Pwm vs mppt amps

Might describe your system with battery type and size.

If the batteries are capable of only absorbing 16 amps that's all you will get. Are they older batteries?

The general idea is that if you have 17.5 volts coming in up to 18.9 volts, that the wattage above the voltage that the batteries are charging at the amperage they are providing will be converted into amperage at the lower voltage. Clear as mud?

So if you are in bulk near absorb or close to absorb voltage say 14.8 volts, at 4 amps and your panels are providing 17.5 volts, you would gain about  1.7 volts x 4 amps or about 7 watts per panel, or 28 watts for the 4 panels. This pretty much only applies in bulk, once you hit absorb the batteries start accepting less current. 28 watts is about 10% of the 300 watts you should expect from your panels.

If they panels can produce 5 amps then a few more watts, but apparently your battery is accepting a maximum of 16 amps. Most MPPT CC work at a very high rate of return around 95%. You would also want to reconfigure your array so that you had strings of 2 panels. Most/All MPPT type controllers need a bit of head space above the charging voltage to operate properly.

If your charge controller says you are getting 21.89 amps from the array when you have a load, but only 16 amps when you are just charging, then it's not a problem of available current/amps. The batteries are only accepting 16 amps....

Do you have a single unit charger/inverter? perhaps it's a mis-understanding of the values?

mountainman said:

Don't understand the 230 watts 14.4 volts 16 amps peak charging. 

It's the way PWM - Pulse Width Modified, charge controllers work, the voltage must be above the charging voltage for the panels to begin with. Then the charge controller "Pulses the current to the system and limits the voltage by switching on and off many times a second to limit the voltage. 

Before MPPT type charge controllers, panels were made in voltage ranges to charge batteries. The higher STC VMP is for several reasons, one of the major reasons is the loss of voltage in Normal Operation. I couldn't find a panel in the 100 watt range that had published NOCT values, but here's specs of a Astroenergy panel;

You can see that the voltage drops from a VMP of 35.77 to 32.67 or about 9%, this is at the panel. Note the over all drop of wattage from 305 watt to 213 watts, about 70% of the rated power vs the Normal operating power. 

Just want to give you a feel, 21 watts is "sort-of" right, but the loss at the panel has already been taken into account using the PWM controller. 

In addition, the times when a MPPT type really make a difference is during bulk charging and over cast days. In normal operation, you may well see zero benefit from MPPT type charge controller. In general systems are designed to discharge only the top 20% during a normal daily cycle. Well the top 20% barely gets you out of bulk. Once a system reach absorb or shortly after the batteries limit the amount of charge they can take in and an array if designed to charge at 13% of the battery capacity will not rely on the 'extra' available since the batteries are already limiting the current.

Hard concept to explain. If you have the capacity an additional panel might be cheaper than a MPPT charge controller, though keeping an even number of panels would be advised as if/when you switch you will want to run strings of panels so you can provide about 30% more voltage than the charging voltage so a MPPT charge controller can work properly.

Photowhit said:

Before MPPT type charge controllers, panels were made in voltage ranges to charge batteries. The higher STC VMP is for several reasons, one of the major reasons is the loss of voltage in Normal Operation. I couldn't find a panel in the 100 watt range that had published NOCT values, but here's specs of a Astroenergy panel;

You can see that the voltage drops from a VMP of 35.77 to 32.67 or about 9%, this is at the panel. Note the over all drop of wattage from 305 watt to 213 watts, about 70% of the rated power vs the Normal operating power. 




Here's a 120 watt STC rated panel showing a mere 87 watts at NOCT level output.