Oscilloquartz BVA has been sold. Thank you all who expressed an interest.
I've had good luck with Iota brand chargers for 12 and 24 volt... I
think they are "DCL" series or something similar. They are available in
various amperage and include a smart-charger circuit. I know Amazon
sells several models and the prices are in the $100-200 range. One of
their selling points is that they are electrically quiet, though I
haven't done any real tests, and are designed to work as a regular power
supply (ie, they don't flake out if there's no battery load attached.
John
On 9/25/20 1:22 PM, Bob kb8tq wrote:
Hi
Properly charging batteries is a bit complicated. Why does “properly” matter? You want them to be fully
charged, but not damage them in the process. That generally involves some sort of variable voltage
for the charging source. If you decide to go with Lithium based parts, you can get BMS (battery management)
IC’s that can help with the charging and the balancing ( = you want them all at equal voltages) of the cells.
If you look at older gear, this sort of thing didn’t get a lot of attention. Most of the backup battery setups
worked poorly as a result.
======
One “cute” alternative is to do a battery + boost converter ( = switcher) instead. If the device only operates
during a power outage, noise is not a big deal. Everything that is attached to the OCXO output is dead anyway ….
The advantage of a switcher is obviously efficiency. A fully charged “12V” LiFePo4 stack could easily be at 14.8V.
Fully discharged it might get down to 10.4V. Allowing for that 1.4:1 output ratio with a linear regulator means a
lot of (expensive) battery energy goes up in heat ….
Bob
On Sep 25, 2020, at 11:55 AM, Mark Spencer mark@alignedsolutions.com wrote:
Pondering the backup power issues for my BVA a bit more, I am thinking a dedicated DC battery bank (maybe 5 or 6 nominal 6 volt batteries in series) powering a suitable linear regulator circuit is probably the direction I will go in. I suspect there are more elegant and or simpler approaches but I think from my perspective as a hobbyist this is probably the best direction for me.
I like the idea of using a diode arrangement to facilitate changing the power source for the BVA. I expect I will also add some form of over voltage protection as well.
I need to ponder the likely voltage drops in the voltage regulator and diodes along with the voltages the batteries will provide as they discharge under load.
It seems I have another winter project.
Thanks all for the suggestions.
Mark Spencer
mark@alignedsolutions.com
604 762 4099
On Sep 25, 2020, at 7:16 AM, Magnus Danielson magnus@rubidium.se wrote:
Hi,
On 2020-09-24 23:47, Tom Van Baak wrote:
Next time I power down mine is to integrate a new supply and back-up
May I recommend PowerPole connectors and frequent use of diode-OR. For
details see:
http://leapsecond.com/pages/powerpole/diode-or.htm
I got the inspiration when my Dad was in the hospital and I saw how
they did IV tubes with multiple injection points. It seemed so simple,
clever, reliable. Details [1] and graphic photo [2].
So now I use diode-OR "Y" connectors on all my long-term standards. It
allows me to replace either power supply live without interruption at
any time. Come to think of it, they call it an IV in the hospital. And
here in my lab the I is about 0.18 and V is 24 so my IV is 4 watts. ;-)
That's how we do it in Telecom, but on the 48V level. I managed to drive
my company into do it with 48V all the way to the various boards,
because that way the protection switching out there handled multiple
faults. Also, for some reason there is this line of DCDC converters from
48V to about anything. We kept doing that since, even if the diodes now
been replaced with MOSFETs to lower losses.
If you look into say the 5065A that's how it's done there too.
As for power-pole, those are great connectors, but I need to keep 12V,
24V and 48V in the lab, so I need to get the different color codes not
to interchange them. You usually react when you see a yellow-black
trying to mate with a red-black. So, I recommend folks to do the same.
Once one got started with the Anderson PowerPole, it becomes more and
more a solution.
But yeah, thanks for reminding me that I need to progress on the
power-pole and power supply projects. I'll do that after the PiDP-11
project.
Cheers,
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Mark Spencer writes:
The bit I am struggling with re using a 24 volt battery system in this
application is what happens when AC power is removed and the terminal
voltage of the battery starts to fall.
Don't overengineer your supply (unless you absolutely want to :-)
It looks like the BVA is specified at 24V ±10%, which is 21.6-26.6V.
Nobody says 24 Volt is optimal in that interval, and I have
never been able to measure any difference on any OCXO, as long as
I stayed a few hundred millivolts above the lower limit.
I would run the BVA for a week at 24V, collecting PPS data against
a GPSDO or other suitable source.
Then I would run it for a week at 22V, collecting the same data.
If I could not tell the data from the two runs apart, I would design
a 22V supply.
The BVA is spec'ed at 3W steady state, at 22V that's ~150mA.
In long-run applications you get the name-plate capacity, so two
12V x 15 Ah VRLA blocks would keep your BVA happy for four days,
24Ah would last a week etc.
"Small" come from a lot of dubious manufacturers and which means
badly recycled and impure lead. For a golfcart that doesn't matter,
but it is a big disadvantage in long-run applications like this.
Saving 5 bucks on lead-acid batteries are usually a bad deal in the
long run, but on the other hand, dont say no if serious battery-people
offer you a couple of pre-owned large batteries cheap, just make
sure you can lift them.
Lead-Acid in long-duration applications should not be discharged much
below 1.85 V, and 12 cells times 1.85V = 22.2 Volt. Subtract a
diode drop, and now you know where the 24V±10% spec comes from in
the first place.
At 27.6 V float-charge, your linear regulator will have to deal with
(27.6-22)V * 150mA = .84W.
A LM317 would do a fine job, but you can reduce the voltage drop
and get longer runtime with a PNP based home-brew supply.
The float-charger should be able to power the BVA and also recharge
the battery in less than a day, so with 15Ah blocks, I would aim
for around 1-1.5 ampere.
Your batteries will live longer if they have individual chargers,
so something like a 2x12VAC 40-50W torroid trafo, two bridges, two
caps, two LM317's plus resistors and trimpots will do fine.
Poul-Henning
PS: practical hints:
Your local car-nut-emporium has fuseholders like these for cheap:
https://www.thansen.dk/bil/udstyr/eludstyr/kontakter-ledning-sikring/sikringer/sikringsholdere/sikringsholder-m.-kabel-fladsikring/n-497642816/pn-1939736599
Take two, crimp ring-lugs on one end of them, and bolt them directly
to the battery terminal: one for charger, one for load.
When using them next to batteries, the "contra" diode "backwards
across" the LM317 is mandatory.
"Real" UPS installers often have spare batteries which have been
kept on float-charge but otherwise unused, in case of a failure on
customer site. At end of contract, they dont need them any more.
Telephone people with 2V batteries are interesting too, but their
12V blocks are usually dead by the time the swap them out.
Power-grid people, in particular the nuclear plant people, can also
be a good source very, very good batteries with lots of life in
them still, but be very aware of the weight and the short-circuit
currents.
If you end up with pre-owned liquid electrolyte batteries ("OPzS")
make sure the hydrogen gas can vent safely out of the building.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
Yes, Powerpole connectors are wonderful; I use them extensively and in
various color combinations for different voltages.
Yes, it would be nice to have a Powerpole option for the Mini-Box
Y-PWR-Hot-Swap-Load-Sharing-Controller identified below, but it would be
even better if it would operate with 48 volt supplies for ex-telecom
equipment. Unfortunately, the current design is rated to only 30 vdc.
The board would need redesign and would be larger, which I don't see as
a problem.
Interesting product, though. Thanks to Poul-Henning for identifying it.
Larry
On 9/25/2020 4:50 AM, Poul-Henning Kamp wrote:
Tom Van Baak writes:
May I recommend PowerPole connectors and frequent use of diode-OR. For
details see:
+1 on the power-polery.
I really wish somebody would do a version of this with power-pole:
https://www.mini-box.com/Y-PWR-Hot-Swap-Load-Sharing-Controller
--
Best wishes,
Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
Bob kb8tq writes:
Properly charging batteries is a bit complicated.
With VRLA lead-acids: Not really, constant voltage 2.3V/cell, current limited to $Ah/10 and you're done.
For the tonnage of batteries relevant for us, when used indoors, temperature-compensation and all that is not relevant.
Charging Lithium on the other hand is several kinds of nightmares, many of them involving unquenchable flames.
One “cute” alternative is to do a battery + boost converter ( = switcher) instead.
[...]
The advantage of a switcher is obviously efficiency. A fully charged “12V” LiFePo4 stack could easily be at 14.8V.
Fully discharged it might get down to 10.4V. Allowing for that 1.4:1 output ratio with a linear regulator means a
lot of (expensive) battery energy goes up in heat ….
Yes, for most stuff I would just slap a good isolated DC/DC converter on a single 12V battery and be done with it.
But for a BVA I would choose more expensive batteries over switching noise any day...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
Larry McDavid writes:
Yes, it would be nice to have a Powerpole option for the Mini-Box
Y-PWR-Hot-Swap-Load-Sharing-Controller identified below, but it would be
even better if it would operate with 48 volt supplies for ex-telecom
equipment.
There are tons of chips in that market, precisely because of hotplugging
telecom kit. LT makes a lot of it.
Another interesting gadget are "smart bypass diodes" for solar panels:
https://www.ti.com/product/SM74611
Disadvantage: They cycle between conducting and charging their bias, and I have no idea how noisy that is.
Advantage: Packages which can be easily soldered by hand.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
Hi
Two basic types of SLA / VRLA batteries out there: AGM and Gel. For the AGM
variety, you want a bit more to your charger. I haven’t worked with Gel cells in
a while so they may indeed be easier.
Bob
Properly charging batteries is a bit complicated.
With VRLA lead-acids: Not really, constant voltage 2.3V/cell, current limited to $Ah/10 and you're done.
For the tonnage of batteries relevant for us, when used indoors, temperature-compensation and all that is not relevant.
Charging Lithium on the other hand is several kinds of nightmares, many of them involving unquenchable flames.
One “cute” alternative is to do a battery + boost converter ( = switcher) instead.
[...]
The advantage of a switcher is obviously efficiency. A fully charged “12V” LiFePo4 stack could easily be at 14.8V.
Fully discharged it might get down to 10.4V. Allowing for that 1.4:1 output ratio with a linear regulator means a
lot of (expensive) battery energy goes up in heat ….
Yes, for most stuff I would just slap a good isolated DC/DC converter on a single 12V battery and be done with it.
But for a BVA I would choose more expensive batteries over switching noise any day...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
Bob kb8tq writes:
Two basic types of SLA / VRLA batteries out there: AGM and Gel. For the AGM
variety, you want a bit more to your charger.
Yes, if you buy batteries for N * 100K $money, spending more money
on your charger is a good investment.
But if you have two batteries doing float-charge/long-run/tiny-load,
in a benign environment in a corner of your lab, the internal
variance between batteries in that same production lot, will
overshadow any imaginable benefit a fancy charger could bring.
I haven't worked with Gel cells in a while so they may indeed be easier.
They are for the same reasons they suffer cyclic use better.
But for a float/long-run application, it makes absolutely no difference.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
When I was still RVing and wanted an electrically quiet charger I built my own
"smart charger: using the guts of an Astron 35A linear power supply with an
added uc3906 based controller. I later replaced it with a higher efficiency
Iota 30A supply with an IQ4 charge controller. It doesn't hurt that they are
based here in Tucson :-)
Wes N7WS
On 9/25/2020 11:25 AM, John Ackermann N8UR wrote:
I've had good luck with Iota brand chargers for 12 and 24 volt... I think they
are "DCL" series or something similar. They are available in various amperage
and include a smart-charger circuit. I know Amazon sells several models and
the prices are in the $100-200 range. One of their selling points is that
they are electrically quiet, though I haven't done any real tests, and are
designed to work as a regular power supply (ie, they don't flake out if
there's no battery load attached.
John
For what it is worth I ran two identical AGM 12 volt batteries for approx 7 years or so in my home lab.
I carefully adjusted the terminal voltage while float charging them via a blocking diode and checked the voltage every few months. I also confirmed that the terminal voltage of each 12 volt battery was essentially the same. The manufacturer provided data re suitable float voltages at various temperatures. The temperature in my time lab is fairly stable.
After over six years of service they powered two of my OCXO's for approx 48 hours during a lengthy power outage when I was not home. It all worked as I expected (I had chosen the batteries to provide at least 48 hours of run time with some margin) and after approx 7 years I had to replace the batteries when it became apparent they were not charging (the power supply I charge them with has an ammeter which helped me realize there was an issue.) I expect to get a similar life span from the replacement batteries. The second set of batteries at first had a significantly higher voltage difference when being float charged, the battery vendor replaced either one or both of the batteries and all was good.
I would not be surprised if the deep discharge of the first set of batteries contributed to their subsequent demise.
The experience of others may differ from mine (:
Mark Spencer
mark@alignedsolutions.com
604 762 4099
Two basic types of SLA / VRLA batteries out there: AGM and Gel. For the AGM
variety, you want a bit more to your charger.
Yes, if you buy batteries for N * 100K $money, spending more money
on your charger is a good investment.
But if you have two batteries doing float-charge/long-run/tiny-load,
in a benign environment in a corner of your lab, the internal
variance between batteries in that same production lot, will
overshadow any imaginable benefit a fancy charger could bring.
I haven't worked with Gel cells in a while so they may indeed be easier.
They are for the same reasons they suffer cyclic use better.
But for a float/long-run application, it makes absolutely no difference.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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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Good evening TGIF!
You've all given me some great ideas. I'm a computer scientist so tell me
what's wrong with this?
Can't I just use a high quality APC backup power system like we use to
power racks of gear in our Telco and compute closets? A good one runs the
full AC load the rack runs on. I've had maybe one or two short power
outages in the last year and half at this house. The worst was less than a
couple hours. Wouldn't it be good to put the few linear power supplies I
want to keep on connected to the UPS. If I lost the counters or the DMM or
really even the computers it's not that big of a deal isn't it the
oscillators and OCXO's and their power supplies that really need to stay
on? If I reduce the must have to them isn't it really all I need? I can
restart the monitoring and computers. Ok so maybe I might get a small gap
in data but the key is keeping the power supplies that drive the
oscillators and their ovens running right?
Thanks,
Bill