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Author Topic: Pierre's 170W in 1600W out Looped Very impressive Build continued & moderated  (Read 430012 times)

konehead

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Hi Dog- one
I looked up parametric resonance and the word parametric comes from "parameters" so you could maybe say parametric is similar to "changing the parameters"
Anyways one analogy I read about with resonance is someone on a swing, and to get more power and greater length to swing, the person on swing will stand up and sit at points on swing to create a stronger swing... so sort of vertical actions applied to horizontal swing motions using weight and gravity at cost of more physical effort to get more power into the swing. (whatever eh)


Anyways about super cap working as very heavy load to create a shorted condition, I would think not a drained down super cap bank, but instead like Pierre does, pre-filled super caps which will accept and store the energy easily, and still have the inductor "see" this load as a short (very heavy load) but not so heavy that it becomes a brick wall to the extra energy produced and cap will not full any faster or higher or fill at all...so sort of perfect world in cap's internal resistance is needed where inductor sees a short and cap size just right so it works as receptor and "resonant chamber"
I would guess if Pierre did not pre-fill his caps his DZ generator would not work at all...

listener192

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A couple of points about the BTS7960B bridge boards.
They are missing a recommended 270nf cap across the supply rails close to each device.
Overvoltage protection kicks in at 27.5V which turns on the HSS and turns off the LSS.

If this gets invoked, then other LSS's will be on sequentially throughout the switching sequence, effectively causing the on HSS device to conduct current continuously.
This is not desirable behavior in this application.
 The later  BTN8962TA device that replaces the BTS7960B, does not have this feature, relying only on thermal and current limitation.

The BTN8962TA pulse current rating is higher than the BTS7960B however, the continuous current rating is only 30A compared with 40A. Otherwise the the later device is pin for pin compatible.

A few weeks ago I had a mysterious failure of a single high side device , while the supply was increase to 30V and I attribute this to the over-voltage protection. The device in question had a permanent HSS short afterwards.

Just a warning for anybody using these boards that wants to increase supply voltage, to achieve the same current at higher switching speeds.

L192

 
 
« Last Edit: June 25, 2018, 06:50:44 PM by listener192 »

listener192

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In an AC generator, with a DC energised rotor, the flux splits and travels round the stator to the opposite rotor pole, largely closing the flux.
In the DZ generator, each adjacent pole pair is energised at the same time. With a N and S in registration with the rotor, some of the flux will tend to close through the airgap between the adjacent pole rather than close through the stator to the opposite pole. This is a large difference between the generator types.

Experiment:
If you remove 2 poles, 1  from either side of the stator and then switch the remaining poles back and forth i.e. clockwise then anti-clockwise,  the poles will always couple flux fully through both sides of the stator and across the rotor.
Rotating the poles continuously in the same direction would just use more switch steps than required, as rotor induction only need be over a limited angle of arc. Some pole separation would decrease the flux cancellation.

L192

listener192

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Here is a drawing of the diodes in action that Pierre drew on the back board in one of his videos.   You should see why we have to shut off the field in rotation now.  Keep the code the same using overlap mode.  This also explains why you do not want the coils in series.  You want to isolate the field(s) and you can run them in parallel.
No the field is not shut off in rotation. This waveform shows a pulsed signal riding on top of the output sine, these are not recovery pulses, although as there is pulsing, there could be recovery current via the switch body diodes.

Attached is a simplified drawing of how this could be achieved.
Only a few MOSFET switches shown for clarity. Coil connections and switches remain unchanged only the supply rail is modified.

This could be accomplished with one relay or two MOSFETS.

L192
« Last Edit: June 27, 2018, 11:09:40 PM by listener192 »

Andy71

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Yes exactly
That's how I built it a few weeks ago.
For the coils to fully drive through please use PNP and NPN FET types.
I send you the circuit diagram again.

listener192

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Yes exactly
That's how I built it a few weeks ago.
For the coils to fully drive through please use PNP and NPN FET types.
I send you the circuit diagram again.
Hi Andy71,
I am using the BTS7960 bridge boards, so that it how they were connect from the start.
The main point of my post was not to show the waveform switches but to show how we could achieve the pulses that Pierre had riding on top of the sine waveform (see post 1186).

The only problem I see with your circuit is that you have no isolation for your MOSFET drives. One device failure could destroy an arduino digital pin, or even take out the whole board.
At some point in experimentation it is likely this will happen. I have had switch failures twice now as I have pushed current limits.

Regards
L192

listener192

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No the field is not shut off in rotation. This waveform shows a pulsed signal riding on top of the output sine, these are not recovery pulses, although as there is pulsing, there could be recovery current via the switch body diodes.

Attached is a simplified drawing of how this could be achieved.
Only a few MOSFET switches shown for clarity. Coil connections and switches remain unchanged only the supply rail is modified.

This could be accomplished with one relay or two MOSFET's as shown.

L192
Further points on this circuit...
There is never a period where all switches are off, so coil current is maintained.This is achieved with +25V.
The caps in series provide +50V to drive an ON/OFF pulse above the sine waveform (when looking at the output waveform) i.e. a further pulsed increase in current through the coils.

When the pulse turns OFF, the input caps have switched back to the parallel configuration +25V, this allows substantial current to flow through the body diodes back to C2, as the flyback voltage is 25V higher than C2 voltage.

The problem with this is I can't test it at +25V input, as the BTS7960B over voltage protection will turn on the HHS at +27.5V, as advised in a previous post.
So I could only test at say +12V.



L192
« Last Edit: June 28, 2018, 03:07:08 PM by listener192 »

listener192

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Attached is the result of the experiment, as shown in the circuit posted previously.
The cap charge scheme did not work very well, with the top cap only developing about 5V, so the bottom cap has about 25V, you can see this in the dark blue waveform.When the caps are switched in series, about 30V is developed. You can only see a very small increase in current due to the top cap not adding much voltage to the stack.
When the pulse is turned off, the rail drops back down to about 25V, however a large recovery current is developed into cap due to the lower potential on the parallel caps.
In this timing I am switching the overlap coil off immediately after the one preceding it is turned on, then apply the pulse (width determined by delay X), then followed by another delay X, followed by the next sequence.
The next experiment will be to use the circuit shown below. This should allow a decent current pulse and be able to show a large pulse voltage on top of the stepped output sine.Possibly the caps on the bridge boards will absorb some of the voltage pulse, as they charge from +12.5 volt to +25V.
Note: the external recovery diodes shown as D1 & 2, allow the coil flyback to recover directly onto the lower cap bank.If you were using relays a higher DC voltage could be used (compared to the BTS7960B device limits).

L192

listener192

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The experiment using the cap bank in two series sections was problematic with the top bank getting warm.
I changed over to the circuit attached, so just a single pulsed 25V DC supply.
The recovery voltage was enough to maintain the waveform between pulses.
In the second scope shot you can see the supposed recovery current however, I think this is actually just bleed through during the pulse period.
The first scope shot shows the output off load and the second on load. Not much in the way of voltage pulses.
I had the timing a little different in this run, so I will try also in the previous configuration.
Rotor induction is still poor, infact generally worse since I cut down the end of the rotor to 6 slots from 9.All this tells me is that I just reduced the flux linkage.


L192

listener192

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Long Poles:
This test reverts back to long poles which  briefly tried before. 
11 slot span rotates and reverses polarity on 2nd pass (visible in current waveform), still with (short) overlap, so there are no interleaving poles to short out the flux.
Output voltage in blue input current in yellow.Scope shots for unloaded and loaded output.
Not a bad output for only 2A RM,S  26.5 DCV input. The 6 pole configuration was running 10 times this current for the same off load output.

Note the unloaded waveform and the  spikes due to the increased inductance of 12 coils in series. The coil resistance and double the inductance is the limiting factor for current.Note a 50/60Hz output is achieved and if you reduce the switching rate this output does not increase.

The bridge boards will over volt at 27.5V, so current cannot be increased by increasing applied DC voltage.
So the only way to increase coil current is to reduce coil resistance and inductance, this means parallel coils which means breaking up the 360 degree series chain.
Of course this is just a reiteration of what Pierre has already disclosed.



L192

 

konehead

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Hi Listener
Not so bad looks like about 40W output for 52Winput (?)
Can you try paralleling just two coils of the "long pole" string?
Such as the first and the last coils,  (#1 and #11) then the "trapped" coils in between (#s 2 3 4 5 6 7 8 9 10) all these un-pulsed coils in between  become induced pickup windings, which will make power everytime the two energized parallel coils get some juice.
Maybe then string the 6 pole pattern then in series, not parallel so resistance is not so low and tons of amps is drawn however Pierre was talking about 160W input so you could put 3 times more power into it via it drawing more current...
Anyways just an idea!
Thanks for continuing your experimenting and reporting to everyone  what you find...

« Last Edit: July 02, 2018, 07:32:13 PM by konehead »

listener192

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No its only about 4.2W out for 52 W input. The scope shots are showing output voltage and input current.But there is no fall off in output voltage until you get above 150Hz, so 50/60Hz is achievable.

I am looking at how I can parallel drive 10 coils and then connect them in series at switch off.

Probably the reason that Pierre wanted to use a higher DC voltage was to get more current through the coils, as you can only do so much with parallel coil arrangements.
The BTS7960B half bridge devices become a real limitation, with regards to voltage. The BTN8962 half bridges can be operated up to 40V, performance only limited by their current limiter, whereas the BTS-7960B voltage limits at 27.5V.
Attached is the data sheet for the BTN8982 half bridge 50A continuous 40V  same pin out as BTS7960B. If the devices are replaced, this is the one to go for.

I noticed that 10 coils in series start to produce recovery current, on switch off. To get high levels of recovery current, either the cap potential need to be well below rail or the flyback voltage needs to be much higher than rail. The unloaded output voltage waveform starts to look more like that drawing with the spikes on the sine wave. The experiment pulsing the rail just didn't result in any meaningful voltage spikes.

I also noticed with this 10 coils scheme, that more flux is crossing the rotor, as at low frequency the rotor rotates unless firmly wedged.
The 6 pole scheme just lock the rotor in plus. PmgR's simulation shows that my rotor should be 3 stator poles wide instead of the 6 stator pole width I have an the rotor.
 L192

listener192

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Hi Listener
Not so bad looks like about 40W output for 52Winput (?)
Can you try paralleling just two coils of the "long pole" string?
Such as the first and the last coils,  (#1 and #11) then the "trapped" coils in between (#s 2 3 4 5 6 7 8 9 10) these two become induced pickup windings, which will make power everytime the two energized parallel coils get some juice.
Maybe then string the 6 pole pattern then in series, not parallel so resistance is not so low and tons of amps is drawn however Pierre was talking about 160W input so you could put 3 times more power into it via it drawing more current...
Anyways just an idea!
Thanks for continuing your experimenting and reporting to everyone  what you find...
Clarification 10 coils in series (between wire tap 1 and wire tap 11).

Jeg

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You can use two additional discreet MOSFETs (one on high side input and one on low side ground connection) with the body diode in reverse direction. So on high side the drain of one of these FETs would be connected to all the drains (Vdd inputs) of the high side H-bridges. On the low side the source of the other FET would be connected to all the sources of the low side H-bridges (GND/sense connection). In that way you have two body diodes in reverse all the time which will prevent any recovery through the body diodes.

PmgR

Hi pmgr
Can you please say some more on this? Do you mean just using the body diodes without driving those two mosfets? And if yes, is there any particular reason for choosing this method instead of two simple diodes?

Thanks

konehead

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Hi everyone
I made a mistake describing the idea I had, with only two coils (the end ones) of the string of 10 coils in a pole....I corrected it in my post a couple posts back.
Should read something like "all the un-pulsed coils in between become induced pickup winds" where before I described the coils in between as "these two" which made no sense
So I meant to say all those coils trapped and between the two energized pulsed coils become induced pickup coils....