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 <af-boun...@af.afmug.com> *On Behalf Of *Mathew Howard
*Sent:* Thursday, August 17, 2023 10:51 AM
*To:* AnimalFarm Microwave Users Group <af@af.afmug.com>
*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 <dmmoff...@gmail.com> 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 <af-boun...@af.afmug.com> *On Behalf Of *Mathew Howard
*Sent:* Wednesday, August 16, 2023 5:01 PM
*To:* AnimalFarm Microwave Users Group <af@af.afmug.com>
*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 <dmmoff...@gmail.com> 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 <af-boun...@af.afmug.com> *On Behalf Of *Mathew Howard
*Sent:* Wednesday, August 16, 2023 4:11 PM
*To:* AnimalFarm Microwave Users Group <af@af.afmug.com>
*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
<af@af.afmug.com> 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 <dmmoff...@gmail.com> 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 <af-boun...@af.afmug.com> *On Behalf Of
*Steve Jones
*Sent:* Tuesday, August 15, 2023 10:27 AM
*To:* AnimalFarm Microwave Users Group <af@af.afmug.com>
*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
<i...@wirelessmapping.com> 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:af-boun...@af.afmug.com
<mailto:af-boun...@af.afmug.com>] *On Behalf Of
*dmmoff...@gmail.com
*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:*dmmoff...@gmail.com <dmmoff...@gmail.com>
*Sent:* Tuesday, August 15, 2023 6:56 AM
*To:* 'AnimalFarm Microwave Users Group'
<af@af.afmug.com>
*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 <af-boun...@af.afmug.com> *On Behalf Of
*Steve Jones
*Sent:* Monday, August 14, 2023 9:57 PM
*To:* AnimalFarm Microwave Users Group
<af@af.afmug.com>
*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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