Help with 48V AGM battery bank

Re: Help with 48V AGM battery bank

In your drawing, you say 2v @ 60 AH battery cells... I assume you intended to type 600 AH?

You should also have a fuse/breaker for the + cable to the Inverter.

All fuses/breakers should be installed as close as possible to the current source... In this case, close to the battery bank.

And high current 48 volt cables should be short and heavy between Charge Controller to Battery bank (somewhere around 0.40 to 0.20 maximum voltage drop (for optimum battery charging/voltage sense by charge controller). If you use the MorningStar TS line of charge controllers, they include Remote Battery Voltage Sense Connections. Connecting those up will make the Battery to Charge controller less sensitive to excessive voltage drop.

And you should review the voltage drop for the Battery to Inverter connection. Too long of battery to inverter leads (and/or too small of diameter) can cause the inverter to shutdown (under-voltage) with heavy loads/starting surge current.

Also, I would suggest a Battery Monitor so you can watch the state of charge of the battery bank (AGM batteries--you cannot measure specific gravity of the electrolyte with a hydrometer). People drawing too much energy from a battery bank and never getting the bank back to full charge is a common form of "battery abuse" and will shorten the life of a battery bank to a year or even months (in severe cases).

lastly, get the Remote Battery Temperature Sensor for both charge controllers. This too will help insure the batteries are quickly, and safely charged (cold batteries require higher charging voltage; hot batteries require a lower charging voltage).

Off-Grid inverters need the battery bank to store energy for use.

However, during the day, your Inverter power for the AC loads will come directly from the solar panels--so you will avoid battery losses during sunny days for those loads (i.e., AGM batteries are around 90-98% energy efficient).

Many people have setup manual or automatic monitoring of the battery bank... For example, when the charge controllers go to "float charging" (drop voltage a bit and no longer are pumping current to the batteries--i.e., batteries are full), they then turn on optional loads (water pumping to cistern, irrigation, etc.).

-Bill

Re: Help with 48V AGM battery bank

I would suggest that you connect the fusing/breakers like this (normally, you would not want one breaker opening to take out everything--solar array+inverter+other loads):

[FONT=Fixedsys]Batt+ ----350A fuse------- 250A brkr ------ inverter
                      |
                      |__63 A breaker __ charge controller
                      |
                      |__63 A breaker __ charge controller
[/FONT]

I do not know European breakers and wiring--but in North America, wires and circuit breakers are rated to carry 80% of their "rated load".

If you have a 100 amp load (or charging current, you need to make the circuit breaker 1/0.80 or 1.25x the continuous current:

• 100 amps * 1.25 Safety Factor = 125 amp fuse/breaker/wire minimum rating.

If you run a 100 amp load on a 100 amp breaker/fuse, the over current protective device is designed to eventually open/trip (minutes to hours).

Also, make sure you use fuses/breakers rated for 60 VDC minimum and 10,000 AIC (amp interrupt current)--or whatever the standard for your region would be.

DC current is much different than AC current when used for switches/circuit breakers. DC Current tends to sustain arcing (sparks) across the contacts much better than AC current. So DC switches/breaker are usually much larger than the same AC rated device.

60 VDC, high interrupt current circuit breakers are not easy (or inexpensive) to find. Make sure they are rated (voltage/current) for your DC application.

Also, the Battery Monitor Shunt needs to be connected:

[FONT=Fixedsys]
                  |--------To Battery Monitor
                  |    |---To Battery Monitor
                  |    |        
Battery Minus====BM Shunt======Inverter Minus
                            |
                            |= charge controller Minus
                            |
                            |= charge controller Minus
[/FONT]

You want all battery current flowing through the shunt so you can keep track of all the current flow (charging / discharging) to monitor the battery bank state of charge.

You might want to look for wiring diagrams from your vendors... I know that Outback power has a nice library of wiring diagrams. You should probably look through them. They have many samples and will show much more detail (for simple and complex installations).

The maximum temperature rise (panel mounted near roof with little air flow) is typically assumed to be 35C rise.

So, 40C air temperature + 35C rise = 75C panel/cell temperature.

Ideally, your Vmp-array should be around 70 VDC minimum. However, with MPPT charge controllers that have ~150 VDC maximum input voltage (like the TriStar MPPT), you should be aiming for a Vmp-array of around 100 VDC maximum.

If you installation is in an area that does not get very cold (like an island or similar), you might be able to go above 100 VDC Vmp-array.

There are two conditions you are looking to meet. 1) is Vmp-hot (minimum panel voltage when array is hot to charge the battery bank; and 2) Voc-cold (maximum solar array voltage when array is very cold and no current flow).

What is the Brand/Model (Vmp/Voc) rating of your solar panels you are planning on using?

You might try sending a PM or Email to user "peterako"==He is from Greece and has a solar and wind power system (he has not been here since April of 2011, so he might not read this thread).

Your English is pretty good and very readable/understandable. Δεν θα θέλατε να διαβάσουν ελληνικά μου. (Google Translate).

Stephendv is out of Spain, and Russ is out of Turkey--And we have some other members from Europe that can probably give you some suggestions on sources for the DC parts if you have trouble locating supplies locally.

-Bill