Off Grid Living / Camping => Off Grid Living / Alternative Housing => Topic started by: lighthunter on May 02, 2021, 01:30:19 pm

Title: Battery data Flood Lead Acid
Post by: lighthunter on May 02, 2021, 01:30:19 pm
One recurring question that comes up often when considering the cost of a battery for an RE system is "what about a used forklift battery?
After several years of use i thought it might be useful to some
if i share data from a typical used traction battery to give an idea what to expect.

The speciman, a 510AH 48v 2000lb lead antimony made by enersys. 5 years ago it was sitting in a warehouse with a charge level of near zero less than 43v if i remember correct. I dont think i even had a way to measure specific gravity but by voltage im sure it was slightly above water. Pretty severe sulfation. It took weeks of slow charging but it came around.

It gets cycled daily from 1.250sg to 1.150sg
It has about 64.3% round trip efficiency which means if you discharge 9kwh (180AH) then you put back 14kwh.

Each day, provided sun is out, the bulk charge rate is from 40-60amps which terminates at 57.5V at around 2 pm, then absorb continues at 12-15 amps 53-56v which brings it to a moderate gassing level by 5pm.

After 180AH of discharge the resting voltage was 48.3
usable capacity is around 220AH

So these batteries are not terribly efficient some are better than this but it does a ton of work every day and i think these numbers would be typical for an end of life lead antimony. I think this chemistry always has a higher self discharge than other types though.

Certainly lithium is a better performer but they also cost more. The efficiency is a pretty good hit when its cloudy but when sun shines an  extra 5kwh is no big deal.

Our average continuous usage is 850w and the array size is 4500w on a sunny day, production can hit 30kwh.

(no clue why photo upside down,  ha! I even uploaded 2 identical images one upside down and one right side up, they both show up inverted. Oh well not a big deal.
Title: Re: Battery data Flood Lead Acid
Post by: noneyabussiness on May 02, 2021, 04:21:17 pm
+1 for traction battery,  mine is 2nd hand ceil battery,  i don't have the numbers like above but mine is in better condition I think, 660ah at c5 rate , i use between 200 and 300ah every night ( I also have 200ah of vla LA as well , that Ive cracked and filled a bit with extra water and resealed) . Minimum watering ( bout once a month) , by the ah gauge they hit full usually just after lunchtime as long as sun out...cost 3.5 grand with a 12 month warranty.. love it
Title: Re: Battery data Flood Lead Acid
Post by: Pete on May 02, 2021, 05:38:27 pm
Sounds pretty good for a badly treated battery bank. I have used flooded batteries for decades now, but recently I changed over to SLA, one thing I found when running a 12 volt system with them was that they did not like to take a very high current. I have a 2500 watt panel setup but the best charge I ever saw going into the 12 volt bank was only around 1kw.
Since changing over to 24 volt we regularly see upwards of 1500 watts going in.
Our problem ( if it is a problem) is that we use very little from the batteries, usually only around 5% capacity each night, so our batteries are fully charge by around 10:30am. We use power in the afternoons to pump water, etc.
Still where we live we get a lot of foggy days and plenty of rainy ones, so it is good to have plenty of storage (660AH , 24 volt now)
We are in the process of dumping Gas usage, at the moment we have a gas stove and a backup Instant Gas hot water system.
We will be going to a small  2400 watt oven and an induction cooktop. As most of our cooking is done in the day time we should get free of gas with no problems. Our wood heater has a wetback and also the solar hot water system has a backup electric element too.
Title: Re: Battery data Flood Lead Acid
Post by: noneyabussiness on May 03, 2021, 01:04:14 am
Mine is 48v, so not that badly treated, would never bother with 12v unless low load,  currents just get to high... regularly over 6kw going into batteries before we moved, beauty of 48v.. thought of going " lithium " but just way too expensive for my requirements..
Title: Re: Battery data Flood Lead Acid
Post by: Pete on May 03, 2021, 06:13:02 am
Yes I agree, Lithium is pretty expensive, even going 48 volt with AGM or Gel is too expensive for me. New 24 volt bank was pricey enough. We don't plan on drawing more than 2400 watts at any one time and even then only for short time cooking.
Good to hear that your system is working well.
I would have thought that fork lift batteries would be pretty heavily cycled, but then maybe some only get used a few hours a day. Nice to hear how they perform
Title: Re: Battery data Flood Lead Acid
Post by: lighthunter on May 03, 2021, 11:07:16 am
"mine is in better condition I think"

yes, this one is fairly spent. The self discharge is what kills this one, it takes 4-5 amps of continuous charge just to offset self discharge, 1-2kwh in 24 hrs. I was pretty bummed about the performance until i learned that batteries arent to charge up and look at. Just work it and dont worry about it and ive gotten along with it much better. Everyone has a little different situation though. Sounds like you guys have systems that work for you. I never tried 12v but 24v did work for me for a time. 48 with large battery helped the grid tie a lot, i never see it trip out anymore because of volt instability.

Title: Re: Battery data Flood Lead Acid
Post by: Pete on May 03, 2021, 05:38:24 pm
Hi LH, I have read enough here to agree that 48 volt seems the way to go. I started using solar about 40 years ago, so 12 volt was it, I stuck with 12 volt until last year when I changed to 24volt. I mainly did that as I did not want to have to run my generator to use my air compressor on rare occasions, and also to lower battery current.
So far it is great, I can even use my MIG welder for small jobs.
We had grid power when we moved to the mountain we live on , but did not like power bills so got rid of it and cut the poles down.
Being and off grid person for so long, I could not come to grips with paying bills for power when there is a great big thing in the sky that supplies it free.
Title: Re: Battery data Flood Lead Acid
Post by: lighthunter on May 04, 2021, 09:44:31 pm
Hi Pete, i couldnt agree more. We do have the grid still and i do pay enough of a bill to keep em happy. My old man warned me not to get rid of power company for resale value of realestate. HA! i do agree with him  however a working solar setup also boosts the price of property. At least my insurance agent thinks so. Once i described the solar install they had the appraisal near ten times what i paid for it. I didnt go for as i couldnt have paid the premium.

24v actually worked fine for me. I had only two 40AH lithiums for the 24 so very undersized but we are usually between 500-2000 watts and usually under 1kw so backcharging is higher than use.
Nothin wrong with usin what you have!

Title: Re: Battery data Flood Lead Acid
Post by: Pete on May 05, 2021, 12:17:05 am
Hi LH, yep as far as we are concerned resale value is not an issue. My partner and I plan on leaving here in a box. That is unless our government approve home cremation (Indian Style) then we will burn whoever croaks it first.,May have to work on a timer ignition setup the the other one.