[time-nuts] Oscilloquartz BVA has been sold. Thank you all who expressed an interest.

[Bob kb8tq]

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 at 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 at alignedsolutions.com
> 604 762 4099
> 
>> On Sep 25, 2020, at 7:16 AM, Magnus Danielson <magnus at 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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