Pulse Width Modulation Battery Charging vs Consistent Current Charging
To pulse or not to pulse, that, is the question.
PWM or Pulse Width Modulation is one of the newer battery charging algorithms in charge controllers, battery chargers, and inverters. For ease sake, a PWM charge regimen includes on and off cycles in quick repetition. This repetition creates a frequency of EMI that can be picked up by some electronics. This page looks at the pros and cons of pulse charging versus constant current charging of batteries.
Why Pulse Charging is Good:
To achieve the highest efficiency possible, electrical power circuits transition from off to on in an extremely short time. By turning a circuit totally off you reduce the amount of power consumed by the device. So every time your charge controller needs to wait a second to get power to "Push" into the batteries, it should turn itself all the way off. By doing so, the machine saves a bit of energy, and increases it's efficiency.
Why Pulse Charging is Bad.
We know that a pulse involves a circuit being on, and off. On is max power, off is zero power, and this transition takes place in microseconds or nanoseconds. Internally, within the charge controller circuits must be designed in this manner to be efficient. Why? Solid state devices operate with the least energy loss when they're completely off. Electronic circuits also work best when fully energized and have good conductivity. As voltage rises, resistance falls, so a fully "energized" circuit is by far the most efficient. To waste time in the middle is also a waste, so the transition must be from one extreme to the other, without any middle ground, either ON, or OFF. Therefore, the transition from off to on is done in one step, from zero to max power to zero... over and over again.
Micro-processors (CPUs in computers and laptops chips in cars and cellphones), as well as radio wave signals (FM & AM), telecommunications signals (Cable & Cell phones), and communications circuits that receive the info (radios and televisions) all work on the same frequencies. When a device emits EMI, these circuits are either interfered with, or pick up the interference and show it as distortion in some way. Screens show snow, speakers buzz, computers crash, cell phones echo, and so on.
So when should I use PWM? and when should I avoid PWM?
Since PWM brings efficiency to the power generation table, (a.k.a. it is more efficient than constant current charging algorithms) you should try to use PWM in all installations. However, if the client is using very sensitive electronics, broadcasting, or similar types of activities, PWM should be avoided. This usually falls down to the installers discretion.
Not efficient enough for the client, expect a call.
Getting fuzz on the TV, expect a call.
So this is a judgement call, and should be left as a per install question. I typically turn on PWM when in doubt, and then if there is a problem with it, turn it off. The efficiency of a solar system is where the money is though so you want it on. Most clients use their power bill, or lack thereof, as the mark of success. PWM can help you achieve more power generation as you battle a bit less loss. On the other hand, if I can't use my computer, the power is worthless to me.
To pulse or not to pulse, that, is the question.