Even if you have a more than sufficient solar array to charge your battery bank, there are times when you need an alternative method of charging.
A two or three -day storm with heavy clouds will drain a battery bank. Some form of damage, or a panel update, may render your array inoperable for a day or two.
Whatever the case, there are a few procedures you can use to charge your battery bank without your array.
Here are some of the key points we’ll be looking at;
- What details you need to know about your battery
- How to charge your battery manually
- Using an inverter to charge your battery
- Stand-alone charger to get you going
Let’s take a look at the solutions to fix your problem – we’ve got a few.
Solar Battery Bank Specifics Before Charging
Before doing any work on a battery bank, you must know a few things for certain. Being wrong about any of these could cause your charging efforts to fail, or possibly even ruin your batteries.
If you are unsure about these items ask the person who installed the system, or you can do some testing to confirm the information.
Solar power systems are one of three Direct Current (DC) voltages: 12, 24, or 48. Most RV or small cabin systems are 12 or 24 DC volts. Most larger, whole-house systems are 24 or 48 DC volts.
These are only general guidelines, not rules. Any system can be any of these voltages. Be sure you KNOW your voltage.
Attaching a 12-volt charger to a 48-volt system will do nothing. Connecting a 48-volt charger to a 12 -volt system will destroy the batteries.
Polarity and Connections
Solar power battery banks are typically comprised of 6-volt or 12-volt batteries. Occasionally, 2-volt batteries are used. Batteries linked in series (+ to – to + to -) will increase voltage.
Four 6 volt batteries in series will total 24 volts. You must know the connection pattern to determine the Positive (+) and Negative (-) terminus of the battery bank and the bank voltage.
Usually, the inverter and/or charger will be connected at these points. Again, you must confirm this information.
Amp Hour Capacity
Every battery bank has an amp hour (Ah) rating. This number indicates the number of amps the bank can provide for an hour.
Batteries linked in parallel increase the Ah capacity of the bank. Batteries linked in parallel ( + to + to + and – to – to – ) increased the amp Ah capacity.
The voltage does not change. Two 12-volt, 100 Ah batteries in parallel totals a 12 volt, 200 Ah battery bank. You need to know this value to determine the charging rate for the battery bank.
The charge rate should be limited to 10 % of the Ah capacity of the battery bank. For example, a 400 Ah bank should be charged at no more than 40 amps.
Refer to the battery manufacturer for specific charge rates of your batteries.
What You Need For Manual Charging
Once you know what the voltage and amp hour rating of your battery bank is, you need to determine what tools you need to charge. There are four basic charging configurations that can be applied to a solar battery bank. There is a fifth scenario that we will look at only briefly as it is not a very probable solution.
- Utility Line Power to Inverter/Charger
- Utility Line Power to Stand Alone Charger
- Generator Power to Inverter/Charger
- Generator Power to Stand Alone Charger
- DC Generator with Charge Controller
Utility Line Power Through a Inverter/Charger
Many larger, whole-house type inverters are actually Inverter/Chargers. These units have the capability to charge a battery bank by rectifying AC current to DC.
When properly configured, such a unit will supply the home with AC current while charging the battery bank. If the AC supply is sufficient, the battery bank will charge at a full rate.
When the batteries are full, the Charger will turn off and return the unit to Inverter mode. To determine if your inverter is also a charger, look at the manual if it is available.
If the manual is not available, look at the main power bus of the unit. An Inverter Only will have DC-IN and AC-OUT terminals.
An Inverter/Charger will also have AC-IN and DC-OUT terminals. Line service from the grid can be wired to the AC terminals to power the DC charging side of the unit.
Generator Power Through a Inverter Charger
In this scenario, a gasoline-powered generator takes the place of utility line power. The connections and operation of the Inverter/Charger will be the same.
The only difference is that you will need to start up the generator before turning on the Charge function of the Inverter/Charger.
The quality of the generator is a factor in this scenario. Inexpensive portable generators tend to have erratic fluctuations in their power output. This “noise” in the signal makes it inefficient.
In some extreme cases, the charger can not use the AC current produced to create DC power. If you pursue this course, be sure to purchase a quality generator that produces sufficient clean power to supply your system.
Utility Line Power Through a Stand-Alone Battery Charger
If your inverter is not also a charger, this is the next simplest path to charging a battery bank. You must purchase a charger of the correct DC voltage.
The charger voltage must match your system voltage (12, 24, 48).
The charger must also have a charge rate appropriate to your battery bank’s Ah capacity.
For example: If your battery bank is 24 Volts DC with a 400 Ah capacity, you will need a 24-volt charger with a charging rate of 40 amps or less.
A charge rate below 40 amps is acceptable. It will just take a little longer to charge your bank.
It can be tricky to find a charger with the exact amp rating. Most stand-alone chargers have rate settings of 2, 5, and 25.
Generator Power Through a Stand-Alone Battery Charger
Again, this scenario simply replaces Utility Line power with a generator. The same guidelines apply.
On the plus side, stand-alone chargers tend to be a little less temperamental about AC-IN current than Inverter/Chargers are. Any good quality generator of sufficient power will be adequate.
Using A Stand-Alone Battery Charger
It is best to charge the battery bank when not in use. Fluctuations in battery voltage will confuse a stand-alone charger and it may not operate correctly.
It would be wise to turn off your inverter for this process
When using the stand-alone charger, you must manually hook the charger to the battery bank. You will first need to find the Positive and Negative terminals of the battery bank as we discussed earlier.
Follow the manufacturer’s guidelines to set the unit appropriately and connect to the terminals as instructed.
Every unit is different. Do not assume the sequence is the same as chargers you may have used in the past.
DC Generator With Charge Controller
The use of a DC generator is a viable option. However, the DC circuit on a typical consumer generator is almost always 12 volts, has low current, and is unregulated.
There are full-power DC generators available. They tend to be quite expensive and fairly elusive. If you were to come by a DC generator of the appropriate voltage, it could be used to charge a battery bank.
It would require a charge controller similar to the one that charges your batteries now. I would not suggest using the controller from your array for this purpose.
It would be best to find a controller intended for mechanically driven power sources.
Such a device would be quite similar to your array controller but would have an input structure intended for a mechanically generated power supply.
Solar power is a tool we use to get off the grid, save fuel, and cut down on pollution. However, solar power is not perfect.
Sometimes we may need a mechanical backup to help it out. We should not fret over reverting to gas or the grid for a few hours once in a while. Good Luck. Be safe. Have fun.