Low cost MPPT Charge Controller

Discussion in 'Off Grid Living' started by techsar, May 30, 2015.

  1. techsar

    techsar Monkey+++

    With the current trend towards photovoltaic solar power production, many folks have started out using a rather inexpensive PWM (pulse width modulated) charge controller. There is nothing wrong with doing this, especially if there is a strong doubt as to whether they are going to stick with solar and perhaps grow their system. I was in this category myself for a while.

    Maximum Power Point Tracking (MPPT) charge controllers have been on the market for several years now and some of the big selling points are a 10% to 30% increase in harvested output, the ability to use higher (or odd) voltage panels with a lower voltage battery bank and the resultant savings in smaller wiring from the panels/combiner box to the charge controller. The major drawback has been the price.

    Chinese MPPT controllers have invaded the market, selling for as little as $50 for a 10 or 12 amp controller. Looking into the construction left me with cold chills! Poor circuit layout, undersized components and weakly worded warranties turned me off of them entirely (not counting the country of origin.) So the search was on for an MPPT controller that did not have the shortcomings of the Chinese, but was priced below the $550 starting point for major, proven brands.

    After a little consideration, we decided to give the Intronics MPPT75HV a try. US made, rated at 75 amps output and relatively dirt cheap. Under $300. Smaller footprint than the Xantrex C60 I've been using, well built - both physically and component wise - it seemed like the ideal candidate to use on some 28 volt panels I found...

    How well does it work? Quite well, IMHO. Here are some pics showing how it reacts on a cloudy day, transitioning to sun:
    20150530_130523. 20150530_131010. 20150530_131108. 20150530_131114.

    Just a couple of items of note. The battery bank was nearly full, so not much of a charge was needed and the batteries are AGM type with a maximum charge voltage of 14.9 volts - flooded lead acid batteries typically have a lower charging voltage...and this is adjustable on this unit.

    Hope you enjoyed, and maybe even learned a thing or two ;)
  3. azrancher

    azrancher Monkey +++

    OK so I don't have an MPPT charger controller since I am grid tied, tell me what I am seeing?
  4. techsar

    techsar Monkey+++

    The pictures show how the panel voltage and amperage increase going from cloudy to sunny, while the battery charging voltage only rises slightly while the amperage is higher than that coming from the panels. These are also 28 volt panels into a 12 volt battery bank, not a recommended scenario with a PWM controller.
    A PWM controller would shunt the higher panel voltage into a heat sink and the output amperage would not increase above the panels' input. The MPPT controller gives you more usable power from your panels by converting the excess voltage into amperage. It would likely show up even more in colder temps as the panels tend to produce more when cool (mid 80's today).
    Pic 1 shows a negligible current increase (perhaps just rounding in calculations), 2 shows +%14, pic 3 +%37 and 4 shows a %59 increase in current. I would not count on the higher numbers as typical, but it does graphically show the increase in efficiency as opposed to a PWM charger.
    I hope this answers your question :)
  5. buism

    buism Neophyte Monkey

    Techstar, I am starting my first battery setup. Starting with one or two 27dc marine batteries with multistage auto AC charger. I hope to add a 100w panel down the road.

    The main purpose of the battery is to provide emergency backup power for charging AA batteries, laptop and other small devices in the event of power failure.

    My quesiton is, with this small of a setup, is there any real advantage to a MPPT controller over a PWM controler?
  6. techsar

    techsar Monkey+++

    First off, let me say "Welcome" buism! Find a branch in the tree and make yourself comfy.

    If you have no plans to expand your system, the price difference between MPPT and PWM is going to make it pretty hard to justify the added cost. But even if you don't expect to have your system grow, I would strongly recommend getting a charge controller that has "headroom" so that you aren't running near it's maximum capacity. Same for wiring. Go oversize for 2 reasons - less current loss, and if you do add on, you already have the wiring to handle (some) increase.

    For the difference in cost (MPPT vs PWM,) you could conceivably buy another 100 watt panel (or two!) and see a much higher charge rate...but then you might as well be using some of that power - to replace it ;)

    Since this is to be your first setup, let me make three suggestions:
    1: Clean connections! Anything else will cost you in lost power, and heating (fire potential)
    2: Ventilation - charging and discharging batteries give off hydrogen gas, make sure there are no open flames, heaters, etc in the area.
    3: Watch that electrolyte level. Let it drop to where the plates are exposed and a battery will died an early death.

    Again, welcome. If you have questions, lots of good folks around to help. Ask away!
  7. techsar

    techsar Monkey+++

    I agree. Trace (now Schneider IIRC), Outback and Midnight all have great products, with good support crews. I was just looking for an opportunity to try another US producer, but at a lower price point...and see how their product measured up. The Intronics has no fancy control interface (such as Outback's Mate, for example) but does have choices for integrating into many systems. I know 12, 24 and 48 are supported, maybe more.
    I'll be interested in how it holds up in the long run (my Xantrex C-60 has been going 24/7 since spring of 2006 with no problems) and if there is an issue, how customer support handles it.
  8. techsar

    techsar Monkey+++

  9. techsar

    techsar Monkey+++

    Give me a moment...I'll put it on here...see if that works for you [beer]
    ...and yes, I run 4 gauge about 2.5 feet from the CC to the batteries.

    Attached Files:

  10. BTPost

    BTPost Old Fart Snow Monkey Moderator

    I had a Friend who owns a Welding Supply House, give me 50Ft of Old Welding Cable, a few years back.... That is what I use for Battery Bank Jumpers, and Battery Bank/Inverter Cables... It is very fine Stranded Copper in about 4/0 size... I then Solder on Terminals, and after they cool, I then Crimp them in a Vise, and then Reheat the Terminals to ensure No Cold Solder Joints...
    I still have about 35 ft of that stuff left....
    techsar likes this.
  11. techsar

    techsar Monkey+++

    That's about the best wire on the market for high amperage applications. Flexible, too, unlike what is commonly found in automotive-type applications. A worthwhile investment on any battery bank!
  12. techsar

    techsar Monkey+++

    Yup. For that particular array, there are 5 200 watt Sharp panels @ 28 vdc into a combiner box, 6 gauge to the CC, only a 20 foot run. Figuring the max output is going to be near the limit of this controller. (42 cell panels, btw)
  13. techsar

    techsar Monkey+++

    Ok. Six month update. The Intronics MPPT75HV developed an issue, specifically "chattering" when it exceeded 33 amps input along with showing battery voltage instead of panel output on the input display. A full reset did nothing to correct this. It was covered under warranty, yes, but I opted for a refund...looks like a Midnite Solar Classic 150 is in my future.
    Live and learn...and figured anyone else looking could learn from this experience.
  14. T. Riley

    T. Riley Monkey+++ Site Supporter++

    image. This is my solar setup if anyone is interested. It provides between 3,600 and 4,500 watts per day of useable power. Total cost was $4,500 before a $1,600 tax credit. It will provide all the light I need at night plus run my attic fan or fireplace blower.
  15. T. Riley

    T. Riley Monkey+++ Site Supporter++

    This is what the setup looks like in the laundry room of the house. The batteries are in the rack beneath the inverter.
  16. T. Riley

    T. Riley Monkey+++ Site Supporter++

    I don't get my feelings hurt. Alternatives and benefits please.
    Homer Simpson likes this.
  17. techsar

    techsar Monkey+++

    Another item that could come back to bite you quickly - according to your diagram, you are running 4AWG wire between your batteries and to the inverter. This is grossly under sized for the potential current that model inverter can draw under normal use. 2/0 cabling would likely be about right, given the short run in the picture. 3/0 or 4/0 would be better. though.
  18. T. Riley

    T. Riley Monkey+++ Site Supporter++

    The circuit breakers on either side of the controller are 80 amp DC. Each of the interconnect plug feed a different side of the panel so all 120vac is hot. All 220 as well as circuits to the microwave, frig., freezer are thrown. Only lights, wall outlets, fireplace insert blower and attic fan are online. Larger battery to inverter wire is a good suggestion and one I will follow up on. Guys, no one is going to hurt my feelings. I am old enough to know I am not an expert at most things, thus the post. I appreciate the comments. This setup is exercised once a month. It is for the after times only. I have a whole house propane generator with an automatic transfer switch and 800 gallons of propane for the here and now.
  19. T. Riley

    T. Riley Monkey+++ Site Supporter++

    Here are the specs on the nine panels I have wired as show above. They are Grape Solar 100W POLY GS-Star-100W
    The circuit breakers are 12V/80Amp car type.

    Panel Electrical Specifications
    (STC* = 25 ºC, 1000W/m2 Irradiance and AM=1.5)
    Characteristic Details
    Max System Voltage 600 V
    Max Peak Power Pmax 100 W (0%, +6%)
    Maximum Power Point Voltage Vmpp 18.0 V
    Maximum Power Point Current Impp 5.56 A
    Open Circuit Voltage Voc 21.9 V
    Short Circuit Current Isc 6.13 A
    Module Efficiency (%) 14.63%
    Temperature Coefficient of Voc (-0.32% /ºC)
    Temperature Coefficient of Isc (0.04% /ºC)
    Temperature Coefficient of Pmax (-0.45% /ºC)

    I wanted to keep it as simple as possible. Replacing the breakers would not be a problem. Any other suggestions without getting an electrical engineer involved would be appreciated. The 400 Watt Kit for Grape Solar is what I started with wired as they instructed I then added five additional panels, rewired them and swapped out the charge controller. The battery to inverter run is less that 12 inches of 4AWG. I am open to any suggestions @Cruisin Sloth
  20. T. Riley

    T. Riley Monkey+++ Site Supporter++

    So the single 8awg red from the panels are replaced with three 10awgs reds which each having its own 10 amp breaker after which they are tied together with the one red going to the charge controller? That's what I understand from your reply. What are the specs on the breakers?
    I don't understand DVM. I think the idea is to check the voltage at the battery then at the inverter post and it should be no more than 1.1% less. Correct? Neither the charge controller or inverter are grounded at this point. I was unsure if I needed a new independent ground for these or the same ground to the main house breaker could be used. Again, thanks for the advice. The panels have an independent ground.
  21. BTPost

    BTPost Old Fart Snow Monkey Moderator

    DVM = Digital Volt Meter


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