DIY power system build thread

[sheddi]

Have to admit when I saw your list of items to power and the size of the battery box it looked like an expensive failure waiting to happen. Looking up the specs on some of the options available now has changed my mind. The advances in offgrid power have come a long way in the last 20 years when I built my first system - T-105 FLA batteries at 120 pounds for the smallest 12v system, only 50% depth of discharge if you wanted them to last very long, and panels costing 4-5 dollars per watt.

I had kind of assumed I'd need 1000 Wh of capacity but I am still going to put off doing math until I'm further along in the project.

Much like CrossCut my mind is still in the 1990s when it comes to battery technology.

Taking your 1000Wh (which I'm calling 85 Ah at 12v nominal) as a benchmark, I am pleasantly surprised to discover that I can buy that in the UK as LiFePO4 for about £400 (US$560), and I could cycle it to 100% DOD every day for 5-10 years.

Or I could buy 260 Ah of AGM lead-acid, which will be bigger and heavier, for £300 (US$420) and cycle them to 33% DOD daily for two years.

Or if I was really cheap I could buy the same 260 Ah of flooded lead-acid for £150 (US$210), and cycle them to 33% daily for 6-12 months.

I guess it comes down to how often I expect to use them. If I was geniuinely of grid, or living in a boat or RV, I would be using the battery every day and space/weight would be at a premium. The LiFePO4 would be a clear winner. The same would be true if I had a time-of-day electricity tariff and I wanted to use the battery to exploit it. But for a standby application in a house or apartment, where I might only use them a handful of times a year decade and the rest of the time I can care for them on float charge, the lead-acid options could be adequate and I'd save a few bucks.

And one benefit of the lead-acid options is that you've actually got 260 Ah of capacity, not 85 Ah. Yes it would destroy your cyclic lifetime but, if you found that you _really_ needed 3000 Wh between charges (maybe the sun isn't shining on your panels, or the grid is down for longer than the power company promised*, or ZOMBIES), you have the option. If you've only got 85 Ah and you've used them all, well there isn't any reserve capacity.


* Interesting aside: here in the UK, at least, there's a regulatory obligation on the power companies to restore power after an interruption. If you're without power for more than 12 hours, the power co is on the hook for compensation. Which is why, the one time in the last ten years that we had a serious outage, after 11 hours the power co parked a humungous diesel generator next to the substation that serves my street and the neighbouring ones, and hooked it up. Every couple of days they'd come around with a bowser full of diesel and refuel it. We had that generator in place for about 2 months, if memory serves, while they found the underground fault made good.

https://www.citizensadvice.org.uk/consu ... power-cut/

[RonnyRonin]

But for a standby application in a house or apartment, where I might only use them a handful of times a year decade and the rest of the time I can care for them on float charge, the lead-acid options could be adequate and I'd save a few bucks.

I'm in a similar boat, and part of the battery research I'm putting off is which chemistry and form factor is best for sitting around and not being used very often.

I'm also tempted to play craigslist roulette, as right now there is a (claimed to be) new 12v, 225ah flooded lead-acid battery for $165. At 128 lbs it is far from what I really want, but the price per capacity is pretty hard to argue with and I don't think that price is out of the ordinary around here.

[woodsghost]

But for a standby application in a house or apartment, where I might only use them a handful of times a year decade and the rest of the time I can care for them on float charge, the lead-acid options could be adequate and I'd save a few bucks.

I'm in a similar boat, and part of the battery research I'm putting off is which chemistry and form factor is best for sitting around and not being used very often.

I'm also tempted to play craigslist roulette, as right now there is a (claimed to be) new 12v, 225ah flooded lead-acid battery for $165. At 128 lbs it is far from what I really want, but the price per capacity is pretty hard to argue with and I don't think that price is out of the ordinary around here.

I would not touch a flooded lead acid battery for this application. It will off gas dangerous gases, especially considering use in an apartment.

Also, lead batteries only get half the capacity without undue damage to the battery. If you used the full 225AH you would only be able to run the battery a handful of times before it died. Or you would see greatly degraded performance. All lead acid batteries can only discharge to 50% of rating without damage. So that is a 128lb, 112.5AH battery which off gases dangerous fumes and needs to have the water topped off on occasion.

If considering lead acid, I would go with sealed AGM or gel. Remember, a lithium (various chemistries) battery will cost 4x what a lead acid battery does, but effectively has 2x the capacity. So really you need to compare the price of a 100AH lithium to the price of a 200AH SLA battery, and that will give you the true bang for your buck.

[woodsghost]

But for a standby application in a house or apartment, where I might only use them a handful of times a year decade and the rest of the time I can care for them on float charge, the lead-acid options could be adequate and I'd save a few bucks.

I'm in a similar boat, and part of the battery research I'm putting off is which chemistry and form factor is best for sitting around and not being used very often.

I'm also tempted to play craigslist roulette, as right now there is a (claimed to be) new 12v, 225ah flooded lead-acid battery for $165. At 128 lbs it is far from what I really want, but the price per capacity is pretty hard to argue with and I don't think that price is out of the ordinary around here.

I would not touch a flooded lead acid battery for this application. It will off gas dangerous gases, especially considering use in an apartment.

Also, lead batteries only get half the capacity without undue damage to the battery. If you used the full 225AH you would only be able to run the battery a handful of times before it died. Or you would see greatly degraded performance. All lead acid batteries can only discharge to 50% of rating without damage. So that is a 128lb, 112.5AH battery which off gases dangerous fumes and needs to have the water topped off on occasion.

If considering lead acid, I would go with sealed AGM or gel. Remember, a lithium (various chemistries) battery will cost 4x what a lead acid battery does, but effectively has 2x the capacity. So really you need to compare the price of a 100AH lithium to the price of a 200AH SLA battery, and that will give you the true bang for your buck.

I should add, you should size your system for 3 days of no solar input. There are always cloudy days and rainy days. Maybe not where you are? But typically in the US it is recommended that one size the system for running your needs for 3 days without any solar input. As a Prepper, I would at least consider upping that to 5 days. Or maybe building a second backup system would be better.

Just some thoughts.

[RonnyRonin]

I would not touch a flooded lead acid battery for this application. It will off gas dangerous gases, especially considering use in an apartment.

Also, lead batteries only get half the capacity without undue damage to the battery. If you used the full 225AH you would only be able to run the battery a handful of times before it died. Or you would see greatly degraded performance. All lead acid batteries can only discharge to 50% of rating without damage. So that is a 128lb, 112.5AH battery which off gases dangerous fumes and needs to have the water topped off on occasion.

If considering lead acid, I would go with sealed AGM or gel. Remember, a lithium (various chemistries) battery will cost 4x what a lead acid battery does, but effectively has 2x the capacity. So really you need to compare the price of a 100AH lithium to the price of a 200AH SLA battery, and that will give you the true bang for your buck.

I definitely know about the risks and limitations with LA, and I'd have to treat a FLA much different than I would like to use it in this case, but quite simply I haven't seen half sized lithium batteries out there for even twice the price, so its at least tempting to consider. Like I said my back of the napkin goal is something in the neighborhood of 1000Wh so 225ah would exceed that at 50%. I likely will talk myself into lithium eventually, but I'm trying not to rule anything out this early on.

[sheddi]

In this guy's video description he has lists of parts if you want to buy them, so that is pretty helpful.
Like my own 15AH battery setup, this is pretty minimal and short in duration for what it can do. But he has a well thought out project and good reasons behind everything he did.

https://m.youtube.com/watch?v=g2cLMk3nD3Y

Rather than watch the 52-minute video I read his Instructable (the same build):
https://www.instructables.com/Ammo-Can- ... er-Supply/

I like that idea. Ammo cans are a little bit harder to come by in the UK (although I see a selection on eBay) but I can get one of those solar power controllers for under £6 (eBay again). I've got most of the other components in my parts box. I'll have to give it as go some time.

[sheddi]

Or the "keep me accountable" guilt thread.

Hopefully your project will be the kick in the ass I need to assemble mine. I have all the parts, just not the motivation.

See, it's this thread and Blast's video that gave me the push to put together my demo. ZS is a mutual support group for demotivated geeks

[Blast]

See, it's this thread and Blast's video that gave me the push to put together my demo. ZS is a mutual support group for demotivated geeks

Our second motto, "I'm definitely going to do that!"
Our third motto, "Really, I swear!"

-Blast

[sheddi]

In this guy's video description he has lists of parts if you want to buy them, so that is pretty helpful.
Like my own 15AH battery setup, this is pretty minimal and short in duration for what it can do. But he has a well thought out project and good reasons behind everything he did.

https://m.youtube.com/watch?v=g2cLMk3nD3Y

I like that idea. Ammo cans are a little bit harder to come by in the UK (although I see a selection on eBay) but I can get one of those solar power controllers for under £6 (eBay again). I've got most of the other components in my parts box. I'll have to give it as go some time.

OK, I've scrounged up an ammo can and (as you'll have seen from other threads) I've got one of those ultra-cheap shunt solar regulators.

I don't really want to use that 6Ah motorbike battery for a power station build, it's an awkward sive and was replaced because it didn't like cold weather. I've run through a few options since then:

• 12v 12ah SLA (free). I've got one here I salvaged from an old UPS but it seems that it's unhappy. It sits there at Vbat = 12.5v; it won't accept any appreciable charge but if I put a 0.25A load on it, Vbat drops to 10.8v. I suspect one of the cells is shot.
• 11.1v Li-ion (US$40). I was looking at salvaging 18650 cells from NOS laptop batteries and DIYing a pack but then spotted these ready-made 3S4P packs on Aliexpress. The downside is the hassle of Li-ion voltages and charging in a lead-acid world.
• 12v 6Ah LiFePO4 (US$33). I was about to buy a Li-ion pack and a boost device to get it back up to 13v when I saw this Miady 12v 6Ah LiFePO4 which looks a steal at that price. It does however have a limited discharge current of 6A, which might restrict some "power bank" applications.
• 12v 30Ah LiFePO4 (US$60). I went back to AliExpress to see whether the Miady battery was available there, and that took me down a rabbit hole to this 4S3P LiFePO4 battery pack. The capacity value is almost cetainly a lie (it would need 10Ah 32700 cells and I can't find any independent evidence they exist) but even with 6Ah cells, for an 18Ah LiFePO4 battery it's a good price.

I've ordered one of those last batteries from AliExpress. It's on a slow surface shipment (air freight of lithium batteries is problematic) and should be with me in 6-8 weeks. When it turns up I'll report back. It will be my first ever LiFePO4 battery and I'm mildly excited by the prospect.

(I should add that I blew my budget. I was hoping to get a battery for GB£30 / US$40 but the added bang-for-the-buck of that last pack was too tempting.)

Edit to add:
For roughly the same price as the 30Ah LiFeO4 battery plus taxes and shipping, I could have bought (locally) a much larger 55Ah flooded lead-acid battery (not suitable for a portable power system) or a pair of 15Ah Ah AGM battery.. If the LiFePO4 really is 30Ah then I'm definitely up on the deal, if it's 18Ah then I'm roughly even on cost-capacity with AGM but have advantages w.r.t. weight, volume and life.