HI We seem to have drifted a bit.
This started out as a supply for the Z3xxx Lucent GPSDO’s. In those units, you have a 24 volt switcher that is driven off of the battery or linear supply. Since it’s designed as an isolated supply, I doubt the switcher in the GPSDO is looking for a very clean input. The same is true of it’s need for a tightly regulated input. Yes it’s efficiency will vary a bit with input and so will heat in the box. Still, not a real big deal if the voltage drops a volt or so when you go onto backup. The GPS is still running to keep everything lined up. How fast to you need to re-charge the battery bank? For me, not very fast. To keep the batteries healthy, maybe a bit faster than I would like. Lower charge current is another reason to go with a smaller battery if you can get away with it. Bob > On Oct 26, 2014, at 6:03 PM, Poul-Henning Kamp <p...@phk.freebsd.dk> wrote: > > -------- > In message > <CAGVVbuFAM=u5Uhdf+wgTUNuoeMZ+=pzwq4jpugjnjdd60fg...@mail.gmail.com> > , Brian Lloyd writes: > >>> There are a variety of inexpensive wall-wart packaged float chargers for >>> lead acid batteries around. Might be easier to just get something off the >>> shelf. >> >> Some of these things are *extremely* noisy. > > Well, yes and no. > > It's amazing how much noise doesn't make it past the lead-acid battery > due to its low internal resistance. > > The real issue is not the chargers noise in float mode, where it is > barely loaded, but in bulk-charge mode, where it works full bore. > > Unless you want to burn a LOT of heat charging your batteries with > a linear regulator, you are better of shaving the noise after the > battery. > > For OCXO's, the 14.5-11.6V supply range is going to be much more > important than the noise from the charger. > > In other words, you will need some kind of regulation between > the battery and the OCXO, and that is where you should cope with > the noise. > > A couple of other concerns should worry you too: Isolation and > short-circuit current. > > The design I will suggest, is to find a good charger which takes > care of your battery, and have it do only that. > > Driving the load with the charger almost invariably means the > battery doesn't get optimal conditions which is why it will > croak in 5 years instead of the 20 years in the datasheet. > > Find another power supply for your load, at a voltage slightly > above the chargers bulk-mode (14.5 V) voltage, and use two > solid diodes to "or" the battery and the "production supply" > onto your "DC-bus". > > Don't skimp on the ATO fuses, put one right next to the battery. > > Your OCXO should be driven using a small isolated DC/DC converter > from this DC bus. > > It is important that the converter is isolated: It prevents > ground-loops, but it also allows you to common-mode filter the > supply to the OCXO to get rid of any noise from the DC/DC > converter. > > Yes, it is alot more complex, but the result is also much better. > > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.