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]> *On Behalf Of *Mathew Howard
*Sent:* Wednesday, August 16, 2023 5:01 PM
*To:* AnimalFarm Microwave Users Group <[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]> 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]> *On Behalf Of *Mathew Howard
*Sent:* Wednesday, August 16, 2023 4:11 PM
*To:* AnimalFarm Microwave Users Group <[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]> 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]> 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]> *On Behalf Of *Steve Jones
*Sent:* Tuesday, August 15, 2023 10:27 AM
*To:* AnimalFarm Microwave Users Group <[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]> 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]
*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] <[email protected]>
*Sent:* Tuesday, August 15, 2023 6:56 AM
*To:* 'AnimalFarm Microwave Users Group' <[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]> *On Behalf Of
*Steve Jones
*Sent:* Monday, August 14, 2023 9:57 PM
*To:* AnimalFarm Microwave Users Group <[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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