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Re: Very low power dynamo (alternator actually).

>> >> >>> >>>"John Larkin" wrote in >>>message >>>news: snipped-for-privacy@4ax.com... >>>> >>>> >>>>>>>>>> >>>>>>>>>>>> >>>>>>>Tinkering with the old Sturmey archer bicycle dynamo, I was wondering >>>>>>>whether it would charge a 1.2Ah SLA any better if the loading was >>>>>>>modified. >>>>>>> >>>>>>>The generator is rated 6V/3W, but off load at a decent rate of knots >>>>>>>it >>>>>>>can >>>>>>>produce over a couple of hundred volts. >>>>>>> >>>>>>>What I was wondering was whether its possible to get more energy into >>>>>>>the >>>>>>>battery by letting the generator output voltage stretch its legs so to >>>>>>>speak >>>>>>>and convert the excessive voltage down with a buck converter. >>>>>>> >>>>>>>Can anyone advise on the practicality of this please? >>>>>>> >>>>>>>Thanks. >>>>>>> >>>>>> >>>>>>Bwahahahahaha! So this was the original post? Bwahahahahaha! >>>>>> >>>>>> ...Jim Thompson >>>>> >>>>>Perhaps Larkin would be happy to address Ian's question, "What I was >>>>>wondering was whether its possible to get more energy into the battery >>>>>by letting the generator output voltage stretch its legs so to speak >>>>>and convert the excessive voltage down with a buck converter"? >>> >>> >>>Well its what I wanted to hear anyway, I might start thinking about a >>>design >>>for a buck converter to try it out and see what happens, might be possible >>>to get away with a MC34063 - failing that maybe a discrete component >>>design. >>> >>>Unfortunately my workshop has been dismantled for refurbishing and most of >>>the stuff crammed into the shed - so no room to work in there either. >>> >>>When I tried LTspice I found it a PITA to use - maybe while deprived of my >>>workshop I should give it another chance. >>> >> >> I love LT Spice. It's not hard to use, and well worth the short >> learning curve. >> >> Here, try this: > > >Thanks - might download it tomorrow. >

I committed a Great Sin on Friday: I *designed* a circuit by fiddling with Spice. It's a double-terminated LC filter feeding an opamp driver diffamp, an ADA4950-1, with an offset generator voltage divider, and all sorts of entangled loadings. Looking at the algebra, I bailed. Since I'd probably want to sim it to check any computed (and stocked!) parts values, why not just Spice it and fiddle?

ftp://jjlarkin.lmi.net/ESM_sig_in.pdf

John

Reply to
John Larkin
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Its very doable. I had no idea those old dynamos put out so much.

NT

Reply to
NT

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I'm not seeing "all sorts of entangled loadings"? What kind of response were you looking for?

Reply to
Fred Bloggs

I want the ADC driver to swing from -0.75 to +0.75 diferential output (into an LTC2242-12 ADC, which alone fills the next sheet of the schematic) as the signal swings 0 to +3. The ADA4950 isn't a high input impedance, and its VCM will be 1.25 volts. And I need to keep the filter properly terminated.

John

Reply to
John Larkin

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OIC- well isn't that just constant-k design or something...

Reply to
Fred Bloggs

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It would be cool if I could set up performance targets and let Spice do the iterations for me. One of my guys does that sort or brute-force circuit design - lets it run for hours - but he uses Octave and some optimization program around that. He'll design filters by just pushing poles and zeroes around iteratively.

I'm still constrained by wanting to use parts we have in stock, or stock parts plus a minimum of new purchases.

Seems like I spend a lot of time trying to use stock parts, and use parts aleady present on the schematic somewhere else. I did write a program that finds the best in-stock resistors to hit a given ratio and Thevenin impedance.

ftp://jjlarkin.lmi.net/Rugrat.jpg

but that's just a hint of what could be done. I want to tell Spice "here's a list of parts I have in stock, and here's the output I want, wake me up when you're done. Go to Digikey if you have to." I suppose I could accomplish the same with a smart intern.

John

Reply to
John Larkin

Having noticed quite a few apps on the LT d/l page, I wondered what switchercad does?

Reply to
Ian Field

Switchercad is - I think - just another name for LT Spice.

John

Reply to
John Larkin

I remember in my old microwave filter class that we had just started using Touchstone to design microstip filters. A couple of the guys tried using the optimiser, and would set it up late and night, and come in the next morning to see the results. They were doing a band pass filter, but forgot to put in the 'stop' bands, just the pass band.

The next morning, they came in to find it had optimised it to a single transmission line... ;-)

Charlie

Reply to
Charlie E.

On an intellaSys (*) project some village idiot manager hired some clown peddling optimization software, and asked me to give the clown one of my cells to optimize.

So I gave him my internationally famous band-gap that is flat as a pancake and always starts up at very low VDD, any temperature, any process corner.

The "optimizer" completely killed it and couldn't ever get it to work again ;-)

So I was fired ;-)

(*) The rumor mill says they have crashed and burned... just another investment black hole. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Most elegant!

John

Reply to
John Larkin

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That's more or less what I did with my electromagnetic simulator--a fast clusterized FDTD engine with a big script wrapped round it to do the multidimensional optimization, among lots of other things.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
Principal Consultant
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Reply to
Phil Hobbs 

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Indeed.

Aren't you even beginning to be annoyed by the pilot fish who feeds on
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Reply to
John Fields

What a weird, foul old hen you are.

John

Reply to
John Larkin

flattering will get you no where John!

Jamie

Reply to
Jamie

He's still obsessed with excrement, too. He mentions it a lot more than he mentions electronics. Yuk.

John

Reply to
John Larkin

It's unfortunately been over 20 years since I've touched power conversion, so I can't contribute much of a practical basis to this discussion, but here are my theoretical contributions.

Bike dynamos are designed with "excess" inductance, such that as the frequency and internal voltage rises with speed, the unit current limits at approx 0.5 A. A number of people use series capacitors to cancel part of this inductance in order to get more current out of their dynamos. If you wanted to extract the maximum possible DC power out of one of these, I would consider trying the following:

- Since the AC voltage output is low at low speeds, synchronous rectification should be more efficient than using a diode bridge.

- Due to the high series inductance, I think it makes sense to pull as close to sinusoidal current from the dynamo, so something resembling a PFC front end might be useful.

- Tracking the frequency of the incoming AC and using that in the control seems to be an obvious path to follow.

- Frequency dependent series compensation might be useful, although if the PFC front end can have an adjustable leading power factor, that might do it to.

Reply to
Ralph Barone

Being insulted by such a creepy weirdo somehow seems rather trivial compared with being isulted by anyone of any conseqence.

Reply to
Ian Field 

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If I was obsessed with poop I'd reply to _all_ of your posts but, as
it is, I generally prefer to steer away from the threads you infect
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Reply to
John Fields 

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And yet, instead of ignoring, as one would have done if the insult was
trivial, you chose to respond, in whatever venue.
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Reply to
John Fields

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