PWM questions

stoichiometry
stoichiometry Solar Expert Posts: 27
Hello there!

Since my last post ive put up my panels, wired the cabin and am making ice cubes!!! It's fantastic!

I've a question on batteries and PWM.

So, I've got 220ah 6 volt batteries. 2 strings of 4 (two 24 volt banks)
I'm using a PWM and using 29.2 as PWM voltage.... And I see PWM 10 to 99 percent displayed but I never quite get to float... Why might this be? I've been really careful to make sure all wires are of equal length in the battery bank. Could my PWM voltage be too high or too low? I hear H2 and O2 being made...

Thanks,
M
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Comments

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: PWM questions

    Do you have the link to your last post? And does that last post list what you have for batteries, controller, panels etc? Would help to know that info.
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions
    Do you have the link to your last post? And does that last post list what you have for batteries, controller, panels etc? Would help to know that info.

    So-- I'm doing this on a budget, so please don't make fun of my choice in components. It's sort of an experiment in progress-- I'm building a wind turbine too.

    Anyway. I've got 6 evergreen Panels. (205watts wired in pairs or 3 strings @ 24 nominal volts and 11.5ish amp max)

    8 - gc2 batteries, morningstar pwm60

    Does this help?
    M
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: PWM questions

    In addition to what Wayne asked (I actually looked through previous posts but did not find a definitive equipment list other than Evergreen panels);

    Got array? About 1650 Watts worth?
    Got hydrometer? Nothing beats an SG reading for indicating SOC.
    Normal Absorb charge Voltage (PWM is a type of controller, not a charge stage) is 28.8 Volts for FLA batteries. Some (Trojan & Interstate) manufacturers recommend higher.

    Without the details no one can be more specific.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: PWM questions

    Second post showed up while I was posting. :roll:

    A little shy on array size at 1230 Watts. Probably takes a while to get through Bulk (depending on how much your using of your 440 Amp hour capacity) and you're running out of daylight before you finish Absorb.

    Take one string of the batteries off line for a day and see what happens. Your 11 Amps peak is 2.5% of your battery bank; far below the recommended 5% minimum.

    What do I always say? (All together:) "You need more panels for that battery bank!" :D
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions
    Second post showed up while I was posting. :roll:

    A little shy on array size at 1230 Watts. Probably takes a while to get through Bulk (depending on how much your using of your 440 Amp hour capacity) and you're running out of daylight before you finish Absorb.

    Take one string of the batteries off line for a day and see what happens. Your 11 Amps peak is 2.5% of your battery bank; far below the recommended 5% minimum.

    What do I always say? (All together:) "You need more panels for that battery bank!" :D

    Thanks- I get through bulk very quickly... My fridge and radio don't draw much ( less than 1000 watts per day). After bulk I get to PWM and the amps slowly drop but it rarely gets o float. It did yesterday ... But didn't today. Perhaps, I'll try a PWM voltage of 28.8 instead of 29.2 ...?

    I'll look into getting sg readings tomorrow. (I've got hydrolysis of water.. Fwiw)

    Best,
    M

    More soon,
    M
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: PWM questions

    For flooded cell battteries, 29.2 volts is not bad. I would not back down on the voltage setting.

    Have to look strong later, but there have been some complaints about morning star controllers set to other than default charging settings not regulating voltages properly... Not sure what models may be affected.

    I am posting from my phone so can't search for details at the moment.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: PWM questions

    Six 205 watt panels wired as three parallel strings should yield about 33 amps at max sun.
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions
    BB. wrote: »
    For flooded cell battteries, 29.2 volts is not bad. I would not back down on the voltage setting.

    Have to look strong later, but there have been some complaints about morning star controllers set to other than default charging settings not regulating voltages properly... Not sure what models may be affected.

    I am posting from my phone so can't search for details at the moment.

    -Bill

    Bill,

    I too am posting from my phone... Hence the brevity of my messages. I wonder if it is because even at idle my inverter draws a bit of current and this is "sensed by the charge controller as a "depleted" battery? I got thru bulk by 9:30 this morning but PWM and various percentages were being displayed all day. I just switched to one of the "standard" programs and will see why happens tomorrow.

    Ccboot- I know I'm a bit low on the number of panels. I agree - i would like to have more panels... I figure it's incentive to get my turbine up and running.

    Best,
    M
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions
    RCinFLA wrote: »
    Six 205 watt panels wired as three parallel strings should yield about 33 amps at max sun.

    It certainly does! I get almost 1000 watts in the morning during bulk when there is still dew in the lawn. I just never get completed thru the PWM absorption stage.... Or maybe I do, but Maybe the charge controller or the way I have the inverter connected is causing *funny* readings?!? Dunno?!
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: PWM questions

    RCinFLA; I think he meant 11 Amps per string. At least I hope so. Otherwise two of them aren't connected, eh?

    stoichiometry; It's normal for inverters to draw current even when there's no load. It will not affect charge controller operation. Mine sucks down 20 Watts doing nothing, but the batteries still go to Float. But then I'm not charging at 2.5%. :roll: Are you sure you need 440 Amp hours of battery?
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions
    RCinFLA; I think he meant 11 Amps per string. At least I hope so. Otherwise two of them aren't connected, eh?

    stoichiometry; It's normal for inverters to draw current even when there's no load. It will not affect charge controller operation. Mine sucks down 20 Watts doing nothing, but the batteries still go to Float. But then I'm not charging at 2.5%. :roll: Are you sure you need 440 Amp hours of battery?

    Cbcoot,

    I probably don't, but had been given advice (not here... Fwiw) that two strings would be appropriate for my load/ panel/ etc. I think you and the other poster agree . I have three strings, each producing just over 11 amps for a total of almost 34-35 amps. I still don't understand why I can't get to float? I was down to PWM absorb at less than 2 amps in *full sun* at noon today. The reported Voltage was 29.2. It just never Kicked over to float? Perhaps the inverter draw or the voltage was a bit high?




    The sun is down, and my per battery voltage indicates full charge. I'll try to get a hydrometer and report the readings. Any tips on when or how to take the readings?

    Best,
    Matt
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: PWM questions

    Hi again M,

    Just for the record, what IS the model and manufacturer of your Charge Controller?

    I must admit that I am with you in the area of electric kitchen appliances ... Love my electric drip coffee maker, and of course an electric toaster. Whatta way to wake up!

    Thanks, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: PWM questions

    Let's see if we're all on the same page.

    33 Amps peak charge current (good, even for 440 Amp hours).
    Morningstart Tristar 60 PWM controller?
    Absorb Voltage set at 29.2
    Sometimes goes to Float, sometimes doesn't?
    Float Voltage set to what?
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: PWM questions

    I used to have a Morningstar PWM-60 and found it seldom went to float. As I remember, the reason in my case was that it had to maintain a certain voltage for something like 3 hours before it would switch to float. My problem was that whenever the water pump started, the voltage would drop for a minute, then the CC would start counting from zero again. Wasn't happy about that. No such problem with the Outback MX-60.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: PWM questions

    Wayne, I think you win the prize! :D

    He probably doesn't want to buy a new charge controller, though. Probably doesn't want to watch the Voltage for three hours every day to see if this is happening.

    Maybe just lower the Absorb Voltage to 28.8 and see what happens.

    Once again the MX60 proves champion. :p
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: PWM questions

    Once again the MX60 proves champion. :p

    Yes, and now I'm worried about the Morningstar MPPT-60 I have on the way. I surely hope it has a different program than the old PWM unit had. Until now, I'd forgotten all about it since having the MX-60.:cry:
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions
    Wayne, I think you win the prize! :D

    He probably doesn't want to buy a new charge controller, though. Probably doesn't want to watch the Voltage for three hours every day to see if this is happening.

    Maybe just lower the Absorb Voltage to 28.8 and see what happens.

    Once again the MX60 proves champion. :p

    Cbcoot and Wayne,

    I think this is exactly it. The stall in the absorb and constant cycling through this stage seems to be a result of a 100watt draw from the fridge. Ughh. I probably can't return the controller. I'll try adjusting the voltages and see what happens. In the meantime, can you tell me who makes the mx60 and the models/makes o other ones that work 'properly'?

    Best,
    M
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions
    Vic wrote: »
    Hi again M,

    Just for the record, what IS the model and manufacturer of your Charge Controller?

    I must admit that I am with you in the area of electric kitchen appliances ... Love my electric drip coffee maker, and of course an electric toaster. Whatta way to wake up!

    Thanks, Vic

    Hey Vic!

    I'm enjoying a fully charged phone this morning (I'm typing from it now), electric coffee pot is on, and I'll make toast when the wife wakes up. It IS a good morning. Smile.

    For the record, I've got a morningstar tristar 60. Now, I'm regretting having bought it...

    Best,
    Matt
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: PWM questions
    Cbcoot and Wayne,

    I think this is exactly it. The stall in the absorb and constant cycling through this stage seems to be a result of a 100watt draw from the fridge. Ughh. I probably can't return the controller. I'll try adjusting the voltages and see what happens. In the meantime, can you tell me who makes the mx60 and the models/makes o other ones that work 'properly'?

    Best,
    M

    Regrettably the Outback MX60 is no longer made. It has been replaced by the Outback FM60 and its higher-current brother the FM80. More regrettably there have been certain reliability problems reported with the newer models which may or may not have been worked out yet.

    This is MPPT territory; the more expensive controllers have more programmability. In addition to the Outback units, there's Midnight Solar's Classic 150/200/250 and the Xantrex XW MPPT 60. Morningstar makes MPPT versions of the Tristar as well. But your PWM version was about $200 and the MPPT equivalent is $500+. With arrays over 400 Watts it can be worth it, if you can afford it. They all have their quirks and failings; you just have to live with them.

    Speaking of which, if this is a case where the sudden low causes a V drop out of Absorb range lowering the set point may not help; it may just reduce the set point (drop 0.5 Volts and out of Absorb regardless of what Absorb is set to). Another thing to check is the wire size on your inverter connections and charge controller connections; too small may be allowing a drop the controller can't compensate for rapidly enough. The 100 Watt draw of the 'frige isn't doing it; it's the surge when the compressor starts.

    So what's the inverter you picked and how big (gauge) and long are the wires connecting it?
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: PWM questions

    I've got the MS Tristar MPPT 60, and have had 0 issues with it. I have a 1/2 hp pump that comes on mid day for a couple hours, and everythings been fine, on the days with sun.
    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 ,

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: PWM questions
    mike90045 wrote: »
    I've got the MS Tristar MPPT 60, and have had 0 issues with it. I have a 1/2 hp pump that comes on mid day for a couple hours, and everythings been fine, on the days with sun.

    This is great news! Makes me feel a whole lot better about the one I have on the way. Thanks for sharing that Mike! I never had that (lack of float) problem with the Sunsaver MPPT because it was on the micro hydro which could never drive the batteries to float anyway, just kept them from discharging overnight and on heavy overcast days while running 2 freezers and a fridge. Yes, I do realize how lucky I am, and would be really going back into the dark ages if I had to give it all up and revert to living on grid! The new TS MPPT-60 by the way is to replace the Sunsaver MPPT, because my constant tinkering has greatly increased the efficiency of the hydro far beyond my initial expectations, to the point where it's output is extending into, and perhaps at times reaching beyond the limits of the Sunsaver in both input voltage and output amperage. In fact I think I cooked the Sunsaver. A month ago it started staying in "Bulk" mode when the turbine was shut down, and allowing battery voltage to appear back at the hydro terminals. Then last night, it began to consume power on it's own and now runs very hot, with reduced output. Still does it's sweeps etc as if nothing is wrong, and no alarm lights are lit, but it's definitely not working right. Up until this happened, it never got more than the chill off it. Such a shame, it was an awesomely working little unit.
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions

    Solar friends!

    I came home after hiking and a change to the absorption voltage has resulted in a "float" condition!!! Thanks for the help. I'll keep you updated with my wind turbine project as it progresses.

    Best,
    M
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: PWM questions
    Solar friends!

    I came home after hiking and a change to the absorption voltage has resulted in a "float" condition!!! Thanks for the help. I'll keep you updated with my wind turbine project as it progresses.

    Best,
    M

    Great news! Thanks for the update.
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions

    Maybe I spoke too soon... In spite of turning down the absorb voltage to 28.8 Volts and getting to "float mode" yesterday, I'm unable to today... Any other ideas?

    Best.
    M
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: PWM questions
    Maybe I spoke too soon... In spite of turning down the absorb voltage to 28.8 Volts and getting to "float mode" yesterday, I'm unable to today... Any other ideas?

    Best.
    M

    Well I did specifically mention the possibility (Post #20).
    So you're left with investigating the wire sizing to see if you can eliminate the V drop or changing the controller for a really expensive MPPT type. Other than that - switch the load off 'til Abosrb is done?
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: PWM questions
    Maybe I spoke too soon... In spite of turning down the absorb voltage to 28.8 Volts and getting to "float mode" yesterday, I'm unable to today... Any other ideas?

    Best.
    M

    You are now, not charging your battery fully, because you are using less voltage for the FULL point. It worked for 1 day, because the battery was fuller when you started.

    Try:
    Put the setpoint back to normal
    Run the generator in the AM for 30-60 min to bulk up the batteries
    conserve/reduce your daytime load till you finish absorb.

    With days getting shorter, this will get worse and worse.
    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 ,

  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions
    Well I did specifically mention the possibility (Post #20).
    So you're left with investigating the wire sizing to see if you can eliminate the V drop or changing the controller for a really expensive MPPT type. Other than that - switch the load off 'til Abosrb is done?

    Wiring from panels to combiner is 10awg.
    Then 4 awg from combiner to controller and subsequently to batteries.
    1/0 to inverter.

    I can start saving pennies for a new charge controller, but I'd prefer to find a less expensive soln.

    Best,
    M
  • stoichiometry
    stoichiometry Solar Expert Posts: 27
    Re: PWM questions
    mike90045 wrote: »
    You are now, not charging your battery fully, because you are using less voltage for the FULL point. It worked for 1 day, because the battery was fuller when you started.

    Try:
    Put the setpoint back to normal
    Run the generator in the AM for 30-60 min to bulk up the batteries
    conserve/reduce your daytime load till you finish absorb.

    With days getting shorter, this will get worse and worse.

    Mike,

    This shouldn't be... I should have more than enough solar, just one hour in good sun and I replace the ca. 900 watts hrs I use each day. I think the fridge is drawing the voltage down which is resetting the absorb stage. I'm told some controllers deal with this better than others. Is it bad to stay at absorb voltage for a "few" hours? Does it mean that I just need to keep a close eye on electrolyte level within each cell?

    I'll try your suggestion. Any other thoughts?

    Best,
    M
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: PWM questions

    So the situation is: something turns on and causes a momentary V drop below whatever Absorb is set to, causing the charge controller to start Absorb again from zero minutes when the Voltage returns to normal.

    Other than actually watching the thing to confirm this is what is going on I can't think of anything else to do. If this is what is going on it's a pretty stupid way for a charge controller to work: the normal course is if it drops out of Absorb for 1 minute the Absorb time is lengthened by 1 minute, not it starts from zero again. :confused: Anyone else seen this odd behaviour?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: PWM questions

    (Having just read the Morningstar manual and found it fastidiously avoids explaining its Absorb function time process ...)

    Got battery sense wires hooked up?

    Now I'm really out of ideas.