At 07:29 PM 10/19/08, you wrote: >I have a Astron 60 Amp Power supply with the battery back up >option it works Great I have it Fused. However in the Testing I >noticed that on Battery Back up I only loose about 10 Watts that >is fine, But as the Battery drains down the Repeater gets >Distorted and of Course this is normal too Because of the input >Voltage getting Lower , > >Now the question and I have not seen this talked about I would >assume all I would need is a Normally closed Relay and as the >Voltage dropped below a Certain Level it would open and just break >the connection to the Battery back up , Is this the way to do it > >Thanks > >Don KA9QJG
What you are looking for is a device called a "Low Voltage Disconnect" or LVD. Yes, you really want one because many battery chemistries are such that an over-N% discharge will damage the battery - and the N can be as low as 50%. An LDV is a very common item in any battery powered environment - for example an Recreational Vehicle (RV) (i.e. motor home), or a solar powered cabin, or any "off-the-grid" system. The RV suppliers solid-state low-voltage dropout devices to save an RV batteries when a set-point voltage is reached. That way there is still enough battery left to start the vehicle. A relay as you describe will do the job, but it's additional drain that you don't need. Also you will have to hand-pick the relay as most 12v ones won't dropout until 8-9v or so and the battery is damaged by the time it hits 10v. If you add a comparator circuit to drive the relay you are already half-way to a solid state LVD circuit. When the AC is off the battery charge is all you have, and you want to maximize the time that it can run the repeater. Some relay coils draw 1/2 amp - and on some systems that's more than the receiver and the controller together draw. And once the relay drops out, the coil is STILL connected and drawing juice, draining the dead battery even further. Google the term "Solar Panel Charge Controller", and get one that will handle your load current (plus some headroom for expansion later), then connect it as per the instructions except that the Astron is on the Solar Panel connections, and the entire repeater hardware package (including the controller), is on the load connection. The charge controller not only will provide the low voltage disconnect function but will also manage the battery charging better than the Astron trickle charger circuit (which consists of one resistor). Add a 5v wall wart to a digital input so when the AC power fails your controller will know it and can alert you (one local system has a single short beep for a reset beep, and the morse letter "B" for the reset beep when they are on battery. The reset beep switchover is controlled by the 5v wall wart on an extra digital input). Mike WA6ILQ PS - "Home Power Magazine" is the 6-times-yearly bible of the off-the-grid community published by Richard and Karen Perez (N7BCR and KA7ETV). If you are interested in solar power for a repeater site, or in cutting your home power bill, this is the magazine for you. Since 1987, they have published over 100 issues with articles on solar, wind, and microhydro electricity, energy efficiency, solar hot water systems, space heating and cooling, green building materials and home design, efficient transportation, and more. Their web site at <www.homepower.com> is worth a visit for subscriptions, CD and book orders. And the magazine staff walks the walk as well - the entire magazine production is done with off-the-grid computers and solar and wind power. Their web site is a fount of information, as are their back issues which they sell in PDF form on CDs. Yes, every issue ends up a single searchable PDF file, and they sell multi-year collections on CDs. No, I've no interest in the magazine except as a long-time (over ten years) subscriber. The advertising pages in the magazine pay for the production and are useful as a source of vendors of panels, charge controllers, batteries, energy efficient appliances, and more.
