mppt voltages

mike74820 · May 2016

im getting new 100/30 amp mppt controller soon. i want to know how to hook the panels up too it, i have 3-100 watt 12 volt panels. do i hook them up 12 volts, or can i hook them up so they add up to 36 volts. or buy another panel and make 2 runs of 24 volts? ill be hooking this up to a 12 volt battery bank

vtmaps · May 2016

Without knowing the specs of your controller (what make and model?), I can't be certain. Probably 3 panels in series (36 volts) or 4 panels in series/parallel (24 volts) will work OK.

--vtMaps

mike74820 · May 2016

im looking at the blue solar mppt 100/30 model, made by victron energy it around 210 $

vtmaps · May 2016

That controller has a max input voltage of 100 volts. I don't know exactly what panels you have, but three of them in series probably has a Voc of less than 70 volts. Under cold weather conditions that Voc will remain under 100 volts, so I think you are OK with three in series.

--vtMaps

BB. · May 2016

Do you have a long wire run from the array to the solar charge controller+battery bank (higher Vmp-array voltage/smaller gauge wiring) or is it a short run (run lower Vmp-array voltage and the charge controller will be slightly more efficient/run cooler)?

Batteries are expensive and solar panels are cheaper these days--It does not usually hurt to add and extra panel (assuming wiring/controller/battery bank) can manage the current (AH of battery bank? Your average loads? Daytime or nighttime loads?

-Bill

mike95490 · May 2016

It's all cost / efficiency trade off. The MPPT is most efficient being fed about 2x battery voltage. Long wire runs have restive losses. Parallel panels have lots of amps and loss in the wires.

mike74820 · May 2016

the run only like 15 feet, just wanted to get the most out of my 3 panels when i decide on getting the mppt controller , my load right now is
just my 12 volt computer, it only uses about 1 amp, battery size is 235ah, i want to see if i can run my new led tv on the inverter i got, i know it pulls around 3.5 amps.

BB. · May 2016

For such small distances and relativley small solar array--PWM or MPPT would be fine. In hot weather, the MPPT with (at least) two panels in series would give you a bit more charging power (Vmp-array >> Vbatt-equalizing).

Assuming 4.5 hours minimum per day, 300 watt array, fixed and tilted to latitude:

300 Watt Array * 0.52 off grid AC system eff * 4.5 hours of sun minimum (typical average) = 702 Watt*Hours per day (typical winter minimum?)
300 Watt array * 0.61 off grid DC system eff * 4.5 hours sun = 823.5 WH per day
823.5 WH per day * 1/14.5 volts charging = 58 AH per day minimum @ 12 volts

And, the question about tv drawing 3.5 amps--Is that the 12 VDC inverter DC input current when running the TV?

I would suggest a daily load system has, at least, 10% rate of charge:

235 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 443 Watt minimum array

Your 300 Watt array is a bit on the small size--But should be enough to keep the battery bank "happy" as long as you do not over discharge the battery.

It is all about loads (and your ability to reduce them during bad weather or after heavy power usage)--What is the computer loading and how many hours per day do you want to run it (and the TV)?

-Bill

mike74820 · May 2016

i actually do bulk at 14.8 and float is around 14.3 did this because of sunking and handy bob ? saying with solar you need to push as much into your battery as can during the day. and yes the inverter is a 12 volt one i know it bad but it all i could afford at the time, it is a 400 watt pure sine wave one.

BB. · May 2016

As long as these are flooded cell deep cycle batteries--The charging/float voltages are fine (I would drop the float voltage if you leave for more than a week at a time--Avoid severely over charging the batteries).

If you need to refill the batteries every 1-2 months--You are probably doing fine on the general charging. If you need to fill the batteries more often than once every 4 weeks, you probably need to dial back on the float voltage.

Do you have a hydrometer to monitor your specific gravity of each cell?

-Bill

mike74820 · May 2016

yes i got one of those temp compensated ones. and yes the are flooded cr 235 crown 6 volt battery's

Vic · May 2016

Hi mike,

We do not know your location, and the temperatures that your batteries will be exposed to. But, it is a very good idea that any charge source, like the Charge Controller CC) has the ability to use a Battery Temperature Sensor (RTS or BTS). And that you make sure that you order the BTS, if it is not included with the CC. Many inexpensive CCs have no provision for using a BTS.

Agree with BB Bill, that your Float voltage is, (very, very) high. For off-grid systems, Float is a voltage that will just barely keep a fully-charged Lead-Acid battery, charged. A 14.3 Vfloat is above Gassing voltage for your Crown CR-235s. It IS a charging voltage.

If your CC is correctly set up, there is no reason to make the transition to Float, if the battery is not fully charged. If the battery IS fully-charged, then doing more charging after the Absorb stage (ie, in Float) will needlessly heat the battery, cause excess water use, and add to the normal plate erosion that goes with fully charging a Flooded battery.

It is a very good thing that you have, and will use your Hydrometer.

FWIW, Vic

Photowhit · May 2016

mike74820 said:

i actually do bulk at 14.8 and float is around 14.3 did this because of sunking and handy bob ? saying with solar you need to push as much into your battery as can during the day. and yes the inverter is a 12 volt one i know it bad but it all i could afford at the time, it is a 400 watt pure sine wave one.

Ask SunKing if he has ever lived off grid? Ask him who explained that Net metering was a national policy! I'm happy with my system and the life of it, I've used the cheapest 6 volt golf cart batteries and managed 5 years on a single string of 4 in a 24 volt system including running an air conditioner over the summer months. I posted a photo and SunGod didn't believe it. Basically go ask him on the forums he 'lords' about on...

Sorry, Not a fan, I've been off grid 15+ years now, made a few mistakes, some involved wasting time correcting SunGod...

mike74820 · May 2016

i know sunking is a meany, but his are you killing your battery's and handybobs solar, say pretty much the same thing. according to crown specs the constant voltage charge should be between 2.37 and 2.42 per cell, so i think pretty close to what they want to charge at. and for vic im in Oklahoma about and hour away from Texas boarder and the battery's are inside the house in a room with and open window open 24 hours a day ,

Photowhit · May 2016

The problem is you aren't doing that for 3.5-4 hours are recommended, during the summer months you are holding that high voltage for 6-8 hours. The reason we would worry about out gassing and needing to watch your electrolyte levels carefully.

http://www.supac.co.uk/media/CR-235.pdf

If you would like to describe your system and it's uses, we could better help you.

SunGod is not mean, he's more arrogant, once told me he would apologize if I showed him one thing he said that was wrong. I had a list of 6 without trying. He has some little letters after his name and bullies people around, but will not admit when he's wrong or makes a mistake. That is dangerous! Bill, here, is very quiet and knowledgably. Doesn't point out that he's gone to bat for at least one issue in the NEC code that he felt was wrong, writing a paper getting prominent engineers in the industry to sign on... Bill is a real asset, while SunGod is just a real....

mike74820 · May 2016

i am liking the new mppt controller i decide on, it been hazy all day and it been constantly putting out around 10 amps since 10 am now. for you folks who didn't like my setting, this controller only had a dial to turn up bulk basically. so i set it on the setting that gives me 14.7 bulk and 13.8 absorb, so i hope that better

mppt voltages

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