worsening fuel economy

[Tex 36,817]

Baz, back 'in the day' it wasn't uncommon for folks to remove the air con drive belt because it really did have a noticeable affect on fuel consumption. But things have moved on since then. Cars (not bikes, alas) now have 'smart charging' systems that produce only what is required with a beneficial effect on fuel consumption.

 

Car manufacturers have been very active in trying to reduce consumption both as a 'genuine' and 'perceived' benefit to the buyer (lower annual taxation for the 'greener' models). Bike makers are lagging behind (again) but with, economy being quite low on the priorities of most buyers, who can blame them?

Edited December 5, 2016 by Tex

[embee 7,288]

It's not quite a simple as dumping all the power. The reg/rec recirculates the current in the stator (as Stelios refers) to regulate the output voltage. The heat generated in the reg/rec is due to the voltage drop across the semiconductors, it's not dumping all the potential output power as such. There is high current in the stator but the resistance of that is low so heat dissipation is not huge.

 

It's perhaps easier to think of it as a water pump. If the output is connected directly back to the intake, the flow (current) is great but the amount of power required to run the pump is quite small, just overcoming the resistance of the pipe (equivalent to the reg/rec). If you start restricting the pipe the pressure goes up (voltage) and flow can be diverted off to drive something else (load). The power required by the pump is then the product of the pressure and flow (volts x amps).

 

The total heat loss in the reg/rec is the result of the combination of the volt drop across the regulator semiconductors which recirculate current in the stator, and the volt drop across the rectifier semiconductors which deliver current to the load. Depending on type, the volt drop across the diodes is of the order of one volt, so for example if the total current flowing is 20amps the heat in the reg/rec will be 20watts. This is where the MOSFET type reg/recs are a benefit, the volt drop across the MOSFETs is typically lower so heat produced is less.

 

Permanent magnet alternators are not as efficient in terms of losses as a regulated alternator such as used in cars where the output is regulated by varying the rotor current and thus magnetic field strength, thus only producing the required amount in the first place, but they are not generating the full output power all the time. It is not "dumping" excess power, it's allowing recirculation to minimise the waste power.

 

This shows how the regulator circuit is separate from the rectifier circuit in a typical motorbike reg/rec

All energy used in a vehicle comes from fuel one way or another, and yes running aircon is quite expensive, but when switched off the compressor is clutched out so you're only spinning a belt.

[fred_jb 10,269]

I don't suppose bikes will be doing this any time soon, but I believe that some cars, particularly hybrid drive types, will if possible only generate electrical energy during deceleration, so-called regenerative systems.  This is therefore effectively "free" energy as generating electrical energy when decelerating just helps to slow the vehicle and uses part of the energy which would otherwise just be turned to heat in the brakes.

[Tonyj 6,907]

Cheers for that Murray , just looked in at 7.10am and I've been to school already .:0) . Just waiting for my time to shine on here ( nearly wrote hear ) with a kitchen question :0)) and I've put the dunce hat on because of the spelling faux pas.

[Callisidrin 447]

I too have data from the last year which includes the daily mean temperature and if it was raining or not. When I plotted the mpg per fill up with the mean temperature I too get a trend line which is a sine wave matching roughly the seasonal differences in consumption. Take away the trend line and it's a series of haphazard spikes and troughs, some of them going the opposite way to what you'd think.

My trend variance through the year averages a drop of between 5 and 8 mpg.

I have no heated gear or any additional electrical items that would have any significance, besides the alternator is being constantly driven so there is no variance in the power requirements to drive it. In summer I would expect fuel consumption to go up because you tend to have a bit more fun. In winter the opposite as you tend to be more cautious. Friction, tyre pressures / wear, wind resistance, fuel brand, grad of oil, amount of weight carried, screen height, full face / open face, chain lubrication, chain tension, brake pads dragging, the list goes on. All in all there are a lot of small factors to take into account seasonally, but mostly these should cancel each other out through the year.  Even atmospheric pressure varies meaning there is more of less oxygen to burn. For something like F1 racing all these factors can have significant effect in the amount of fuel they need. But for us mere mortals, these variances aren't really that significant.

Agreed, there is a variation throughout the year in consumption, but I'm damned if I could give you a definitive answer as to exactly what causes it.

Having said that though...

A big factor returning a low mpg is, a badly maintained bike especially tyres Will lower your fuel consumption, look after your bike and it will look after your pockets.

[TJW 44]

Guys, 

 

I've replaced the cush drive / damper rubbers of the rear wheel after 18,000 miles of pretty much stop-and-go traffic in and around London … and the average fuel-consumption-average has gone up to the previous usual 65mpg (after the first tank-stop afterwards) ...