Classic sizing

[p4f]

I will try to make this short as to not bore too many   I have a solar/wind system I am putting together for learning and eventually build upon.  Going to power up some things in my shop as I learn.  I have a used MM5000 inverter that I am going to use as off grid only.  I was going to use the CC controller portion of it for my solar, but I recently learned the charging set points are for SLA batteries only, not FLA like I want to use.  I can get my hands on software to change set points, but I don't think this will work; here's why...
So in doing the sizing tool on the site to calculate what panel configuration to use with what Classic I noticed this note on the bottom of the page stating that most MPPTs like to work at 130% of battery voltage.  With the 8 used 185w panels I have with the VMP of 36.29 for me to hit that 81volt number required for a 48v battery I can't do 4 strings of two panels each as I'm not high enough (if you use the vmp for calcs not the voc).  So I would have to do 2 strings of 4 and I would be above the 120v max on the MM5000.
So I was going to buy a Classic 250 and run the 2 strings of 4.  Works out in the calcs even with the -40f weather we can see where we are at.  The note does say also that higher voltage is less efficient, so should I be concerned with this?  Wire size is more desirable with the 2/4 combo, but it would be nice to use  either the 150 or 200 due to price and efficiency but if the 130% rule applies, I can't get there with panel configuration. 
Other question I had was the garage sale SPDs.  They are the type 1.  In the reading I have done defining the 1s and 2s those 1s are ok to use prior to the control/distribution equipment?  So like I could use them on my panel junction box, and on my 3phase homebrew turbine?  It's just after devices like charge controller, inverter and distribution where a type 2 is needed, or 1s could be used with additional forms of over voltage protection?

[tecnodave]

p4f,

Welcome to the forum.

First off I do not know what a MM5000 inverter is but if it has a built in MPPT controller it is probably of Chinese manufacture. I have a similar 5000 watt inverter/controller in my junk pile. It didn't work well as either device but the inverter portion was better.....nuff said about that.

On the MidNite Classic controller.......my advice would be to not use a higher voltage than necessary to achieve results. My feeling is that unless you are at a large distance from array to controller stick with the Classic 150.  It's more efficient and panels are cheap.  I'm guessing that your 185 watt panels are 72 cell, maybe Sharp or some similar panel. Buy one more and use 3 strings of 3 panels each. The panels do not have to be an exact match.  They all should be the same number of cells and the same type I.e. Monocrystalline or polycrystalline  with close to the same voltage and amperage....VMP & IMP. I have a mixed bag of 72 cell Sharp NE-165's and NE-170's working well togather on one Classic 150.  My other banks are 96 cell multilayer monocrystalline panels with an amorphous layer of polycrystalline on top. These panels are high voltage at 53.5 volts at MPP so they that their own controller .  My string voltages are 72 volts for the Sharps and 53.5 volts for the Sanyo HIT panels . My battery systems are 24 volts.

I have experimented with various string configurations using the Sharp panels in strings of 3 vs strings of 2 for a VMP of. 105 volts or 72 volts. As well as using the Sanyo panels in all parallel vs in strings of 2 for a resulting VMP of 53.5  or 113 volts.  I have two Classic 150's and two Kid's.  Side by side tests were done on each configuration.

Results..... The array with the higher string voltage would cause the controller to run hotter with no apparent increase in usable power. With the Classics the controller with the higher string voltage would be 12-15 degrees hotter and the fans would constantly  run. This was particularly noticeably after bulk charging when all the available solar energy was not needed. The same result was noticed with the Kid controllers , the temperature would be 15-20 degrees hotter with the 113 volts in vs 28.8 voltage charge.  4-1 voltage conversion .   vs. 53.5 volts in vs 28.8 volts charge   2-1 voltage conversion.

Electronics just doesn't like the heat......

The Classic is an excellent choice as a controller as it can be programmed to any battery bank better than any other so a Good choice there.

Have fun learning, it's been a fun trip. You will learn a lot here and do check out forum.solar-electric.com   Another great source of information from solar expitmenters, tinkers, and real pro,s in the business.

David

[p4f]

David,
The MM5000 is/was an all in one made by Advanced Energy Products, later Beacon Power and the M-5 unit.  They were not without their problems. 
Thanks for your input on panel configuration.  My panels are a mixed group with 4 being some old ET Solar 185, 2 Hanwha 190, and 2 Makesen 180.  All very close to each other in rating.  I have not checked if the Hanwha or Makesen size is still available.  I know the ET Solars are not.  I will have to give some thought to what your saying, and then therefore sizing.  My biggest question I guess was to the minimum voltage concept to look out for as spelled out in the notes on the string sizing page.  I wasn't aware that the MPPT worked like that.  I thought it was a combo of volts and amps with the mppt CC converting it to what it needed based off battery size programmed in (my case 48v) 
David

[tecnodave]

P4f,

There are several different designs of MPPT circuitry. I have taken apart several Chinese units and they have very small inductors and capacitors in the MPPT front end. I installed a Victron Smart Solar MPPT controller which included the claim that it would work with only 5 volts difference between battery and p.v. maximum power point to start and only 1 volt difference to operate. Well I hooked 2 72 cell panels in parallel to charge a 24 volt set of Surettes......it did work but not well at all....I netted only 90ish watts out, changing the wiring to series raised the input vin to 72 volts....walla much better, I netted 408 watts from the 500 watt pair........well it did work with only 4.5 volts difference between battery and p.v. Volts....but a PWM type of controller would be better in that application.

The Classic uses a two stage converter in the MPPT front end.  This design works much better as it uses two large inductors and sets of capacitors. This will require more "voltage overhead" ....more difference between batt volts and p.v. In volts. But will produce more power to the batteries than the simpler designs.  I haven't looked too much into the Outback design as I don't have one but it probably have a similar design.

The Chinese units are built to a price point. The electronics are scrimped on. The inductors (these are what really does the work in voltage transformation) are tiny in comparison. I had several EP Solar Tracer MPPT controllers and had them open many times attempting to set the voltage high enough to properly top off my L-16 Surettes. I failed at that and had to run a generator to top off my batteries every week. In comparison my MidNite Kid controllers have an inductor 10 times the size of the Tracers.

It's all about design to a purpose, not to a price point. The team at MidNite are very intense engineers and left no stone unturned in polishing this product to its finest. I am biased, I'm a retired electrical engineer and have always worked in high end commercial product. I have never repaired a television, but have done many high power transmitters, commercial communications, industrials power systems, etc. and I do recognize good design.

In my experimenting I have found the ideal voltage transform ratios for my 24 volt systems.
I'll put it in terms of voltage ratios between battery max e.g. voltage and solar VMP.   Maximum utility is at 1.8 to 2.7  times voltage ratio.  Too high a voltage conversion and power will be lost as heat, too low and units will search for the maximum power point too much.

One of the worst cases I have seen was a installation of 3 Classic 150 charging 22 12 volt batteries in parallel from a 145 volt solar array. There were large aluminum heat sinks epoxy bonded to the back of the classics with many fans attempting to cool this mess. The voltage transform ratio would be 10-1 down conversion. It did work....he had a hell of a heater!  Could not tell this guy anything so I bailed out....wished him best of luck with it

So I did go look up the MM5000...... It is made in China and designed for a price point....not impressed with that. The unit in my junk pile is not the same one. Use it until you get something better........if the idle draw is not too drastic.  The Classic is 1000's of times better as the controller for your use.

Solar panels have become a commodity with many units available. I buy from a large contractor who does huge systems and replaces existing systems. I recently bought 60 Sanyo HIT multilayer panels at .020 / watt.  $40.00 per panel.  Hard to beat that.  These panels have the MC-3 connector and would not be acceptable to many building inspectors as the code has changed requiring MC-4 locking connectors.  Connectors are a $1.00 each in quantity and good crimper can be had for $50. The inspectors do not know that much detail and have never noted the changed connectors.

Look around used panels are cheap to free for hauling them away.  I have been paid to remove complete grid tie systems due to poor design and installation when the house sells to a new buyer.

Keep reading, tinker a lot and you will learn much from people who share their work here and on other forums. This is where I have found the best user information, also frequent ...forum.solar-electric.com

David

[p4f]

Thanks David.  Not overly concerned about buying another CC controller if need be.  I think I read too much, and then end having more questions than answers.  I spent a good deal of time reading on the other forum.  Found quite a bit of info on battery bank size, and suggested wattage to adequately recharge.  As a experimental system I was just going to start with GC2 batteries 16 of them in 2 banks for 430ah @48v.  Bill over there had some good advice he gave out to others on bank sizing and watts needed at % charge rates with 10% being the minimum suggested for off grid.  I should be looking at more like 3kw verses the 1.5 that I have to service that 430ah in a timely manner in Dec in WI.  I have the wind too, but if it don't blow.....
So to be more to the point; charge controllers, a few questions. 1) I have read you don't want to typically have more than a 3 to 1 conversion rate.  It's unclear to me weather that number is based off actual 48 battery voltage, or the amount you need to push power in (58?) Also on the panel side then.  Which number are we using?  I assume the VMP under STC, not the voltage your going to get at colder temps.  So you don't want to be too low either.  Midnight posts what they do on the calculator which I posted in first post that you want a minimum of 81volts taking 130% of equalizing voltage of 62.3.  This buffer is needed for the excessively hot days when panel output goes down so your not starving the classic.  Kinda a delicate balance as your aiming for a number between 81v, and 150ish, or 180ish (don't know which because I'm not sure which number to multiply with) And also again you have to take into account the cold.  I've also read (maybe by disgruntled buyers, not sure) not to buy the 250.  If at all possible stay in the 150 size with 200 being ok.  That would be fine by me price wise  Just seems the whole thing gets to be a bit of a juggling act with panel ratings etc.  At least with the used panels I picked up. 
I sure have not seen panels available in our area like your saying.  Usually people selling them on CL within a decent driving distance they aren't much cheaper than new.  The 8 panels I got came over the course of about 6 years or so, 2 different deals popping up that were too good to pass up.  The ones I have are such odd ducks though at 185w for 24volt charging.  I would like to have 9 so I can do 3 strings of 3. It would probably get me closer to a CL200 with the 250ft I have to go with wire.  Thought about just adding a couple of 100w panels from Amazon strung together.  The ratings of a 200w series are within that 10% realm of the 185s I have.
My MM5000 will just get used as an inverter.  It is probably a bit large for 430ah.  I should go back and look again what the power consumption is.  It probably isn't the most efficient unit.
Any thoughts on the MN spds they have on garage sale?  Like I said if I read right I understand type 1 being ok for on the utility side, or in off grid I would think on the generation side.  Type 2 though needed after equipment.
David

[Westbranch]

you don't want to typically have more than a 3 to 1 conversion rate.

to round out the numbers, BB is saying you don't want the PVs  feeding more than 150V  into the charge controller and then send 48 volts to the battery.. that much DOWN conversion creates a lot of lost power as HEAT... plus wear and tear on the electronics...

[p4f]

Thanks for chiming in, but the question was more to which set of numbers do you really use?  We are not charging at 48 volts.  MN says you want at least 130% of equalize for the hottest day of the year, so 81 volts.  Even to use equalize volts of 62.3 (according to MN) your 3 to 1 rate is 180 going in.  Then on the panel side I assume you want to use the STC numbers as posted on the tag, not the coefficient ratings hot or cold.  So I could put 4 of my panels together using the vmp of 36.29 (STC) and be at 145.16 and be below a 3 to 1 at even 48 volts, but not if temps drop.  Still can't get by with a CL200 though cuz I would have to figure in my coldest day of the year scenario.  All kinda a juggling act

[tecnodave]

p4f,

The range of input voltage that will work the best will be 62.3 X 1.3 =81 volts (lowest) and 62.3 X2= 124 volts.    No need to push it to 3-1 voltage ratio. If you plan 3 panels in each string that will be about 105 volts in.  Plenty of headroom for that surprise freezing morning that sends VOC sky high.
No need for any input voltage higher than that. Increasing input voltage will not produce more power....instead the classic will work harder and waste more power as heat. Power lost as heat is power that is lost to the batteries.  And heat takes its toll on the gear.

david