Switch to MPPT charger controller?

I have a small 12V system with two - 115watt panels in parallel charging a pair of 6v - 415ah lead acid batteries in series with a PWM charger controller (Sunsaver 20 w/LVD). This system has been in operation for a little over 3 years. I am thinking about switching out the PWM charger controller for an MPPT charge controller to improve charge efficiency, especially in the fall/winter months. Would there be any concern with the batteries in changing the charge method? Also, I would like to add to the system but the current panels have been discontinued. If I were to switch to MPPT could I then add additional panels in the 110-120watt range to the same charge controller or would it be better to add another charge controller in parallel with all panels attached to it being identical?

-Todd

Comments

  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Switch to MPPT charger controller?

    Switch the the MorningStar Sunsaver Mppt and put your two panels in series instead of parrallel.

    You get less losses in your wiring and should see better current into the battery than the PWM controller as the panels will be operated at vmp, not the battery voltage as it does in your current setup.

    As to the future, deal with that when and if you actually buy more panels, you may find the increase in going to Mppt is enough of a bonus in energy production to not have to get more panels.
  • wxh3wxh3 Solar Expert Posts: 70 ✭✭✭✭
    Re: Switch to MPPT charger controller?

    I am currently debating doing this now. I now have two 135W panels that operate at 17.7V at peak power under "standard test conditions." I am using a Morningstar Pro 30A PWM controller to charge two 110AH batteries.

    If I understand correctly I should get pretty good savings by using the MPPT since I am not effectively "wasting" the extra voltage by operating panel at lower V. Originally I was thinking that I couldn't use The Morningstar model because the amps in my system would be too high...then I realize that with this controller I would hook up my panels in series for a "24V" solar system and there should not be any problem.

    Is there any good reason not do this besides the cost and wasting my current controller with its nifty meter? This MPPT has no problem (efficiency loss?) in converting from ~30+V to charge a 12V battery? (I guess I could even switch totally to 24V by putting my batteries in series...however my pure sine inverter is 12V...)

    I am in the deep southern USA so my panels get pretty hot in the summer. The peak power voltage in that case drops anyway (how much, I can't say) and my savings may become relatively small I think.

    I think I don't really need the extra power now anyway given my load. However, maybe come winter things will be different when my sunlight goes down. If I didn't already have the current controller it would be a no brainer I think!
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Switch to MPPT charger controller?

    The one major catch with the Morningstar MPPT is the current limit of 15 amps.

    That comes out to around 200 watts into a 12 volt battery.
  • wxh3wxh3 Solar Expert Posts: 70 ✭✭✭✭
    Re: Switch to MPPT charger controller?
    Windsun wrote: »
    The one major catch with the Morningstar MPPT is the current limit of 15 amps.

    That comes out to around 200 watts into a 12 volt battery.

    Oh yeah. So basically I would have to put my batteries in series and get a new 24V inverter...
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Switch to MPPT charger controller?

    For your configuration, in typical conditions you should OK on the units 15 amp limit at 12V configuration on the battery. Your 135Watt panels in heat will have these type of deratings

    Heat, figure the panels will be about +45C over standard in Florida ,( .08v/C loss in V ) 3.6V * 7.7A = 27.7watts

    Angle, most of the year, fix mount panels are NOT perpendicular to the sun, at least a 5% reduction = 135 - 27.7 * .95 = 102 watts

    Irradiance, in Florida, clear conditions are about 940wMsq ( STC is 1000 ) = 102watts * .94 = 96

    There are also wire losses that tac on a few more watts ...

    So your 270 STC watts , typically will be more like 192 watts PEAK ... lower most of the day

    I did extensive testing ( long term 8 different configurations one of which was a pair of brand new KC-130's ) on the MorningStar SunSaver Mppt. It went into current limit for maybe 30 minute of the day and just barley, the actual current available was about 15.5. These were NIB panels, at correct angle and ground mounted ( lower panel tempatures )

    I wouldn't go any larger wattage wise on a single SunSaver, but I doubt you could find any other controller that would net harvest more energy for you configuration.
  • System2System2 Posts: 6,290 admin
    Re: Switch to MPPT charger controller?

    Actually I don't believe you would need to make any changes to your battery configuration using the Morningstar MPPT controller the original responder recommended. I downloaded and looked at the operation manual for that controller to better understand that response.

    The manual states that the controller will charge either 12v or 24v batteries from 12v or 24v solar input. The max input of 200 watts for 12v and 400 watts for 24v refers to solar input only according to the manual. I found nothing in the manual that indicated you can't funnel the 24v/400 watts into a 12v battery configuration.

    So unless I missed something in the manual it would appear that no changes to an existing 12v battery configuration - just change your panels to the 24v series configuration. The built-in DC LVD load controller supports both 12v and 24v batteries as well - again with the same 15amp max.

    I like this idea and it looks like it will work well for my needs. I've kept pretty good track of the current charging performance with the PWM controller, so it should be pretty easy to verify just how much of an improvement this provides before deciding whether or not to add more panels. Great info - thanks!

    -Todd
  • wxh3wxh3 Solar Expert Posts: 70 ✭✭✭✭
    Re: Switch to MPPT charger controller?

    ttavasc...I believe the technical spec does state "max battery current" is 15amps.

    My question is what happens when I hit the limit? It just doesn't put out any more current and I lose power? Or could I damage something?

    Guppy..maybe I wouldn't hit the limit too much in the real world...but still 15amps x ~12V = ~180W which quite a bit less than the 270W @ STC panels that I have!
  • System2System2 Posts: 6,290 admin
    Re: Switch to MPPT charger controller?

    wxh3 - I did see the max battery current of 15amp in the manual, but it's unclear in the manual how the controller handles a higher input voltage scenario. I did some additional searching on Morningstar's support site and finally found a small data sheet that is more explicit than the manual regarding this. It is in fact max of 200 watts for a 12v battery and 400 watts for a 24v battery. I've never thought about using the higher voltage on the panels with the lower voltage battery - it's still a bit new to me, so I appreciate everyone's input.

    My 230 watts is a bit less than your 270 watts, and I'm in the Pacific Northwest so it appears that this would still work for me. I need to run the numbers like Solar Guppy did for Florida, but I suspect it will still be OK. The other option I'm considering is swapping the PWM controller for a Blue Sky Energy Solar Boost 3024i MPPT - a 30amp 12v/24v charge/load controller with LVD. It's a bit more $$ but would appear to support the same configuration that Solar Guppy originally proposed, and would probably provide you with a bit more breathing room on the 270 watts.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Switch to MPPT charger controller?

    The SunSaver Mppt is 15amp for the battery maximum, regardless of battery voltage. You can have on the Solar side panel voltages, upto 75V maximum

    Typical charging is 13.5-14.0 volts for Bulk ( if your only getting 12V durring a charge your battery is dead and the SunSaver 15 amp limit will be the least of your problems :roll: )

    13.5V * 15A = 202.5 watts
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Switch to MPPT charger controller?

    To be a KISS advocate. Since you are considering changing controllers anyway, make sure that you buy enough controller to have some "headroom" to grow. A few dollars more for a controller that will allow you to add some panels in the future is only smart in my mind. I started with a 15 amp controller thinking I would never have that much capacity. I am now running a 25 amp, and wish it were bigger.

    Icarus
  • wxh3wxh3 Solar Expert Posts: 70 ✭✭✭✭
    Re: Switch to MPPT charger controller?
    Typical charging is 13.5-14.0 volts for Bulk ( if your only getting 12V durring a charge your battery is dead and the SunSaver 15 amp limit will be the least of your problems :roll: )

    13.5V * 15A = 202.5 watts

    I think my bulk charge voltage is often lower than that, esp. when battery is more depleted. Still, probably should have used at least 13V in my calc!

    I wonder if Morningstar has any plans to make an MPPT controller that has >15 amp battery current...
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