Well, he said that the data recorder was designed for and currently uses three AA alkaline batteries. Those things have far from a flat discharge voltage curve so I assumed that the data recorder had some sort of internal regulation.
I also assumed he would have to add another battery anyway since not many utility packs have anything close to the capacity it would require to deliver 0.7 amps for "several days". Five days times 24 hours per day times 0.7 amps is about 80AH, and you still have to derate that for the practical discharge threshold of a normal battery. We're talking well over 100 AH, and I'll bet that the utility power pack they're using has less than a tenth of that. Maybe it is important to run everything off one battery, but if so I'll bet it won't be the one they already have. Dave AB7E On 1/6/2012 1:07 PM, Jack Smith wrote: > While a 6V battery may work, I would be concerned with voltage > regulation. If the data logger is a true 5V device, a simple series > diode may not keep the supply within acceptable limits over the typical > range of battery voltage from full charge to discharge. An analog LDO > regulator would be a better choice than a diode. > > However, a 12V battery supply would, according to the original post, > also allow the receiver to be powered from one source. > > Jack K8ZOA > > > On 1/6/2012 12:49 PM, David Gilbert wrote: >> Why not just use a 6 volt motorcycle battery (two or three in parallel >> if necessary) with a series diode? The total weight isn't going to be >> any different no matter what you do ... one battery for everything or >> separate batteries for receiver and data logging. AH capacity is AH >> capacity. The efficiency would probably be above 85% if a diode rated >> for a couple of amps was used, assuming a Vf around 0.7 volts, and it >> would be tough to beat for quiet. >> >> Dave AB7E >> >> >> >> On 1/6/2012 9:34 AM, Jack Smith wrote: >>> There are quite a few simple switching regulator chips for 12V --> 5V, >>> requiring only a handful of parts to make a complete switching >>> converter. For example, National Semiconductor (now TI after the recent >>> purchase) LM2591HVT-5.0/NOPB. Stocked by Mouser and DigiKey at about $6. >>> This series is available in a through hole 4-pin TO-220 style device so >>> breadboarding up a one-off power supply isn't too difficult. >>> >>> With careful attention to detail, bypassing and shielding it should be >>> possible to build a quiet 5V, 1A supply around these parts. It can be >>> small enough to fit into a 2"x2"x1" Hammond die cast enclosure, and you >>> can use feedthrough caps for input and output, along with some internal >>> LC filtering. >>> >>> Still, 5V at 700 mA with a switching regulator and a 12V battery >>> (assuming 100% efficiency which isn't possible of course) the setup will >>> require 300mA from the battery. For 100 hours of operation, you're >>> looking at a 30 Ah battery requirement. While a battery will output more >>> Ah with a 100 hour discharge cycle, it's not that much more. A 35Ah >>> sealed 12V gel-cel type lead acid battery will run you about $100. >>> >>> For serious long duration battery operation, I would look for a more >>> thrifty data logger. >>> >>> Jack K8ZOA >>> >>> >>> On 1/6/2012 10:10 AM, John Gibson wrote: >>>> Dear Elecraft list members, >>>> >>>> The recent thread on noisy switching power supplies leads me to a related >>>> question. My son n8fyk, who teaches radio astronomy, has set up a project >>>> with his students. They are using a 15m direct-conversion Radio Jove >>>> receiver in the field to monitor radio emissions from Jupiter, the sun, >>>> and the galaxy. The receiver operates from 12V, which is readily supplied >>>> by a portable utility 12V battery pack. Their problem is powering their >>>> data recorder, which needs about 5V at 0.7A. >>>> >>>> The data recorder is designed to operate from three internal AA alkaline >>>> cells, but these give a limited run time. My son would like to be able to >>>> leave the receiver and recorder for unattended operation for several days >>>> at a time. >>>> >>>> One solution would be to use a 12V-to-5V power converter between the 12V >>>> battery and the data recorder. For long battery life, it would be nice to >>>> have the efficiency of a switching converter. Such a converter would have >>>> to be RF-quiet, so as not to interfere with their weak-signal reception. >>>> >>>> I will be interested to hear what list members recommend. >>>> >>>> Thank you and 73, >>>> >>>> John, no8v >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
