Jim, You're welcome! By definition, a "float voltage" cannot cook a battery, since it is the voltage that the battery manufacturer specifies for indefinite connection. This is what gel-cells used in alarm systems and emergency lights are charged to, and they are floated continuously, 24/7/365.
Ironically, many low-voltage-cutoff devices consume power to operate, and so hasten the discharge of the battery. Such devices should be chosen with care, especially if an extended power outage is a very rare event. After all, if your repeater is at a shared commercial site, I don't think power restoration is going to take long. Most gel-cells can handle a few deep discharges will no lasting damage. While it's true that some repeater owners believe that a low-voltage cutoff is absolutely necessary, it's also true that many stations simply stop working when the input voltage drops below a certain level, and therefore comprise a built-in low-voltage cutoff!! I specify Schottky diodes for power switching, simply because they have very low forward voltage drop- usually around -.4 VDC. The power dissipated in such a diode is so small that no heat sink is normally needed. I usually mount the diode right on the output terminal of the power supply. I use a short piece of one inch wide, 1/4 inch thick copper bar to mount an International Rectifier #122NQ030R Schottky diode, which itself has a 1/4-20 terminal screw. Very rugged and very reliable. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of kh6...@netscape.net Sent: Monday, May 31, 2010 11:52 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Astron switching supply for Battery Charger?? Eric, thanks for your email. What are your comments on a cut-off circuit to open the battery charger, when the battery is fully charged? I would not like to 'cook' the battery. What about a a low voltage circuit that opens the load, for long periods of no AC? I acquired the diodes from Astron, where is the best place to mount the diode/heat sinks? On the power supply or on a rack panel, with good wires from the terminals to the diode terminals. Thank you for your comments. 73's, Jim Kh6jkg. -----Original Message----- From: Eric Lemmon <wb6...@verizon.net> To: Repeater-Builder@yahoogroups.com Sent: Mon, May 31, 2010 5:00 am Subject: RE: [Repeater-Builder] Astron switching supply for Battery Charger?? John, There's nothing about a switching power supply that might disqualify it for battery float service. However, you should isolate the output of any power supply from the battery with a Schottky diode, so that a failure within the power supply- or the firing of the crowbar SCR- will not impose a dead short on the battery. After determining the correct float voltage for your battery plant, say, 14.2 VDC, set the output voltage of the power supply slightly higher to account for the small forward voltage drop of the Schottky diode. The load should be connected directly to the battery, not to the power supply. I have several Astron switching power supplies in service, along with several similar units made by Duracomm and Samlex. They have all been extremely reliable, and the high switching frequency results in no perceptible buzz or ripple in the output. A decade ago, some switchers were poorly designed and radiated spurious signals into the HF bands, but none of the name-brand switchers produced today have that problem. In fact, Motorola uses Duracomm and Astec switching power supplies in most of its commercial repeater equipment. One thing to be aware of is that some Astron power supplies, both linear and switching, have an internal jumper that ties the negative output to chassis ground. This jumper must be removed to avoid some problems with ground loops and erratic controller functions. The presence of this jumper can be tested by measuring the DC resistance between the grounding prong of the AC power plug and the negative output terminal. If the resistance is above 10,000 ohms, you're good to go. Otherwise, you've got to get under the hood... 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> [mailto:Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of ab6li Sent: Monday, May 31, 2010 7:31 AM To: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> Subject: [Repeater-Builder] Astron switching supply for Battery Charger?? Hello to the group. Has anyone used an Astron SS series switching supply for a battery float charger? I have seen the info on using the standard Astrons but I like the efficiency of the switcher. Any comments? Thanks in advance. John ab6li
