PDA

View Full Version : 3-stage PWM vs 4-stage MPPT?



Alex9
06-11-2012, 05:20 AM
If I understand correctly, a pwm charge controller uses 3 stages bulk, float and absorb. The TriStar TS-MPPT-45 cc says it uses a 4 stage method or bulk, absorption, float and equalize. What is the difference between the pwm and mppt versions of what seems to be the same thing?
I have a basic understanding that with pwm what goes in goes out more or less, and mppt tries to get the most out of your panels with dc to dc conversion.
ex. Say you're getting 18v and 7amps off of a panel on a small system and the cc goes into float and then it only puts say 1amp into the battery bank during that whole stage, does the 4-stage mppt waste those amps/volts in float mode too or does it convert it to something that the battery bank can handle? Is float mode always wasteful?

epsgunner
06-11-2012, 07:14 AM
Most controllers are 3 stage.. the 4th (Equalize) is done sometimes MONTHLY and MANUALLY, its not part of the normal daily process....

My Morningstar TS-45 (PWM) has the same 3 and then equalize is the 'service' to equalize the battery/bank.

Hope that helps explain some..

inetdog
06-11-2012, 07:49 AM
I have a basic understanding that with pwm what goes in goes out more or less, and mppt tries to get the most out of your panels with dc to dc conversion.
ex. Say you're getting 18v and 7amps off of a panel on a small system and the cc goes into float and then it only puts say 1amp into the battery bank during that whole stage, does the 4-stage mppt waste those amps/volts in float mode too or does it convert it to something that the battery bank can handle? Is float mode always wasteful?

Either a PWM or an MPPT controller will not deliver more energy to the battery during Float than it takes to keep the battery at the nominal float voltage. This should basically be enough to assure that self-discharge of the battery is accounted for, and a little bit more. There is just no way to put more energy into the batteries at this point.

Either type controller will not pull the additional power from the panels. So it is not being dissipated anywhere, it is just not being generated. It is the solar energy hitting the panel that is being "wasted." If the controller has a set of "load" terminals, it can continue to take up to maximum power from the PV and send it to whatever is connected to those terminals (at the nominal battery voltage.) You could use this for non-time-critical loads such a pumping water into a storage tank or some other creative use for the extra solar energy (raising a heavy weight that can be used to run a giant grandfather clock, for example.)
:-)

Alex9
06-11-2012, 01:56 PM
Either a PWM or an MPPT controller will not deliver more energy to the battery during Float than it takes to keep the battery at the nominal float voltage. This should basically be enough to assure that self-discharge of the battery is accounted for, and a little bit more. There is just no way to put more energy into the batteries at this point.
:-)

I see. Thanks for clarifying that. So mppt vs pwm is all in the bulk stage then. Thanks.