batteries on 24v system

castilloj
castilloj Solar Expert Posts: 208 ✭
in Off Grid Solar & Battery Systems #1
Hey guys,
so i have 8 rolls -S600 batteries, one of them look to be bad. when i check with the hydrometer is shows recharge while the others say Good. could i just rewire my batteries into 4 instead of 8? Ived been noticing that after running the generator for 6 hours till 11 pm , my inverter shuts down at 4 am at 23v.
thanks
Jose
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: batteries on 24v system

    Just so we're straight on the existing configuration ...

    You have eight 6 Volt batteries on a 24 Volt system. That's two parallel banks of four in series.
    Yes you can leave four of them out and still have one bank of four in series for 24 Volts.
    But, you will halve your Amp hour capacity.
    This brings up the issue of why the inverter is shutting down at night. One bad battery in the bunch dragging the others down? Not likely, but not impossible (if it is internally shorted for instance). How much load is running over night? That would be the deciding factor on whether or not half capacity will work.

    If you have the equipment to do it (and probably you don't) you could try equalizing the one battery with the low SG readings and see if it improves. Most likely it is ruined, though.
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #3
    Re: batteries on 24v system

    Yes 8 6v batteries connected series /parallel.
    Im using a fx2524 inverter/ solar array giving me 660w SWEEP PMAX right now at 11:07 am.
    I also have hooked up a 200w Chinook wind generator.
    at night i run 3 ceiling fans, 3 box fans, tv,satellite box,satellite internet modem,router.
    When i turn off the genset my Mate says im using 5 amps.
    Also when the generator is running the mate would say that im at 28.8 v but as soon as i turn off the genset it goes to 24.8.
    Is that normal?
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #4
    Re: batteries on 24v system

    It may be of some interest to know what is the charging current of the generator??
    Also what is the load on the inverter ?/
    at 11pm what is the battery voltage?? taken at least 15 minutes after the generator stops
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #5
    Re: batteries on 24v system

    im using a sdmo 11kw diesel generator. i have 120 ac power into inverter.
    Ived been told that im undercharging my batteries especially since my inverter tops at 14 amps. i was hoping that the solar panels and wind generator would help in charging.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: batteries on 24v system

    A 660 Watt array is far too small for that much battery. Unless you've been using the generator regularly they have probably been chronically under charged and have all lost capacity due to sulphation. I wouldn't put much credit in the wind turbine's output unless you have some recorded production numbers to show it's contributing.

    Using 5 Amps is a lot; 5 * 120 VAC = 600 Watts
    That's 25 Amps @ 24 VDC. Overnight (12 hours) that would be a whopping 300 Amp hours. The S600 is 450 Amp hours. With two parallel banks you've got 900 Amp hours, so 300 would be 1/3 capacity. That would be acceptable. With one bank ... You're looking at a 66% DOD which is far too much.

    I don't know how much you rely on your generator for charging, but that size battery bank would want about 3.3 kW of solar array for full charging. I think you've got a severe mismatch between battery capacity and charging capacity and as a result the batteries are permanently depleted.

    The depth of the Voltage drop when you take the gen off charging is another indicator of this. You also may be disconnecting it too soon. It should run at 28.8 Volts Absorb level for a couple of hours or more until the inverter charger (assuming it's programmed correctly) drops the Voltage to the Float level, which should be around 27.6. With no charge source the bank ought to be able to maintain over 25 Volts on its own for some time.
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #7
    Re: batteries on 24v system

    i run the generator from 8 am till 12 noon then 6 pm to 11 pm.
    with these run times what should i program the charger?
    right now
    absorb setpoint is at 28.8
    absorb time limit- 2.0 hrs
    float setpoint 27.6 vdc
    float time period 1.2 hrs
    refloat setpoint 25.0
    equalize setpoint 28.8 vdc
    equalize time period 3.0 hrs
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #8
    Re: batteries on 24v system

    also my low battery cut-in setpoint is at 25.0 vdc
    and my low battery cut-out setpoint is at 22.0 vdc
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #9
    Re: batteries on 24v system
    castilloj wrote: »
    When i turn off the genset my Mate says im using 5 amps.
    Also when the generator is running the mate would say that im at 28.8 v but as soon as i turn off the genset it goes to 24.8.
    Is that normal?

    With a 600 watt load a drop to 24.8 volts might be normal, I have never had such a large battery bank, but particularly with a bad battery/cell I wouldn't think this was odd. On my older 220Amphour 24 volt bank, I would be surprised to see 24.8 volts with a 600 watt load.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: batteries on 24v system

    A couple of other things:

    The 14 Amp limit of the FX's charger is on the AC side. That translates to roughly 70 Amps on the DC side. This is still a little bit low for recharging that 900 Amp hour battery bank, but should be workable.

    Running an 11 kW gen set to supply slightly less than 3 kW of power (1680 Watts for max charge plus 600 Watts for load) is going to be heavy on the fuel usage.

    Your Voltage level set points should be fine. You could up the Absorb time to its maximum (4 hours as I recall). You might also try running an Equalization cycle on the whole battery bank just to see if there's any improvement in the 'bad' battery.

    Frankly, you have an "unbalanced" system and it appears the batteries have been chronically undercharged. Sorry it keeps coming back to that.
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #11
    Re: batteries on 24v system

    But do you think if i just used 4 batteries instead of the 8 i should be ok?
    I jst want to make sure power lasts thru the night.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #12
    Re: batteries on 24v system
    castilloj wrote: »
    But do you think if i just used 4 batteries instead of the 8 i should be ok?
    I jst want to make sure power lasts thru the night.

    You have to drop some of those massive loads. Your battery is likely damaged, and will need replacement. but before you replace it, you have to resolve your high loads, and low charge capability, or you will still have long genset runtimes, and dead batteries.

    Suggestions:
    1) Drop at least half of those loads. (how many people are using all that stuff at once) ?

    2) re-size your genset to fit your load, not 4x over size.

    3) larger AC charger.
    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 ,

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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #13
    Re: batteries on 24v system

    Suggestions:
    1) Drop at least half of those loads. (how many people are using all that stuff at once) ? I have 3 bedrooms with 7 kids under 6

    2) re-size your genset to fit your load, not 4x over size.- what do you mean resize?

    3) larger AC charger.
    What kind of charger do you suggest? Something to supplement my inverter?
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #14
    Re: batteries on 24v system

    Ok I understand your suggestion on the size of the generator.
    I use a 11 kw genset because I need it to run a washing machine/ a couple of freezers/ fridge a 18,000 btu air conditioner.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
    Re: batteries on 24v system
    castilloj wrote: »
    Ok I understand your suggestion on the size of the generator.
    I use a 11 kw genset because I need it to run a washing machine/ a couple of freezers/ fridge a 18,000 btu air conditioner.

    Holy moly.

    How do you keep the refrigeration equipment going without the generator? Do you run them off the inverter and supplement with the generator as needed? Frankly your cumulative loads would overwhelm a 2.5 kW inverter. How's the budget? Bad, I'll bet.

    Start by getting a Kill-A-Watt meter (about $30) and begin measuring everything that plugs in to the wall, one at a time, for at least a day each. You need to get a really good set of numbers for your power usage and see where you can cut back. I know; with kids it's nearly impossible. They think switches have only one position: 'ON'. :cry:

    With more of a holistic approach I think we can help you get the usage down and the power up. A bit of rewiring may be in order, so that only things like the refrigerator are on the inverter and things like the washing machine and AC unit only run from the generator.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #16
    Re: batteries on 24v system
    castilloj wrote: »
    Suggestions:
    1) Drop at least half of those loads. (how many people are using all that stuff at once) ? I have 3 bedrooms with 7 kids under 6

    ouch!

    2) re-size your genset to fit your load, not 4x over size.- what do you mean resize?

    If you are just charging batteries, you can use a 3,000w generator, not the 11KW.

    3) larger AC charger.
    What kind of charger do you suggest? Something to supplement my inverter?
    Yes, if you can recharge faster, you don't have to run the genset as long. Orr maybe a larger inverter, with a larger charger, you don't have to fully load the inverter. Depending on your budget, maybe a 48V system might not be a bad idea. less overall lossess.
    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 ,

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #17
    Re: batteries on 24v system

    I agree with Mike; if you're going to try and run everything off inverter power a 48 Volt system would be a good idea. Looks like you'd need a fairly substantial one at that.
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #18
    Re: batteries on 24v system

    No I don't run all of that from the inverter. I have a 2 floor house. First floor I have 2 freezers and a commercial refrigerator and washing machine. On the second floor I have the 18,000 btu ac.
    The generator feeds a 100 breaker box on the first floor from there I feed the inverter and upstairs. The air conditioners are on separate breakers.
    When the generator is on the ac and freezers come on when it's off Inverter power just powers the second floor fans,tv,satellite box,router.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #19
    Re: batteries on 24v system

    If your goal here is to optimize the system as is, then you will need to replace that battery bank (it's substantial but should handle the required loads) and upgrade either the solar or/and the generator charging capacity. If the inverter charger is putting 75 Amps @ 28.8 VDC in that should be enough, especially in conjunction with whatever is coming from the solar panels. But you might want to lengthen the absorb time as I suggested before.

    Also, how old are these batteries? Nothing lasts forever; not even Surrettes.
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #20
    Re: batteries on 24v system

    The batteries are almost a year old.
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #21
    Re: batteries on 24v system

    Also do you still think that I should still have the 8 batteries hooked up or only connect 4?
    There is no way I can replace these batteries anytime soon, but I wondered wether I can repair the one bad cell battery?
    Should I try to equalize the bank overnight?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #22
    Re: batteries on 24v system
    castilloj wrote: »
    Also do you still think that I should still have the 8 batteries hooked up or only connect 4?
    There is no way I can replace these batteries anytime soon, but I wondered wether I can repair the one bad cell battery?
    Should I try to equalize the bank overnight?

    You have a problem with one of the batteries. If that can't be corrected by equalization you're down four batteries.

    That brings up a new problem; 450 Amp hours of battery will be destroyed quickly by the expected power usage.

    Equalization should be done for one hour at a time. There should be no loads on the battery (use the gen and the inverter will shift all loads to the gen). Check the SG readings on all cells before, run the equalization, let them sit for a few hours, and check the SG again - especially the 'low' cells - and see if there's any improvement. If there is, you can equalize again and again until there's no improvement. It's a long and tedious process. If there's no improvement on the first attempt, that battery is shot.

    If you can't shed any loads you can't run with half your battery bank. It's not a happy situation, that's for sure.
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #23
    Re: batteries on 24v system

    So run EQ on the mate but just do it for an hour. Before I run EQ check SG levels and recheck after the hour is up.
    What do you mean no loads on the batteries? Because when the generator is on everything runs from the generator.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #24
    Re: batteries on 24v system
    castilloj wrote: »
    So run EQ on the mate but just do it for an hour. Before I run EQ check SG levels and recheck after the hour is up.
    What do you mean no loads on the batteries? Because when the generator is on everything runs from the generator.

    Sorry. Sort of standard instructions. Many off-grid users EQ from panels and I get in the habit of reciting instructions (or at least parts of them) by rote. :blush:
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #25
    Re: batteries on 24v system

    If the battery isn't a year old you need to speak with Rolls Surette, sounds like it's under warranty, my understanding is they are very good with warranty even when batteries are abused!

    Likely they will direct you to do an eqalizing charge, do as they suggest!

    I personally would suggest starting with a 2 hour Equalizing charge, monitoring for heat buildup... but we likely all have our own methods, I do an equalizing charge every month now, (I only do them every 4-6 months for the first couple years)

    Trojan batteries are the only floaded lead acid I know of in which an equalizing charge isn't part of routine maintenance.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #26
    Re: batteries on 24v system
    Photowhit wrote: »
    Trojan batteries are the only floaded lead acid I know of in which an equalizing charge isn't part of routine maintenance.

    Hence my preference for Trojan batteries; I'm lazy. :p

    Besides, there seem to be more and more failures of Surrettes lately? :confused:
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #27
    Re: batteries on 24v system
    Cariboocoot wrote: »
    Besides, there seem to be more and more failures of Surrettes lately? :confused:

    Yes, I don't know if it's a trend, but here and the other solar/off grid forum I interact with it sure appears to be a trend, perhaps that's why they haven't done much complaining, just replacing bad batts almost w/o question.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • castilloj
    castilloj Solar Expert Posts: 208 ✭
    #28
    Re: batteries on 24v system

    hey guys , could i replace my bad Rolls s600 with a trojan T105? here in haiti there is only trojans T105 batteries available.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #29
    Re: batteries on 24v system
    castilloj wrote: »
    hey guys , could i replace my bad Rolls s600 with a trojan T105? here in haiti there is only trojans T105 batteries available.

    Not a good idea. The S600 is 450 Amp hours and the T105 is 225 Amp hours. Full charge rate for the Surrette will be too much for the Trojan; it will cook.
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  • Kefalonianman
    Kefalonianman Solar Expert Posts: 60 ✭✭✭✭
    #30
    Re: batteries on 24v system
    Cariboocoot wrote: »
    A 660 Watt array is far too small for that much battery. Unless you've been using the generator regularly they have probably been chronically under charged and have all lost capacity due to sulphation. I wouldn't put much credit in the wind turbine's output unless you have some recorded production numbers to show it's contributing.

    Using 5 Amps is a lot; 5 * 120 VAC = 600 Watts
    That's 25 Amps @ 24 VDC. Overnight (12 hours) that would be a whopping 300 Amp hours. The S600 is 450 Amp hours. With two parallel banks you've got 900 Amp hours, so 300 would be 1/3 capacity. That would be acceptable. With one bank ... You're looking at a 66% DOD which is far too much.

    I don't know how much you rely on your generator for charging, but that size battery bank would want about 3.3 kW of solar array for full charging. I think you've got a severe mismatch between battery capacity and charging capacity and as a result the batteries are permanently depleted.

    The depth of the Voltage drop when you take the gen off charging is another indicator of this. You also may be disconnecting it too soon. It should run at 28.8 Volts Absorb level for a couple of hours or more until the inverter charger (assuming it's programmed correctly) drops the Voltage to the Float level, which should be around 27.6. With no charge source the bank ought to be able to maintain over 25 Volts on its own for some time.
    Reading your forum I have a question I hope you can help me with

    I am using 430 amp / h battery configuration 24v and have four solar total 434 w and two turbine 700 w each

    Although it's summer here and the turbines are not producing a lot can I ask the following

    If I charge my batteries unto 28.8 v and then have a 300 w load I get around 10 hours from the batteries and then they take about 4 kw to recharge from mains

    Does this sound right ?

    I am looking at installing 10 * 185w solar panels o. Roof as well and then maybe increasing my battery bank to 900w

    Can I have your thoughts on this also

    Finally I am using the yahoo widget and it shows when inverting 0.237 kw and the battery voltage say 25 v and amps at -13 and then produces a graph to show the kw this is just the kw used from the batteries I presume and not what I have produced. It seems that I use my batteries up and the. Charge from the mains how do I determine what I am producing towards this figure

    Many thanks in advance

    Paul
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #31
    Re: batteries on 24v system

    Paul;

    If you really want to know what's going in/out of your batteries get a battery monitor: http://www.solar-electric.com/metersmonitors.html It will show all the current going in and out of the batteries regardless of source or destination.

    Most of the meters supplied with charge controllers and inverters are not all that accurate. In fact, any meter is only accurate in reference to another meter. This includes battery monitors which require a bit of programming in order to get a good reading.

    Otherwise, four 434 Watt panels (odd size :confused: ) is 1736 Watts total and should have no trouble recharging 430 Amp hours of 24 Volt batteries. Even without the potential contribution of the wind turbines.

    If you run 300 Watts steady for 10 hours that's 3 kW hours, and again the batteries should be able to provide this. Likewise the panels should be able to "replace" this. System losses might be higher than expected, which could throw things off a bit.

    Using 4 kW from the mains to "replace" 3 kW used isn't out of order either, again due to system losses. For one thing it usually takes about 20% more power to replace what the batteries have produced, and there's always the bugabear of Power Factor of the charger.

    Increasing a battery bank isn't as simple as just adding batteries and panels. The new batteries and the old batteries, even if they are the same model, will have different capacities because the old batteries have aged and loss some Amp hours. How much difference depends on the time, number of and depth of cycles, and recharging. Lightly used batteries that have been kept up and aren't more than a couple of years old - not much difference from new. Cycle them to 50% DOD daily for five years and miss charge them a few times ... it's like adding years to the age, and takes Amp hours off.

    A 900 Amp hour battery bank would want about 3.3 kW of array for proper recharging. Adding 1850 Watts of panel should be more than enough. At this point you would need two charge controllers, as 80 Amps is the limit for the best of them. This is also when you think about switching up to 48 Volts, if you really need 10 kW hours worth of power potential. That's huge in off-grid terms.
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