I put four of the sealed 12v lifepo4 batteries in an electric lawn mower
(it originally had lead acid), and it works well enough, but yeah, a single
BMS is preferable, and I haven't seen any that say they can do more than 4
in series anyway.
With lifepo4 you'll need 125 cells to get 400v... I'm not sure where you'd
find a BMS that will handle that though. I assume there must be something
out there.
On Thu, Aug 17, 2023 at 4:06 PM TJ Trout <t...@voltbb.com> wrote:
> Many of them have integrated heaters.
>
> Sealed lifepo4 batteries should only be used at the nameplate voltage 12v
> for example, some will support up to four in series for a 48 volt
> configuration but it's a hack job to do it that way.
>
> If you need 400v at 100ah you will need 110 qty of 100ah cells and a
> compatible BMS.
>
> On Thu, Aug 17, 2023, 1:51 PM Chuck McCown via AF <af@af.afmug.com> wrote:
>
>> My electric car loses significant range at temps below 35F and as a
>> double whammy, will not accept a full charge at low temps either.
>>
>> Lead acid work at low temps but if they get too far discharged they will
>> freeze. Gates Cyclons were advertised to be able to be fully charged and
>> discharged when frozen.
>>
>> *From:* Mathew Howard
>> *Sent:* Thursday, August 17, 2023 2:13 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 <part15...@gmail.com> 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, dmmoff...@gmail.com 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 mailto:af-boun...@af.afmug.com *On Behalf Of *Mathew Howard
>>> *Sent:* Thursday, August 17, 2023 10:51 AM
>>> *To:* AnimalFarm Microwave Users Group mailto: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] *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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