36 volt gifted

mountainman · August 2020

3 months ago a friend of mine decided to experiment with solar.
So the first thing he buys is a 36 volt 2000 watt inverter.
Got it for a deal he said.
Next he purchased 3 new 345 watt q cells.
6 200 ah GC batteries and a make sky blue Controller.
Today he calls to tell me he's moving and if I want all of his system come get it.
He informed me the inverter quit
About a month ago.
But every thing else was fine.
He ran the panels in series.
Question is what to do with it?
what's my best option
Buy a matching panel?
Buy another 36 volt inverter?
Or Buy 2 more batteries and go 24 or 48 volts?
I know you should figure loads first
but this was gifted to me.

mike95490 · August 2020

The price is right if you have the storage and mounting space.

mountainman · August 2020

Batteries are super start name brand from o'Reilly (ev125) cant seem to find the 20 amp hour rating.

MichaelK · August 2020

Outback used to make a 36V inverter, but I don't see any for sale, even checking outback.com? I'm guessing that 36V is being phased out? That leaves you with no-name brands you buy off of ebay. I'd say to go with 24V and stick with quality name-brand equipment. 48V if you want to power big-ticket items like a wellpump.

mountainman · August 2020

I agree 36 volt is not what I would have built.
I could use 4 of the batteries for 24 volts. And save 2.
Or buy 2 more and have 2 banks 2s2p
if a battery goes bad. I still have some power
But I'm leaning towards the benefits of 48 volts
No batteries in parallel
Seems 24 and 48 inverters are close In price.
And small 300 watt 48 inverters
Are more available now.
Less amps. cheaper wire and more room to grow.
Along with adding 2 batteries I'd need to add a panel or 3.

I'm still researching for the 20 hr rate of the super starts.
I no you shouldn't mix brands. But I have a couple 200 ah GC batteries about the same age.
And I've considered adding them to the other 6. Bad idea?

mountainman · August 2020

Frequent hurricanes this time of year power can be out for weeks.
Id like To be able to run a energy star
Refrigerator 1200 wh/ day
70 watt box fan 6 hours 420wh
and a 30 watt led tv 8 hours 240 wh
4 12 watt led lights 6 hours ~300 wh
Charge 2 phones. 20 watts for 2 hours. 40wh
Couple times a week 5 minutes of microwave.
~2.4 kwhs per day.
2000 watt inverter.
with 4 panels 1400watts ~9% charge rate or 6 panels 2000 watts ~13+. Does this Sound doable on a 200 amp hour 48 volt system.

Photowhit · August 2020

That should be about right for the load, with 4 GC known good batteries and 1300 watts of array, I'd like a bit more cushion, but for an emergency, Understand that you have about 1 day's worth of storage before hitting the 50% mark, If you typically have long sunny summer days during hurricane season, you should be okay. Understand that you don't normally live on solar electric, so might not be aware of all your loads. You would want a 1100-1500 watt inverter minimum, Might see if there is a known locked rotor load for your fridge.

mountainman · August 2020

With 4 200 ah GC on 24 volts.
My calculations 200*29/,77*.14= 1054
3 of my panels 345=1035.
For more cushioning. necessary for 2 days reserve.
8 GC batteries 4s2p 400*29÷.77*13.5= 2030 or 6 of my size panels 2070 watts.
At this time I'm not planning on a well pump. I have county water.
but on the hot summer days a10000 btu ac is a consideration for sunny day time use only.
wouldn't a 48 volt configuration be a better choice?
Would mixing q cells
And non q cell panels be an issue provided that they are within 10% of power ratings?

mike95490 · August 2020

mountainman said:

wouldn't a 48 volt configuration be a better choice?

Would mixing q cells
And non q cell panels be an issue provided that they are within 10% of power ratings?

I would say 48V is a better choice

You don't match the Power ( watts) you match the
VOLTS for panels in Parallel
AMPS for panels in Series
Within 10% or so.

Panels in parallel, the lowest Voltage panel sets the array voltage.
Panels in series, the lowest Amp panel limits the array amps

softdown · August 2020

Tons of off gridders do fine with 24 volt systems. The math on 36 volts is much better - for the most part. I seriously would not mind using a 36 volt system though you will be exercising your calculator more. There is lots of 36 volt equipment out there since many golf carts run on 36 volts. Been eyeing some lithium batteries being sold for either 36 volt or 48 volt - the battery packs being about 42 volts.

Its a wonder that most systems seem to work - it seems like so many goober stuff together with little concern about compatibility. More about "scored a deal" on that. Next time I see a 6000 watt inverter running on two golf cart batteries.....

Could be a fuse in the inverter. Maybe a capacitor. An inverter dude could likely fix it but inverter dudes are scarce.

mountainman · August 2020

At 24 volts the controllers max is 4
Panels. 2 in series
If I use 48 volts the max the controller can handle is 8 345 watt
Panels And 3 in series.

If I add 3 other panels in series. A total of 6 panels
Then parallel the 2 strings
wouldn't the volts and amps need to be closely matched?

These are what I have hanwha.

Photowhit · August 2020

My reasoning is that your panels would not work with that charge controller for 48 volts. The VMP is too low to run them in pairs and the VOC is too high to run them in strings of 3.

I too, think 48 volts is a better solution. I don't know what you want to do, or spend. There are no known UL 1741, 36 volt inverters that I am aware of. If you could run 48 volts system, you would need an inverter as well as a different charge controller, and if you wanted more than 4 batteries, you would either need to add new batteries to run with old, not a good idea unless the batteries are less than 6 months old AND you know they have been well cared for or replace the current batteries with 8 new ones... It can become quite an expensive rabbit hole.

Another option is to spread out the expenses, run a 48 volt system now with 4 of the current batteries, until they die. Buy a cheap PWM charge controller to handle charging, and run the panels in pairs now understanding that you will want to run the panels in strings of 3 later so any addition should take that into consideration.

In this manner, You have the expense of a new inverter and a PWM charge controller now.... In a year or 2 if the batteries are hanging in there, add 2 or 5 panels (understanding you wouldn't be able to use the extra), This would give you a bit better run time even with the undersized battery bank, since you will have added production during the day. Then when the batteries die buy a fresh set of batteries with 8, and either then add a quality MPPT charge controller or do so later...

softdown · August 2020

There are lots of lesser known 36V inverter names on Amazon but this is of interest: https://www.amazon.com/ask/questions/Tx1ZJDT1LMFSKRJ/ref=ask_dp_dpmw_al_hza

"And I would stay away from this inverter it is a modified sine wave that uses a balanced circuitry. Which means it moves voltage through line 1 and the neutral wire. You Can not use this inverter on a breaker panal. Only one item per plug."

mountainman · August 2020

So 147 volts voc 3 in series is to high
For a 160 volt controller.
for a 48 volt system I'd need a 200 volt controller.
Because I'd need 3 in series to get the vmp high enough for charging 48 volt batteries with mppt. Right?
Let's figure 24 volts 8 batteries 4s2p.
Batteries were bought 5 2020 3 months old
Checked the voltage today 6.5 volts.

Ive considered using 2 that I already have of a different brand us battery 6 months old.
Or buy 2 new of the same brand.
I could sell mine and recoup som of the expense.
Buy one more panel 4 total 2s2p
I have 60 foot of 8 awg PV cable.
And 6 foot of 4 awg controller to battery.
For now use the elcheapo controller
Till funds allow for a better one
200 volt 60 amp. Not sure yet but Probably morning star mppt.
Then rewire all 8 batteries in series for 48 volts.
And add 2 more panels for a total of 6 3s2p
2000 watts @ 200 ah 48 volt 13% charge rate.
Wouldn't 2 in series work for charging at 24 volts? 400 ah @ 24
With almost 1400 watts I'd be close to a 10% charge rate.
No Matter what voltage I use I'm gonna have to buy an inverter.
But going 24 now and 48 later
I'll have to buy 2 inverters.
Maybe a cheap 24 for now and a better quality for my final 48 system.
What is the largest inverter I should use on a 400 ah 24 volt 1400 watt panel system.
Or a 200 ah 48 volt 2000 watt panel system?

mountainman · August 2020

@Photowhit for charging 48 volt battery what's the recommended vmp?
I thought it was 48x1.5. 72 volts.

BB. · August 2020

Vmp-array ~ 70-72 volts (4x ~18 volt Vmp panels as an example) will work fine with a PWM controller.

You can run a MPPT controller at Vmp~72 volts for a 48 volt battery bank... But ideally, if you want the "advantages" of MPPT function, you really want a minimum of ~1.3x Vbatt-max charging voltage... For example a 48 volt battery bank would charge near 60 volts:

60 volts * 1.3 MPPT "fudge factor" = 78 volts Vmp-array minimum suggested

This allows for voltage drop across the MPPT controller (so the "buck mode" converter can operate in its range) and to allow for hot panels and "depressed" Vmp-array (as panel temperatures rise, Vmp-panel/Vmp-array falls).

If you run an MPPT controller at Vmp~70-72 volts, the controller for the most part, just operates as a less efficient PWM controller.

-Bill

Photowhit · August 2020

mountainman said:

@Photowhit for charging 48 volt battery what's the recommended vmp?
I thought it was 48x1.5. 72 volts.

You want 30% above the charging voltage, so for a 48 volt system would have a absorb voltage around 59 volts, so 59 x 1.3 = 76.7 volts.

mountainman said:

Not sure yet but Probably morning star mppt.

I believe Morning star's 60 and 45 amp MPPT are specifically bad choice with those panels. I've run numbers in the past for people, and found no recommended configuration for 72 cell panels. They have a string sizing tool, you can check it out your self here;

http://string-calculator.morningstarcorp.com/

It may be that your current charge controller would work similar to a PWM charge controller if you introduced the lower voltage VMP panels in strings of 2. Bill may have already addressed this. My understanding is the best use/ energy preservation feature is just negated if the presented voltage is lower than that needed to work in MPPT mode. But it might have more lost energy searching and trying to run more efficiently. I honestly just don't know.

mountainman · August 2020

2 of my panels are 75.6 vmp
1.1 volt shy of 76.7
I ran Morningstar calculator.

Image: https://us.v-cdn.net/6024911/uploads/editor/y1/hhvoevf46n5p.jpg

mountainman · August 2020

When running the calculator two things caught my attention.
With 3 in series using my record 0f
Max voc was slightly under make sky blues claim of 160 max voc.
And at 104f 2 in series vmp

was only slightly higher than 64 volts.

mountainman · August 2020

I've come to the conclusion that since this will mainly be a back up system for hurricanes.
I'm going to make the best of what I already have. 8 GC in series.
Seems 48 volt 1500 watt pure sine inverters are cheaper than 24 volts.
If mixing old and new destroy the batteries they are still under warranty.
I'll Use the charge controller I have
Even If it works like a pwm.
Since I cant put all 3 panels in series. I'm gonna add 1 panel 2s2p
No combiner or breakers to buy.
A 1400 watt system all for the price of a single panel and inverter.
Some power is better than no power.
Any one local to N.C. got a 345 watt panel and a 1500 watt inverter laying around for sale?

mountainman · August 2020

@Photowhit are you saying morning star mppt is not a good choice for 72 cell panels on a 48 volt system?
Or any voltage system?

I ran this with 20 min 30 max volts

Photowhit · August 2020

mountainman said:

@Photowhit are you saying morning star mppt is not a good choice for 72 cell panels on a 48 volt system?

YES!, I've run 72 cell panels several times on their String sizing tool in a 48 volt system and had zero returns as acceptable. Either the VOC with strings of 3 were too high or the VMP of 2 panels too low.

I'm not saying they don't make a great product, or that it wouldn't work for a 24 volt system. I have complete respect for the company and the product!

mike95490 · August 2020

It's going to be the same result with nearly any honest string sizer tool for any CC. They all need about 130% of max recharge voltage (your EQ voltage) or the controller does not have enough voltage to operate with.
Gensun makes a "step up" MPPT controller but it does not downconvert

softdown · August 2020

It is 2020. Why are we making panels with outputs that create difficulty in realizing efficient voltage outputs?

While I am it - the current market in solar lithium batteries is an absolute clown show. There are a few reputable offerings and a large number of "others".

For example: Daly is still considered one of the reputable offerings of BMS (battery management systems) They finally produced a "low temp. charging cut off" after considerable pressure was exerted. The problem? It does not work. Imagine destroying $700-$800 batteries because you charged them below 32F. Especially after paying an additional $50 for a 'low temp charging cut off" feature.

mountainman · August 2020

Hats off to all of you for your patience trying to get some one to understand what you already know.

72 cells are 24 volt panels would seem 2 in series would be 48 volt panels.

But the reality is with mppt it would take 2 72 cell in series for the vmp to be high enough especially on hot days to charge a 24 volt battery.

Photowhit · August 2020

mountainman said:

Hats off to all of you for your patience trying to get some one to understand what you already know.
72 cells are 24 volt panels would seem 2 in series would be 48 volt panels.
But the reality is with mppt it would take 2 72 cell in series for the vmp to be high enough especially on hot days to charge a 24 volt battery.

You got it! Pretty much spot on!

The history of it is, that at one time, panels were made to charge specific battery voltages, the reason a 36 cell panel that typically outputs about 17.5-18 volts was called a 12 volt panel. There weren't truly functional consumer MPPT charge controllers until Blue Sky some time in the early 2000's. Before that people used PWM and panels made for specific battery voltages.

The big driver was the grid tied solar industry, which drove panel manufacturers to started making larger panels in 54 and 60 cell designs, that best used the available inexpensive materials. The higher voltages and lower prices to reach high enough voltages in strings, to back feed the grid made it attractive for the off grid battery based system to expand the MPPT charge controller market to use these higher power panels. The MPPT technology allowed for panels to be made to the most economical size rather than conform to specific battery voltages.

As the technology advanced, panels became larger and 72 and 96 cell panels moved into the market. So once again, there is a niche market for certain sized 24 and 48 volt systems to economically use PWM charge controllers with the newer 72 cell panels.

mountainman · August 2020

One last question. With a 200 volt controller such as midnite classic (expensive) couldn't i use 3 or 6 3s2p 72 cell panels in series and charge a 48volt bank?

Photowhit · August 2020

mountainman said:

One last question. With a 200 volt controller such as midnite classic (expensive) couldn't i use 3 or 6 3s2p 72 cell panels in series and charge a 48volt bank?

Yes, in fact you could use the Midnite classic 150 (or some other manufacturers such as Schneider) they offer an additional safety margin. The 150 volts max voltage while running, but there is an additional safety margin of adding the system voltage above the 150 volt max, that the charge controller will just not function until the temperature rises at the panels and the voltage drops to a safe level. These ultra cold temps tend to be in the morning, when there would be little charging going on, so you wouldn't lose much charging. This feature is called HyperVOC, Midnite has a PDF of this feature here;

http://www.midnitesolar.com/pdfs/whyHyperVOC.pdf

Midnite's string sizing tool is here;

http://www.midnitesolar.com/sizingTool/

BB. · August 2020

Midnite has a pretty good sizing tool (different links for full size "Classic" vs the smaller controllers). This is for the classic series:

http://www.midnitesolar.com/sizingTool/index.php

Note: The higher the Vpanel operating voltage (max voltage rating), the lower the current to the battery bus the controller can output/max rating (higher voltage silicon devices have higher internal resistance, so they simply must have lower max current ratings).

https://www.solar-electric.com/misocl200mpc.html

Model Number	150	200	250
Operating Volts Input	150VDC	200VDC	250VDC
Battery Charge Volts	12-93 Volts	12-93 Volts	12-93 Volts
Max Current Output at 25°C (77°F)	96A @ 12V	74A @ 12V	60A @ 12V
	94A @ 24V	70A @ 24V	62A @ 24V
	83A @ 48V	65A @ 48V	55A @ 48V
De-rated Current at 40°C (104°F)	80 Amps	66 Amps	52 Amps

-Bill

mountainman · August 2020

Seems my best option with my 345 panels is to stick with 24 volts.
And use my m.s.b mppt controller.
Series parallel my 8 batteries.
And buy another panel. 2s2p.
Found one just like mine used for $220
Its only 350 miles (pick up only). Lol
The controller would be almost maxed.
With a 450 ah 24 volt system.
@BB. Using your calculations a 1836
Watt max inverter.
Using a 1500 watt inverter what size battery interconnect cables should I use?
I currently have 4 12" cables
They are 1 gauge.

BB. · August 2020

What is your bank? 4x 6 volt @ 225 AH "GC in series x 2 parallel strings for 450 AH?

A 1,500 Watt inverter on a 24 volt battery bank:

1,500 Watts * 1/0.85 AC inverter eff * 1/21.0 volt minimum battery voltage = 84 Amps

NEC chart (without the "details"):
https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

Says 1 AWG is 110 to 150 Amp max rating (in conduit). Certainly not an issue when your "average load" is something like ~84 amps to 42 amps (one string, to two strings perfectly sharing).

You could go down to 3 or 4 AWG based on the inverter ratings.

For battery charging--I really like to use the 1.25 (1/0.80) NEC derating for continuous current. A charger rated at (for example) 50 amps--Will output 50 amps for hours into a "well discharged" battery bank:

50 amps * 1.25 NEC derating = 62.5 minimum suggested branch circuit rating for wiring and fuses/breaker (reduce the chances of "false trips" during hours "on charge").

The question to always double check, is to use a voltage drop calculator... For a 24 volt battery bank, I would suggest a maximum of ~1.0 volts from battery bank to DC loads. And for charger to battery bank, 0.1 to 0.2 volts max drop (rise) for accurate battery charging.

https://www.calculator.net/voltage-drop-calculator.html

So several calculations--Based on current (and whether variable loads like AC inverter, or "constant heavy loads" like battery charging) and based on voltage drop (prevent inverter from early shutdown, and to most efficiently/quickly charge the battery bank).

-Bill

36 volt gifted

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