6V AC (sin) generator (2A+)

[dr pepper]

An audio amp is a reasonable way of emulating a dynamo, the o/p from a dynamo will have all kinds of noise and junk that a sig gen wont, however I dont think that wil make a big difference, the class of the amp I dont think will make a lot of difference, this is hardly an audiophile application.
If you want a more accurate test, maybe use an mp3 recorder and use it to record the waveform made by a dynamo while riding a bicycle on a typical trip, then play it back through the amplifier / converter, this wont be perfect but with a simple setup it will be reasonably close.

 

[Cicero]

0.1Hz...jeepers. Tell me how your class-A amp handles that?

 

[dr pepper]

Thats a good point an amp kit would probably not be designed to go that low.
Thats why I mentioned a tda monolithic device, they can go to dc.

 

[ACharnley]

While the dynamo can do that it's not practical for the device to include such capacitance, so I detect the frequency and shut off when it gets too low.

Awaiting for some 1.6A fuses to arrive, the 100W amp blew it on the second go. But it worked beautifully the first time around at 500hz.

Andrew

 

[dr pepper]

Ok what do you mean by not having high capacitance?

A poly fuse is a handy device as it self resets, but it'd only be any use on the dc supply to the amp as such low freqs might make the fuse reset between cycles.
If your protecting the dynamo then a circuit breaker would do that, but if your protecting the amp then a quick blow fuse might be better.

 

[ACharnley]

When the frequency is very low the output is a 0-6-0 pulse which would require large(!) capacitance to smooth. It's not practical for the size of the case.

 

[ACharnley]

It has gone reasonably well;

The first amp blew both it's transistors (integrated). Luckily it was my brothers...

The second amp completed the first test then blew it's internal fuse on the second. I'm awaiting a 1.6A replacement before restarting.

The first channel on my signal generator has blew. Second is ok...

Bigger issue (potentially)

I have two 5W 20v zeners back to back for voltage protection. The voltage didn't rise above 6V but the frequency went a bit crazy in the testing phase, probably 20khz. It wouldn't get anywhere near this in real life but regardless one of the zeners is damaged with 80mA flowing in reverse at 6V and 150mA at 7.8v. Effectively it's lost it's ability to block. Are zeners frequency sensitive before they fail?

 

[ChrisP58]

It has gone reasonably well;

The first amp blew both it's transistors (integrated). Luckily it was my brothers...

The second amp completed the first test then blew it's internal fuse on the second. I'm awaiting a 1.6A replacement before restarting.

The first channel on my signal generator has blew. Second is ok...

Bigger issue (potentially)

I have two 5W 20v zeners back to back for voltage protection. The voltage didn't rise above 6V but the frequency went a bit crazy in the testing phase, probably 20khz. It wouldn't get anywhere near this in real life but regardless one of the zeners is damaged with 80mA flowing in reverse at 6V and 150mA at 7.8v. Effectively it's lost it's ability to block. Are zeners frequency sensitive before they fail?

Please check how your zeners are connected. They should be wired end to end in series, but pointing in opposite directions.

Back to back usually means that they are in parallel. That does not work for zeners as they look like a regular diode in the non-zener direction. So back to back zeners (of any voltage) will look like two regular diodes and will clamp at about 0.7 volts.

Also, you need some resistance in the circuit before the zeners to limit the current.

 

[ACharnley]

OK I'll not use the term back-to-back again. It was meant as in series in opposite direction. One of them has failed and to me it's frequency related. There's no resistance as they are there to shunt heat (they are big 5W models and heatsink/pasted). The total input wattage won't go above 5w each in real life (although it could under the test environment my meter never went above 6V and they are 20V rated).

 

[audioguru]

The total input wattage won't go above 5w each in real life (although it could under the test environment my meter never went above 6V and they are 20V rated).

A 20V zener diode in series with another in the opposite direction does not conduct until the voltage reaches 20.6V so there is no way it conducts with only 6V. But your meter cannot accurately show the voltage of spikes or pulses that might be higher than 20.6V and are blowing up the zener diode.

 

[ACharnley]

Yep, though even if the voltage became 100V it's the heat from current that would destroy it, and it never got hot (until it failed and began passing current continuously). That's why I'm wondering if it has capacitance in reverse before it blocks and if a particular frequency (regardless of the voltage level) can pass through. It could of course just be a faulty zener, it's not the first time I've been duped by Chinese components....

I am pretty sure I momentarily went overboard with the signal generator (15,000hz etc)

I did Google, there's a thread asking why zeners are not used in high frequency but no answer to it.

 

[audioguru]

A 5W Chinese zener diode has a nice big case with a tiny 1/4W zener diode inside.
Didn't you see the video of a Chinese "2400mAh" Li-Ion 18650 battery cell that actually has a 66mAh Li-Po battery cell inside?

EDIT: 15kHz is not a high frequency. A zener diode has some capacitance which is why they are not used to clamp radio signals.

 

[ACharnley]

The two fake capacitors on the PCB are enough punishment. I hope it's not so!

 

[ACharnley]

Both Class A/B amps are toast (my brother is pissed ). How about one of these instead.

**broken link removed**

 

[ChrisP58]

I'm going to step back and look at your problem from a different point of view.

Instead of trying to emulate you dynamo on a bike running at different speeds, why not just use the dynamo? Mount it to a bike wheel on a frame and drive the wheel with a variable speed motor.

It will be a lot simpler to correlate wheel RPM with whatever bike riding speed that you want to cover.

And, as an electrical power source, the dynamo will exactly match the source characteristics of the in use conditions. But, the source characteristics of any signal generator/amplifier/transformer combination that you try to emulate it with, will almost certainly be different.

 

[AnalogKid]

Both Class A/B amps are toast (my brother is pissed ). How about one of these instead.
**broken link removed**

The frequency response range is not stated, but it has input coupling capacitors. The odds that these are sized for flat response down to 0.1 Hz are zero. This will be a problem for any off-the-shelf audio product, although many can be modified to meet your bandwidth.

ak

 

[KeepItSimpleStupid]

The Kepco BOP 20-5m https://www.kepcopower.com/bopmod.htm will likely work for you.

So, might the obsolete HP HEWLETT PACKARD 6825A Bipolar Power Supply / Amplifier +/- 20V +/- 2A
The latter is just plain weird. I used a bunch in their heyday. A real pain to repair.
You will need a signal generator in both cases, of course. I think the specs are 0 to 15 kHz but don't quote me on it.