ADICON Support Forum Applied Digital, Inc.
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#13436 - 03/12/03 09:36 AM More on power.....
M. Scott Offline
newbie


Registered: 03/11/03
Posts: 6
Loc: New Hampshire
I have an Ocelot and just got a SECU-16. My first question is about the SECU-16- there are two power screws- and no polarity. It says it will accept power between 9-12 AC or DC- so my guess is that they full wave rectify whatever you give it inside- so it probably doesn't matter. Is this so? So I guess there is no grounding of this thing?!

So now lets assume I get a 12VDC power supply (a beefy one that will do several amps) and park it next to my Ocelot. I want to daisy chain all my Adicons together (I will probably be buying more). If I put them rather far apart- say 30 feet for now- how thick does the wire need to be. Is there enough internal capacitance on this thing or would I need an external cap. I guess it can handle voltages down to 9 VDC- so it should be ok. It says it needs 250mA- so I guess I could calculate the thickness I need- but I am looking for some experience. I was hoping to use one piece of cat 5 and use one pair for the two comm signals- then I was going to split the three unused pairs and wire up three of the wires to power and three to ground. Any feedback- good idea? Bad idea? Noise problems?

Thanks,
Mike Scott

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#13437 - 03/12/03 10:16 AM Re: More on power.....
Mike Chwojdak Offline
journeyman


Registered: 01/15/03
Posts: 86
Loc: Rochester, NY
The ADI units have diodes and filter caps on the inputs so they can handle AC or either polarity DC to make for a mistake proof installation. The resistance of the wire used in CAT 5 cable coupled with the low draw of the modules makes it ideal for connecting them. I have an Ocelot talking to a SECU16I 100 feet away using Cat 5 cable for comms and power. If you want to be conservative you can parallel two or three pairs for the power. Care needs to be taken in selecting a power source. A unregulated "wall wart" rated for 12 volts at 1 amp will measure 12 volts at the full load of 1 amp. At a smaller load of say 200 mA, the voltage could be as high as 18 volts or more. This is beyond the ADI spec.
The exception to paralleling is the Speakeasy module which requires a separate 12 VAC supply for good sound quality I am told.

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#13438 - 03/12/03 10:46 AM Re: More on power.....
Guy Lavoie Administrator Offline
Beyond All Hope
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Registered: 12/21/02
Posts: 6548
Loc: Montreal, QC, Canada
The other thing to be careful about is related to the presence of the bridge rectifier on the power supply input to the modules: you cannot use the same power source to power both the modules and anything connected to the module's inputs, because there is no "common" between the power source and the logic common terminal.
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#13439 - 03/12/03 12:17 PM Re: More on power.....
gregking Offline
newbie


Registered: 02/19/03
Posts: 7
Loc: Lewisville,Tx
This is the kind of gotcha's that I was wondering about in my question about using a PC power supply.

I think they are typically "regulated", but I didn't really understand what that meant. Is it correct to equate "regulated" with delivering a nice constant xxx volts?

greg

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#13440 - 03/12/03 12:25 PM Re: More on power.....
cyborg1701d Offline
junior


Registered: 02/13/03
Posts: 43
Loc: chicago
if you use a pc power supply with the 12v out can you use another output from the same power supply to turn on a 12v relay. I want to have the sedc16 relay pass the 12v to another 12 external relay to trigger a larger voltage move.
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#13441 - 03/12/03 12:27 PM Re: More on power.....
Guy Lavoie Administrator Offline
Beyond All Hope
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Registered: 12/21/02
Posts: 6548
Loc: Montreal, QC, Canada
That's right. A regulated power supply monitors the voltage at it's output and will regulate the flow of current to maintain the voltage at the designed value. If the load draws more current then it will respond accordingly to maintain the voltage level. This is similar to a cruise control on a car that will "press" the gas pedal harder if the car is going up a hill in order to maintain the set speed.
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#13442 - 03/12/03 12:45 PM Re: More on power.....
M. Scott Offline
newbie


Registered: 03/11/03
Posts: 6
Loc: New Hampshire
When you say that you cannot use the same 12V supply on the inputs- you are assuming that the ground is not brought over as well and tied in?
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#13443 - 03/12/03 12:56 PM Re: More on power.....
Guy Lavoie Administrator Offline
Beyond All Hope
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Registered: 12/21/02
Posts: 6548
Loc: Montreal, QC, Canada
What I'm saying is that due to the presence of the bridge rectifier, even if you use a DC power source for the modules, the supply's "ground" will be about 0.7 volts higher then the module's "common" terminal; this is the normal voltage drop of a forward biased rectifier diode. If you try to connect the two together, you will short out the diode in question. With a DC source this would probably still work ok and the supply positive would be about 0.7 volts lower (due to the diode also in it's path) giving you around 11.3 volts DC in the module. With an AC source, you might damage the module because of the polarity inversion every half cycle.
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#13444 - 03/12/03 06:11 PM Re: More on power.....
cyborg1701d Offline
junior


Registered: 02/13/03
Posts: 43
Loc: chicago
I will agree with you but if i am just using the voltage on the switch side of the relay to send voltage to the other relay to turn on it should not matter becuse they never see each other. one side feeds the unit and the other is used just to turn on a dc relay. then only common is before the full wave. i do not want to use it for a sensor input only output relays.

or am i just dreaming.

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#13445 - 03/12/03 06:22 PM Re: More on power.....
Guy Lavoie Administrator Offline
Beyond All Hope
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Registered: 12/21/02
Posts: 6548
Loc: Montreal, QC, Canada
That's right, there's no problem with relay outputs because they are just dry contacts (ie: not connected to any power inside the modules). As my post above says, the problem is with module inputs.
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"If you don't know what you're doing, do it neatly..."

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#13446 - 03/13/03 03:40 AM Re: More on power.....
M. Scott Offline
newbie


Registered: 03/11/03
Posts: 6
Loc: New Hampshire
This is good information.

So I am planning on using an analog input and was going to divide my 12 V source down varying on which contacts are shut. I guess my values will need to be recalculated with 11.3V.

Is the drop really as high as .7V? That seems high for a device which is drawing just 200mA. I guess I could always dig out the fluke and measure it :-)

Had much success playing with the modules last night- thanks for the help.

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#13447 - 03/13/03 04:22 AM Re: More on power.....
Mike Chwojdak Offline
journeyman


Registered: 01/15/03
Posts: 86
Loc: Rochester, NY
The forward drop of a diode is constant regardless of load. Its part of the reason they call them semiconductors. Schottky diodes have only a drop of 0.3 Volts. ADI's input design is typical of alarm panels which are fed by 12 volt AC transformers. The alarm panels are nice enough to feed out 12 volts DC to power various devices like smoke and motion detectors.
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#13448 - 03/13/03 04:40 AM Re: More on power.....
Guy Lavoie Administrator Offline
Beyond All Hope
*****

Registered: 12/21/02
Posts: 6548
Loc: Montreal, QC, Canada
Scott, it's a bit more complex then that. Let me explain it in detail: A forward biased silicon diode will drop about 0.7 volts, which will vary slightly depending on current. It doesn't behave as a linear resistance whereby the drop would be proportional to the current (ohm's law).

Now let's look at the voltage levels at every point in the circuit (respective to the power supply's common, or - terminal) to understand what happens. Let's assume a 12 volt DC regulated power supply is connected as the power source for your modules. The voltage starts at +12V and goes through one of the diodes of the bridge rectifier in the module. The regulator inside the module sees a level of +11.3V. the power then "exits" the module going through another diode of the bridge rectifier before reaching the power supply common, so the module's common is actually at 0.7 volts, goes through the diode, and then gets to 0 v at the supply common.

Now imagine that you're connecting a sensor that puts out a 0 - 5V signal and you're powering the sensor from the same power supply. When that sensor is connected to the module's input, the module will actually see the input as ranging from 0.7 to 5.7 volts since it's common is 0.7 volts above the power supply's and sensor's common. The readings will be skewed. You might try and limit the output range of the sensor and/or subtract an offset for the reading in your program to account for the difference, or even power the sensor using a forward biased diode in series with each power terminal to bring the levels more or less together by simulating the module's bridge rectifier for the sensor, but not having the commons actually connected together could cause falkey readings.

All that to say that while it can be done, it's not the recommended approach and doesn't really appear to be worth the trouble that can be avoided with a $5 wall wart.

Note: Inside the module, the voltage supplying the module is not 12 volts but 10.6 since we're going through two diodes. Note that most modules use a 7805 regulator that produces 5 volts so this level is not a problem.
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"If you don't know what you're doing, do it neatly..."

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#13449 - 03/13/03 06:23 AM Re: More on power.....
M. Scott Offline
newbie


Registered: 03/11/03
Posts: 6
Loc: New Hampshire
The drop is certainly not constant and it is definitely load dependant. Moveover, it is very temperature dependant. When the SECU can detect voltages changes of 100mV (is this correct?! I haven't played with this part yet- recall it was like 90mV and change)- the varying in the drop matters. However, the V-I curve is steep- so once I measure what is actually is in my enviornment, it should change little.

Regardless, I understand what you are saying Guy- it is your basic diode bridge and the voltages will vary depending on what you call "ground".

In considering my setup more- I am probably just going to go with supervised inputs anyways. :-)

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#13450 - 03/13/03 06:58 AM Re: More on power.....
Guy Lavoie Administrator Offline
Beyond All Hope
*****

Registered: 12/21/02
Posts: 6548
Loc: Montreal, QC, Canada
An analog SECU16 input can detect a change of about 20 mV (19.6 mV to be exact). This corresponds to 5 volts divided into 255 steps.
_________________________
"If you don't know what you're doing, do it neatly..."

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#13451 - 03/16/03 09:21 AM Re: More on power.....
JC Offline
journeyman


Registered: 02/12/03
Posts: 67
Loc: Mascouche, Quebec, Canada
If you're using a DC power supply, connect the - to the COMMON terminal of the SECU16 and + to any POWER terminal. The bridge will route the + to the appropriate place in the regulator circuit.

Have done this and it works fine. Common is common everywhere.

DO NOT DO THIS WITH AN AC SUPPLY.
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