Sunday, November 27, 2011

Making friends with Alessandro Volta, James Watt, and André-Marie Ampère

If I were an engineer, or a particle physicist, I would be qualified to tackle the laws of the universe.

As some of you may know, I am a lawyer.  That means that I am only licensed to handle man-made laws.  That's why I'm pretty sure there's no law that says I can't dabble in the laws of physics.

That is all the more true if the experiment I contemplate involves the more or less inconsequential, microscopic, minuscule corner of the universe in the dark, tiny places inside my Vespa.  Unless I manage to do something with the Vespa's electrical system that causes a black hole to form, or that creates a teensy bit of anti-matter, life as you and I know it will probably snake on into the future pretty much as we expect.

This puzzle-post is the first tentative dip of my right big toe into the most complex yet of my Vespa LX 150 modifications.

There will be more posts as I venture down into this rabbit hole, and be forewarned, I may yet decide to stop in my tracks and head off in the direction of trading up to a Vespa GTS of one variety or another.  Only time and this blog will tell.

For now, you will find below the bits and pieces of the puzzle as they lie helter skelter in my lawyer's brain, ill-equipped as it is for this journey [Ed.: when you see entries like this, it's me, making a snarky comment]:
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Oxford grips draw up to 4 amps (source: Oxford web site, user manual).

The pair of heated grips draws an average 3.6 amps when in operation.  Each grip can draw up to a maximum of 2 amps, so that means 4 amps of total draw at the maximum heat setting, of 28 to 30 watts. (source: Oxford web site, user manual) [Ed.: that's a math or physics mistake on Oxford's part.  In a 12 volt system, 3.6 amps is 43.2 watts and 4 amps is 48 watts.]

The Oxford electronic control automatically shuts off the grips to protect the battery from excessive discharge.  The shutoff point is 11.5 volts (source: Oxford web site, user manual).
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"The battery capacity that battery manufacturers print on a battery is usually the product of 20 hours multiplied by the maximum constant current that a new battery can supply for 20 hours at  68 F° (20 C°), down to a predetermined terminal voltage per cell. A battery rated at 100 A·h will deliver 5 A over a 20 hour period at room temperature." (source: Wikipedia)
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"There are only a few amps of excess alternator capacity on an LX150 to charge the battery above what is necessary to power the stock lighting. One 35-watt driving light uses 3 amps. You do         the math." (source: - "12 lamps on 1 LX"  - comment posted by SilverStreak on the thread posted by another MV member, Sunday, October 17, 2010)

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"You cannot convert watts to amps, since watts are power and amps are coulombs per second (like converting gallons to miles). HOWEVER, if you have at least least two of the following three: amps, volts and watts then the missing one can be calculated. Since watts are amps multiplied by volts, there is a simple relationship between them.

However, In some engineering disciplines the volts are more or less fixed, for example in house wiring, automotive wiring, or telephone wiring. In these limited fields technicians often have charts that relate amps to watts and this has caused some confusion. What these charts should be titled is "conversion of amps to watts at a fixed voltage of 110 volts" or "conversion of watts to amps at 13.8 volts," etc."


"The Following Equations can be used to convert between amps, volts, and watts.
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"Re: Heated grips?

pdxvespa wrote:

Has anyone installed heated grips? More to the point, can the electrical systems of the ET/LX/GT handle the extra load?  And if so, what does the installation involve.....?

phr3d answered:

1) Nope

2) Do you have specs on one?

I can do the math to verify. The regulated output at 3000 RPM is 7.5 A <----- Haynes is wrong here. I can't find it in my Workshop manual, so guessing 7.5 since it is fused at that. The Typhoon 125 puts out 8.5 A, so should be close.

Stock Battery is 9 a-H

Full Load:
Side Lamps   5 W
Brake      21 W
Turn      2 X 10 W (we'll assume you won't indicate both directions, but still 2 for front and rear)
Plates      5 W
Inst/Warn   1.2 W
Headlight   35 W

87.2 Watts /12 V = 7.27

Normal Running Load:
Side Lamps   5 W
Plates      5 W
Inst/Warn   1.2 W
Headlight   35 W

46.2 Watts /12 V = 3.85
So at 7.5 Amp out put at 2000 rpm (guessing this, see above). We have 0.23 Amps to spare under close to full load, and 3.65 under "normal". Hope I didn't miss anything.

3) I would take it to the battery, inline fuse it for whatever the Grip warmer is rated at. Relay it some something that only turns on when the engine is running.

Edit: Forgot it should be 2 x 10 W for turn signals because of front and back. Seems close to being in a drain situations."

(source: - "Re: heated grips" - posted by phr3d on November 13, 2005)
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Vespa OEM battery specifications:
  • 12 Volts
  • 9 Amp Hour @10 hr rate
  • 0.9 Ah Charge Current
  • 130 CCA
(source: - Vespa LX150)
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"Charging rate
Charging rates for a trickle charge are very low. For example, if the normal capacity of a battery is C (ampere-hours), the battery may be designed to be discharged at a rate of C/8 or an 8-hour rate. The recharge rate may be at the C/8 rate or as fast as C/2 for some types of battery. A float or trickle charge might be as low as C/300 (a 300-hour discharge rate) to overcome the self-discharge. Allowable trickle charging rates must conform to the battery manufacturer's recommendations.
For a 12 V 60 Ah battery a C/300 rate would mean 60 A / 300 = 0,20 A = 200 mA"
(source: Wikipedia - Trickle charging)
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SonjaM said...

Watt? I mean: what? I guess my business oriented brain cannot process this. I try to follow you into that rabbit hole but I am not sure how far I can go with you without frying my brain...

Keith - Circle Blue said...

My head hurts . . . but my hands are warm.

Dar said...

I think when I started following you down the rabbit hole I took a wrong turn somewhere and you lost me. Clicking my heels & saying "There is no place like home." Oh wait wrong story. Hope you get the heated grip thing sorted out.

Unknown said...


I have crunched your numbers and have come up with your solution.

connect your grips; either direct to battery or via: relay to ignition and only turn it on whilst riding over 30 Kph, and connect it to a battery tender/maintainer when parked (to maintain battery at full strength)

and carry those one-time use hand/toe warmers for emergencies

Riding the Wet Coast

The copyright in all text and photographs, except as noted, belongs to David Masse.