I'm no analog electronics expert by any definition of the word so I apologize if this question is stupid. I'm looking for a device ( preferably no assembly required ) that functions as the hypothetical device in the subject : something that takes a control voltage of 0-12 volts and adjusts the output from a voltage source ( a power supply ) from 0-24 volts linearly w.r.t the control voltage while handling up to 80 watts of power.
Heh. Yeah. That was the first thing I thought of. I did many extensive Google searches but came up with nothing that really fit my needs. ( or my wallet )
Thanks. I was using "voltage controlled" power supply. Maybe I'll get more relevant results with this.
While the voltage-controlled power supply already mentioned will fill the bill, we might be able to suggest a different (less expensive, etc) approach if you gave us the "big picture" of what you are trying to do.
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Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis
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I've done numerous Google searches with many variants on "voltage programmable power supply" but almost all the results are irrelevant as they're "high voltage -- programmable power supply" . When excluding "high" there are only a few hits, mostly patents, that refer to "voltage controlled power supply" but don't specify any model. The only real info I got was from this message :
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:
"I'd look at something like a used HP 6266B, which will give you 0 to
40V at 5 Amps. You can program it from an external voltage or current source (or resistance source, with opt. 002). Programming speed isn't too fast, but it is sufficient for most ATE apps. "
When I looked at the specs of said supply on eBay, it indicated it was "analog programmable" and had "sense" inputs. So, I searched again but this time I used "analog programmable" -- got a truckload of hits. Unfortunately when the search is restricted to only those hits that have a service manual, then it's down to only a few hundred. Even in the service manuals though, I've yet to find a complete description of the "analog programming" process, only a mention that the device supports "analog programming" .
I have an automatic DC fan controller that can vary the voltage depending on a temperature sensor between 0 and 12 volts while being able to handle 20 watts of power. The problem is that the fan I need uses 24 volts and over 70 watts at max voltage.
--
Maybe.
What \'analog programming\' is referring to is that the supply\'s
output voltage can be controlled by (instead of cranking the knob(s)
on its front panel) connecting a voltage source, a current source,
or a resistance to some terminal blocks on the rear panel of the
supply.
From your more recent post:
"I have an automatic DC fan controller that can vary the voltage
depending on a temperature sensor between 0 and 12 volts while
being able to handle 20 watts of power. The problem is that the fan
I need uses 24 volts and over 70 watts at max voltage."
and from an earlier post:
I\'m looking for a device ( preferably no assembly required ) that
functions as the hypothetical device in the subject : something that
takes a control voltage of 0-12 volts and adjusts the output from a
voltage source ( a power supply ) from 0-24 volts linearly w.r.t the
control voltage while handling up to 80 watts of power.
It appears that what you\'d like to be able to do is use the 0 to 12V
output from the controller as a control signal to drive the larger
power supply needed to drive the 70 watt fan.
Something Like this: (View in Courier)
MAINS>----------------------+
|
+----------+ |
MAINS?>--| | |
| | |
+----| | +---+---+ +---+
| | |---| +|---|+ |
[SENSOR] |CONTROLLER| |SUPPLY | |FAN|
| | |---| -|---|- |
+----| | +---+---+ +---+
| | |
MAINS?>--| | |
+----------+ |
|
MAINS>----------------------+
where the connections to the supply voltage control terminals are
the outputs from the controller?
Please allow me to stimulate some other ideas out there:
If you really need an "analog" output to drive your fan motor, you might want to consider using a power op-amp (Apex at
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is a good source). They can be used just like regular op-amps (i.e. be configured as voltage followers, or with a DC gain of 2 -- to convert your 0-12V input into a 0-24V output. Bear in mind that the op-amp supply voltage would probably need to be a few volts higher than the required op-amp output voltage. Apex apps or sales engineers could probably suggest an appropriate device and circuit.
However, your existing DC fan motor might be happy being driven via a "PWM" (pulse width modulator) driver. PWM drivers are more compact, require a much smaller heat sink (i.e. are much more efficient), and would be much cheaper. If your motor can be driven via PWM, that is probably the most sensible way to go. The easiest approach is to simply buy an appropriate "motor driver", available from most motor distributers. Many will accept a DC control signal of 0-10V (which can easily be derived from your 0-12V signal via a resistor or two.)
--
OK, what do you want to do now, and how much money do you have
available to throw at getting the problem solved? Material, that
is. As long as I don\'t have to start wielding a soldering iron
I\'ll be happy to help you for free, :-)
BTW, do you have a schematic or a link to the controller\'s data
sheet?
Nah. But I want you to come over to my house and complete the construction of my 20 ft tall Tesla coil -- I have completed the first steps : ordering the plans. ;) :P
On Tue, 1 Jan 2008 11:08:36 -0800 (PST), Jonathan Busby wrote:
--- OK, since it's a brushless fan it's not really designed to be pulse-width modulated and since you've got a $100 cap on the project, here's what I'd do: (View in Courier)
A1 is a Kepco RKW 24-4.5K, $79, (or an RKW 24-6.5K for $99) from Kepco at:
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A2 can be pretty much any 12V wall-wart you might have laying around as long as its output stays under 15V under high line and no load conditions.
You'll probably need a heat sink for the MOSFET, but I haven't got a good handle on what current VS voltage looks like for a brushless motor. However, assuming that the relationship is roughly linear means that with 24V across the fan pulling 3.25A through it, 14V (at the low end of its range) will pull:
14V ----- = 0.583 of 3.25A, 24V
So:
0.583 * 3.25A = 1.89A.
With the supply at 24V and the fan at 14V means the MOSFET is dropping 10 volts with 1.89 amps through it, so it's dissipating:
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