Forum Discussion
412 Replies
BFL13 wrote:
jrnymn7 wrote:
O.K., thanks. I'll have to do some reading up on PWM controllers, to see if they're anything more than simply a high frequency "on/off" controller, with no way of adjusting for changes in panel voltage.
They don't do anything to panel voltage. There is no buck converter. Panel voltage is battery voltage plus a bit for line loss. What you want to study is your panel's IV curves. All the answers are right there! Go in at the Vbat you are at and that is your "expected amps" at STC. (Isc of the moment)
How do you know you are at STC? Simple. Disconnect panel and measure across its terminals with an ammeter. That is the Isc of the moment. Could be anything up to rated Isc or above.
On a sunny day with the sun high in summer, with the panel aimed at the sun, you should get at least rated Isc. Next check is what are the batteries getting? Re-connect and now you should see the same amps to the battery on your Trimetric or whatever.
You should be getting close to the Isc of the moment or else you have a wiring or connection problem somewhere.
12v PWM is way too easy! None of that anxiety-prone MPPT complicated stuff to worry about whether you are getting your money's worth of amps. :)
lol, I hear ya.
I did come across an article though, by morningstar, about their lastest and greatest new technology...
pwm!
I'll post it if anyone wants to read it.- That's the description to search for the maximum power point. In order to do a complete search, the controller needs to do a sweep. There may be several peaks and valleys in the I-V curve. The first peak that the controller finds may not be the larges peak (meaning it's not at the maximum power point). Hence the sweep.
However, this has no relevance when the controller is in absorption mode. The controller doesn't care about the maximum power point. It outputs a constant voltage.brulaz wrote:
jrnymn7 wrote:
...
So, is the "mppt-capable" controller still doing something the pwm cannot do? IOW, Can the pwm raise or lower panel voltage to accommodate for variances in lighting, or just for variances in Vbatt?
dunno about pwm controllers.
But JiminDenver's quote about MPPT controllers pretty much agrees with Rogue's manual. Rogue talks about occasionally doing a "sweep" of the panels (guess that means changing the voltage and seeing what happens), especially when changing modes. And it the frequency of "sweeps" can be adjusted.
But it also "dynamically" checks panel output as well without a sweep. Much of this is probably proprietary, but my guess is that in MPPT mode is constantly trying adjacent voltages to see if the current output increases. jrnymn7 wrote:
O.K., thanks. I'll have to do some reading up on PWM controllers, to see if they're anything more than simply a high frequency "on/off" controller, with no way of adjusting for changes in panel voltage.
They don't do anything to panel voltage. There is no buck converter. Panel voltage is battery voltage plus a bit for line loss. What you want to study is your panel's IV curves. All the answers are right there! Go in at the Vbat you are at and that is your "expected amps" at STC. (Isc of the moment)
How do you know you are at STC? Simple. Disconnect panel and measure across its terminals with an ammeter. That is the Isc of the moment. Could be anything up to rated Isc or above.
On a sunny day with the sun high in summer, with the panel aimed at the sun, you should get at least rated Isc. Next check is what are the batteries getting? Re-connect and now you should see the same amps to the battery on your Trimetric or whatever.
You should be getting close to the Isc of the moment or else you have a wiring or connection problem somewhere.
12v PWM is way too easy! None of that anxiety-prone MPPT complicated stuff to worry about whether you are getting your money's worth of amps. :)- Hi jrnymn,
My (limited) understanding is that Pwm controllers operate at V-bat. - O.K., thanks. I'll have to do some reading up on PWM controllers, to see if they're anything more than simply a high frequency "on/off" controller, with no way of adjusting for changes in panel voltage.
jrnymn7 wrote:
...
So, is the "mppt-capable" controller still doing something the pwm cannot do? IOW, Can the pwm raise or lower panel voltage to accommodate for variances in lighting, or just for variances in Vbatt?
dunno about pwm controllers.
But JiminDenver's quote about MPPT controllers pretty much agrees with Rogue's manual. Rogue talks about occasionally doing a "sweep" of the panels (guess that means changing the voltage and seeing what happens), especially when changing modes. And it the frequency of "sweeps" can be adjusted.
But it also "dynamically" checks panel output as well without a sweep. Much of this is probably proprietary, but my guess is that in MPPT mode is constantly trying adjacent voltages to see if the current output increases.- PPT doesn't exist. I didn't see it in your link. They did say the power point tracker is a dc/dc converter. In other words it's pwm control. Virtually all dc/dc converters are pulse width modulated.
JiminDenver wrote:
Salvo wrote:
There's no such thing!
When the charger controller is not working in mppt mode, it's working as a voltage regulator (constant voltage). That means pwm control.jrnymn7 wrote:
"Not sure what PPT is?"
I think maybe it's this...
"the controller is not looking for maximum power, but only the power needed to supply the demand."
Just because one person doesn't know or understand something doesn't mean it doesn't exist. From Arizona wind and solar. click
Excerpt
How a Maximum Power Point Tracker Works:
The Power point tracker is a high frequency DC to DC converter. They take the DC input from the solar panels, change it to high frequency AC, and convert it back down to a different DC voltage and current to exactly match the panels to the batteries. Salvo wrote:
There's no such thing!
When the charger controller is not working in mppt mode, it's working as a voltage regulator (constant voltage). That means pwm control.jrnymn7 wrote:
"Not sure what PPT is?"
I think maybe it's this...
"the controller is not looking for maximum power, but only the power needed to supply the demand."
Just because one person doesn't know or understand something doesn't mean it doesn't exist. From Arizona wind and solar. click
Excerpt
How a Maximum Power Point Tracker Works:
The Power point tracker is a high frequency DC to DC converter. They take the DC input from the solar panels, change it to high frequency AC, and convert it back down to a different DC voltage and current to exactly match the panels to the batteries. MPPT's operate at very high audio frequencies, usually in the 20-80 kHz range. The advantage of high frequency circuits is that they can be designed with very high efficiency transformers and small components. The design of high frequency circuits can be very tricky because the problems with portions of the circuit "broadcasting" just like a radio transmitter and causing radio and TV interference. Noise isolation and suppression becomes very important.
There are a few non-digital (that is, linear) MPPT's charge controls around. These are much easier and cheaper to build and design than the digital ones. They do improve efficiency somewhat, but overall the efficiency can vary a lot - and we have seen a few lose their "tracking point" and actually get worse. That can happen occasionally if a cloud passed over the panel - the linear circuit searches for the next best point, but then gets too far out on the deep end to find it again when the sun comes out. Thankfully, not many of these around any more.
The power point tracker (and all DC to DC converters) operates by taking the DC input current, changing it to AC, running through a transformer (usually a toroid, a doughnut looking transformer), and then rectifying it back to DC, followed by the output regulator. In most DC to DC converters, this is strictly an electronic process - no real smarts are involved except for some regulation of the output voltage. Charge controllers for solar panels need a lot more smarts as light and temperature conditions vary continuously all day long, and battery voltage changes.
Smart power trackers
All recent models of digital MPPT controllers available are microprocessor controlled. They know when to adjust the output that it is being sent to the battery, and they actually shut down for a few microseconds and "look" at the solar panel and battery and make any needed adjustments. Although not really new (the Australian company AERL had some as early as 1985), it has been only recently that electronic microprocessors have become cheap enough to be cost effective in smaller systems (less than 1 KW of panel). MPPT charge controls are now manufactured by several companies, such as Outback Power, Xantrex XW-SCC, Blue Sky Energy, Apollo Solar, Midnite Solar, Morningstar and a few others.- "That voltage required by the solar panels for a certain power output varies depending upon light conditions. And so the voltage will vary depending upon light conditions."
So, is the "mppt-capable" controller still doing something the pwm cannot do? IOW, Can the pwm raise or lower panel voltage to accommodate for variances in lighting, or just for variances in Vbatt? jrnymn7 wrote:
So, it's not "looking" for anything at all, in other words, there simply is no tracking going on at that point?
On the battery side it's maintaining a constant voltage by providing the current needed by the battery and any loads.
On the solar side it applies the voltage needed by the panels to get the power required on the battery side (and any internal losses). That voltage required by the solar panels for a certain power output varies depending upon light conditions. And so the voltage will vary depending upon light conditions. Is that "tracking"?
It seems to me that MPPT is only different in that the voltage gets you the max power possible. Not just that needed for maintaining a constant voltage on the battery side. (and of course there's the algorithm for determining that MPP as well).
