[time-nuts] Re: Backup DC power with current battery technology?

[John Ackermann N8UR]

All -- thanks for the responses!  They've been very helpful.

Just to summarize a couple of interesting/important things I've learned:

*  Don't confuse generic "lithium" batteries with the specific LiFePo4 
type -- the other/earlier types have significant safety issues that the 
newer technology greatly moderates.

*  I looked at inverter/charger options but most are much larger than I 
need (seems like 3KVA is about the smallest) and consequently a whole 
bunch more expensive.  If you ordinarily have mains power available, a 
traditional UPS seems to do the same thing in more reasonable sizes and 
for less money.

*  Bob LaJeunesse suggested paralleling AC power supply with battery 
using Schottky diodes.  That allows the battery charger to be whatever 
it needs to be without having to power the load as well.  And it 
provides an additional redundancy in that you can disconnect the 
battery/charger for maintenance without affect the downstream gear.  I 
like that idea a lot and think I will do something along those lines.

Thanks!
John
----

On 5/27/24 11:38, paul swed via time-nuts wrote:
> Good morning to the group. Since this thread started I have been reading
> about the LiFePo4 batteries.
> They really can be treated much more like a traditional 12V battery in some
> respects. It seems they come with a battery management
> system internally. Price is easily 3-4X typical batteries. Though honestly
> PB batteries are all over the place in cost.
> Very hard to compare.
> There are youtube videos of LiFePo4 tear downs and those are really
> interesting in the wide range of mechanical construction.
> By looking at the specs you have no idea what you are buying. Well the same
> goes for PB batteries....
> John thanks for getting the mind working and relooking at the battery
> technology.
> Paul
> WB8TSL
> 
> On Mon, May 27, 2024 at 11:07 AM Germán Herrera via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
>> Hi John
>>
>> Probably a little overkill, but I have good experience with the Mini-Box
>> OpenUPS boards (the original, one not the OpenUPS2). It can be setup
>> with multiple cell chemistries, does balancing, has wide input/output
>> voltage, 6A (10A peak) output current, etc.. Only issue (beside cost) is
>> that it's switching, so maybe the added noise makes this a no-go.
>>
>> BR, German
>>
>> On 2024-05-26 11:39, John Ackermann N8UR via time-nuts wrote:
>>> I need to replace the batteries in my 28 VDC power distribution system
>>> in the clock room.  It's currently two series 12V AGM batteries with an
>>> IOTA Engineering float charger.
>>>
>>> This system has two purposes: (a) primary power for some OCXOs and
>>> other gear; and (b) failover power for some AC/DC gear like HP
>>> standards. Under normal conditions, power draw is 2 or 3 amps.  During
>>> mains outage, it could reach 10 amps.  Now that I have a house
>>> generator, long run-time isn't a big issue so 25 Ah or so of capacity
>>> is plenty.
>>>
>>> I haven't explored LiFePo4 batteries until now, and I'm having trouble
>>> finding a charger that can provide significant continuous load current
>>> while maintaining a battery floated across the line.  Does anyone have
>>> recommendations for something like this?
>>>
>>> Thanks,
>>> John
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