The temp issue as I understand it is the low temp disconnect when charge
so as not to try and charge when the batteries are too cold. The LiTime
batteries now have low temp disconnect in their internal battery BMS.
Their prices are very good. The longevity of LiFePo batteries more than
justifies the slightly added cost for the battery. If the temperature
does not stay below the disconnect temp for longer than you have run
time, you are good. Remembering the LiFePo batteries give you full
capacity of their rated WH not only 50% like lead acid. They are a lot
lighter too. So more useable WH can also reduce your battery count (and
overall cost) that you need. Use a proper LiFePo charger and the
charging profile lets you dump almost full capacity to the batteries
that the panels produce. This should get the battery up to or closer to
the full voltage sooner, allowing you to run the equipment off the power
from the panels for a longer period of time as well. This of course
stretches your battery capacity too. When you can push full current
through the charger to the batteries, even short periods of sun can get
your battery charged or partially charged faster than the charging
profiles required for lead acid or AGM batteries.
Thank you,
Brian Webster
*From:*AF [mailto:[email protected]] *On Behalf Of *Mathew Howard
*Sent:* Thursday, August 17, 2023 4:14 PM
*To:* AnimalFarm Microwave Users Group
*Subject:* Re: [AFMUG] battery nerd question
Yeah, temperature is the main problem I'm seeing with going to lithiums.
I can throw an SLA battery in an unheated box at our towers and it's
going to work good enough, even in the middle of winter, but the minimum
charging temperature for LFP batteries is 32F, which we're going to be
below for a good part of the year.
On Thu, Aug 17, 2023 at 3:08 PM Bill Prince <[email protected]
<mailto:[email protected]>> wrote:
Things have evolved. You can get LFP batteries for "almost" the same
price as lead acid. Sometimes less even. They occupy less than half
the space as lead acid, and will last at least twice as long. There
is the issue of temperature sensitivity and they will need help for
extremely cold environments.
bp
<part15sbs{at}gmail{dot}com>
On 8/17/2023 12:36 PM, [email protected]
<mailto:[email protected]> wrote:
Ooh What lithium batteries are we talking about?
Last time I checked (a number of years ago), it was around 5x
the $/Wh to buy Lithium.
*From:* AF <[email protected]>
<mailto:[email protected]> *On Behalf Of *Mathew Howard
*Sent:* Thursday, August 17, 2023 10:51 AM
*To:* AnimalFarm Microwave Users Group <[email protected]>
<mailto:[email protected]>
*Subject:* Re: [AFMUG] battery nerd question
Well, right. It doesn't scale well, because battery costs and
space requirements will quickly become a problem. Batteries
don't last forever, so you have to factor in replacement costs
too, which will be a significant ongoing cost for a larger
system. I'm pretty sure that lithium batteries would be cheaper
long term now, since they should have a lot longer life span and
the initial cost isn't a lot higher, but then heating is
required, which means you need more power.
On Wed, Aug 16, 2023 at 7:02 PM <[email protected]
<mailto:[email protected]>> wrote:
That’s building strictly for a 20W load though. Building
for a tiny load does make the costs easier. But if you
wanted a second AP, bigger backhaul, or anything else you
can’t do it without growing the whole power system
proportionally.
Steve was talking a 50W load today. The real high end
hardware now is using a lot of signal processing either to
reassemble useful data out of garbage or for beam steering,
or both. So you end up needing 100-150W for an AP. You’d
be hard pressed to find a licensed backhaul under 35W, and
most of them are 50W+. We could say we won’t deploy that
equipment….but building for a 20W load takes the choice away.
A 20A 240v circuit is 4800W. Or a 20A 120V circuit is
2400W. Even 2400W would power almost any WISP deployment.
Building solar to handle any load you might have is
expensive, and building for only low power handcuffs you.
You do your thing your way, no judgement. If it’s working
for you then it’s good, but I can’t see myself going that
direction.
-Adam
*From:* AF <[email protected]
<mailto:[email protected]>> *On Behalf Of *Mathew Howard
*Sent:* Wednesday, August 16, 2023 5:01 PM
*To:* AnimalFarm Microwave Users Group <[email protected]
<mailto:[email protected]>>
*Subject:* Re: [AFMUG] battery nerd question
I'm at about the same latitude as you. My experience is that
having extra battery capacity is more helpful than
oversizing the solar panels, so I'd probably go with Chuck's
numbers for batteries if I was putting something together
now, and solar panels are cheap now anyway, so figure 400
watts (if mounting space allows for it, which could be an
issue if we're trying to fit it on a pole).
A quick check on Amazon shows 100ah SLA batteries for $160,
so 6 of those would give me 7200 watt hours, for just under
$1k. At $1500 (which is mostly just adjusting battery and
panel sizes from where I started at $1k), I'm right in line
with Chuck's estimate, aside from the battery costs.
On Wed, Aug 16, 2023 at 3:33 PM <[email protected]
<mailto:[email protected]>> wrote:
I end up closer to Chuck’s estimate. In Southern or
Central NY State I’m 2 degrees north of Salt Lake City. 42N
What’s your latitude?
*From:* AF <[email protected]
<mailto:[email protected]>> *On Behalf Of *Mathew
Howard
*Sent:* Wednesday, August 16, 2023 4:11 PM
*To:* AnimalFarm Microwave Users Group <[email protected]
<mailto:[email protected]>>
*Subject:* Re: [AFMUG] battery nerd question
Yeah, that's what I'd do in a difficult to access
location. I did a site like that here (Wisconsin) with
200 watts of panel (I think the actual load is around 15
watts, so a bit more than 10x), and ~4kwh of battery. It
had some issues in January a couple years, but I
attributed that more to using cheap flooded deep cycles,
rather than not enough capacity. With AGMs, it's gotten
through the last couple of winters without issues. 4kwh
of AGMs can be had for around $800, last I checked.
Probably looking at closer to $1500 when you add in
enclosures and mounts, but some of that is replacing
parts that are needed with AC power anyway (smaller
enclosure, backup batteries, power supply), so that
offsets it a bit.
On Wed, Aug 16, 2023 at 2:50 PM Chuck McCown via AF
<[email protected] <mailto:[email protected]>> wrote:
Using my historical rules of thumb for off grid,
snowed in mountain top location for a 20 watt load I
would do the following that has never failed me:
Load X 20 so 400 watts of panel. So less than $200
these days.
2 weeks of battery autonomy.
20 x 24 x 14= 6720 watt hours. $2K of batts
Plus enclosures, mounts, charge controllers.
$2500 and it will never go down in the winter. At
my Utah latitude on top of Utah mountains.
*From:*Mathew Howard
*Sent:*Wednesday, August 16, 2023 1:07 PM
*To:*AnimalFarm Microwave Users Group
*Subject:*Re: [AFMUG] battery nerd question
It depends on how much stuff you're trying to run. A
minimal micropop can be done with less than 20 watts
of load (single AP and backhaul). I can put together
a solar setup for around $1000 that will power that.
On Tue, Aug 15, 2023 at 12:50 PM
<[email protected] <mailto:[email protected]>>
wrote:
I can save you the suspense. If you have access
to electric that’ll be cheaper than solar. The
problem is the need to run 24/7. You have to
design around the December-January months. I’m
in NY State, and at our latitude we only get a
few hours of average production per day during
those months. And obviously if it’s snowing for
a week you need to be able to ride through that
on mostly battery power. Even with a modest
load it takes a silly amount of panels and
batteries to stay up 24/7 in the winter. More
than you’d ever be allowed to put on a utility
pole.
Talk to your electric co about the smallest
service you can get. Explain what you’re trying
to do and that your max load is very low.
NYSEG normally doesn’t do less than 100A, but
they made an exception and let us do 60A. You
need a meter can, a service rated panel, a
conduit up the pole and a weatherhead. Then you
either have an outdoor outlet, or have an outlet
inside your enclosure. You’ll want the smallest
service they’ll let you do because of the wire
size on the service cable. A 20A (if they’d
allow it) would only need a 12/3 with ground,
and that’s up to 4800 Watts (240x20) so it’s
still more than you’d ever need. A 12/3 is way
cheaper than a 100A service entrance cable.
My figure is 8 years old, and obviously there’s
been inflation since then, but I went to the
same contractor who does electric installs for
the cable company and they quoted me about
$1000. Even if it’s 3x that for you today you’d
still never beat that with a solar installation
even if they’d let you do it. And I’m not some
knee-jerk anti-solar lunatic, I’m just saying
I’ve run the numbers and it doesn’t add up.
People do it when they’re off grid, or when the
electric service is unreliable in the area, or
sometimes just for the PR/marketing power of
being “solar powered”. Those are all fine
reasons, but doing it for cost savings isn’t
going to work out.
-Adam
*From:*AF <[email protected]
<mailto:[email protected]>> *On Behalf Of
*Steve Jones
*Sent:* Tuesday, August 15, 2023 10:27 AM
*To:* AnimalFarm Microwave Users Group
<[email protected] <mailto:[email protected]>>
*Subject:* Re: [AFMUG] battery nerd question
we have a dozen or so, but are looking at pole
mount micropops (our own poles). We are losing a
grain elevator site because they decommissioned
the elevator and theres no real options for the
customers in some of the areas. Im just trying
to get to something we can get solar power with
enough battery to last through overcast. So Im
calculating per battery runtimes, then will look
at number of batteries we would need to survive
vs paying for a ROW meter vs losing the
customers. Just have to get to the cost per
customer to retain them and the benefit gained
per pole
On Tue, Aug 15, 2023 at 8:53 AM Brian Webster
<[email protected]
<mailto:[email protected]>> wrote:
How many of the batteries do you have? Do
you need any voltages other than the 48
volts? If you have 4 batteries and only need
48 volts then wire them in series and not
have to deal with the converter.
Thank you,
Brian Webster
*From:*AF [mailto:[email protected]
<mailto:[email protected]>] *On Behalf
Of *[email protected]
<mailto:[email protected]>
*Sent:* Tuesday, August 15, 2023 6:59 AM
*To:* 'AnimalFarm Microwave Users Group'
*Subject:* Re: [AFMUG] battery nerd question
*You’re around C/30 which should be on the
high end /of capacity/.
Lower load usually means a little extra
capacity out of the battery. I realized
that sentence might have been ambiguous.
*From:*[email protected]
<mailto:[email protected]>
<[email protected]
<mailto:[email protected]>>
*Sent:* Tuesday, August 15, 2023 6:56 AM
*To:* 'AnimalFarm Microwave Users Group'
<[email protected] <mailto:[email protected]>>
*Subject:* RE: [AFMUG] battery nerd question
You can do the whole thing in Watts.
12V * 150ah = 1800 Watt-hours
1800Wh / 50W = 36 hours
If they’re telling me 95% efficiency, I’d
assume 50W out needs 53W in (50 / 0.95).
There’s usually an efficiency curve for the
device based on load and temperature so it
wouldn’t be 95% in all circumstances. Your
system should be drawing less than 5A off
the battery, and if your multimeter has a
10A fuse like most do, then you could put
the meter in line and actually measure the
amperage before and after the converter.
Then you’d know for sure.
And the battery’s total capacity will have a
curve based on C-rate so there’s some
variability there too. Usually it lasts
longer when you’re drawing lower amperage.
You’re around C/30 which should be on the
high end.
Age and maintenance of the battery affect
runtime as well. If I want 6 hours of
runtime then I plan Ah for 12 hours runtime.
When my batteries are halfway toasted I’m
still getting useful life out of them.
*From:*AF <[email protected]
<mailto:[email protected]>> *On Behalf
Of *Steve Jones
*Sent:* Monday, August 14, 2023 9:57 PM
*To:* AnimalFarm Microwave Users Group
<[email protected] <mailto:[email protected]>>
*Subject:* [AFMUG] battery nerd question
Just trying to cipher runtimes
I have on hand 150ah 12 volt batteries, so
thats what id be looking to use.
Excluding the conversion loss of a 12v to
48v step up converter is the math correct here?
12v 150ah=1800 watt hours
1800 watt hours at 48v = 37.5ah
50 watts of radio running 48v = 1.04 amps
37.5ah @ 1.04 amps = 32.77 hours runtime
does a step up that claims 95% efficiency
mean 95% of the watt hours?
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