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Offline sloTopic starter

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many parallel power supplies
« on: July 30, 2008, 07:43:44 PM »
My first bot (in 70% complete build state) has many different power supply needs listed at end.   Most things run off lead acid 12v bus battery with linear regulators(problems there).  While that and a smaller 12v lead acid battery in series supply drive power and 2 sensors. 
First question is such an unbalanced system safe and practical?  My only battery charger is a single 12v Schumacher SC-6000A which I apply alternately to each battery in turn without disconnecting anything, often while parts of the bot are still operating (for example the computer I am typing this on right now.)
Second, I made a perfboard with LM317t R1=220 R2=1k  C1=0.1uF on input, no output cap for 7v microcontroller supply(works).  On the same board with parallel 12v input is a 7805 regulator with no caps(never worked).  I verified no solder bridges, 12v and ground is present at 7805 pins but no output (actually fluctuating voltage around 200mV).  I tried 3 different 7805 chips.  Load for test is a 6v 25mA lamp.  Could the other regulator somehow interfere with the 7805?  Do I really need to add caps?  Is there a better way to do this?  The speed controller provides a 10ma 5V regulated output is there a way to boost this with a transistor?  I am still learning electronics.  For the 4.5v for GPS I planned to simply insert a diode in the 5v supply to drop .7v.  Does anyone know what specs the rino serial interface is?  The stock cable is a 9 pin PC serial but I find it hard to believe it is RS-232 +/-15v from 3 AA batteries.  I had to build a custom cable to provide power at the same time as communication.  I don't have an oscilloscope. 

  24v 15A each for 2 wheelchair motors(Dimension engineering sabertooth 2x25), 18-30v 4w for 2 ultrasonic sensors, 6-24v 125w computer supply(M3 from logic supply) 10-30v for Omron photoelectric switch and capacitive proximity sensor, 12v nominal for LCD monitor 3A, wireless router 12v 1A, pyrosensor 9v nominal, 7v for microcontroller (currently Vex, may change to Axon, Arduino, or other), 5V for 4line serial LCD display, DE 3 axis analog accelerometer,  plus other sensors, logic switches, LEDs, etc, 4.5v MAX for Garmin rino GPS/FRS radio

Offline airman00

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Re: many parallel power supplies
« Reply #1 on: July 30, 2008, 07:51:58 PM »
Best way is to all use one main power source and make sure to use switching regulators - more efficient
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Offline sloTopic starter

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Re: many parallel power supplies
« Reply #2 on: July 30, 2008, 09:12:33 PM »
What are the advantages of a single power source? 
At this point I am nearly out of money and have already spent way too much for what was originally supposed to be simply a range extender for my wireless network.
As is I have a great deal of redundancy built in.  If the computer drains the large battery the drive battery remains unaffected I think, so I should be able to limp it home or swap it in if I'm doing something critical.  The computer supply is a switching unit I believe and it imparts a slight distortion to the monitor.  I worry that additional switching units with different frequencies will make it worse.

Offline airman00

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Re: many parallel power supplies
« Reply #3 on: July 31, 2008, 05:27:32 AM »
The reason you want one power source is that it's easier to charge and its a cleaner electronics setup 

Truthfully you could use separate batteries and then use a special connector which is the output from multiple chargers :P
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

www.Narobo.com

Offline brijesh

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Re: many parallel power supplies
« Reply #4 on: July 31, 2008, 02:46:50 PM »
7805 with no caps at the output does not work. I can tell you from my experience, did that once and didn't work.

Offline sloTopic starter

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Re: many parallel power supplies
« Reply #5 on: August 07, 2008, 08:54:05 PM »
Added .1uF output cap and .22uF input and it now works.  Strange as these were advertised as needing "no external components".  Thanks brijesh.

Offline ceruleanplains

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Re: many parallel power supplies
« Reply #6 on: August 15, 2008, 10:09:48 AM »
my guess is your voltage input was oscillating and screwed with your chip - did you hook it up to a scope by chance?

Offline Iron Man

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Re: many parallel power supplies
« Reply #7 on: August 15, 2008, 11:23:36 AM »
he doesn't have a scope.

Offline Spoil9

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Re: many parallel power supplies
« Reply #8 on: August 16, 2008, 09:17:33 AM »
About the 7805, I'm using one I bought from Radio Shack to power a PIR and a remote doorbell set up I built. I am not using any caps on it and everything seems to be working fine. Do you only need caps on the 7805 when working with high drain items or should I go back and add one?

I don't have a schematic on hand now, but basically what I'm doing is running a 9V battery through a 7805 which powers a 5V PIR sensor. When the sensor "see's" motion it trips a transistor that allows power to flow from the 7805 to a remote doorbell that has been shorted. The idea is that when this thing sees motion, I'll hear a doorbell alarm in another room of the house, garage, etc.
So far, no caps, no problems.
Knowledge is Power. Power Corrupts. Study Hard. Be Evil.

Offline Iron Man

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Re: many parallel power supplies
« Reply #9 on: August 17, 2008, 12:29:30 PM »
spoil9,
i hope you don't have many cats in your neighborhood.

Offline Admin

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Re: many parallel power supplies
« Reply #10 on: August 22, 2008, 10:23:47 PM »
Quote
About the 7805, I'm using one I bought from Radio Shack to power a PIR and a remote doorbell set up I built. I am not using any caps on it and everything seems to be working fine. Do you only need caps on the 7805 when working with high drain items or should I go back and add one?
The caps are useful for 'sudden drain' situations, like with motors, or turning things on and off. But if your circuit uses current at a steady rate, the caps are pretty much useless.

Offline Spoil9

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Re: many parallel power supplies
« Reply #11 on: August 28, 2008, 09:32:29 PM »
sweet, thanks Admin.
Knowledge is Power. Power Corrupts. Study Hard. Be Evil.

 


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