worried that just after purchasing Batterytender Plus my dealer informed me that the latest batteries need to be charged that high. Even though the specs said charger only goes to 14.5, my voltmeter say's it does better I'm hoping it did the trick over Winter and bike will turnover when I put the battery back on.

Can't comment on the other stuff you asked, I'm pretty limited when it comes to wiring/voltage stuff. I know how to R/R battery and where ignition key switch is though, and could probably replace a bulb and fuse if motivated enough...

-Jack

[Honclfibr]

Originally posted by benSV

(Wishing I had taken some EE courses)

Ben [/B]

Ok, I have a bit of time to kill at work, so here's a few basics. A freshly charged, new battery, will be outputting anywhere from 12 - 14 volts, with about 13.5 being the nominal. As you draw current from the battery, the battery voltage will drop, until the point where it's voltage is insufficient to run your starter motor, around 8 or 9 volts. This is the point where you say "bad battery, to the charger with yee" and slap a charger on it.

As the charger charges the battery, the battery's voltage will increase. Since the rate of charge is (approximately, neglecting changing battery internal resistance) proportional to the difference in voltage between your source (charger) and the load (battery), as your battery voltage increases, you will draw less and less current, until your battery reaches the same potential as the charger, at which point you should draw no current and have a fully charged battery.

This same scenario happens whenever you're riding. Your bikes charging system puts out between 12 and 15 volts, which charges the battery and powers the bike's systems. Now this is where the jacket issue comes in. The bike's charging system should never make more than 15 volts or so, assuming your regulators are doing there job. However, if you're loading the charging system down (say, with heated clothing) it can certainly drop. Since the heat being put out through your jacket is directly proportional to the square of the voltage of your charging system, this would cause a perceived drop in heat as the potential decreased. However, your battery would not be drained as long as the charging voltage stayed above the battery voltage. For instance, let's say your bike's charging system is capable of putting out 14 volts, but that when you're idling around your jacket is taxing is and it drops to 12 volts. Say your jacket provides a load of 1 ohms. Then, the heat of your jacket just dropped from 14*14/1 = 196 watts down to 12*12/1 = 144 watts. You just lost about 25% of your heat, which you certainly might notice.

Now the other possibility is that the 12.x volts you measured across your jacket wasn't indicative of a worst case scenario. I don't know how complicated these jackets are, but I would imagine they incorporate some sort of controller which modulates the heaters in the jackets depending on the temperature. What this means is, if you're checking your system voltage with your jacket connected in a warm garage, or even outside just sitting there rather than riding and losing heat to the wind, the jacket may not be drawing as much load as it is when you're driving down the road on a cold day. It's possible that your charging system could be dropping below 12 volts worst case. At this point your battery takes over, which means you're draining your battery, not charging it, while you're riding. Next time you ride, check your battery with a voltmeter before and after you ride. If the voltage decreases, you're drawing more than your charging system can handle, and so your battery is supplementing. If you ride long enough like that, your bike will die and won't start again. And, of course, it will be cold out...

If I've goofed, please feel free to correct me. I'm a Computer Engineer, which means I've taken some basic electronics courses, but I may have oversimplified or glossed some second order effects which played a part here. I'm much better with flipflops and transistors than battery dynamics.

[stoinkythepig]

You are dead on except for this statement: (I think)

I don't know how complicated these jackets are, but I would imagine they incorporate some sort of controller which modulates the heaters in the jackets depending on the temperature. What this means is, if you're checking your system voltage with your jacket connected in a warm garage, or even outside just sitting there rather than riding and losing heat to the wind, the jacket may not be drawing as much load as it is when you're driving down the road on a cold day.

I don't think they are that sophisticated. I suspect changes in the controller setting just change the period the controller is on versus the period the controller is off (duty cycle) On high the jacket is just on. Anything in between high and off would probably be just a change in duty cycle. Temperature has nothing to do with it.

[Honclfibr]

Originally posted by stoinkythepig
You are dead on except for this statement: (I think)




I don't think they are that sophisticated. I suspect changes in the controller setting just change the period the controller is on versus the period the controller is off (duty cycle) On high the jacket is just on. Anything in between high and off would probably be just a change in duty cycle. Temperature has nothing to do with it.

Ah yes, that makes sense. I spend way too much time in the industrial control world, where we always have to have a feedback loop. In the consumer world, humans work great for closing the loop. When things get too hot, they turn the controls down; too cold, they turn 'em up.

I was thinking that 77 watts seemed pretty low to do anything useful as far as keeping you warm. Unfortunately, the heat loss equation for a motorcyclist moving at speed is far beyond my knowledge. But given that incandescent lightbulbs are about 25% efficient, your whole vest is only providing as much heat as you'd feel off a 100 watt bulb. Distributed across the whole jacket. I guess they must work though, I've seen people using these things...

[RandyO]

I was thinking that 77 watts seemed pretty low to do anything useful as far as keeping you warm. Unfortunately, the heat loss equation for a motorcyclist moving at speed is far beyond my knowledge. But given that incandescent lightbulbs are about 25% efficient, your whole vest is only providing as much heat as you'd feel off a 100 watt bulb. Distributed across the whole jacket. I guess they must work though, I've seen people using these things...


Not quiite.... a 100 watt incandecent light bulb's primary purpose is to produce light, but it is very inefficient at it so it produces quite a bit of heat too, the 77 watt vest produces heat only and no light, so it produces more heat energy than the light bulb.

Gerbings are the exception, most electric vest are only 35 or so watts, and plenty warm enuf

[Honclfibr]

Originally posted by RandyO
Not quiite.... a 100 watt incandecent light bulb's primary purpose is to produce light, but it is very inefficient at it so it produces quite a bit of heat too, the 77 watt vest produces heat only and no light, so it produces more heat energy than the light bulb.

Incandescent lightbulbs are so inefficient that light generation is actually secondary to heat generation. I gave them an efficiency rating of 25%, which was being generous. I believe the actual number is somewhere around 5-10%. So saying that a 100 watt lightbulb produces as much heat as this vest isn't really all that far from the truth. Granted, however, the vest is probably much better insulated since, as you mentioned, the *purpose* of the vest is to keep one warm.

Gerbings are the exception, most electric vest are only 35 or so watts, and plenty warm enuf

Interesting. What this tells me is that it doesn't take all that much heat to keep one warm with these things. You seem to know a good deal more about heated gear than I do. Has anyone ever tried to harness the heat of the exhaust to keep warm? Seems as though if you could pass a small amount of fluid across the pipes and through a properly insulated jacket, you could pull 35 watts of heat off the pipes without straining the charging system a bit. But maybe this isn't as simple a problem as I'm thinking. Too bad, all that waste heat sitting 2 feet away and we have to resort to generating more.

[RandyO]

it would prolly be easier on a liquid cooled motor to have a quick connect heater hose to the cooling system, exaust heating isn't the best..... speaking from my experience with air cooled VWs

[benVFR]

Yowsers... I will be happy to let someone else test out that water-heating system when you guys design it.

Ben

[Honclfibr]

Originally posted by benSV
Yowsers... I will be happy to let someone else test out that water-heating system when you guys design it.

Ben

"On the positive side, the third degree burns from when the vest burst on impact really took my mind off the road rash."

Hmm...yeah, I think we may have some kinks to work out before the "Holigan" vest goes head to head with the "Gerbing".

I did forget about the engine coolant Randyo, that does make a lot more sense, why add *another* liquid heat transfer system when the bike already has one. BTW, what was your experience with air-cooled VWs? Did the heaters not work so well?