You are correct that this isn't a double conversion UPS (or
plant), the mention I was referencing was double conversion UPS types.
That being a 120v charger to battery to 120v (or 240, or 480)
inverter which is the style of system you are describing (always
on double conversion but missing the inverter at the end) due to
their stability as there are no blips or phase errors making it
through.?? Everything can be run via this system with buck
converters (if lower than 14v) easily and I've configured systems
like these in the past.
With dual conversion systems (or single in this case) you never
want the battery to take the load as that causes cycling and the
battery wears out faster, the charger (or supply) should always be
able to take 100% of the load plus charge the battery with the
battery only taking effect once the power goes out, which leads me
to...
Yes, the site has a generator, it appears to be propane and
SHOULD ATS at about 45 seconds due to being a small engine, I also
have install experience with these systems.?? The only reason to
have a larger than 10 minute battery life would be if the gen
fails due to any number of reasons at or upstream from it, it's up
to the club to decide how resilient to be beyond gen transfer
time.
I do have a curiosity with this though.
"As Jerry described it to me, the power supply pushing power into
the battery doesn't need to keep up with demand, because demand is
on the battery. The power supply is probably at the bottom end of
1/C so that when the battery is full it's not overcharged. I can
e-mail him to clarify if you'd like."
A power supply doesn't push power, it supplies power at the
demand of the load, in this case the battery and connected
equipment.?? The battery float voltage is where the battery stops
drawing energy to charge and will be minimal due to the parasitic
draw in the battery construction.?? There must be design in this
system so that the charger doesn't overcharge the battery but can
also supply the primary load, I use a RecPro supply in my car to
do just this. My charger runs 75A at most but also sits in various
stages to keep the batteries topped off in the event I stop using
it for awhile so it's ready to go when I come back.
If this is a bit rambly my apologies, it's a bit of an open
subject that I know a good bit about, I'm happy to explain things
in more detail if you need.
Miranda
On 3/6/2025 7:29 AM, Anthony KB3DVS
wrote:
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For the repeater, the light weight and energy density, potential
fire risk, and higher cost of Lithium anything and specialized
charger is not needed in my opinion
I don't think it's double conversion...
wall 110v > 12v power supply > lead acid battery > gear.
Another advantage is that one big battery can power everything DC.
Just as we have one UPS powering everything. Just less complex.
With an APC UPS we have
wall 110v > 12v charger / battery / AC inverter > 110v >
12v power supply > gear
which has a a double conversion to 12v? to charge the battery and
back from 12v battery to 110v outlet, which then gets converted
back down to 12v with our power supplies for the radios. That's a
whole lot of extra back and forth IMHO.
As Jerry described it to me, the power supply pushing power into
the battery doesn't need to keep up with demand, because demand is
on the battery. The power supply is probably at the bottom end of
1/C so that when the battery is full it's not overcharged. I can
e-mail him to clarify if you'd like.
It's like a small watering can slowly, but consistently filling up
a big bucket.
As for the relay, it can be a sense circuit into the raspberry pi
that already does the announcements so that when it ID's and
there's no power coming from the wall-powered power supply, the ID
changes in a way that we'd know it's on battery, versus if there's
AC available. But this may not even be needed.
But if the power to the tower goes out, doesn't the tower have a
big generator that's supposed to kick in and supply power after a
few minutes. So our system, at a minimum, just needs to carry our
gear for a few minutes so nothing resets?
Yes, more run time can be good if there's a generator issue, but I
believe that was one of the benefits of locating at the tower was
the city-supplied backup power.
Anthony Burokas
General Class Ham (KB3DVS)
VP: Plano Amateur Radio Klub ¨C http://k5prk.net
25-year video producer ¡ª IEBA.com
On 3/5/25 9:55 PM, Miranda Schwarck
KE5YZP via groups.io wrote:
Essentially what you're describing is a double conversion
UPS, the most expensive and quality UPS available.?? You don't
even need to use a battery cycle system, just use a charger
that can keep up with demand of charge but won't overcharge
the battery (DC-DC charger on one side with diodes on the
other), the system will keep itself topped off until an outage
then it will start discharging.?? For triggering it's normally
a 120v to 3.3v relay powered by wall voltage that can trip
pins on a pi which will then start either beeping during
transmissions or doing voice announcements at interval.?? The
ideal charging system would be single charger so there's no
need to attempt to load balance the chargers when it gets to
float voltage.
I can definitely rebuild this to do so but we would have to be
sure that we have overtemp sensing on the batteries (I've seen
some over 145*F) and that the city is OK with that kind of
battery in the facility.?? As it's not likely to off-gas or
burn it should be fine but if we wanted to use LiPo or LiFePo4
then there's a risk of that even if it's very small on the
LiFePo4 batteries. ? I essentially have this exact same system
with LiFePo4 batteries in my car so that when the car is
shutoff it has 200AH of? reserve which is charged as soon as
the car is plugged in or started and becomes feed through in
that condition.
Miranda
On 3/5/2025 1:01 PM, Anthony KB3DVS
wrote:
A suggestion I had made a bit ago was to use a lead acid or
AGM battery in between the AC supply and the radios.
I worked with a ham in Alaska, who manages several repeaters
and remote tower sites and this is how he does it, for
simplicity and reliability.
The AC is on a timer, to be able to charge the battery within
a few hours.
All the radio and compute runs off fused DC taps, (and voltage
converters) so that if AC dies, the DC is still there and he's
got 100+ AH batteries to carry it for days. He's got a bit of
compute to make an announcement / send a message if AC is
lost. There's diodes on the leads to the batteries to prevent
any backflow form the battery to the AC power supply.
The DC can directly power multiple radios / compute at the
same time as opposed to needing multiple AC adapters.
It's also cheaper than a similarly sized UPS solution that
converts the DC battery back to AC that is then converted back
to DC for the radios and compute.
Just an idea to consider if we're re-jiggering the power
solution for a rack of radios and compute.
Anthony Burokas
General Class Ham (KB3DVS)
VP: Plano Amateur Radio Klub ¨C http://k5prk.net
25-year video producer ¡ª IEBA.com
On 3/5/25 11:40 AM, Miranda
Schwarck KE5YZP via groups.io wrote:
Tim,?
?
If we have someone willing to donate parts then I'll
take that over a paid replacement.? ?With both
transmitters enabled transmitting the time we were at 30
amps, if all radios were transmitting we might get to 45
amps since APRS doesn't transmit, or not often anyway.?
?This means we should be able to take those two supplies
plus the one still there and move the site back to
permanent hardware changing up the power distribution just
a bit.?
?
We also should determine if the D-Star rack would
benefit better from those supplies than the FM rack due to
form factor or loading issues, as I didn't have a key I
was unable to do any diagnostics on it.?
?
Miranda
