[time-nuts] float chargers for oscillator backup power
EWKehren at aol.com
EWKehren at aol.com
Sun Oct 26 19:30:24 EDT 2014
Living in south Florida backup power is short term and long term. As lab
batteries I use T 105 also known as Golf Cart batteries. Costco has those 6
Volt 200+A batteries for less than $ 80. Super price. Yes I have Costco
stock. For charging I use a VIctron Energy Phoenix 12 V 30 A charger. On the
boat two 28 V 100 A chargers. No afilliation.
These people know what they are doing and if nothing else download info on
their chargers they know all about how to get maximum life and performance
out of batteries. You will find them in top end boats and RV's but the
bulk of their business is off grid power. If you have been on an African
Safari, the power most likely was Victron Energy. I think they still have also a
very good application note.
A T 105 like battery if maintained is good for eight years plus. On golf
carts if used daily they typically last at least 4 years and I talk 70% plus
Bert Kehren Miami
In a message dated 10/26/2014 6:03:37 P.M. Eastern Daylight Time,
phk at phk.freebsd.dk writes:
<CAGVVbuFAM=u5Uhdf+wgTUNuoeMZ+=PzWQ4JpugjNJdd60FGp0A at 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
>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
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
A couple of other concerns should worry you too: Isolation and
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
Yes, it is alot more complex, but the result is also much better.
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
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