-------- 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 [email protected] | 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 -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
