Wethead alternator and battery

[StuartV]

This may have been covered in the wethead threadfest. But, I'm not reading 4,000 posts to find out.

I was just comparing specs between the '12 GS and the '13 GS. I noticed that the '12 alternator output is 720W and the '13 outputs 580W. That surprises me. 140W less output seems like it will make a HUGE difference to those that want to run a few high output fog and driving lights and a full set of heated gear all at the same time.

I suppose the '13 could have other changes to its electrical system that reduce its electrical draw while running, but it would have to draw a 140W less power to have the same surplus available to use for accessories. Is that even possible?!?

I also noticed the '13 battery is spec'ed at 11.8Ah, vs 14Ah for the '12. That also surprises me because with the '13's higher compression motor, it seems like it would take more juice to spin it over.

But, maybe these two things go hand in hand? Is the '13 so much more efficient electrically that it can have such a smaller alternator and smaller battery without any compromise in functionality compared to the '12?

My gut says no. And my gut says the smaller battery is purely to save weight - since the specs says the '13 is already 9 pounds heavier than the '12.

[EJ_92606]

from the press release: At each exhaust camshaft there is an centrifugal-force-driven decompression facility which facilitates the start-up process. This makes it possible to save weight in the starter motor and battery.

[StuartV]

Originally Posted by EJ_92606

from the press release: At each exhaust camshaft there is an centrifugal-force-driven decompression facility which facilitates the start-up process. This makes it possible to save weight in the starter motor and battery.

Aha. And (I should know this, but I don't), presumably, this auto-decomp is not a feature of the oilhead motor?

Doesn't give a lot of confidence that the wethead will be nearly as capable of running aftermarket electric stuff as the oilhead. Bummer. And surprising, to me.

[EJ_92606]

Press release shows 620w for the wethead, although I know the 580 was quoted in some magazines. Times are a changing in lighting and with new LED lights, I think the power will be fine...now if you want to mount some old halogen high wattage lights, then perhaps its an issue.

[StuartV]

Originally Posted by EJ_92606

Press release shows 620w for the wethead, although I know the 580 was quoted in some magazines. Times are a changing in lighting and with new LED lights, I think the power will be fine...now if you want to mount some old halogen high wattage lights, then perhaps its an issue.

580W is what it says on BMW's USA website in the specs for the bike.

Is the Wethead actually using LED lighting? If not, then, well, I'm a little dubious that 140W (or even 100W) less output won't result in an overall lower amount of surplus available to the rider for aux lights and heated gear. A full set of heated gear alone can consume 140W. A pair of Rigid Duelly D2 lights is, I think, 56W. Clearwater Kristas are even more. So, a set of driving lights PLUS a set of fog lights, plus electric gear and you are easily talking about pulling 200+ Watts of power. And this isn't counting powering heated grips, a radio, radar detector, chargers for cell phones, intercoms, and MP3 players. And if you have a passenger in electric gear, there's another 100W+ of draw.

Does the Wethead really have 300W or more output to spare?

[WindSailor]

Originally Posted by StuartV

This may have been covered in the wethead threadfest. But, I'm not reading 4,000 posts to find out.

I was just comparing specs between the '12 GS and the '13 GS. I noticed that the '12 alternator output is 720W and the '13 outputs 580W. That surprises me. 140W less output seems like it will make a HUGE difference to those that want to run a few high output fog and driving lights and a full set of heated gear all at the same time.

I suppose the '13 could have other changes to its electrical system that reduce its electrical draw while running, but it would have to draw a 140W less power to have the same surplus available to use for accessories. Is that even possible?!?

I also noticed the '13 battery is spec'ed at 11.8Ah, vs 14Ah for the '12. That also surprises me because with the '13's higher compression motor, it seems like it would take more juice to spin it over.

But, maybe these two things go hand in hand? Is the '13 so much more efficient electrically that it can have such a smaller alternator and smaller battery without any compromise in functionality compared to the '12?

My gut says no. And my gut says the smaller battery is purely to save weight - since the specs says the '13 is already 9 pounds heavier than the '12.

Yep - my gut says no too.

Here's my approximation for amp draw on the some basic items based on 14v. These could be way off (the heated gear I've got at max level) - but by the same token I don't know too many items that run at 100% load that last very long. Just sayun....

Amp draw

• 4 - Low Beam Headlight based on 55W halogen
• 4 - High Beam Headlight based on 55W halogen
• 6 - Brake - turn signals - fuel pump - other extaneous items etc.
• 3 - Heated grips (max value?)
• 10 - Rider heated gear (max value?)
• 10 - Passenger heated gear (max value?)

Which adds up to 37 amps = 518 watts at 14 volts or 532 watts at 14.4 volts

That leaves 48 watts or roughly 3 amps (at 14.4v) left for extraneous items such as GPS and aux lighting... again that's at 100% rated load of the alternator.

This alone might prompt me into waiting for future versions.

[StuartV]

Yep. As EJ said, time are a-changin'. LED lights are making a big difference in how much juice a bike uses. But, ALL the time are a-changin', which means we riders are finding plenty of ways to use all that extra juice that's saved by having LED lights.

In days gone by, riders (and passengers) weren't running full electric suits and Baja 1000-worthy lighting and radios, heated grips, heated seats, semi-truck horns, phones, onboard compressors, electronic fuel injection, electric fuel pumps, GPS, etc. etc..

Even if the website specs are wrong and it really does put out 620W, it still seems like a big step backwards. Auto-decomp may validate a smaller, lighter battery, but I definitely don't see how the charging system is affected by that.

[WindSailor]

Truthfully - I am in awe of the new waterhead. Personally I think it is a big leap forward; and at the same time I really like the simplicity of my '11 GSA (being oil / air cooled). Getting the bodies synced at 4K miles had made it smooth - smooth - smooth. You wouldn't think that a new bike needed adjustment, but mine did and what a difference. I'm throwing that in there in case someone else needs it with the new waterhead (if you've got a vib at 4.5k or so... get the bodies synced).

They must have been working on the new design for awhile. The -only- thing I can kick around is that rating / implementation of the new alternator. If I remember correctly from someone else's post the 580 (or so) watt alternator was the biggest available alternator on the market that can be used in that type of motor design.

And to be honest, I'm probably running max amp load (with the previous list) less than 5% of the time I'm riding. That's with the wife on and riding on cooler / colder days and at night or early morning... which isn't that often. I don't want her on back if the odds of riding completely safe is compromised. Other than that - most of the time I'm riding it's solo.

I may have been harsh on the new wattage limitations, but it's more of a concern than anything else. It won't make me jump and ride a Harley any time soon. I've seen waaaaayyyyy to many tow trucks in route to go there...

If I opt to get the new waterhead at a later date, I'll still have a great big grin on my face.

[StuartV]

I'm less in awe than you are, WS. My feeling is that it's fine for a touring bike to have complexity. But, for an actual adventure bike - one that will be ridden to remote locations, far from dealers or mechanics - simple is key. So is low weight. I don't think even 10 extra pounds is a very good tradeoff for 15 extra HP on an adventure bike that's already making over 100. Actually, I'm not sure it's a good tradeoff on any bike. But, I developed my preference for light over powerful many years ago. And that's why I'm still riding an '05 GSX-R1000 over a Hayabusa or ZX-14 or any of the newer 1000cc sportbikes.

I don't think water-cooling is particularly desirable for an adventure bike, either. Not to say that any of that would necessarily keep me from buying a Wethead.

For sure, not having enough charging capacity to keep me and my girl warm would, though!

[Marki_GSA]

I could be wrong here but wasn't it only the GSA that had the 740W alternator? I thought the GS always had a smaller system anyway although it was in the 600 something range.

[StuartV]

My info came from here:

http://www.bmwmotorcycles.com/us/en/index.html

View the R1200GS. Click on the Compare Models tab. There, you can compare the New R1200GS to the R1200GS (the old one). That's where it says 580W vs 720W.

[def]

My 2001 REProm shows alternator output to be 50 amps at 4000 RPM.

[StuartV]

Originally Posted by def

My 2001 REProm shows alternator output to be 50 amps at 4000 RPM.

And 50 * 14.4 = 720W....

[Marki_GSA]

maybe it was the early pre GSA models that had the smaller alternator or maybe I just imagined it.

[def]

Originally Posted by StuartV

And 50 * 14.4 = 720W....

Thank you Mr. Ohm....nice law you've got.

My REProm shows output as 700 watts with voltage limited to 14.0. Do I assume the later model regulator/rectifiers now regulate max voltage at 14.4 volts?