Two controllers,one battery pack

bumper
bumper Registered Users Posts: 14 ✭
in Solar Beginners Corner #1
3 solar collectors charging 6 batteries (12 volts) charged with 25amp controller, can I hook up another controller with more solar collectors into the same battery pack just as if tho there were no other source or controller connected to it? Con fussed but believe it would be ok:blush:
Thanks
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,591 admin
    #2
    Re: Two controllers,one battery pack

    Should be fine... I would suggest you run a new/separate cable from the new charge controller back to the common battery bus connections.

    If you share one cable with several charge controllers, the extra voltage drop and "noise" from the controllers as the regulate could confuse each other.

    Normally, we recommend a range of 5%-13% for the rate of charge (100 AH battery bank; 5-13 amps rate of charge). You can go over 13% for solar--but it tends to be expensive and wasteful (batteries quickly recharge before sun goes down).

    You can go as high as 25% or so rate of charge--but you do have to watch the batteries do not overheat and for some batteries (such as GEL) they have a hard limit on maximum rate of charge (GELs generally recommend 5% maximum rate of charge).

    Having paralleled batteries--you should make sure that the wiring is "balanced":

    SmartGauge Electronics - Interconnecting multiple batteries

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Tricksailing
    Tricksailing Registered Users Posts: 25 ✭✭
    #3
    Re: Two controllers,one battery pack

    I had basically the same question for a boat with 4 * 135W Kyocera panels,which seems to be a baby system compared with most discussed here.

    I had separate Flexcharge controllers for each panel (2 * 14A and 2 * 25A). They seem to be the on/off type until they died.

    Now I'm trying to upgrade and seem to have a choice between PWM and MPPT controllers. I like the idea of having separate controllers to provide redundancy when I'm in places where getting replacements proves difficult. If I understand correctly, this means I use PWM with 1 or more panels connected in parallel, or MPPT controllers with panels connected in series or parallel. I suspect that the MPPT controllers would get totally confused, chasing each other up to higher than optimal voltages. Not sure what would happen with the PWM chargers.

    Any better insight/recommendations from the experts here? Efficiency isn't as big a priority as keeping enough power on the boat for refrigeration, desalination, radio communications and other minor electronics over a 2-4 week passage at sea (about 120Ah/day). Operation will usually be close to tropical latitudes.

    Thanks, John
    5kW grid-tied SMA + 2kW grid-tied SMA (total 4kW emergency daytime power) + 2kW genset, 500W off-grid marine system. Baja Sur.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Two controllers,one battery pack

    John;

    Ideally on a boat you want a separate controller for each group of panels in the same location, as the amount of light falling on them can vary greatly. Paralleling panels usually works better on a boat too, as they aren't as affected by shadows from masts et cetera as would series connected panels.

    There is little advantage to be had from MPPT under such circumstances, as your 540 Watts total would be divided up into two or more separate arrays. if you want to squeeze out everything you can get, Morningstar makes a 15 Amp MPPT controller: http://www.solar-electric.com/mosumpsochco.html
    Although it would be crazy to run one per panel and 270 Watts might be a tad much for one even on a boat. Boats suffer from poor insolation, which lowers panel output, and usually high temps (stick to warm waters! :D ) which also lowers panel output. Even so, the 15 Amp controller might "clip" some power from two 135 Watt panels.

    The next step up from the MS 15 Amp unit is a Rogue 30 Amp MPPT: http://www.roguepowertech.com/products/mpt3024.htm

    But you might find that ordinary PWM type controllers are good enough. The MPPT might gain you 10-15%, or not that much; too many variables with ships at sea.

    Under normal circumstance you could expect 540 Watts of panel to support about 350 Amp hours of battery. So how much battery do you have?
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  • Tricksailing
    Tricksailing Registered Users Posts: 25 ✭✭
    #5
    Re: Two controllers,one battery pack

    Thanks for the good info, Cariboo. I have a pair of 4D Gel-type batteries (183Ah each) and a group 31 (97Ah) giving me about 460 Ah of deep-cycle capacity. I understand that battery life is improved if they are not discharged beyond 50% and that the last 10 - 20% of the charge isn't as efficient. That gives me a usable capacity of between 140 and 230 Ah. At least the system seems to work for me as I rarely need to use supplementary power supplies.

    You've convinced me that MPPT is probably not worth the investment, so I'm looking at PWM controllers. Random, unpredictable shading is a fact of life on a boat. Some manufacturers indicate that PWM chargers can be connected in parallel for higher currents. One good option for me looks to be a Morningstar Sunkeeper 12 on each panel. They can be installed on the solar panel junction box which would ease congestion in my electrical cabinet. Hmmm.... the 2 newer Kyocera panels (KD135s) have more compact, sealed junction boxes which wouldn't accommodate the SK12. Another alternative would be to parallel connect pairs of panels and use a ProStar. Presumably I'd need 2 of the 30A controllers for 4 panels.

    FYI - the Why PWM? link on the NAWS web page - http://www.windsun.com/ChargeControls/ChargeCont.htm is incorrect. It seems to have moved to http://www.morningstarcorp.com/en/support/library/8.%20Why%20PWM1.pdf.

    John
    5kW grid-tied SMA + 2kW grid-tied SMA (total 4kW emergency daytime power) + 2kW genset, 500W off-grid marine system. Baja Sur.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Two controllers,one battery pack

    Oh dear. Problems arise.
    Not just that gel batteries aren't the best choice for RE power systems, but mostly that you can't mix different battery types, or capacities. In this case it looks like gels and FLA's, which will want too quite different charging Voltages, as well as 183 Amp hours & 97 Amp hours which will want two quite different charging currents. This is a recipe for disaster. You either severely under-charge one or severely over-charge the other.

    Unless you get a consistent battery bank or separate the batteries so they are charged/discharged independently you will have trouble.

    There is no problem with paralleling multiple controllers. Batteries don't care how many charge sources they have, so long as all agree on settings (as in same Absorb Voltage). Battery temperature can be an issue here, as you probably don't want RTS for each and every controller. That would get cumbersome!

    You really need to get the battery bank sorted out first. Get some good numbers on how much power is required and get it supplied by batteries that are all the same.

    BTW, to fully recharge 460 Amp hours @ 12 Volts from solar you'd need about 700 Watts of panel, possibly more given the inconsistencies of shipboard mounting.
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  • Tricksailing
    Tricksailing Registered Users Posts: 25 ✭✭
    #7
    Re: Two controllers,one battery pack
    Cariboocoot wrote: »
    Oh dear. Problems arise.
    The story of my life! !8)
    But having someone point out my waywardness helps me straighten out - thanks!

    All of the batteries are gel type - just one is a different capacity. Gels were there when I bought the boat and I replaced with matching ones. At the time, I understood that Gel batteries lasted longer and were more more forgiving of deep discharge. Low maintenance is an issue because of tricky access.

    I hadn't caught the capacity issue, assuming that all the batteries would charge equally relative to charger voltage. Not true as internal resistance on lead acid batteries drops with increasing charge level (http://batteryuniversity.com/learn/article/how_does_internal_resistance_affect_performance). Given that information, I'm surprised the 97Ah hasn't died years ago from overcharging. It's been installed for 10 years and still seems to work well when I check its performance (charge/discharge) with the other batteries disconnected. Does that make sense? My charge controllers cut out at 14.1V. Anyway, I guess AGMs of a single capacity are probably the way to go come replacement time. In the meantime, I can isolate the 97Ah (starting battery) with it's own charger - which I assume I could source from one of the panels with a second charger supplying the 4D bank.
    Cariboocoot wrote: »
    There is no problem with paralleling multiple controllers. Batteries don't care how many charge sources they have, so long as all agree on settings (as in same Absorb Voltage)
    I see that from the battery point of view, but isn't it an issue for controllers, especially for MPPT controllers which presumably change the charging voltage. Doesn't that confuse the other chargers in terms of optimizing charge? (this was the original question in the thread). Maybe your comment was relative to the type of chargers that I would be using.
    Cariboocoot wrote: »
    really need to get the battery bank sorted out first. Get some good numbers on how much power is required and get it supplied by batteries that are all the same.

    BTW, to fully recharge 460 Amp hours @ 12 Volts from solar you'd need about 700 Watts of panel, possibly more given the inconsistencies of shipboard mounting.

    Suggestions would be appreciated here (although we're getting a bit off-thread). My first question would be are you assuming I have 460 Ah of usable capacity? My own assumption has been that a 460Ah bank gives me no more than 230Ah of usable capacity. The second problem I have is that I'm not quite sure how best to deal with variable supply and demand. There must be a difference with off-grid installations relative to grid-linked systems in terms of storage capacity (Maybe this is an issue for another thread). At sea, fossil fuel based generators are a little too fuel hungry for backup (at least in a sailboat!). My daily demand in summer is around 100Ah with an additional 60-80 Ah every second or third day for water desalination. A couple of cloudy days take all of my battery usable capacity. On the more commonplace sunny days, I usually see my charge controllers turning off with a few hours of daylight left. Maybe my ability to follow the sun helps here too!;) - I spend most of my time within 25 degrees of the equator which probably gives me a significant boost in panel output. Of course, another issue on a small boat is the space to put that extra panel!

    In terms of power, that translates to a fairly consistent average daily power consumption of about 50 watts (~1.2kWh/day) with an additional 250 watts over a 3-4 hour period (750-1000Wh/day) every 2-3 days (~1.5kWh/day average). The rated capacity of my panels add to 530W (2 of my panels are 130W rather than the 135 I indicated in my original post). Also, my panels articulate and I watch them pretty carefully on the high demand days (separate ammeters on each panel).

    John
    5kW grid-tied SMA + 2kW grid-tied SMA (total 4kW emergency daytime power) + 2kW genset, 500W off-grid marine system. Baja Sur.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Two controllers,one battery pack
    Tricksailing wrote: »
    All of the batteries are gel type - just one is a different capacity. Gels were there when I bought the boat and I replaced with matching ones. At the time, I understood that Gel batteries lasted longer and were more more forgiving of deep discharge. Low maintenance is an issue because of tricky access.

    This is better; at least they'll all want the same charge Voltage. The capacity differences are an issue, but if the current is less than maximum they may be able to suck that up. With this kind of mismatch on FLA's being pushed to 10% capacity ... you could watch the small battery boil itself to death. :cry:
    Anyway, I guess AGMs of a single capacity are probably the way to go come replacement time. In the meantime, I can isolate the 97Ah (starting battery) with it's own charger - which I assume I could source from one of the panels with a second charger supplying the 4D bank.

    That sounds like a good plan. AGM's will take more current stress than gels or FLA's and are a compromise charge Voltage in-between. I'd suggest getting a battery monitor for any type of sealed battery as you have no other way of knowing what's going on with them; Voltage alone doesn't mean much.
    I see that from the battery point of view, but isn't it an issue for controllers, especially for MPPT controllers which presumably change the charging voltage. Doesn't that confuse the other chargers in terms of optimizing charge? (this was the original question in the thread). Maybe your comment was relative to the type of chargers that I would be using.

    Actually multiple MPPT controllers will "get along", even of different brands. You can mix MPPT and PWM controllers too. They all "look at" battery Voltage and adjust their output accordingly. One will inevitably be the "dominant" controller; with the largest array and/or highest Voltage set points. I've never heard of any mix of controllers causing any real problems.
    Suggestions would be appreciated here (although we're getting a bit off-thread). My first question would be are you assuming I have 460 Ah of usable capacity? My own assumption has been that a 460Ah bank gives me no more than 230Ah of usable capacity. The second problem I have is that I'm not quite sure how best to deal with variable supply and demand. There must be a difference with off-grid installations relative to grid-linked systems in terms of storage capacity (Maybe this is an issue for another thread). At sea, fossil fuel based generators are a little too fuel hungry for backup (at least in a sailboat!). My daily demand in summer is around 100Ah with an additional 60-80 Ah every second or third day for water desalination. A couple of cloudy days take all of my battery usable capacity. On the more commonplace sunny days, I usually see my charge controllers turning off with a few hours of daylight left. Maybe my ability to follow the sun helps here too!;) - I spend most of my time within 25 degrees of the equator which probably gives me a significant boost in panel output. Of course, another issue on a small boat is the space to put that extra panel!

    Oh boy. Lots of different stuff to discuss there.
    Battery recharge rate is dependent on the total Amp hour capacity, not the "usable". If you have 460 Amp hours you want to try for 46 Amps peak potential current, whether you use 25% or 50% of the capacity. You don't go below 50% capacity because of the likelihood it won't recharge at all which will increase with frequent or deeper discharge.
    Grid-tie systems usually have only the grid for their "storage". Those that are hybrid (with battery back-up ability) are subject to the same charge rules as off-grid systems, but usually have no shortage of charge power available due to the value of "maxing out" the inverter to make sales to grid viable.
    Staying near the Equator is a big help; longer daylight hours and not so much problem with poor panel angle. Up here ... two hours of daylight in Winter and panels tilted to 72 degrees ... ugh. :cry:
    In terms of power, that translates to a fairly consistent average daily power consumption of about 50 watts (~1.2kWh/day) with an additional 250 watts over a 3-4 hour period (750-1000Wh/day) every 2-3 days (~1.5kWh/day average). The rated capacity of my panels add to 530W (2 of my panels are 130W rather than the 135 I indicated in my original post). Also, my panels articulate and I watch them pretty carefully on the high demand days (separate ammeters on each panel).

    Yes, you definitely need to think in terms of average daily Watt hour consumption. 1.2 to 1.5 kW hours isn't hard to manage. Using the famous Icarus formula (array Watts * hours of sun /2 = AC Watt hours available) we'd get about a 600 Watt array to do that, and you're just shy at 530 Watts.

    I think you're well on your way to a happy system. Much will depend on how the panels can be placed around the boat. Any in the same location can share a charge controller. You may need to pay particular attention to wire lengths, as they can end up being deceptively long when routed "out of the way" on a boat. Long wire runs will use up Voltage and drop power, necessitating larger than normal wires. This is another case where the extra money for MPPT controllers can be worthwhile, if you have more than system Voltage available from the panel(s).
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  • Tricksailing
    Tricksailing Registered Users Posts: 25 ✭✭
    #9
    Re: Two controllers,one battery pack

    Thanks very much for all of your discussions / information Cariboocoot. I really appreciate all of the contributors to these forums. Much has been clarified for me. Conventional wisdom puts me slightly under specs on panels and over capacity on batteries.
    Cariboocoot wrote: »
    I'd suggest getting a battery monitor for any type of sealed battery as you have no other way of knowing what's going on with them; Voltage alone doesn't mean much.
    I just dread shoehorning more electronics into my already stuffed panel. My panel has volt and amp meters and I try to estimate battery charge state from voltage when the ammeter has shown 0 net flow for, ideally, 30 minutes. I try to be conservative on that and also watch how fast voltage changes when there is a current flowing.
    Cariboocoot wrote: »
    you have 460 Amp hours you want to try for 46 Amps peak potential current, whether you use 25% or 50% of the capacity.
    Shouldn't gel cells only be charged at 5% capacity? which means 23A max? I think I read this on the NAWS site.
    Cariboocoot wrote: »
    Yes you definitely need to think in terms of average daily Watt hour consumption. 1.2 to 1.5 kW hours isn't hard to manage. Using the famous Icarus formula (array Watts * hours of sun /2 = AC Watt hours available) we'd get about a 600 Watt array to do that, and you're just shy at 530 Watts.
    Hmmm..... I still have trouble with this. I really need battery storage as backup for those cloudy days (they really happen in tropical climes - even in summer) because I'm reluctant to start engines. On the other hand, I don't feel I need the charging capacity to charge the entire bank every day. Presumably, there is a range of charge rates that are relatively optimum for maintaining batteries although I haven't found any mention of what the lowest tolerable charge rates may be for the different battery types.
    Cariboocoot wrote: »
    Up here ... two hours of daylight in Winter and panels tilted to 72 degrees ... ugh.
    Boy, that seems like a challenge for solar! I grew up in England where frequent cloudy days and a 54 degree latitude seemed way too challenging for solar. Now I'm at about 20N and had 28 amps out of my panels at 8:30 am this morning! It's cloudy now (2 pm) and I'm down to 19 amps. Conservatively, that probably gives me 100Ah (~1.2kWh) already today. Sunset is around 6, so I suspect Icarus gives a pretty low estimate for here.
    Cariboocoot wrote: »
    is another case where the extra money for MPPT controllers can be worthwhile, if you have more than system Voltage available from the panel(s).
    Now you're pointing me back towards MPPTs. Is there a problem if I parallel 2 panels into an MPPT and one of the panels gets shaded?
    5kW grid-tied SMA + 2kW grid-tied SMA (total 4kW emergency daytime power) + 2kW genset, 500W off-grid marine system. Baja Sur.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,591 admin
    #10
    Re: Two controllers,one battery pack

    We are always working with rules of thumbs because we don't know your battery brand/model/application--You are correct that one should limit charging to 5% per the battery FAQ, but always check with the battery manufacturer's website/data sheets to see what they say.

    AGM's would probably be a good idea for your next bank.

    MPPT charge controllers work very well larger solar arrays where you can run several panels in series... The MPPT works a bit like an AC Transformer... It can down convert (efficiently) higher voltage / lower current to the lower voltage/high current used by the battery bank. Saves lots of copper wire costs (smaller wires).

    In your case, boats are typically in warmer weather (don't sail to good in ice packs ;)) so you do not get that much increase in Vmp (which increases in colder temperatures), so MPPT controllers don't offer as much help in "matching" Vmp to Vbatt (in warmer weather).

    And since your panels are pointing in different directions with different possible shading--putting the panels in series is not probably going to help much anyway--plus it will not really reduce your wiring lengths much anyway (no long wire runs from a multi-panel array). An MPPT controller will not hurt anything (and frequently have more options like logging, remote battery temperature sensors, and cost a bunch more money)--but if you can save money with a PWM controller that otherwise meets your needs--why not.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Two controllers,one battery pack

    Yup.
    It's got to the point where our generalized advice isn't going to do you any more good.
    I think we're all in agreement that AGM's will be better for you, so plan on that for when the gels go. And yes they do need lower Voltage and current. FLA's will take the highest Voltage and AGM's will take the most current (but are pickier about Voltage). Gel batteries tend to be picky about Voltage and current. And they make a mess when they explode! :p

    The other big thing for your particular install is going to be how much panel you can put where. That's going to be what determines the length of wire runs and whether or not there's a big enough advantage to MPPT controller(s) to justify the extra expense. Panels in parallel on either type of controller are less affected by one in shade than panels in series.

    It's always a problem with any design: there's usually six different ways to get the same result and you have to pick the one that works best for you. :cool:
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  • Tricksailing
    Tricksailing Registered Users Posts: 25 ✭✭
    #12
    Re: Two controllers,one battery pack

    Thank-you very much for all the great comments and suggestions. You've really improved my understanding of contemporary solar systems. For now I'll probably go with a couple of 30A MPPT controllers with 2 panels paralleled into each.
    5kW grid-tied SMA + 2kW grid-tied SMA (total 4kW emergency daytime power) + 2kW genset, 500W off-grid marine system. Baja Sur.
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  • Tricksailing
    Tricksailing Registered Users Posts: 25 ✭✭
    #13
    Re: Two controllers,one battery pack

    Update.....

    I ended up with a pair of ProStar-30 PWM controllers with 2 panels paralleled to each. The MPPT boxes were too big for the available space. Performance seems very good, but they are NOISY when in PWM mode. They make an audible tone at maybe (guessing here) 100-200Hz and also generate electrical interference which is picked up by a nearby VHF radio. Interestingly, it doesn't interfere with transmissions, has a constant volume regardless of the radio volume setting and goes away when the radio is turned off.

    It's not serious enough to be a major problem - or even get me working on filters, but some people may find it annoying.

    The 2 units work fine together. When controlling, one provides the bulk of the charge as the other gradually backs off.
    5kW grid-tied SMA + 2kW grid-tied SMA (total 4kW emergency daytime power) + 2kW genset, 500W off-grid marine system. Baja Sur.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,591 admin
    #14
    Re: Two controllers,one battery pack

    Do your controllers have the Telecom Noise Jumper (section 7.5 B pdf manual)?
    B) Telecom Noise Jumper
    Some telecom equipment will produce noise when the ProStar begins PWM
    regulation. If this occurs, a jumper can be cut to eliminate the noise. Instructions
    follow:
    • First, try to improve the system grounding which often eliminates the noise. The PWM battery charging provides a significant benefit to the battery, and it is worth trying to preserve the PWM charging.
    • If the noise continues, disconnect the controller and remove the ProStar assembly from its plastic case.
    • Locate a vertical resistor in the upper right hand corner of the board, near the microcontroller. This is identified as “J11“ on the board.
    • Cut one leg of the resistor and separate the leads. This will convert the battery charging to a typical “on-off“ regulation of the solar energy.

    The switching is very slow, so the noise will not be noticeable. The equalization and float features of the battery charging algorithm are preserved in the “on-off“ mode.

    In the future, this can be reversed back to PWM if the cut jumper leg is soldered
    back together.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Shadowcatcher
    Shadowcatcher Solar Expert Posts: 228 ✭✭✭
    #15
    Re: Two controllers,one battery pack

    For future reference Steca PMW's will handle up to 47 volts.
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