kitchen appliance off of small setup

johnelarue
johnelarue Solar Expert Posts: 33
A question on amps and power if you have a minute.

I have two 105AH RV semi-deep cycle Delco batts, charging off of 3- 50watt PV's.

I want to run a 500watt kitchen appliance. How long can I run it to 30% depletion of batts, and 50% depletion. ?

And how many watt inverter would I need.

Sorry for the beginner question but can't get it straight, thanks.

john
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Comments

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: kitchen appliance off of small setup
    johnelarue wrote: »
    A question on amps and power if you have a minute.

    I have two 105AH RV semi-deep cycle Delco batts, charging off of 3- 50watt PV's.

    I want to run a 500watt kitchen appliance. How long can I run it to 30% depletion of batts, and 50% depletion. ?

    And how many watt inverter would I need.

    Sorry for the beginner question but can't get it straight, thanks.

    john

    Well John, just a quick rough estimate - -
    Your two batteries, under totally ideal conditions, might provide 60 Amp Hours before hitting that 30% mark. 60X12= 720 watt hours. Considering inverter and other inefficiencies, you might reasonably expect to run your 500 watt appliance for one hour. That's assuming you run no other items, no lights, nothing until your batteries are fully recharged again.
    Now, how long will it take to recharge them with your 150 watts of PV?
    Again, considering normal inefficiencies, and assuming 4 hours of good strong sun falling on the panels each day, you should expect to add perhaps 400 watt hours (33 Amp Hours) to your batteries. That's approximately one half what you just took out of your batteries. Thus, to run your 500 watt appliance for one hour, will require approximately 2 full days of good strong sun on your panels. And remember, this is assuming NO other loads of any kind on the batteries.
    To drain the batteries down to 50%, you would be looking at close to 4 days of good strong sun (with no loads of any kind during those 4 days) to bring the batteries back up on full charge. If you hit a few cloudy days, well, you could be looking at a week or more to recharge them, again assuming you take nothing back out during that time.
    Hopefully this helps you decide where you want to go with your system, and/or what changes you want/need to make.
    We all have to start somewhere, and it's good that you're asking questions.
    The secret to successful solar power, is to keep all loads as small as possible, and conserve, conserve, conserve.
    Regarding inverter size - - you might consider two different inverters. A small one for small loads such as lights, and a larger one, perhaps 1000 watts, that would only be operated when needed for heavy loads. Reason being, it takes power just to run the inverter, and the bigger the inverter, the more power required just to keep it running. (wasted energy) Also be aware that non pure sine wave inverters can cause some appliances and other items to smoke or otherwise operate improperly. Which ones? It's trial and error, win some, loose some.
    Hopefully you continue on your solar journey.
    Wayne
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: kitchen appliance off of small setup

    500 watts from a 12v inverter running with 87% efficiency will draw 500/0.87 = 575 watts from battery. At 12.4 vdc this would be 46 amps. That is really too much current to pull continously from a 105 AH battery without damaging it. A 105 AH battery max continuous amperage draw should be no greater then about 25 amps. (same goes for charging current rate)

    At 46 amps, a 105 AH 20 hr discharge rating will be about equivalent to a 55 AH battery.

    30% discharge of 55 AH is 16.5 AH. 16.5 AH/46 amps is about 11 minutes.

    50% discharge of 55 AH is 27.5 AH. 27.5 AH/46 amps is about 36 minutes.


    I assume we are talking about a typical 'marine' 12v lead acid battery. An AGM may get away with it but I would not put that much stress on a $250+ battery.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: kitchen appliance off of small setup
    RCinFLA wrote: »
    That is really too much current to pull continously from a 105 AH battery without damaging it.

    He has two of those batteries, I assume in parallel.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: kitchen appliance off of small setup

    With two in parallel the effective AH yield at 23 to 25 amps from a 105 AH @ 20 hr rate will be about 65 AH each, 130 AH's for the two in parallel.
  • johnelarue
    johnelarue Solar Expert Posts: 33
    Re: kitchen appliance off of small setup

    Thank you very much for the detailed replies, greatly appreciated!
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    RCinFLA wrote: »
    500 watts from a 12v inverter running with 87% efficiency will draw 500/0.87 = 575 watts from battery. At 12.4 vdc this would be 46 amps. That is really too much current to pull continously from a 105 AH battery without damaging it. A 105 AH battery max continuous amperage draw should be no greater then about 25 amps. An AGM may get away with it but I would not put that much stress on a $250+ battery.

    Talking about stress:

    As some of you may know, my battery bank consists of 4 GC 6 volts batteries in series (24 volts; 200 amps). Now and then I see myself forced to connect a small water heater(4 gallons, 1,400 watts (12 amps)) to my pv system, for no more than 8 or 10 minutes a day. Is that "too much stress"? (By the way, I only do that when my batteries are fully charged and the sun is shining, so my mx60 is inputing around 600 watts or more in the batteries.)

    System: 6 kyoceras 130; mx60 controller, 4 Interstate golf cart batteries; 1 big and old AIMS 5000 inverter (msw).

    Thanks
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: kitchen appliance off of small setup
    JESSICA wrote: »
    Talking about stress:

    As some of you may know, my battery bank consists of 4 GC 6 volts batteries in series (24 volts; 200 amps). Now and then I see myself forced to connect a small water heater(4 gallons, 1,400 watts (12 amps)) to my pv system, for no more than 8 or 10 minutes a day. Is that "too much stress"? (By the way, I only do that when my batteries are fully charged and the sun is shining, so my mx60 is inputing around 600 watts or more in the batteries.)

    System: 6 kyoceras 130; mx60 controller, 4 Interstate golf cart batteries; 1 big and old AIMS 5000 inverter (msw).

    Thanks

    As a rule of thumb a battery can take a discharge rate equal to its charge rate. But your 12 Amps AC translates into about 58 Amps @ 24 VDC. That's pretty rough for 200 Amp hours of battery, were it sustained. In one hour more than 25% of the battery's capacity would be gone (not an exact figure, but close). In ten minutes - not so bad. Having the panels at peak output will take some of the strain off too, as you have surmised. Yes, it will shorten the battery life. But it's not likely to cause a sudden catastrophic failure.
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    As a rule of thumb a battery can take a discharge rate equal to its charge rate. But your 12 Amps AC translates into about 58 Amps @ 24 VDC. That's pretty rough for 200 Amp hours of battery, were it sustained. In one hour more than 25% of the battery's capacity would be gone (not an exact figure, but close). In ten minutes - not so bad. Having the panels at peak output will take some of the strain off too, as you have surmised. Yes, it will shorten the battery life. But it's not likely to cause a sudden catastrophic failure.

    Thanks, Cariboocoot.

    Would a battery bank of same size, but AGMs, be "toughfer"? Are AGMs inherently more capable of sustaining such discharge? Or would I have to size up the bank anyway? [Note: I will have to upgrade my bank in about a year. So, I am thinking of going to AGMs, but only if the change (and $) are worth it.]
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: kitchen appliance off of small setup

    AGM's can take higher charge and discharge currents than FLA's so they are a better choice for heavy discharge applications. They produce less internal heat, and as we all know heat is the enemy of everything electrical.
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    JESSICA wrote: »
    [Note: I will have to upgrade my bank in about a year. So, I am thinking of going to AGMs, but only if the change (and $) are worth it.]

    Did I say "in about a year"?

    Oh boy. How wrong I was!

    Yesterday, after my monthly equalization process, battery full, and mx60 showing “float” for about 30 minutes, I plugged my small freezer (around 90 watts) and a fan (60 watts) to my inverter. After less than an hour, battery bank voltage dropped to 23.4, and my inverter started to beep, indicating a low voltage condition.
    I unplugged everything and let the batteries charge again. In less than 10 minutes my controller and a craftsman voltmeter showed 27.4 volts. Thus, I plugged both appliances again… and in less than 15 minutes “23 volts” again, and the same “beep”. So I disconnected everything and let the batteries charge for the rest of the afternoon (3 – 4 hours, from 2:00 to 6:00 PM; sunny day). This morning, same thing happened again.

    I am no expert, but I fear my batteries have gone kaput. Am I wrong? Can I do something to save them? Is there still some life in them?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: kitchen appliance off of small setup

    even though agms are tough they are still lead acid batteries that will be diminished in their capacity when strained. if you can manage 400ah i think you will see a good improvement over what you have and if they are agms it would be even better. it will cost you any way you look at it.:cry:
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: kitchen appliance off of small setup
    JESSICA wrote: »
    Now and then I see myself forced to connect a small water heater(4 gallons, 1,400 watts (12 amps)) to my pv system
    Thanks
    There are a very few things in this world that are really, really bad ideas and EXTREMELY inefficient. Using solar produced electricity in an off grid battery system to run an electric water heater is definitely one of them! Sort of like using a staple gun to hunt polar bears. Seriously, please look into solar hot water panels. For small amounts, even a coil of black plastic pipe coiled out in the sun will give you hot water without destroying your PV system.
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    There are a very few things in this world that are really, really bad ideas and EXTREMELY inefficient. Using solar produced electricity in an off grid battery system to run an electric water heater is definitely one of them! Sort of like using a staple gun to hunt polar bears. Seriously, please look into solar hot water panels. For small amounts, even a coil of black plastic pipe coiled out in the sun will give you hot water without destroying your PV system.

    Very, very good advise, but too late!

    Thanks anyway.
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    niel wrote: »
    even though agms are tough they are still lead acid batteries that will be diminished in their capacity when strained. if you can manage 400ah i think you will see a good improvement over what you have and if they are agms it would be even better. it will cost you any way you look at it.:cry:

    Ok.

    As you may remember, I have 6 kyoceras (130) panels, good for around 700 -800 watts when the sun is shining. From around 8 AM until 4 PM, weekdays, the only thing connected to my pv system is my fridge (120 running watts) and a small radio. Thus, my batteries are usually in "float" for 4 or 5 hours, and I switch back to the Grid at sunset. Do you think that, under these circumstances, my panels era capable of fully and appropiately charging a battery bank twice as big as the present one? [Present, and damaged, bank is composed of 4 golf cart batteries, 205 amps, Powerfast, bought at Sam's.]

    Thanks
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: kitchen appliance off of small setup

    Just running the numbers... Assuming 5-13% rate of charge, 77% panel/charge controller efficiency:
    • 4 batteries * 6v * 205 AH * 1/0.77 derating * 0.05 rate of charge = 319 Watts minimum
    • 4 batteries * 6v * 205 AH * 1/0.77 derating * 0.13 rate of charge = 831 watt panel ~cost effective maximum
    Or looking at your array size:
    • 6 panels * 130 watt * 0.77 derating * 1/0.13 rate of charge * 1/24 volt battery = 192 AH @ 24 volt minimum battery bank
    • 6 panels * 130 watt * 0.77 derating * 1/0.05 rate of charge = 500 AH @ 24 volt battery bank maximum...
    If you are looking for flooded cell batteries--you should be in the ~10% range of rate of charge... You could go to 5% rate of charge--but with higher self discharge and possibly not as good mixing of electrolyte with "tall" batteries--would be better to not be at 5%.

    If you are looking for AGM, you can go down as low as 5%.

    In the end--what are you looking for? Emergency standby power (several days of outage after a storm)? Then tending towards 5% rate of charge is OK (larger battery bank for days of backup power).

    If you are looking for daily cycling--I would tend towards the 10%-13% rate of charge (smaller battery bank).

    How long did your Sam's bank last? Any ideas why it failed when it did?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: kitchen appliance off of small setup
    JESSICA wrote: »
    Ok.

    As you may remember, I have 6 kyoceras (130) panels, good for around 700 -800 watts when the sun is shining. From around 8 AM until 4 PM, weekdays, the only thing connected to my pv system is my fridge (120 running watts) and a small radio. Thus, my batteries are usually in "float" for 4 or 5 hours, and I switch back to the Grid at sunset. Do you think that, under these circumstances, my panels era capable of fully and appropiately charging a battery bank twice as big as the present one? [Present, and damaged, bank is composed of 4 golf cart batteries, 205 amps, Powerfast, bought at Sam's.]

    Thanks

    if the loads are only that frig and radio drawing when the pvs are supplying their power i'll agree with you, but if running 24/7 with cycling plus the stated 1400w from the heater you mentioned then you need to up the battery bank capacity.
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    BB. wrote: »
    In the end--what are you looking for? Emergency standby power (several days of outage after a storm)? Then tending towards 5% rate of charge is OK (larger battery bank for days of backup power).

    If you are looking for daily cycling--I would tend towards the 10%-13% rate of charge (smaller battery bank).

    How long did your Sam's bank last? Any ideas why it failed when it did?

    -Bill

    Bill:

    1) First option (Emergency standby power (several days of outage after a storm). Nevertheless, since I already have the system, why not use it a little everyday?
    2) 3 years. Don't really know why it failed. But, given what others members of this forum wrote, I am pretty sure it was a mistake to power the water heater (12 amps) with them. Though it was connected to the system maybe only 8/9 times, and only for 8-10 minutes a day, i tend to think it was too much for the batteries.
    Batteries are more or less "cheap" ($72 each), so it is not a big loss. But I was expecting (hoping) they lasted a little longer.
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    niel wrote: »
    if the loads are only that frig and radio drawing when the pvs are supplying their power i'll agree with you, but if running 24/7 with cycling plus the stated 1400w from the heater you mentioned then you need to up the battery bank capacity.

    Niel:

    As one of your presidents said: "Read my lips: I will NOT, ever, power my heater again with my pv system".

    My small system has never been used 24/7. As I told Bill, I installed it as a back up system, because Grid service in my area stinks big time. But sadly, I got carried away, and since it was so fun to receive small electric bills, I started to use it with loads that - it now seems - were too heavy for my batteries and/or inverter.
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    BB. wrote: »
    If you are looking for AGM, you can go down as low as 5%.

    -Bill

    I am trying to buy AGMs, but, first, I have not found them in Puerto Rico (at least, not anywhere close to town); second, it is VERY expensive to ship them from USA, and third, they are expensive themselves. (There is a place in San Juan, our capital, where they sell some Brazilian made agms, "Moura" brand, at around $600 each.)

    Any recommendations will be appreciated.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: kitchen appliance off of small setup

    Three years is not great--but probably OK for Golf Cart Batteries.

    Regarding the heater--you where pulling 1,400 watts? Which, at 24 VDC would have been:
    • 1,400 watts * 1/0.85 inverter eff * 1/24 volts = 69 amps
    • 68 amps / 205 AH = 2.9
    The maximum typical surge current should be around C/2.5--So you were pulling a fair amount of current. Whether that was enough to take several years off of the batteries--not sure.

    If the batteries were "warm" (towards ~95F instead of 77F or lower)--that could account for much of the shorter life (10C increase is would cut the expected life by 1/2).

    Sounds like you are charging the bank well... Last couple of questions--were you filling the batteries with distilled water (or possibly filtered rain water)?

    How often did you have to refill the batteries--Roughly every couple months?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    BB. wrote: »
    If the batteries were "warm" (towards ~95F instead of 77F or lower)--that could account for much of the shorter life (10C increase is would cut the expected life by 1/2).

    Sounds like you are charging the bank well... Last couple of questions--were you filling the batteries with distilled water (or possibly filtered rain water)?

    How often did you have to refill the batteries--Roughly every couple months?

    -Bill

    Bill:

    Room temp. was/is around 85F where the batteries are.
    Yes, I always use distilled water. First two years, there was almost no need of watering, but during the past 6 - 8 months I had to water them almost every week, though not all cells required watering every time.

    Batteries are not completely dead. Last night, just to experiment, I plugged a fan to the inverter and turned it on at around 10:00 PM. When I turned it off this morning (5:00 AM, mx60 was in sleeping mode) battery voltage was still at 23 volts. (fan draws 40 watts)

    P.S.: Is there a way (other than a copy-paste) to save some of these posts in my computer? There is valuable info here, and it would be very helpful to have it handy when needed.
  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    Re: kitchen appliance off of small setup
    JESSICA wrote: »

    P.S.: Is there a way (other than a copy-paste) to save some of these posts in my computer? There is valuable info here, and it would be very helpful to have it handy when needed.

    Under the File tab:

    "Save As" Web Archive

    Then choose destination where you would want all web archives for future browsing.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: kitchen appliance off of small setup
    JESSICA wrote: »
    P.S.: Is there a way (other than a copy-paste) to save some of these posts in my computer? There is valuable info here, and it would be very helpful to have it handy when needed.

    I use the SUBSCRIBE to the Thread, and set weekly monitor/notify, and archive the emails I get
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: kitchen appliance off of small setup

    Above the first post is a "Thread Tools" button... Do a "show printable thread" and it will take you here:

    http://forum.solar-electric.com/printthread.php?t=11474

    This gives you the entire thread, less pictures.

    Regarding water use... Not needing water may be an indication of undercharging during battery early use. Now using a lot of water probably indicates the batteries are sulfated and not long for this world.

    85F will reduce battery life somewhat...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    BB. wrote: »
    Now using a lot of water probably indicates the batteries are sulfated and not long for this world.

    85F will reduce battery life somewhat...

    -Bill

    Is there anything I can do to "de-sulfate" them (don't know if this word exists! I mean: to reverse the "sulfated" condition)? Isn't that the purpose of equalization?

    PS: Thanks to all for the tips about saving posts/threads
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: kitchen appliance off of small setup
    JESSICA wrote: »
    Is there anything I can do to "de-sulfate" them (don't know if this word exists! I mean: to reverse the "sulfated" condition)? Isn't that the purpose of equalization?

    Not really. Some people claim desulphators work, but you won't find much support for them around here.

    Equalization will get the SG back to a consistent number across all cells if the batteries aren't too far gone, but can't reverse the effects completely or do anything about plate erosion. Batteries are pretty much one-way in their lifespan. Nothing you can do to stop the inevitable decline, only slow it down. The same as with people. :p
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: kitchen appliance off of small setup

    There are desulfators... And there are battery additives like EDTA.

    However, desulfators don't have a lot of test information that shows that they reliably work in recovering battery function. And EDTA will (may?) cause the crystallized lead sulfate to fall off the plates--but will not restore the lead sulfate back to a useful form (can just remove the "lead sulfate" as an insulator).

    And since desulfators work by "pulsing" the battery--it has been seen that the "electrical noise" from desulfators can confuse charge controllers (especially MPPT type?) and cause the charge controller to reduce its output current--you have to be careful that desulfators do not reduce your system performance.

    Some batteries with very thick plates (like Forklift/Traction Batteries) can "survive" sulfate formation a bit better because there is more active lead with the heavier plates.

    So--No, there is not a lot you can do at this point for your current battery bank (as far as I know).

    In the end, keeping batteries cool and > 75% state of charge (don't let go below ~75% state of charge for a day, days, weeks, etc. at a time), plus proper battery maintenance is about all you can do.

    AGM batteries are probably not worth the expense for you... Good quality flooded cell batteries with proper maintenance will probably last longer than AGM anyway. You might look into:

    wind-sun_2158_426272Water Miser Battery Caps


    To keep the water use and "misting" problem (electrolyte on battery tops/cable ends causing corrosion) down.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    Re: kitchen appliance off of small setup
    BB. wrote: »
    Some batteries with very thick plates (like Forklift/Traction Batteries) can "survive" sulfate formation a bit better because there is more active lead with the heavier plates.

    -Bill

    Just one more question, and I won't bother you anymore:

    Are forklift batteries suitable for pv systems like mine? Are they true deep cycle?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: kitchen appliance off of small setup
    JESSICA wrote: »
    Just one more question, and I won't bother you anymore:

    Are forklift batteries suitable for pv systems like mine? Are they true deep cycle?

    Bother us all you want; that's why we're here. :D

    Forklift batteries are suitable for RE systems in that they can take repeated deep discharge and recharging. That's what they do; power electric forklifts all day and get recharged at night.
    But take a look at some of the specs on these Crown industrial batteries and decide for yourself: http://www.solar-electric.com/crinba1.html

    They have two things against them; the price new (can sometimes be bought for less used with plenty of life left in them) and the weight. 465 lbs. for 530 Amp hours @ 12 Volts. This can present some serious logistical problems in moving and placing.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: kitchen appliance off of small setup

    As with everything, there are trade-offs...

    From what I understand (again, verify the information I am giving you--I am not a battery expert by any means), the trade-offs with forklift batteries are their physical size+weight (you need some way of getting them off the truck and into your battery locker), they can use more distilled water, and as they get older, they have higher self discharge rates (you need a slightly larger array to make up for losses).

    Also remember that flooded cell batteries are around 80-90% cycle efficient (vs AGM which maybe in the 90-98% efficiency)--All again adding to the solar array power requirements.

    From the Battery FAQ:
    Industrial deep cycle batteries Sometimes called "fork lift", "traction" or "stationary" batteries, are used where power is needed over a longer period of time, and are designed to be "deep cycled", or discharged down as low as 20% of full charge (80% DOD, or Depth of Discharge). These are often called traction batteries because of their widespread use in forklifts, golf carts, and floor sweepers (from which we get the "GC" and "FS" series of battery sizes). Deep cycle batteries have much thicker plates than automotive batteries.

    Plate Thickness Plate thickness (of the Positive plate) matters because of a factor called "positive grid corrosion". This ranks among the top 3 reasons for battery failure. The positive (+) plate is what gets eaten away gradually over time, so eventually there is nothing left - it all falls to the bottom as sediment. Thicker plates are directly related to longer life, so other things being equal, the battery with the thickest plates will last the longest. The negative plate in batteries expands somewhat during discharge, which is why nearly all batteries have separators, such as glass mat or paper, that can be compressed.

    Automotive batteries typically have plates about .040" (4/100") thick, while forklift batteries may have plates more than 1/4" (.265" for example in larger Rolls-Surrette) thick - almost 7 times as thick as auto batteries. The typical golf cart will have plates that are around .07 to .11" thick. The Concorde AGM's are .115", The Rolls-Surrette L-16 type (CH460) is .150", and the US Battery and Trojan L-16 types are .090". The Crown L-16HC size has .22" thick plates. While plate thickness is not the only factor in how many deep cycles a battery can take before it dies, it is the most important one.

    Most industrial (fork lift) deep-cycle batteries use Lead-Antimony plates rather than the Lead-Calcium used in AGM or gelled deep-cycle batteries and in automotive starting batteries. The Antimony increases plate life and strength, but increases gassing and water loss. This is why most industrial batteries have to be checked often for water level if you do not have Hydrocaps. The self discharge of batteries with Lead-Antimony plates can be high - as much as 1% per day on an older battery. A new AGM typically self-discharges at about 1-2% per month, while an old one may be as much as 2% per week.
    I would guess for a typical off-grid system, you would have to size the solar array ~5-10% larger for to account for the extra losses. And, for proper electrolyte mixing, the array should be sized closer to the 10-13% rather than the 5% end of the battery charging rule of thumb.

    The few people here that have used forklift batteries seem to be very happy with them.

    You might look around your area for used forklift batteries... If you can get a set that have some life in them for not much more than scrap value--It might be worth a go to experiment.

    Look for threads started by user "adas"--He has built his shop up in Hawaii using old fork lift batteries (and has even gotten some 36 volt batteries and rewired around failed cells to make 24 volt banks).

    Here is what our hosts says about forklift batteries (this is a Crown 24 volt 530 AH version):
    The Crown 12-85-11 is a heavy duty industrial (fork lift) type battery. These batteries are designed for extremely heavy usage. In a typical solar electric system they will normally last for about 20 years or more. We have been selling these for over 25 years and have the utmost confidence in their reliability.

    Fork lift batteries have a slightly different plate composition from smaller deep cycle batteries in order to withstand industrial usage. The self-discharge is slightly higher and they should be equalized about once a month. Some solar systems are not capable of putting out enough current to fully equalize these batteries - it will require about 40 to 80 amps, depending on which battery you're using. Most inverter chargers can supply that much amperage.

    Specifications
    • 24 Volts
    • 530 Amp-hours at the 20 hour rate
    • Dimensions: 26.13"L x 12.69"W x 23.25"H
    • Weight: 930 pounds
    Warranty: 1500 cycles to 80% DOD for five years full replacement.

    Note: These batteries are very heavy and we highly recommend that you have a small crane or forklift available to move and load/unload it.
    So, you are looking at ~$2,800 + shipping (US prices) for a 20+ year 24 volt 530 AH battery bank...

    Vs 8x Trojan T105-RE 6 Volt, 225 AH Deep Cycle Battery for around $1,200 + shipping which will last around 6-8 years or so... (24 volt 450 AH battery bank).

    So far--That is how it always works out when I run the Flooded Cell calculations... The "better" batteries cost a lot more money. Is is worth paying $2,800 for 20 years vs $1,200 two or three times for 20 year life (and the possibility that something "goes wrong" on your 20 year bank in year X)... I don't know.

    If you have the cash for ForkLift batteries and a large enough solar array (~10% of battery AH capacity)--Personally, I would probably go for it. Much better service life than you would expect from AGM. From the same above battery FAQ:
    Lifespan of Batteries The lifespan of a deep cycle battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors. In extreme cases, it can vary to extremes - we have seen L-16's killed in less than a year by severe overcharging, and we have a large set of surplus telephone batteries that sees only occasional (5-10 times per year) heavy service that are now over 25 years old. We have seen gelled cells destroyed in one day when overcharged with a large automotive charger. We have seen golf cart batteries destroyed without ever being used in less than a year because they were left sitting in a hot garage without being charged. Even the so-called "dry charged" (where you add acid when you need them) have a shelf life of 18 months at most. They are not totally dry - they are actually filled with acid, the plates formed and charged, then the acid is dumped out.

    These are some typical (minimum - maximum) typical expectations for batteries if used in deep cycle service. There are so many variables, such as depth of discharge, maintenance, temperature, how often and how deep cycled, etc. that it is almost impossible to give a fixed number.
    • Starting: 3-12 months
    • Marine: 1-6 years
    • Golf cart: 2-7 years
    • AGM deep cycle: 4-7 years
    • Gelled deep cycle: 2-5 years
    • Deep cycle (L-16 type etc): 4-8 years
    • Rolls-Surrette premium deep cycle: 7-15 years
    • Industrial deep cycle (Crown and Rolls 4KS series): 10-20+ years
    • Telephone (float): 2-20 years. These are usually special purpose "float service", but often appear on the surplus market as "deep cycle". They can vary considerably, depending on age, usage, care, and type.
    • NiFe (alkaline): 5-35 years
    • NiCad: 1-20 years
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset