[time-nuts] float chargers for oscillator backup power

[Chris Albertson]

I had a sail boat with six of those T105 batteries and the big AC charger
too.  But I was running lights, a microwave oven, radios and so on.  Those
batteries held "kilowatt-hours" of energy.  That is gross over kill for a
GPSDO.

The simplest setup for a low power device is a LiPo battery of the kind
sold for use with model cars and airplanes.  They are small, don't cost
much and you can buy the chargers at hobby shops.  These packs are made
from AA size cells that are soldered together then taped and shrink wrapped
and use a (mostly) standardized connector for power output and charging.
You can get set up for the cost of just one T105 battery.

On Sun, Oct 26, 2014 at 4:30 PM, Bert Kehren via time-nuts <
time-nuts at febo.com> wrote:

> 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
> discharge.
> Bert Kehren  Miami
>
>
> In a message dated 10/26/2014 6:03:37 P.M. Eastern Daylight Time,
> phk at phk.freebsd.dk writes:
>
> --------
> In  message
> <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
> 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
> phk at 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.
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-- 

Chris Albertson
Redondo Beach, California