Yeah... for on-grid backup power, running heaters shouldn't be a big problem, but off-grid is a different animal. Warming the batteries up enough to charge could take a lot of power.
All the lifepo4 batteries I've looked at list the minimum discharge temperature at -20C, which isn't terrible, but they need to be at least 0C to charge. The discharge temperature isn't hard cut-off where it won't work or will wreck the batteries sort of thing, as far as I can tell, but the charging temperature is. On Thu, Aug 17, 2023 at 6:02 PM Robert Andrews <[email protected]> wrote: > For off grid, it also has to have heaters. Not being able to charge is > just as crippling if your site never gets above freezing long enough to > charge the batteries in the winter. Getting the batteries heated JUST > off the solar output ( not off of grid power ) is tricky and I am not > convinced that anything less than an 8K solar array is going to keep a > LFP site with any real draw happy over a winter. That's a killer... > > On 8/17/23 13:58, Brian Webster wrote: > > 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? > > > > -- > > AF mailing list > > [email protected] <mailto:[email protected]> > > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com < > http://af.afmug.com/mailman/listinfo/af_af.afmug.com> > > > > -- > > AF mailing list > > [email protected] <mailto:[email protected]> > > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com < > http://af.afmug.com/mailman/listinfo/af_af.afmug.com> > > > > > ------------------------------------------------------------------------ > > > > -- > > AF mailing list > > [email protected] <mailto:[email protected]> > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > < > http://af.afmug.com/mailman/listinfo/af_af.afmug.com> > > > > -- > > AF mailing list > > [email protected] <mailto:[email protected]> > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > < > http://af.afmug.com/mailman/listinfo/af_af.afmug.com> > > > > -- > > AF mailing list > > [email protected] <mailto:[email protected]> > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > <http://af.afmug.com/mailman/listinfo/af_af.afmug.com> > > > > -- > > AF mailing list > > [email protected] <mailto:[email protected]> > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > <http://af.afmug.com/mailman/listinfo/af_af.afmug.com> > > > > -- > > AF mailing list > > [email protected] <mailto:[email protected]> > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > <http://af.afmug.com/mailman/listinfo/af_af.afmug.com> > > > > > > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com >
-- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com
