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#238594 - 02/18/09 9:08 pm Measuring alternator output  
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Derry Hincks Offline
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Bordon, England
I often see requests for testing an alternator to which the usual response is 'The output should be 8.5 volts AC at 3000 rpm into a 1 ohm load.'

As my T100 is in bits at the moment I decided to mount it's alternator onto my bench grinder and make some measurements.

Here is a picture of my installation.



My alternator is single phase and you can see that it was made in May 1969.

With no load my grinder motor runs at 2900 rpm - measured by a laser rpm meter (the reason for the white patch in the photo above.)

At this speed with no load my alternator produces 32.1 volt AC on my meter.



The scope is set at 20 volts per division (2 volts per division on the scope and the scope probe set to divide by 10) so we will call that 160 volts peak to peak. Quite a difference from the meter reading.

Below is a picture of the alternator output with a 1 ohm load.



Now we have 10.5V on the meter and 40V pk-pk on the scope. So my alternator is comfortably above the quoted 8.5v AC.

I hope this helps.


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
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#238595 - 02/18/09 9:12 pm Re: Measuring alternator output [Re: Derry Hincks]  
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Derry Hincks Offline
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Bordon, England


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#238611 - 02/18/09 10:01 pm Re: Measuring alternator output [Re: Derry Hincks]  
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Blapper Offline
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Derry, You may want to go back in and resize the pics down a bit so they are not too large.

HTH







#238691 - 02/19/09 7:54 am Re: Measuring alternator output [Re: Blapper]  
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Duke Of Oil Offline
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Derry,

Excellent demonstration for those of us who wonder why the various measurements are so far apart. What everyone should pay particular attention to is the shape of the waveform on the O'Scope. It is nowhere near an ideal sine wave shape, is it... even under output load? This is why it is crucial that you use a Digital Multi Meter that can perform a "True RMS" measurement. Cheaper DMMs make the assumption that they are measuring a pure AC sine wave (what you would expect from the wall socket to light your lamp). A pure sine wave measuring 1V peak (2 Volts peak to peak) will produce an RMS voltage of 0.707 volts. Thus, you would expect a 40 volt peak to peak (or 20 volt peak) to produce an RMS voltage of... (wait for it)... 14.1 volts. Not what we see here. Why?

Well, first off we don't have anything close to a pure sine wave. Secondly we have a Malpin UT58C meter that sells for under $35.00 U.S or about 20 UK Pounds. Its specifications do not state "True RMS", but maybe the owners manual will tell us for sure. Derry, will your Kenwood do the RMS AC calc and display it? Notice that the waveform is not rounded and sags both on the rising and falling edges. This would imply that something marginally lower than our ideal 14.1 volts is a real RMS number.

Secondly, what are we using for a 1.0 Ohm load? Is the measured tolerance accurate enough to rely on for this measurement. A 10% tolerance load, especially of low wattage (self-heating), can induce a substantial error. Keep in mind, too, that the alternator output will fall as it heats up (like 20+% as it approaches 200 degF). Measure cold and hot to get an overall health analysis.

All that smoke aside, if'n it were me and I stuck my el'cheapo meter on the sucker and saw anything close to 10.5 VAC, I would ride. Well, even if I didn't see that I would ride, and be thankful I pay for the premium AAA Club motorcyle towing service (that I have never used).

So, does it matter? Only if you care about doing things right for the right reasons, or so you like to sleep well or just ride worry free (that's why I pay for the AAA stuff I don't use). If you ride pub to pub (or bar to bar) and keep the old battery on a Battery Tender, it won't matter much. But if you push hundreds of miles a day and some of it through really hot stop and go city traffic (like Los Angeles) ... well, who would even do that? I like to ride hard, fast long distances in the open country (Winnipeg to Monterey in 2 1/2 days and Charleston, WV to Santa Barbara in 3 days, both solo on 1960's Triumphs), and bike charging systems love that, but the batteries will need their water.

Derry, well done. I couldn't get off my backside to go out to the garage to do that. The Kenwood looks well used! Looks like the soldering iron got a little close.

Don

Last edited by Duke Of Oil; 02/19/09 7:57 am.
#238700 - 02/19/09 10:34 am Re: Measuring alternator output [Re: Duke Of Oil]  
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Derry Hincks Offline
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Sorry about the size Blapper, I wish I could get the images to post how do you do it?

Thanks for the input Don, all your points noted.

With respect to true RMS I am not sure that many people will have such a meter (like me). For info I also used my Avo 8 for comparison and found that read approximately 1 volt lower. I used my digital meter in my images as it is easier to read.

BTW I have not seen any comment about about using true RMS in the Lucas documentation (or Triumph) have you?

I can't get too excited about the 1 ohm load. I my case I used 28swg resistance wire from Maplin order Code: BL64U. It is 4.2 ohm/metre. I put two screws in a broom handle 1 metre apart and wound on four turns.

I didn't note any voltage changes as the load warmed up. As you can imagine my set-up has very low thermal inertia so if it was going to change resistance with it's temperature I should have seen it I think.

What I believe my images show is that if your alternator puts out around 30 volts at 3000 rpm with no load then there is probably not much wrong with it and you should look elsewhere for any electrical problems.

At the moment I am not sure whether my readings are typical or not but until we get some feedback from others that have made measurements I'll not know.


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#238735 - 02/19/09 3:53 pm Re: Measuring alternator output [Re: Derry Hincks]  
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Blapper Offline
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Hi Derry, it is simple:

You are using Photobucket right? You click on the image you want to post which makes it big on your screen, hover the mouse over the picture you and a row of options pops downwards in the top left corner of the pic. You then click on resize and select 640 x 480 from the list. That is the right size for the forum. Then if you look bottom right of the screen, you will see a list of 'image link codes' left click on the img code at the bottom of the list, then right click and select 'copy' from your pop-up. You then right click in your message on the forum and select 'paste' to print that image data in your message. That's it. It is even easier than those few words.

You can retrospectively resize those pics above so I'll know when you have done it right! I'm watching and waiting Derry! wink

Blapper redwine

#238736 - 02/19/09 4:03 pm Re: Measuring alternator output [Re: Blapper]  
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Derry Hincks Offline
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Derry Hincks  Offline
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<I'm watching and waiting Derry! wink>

'ere, were you taught by my Mum?!!

Thanks for the info anyway.


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#238744 - 02/19/09 4:38 pm Re: Measuring alternator output [Re: Derry Hincks]  
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Blapper Offline
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laughing I thought you would like that! Well done.

Blapper redwine

#238801 - 02/19/09 9:19 pm Re: Measuring alternator output [Re: Blapper]  
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Duke Of Oil Offline
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Derry,

RMS (Root Mean Square)is a way of expressing an AC quantity of voltage or current in terms functionally equivalent to DC. This is important because our bikes (most of them anyway) use a DC battery based system and we have to charge those batteries with DC, not AC. So our alternator output has to be rectified (converted to DC) and then the voltage level regulated to feed the battery and drive auxiliary equipment like the ignition system, lights, horn, etc. Therefore, it is good to know how much "equivalent" DC current is available to input to our rectifier/regulator system when trying to diagnose a problem. And it is current that you are actually measuring when you read the voltage drop across your resistor. With a 1.0 Ohm load it is a one for one correspondence (Ohms law).

In the days of analog meter movements (D'Arsonval, Weston, iron vane, electrodynamometer) the mechanical inertia and dampening of the electomechanical needle movement made the deflection of the needle naturally proportional to the "average" value of the AC. Then, a calibration value was applied inside the meter so that the needle would read an AC RMS value. This, of course, only worked for a pure AC sine wave, but it was better than nothing, and it is what was used in "the day". As you can see, your output under load looks pretty close to a sine wave and an old analog meter would get you close... as will a modern inexpensive absolute averaging DMM with the same conversion factor built in for AC Ranges.

So, for your two wire alternator output with a single sine wave output you are pretty good with an inexpensive meter. But with a 3 phase device you will see three overlapping sine waves on the combined output, that translates to a DC voltage with ripple riding on it when it is rectified. If you are looking at a car alternator that employs a commutator to feed the electromagnets in the rotor, the output can be a truly corrupted, ratty, crappy signal if the commutator/brushes are going south for the winter. True RMS won't lie about the pre-rectified DC equivalent outputs of the stator windings. This can go on forever, but you get the idea. This is why you run down to the auto parts store and buy a rebuilt alternator... who wants to diagnose those kind of problems.

A 1.0 Ohm load driven by a 10.0 VDC supply will dissipate 100W. Your wire load is built in such a way that it dissipates heat efficiently... just what the old Triumph manuals would have you do. As long as you take your measurements quickly while the heating of the load is not extreme, you are jake. But, heat "bad", big wattage power resistor "good". I like 50% margins... thus 150W.

Something to keep in mind about bike alternators on our old low horsepower machines is that they rob the engine of power. RF alludes to this frequently when he cautions against upgrading your alternator/power system too much. Alternator output rises with RPM and to regulate the voltage (so that the battery doesn't get cooked and the bulbs blow), the regulator dumps current to ground (wasted in the form of heat), and that is energy wasted in terms of pony power for your ride. I have been working on a secret system for storing this kind of energy in a magnetic genie's bottle (lukewarm fusion) to use in charging my cell phone, and popping popcorn on long rides. Don't tell anyone!

Don

Last edited by Duke Of Oil; 02/19/09 9:23 pm.
#238858 - 02/20/09 1:33 am Re: Measuring alternator output [Re: Duke Of Oil]  
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Derry Hincks Offline
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Don,

that was a lot of words but what you were trying to tell me is sadly lost in them (to me). But thank you for the reply.

<they rob the engine of power>
Hmmmmm, let's think about this. Assume our 120w alternator is 50% efficient so absorbs 240w. Now 240w is 1/3 of a horsepower and as my bike produces 30 of them (on a good day) I think I can accept that. To be honest I'd be pushed to determine if my bike was even 1 hp down. Is 50% a reasonable assumption?

But I mounted my alternator on my bench grinder for a couple of reasons. One was to determine how tight the rotor nut has to be to prevent it's rotation. My assertion has always been not very as the alternator absorbs little power. Secondly, I have been developing my own regulator and wanted it fed by a real alternator for testing.

I have been toying with building a bespoke alternator driver. One disadvantage with my current arrangement is that I am limited to 3000rpm or thereabouts. It would be nice to be able to run the alternator at 1000 and 6000 also.

The only other experience I have in this area is when a GSX1100 I used to own developed a flat battery. A look in the manual said to test the alternator by measuring it's output which should be IIRC 50v AC (on each of it's three phases). No messing about there with 1 ohm resistors.

Not quite so simple with my single phase alternator as each of it's three phases are connected internally (in parallel). In the case of the GSX above I could readily see if a phase was down.

Talking of regulators it seems ideal that my alternator puts out 40v AC under load. If we rectify this we get potentially 20v DC which means that I have a headroom of 5.5v for regulation (assuming 14.5v output). But, when off load I will be getting 80v DC which is scary (I have been using a 723 regulator). To this end I have been working towards a combined shunt/series regulator.

A zener on a nice heatsink has a lot going for it. <s>


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#238869 - 02/20/09 3:36 am Re: Measuring alternator output [Re: Derry Hincks]  
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Duke Of Oil Offline
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The Beach, California
Derry,

Sorry if I wasn't more succinct about the absolute averaging versus true RMS. If you have a close to a pure sine wave it doesn't matter. If things aren't working right it can matter. I am an anal personality, so I believe accuracy counts... I use a micrometer to measure cam journals, not a caliper.

50% efficiency for a properly working Lucas bike alternator is probably in the ball park (current variable speed alternators are roughly 65-85% efficient with modern regulatory systems). My point on power was the one that RF has been making... going from 125 watts to 225 watts, when the power is not needed is simply wasted energy in the form of heat, using conventional regulation. I can live with it, too. All power losses are cumulative... and there are some on these forums looking for power boosts from approaches that will yield even less of a gain than chucking the alternator. The good news is that regulation becomes easier as the current load increases pulling the voltage down closer to the regulation point, so if you have the excess capacity and want to add the load, you might as well run that super bright headlight.

If you are looking for more efficient regulation approaches for your project, you might want to be tinkering with Pulse Width Modulation schemes. Yes, you want to go to higher RPMS. Sounds like you are going to have fun.

Don

#238885 - 02/20/09 6:32 am Re: Measuring alternator output [Re: Duke Of Oil]  
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DavidP Offline
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Originally Posted By: Duke Of Oil

If you are looking for more efficient regulation approaches for your project, you might want to be tinkering with Pulse Width Modulation schemes.


Maybe something along the lines of an SCR dimmer?


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
#238967 - 02/20/09 4:50 pm Re: Measuring alternator output [Re: DavidP]  
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Derry Hincks Offline
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Derry Hincks  Offline
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Thanks for the feedback.

On my way back from Tescos this afternoon I remembered that last year I purchased a consumption meter. So on returning back home ....

My bench grinder driving the alternator with no load consumes 194W. With a 1 ohm load this rises to 356W so makes the alternator consumption 162W. If my alternator is producing 'loosely' 100W this makes it's efficiency 62%.

<so I believe accuracy counts>
I can't disagree with that but it all depends on the situation. If you get concerned about the loss of a 1/3HP consumed by your alternator then you check your tappets before the next ride?

Moving on the only difference between a micrometer and a 'vernier' caliper is I believe the hands of the person it is in. Accuracy depends on touch.

Personally I prefer the vernier caliper as with one tool I can measure external, internal and depth dimentions.

All good fun.


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#239177 - 02/21/09 7:16 pm Re: Measuring alternator output [Re: Derry Hincks]  
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Duke Of Oil Offline
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The Beach, California
Derry,

You are possibly better than that (62%). For sure your bench grinder is not 100% efficient. What RPM was it running at?

The best, simplest, way to measure all of this is to place a torque meter in-line with the alternator, add a variable speed drive to the bench grinder, measure the alternator output and RPM and plot some curves. Of course, if your go that far, you might as well put it all in an environmental chamber and bring it up to operating temperature (what's the temp inside the primary after a hard run down to the Box Hill?). Then we should be off to Bonneville with the whole kit, including the chamber, to test with a rider wearing swimming trunks.

At my advanced age, touch is about all I have left that works (at least that's what she says). I am not familiar with the technique you mention that can improve the measurement accuracy of a device beyond its design specs through the use of touch. But, I am not too advanced in my age to learn! My minimum standard is to use a device that can resolve 10 times better than the smallest unit I am trying to measure. None of my calipers can get me to that standard if I am trying to get as good as 0.001 inches. So I use mics and gauge blocks to calibrate them, before I make a measurement that might cause me to chuck a part in the bin for being beyond wear tolerance. Of course, these days I have to use my magnifiers to read the damn things.

As I said earlier, I am not worried about fractional horsepower gains with a British twin (only noted that some here are). If I want more ("Scotty, give me more power!") I will run down to the Suzi shop and pick up a 'Busa. More cost effective.

Don

Last edited by Duke Of Oil; 02/21/09 7:25 pm.
#239214 - 02/22/09 12:35 am Re: Measuring alternator output [Re: Duke Of Oil]  
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Derry Hincks Offline
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Derry Hincks  Offline
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Bordon, England
Getting back to alternators Don I dug out my PC oscilloscope adapter today (a Picoscope) and downloaded the latest software. I lugged my laptop, scope adapter and assorted leads out to the garage to make some measurements.

There are meter facilities in the software one of which is called AC RMS. The description of this function I found confusing so I have emailed Pico for clarification but I believe it is 'true' RMS in multimeter parlance.

But using this meter I measured 11v when loaded and 40v unloaded. The PC scope pk-pk values were the same as before (20v and 160v).

BTW the bench grinder rpms are 2900 unloaded and 2400 loaded.


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#239222 - 02/22/09 1:22 am Re: Measuring alternator output [Re: Derry Hincks]  
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Duke Of Oil Offline
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Derry,

I only have a minute... going to roll out my '63 TR6SS for a quick spin before it gets dark here.

You should be fine with the PC based O'Scope approach. It will digitize the waveform and true RMS is really nothing more than taking the instantaneous value at each sample, squaring that value, summing those squared values, and then taking the square root of the sum. First, of course, you need to make all values absolute or positive going. So, in a general sense, the area under the curve of the current (Amps) waveform (whatever oddball shape it might be) accurately describes the current available. That was why I asked about your Kenwood's capabilities. Any spikes, glitches, sags or weird anomalies will be accurately accounted for (assuming the proper sampling rate) and now you can see what is really going on quantitatively, and power/work wise, without assuming that everything is working right. You, of course all ready know this because you have looked at the waveform on your scope. But others will only have their handy dandy meters. If Pico confirms this mathematical approach (the square root of the sum of the squares), than you have a true RMS calc. With a close shape to a pure sine wave, there will be little difference. The weirder the shape, though, and you have big deltas.

Don

#239302 - 02/22/09 6:05 pm Re: Measuring alternator output [Re: Duke Of Oil]  
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Derry Hincks Offline
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Bordon, England
Thanks for that Don I hope you enjoy your ride.

The kenwood is analogue with no meter functions.

I posed my question to Pico because they talk about the AC RMS meter being used to measure ripple on DC (?). Not quite what I was expecting to read. While I understand that some people may want to measure ripple the vast majority will be happy to just know what the AC voltage is I would have though. However it could be that Pico have added a smart addition to a standard facility.


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#239314 - 02/22/09 8:51 pm Re: Measuring alternator output [Re: Derry Hincks]  
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Duke Of Oil Offline
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The Beach, California
Derry,

Ripple is just an AC signal riding on top of a DC offset. It is what you would expect to see after rectifying and filtering your alternator's output (or the output of any AC sourced power supply... the AC leaking through). Low ripple is generally a good thing on the output of a DC supply, especially if high quality DC is important (like for a computer or audio system). But incandescent bulbs and your battery aren't going to care at all. If your Pico PC Based scope can measure ripple as an RMS measurement, you would suspect it will do a straight AC RMS for you... your email response should point you in the right direction.

If your Pico scope can export the data array of the sampled signal to ASCII text, you could slap it into Excel or Open Office's Calc and you can perform the math there. But I would bet that Pico has an on-screen button that you can push!

Supposed to rain tonight, but let up early. I am taking tomorrow off to have lunch with an old friend at Geoffrey's in Malibu. No rain means another chance to ride. Hate making it up through L.A., but the ride up Pacific Coast Highway through Malibu (after rush hour is over) to Geoffrey's is worth it. Especially the mandatory post-storm stop at Trancas Junction to check out the body surfing.

Don

#239436 - 02/23/09 5:42 pm Re: Measuring alternator output [Re: Duke Of Oil]  
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Derry Hincks Offline
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Derry Hincks  Offline
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Bordon, England
Don,

Interesting that you describe basic electronics to me when I do understand most things in life, but I have no idea what body surfing is as we don't do that where I live. Also I don't ride to 'the Box Hill' but I ride to 'Box Hill'.

However, I have heard back from Pico and they say that my 'scope reads 'True RMS'. So this afternoon I captured these two bitmaps.

http://s692.photobucket.com/albums/vv286/Derryuk/?action=view&current=noload.jpg

and

http://s692.photobucket.com/albums/vv286/Derryuk/?action=view&current=load.jpg

PS the last time I went to Box Hill was on my GSF600N http://rides.webshots.com/album/64950039RNwXNy
with a lady on the back about 10 years ago. She wasn't impressed with me, my bike or Box Hill so I haven't been back <s>.


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#239950 - 02/26/09 7:34 am Re: Measuring alternator output [Re: Derry Hincks]  
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Duke Of Oil Offline
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The Beach, California
"Also I don't ride to 'the Box Hill' but I ride to 'Box Hill'".

You got me there. I am sure that I meant to type "after a hard run down to the Box Hill carpark". I will blame it on the Arrogant Bastard Ale that was mostly my lunch. But it is true that Americans are generally loosey goosey with the articles in our grammatical structures. We think nothing of saying that we are off on a flight to "The Ukraine", but would never say off on a flight to "The Mexico", or to the "The Candada", or "The Great Britain". But we would correctly say that our return flight was to "The United States", but not confuse that with a flight to "The America". On the other hand, we would correctly say that if we fell off our bike, the paramedics would take us to "the hospital", whilst you would incorrectly say (from an American's perspective) to "hospital", absent the article entirely. And the same applies to holidays. We go on "a holiday" and you go on "holiday".

Your plots and measurements look all very reasonable. You reference RPM in your previous post, but not the last, and it looks as if the rotational speed under load is a bit different.

The weather Monday did not cooperate... the storm that was supposed to blow through over Sunday night lingered and only started spitting early Monday AM. I debated about taking the car and finally said what the h@ll and pulled out the rain suit, stuffed my backpack with the mandatory plastic garbage bag, filled it with my wetsuit, two towels and a change of clothes, pulled out the Rat Bike, and left early to go up Pacific Coast Highway through Long Beach, San Pedro, and Palos Verdes to avoid the freeway (you do not want to ride on the 405 in the rain with all the squirrels). Long and slow, but lots to admire along the way.

Geoffrey's was a treat... been going there since it was the Holiday House back in the early '60s. Rumor has it that Jack Kennedy hooked up with Marilyn Monroe there. There were lodging rooms, then, and a cute little Funicular to take you down to the beach. In those days, that part of Malibu was considered a good ways outside of Los Angeles. The Holiday House was not then, nor is it now, a motorcyclists' destination. I am much more relaxed, now, about showing up on a motor. Time was when you could make an appearance on a bike at a restaurant or Hotel and be discretely (sometimes) informed that you were not welcome. Times have changed.

The water at Trancas was cold and the air temp was probably ten degrees warmer at about 68 degF. The surf was disappointing and only running about 2-4 feet, but there were a few good moments, mostly for the other body surfers laughing at the bald guy and the silver haired f*rt pretending to be something other than old.

By the way, my only experience at Box Hill was disappointing as well... was the day before my wedding and the night/morning after a truly notorious drinking session with a group, including a fellow who was a friend of my fiances' brother. After exchanging the obligatory bike stories/lies, this lad suggested that, if I really could ride long and hard, that I could borrow his Norton for a spin, but I would have to ride to Box Hill and Maidstone (sp?) and return to Kensington before 11:00 AM with purchase receipts from both spots to prove that I had been there. The bet was 10 Quid. I set off with no map and no idea... oh, and no breakfast. Made it back around noon, but was mostly sober and only a mild hangover. The future missus was NOT happy... but I was... minus the money.

Don

Last edited by Duke Of Oil; 02/26/09 7:37 am.
#239952 - 02/26/09 8:12 am Re: Measuring alternator output [Re: Duke Of Oil]  
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Posts: 266
Derry Hincks Offline
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Derry Hincks  Offline
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Posts: 266
Bordon, England
Don if that was written under the influence then I wish I could do as well ... <s>

Still, we've had one feedback from the Triumph forum on alternator output which adds to the knowledge base and helps demystify them. I'm currently looking for a three-phase stator so I can make measurements and publish the details.

But if someone has already done it it would be good to hear the results ...


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#240000 - 02/26/09 5:36 pm Re: Measuring alternator output [Re: Derry Hincks]  
Joined: Sep 2002
Posts: 7,812
Alex Offline
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Alex  Offline

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Joined: Sep 2002
Posts: 7,812
Seattle
Originally Posted By: Derry Hincks
But if someone has already done it it would be good to hear the results ...


Apparently these guys have. Seems to jive OK with your one data point.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#240039 - 02/26/09 8:50 pm Re: Measuring alternator output [Re: Alex]  
Joined: Apr 2008
Posts: 266
Derry Hincks Offline
BritBike Forum member
Derry Hincks  Offline
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Joined: Apr 2008
Posts: 266
Bordon, England
Looks like a different measurement to me Alex, they seem to be measuring the output of the regulator.


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
#240453 - 02/28/09 10:13 pm Re: Measuring alternator output [Re: Derry Hincks]  
Joined: Jun 2006
Posts: 804
andrewinpopayan Offline
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andrewinpopayan  Offline
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Joined: Jun 2006
Posts: 804
Halifax, Butt end of Europe
Derry, don't forget that the alternator efficiency will go down as the RPM's rise due to iron losses at the higher frequency.

I can see the timebase setting on your scope, but as the alternator is behaving as 3 pole? then at 2900 grinder RPM the AC frequency off the alternator would be about 145Hz. On the second picoscope "foto" it looks like the grinder has dropped to 2560RPM due to load.

Maybe you could hook up a frequency doubler for the power supply to the grinder, start up on 50Hz and when running switch up to 100Hz?

Last edited by andrewinpopayan; 02/28/09 10:35 pm.

99% of carb problems are electrical.

1959 3TA

BMW R1150 Oilhead
#240483 - 03/01/09 3:17 am Re: Measuring alternator output [Re: andrewinpopayan]  
Joined: Apr 2008
Posts: 266
Derry Hincks Offline
BritBike Forum member
Derry Hincks  Offline
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Joined: Apr 2008
Posts: 266
Bordon, England
Thanks for the feedback Andrew.

<behaving as 3 pole>
It appears to be. The 'phases' are connected in parallel though rather than star or delta as they would be for a 3-phase alternator. I am scanning online for a 3-phase alternator to buy and test if one comes up at a reasonable price.

<frequency doubler>
A neat idea, does such a thing exist do you know?

I had been considering buying a 3-phase variable speed motor for testing but finding one at a cheap price (and power, say 1.1kW) is not easy. Cheaper overall would be to stick to twin-pole single-phase motors of similar power (1.1) and use pulleys to change speed. I would only need three speeds 1:1, 2:1 and 1:2 to cover the whole rpm range (near enough). A lot more construction though but it would keep me off the streets at night <s>.

But really as Mr Lucas quoted 3000rpm for testing I think I am near enough at the moment to get meaningful results. After all if you only want a go/nogo test for your alternator does it really matter if your rpm is 2500, 2750 or 3000.

Interesting though.


Derry.

1969 T100S under reconstruction
GSX-R750K2 (having been rebuilt from a crashed wreck)
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