Battery chat

[Bossrox]

Anything to do with batteries

I'd like to gather others with different battery systems to compare results & schemes of how your using them, types of batteries, drain % cycles, charge efficiency you're getting & any other nuances to get any better ideas what's really working well & what's not.

This is where I'm starting from & as time goes on, will be updating it's evolution as I go along.

I'm in the process of building my system & got a hold of 2 huge barely used Cat industrial 12v 190 a/hr batteries for a super deal @ $250 for both, retail new is around $400 a piece & using them in series for a 24 volt system.

Once I get all my components put together, I'll give a report on the usage I'm able to get from them just on their own without my panels. According to an a/hr to kw/hr conversion chart, these batteries will produce about 4.5 kw/hrs which isn't much so it looks like I need to keep an eye out for some more battery deals.

Another ? I don't know the answer to yet is, does extracting just about all its energy just a few times cause considerable damage to cycle life or does it take many deep cycles to substantially curtail cycle life? Known wisdom says it's best to avoid really deep discharges. Battery longevity is based on the amount of discharge rate they endure & it's pretty well established, for best longevity it's best to keep discharges under 25%, so it's best I shouldn't extract more than a 1.2kw between charges.

Another thing I'm curious about is when it comes to keeping up the levels on flooded cells, why it's customary to add distilled water instead of more battery acid. It would seem to me adding water would weaken the acid.

Well, I found the answer to that, being mostly oxygen & hydrogen are expelled in the cycling process, most of the sulfur stays put thus you are just adding back the water lost from it's gassing.

I found answers to these ?'s & much more @ solarhomestead.com/energy-independence/battery-care/ so if you want to bone up on these & other important solar & battery issues, there's where you can find answers to many ?'s & get you off in the right direction

This site also has some important in depth info about proper charging protocols @ batteryuniversity.com/learn
/article/charging_the_lead_acid_battery

Update: Got my 4000 watt inverter in & ran a 750 watt heater on just the batteries, no solar input for 3 hours & according to the chart further down, with my resting voltage at 25.5 volts, I used about 40% of the batteries capacity which showed me that my used batteries are in peak performance, what a relief but more intrestingly, using 2.25kw should've taking them down to 50% & didn't so I'm even more impressed with these Cat batteries, but showed me also that I need to at least double my bank size.

Update 2: Got lucky & found 6 120 amp/hr AGM batteries barely used for $600 so now I'm @ 1100 amp/hr capacity or about 6.5 kilowatts available @ a 50% discharge.

Update 3: Just landed 8 more used Cat 200 a/hr batteries adding 1600 a/hrs, raising capacity to now at 2700 a/hrs or about 8kw @ a 25% discharge. Things are looking up here!

Update 4: I decided to build a separate shed for the battery bank that now houses 20 of those big 200 a/hr cat's along with 6 / 120 a/hr AGM's totaling a 4700 a/hr bank that'll deliver 11kw's at a 20% drain. Now were talking serious power! But there's still another 1600 a/hrs that'll be added later for a 6300 a/hr bank with a 20% draw of 15kw & a total of 75 kw to fully discharged.

[Bossrox]

Battery desulphators, Epsom's Salt & EDTA, real or snake oil?

I've read a ton of articles on desulphators & never ran across any conclusive scientific evidence these gadgets really do anything but I did find many testimonials & an article from a convincing source that put the battery minder & pulsetech brands to the test on 2 batteries that just wouldn't take a charge, nearly stone dead as they said & put these units on them for a couple weeks & to my surprise, they were restored adequately to be put back in service & used for the next 4 months without any issues before publishing the story.

The negative & positive testimonials weren't enough to push me in any direction but the article swayed me enough to order a batteryminder I got cheap on ebay & the 2 used industrial batteries I got, seem a little resistant on holding a full charge so you'll get a report on my results in the near future. Any opinions?

The conclusion I've come to about EDTA is yeah it'll yank the sulfur off the plates & give you some extra life but also eats up the lead eventually too so you'll get some more months of use out of it but later after the lead is diminished, it's toast so this method looks to be best used on batteries near their death bed.

Epsom's salt I haven't looked into enough to form an opinion on yet altho there's a lot of good results being reported but unless I had a battery near it's end, I don't see it as wise to gamble with a still decent battery that might do some good but could ultimately shorten it's lifespan. Any opinions on those too?

Update: Hooked up the batteryminder & it'll stay hooked up & hopefully deal with any sulphation there may be & eliminate any build-up to come & better than without.

I should have kept notes on my batteries resting volts before I put on the batteryminder but now that it's been working on my batteries for 3 days, it's resting volts after 6 hrs is 25.4, just what the chart below signifies as 100% charged so it looks like I got a hold of a good set of used batteries cheap & or the batteryminder already done good.

Update: It's now been about a year since the above post & I'm now a believer in desulphators or at least the batteryminder brand. When I 1st starting using the batteryminder & getting 25.4 volts at rest, I thought, yeah, seems like it's working but no real convincing evidence. But a year later, the batteries are showing better resting stats than at the start. I'm now seeing up to 26 volts after an overnight rest.

Aging batteries are suppose to develop an internal resistance from sulfation build up so I've read, which amounts to the amps still trying to push into the battery after it's fully charged being an indication of it's condition. A low amp reading after fully charged like 1 amp or less is a great sign, higher indicates there's some degradation.

After a year in service of the 2nd hand batteries I got, I'm seeing about 1 amp on float for a 550 a/hr bank. that along with seeing a 26 volt resting output, convinces me the batteryminder not only delivers on it's claim but took my second hand batteries & appears to made them better than when I got them. I'd even say, they appear to be about as good as new.

Update 2: My battery bank is now up to 3500 a/hrs & shooting for 4700. Batteryminder says their device is good for up to 8 batteries connected together. An average battery is around 100 a/hrs so to have adequate desulphation power, I need a desulphator for every 800 a/hrs of batteries & boy did I get lucky. A batteryminder is typically around 80 - 100 bux a piece & I ran across a clearance sale at a marina online who sold me 5 of them @ $45 apiece, saved me a ton of bux. 5 added to the 1 I already got for 800 amps x 6 = 4800 & once I get all the batteries I'll have, looks to be a near perfect match up.

Update 2.5: It's now been about a month since upgrading the battery bank to 3500 a/hrs with the 6 desulfators. From the start, the lowest back current I was seeing was about 16 amps, now after a month of monitoring, it's slowly dropped to about 10 amps so with a battery bank of 14 - 200 a/hrs & 6 -120 a/hrs, that's less than an amp back current per battery which I find pretty remarkable for used batteries & pretty fair evidence the desulfators are effective at doing what they claim they can do.

Can it go even lower? Will see after another month & I'll let you know but less than an amp per battery back current is a satisfactory stat to me, anything better will just be astonishing to see.

Update 2.75: The test was interrupted as the battery bank was just jacked up to 4700 a/hrs but before adding them, saw my back current down to 8 amps.

So now the test will have to be started all over again & with an additional 1600 a/hrs of batteries planned for the near future, I got another 2 desulfators. Since it will be awhile before the other batts are in, I added those desulfators to the existing system to see if it would speed up lowering the back current charging stats.

Now I have to see what my new back current stats are & wait to see how much it'll improve. Will update that when there's something to report...... Looks to be about 15 amps for the new back current. So adding 6 batteries almost doubles it. Now this ought to be a real good test, we'll see what happens.

[Bossrox]

Wondering what condition a battery is in?

Here's a chart for LiFePO4 batteries from unknown source...



You'll note the section between the yellow coloring is the recommended charge/discharge range to work within for maximum lifespan. As it is, cycling from a full charge to near discharge, lithiums are typically rated for 2000+ cycles but staying inside that range is said to increase it another 1000+.

I found this lead/acid chart that looks like a reputable gauge of judging a batteries state.

The following information comes from AEE Solar.



A hydrometer is very accurate at measuring battery state-of-charge if you measure
the electrolyte near the plates.

Unfortunately, you can only measure the electrolyte at the top of the battery.
When a battery is being charged or dis-charged a chemical reaction
takes place at the border between the lead plates and the electrolyte.

During charging the electrolyte changes from water to sulphuric acid.
The acid becomes stronger and the specific gravity rises as the battery charges.

Near the end of the charging cycle gas bubbles rising through the acid stirs the
fluid to mix it.It takes several hours for the electrolyte to mix so that an accurate reading can
be taken at the top of the battery.

Always try to take readings after a period of no charge or no discharge.

[Bossrox]

The proper level of fluid your batteries should have

According to "Crown" battery makers, levels should be at the bottom of the vent for lead acid batteries. Letting the plates get exposed & overfilling will damage them. Never use any other water but distilled to top them off. That's all folks!

[Bossrox]

Can batteries freeze? Here's the answer.

Answer provided by Progressive Dynamics.

If your battery is partially discharged, the electrolyte in a lead acid battery may freeze. At a 40% state of charge, electrolyte will freeze if the temperature drops to approximately -16 degrees F.

When a battery is fully charged the electrolyte will not freeze until the temperature drops to approximately -92 degrees F.

[Bossrox]

Saving big, look for good used batteries

I got lucky & found 2 used Cat industrial batteries on Craigslist that appeared in nice shape. About $800+ worth new, got 'em for $250 & after a long drain test run, they check out to be in peak health.

Then I ran across 6, 125 amp/hr agm 12 volts made by vmax, also in like new working condition for $600 that retails @ $1800. What a lucky break that was!

I placed an add on Craiglist hoping to run across more like that but nothing yet. Of course I hope you know some battery basics when examining used batteries for their viability before snatching up just any old battery. If it's lead acid, pop the caps & look for excessive sulfation build up. Golf cart places are selling tons of these but they're in pretty rough shape even tho they might be showing full voltage.

Craigslist came thru again! This time I got 8 used monster Cat 200 a/hr in great shape for a grand or $125 a piece. New price, about $400 apiece, so all together, I'm now at 2700 a/hrs in battery power or 30kw from full charge to full discharge but @ 25% discharge where I don't like going past, I can get 7.5kw.

A good test is to charge a battery full up & check the voltage after 8 hrs. If it's a 12 volt & if it's in good shape, you should see 12.7 volts or 25.4 on 24 volt batteries. I'm getting readings of 25.8 to 26v on mine so they're looking great.

Update: Craigslist came thru again! Found a source for some CAT 200 a/hr batteries & picked up 8 for a grand. Going back for another 12 as soon as I can scrape together another grand which will then give me 20 - 200 a/hr batteries plus the 6 - 120's I already have for 4700 a/hrs of battery power weighing @ around a massive 2 tons.

Eventually I'll be adding another 1600 a/hrs & found a source that usually has what I need on hand whenever I'm ready to get 'em

The CAT 4 & 8 d's sell for about $400 a piece new & the vmax 120's at $300 new which is $9,800 worth of batteries I got for around $2,600. My final goal of 6300 a/hrs will take 8 more Cat's for another $6-$700. I can't imagine I could've done any better & what a powerhouse bank size it'll be.

[Bossrox]

Tesla Lithium Ion Batteries looks better

I've just got a fetish to ditch my lead acid batteries for a Tesla model S battery pack which is 24 volts. Can pick 'em up used on ebay for around $1,200. The benefits are way better, Unlike the lead acid,itI can take an 80% discharge without significantly shortening it's lifespan of 3000+ cycles vs the my lead acid that would be toast after a couple hundred cycles if that. The charging efficiency is way better too, 70% lead acid vs 95%+ with Tesla, less solar energy wasted for recharging.

There are some cautions to protecting & running them safely, can't charge them below freezing & have to keep charging voltage under 24.4 volts witch means you have to have a programmable charger & not letting them fall below 19 volt so unless your inverter has such a low voltage shut off, you'll need to put on an external device.

My current batteries have a 4.5 kw potential from full charge to full discharge & the Tesla model S battery is a bit more @ 5.3kw but reality is if you want to keep lead acid batteries very long, you can't take more than 25% at a time which limits you to 1.25 kw per cycle vs the Tesla that appears it could deliver 4kw without much stress & the equivalent of quadrupling my lead acid bank.

Used Tesla batteries are selling on average for $1300, if I were to match the Tesla useable safe drain range with what I'd need in lead acid for a safe drain level, I'd need 6 more of the 190 a/hr batteries like I have now that cost $400 apiece, 6x400= $2400 & according to cycle stat comparisons, Tesla is suppose to be double or better for amount of cycles.

Another plus is it only ways 55 pounds, just 1 of my 190 a/hr batteries weighs 100 lbs or more. That's a buncha power coming from something that light & another bonus is it's charge efficiency. My understanding is lead acid takes 30% more energy to fully charge them than what they gave out, Tesla is suppose to be around 10% & no potentially explosive hydrogen accidents but on the other hand, a few stories of the Tesla's bursting into flames so it's a crap shoot on safety.

At some point it's likely I'll do this but I need to get a bit more info I'm not sure of yet & anybody that has some in depth knowledge about this battery they'd like to share would be appreciated. I just learned than these type batteries are controlled by something called a BMS so 1 question I'd have, is a BMS controller part of the Tesla battery or do you need to add that? I saw a video on youtube of a guy that just hooked it up like a regular battery & adjusted the charge settings on his MPPT controller & was done with it. If I upgrade to this, you'll get a report on it after it's done but it'll be awhile to get up that kinda cash to spend anyways so stay tuned.

Well it's been many moons since I posted the above & I'm already heavily invested in lead acid so the Tesla's are off the table for now. Maybe after I wear out these lead acids, I might look at them again & by then there may be other alternatives, will see.

[Bossrox]

If your batteries are outside, for winter they'll need to be kept warm

If you know much about batteries, they'll struggle on energy output if they're real cold & harder to charge so I wrapped mine in thick insulation & putting a mat heater pads underneath them. I haven't tested it yet & got an 18 watt heater to start off with to see whether it could keep them warm enough for best efficiency. I'll give a report on that as soon as it's done.

Well, it was 44 degrees tonite & the 18 watt pad under the batteries was wired in at sundown, checked it before sunrise & it heated them 12 degrees more for 56 but after a couple of days it's up 20 degrees more, still not enough so I ordered a 28 watt bigger pad & will see how that does.

Update: My battery bank size has increased & was moved into it's own insulated shed. To keep them warm, I ordered some 17.5 watt heating pads for each set batteries, 8 heating pads to stick under them for this winter hooked up to a thermal switch set for a 70 degrees cut off, will let you know if it's enough to get it done.

Well after some pretty frigid nites below freezing, the heating pads performed terrific keeping the battery shed temp at around 70 using less than 100 watts to do it.

[Bossrox]

Lead carbon batteries also a good looking choice

There aren't but a couple companies offering these batteries but the level of discharge they can be taken down to & have a respectable cycle life is impressive.

Outback brand has or should say had 'cuz it appears you can't find any, a 12v 200 a/hr model I've seen as low as $500 with an average 50% discharge is claiming 2600 cycles, bulk charges @ 14.4v with a float of 13.6v.

A Trojan SPRE 12 225 12v in the 255 a/hr range is around $375 with a 50% discharge cycle life of 2000 & a pretty good 4700 cycles @ 20% & they are adopting some form of carbon formula in it's construction, bulk charges @ 14.7v with a float @ 13.5v.

The firefly oasis 12v 115 a/hr battery looks pretty intresting using carbon foam with an amazing cycle life of about 4000 @ 50% & a whopping 10,000+ @ 20% but rather small in a/hrs for the price of around $500 a piece but if you take into account it's cycle life, it looks to come in the cheapest for cost per watts by it's extraordinary cycling claim.

Victron is also offering a 160 a/hr carbon lead claiming 500 cycles @ 100% discharge but their low discharge cycle stats aren't real impressive.

After doing some checking, no one has the outback battery, I've been looking at all kinds of new battery technology & with all kinds of hype of a new ultra battery revolution ready to be launched then some were around briefly but then vanished. It's starting to look like there's some kind of conspiracy to keep anything better from getting in the hands of the average consumer & access only to corporate ventures. Something stinks here.

[Bossrox]

A question about discharge % to cycle rate?

I'll find the answer to this soon I'm sure but right now, when look at the cycle life to discharge rate on battery stats, this is the ? I want to find out..... If you bring a battery down to 50% just once, does that 1 episode reduce it's cycle life to the 50% level permanently or does that just apply to discharging it that much on a regular basis?

[Bossrox]

Sizing your battery bank to your usage

Now that I have my system in real life use, I've been able to monitor my parameters to see what I can expect from the system & what improvements would be needed to reduce using utility power next to nothing.

1st you need panel output to exceed your average daily kw usage. You'll want to be able to meet your demand needs while at the same time have excess to send to your batteries. Many utility companies have stats on your usage by the day & hour so you easily find out what you'll need in panel power to take their place.

I don't know if this is typical, I got my panels used but in great shape. I have 12, 320 watt panels which should give me the ability to put out 3800 watts but my charger will only accept 2900 watts running a 24 volt system. When I eventually go to 48 volts, it will accept 5800 watts & double the power.

For now tho, that 2900 watts on a full sun day in the summer has yielded as much as 18kw, that will be substantially less in winter with the days shorter

Most days aren't gonna be perfect as the sun dodges in & out of clouds or it rains all day or many days in a row but for a fairly good day I've been able to squeeze out about 14 to 16 kw.

Here now in spring, I'm not yet using much A/C so my average daily kw usage is about 12 kw.

During Summer, between 7pm & 9am I'm totally on batteries, so how do I figure what size bank I would need to get me thru the night without depleting them too much? Ideally, less than 30% would be good for battery life but in my case it's about 50% right now, not as good for battery longevity.

*Note: This was my old method when it was spring, now for summer I'm only on battery power for about 4 hours just before sunrise. The A/C's sock the crap outta the batteries.

Well here's what I've come up with as a guideline. My typical usage in Spring when no A/C is needed, is about 400 watts per hour at night x 14 hours for 5.6 kw I'll need from the batteries til the sun comes back up to take over. What would I need to run all nite on battery power?

For every 85 amp/hrs you have in battery capacity = about 1 kw. Since my night usage is about 5.5 kw & don't want to deplete my bank no more than 50%, I need at least 11 kw worth of battery capacity. 11x85 = 935 amp/hrs. I have 1100 a/hrs, so I can stay within my 50% goal with that but ideally to give my bank a good lifespan, I need to keep a drain down to at least 25% which would require a bank size of 3700 a/hrs.

Soon my 2 window a/c's will need to be fired up. The shed A/C runs non stop in summer, the cabin A/C cycles regular at about 40% duty but with both running at the same time, it consumes everything my panels can crank out which doesn't leave very much to send to the batteries.

To remedy that, I devised a circuit to switch the shed A/C back & forth between solar & utility power with a photo sensor switch so when the sun ducks behind the clouds utility power takes over saving the batteries from losing the charge it's building. You can find out more about this gadget in other threads.

Anyways, I hope this helped some of you plan your systems more effectively & some feedback would be nice too.

[Bossrox]

Another choice of battery brand to check out if you want to spring for new batteries.

I luckily ran across 6 like new used VMax 125 amp/hr batteries, never heard of them before that, but after checking out their site, I was really impressed with their catalog & stats.

The VMax battery company makes a huge line of AGM batteries, their biggest 1 is a monster 12 volt 350 amp/hrs @ a whopping 185 lbs for about $700 with free shipping. On their extreme series @ a 25% discharge rate they're claiming 2600 cycles & that's about 7 years, pretty impressive stats! @ 50% it's 1000 cycles or less than 3 years lifespan.

The Trojan SPRE 12-225 is what I was formerly leaning towards & costs about the same but 125 amps less & with AGM's there's no worry about explosive hydrogen gas or keeping up with the water levels, so unless something better shows up, that's looking the best value for new but I'm also looking at rebuilt forklift batteries as another option at a much lower cost per amp/hr than anything else I know of.

[Bossrox]

Understanding Amp Hours, kilowatts & Voltage

Kilowatts & amp hours are both a force of energy so closely related, it's easy to get confused. Those who aren't electrical savvy might think, for example, lets say you got 2 - 12 volt 200 amp/hr batteries hooked in series & you might think that would give you 400 amp/hrs, but no, the right answer is it's still 200 amp/hrs but the voltage is doubled now to 24 volts & the kilowatt output has doubled as well.

So, no matter how many batteries are hooked in series, the amp/hrs will remain the same but the voltage & kilowatts will be multiplied. In parallel, the voltage stays the same but the amp hours & kilowatts are multiplied.

[Bossrox]

Charging your batteries with utility power? Why?

I'm totally perplexed why many inverters have built in chargers for using utility power to charge your batteries or why anyone would use it. It's a waste of energy & $$$ & here's why.

If you don't know this, you should, it takes more energy charging batteries than what you'll get back in power from them.

I've found from my charger output stats, it takes about 13kw from the panels to replace 10kw's used from my lead acids. That's about 70% efficiency. Even with the Tesla powerwall, it's claim is 90% efficiency.

So if you have utility power, it's nutz throwing away $$$ charging batteries & instead using that wasted energy you could be powering your house with, 10 to 30% cheaper.

If your storage capacity is light, it would be much wiser balancing your system use where it's capable of generating demand with enough excess left over to keep your batteries topped off & then when you need to rely on the batteries, only take out what you know your panels can replace the next day then switch to utility power to keep your batteries from going too far into a deficit.

The whole idea around solar is getting the best bang for the buck & charging batteries with utility power defeats that goal.

All this of course is if you have utility power. If not, then this has little application for your situation.

[Bossrox]

Battery charging, energy out vs energy in. The real test.

I've been wondering for some time just what kinda loss is there replacing the power you take from a battery. Well I can calculate that pretty accurately now that I have a graphical interface with my charger & kilowatt meters coming off my 2 inverters.

It will be pretty simple, my charger will tell me how much energy was produced in a day & my kilowatt meters coming off the inverters will tell me just how much usable power was delivered for demand. The differences between the 2 will be the amount of loss went to maintaining the batteries & just a bit of a loss from the inverter.

I'm waiting on a 2nd kilowatt meter to come in for my new 2nd inverter. Yeah, I'm running 2 inverters at once now to cut the heavy load just 1 inverter was being taxed so as soon as that's in, you'll get a report here shortly what the results are. Stay tuned.

Testing results: Ok, here's what I surmised from a week of testing. If you're delivering most of your power from the panels with very little battery drainage, I saw about a 10% loss due to inverter inefficiency however, I've found for about every 10kw of power drawn off the batteries, it took 13kw from the panels to bring them back up to fully charged. So more or less taking inverter loss into account, I'm seeing it's taking about 30% more energy to replace what was taken off the batteries..