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Author Topic: bedini, the daftman SS charger & MHOP  (Read 26197 times)

qtrhack

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Re: bedini, the daftman SS charger & MHOP
« Reply #15 on: November 06, 2014, 06:49:20 PM »
What happens when you remove that voltage source from an inductor?   

the inductor will oppose the drop in current. 

i visualize this like a fish tank of water moving on a wagon.  when the wagon suddenly stops the water keeps moving (inertia) but can't go anywhere because the tank has stopped moving.  so then there is movement of water to the backend of the tank where again it can't go anywhere.  the water will bounce (waves) back and forth until finally settling down to zero movement.  is this a correct analogy?

i also ran a simulation here: http://www.falstad.com/circuit/e-inductkick.html


qtrhack

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Re: bedini, the daftman SS charger & MHOP
« Reply #16 on: November 06, 2014, 07:08:58 PM »
3. I have recommended that Hantek scope to people who are wanting a basic scope on a budget. For under 100 dollars you get the scope, with software that has better math capability than my old Link DSO, and cables, power supply for the scope and two reasonable probes. If I had the money I'd buy one myself.

is this what you would recommend?

http://www.sainsmart.com/hantek-pc-based-usb-digital-storage-oscilloscope-6022be-20mhz-bandwidth.html

ayeaye

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Re: bedini, the daftman SS charger & MHOP
« Reply #17 on: November 06, 2014, 08:22:26 PM »
is this what you would recommend?

http://www.sainsmart.com/hantek-pc-based-usb-digital-storage-oscilloscope-6022be-20mhz-bandwidth.html
I'm sorry but, it is said to be 20 MHz, what that means? In digital oscilloscopes it is usually considered that the bandwidth is 1/20 of the sample rate, like see the specifications of the scopes like Rigol. The sample rate of that scope is 48 Ms/s, so what do you get is a 2.4 MHz oscilloscope. Furthermore, the electronics of usb scopes is much more inferior to other oscilloscopes, it is not good at high speed.

I fully agree that using the computer's sound device for oscilloscope is a toy. Well, considering that the sampling rate is usually some 44 kHz, then the speed is 2.2 kHz, likely not very useful. But the cheap usb oscilloscopes look like toys too.

The mini crt analog oscilloscopes i talked about, they are 10 MHz and one channel. So what concerns the speed, they are much faster than the cheap usb oscilloscopes, and one can get them as cheaply. Furthermore, an analog oscilloscope is even capable of speed two times higher than its rating, thus 20 MHz in some cases. What concerns a single channel, so why cannot the external triggering be used instead? I'm not sure how well it works though, and the electronics of such cheap scopes is also sure not great.

If you can get some old analog oscilloscope cheaply, made by some good company, and when it is in a good condition, then that's great of course. Two channels and 50 Mhz, really great. If there are enough around, anywhere near where you are, some people have no hope of getting any of these. But the caveat is that they often come with faults which you are not able to repair. I think i cannot. The best is to find a good person who in essence just gives away a scope to someone who may need it, they don't sell you one with any hidden faults.

What is that speed, like one never has a 20 MHz signal. It is not about that, it is how much it shows, like fast changes, how correctly it really shows what happens. I'm sorry for talking so much, and its more like one beginner talking to the other, but i think that talking more helps to find out more.

MarkE

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Re: bedini, the daftman SS charger & MHOP
« Reply #18 on: November 06, 2014, 10:09:01 PM »
There are three factors to the bandwidth of a digital oscilloscope:

The sample rate.  The oscilloscope cannot accurately represent waveforms that have signal energy that fluctuates faster than half the sample rate.  2X sample rate / bandwidth is the ragged edge.  5X is comfortable and 10X is very comfortable.  Hantek samples at 48msps.

The analog bandwidth.  Hantek claim 20MHz for the 6022.  This would normally refer to the -3dB point of a first order low pass response.

The probe bandwidth.  A typical X1 1Megohm probe has about 10MHz -3dB bandwidth.  Even very cheap X10 probes easily do 50MHz steady state response.

Based on the sample rate and the analog bandwidth, when combined with a X10 probe, the Hantek should still have good accuracy at 10MHz.  That's pure sine waves not square waves.  It's going to be marginal looking at square waves faster than about 2 MHz. 

It is a great beginner's scope more than adequate for looking at the vast majority of non-RF circuits discussed on these boards.

Here is a listing for $50. starting bid shipped two channel analog 100MHz scope.  It is also a twenty five year old machine.  http://www.ebay.com/itm/Tektronix-Oscilloscope-2235-100MHz-/371183147172?pt=BI_Oscilloscopes&hash=item566c3d58a4




ayeaye

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Re: bedini, the daftman SS charger & MHOP
« Reply #19 on: November 07, 2014, 03:04:09 AM »
I look at this usb scope, and even if it can be used, no way can i love it.

MarkE

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Re: bedini, the daftman SS charger & MHOP
« Reply #20 on: November 07, 2014, 04:50:28 AM »
I look at this usb scope, and even if it can be used, no way can i love it.
Well it all depends on what sort of circuits you want to look at.  If you need more bandwidth than 10MHz then you will need to spend more than $75. for something new that can look at that for you.  I think it is a very good value for hobbyists especially for people working with stuff that switches no faster than a couple hundred kHz such as the vast majority of circuits on these boards.  If you want a nicer 200MHz 4 channel stand alone scope then you very quickly jump up to around $2000. for new from Keysight (HP/Agilent), or Tektronix.

TinselKoala

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Re: bedini, the daftman SS charger & MHOP
« Reply #21 on: November 07, 2014, 08:32:24 AM »
I will go so far as to say that _any_ scope is better than _no_ scope.  If you have 300 dollars that Tek 2235 is a nice deal. It is basically a higher bandwidth version of my old 2213a, same front panel controls. The delayed timebase is nice to have. But of course it does not give you numbers in boxes and only has the basic invert and add "math" functions.

But hey, that Hantek does trace multiplication, it says, and it even does FFT (meaning a spectrum analyzer display). For the price of taking your family to see a movie, I think it would make a great addition to any scope-less workbench. That Hantek, plus a good analog scope like the 2235, would be a pretty reasonable start on an electronics test bench.

tinman

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Re: bedini, the daftman SS charger & MHOP
« Reply #22 on: November 07, 2014, 01:21:29 PM »
You could try this one that i came up with way back when.
A few of the guys had some good results from this circuit.
Please excuse the early day pretty picture circuit drawing ;D

https://www.youtube.com/watch?v=5HwUuPQn2W8&feature=youtu.be

qtrhack

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Re: bedini, the daftman SS charger & MHOP
« Reply #23 on: November 07, 2014, 06:19:22 PM »
You could try this one that i came up with way back when.
A few of the guys had some good results from this circuit.
Please excuse the early day pretty picture circuit drawing ;D

https://www.youtube.com/watch?v=5HwUuPQn2W8&feature=youtu.be

i've got two 2n3055s with your name on it when i get the chance  ;)

thx!!

ayeaye

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Re: bedini, the daftman SS charger & MHOP
« Reply #24 on: November 07, 2014, 08:40:10 PM »
Hantek 6022BE, vertical resolution 8 Bit, what the hell? Gain range 20mV-5V, 8 Steps, what? And it kindly offers software, only in Windows. There is software in Linux for Hantek USB scopes http://www.openhantek.org , but it is only tested on Hantek DSO-2090.

TinselKoala

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Re: bedini, the daftman SS charger & MHOP
« Reply #25 on: November 07, 2014, 09:23:55 PM »
So don't buy one. Nobody is twisting your arm.

You might ask Tinman about his scope, maybe it would be more to your liking. It's only about seven times more expensive than the basic Hantek...

Here's a recent screenshot from my old Link parallel port scope, made in 1997, running on Windows 98:

(And I think the Hantek probably has better software! This scope can't do trace multiplication.)



TinselKoala

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Re: bedini, the daftman SS charger & MHOP
« Reply #26 on: November 07, 2014, 09:34:36 PM »
i've got two 2n3055s with your name on it when i get the chance  ;)

thx!!
I'm thinking that it would work even better if you used ultrafast diodes instead of 1n4007. The UF4007 is a bit faster (75 ns), but my "current" favorite is BYV26E, 1kV 1amp 75 ns recovery time, avalanche rated, inexpensive.

qtrhack

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Re: bedini, the daftman SS charger & MHOP
« Reply #27 on: November 08, 2014, 05:38:25 AM »
my "current" favorite is BYV26E, 1kV 1amp 75 ns recovery time, avalanche rated, inexpensive.

just ordered me a bunch ;)  thx again!!

qtrhack

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Re: bedini, the daftman SS charger & MHOP
« Reply #28 on: November 10, 2014, 11:03:49 PM »
What is an L/R time constant?

http://www.learnabout-electronics.org/ac_theory/dc_ccts45.php

The LR Time Constant.

When a current is applied to an inductor it takes some time for the current to reach its maximum value, after which it will remain in a "steady state" until some other event causes the input to change. The time taken for the current to rise to its steady state value in an LR circuit depends on:

•The resistance (R)
This is the total circuit resistance, which includes the DC resistance of the inductor (RL) itself, plus any external circuit resistance.

• The inductance of L
Which is proportional to the square of the number of turns, the cross sectional area of coil and the permeability of the core.

MileHigh

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Re: bedini, the daftman SS charger & MHOP
« Reply #29 on: November 11, 2014, 12:36:16 AM »
Yes and if you played the animation you see it in action.  The screen cap is attached.

There is one mistake on that page that you repeated.  It's really the "L/R" time constant and not the "LR" time constant.  You don't want to confuse it with the RC time constant.  The first is division, the second multiplication.  Since the L/R time constant and the RC time constant have the same exponential waveform, you see it everywhere on scope traces.  If you randomly watched 10 clips that have a lot of scope shots done by typical experimenters around here, chances are you will observe the exponential waveform in at leas a few, if not most, of the clips.

The time constant can be a microsecond, a millisecond, a second, or a day in length, but they still have the same waveform.