Well... battery manufacturers (lead acid stationary) have used their Ah rating at 1.85 VPC (or some down as low as 1.65 VPC).
Certainly 1.65 vpc is a totally run down battery. 2 volts is frequently listed as 50% DOD. If GNB says you have 200Ah (1.85 VPC) at a certain discharge rate, they actually will deliver the full 200 Ah and it appears many would think 1.85 VPC is 100 useful DOD. 1.85 x 24 =44.4 and most gear will work down to that, but at some point North of 40 volts it usually quits. They also state that at 100% DOD you can get 250 cycles. With 10% DOD you can get 1500 cycles. In all my years working in telco central offices, I have never had one run batts so low that it went off line. You always got a generator going if was going to be an extended outage. We had to put in a minimum of 8 hours run time for RUS funded C.O.s So most telco batts probably get retired with maybe 10 significant discharge events on them in a 10-20 year period. So, in this sense, they are not being misleading stating capacity, but that is for a telco application. Solar powered applications, not so simple. You really gotta decide right from the git-go how many cycles you want your batts to last. From that determine what DOD will get you there, from that you have to figure out the capacity derating factor. Much easier doing this calculation for telco. From: Brian Webster Sent: Thursday, August 17, 2023 2:58 PM To: 'AnimalFarm Microwave Users Group' Subject: Re: [AFMUG] battery nerd question 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]> 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] 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:[email protected] On Behalf Of Mathew Howard Sent: Thursday, August 17, 2023 10:51 AM To: AnimalFarm Microwave Users Group 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]> 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]> 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]] 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? -- 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 ---------------------------------------------------------------------- -- 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 -- 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 -- 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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