Abate Holding Your Breath...Thompson's Design

[snip]

My specialty is circuit design, primarily chips, so I can't help on transformers. I was specifically wondering what you were trying to accomplish with the SCR... particularly wondering if there wasn't possibly a better way to hold current thru the zero crossing.

Larkin? He made a snarky remark about MIT, and how his wife, while at BU, waited tables and thought MIT types were geeks (of course we are :-). I truthfully remarked that, at MIT frats across the river, they had telescopes set up to watch the BU gals parading at their open dormitory windows, showing off their wares. I also asked for the names of the restaurants she supposedly waited at table. They drove Larkin into one of his mentally defective states, and he's not let up since. (And I think he made up the part about waiting tables... he still hasn't provided any restaurant names.) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Jim, you know that JL can't resist replying to your post (above). Let it go, and I feel fairly certain that you will be one-up with the group, if that matters.

John S

That may best be reserved for another thread. But we have discovered = that,=20 for highly inductive loads, applying a gate signal on the positive = excursion=20 of the voltage waveform means that it will be removed at the point of = peak=20 current, and relies on the SCR's current latching characteristic to = maintain=20 conduction through the zero crossing. But there is a point where the = current=20 drops below this level, and I surmise that the current still flowing = will=20 create an inductive voltage "kick" which causes a distorted waveform at = the=20 zero crossing. At this point, the opposite device's gate drive will have =

already been ON for a quarter cycle, so the distortion appears only at = the=20 end of the current waveform.

Sometimes this seems to cause erratic behavior and latch-up, where the = SCR=20 may be turned back on, and sometimes this happens only on one SCR, which =

causes a net DC component and correspondingly very high input current = which=20 trips the mains protection instantly. On a 200 amp source this means the =

fault current is at least 2000 amps, and probably much higher.

I don't know exactly why the continuous gate drive works to solve this=20 problem, and it may not do so completely, but it has been shown to be=20 effective and I don't know of any downside. I don't think maintaining =

300 mA=20 on the gates does any damage. We've had SCRs in the field using this = method=20 for at least ten years, and most failures seem to be due to an open gate =

wire or customer abuse. We have dealt with the former by using the new = SCR=20 trigger board which checks for gate continuity before triggering, and we =

have reduced the latter by using a "programmable overload device", or = POD,=20 which limits the duty cycle of operation.

Last I heard from you it seemed you were interested in this phenomenon. = But=20 I didn't realize you had no experience with transformer construction and =

high isolation DC-DC converter design. Now that I review your areas of=20 expertise I see that the closest relative is switching power supply = design,=20 and they are typically only rated for common mains voltages up to 265 = VAC.=20 It would be really helpful to find one that works on 480 VAC mains, but = I=20 have searched in vain. However I recall seeing something recently that = might=20 be suitable for this purpose.

Thanks,

Paul

Yep. I did a lot of off-line stuff, but before PF correction became a requirement. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

And let us not forget that these non-pm alternators have not used brushes for the field for years now. Nothing but bearings and the unexpected mishap to take place now.

Jamie

brushes=20

According to one reference, some models of wheel hub generators had = problems=20 with water entering the enclosure when the bike was moved from a warm = garage=20 to the cold outdoors and ridden in the rain. The temperature = differential=20 created a relative vacuum in the hub which sucked water in through the = seals=20 which were not designed with that in mind. Newer models apparently = corrected=20 the problem. But if water does enter the assembly it tends to corrode = the=20 rotor and stator poles which have very small clearance and cause them to =

bind.

Paul=20

[snip] [snip]

Huh? How does that work? ...Jim Thompson

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

They have not been using brushes in alternators in cars for a long time now. They may still use them in very large units however.

Since you never believe me on anything, maybe you can believe others.

Here:

Jamie

OK. I've not seen that in a passenger car. My Q45 has slip-rings. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Talking about slip rings. We still operate many large AC motors (Eddy current clutches) via slip rings.. They actually work much better for constant tension control over today's preferred vector systems.

But, they are getting old like the rest of us and soon to see their demise.

Jamie

As one with 50 years dealing with the car companies, they haggle over pennies. So I suspect exciter-based alternators are still rare. I'll ask my Infiniti mechanic if the new ones do/don't have slip rings (my Q45 is a 2005, but only 52,000 miles on it :-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

I took one of Marcel's alternator models, ran it through a 2:1 stepdown transformer, and rectified that. On the sensible parts of the frequency curve, the resulting DC current increases, about doubling the no-transformer current towards the high end. Impedance matching works!

Of course with the transformer you get less output on the low end, but then that's what the added battery is for, to power the lights at low and zero speed.

John

I just found Rick's data for the dynamo, and it appears that the RMS = value=20 is about 1/4 the P-P voltage, instead of 1/2.8 as would be expected for = a=20 sine wave. So I'm curious about the waveshape. And of course impedance=20 matching works, but I think it would be better to boost the voltage and = then=20 rectify it so the forward drop of the diodes has less relative effect on =

efficiency. Perhaps the voltage doubler would be most efficient.

Once converted to DC, impedance matching can be best attained by PWM and = a=20 buck converter. And the step-down transformer (or any transformer) would =

need to have a lot of iron to work at the lower limits where the = frequency=20 is less than 20 Hz, although the voltage is about proportional to = frequency,=20 so that may not be significant.

These days there are much better ways to achieve impedance matching and=20 maximum efficiency than by using a simple transformer. And solid state=20 components are much lighter and cheaper than iron core magnetics, = especially=20 since they need to be specially wound to work optimally at the low = voltages=20 produced by the hub generator (2-7 VRMS).

The power produced by the bike hub generator would seem to be = proportional=20 to speed, but it may drop off at higher speed because of the higher=20 frequency and the inductance. This may result in a relatively constant = power=20 output and a crude form of regulation that results in relatively little=20 variation in brightness over normal speed range.

Paul=20

Is it for sure the impedance matching capability of the transformer that produces the benefit, or the trade-off of current vs voltage? I ask this because I don't see any way to be sure of any of the impedances, so how can we know if the transformer is matching it?

--

Reply in group, but if emailing add one more
zero, and remove the last word.

ftp://jjlarkin.lmi.net/Hub_Alt_1.JPG

Transformer directly off the generator?

The schematic depicts an alternator but aren't bicycle generators actually commutated generators vs alternators?

Even if it were an alternator producing a sinusoidal wave, wouldn't the highly variable frequency be a bit troublesome for the transformer? (huge hysteresis?)

Wouldn't it be better to use a bridge rectifier immediately after the generator/alternator and before further processes?

Wouldn't a simple oscillator keep the frequency within the range where the transformer would be more efficient in a smaller (lighter) size?

The goal is to keep the light from ramping up and down with dynamo output, right?

And to charge the battery when there is excess power whether the light is on or not, right?

What exact type of battery is this, BTW?

Rate of charge info for battery? Was the goal to trickle charge or was it full blown battery charge management with every bit of available current?

Larkin's design seems to use the battery itself as a constant voltage/current source but isn't that a bit of a problem straight off any battery in the middle of charging?

Would the ups and downs of charging be within the tolerances for the constancy to the light?

Could this entire project be done sufficiently with a bridge rectifier and a trickle charge circuit comprised of a limiting resistor, with the battery itself serving as the constant voltage/current source to the lamp? (Low tech)

Would the efficiency advantages of high-tech really be worth the MTBF for more components in this application?

Larkin still hasn't run the simulation. And what is this "_one_ of Marcel's alternator models"? ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

What I've seen is sort of spikey, unloaded. It will probably look a little more sinusoidal loaded. But there are all sorts of alternators out there.

And of course impedance

I think there would be plenty of voltage just rectifying and filtering. But you'd need a switcher that works over a wide voltage range and doesn't blow up when the alternator voltage is really high,

100 volts or maybe more. That's not all that difficult, but a Digikey transformer is a lot simpler and more reliable.

It's only a few watts, so the transformer would be small. Use high enough voltage windings that nothing saturates.

Sure. But the transformer is simple and rugged.

And solid state

What flattens out brightness is the constant *current* (into a load, over the speed range) of these alternators. Both voltage and frequency increases with speed, and there's a lot of inductance.

John

Were there spice/LTspice models somewhere or were you referring to the graphs & tables?

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

That's what I'd like to know.