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mdnanwelch7(at)hotmail.co
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 Posted: Wed Apr 21, 2010 5:51 pm Post subject: Designing a circuit question |
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Dennis,
Upon close inspection of the current in Bob's design, yup, you're right about the current direction.
Back to my idea. I suppose the ammeter might not be too bad of a direction to go, but I still like the idea of a line of 5-6 LEDs, which is an indication of the prop's motor current load. Would this be a simple circuit, and very importantly, can it be a modification to the one Bob came up with? I can sure see an advantage to a combo circuit.....one that shows you visually that you are increasing the current, and eventually the final LED, indicating near max current?
Mike Welch
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nuckolls.bob(at)aeroelect
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| Posted: Wed Apr 21, 2010 10:06 pm Post subject: Designing a circuit question |
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At 01:34 PM 4/21/2010, you wrote:
| Quote: | 'Lectric Bob,
I REALLY like your circuit design regarding the IvoProp
motor. In fact, I'm planning on building one, seeing as how I have
an IvoProp...with the motor.
If I understand the process correctly, by pushing the dpdt
switch, when the motor sees 6 A current, the LED will light
up. Let go of the dpdt switch quickly, and you're in like Flynn.
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Yes, the motor will see pretty much full bus
voltage until it's draw exceeds the set-point for
the current limiter. The votlage to the motor is
reduced at that point to maintain a max current
equal to setpoint. If that value is too low, it
can be increased by paralleling the .1 ohm reistor
with additional resistors as I described earlier
today.
| Quote: |
Here's my question: would it be much of a challenge for the
motor to lighten multiple LEDs (in both directions), as it cycles
from 0 to 10A? Of course, you'd want two separate circuits
indicating if you're headed to flat pitch...or steep pitch, or some
method to insure you're twisting the prop in the correct direction
you intended to.
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That's a given depending on your switch. It's a spring
loaded center off with one direction for increased pitch
and the opposite direction for flatter pitch.
| Quote: | Wouldn't this design I'm asking about be essentially an analog
version of a current meter? Example: say you're at zero pitch,
and you cycle toward steep pitch. As the motor's current draw
increases, it could light a 1A LED, then a 2A LED, a 3A LED, etc, etc.
Same process for the other prop twist.
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No, it doesn't work that way. This light comes on only
when the motor stalls against the stop at either max
or min pitch. It's not intended to be a pitch value
indicator.
| Quote: |
If a guy had this type of design he could routinely set his prop
pitch to a known LED position to achieve maximum value of a
variable pitch prop. He could adjust his engine and prop (LED) to
a known performance characteristic.....i.e......engine rpm 4750,
pitch in the steep direction #5 LED.
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I doubt that exact pitch is that tightly
associated with motor current. However, it wouldn't
be too hard to build a constant speed controller
not unlike that electro-mechanical prop-pitch
controller on the old Bonanzas . . . except
this one would work better.
It would be slow . . . but it could be quite
accurate. When you increased manifold pressure
at some prop pitch setting, you would see an immediate
increase in rpm but it would come back to the set-point
a few seconds after the power increase.
I'm fiddling with a variant of the circuit I
published to convert it to a solid state breaker
instead of current limiter. In this case, you
wouldn't need any heat sink because the device
would be in the current limited mode for a few
tens of milliseconds.
I'll see if I can publish that variant tomorro evening.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Thu Apr 22, 2010 6:27 am Post subject: Designing a circuit question |
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At 08:50 PM 4/21/2010, you wrote:
| Quote: | Dennis,
Upon close inspection of the current in Bob's design, yup, you're
right about the current direction.
Back to my idea. I suppose the ammeter might not be too bad of a
direction to go, but I still like the idea of a line of 5-6 LEDs,
which is an indication of the prop's motor current load. Would
this be a simple circuit, and very importantly, can it be a
modification to the one Bob came up with? I can sure see an
advantage to a combo circuit.....one that shows you visually that
you are increasing the current, and eventually the final LED,
indicating near max current?
|
There are integrated circuits designed to
drive a totem pole of leds. They're common
to many audio systems where a solid state
"VU Meter" is implemented with a gaggle of
leds. See:
http://www.national.com/ds/LM/LM3915.pdf#page=1
You would need a shunt, an op-amp signal
conditioner and the LM3915. This is not
a trivial task to configure. The analog meter
and shunt would be much simpler to implement.
One of our miniature loadmeters could be combined
with a custom shunt.
Bob . . .
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dennis.glaeser(at)hp.com
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| Posted: Thu Apr 22, 2010 6:44 am Post subject: Designing a circuit question |
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Mike,
I think there are ammeters that have LED indicators - but I am definitely NOT the expert on such things. It wouldn't be a mod to Bob's circuit. You could have both an ammeter to show the increasing current and Bob's circuit to indicate and limit max current.
Dennis
----------------------------------------------------
From: Mike Welch
Dennis,
Upon close inspection of the current in Bob's design, yup, you're right about the current direction.
Back to my idea. I suppose the ammeter might not be too bad of a direction to go, but I still like the idea of a line of 5-6 LEDs, which is an indication of the prop's motor current load. Would this be a simple circuit, and very importantly, can it be a modification to the one Bob came up with? I can sure see an advantage to a combo circuit.....one that shows you visually that you are increasing the current, and eventually the final LED, indicating near max current?
Mike Welch
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deej(at)deej.net
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mdnanwelch7(at)hotmail.co
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| Posted: Sat Apr 24, 2010 1:45 pm Post subject: Designing a circuit question |
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| Quote: | I'm fiddling with a variant of the circuit I
published to convert it to a solid state breaker
instead of current limiter.
I'll see if I can publish that variant tomorro evening.
Bob . . .
|
Hi Bob,
If you are still working on this solid state design you talked about, I was wondering if it would be possible to incorporate a feature that allows the user to set for different loads.
In other words, a 2amp setting, a 3 amp setting, etc, etc.........or did you intend on this, anyway?
I'm really looking forward to what you come up with. I definitely plan on building it!!
Mike Welch
Do Not Archive
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nuckolls.bob(at)aeroelect
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| Posted: Sun Apr 25, 2010 6:02 am Post subject: Designing a circuit question |
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At 04:39 PM 4/24/2010, you wrote:
| Quote: | > I'm fiddling with a variant of the circuit I
> published to convert it to a solid state breaker
> instead of current limiter.
> I'll see if I can publish that variant tomorro evening.
>
> Bob . . .
Hi Bob,
If you are still working on this solid state design you talked
about, I was wondering if it would be possible to incorporate a
feature that allows the user to set for different loads.
In other words, a 2amp setting, a 3 amp setting, etc,
etc..........or did you intend on this, anyway?
I'm really looking forward to what you come up with. I
definitely plan on building it!!
|
Thanks! There is no greater validation of
an recipe for success than multiple experiences
by multiple chefs in their own kitchens.
I suspect there are some other folks on the list
who might have some ideas about how to synthesize
all silicon circuit breaker.
Getting it to trip at the right current isn't hard.
What we need to keep in mind about thermal circuit
breakers is their I(squared)*R tripping dynamic
that gives them some degree of immunity to inrush
tripping.
In the design study before us, we're dealing with
a PM DC motor that has a significant inrush
characteristic. so what we'll want to do for THIS
case is design a 'breaker' that is also a current
limiter but with some form of trip-delay . . . say
something on the order of 200 milliseconds.
I'm mulling over several ideas for minimizing
parts count while meeting design goals. Any
electron herders out there want to swap ideas?
Bob . . .
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