dual battery setup

[rev_mook]

Hey all, this is my first post; I'm glad I found this forum.

I've seriously been considering a trip on my R65 from Los Angeles to South Florida (and back) and I have been thinking of ways to power things like camera, laptop, phone, exc.  The plan is to do as much free camping as possible while avoiding hotels, so utility power won't be available most of the time.  

The idea is to place a second battery in a pannier wired to an isolation circuit.  When the bike is running it charges the second battery, and when the bike is off, it is disconnected from the rest of the bike's circuitry (automatically).  While installing the second battery and building the necessary circuit is easy, I've read that the charging circuit in the R65 is a little "wimpy" on various internet forums.

While I haven't done any real math to figure out load tolerances and stuff yet, would I be dumb to just "do it and see what happens"?  I don't want to risk burning out electrical system bits in an experiment.

~Mook

[Bob_Roller]

The charging system on the airhead bikes has a maximum output of 280 watts, that's not taking into account, old degraded components, loose corroded electrical connections, etc. .

A standard OEM charging system, I don't think is up to the task you're going to ask of it .

There are two after market charging system replacements available, one is the Omega system from Motorrad Electrics 450 watts output .

The other is the Enduralast system from Euro Motoelectrics, a little discrepancy on the output of the system, the seller claims 450 watts .

A third party test showed at best 380-400 watts .

Both are around the $500-600US range .

[wilcom]

Back when I didn't know the charging system on these Beemers was fragile I used to run driving lights on my R80 all night long and never had a problem.

The camera and the phone is not much but the laptop could be a pretty good load if you were going to use it for lengthy sessions. The best  would be to upgrade the system like Bob suggested, that's a no brainer.

But being a "shade tree" myself, I would go for it, you can always drop $600 later when it doesn't work out.

JW

[bruce_launceston]

As long as there is a 13volt plus output from the alternator it should charge an extra battery. Charging a battery is not a great load like running a headlight or starter. The additional loads (camera, phone etc) will only be run from the second battery and the dual battery isolator will protect the primary battery from discharge.
These isolators are readily available, I have a neat one fitted to my car that charges my caravan 'house' battery and a sealed AGM battery in a pannier should work ok. The charging wires don't have to be great heavy cables either, just look at your battery charger.

[Barry]

While installing the second battery and building the necessary circuit is easy, I've read that the charging circuit in the R65 is a little "wimpy" on various internet forums.  

Sounds to me like you already have a sound grip of the electrics/electronics involved.  The charging system may be a bit wimpy by modern standards but in it's day would have been considered top notch. Short distance commuting certainly will fail to keep the battery fully charged but if you are touring and using at least 3000 RPM for hours on end it should be fine.  It will all depend on the running load.  The after market upgrades are quite expensive and if it was me the first thing I would do is hook up and accurate digital voltmeter and go ride. That would tell me what the charging system was doing in typical use then if I felt it was necessary I'd look at shedding load with replacement LED's and perhaps 20W halogen running light instead of the headlight. That alone would free up more than enough power to charge your auxiliary battery.

[Rob Valdez 79 R65]

How about carrying along a solar charger?
http://www.espow.com/wholesale-16-000mah-high-capacity-solar-panel-charger-for-laptop-31-unique-adapter-tips.html

[tvrla]

Your idea will work just fine for your cross-country trip.

Of course, make sure everything is in good shape and working properly, but that's standard advice for a trip of any distance.

[montmil]

Suggest you confirm charging voltage and the regulator's output. Also, the primary battery should be "new-ish" to help stack the odds in your favor.

Alternator brushes checked? Some long-distance tourers like to carry a spare rotor. Stators rarely fail or give any problems.

Confirm all electrical connections are clean, bright, tight and have a slight smear of dielectric grease.

And allow me, mook, to be the first to welcome you to our friendly herd.

[rev_mook]

Thanks for those numbers Bob, it was the info I was looking for.

maybe in addition to a battery isolator, some sort of charge controller could be incorporated as well.  The controller could limit the charging current to 1 amp-ish. (10 or 15 watts).  This would protect the motorcycles electrical system without putting much more of a strain on it, while keeping the aux battery topped off.

I like the idea with the little solar panel.  Free power!

~Mook

[Bob_Roller]

Don't know how well versed you are on airhead charging systems, but the Bosch charging system that's installed on these bikes from the factory, doesn't do much, if any battery charging below the 3500-4000 rpm range .

Under than range, it's at best producing enough power for the bikes electrical consumption at that time .

Before I embarked on a trip such as yours, I would give the bikes electrical system a thorough going over .

[tvrla]

As soon as the charge light goes out, the battery is getting charged.

And remember, it's not the voltage, but the current, that's important. I've had bikes that did just fine on 13.5 volts max. That's because I made sure the connections were all bright and shiny. Bad connections are what block current.

Another thing to remember about these systems is the rotor turns half the speed of normal automotive alternators, being attached to the crankshaft rather than the cam. That's the biggest problem right there, but the way they made everything fit into the space allotted.

[Bob_Roller]

When BMW redesigned the motorcycle engines for the oilhead series, they got away from the crankshaft driven alternator .

I guess they may have listened to owners of the airhead bikes and the chronic criticism of the low output of the Bosch charging system they used for decades .

They opted for a standard automotive style alternator run by a multi groove rubber belt .

I think the standard alternator output now is in the 700-800 watt area .

[Barry]

I think the standard alternator output now is in the 700-800 watt area  

That's some improvement over the old bikes. Another way of looking at it though is that Electricity isn't free. Taking losses in to account at full output that alternator would consume getting on for 1.5 HP not at peak power revs but at whatever revs the alternator puts out maximum power say 3000 - 4000 RPM at most if it's geared up.  At 3000 RPM  my engine produces only 12 Hp. (An R65 engine 16HP).

I don't think I could afford to lose approximately 10 % of the engine output.  Just as well the oil heads have plenty of power to spare.