----- Original Message ----- From: Jeff DePolo To: [email protected] Sent: Thursday, April 02, 2009 2:20 PM Subject: RE: [Repeater-Builder] Re: Anyone got a Amp-meter Circuit to Repeater Controller for Telementry Readback?
The classic textbook method would be to put a current shunt in series with your DC source and measure the voltage drop across it. A current shunt is just a precision low-value resistor capable of handling the thru-current, nothing fancy about it. But, at low voltages (like 12V) and low currents (like a few tens of amps), you end up with small voltages across the shunt in the practical world. The resistance of the shunt has to be kept very low, like in the hundreths or thousandths of an ohm, to minimize power loss through the shunt. A 0.001 ohm shunt would only give you 50 mV with 50A through it. Going to 0.01 ohms would give you 500 mV across the shunt at 50A, but obviously you've also dropped the voltage going to the equipment by 500 mV, and since you're running on solar/batteries, losing half a volt under load probably isn't ideal. So, keeping the R low and using DC amplification will probably be necessary when using a traditional current shunt in an installation like this to get any useful resolution out of your controller's A/D converter. A more-modern approach would be to use a Hall effect current sensor. Hall effect sensors come in various flavors, anything from a bare-bones IC that you can use to build your own, or as ready-to-go packaged modules that you your DC+ conductor through, supply it with DC power, and it gives you a sample voltage output (typically 0-5V) proportional to the current through the sensor. Do some web searches and you should find all kinds of info. CR Magnetics comes to mind for off-the-shelf units. --- Jeff WN3A > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Gmail > - Kevin, Natalia, Stacey & Rochelle > Sent: Thursday, April 02, 2009 3:43 PM > To: [email protected] > Subject: Re: [Repeater-Builder] Re: Anyone got a Amp-meter > Circuit to Repeater Controller for Telementry Readback? > > Hi Martin, > > This is a 13.8v system, run off batteries and solar cells, > the reason to be able to monitor current, charging the > batteries and current drain from the repeater system. > I can monitor volts ok, just those damm amps running around. > > Kevin, ZL1KFM. > > > ----- Original Message ----- > From: rahwayflynn <mailto:[email protected]> > To: [email protected] > <mailto:[email protected]> > Sent: Friday, April 03, 2009 12:31 AM > Subject: [Repeater-Builder] Re: Anyone got a Amp-meter > Circuit to Repeater Controller for Telementry Readback? > > > --- In [email protected] > <mailto:[email protected]> , "Gmail - Kevin, > Natalia, Stacey & Rochelle" <spar...@...> wrote: > > > > Hi All, > > > > I am in need of a circuit to read amps to my controller. > > Want to be able to read the current being used at the > repeater site as well as the charging current to the batteries. > > Kevin, > Is your rack on a single phase feed? If so, placing a > current transformer in the black lead will give you a output > current proportional to to the input. Put a resistor across > it and use the voltage input to the controller. The downside > to this approach is the controller will "talk" the current > and label it "volts". > > Martin > > > > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.0.238 / Virus Database: 270.11.3/1970 - Release > Date: 04/02/09 06:09:00 > > >
