If the batteries were in a tight, very well insulated container, keeping them warm will take very little energy. Think of a giant dewar box. Once they are at temp they should hold it. And discharge as well as charge will cause them to heat.
From: Mathew Howard Sent: Thursday, August 17, 2023 5:25 PM To: AnimalFarm Microwave Users Group Subject: Re: [AFMUG] battery nerd question 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
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