[time-nuts] float chargers for oscillator backup power

paul swed paulswedb at gmail.com
Sun Oct 26 20:30:26 EDT 2014

A very interesting subject. If I am not mistaken the HP CS battery backup
supplies use a charger and post regulator/inverter. The charger is well
designed but linear as I recall.  I have one in the basement with 2 X 28
Amp hour SLA batteries. Purchased new. I screwed around with flea market
duds. You get what you pay for as is always the case.

This has been working very nicely for years and the only thing I have had
to do was change the battery set after 7 years. This sets now on year 2.
However its somewhat of a power wasting unit and I suspect the discussion
of this thread could result in a more efficient float charge method. The HP
uses a transformer on the input.


On Sun, Oct 26, 2014 at 7:30 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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