Jim, The Schottky diode approach works best with a switching supply that is inherently current-limiting. Some linear supplies cannot start under load, following a power outage. Although it may take a day or two to recharge an AGM battery when it only sees the float voltage. Ideally, the AGM battery should be bulk-charged at a higher than normal voltage, and then put back on float voltage once it is fully charged.
But, that process involves a more complex and expensive setup than most folks want. My Schottky diode setup works just fine and is simple to implement. Some folks may argue that a low-voltage disconnect feature is needed, but many radios simply stop working once the supply voltage drops much below 9 or 10 volts- sort of a built-in LVD feature. Of course, some radios and controllers will continue to draw current all the way down to zero volts, and I avoid such power hogs for that reason. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jim Cicirello Sent: Monday, December 07, 2009 2:40 PM To: [email protected] Subject: RE: [Repeater-Builder] Astron RM-35M AGM charging abilities? Hi Eric, I have been trying to follow these posts on battery back power. Under this arrangement you describe, will the supply not get hot with the Schottky Diode in place if the battery is discharged very low? I am researching the best way to hook the battery to my Astron which does not have the back-up charger. Thanks for all of the information. 73 JIM KA2AJH From: [email protected] [mailto:[email protected]] On Behalf Of Mike Lyon Sent: Monday, December 07, 2009 12:45 PM To: [email protected] Subject: Re: [Repeater-Builder] Astron RM-35M AGM charging abilities? Sorry. Yes, it's a -BB version. -Mike On Mon, Dec 7, 2009 at 9:31 AM, Eric Lemmon <[email protected] <mailto:[email protected]> > wrote: Mike, I thought that only the RM-35M-BB has a battery backup circuit built-in; I have an RM-35M power supply in service, and it does not have a battery charging circuit. A very simple method of achieving no-break battery backup is to install a Schottky power diode on the positive output terminal of the power supply, and connect both the battery positive terminal and the radio power leads to the cathode lug of the diode. My preferred Schottky diode for this application is an International Rectifier 122NQ030R. The diode is mounted on a 1" wide copper bar that is placed on the power supply's positive output stud. The diode has a 1/4" output terminal, which makes it very easy to add to an existing system. Note that the "R" in the diode part number means that it is reverse polarity. The output voltage setting of the power supply must be increased about 1/2 volt to compensate for the forward voltage drop of the Schottky diode. The voltage should be set so that the AGM battery has the recommended float voltage at its terminals while the radios are operating and the system has stabilized at least 24 hours. This voltage will usually be around 14.2-14.5 VDC, depending upon the battery specifications. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> [mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Mike Lyon Sent: Sunday, December 06, 2009 10:02 PM To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> Subject: [Repeater-Builder] Astron RM-35M AGM charging abilities? Howdy Folks, I am wondering if anyone has experience with the Astron RM-35M and its built-in charging circuit? Has anyone used it to charge 12VDC AGM batteries? I have 3 motorola Maxtracs (2 RX, 1 TX) that are powered from this power supply and I need to put some backup power on the system. I am wondering, should I buy a separate charger for the AGM batteries (Qty. 2) or is the charging circuit within the the RM-35M sufficient? 73's, Mike Lyon KE6MRE
