Charge controller for large 1766AH, 48V battery bank with 6 hour peak sunshine

[Sunking]

OK I have a few minutes. The design process is simple and straightforward. Here are the Cliff Notes from this Thread.

1. Determine worse case daily Watt Hour consumption. Example let's say 17 Kwh per day.

2. Determine Battery Watt Hour Capacity = 5 x Daily Wh. You need 5 day reserve capacity to give you 3 days without recharge (cloudy spells) and never allow batteries to go below 50% DOD. So in our example 5 x 17 Kwh = 85 Kwh

3. Find Panel Wattage. Determine worse case month Sun Hours. Say 5 Sun Hours. Panel Wattage = [1.5 x Daily Watt Hours / Sun Hours, or [1.5 x 17,000 wh] / 5 Sun Hours = 5100 Watts. You multiply by 1.5 to account for all system losses using MPPT Charge Controller. If you use PWM you multiply by 2 which would be STUPID.

4. Determine appropriate battery voltage based on Daily Watt Hours. You want to do this so you only have to use one charge controller. Largest charge controller out there is 100 amps like the Midnight Classic 150. In this example 48 volt battery is as low as you can go. So we select 48 volt battery.

5. Determine MPPT Minimum Charge Controller Size = Panel Wattage / Nominal Battery Voltage or 5100 watts / 48 volts = 106 amps. Pushing the limits of a Midnite Classic 150 but doable. It will clip at 96 amps.

6. Determine Battery AH Capacity = Total WH Capacity / Nominal Battery Voltage. In this example 85,000 wh / 48 volts = 1770 AH battery @ 48 volts

7. Determine Largest Inverter than can be used is simple, No larger than panel Wattage. You could use as small as 700 watts if the load is a 700 watt light bulb on 24 hours a day, or as large as 5000 watts.

[Sunking]

You are making this a lot harder than need be. Gotta go for now.

[SillySnakes]

Alright, I think I understand now. I read the thread Sunking pointed to.

So here is a table of my future panel output wattage as a function of time (thanks to PWatts/SAM simulation). The panel is a 315W STC panel. So in calculating how much total AH this panel will produce a day, I divide each Watts by 48V during each hour....and then sum up all the Amperage per hour to give me total AH of capacity generated at the end of the day, correct ? From this I can plan out how many panels/controllers I need to recharge my 1160AH bank properly per day
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[Sunking]

According to Trojan's website, they clearly state that the battery charging process has to be done at a higher than nominal voltage. For a 48V battery, the charging has to be set to 59.3V during Bulk phase and 64.8V during EQ. So that means that the MPPT Controller will pump out current at the 59.3V... no ? What am I missing here? Look: 1.png



At what point in time does the MPPT controller actually sets the 59.3V charging voltage ? Early on in the charging process or near completion ?

You are looking at a voltage Set Point. Again READ THIS so you understand how a battery charges.

Example if your 48 volt 1766 AH battery SOC were 45% would have an OCV of exactly 48 volts. Such a monster of a battery would have an Ri of 0.0006 Ohms. To make that battery go from 48 to 60 volts on a charger instantly would require [60 volts - 48 volts] / .0006 Ohms = 20,000 Amps. At 20,000 amps x 60 volts is 1,200,000 watts. Do you have 1.2 Mw solar panel with a 20,000 Amp MPPT Controller?

MAX MPPT OUTPUT CURRENT = PANEL WATTAGE / NOMINAL BATtERY VOLTAGE

A 48 volt nominal voltage = 48 volts.

Again the Voltage of a Charging Battery = OCV + [Charge Current x Ri}

Any battery charger is not a pure Voltage Source with unlimited current. They are a Current Source up to the point where the loadcurrent is equal to or less than the chargers current rating. You can certainly set the charger to 60 volts. That does not mean the output voltage is 60 volts. It is only at 60 volts when there is no current.

A Solar CC is different than a commercial AC charger. A 10 amp commercial AC charger provides 10 amps until the Voltage Set Point is reached. Connect a 12 volt battery to a 10 amp AC charger and the current is 10 amps with a starting voltage of 12.1 volts. 10 amps x 12.1 volts is 121 watts. It continues to charge at 10 amps until it nears the Voltage set point of say 15 volts. 10 amps x 15 volts is 150 watts, Power went up and is variable in an AC charger. Current is constant in the AC charger.

Not so with Solar. Power is limited. Say you have a 120 watt panel with a 10 amp CC. Connect it to a 12 volt battery with an OCV of 12 volt, current is 10 amps. 12 volts x 10 amps is 120 watts. Now the battery voltage starts to rise say 13 volts, and panel wattage is still 120 watts means the current is now 120 watts / 13 volts = 9.2 amps. At 14 volts is 8.6 amps. If the Voltage set Point is 14.2 volts, and the battery voltage is 14.2 volts is ZERO AMPS. The battery is saturated and fully charged.

[BackwoodsEE]

So for a 48volt battery using a 60A CC that will come to 2880watts. Now the CC may state you can exceed the calculated wattage by 10 % which may get you to 3200 watts but I doubt it will state it can handle 3600 watts. More than likely it will clip some of the wattage so it does not exceed the 60A rating. All that does is over heat the CC and reduce your true pv generating wattage.

I've watched my TS-MPPT-60 in action with a real-time voltage-current tracing device I designed and built. What the charge controller does to limit battery current is pretty slick, and does not dissipate heat anywhere downstream of the panels. It simply adjusts where it operates on the PV array's IV curve so that less power is drawn from the array.

For example, right now my toy 3-panel array is producing a mere 110-120W to float charge the battery and run a few isolated loads. The PV current is hovering around 98-99V, well above the maximum power point. If I turned on more load (I've done this many times with big incandescent lights while watching the real-time plot), it would slide the voltage down to the MPPT and the PV current would rise dramatically. Occasionally, I've also seen it move the PV voltage up, toward a MPPT that was higher where it got left the last time it reduced power draw.

It's provided me hours of free geek entertainment watching the current voltage and current point slide left/up and right/down along the IV curve as the charge controller adjusts its production to match the inverter's consumption on a float-charging battery. A good MPPT charge controller is a sophisticated device indeed.

[SunEagle]

According to Trojan's website, they clearly state that the battery charging process has to be done at a higher than nominal voltage. For a 48V battery, the charging has to be done even up to 59.3V during Bulk phase and 64.8V during EQ. So that means that the MPPT Controller will pump out current at the 59.3V... no ? What am I missing here? If I want to calculate the amount of current coming from the MPPT at any instant of time it will be: Array Wattage/59.3V. Look:
1.png

Technically you are correct. Although the real current value will be determine by the CC based on the voltage it is providing the battery.

I would go back and check what the manufacturer states is the higher input wattage input to that CC based on the battery voltage (12, 24 or 48). You should be able to get a quick wattage rating by multiplying the battery system voltage by the current rating.

So for a 48volt battery using a 60A CC that will come to 2880watts. Now the CC may state you can exceed the calculated wattage by 10 % which may get you to 3200 watts but I doubt it will state it can handle 3600 watts. More than likely it will clip some of the wattage so it does not exceed the 60A rating. All that does is over heat the CC and reduce your true pv generating wattage.

[SillySnakes]

According to Trojan's website, they clearly state that the battery charging process has to be done at a higher than nominal voltage. For a 48V battery, the charging has to be set to 59.3V during Bulk phase and 64.8V during EQ. So that means that the MPPT Controller will pump out current at the 59.3V... no ? What am I missing here? Look: 1.png
At what point in time does the MPPT controller actually sets the 59.3V charging voltage ? Early on in the charging process or near completion ?

[bcroe]

As far as I'm concerned, Ohms law has 3 terms which all function together. Bruce Roe

[Sunking]

Sources of electricity do not push or pump electricity into anything, Loads (light bulb, charging battery, stereo, etc.) "DRAW", or pull electricity from the source based on their needs, which is controlled by their resistance or impedance.

No Sir that is not true. Voltage is pushing Current into Resistance. With a battery Ohm's Law still applies, but you have to account for the battery Open Circuit Voltage aka OCV. An example I like to use because the math is simple is a 12 volt 100 AH battery with an Internal Resistance (Ri) of .01 Ohm.

Voltage of a Charging Battery = OCV + (Charge Current x Ri)
Voltage of a Discharging Battery = OCV - (Discharge Current x Ri)

Open Circuit Voltage of 12 volt battery at 50% SOC = 12.1 volts. If we charge at 10 amps the voltage is 12.2 volts. If we discharge at 10 amps is 12.0 volts.

Voltage is PRESSURE, the driving force called EMF and it certainly pushes. Current is just the result of the resistance the Voltage is pushing against.

[LETitROLL]

The max current that the solar charge controller will pump into your battery bank at any instant in time is calculated by taking the total cumulative wattage of all the panels connected to that controller in that instant of time and dividing by the charging voltage for the battery bank. Might as well take into account the 90% MPPT current pumping efficiency.

Sources of electricity do not push or pump electricity into anything, Loads (light bulb, charging battery, stereo, etc.) "DRAW", or pull electricity from the source based on their needs, which is controlled by their resistance or impedance.

[Sunking]

Only one minor little problem You do not know what you are talking about. The Voltage of a Charging battery = OCV + (Charge Current x Ri)

Where OCV = Open Circuit Voltage
Ri = Battery Internal Resistance

A 48 volt battery OCV at 50% SOC is 48.4 volts. The Internal Resistance (Ri) of a 1700 AH 48 volt battery is roughly .0006 Ohms. So with 300 amps of charge current the voltage is:

48.4 volts x (300 Amps x .0005) = 48.55 volts.

MPPT Output Current = Panel Wattage / Nominal Battery Voltage.

The nominal voltage of a 48 volt battery is really hard to figure out. It takes 16 years of school to learn it is 48 volts. As the battery voltage rises while charging, charge current tapers down. When Battery Voltage = Charge Voltage, Charge Current = 0 Amps.

So if your battery is 48 volts with a 14,400 watt panel, and the battery OCV is 48 volts or 45% SOC charge current will be 14,400 watts / 48 volts = 300 Amps. As the battery charrges and voltage goes up to:

50 volts; 14,400 / 50 = 288 amps
51 volts, 282 amps
52 volts, 276 amps
60 volts, 240 amps.

If your Controller is set for 60 volts, and the battery voltage is fully charged at 60 volts = 0 Amps. It is clear you do not understand how a battery charges. Try reading this.

[SillySnakes]

Where are you coming up with 60 volts? Your thread title is 48 volt battery.

14,400 watts / 48 volts = 300 Amps.

A 48V nominal battery needs to be charged at 57-60V to force the current into it.
A 26V nominal battery needs to be charged at 28-30V to force the current into it
A 12V nominal battery needs to be charged at 13-14V to force the current into it.

The MidNite Classics actually charge a 48V at 57.5V

Any battery needs to be charged slightly higher than its nominal voltage, otherwise current will go the opposite direction. For example, it would not make sense to connect a 12V solar panel to a 26V battery.

The max current that the solar charge controller will pump into your battery bank at any instant in time is calculated by taking the total cumulative wattage of all the panels connected to that controller in that instant of time and dividing by the charging voltage for the battery bank. Might as well take into account the 90% MPPT current pumping efficiency.

So if I will have a 3600W total power being produced at 9:36:15AM and that is connected into my MidNite Classic 150, the current flowing at that instant of time from the controller and into the battery bank will be:

3600W/57.5V=62.6A --> 90% 0.9*62.6A = 56.34A

[Sunking]

4 x 15 = 60 panels @ 240W = 14400W


14400W/60V = 240A -> 90% Eff -> 216A of charging current total

Where are you coming up with 60 volts? Your thread title is 48 volt battery.

14,400 watts / 48 volts = 300 Amps.

[NEOH]

Will 216A of charging be enough to put back 1160AH of consumed energy back into the battery bank during the 6 hour sun window ?

Yes, it is possible.

[SillySnakes]

Thank you all for the reply, but I think some important info stated in my first post went un-noticed:


I clearly stated and proved that ONE MidNite Classic 150 with 15x 240W panels (@NOCT) will give me about 3600W, which is 60A of charging current.


I then asked the questions 'Does this sound right ? I would need about 4 MidNite 150 Classics, right connected parallel into the battery bank ? " Implying that YES, I am planning on using more than 15 panels (more than 3600W).


4 x 15 = 60 panels @ 240W = 14400W


14400W/60V = 240A -> 90% Eff -> 216A of charging current total



Will 216A of charging be enough to put ack 1160AH of consumed energy back into the battery bank during the 6 hour sun window ?


Thank you very much. Appreciate the patience...trying to learn as much as possible