mppt vs pwm

Bedlam wrote:
Any suggestions on a budget MPPT controller that can handle 600W peak input? I'm considering four 24VDC panels and also looking at whether to run two series pairs in parallel or all four in parallel which would require heavier or redundant wiring to minimize loss.

From what others have shared on the forum, it seems series/parallel would be the way to go. You need a 60a mppt controller, to allow 20% extra over and above the output to the batteries.

Those stick on panels take up a lot of real estate per watt. And if they are damaged or fail, it may be a difficult task removing them.

I was thinking about ganging two of these controllers together (one per pair of panels) for about $205 total cost but that may not suffice:

http://www.eco-worthy.com/catalog/mppt-solar-charge-controller-free-shipping-p-182.html

"BTW who has 150 watt 24 volt panels?"

SMK, That was my first thought, but apparently there are quite a few to choose from.

A 45a controller seems a little on the low side?

600w in = 600w out, 600w / 13v = 46a output + 20% = 55a

(37.5a output + 20% = 45a)

See the link bellow for information. They are peel and stick 136W 24V panels.

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28165028.cfm

I will check out that 45A unit you referenced - Thanks.

Bedlam wrote:
Any suggestions on a budget MPPT controller that can handle 600W peak input? I'm considering four 24VDC panels and also looking at whether to run two series pairs in parallel or all four in parallel which would require heavier or redundant wiring to minimize loss.

Morningstar TS-MPPT-45 will serve you well.
Skip the front display accessory to save cost.

BTW who has 150 watt 24 volt panels?

Any suggestions on a budget MPPT controller that can handle 600W peak input? I'm considering four 24VDC panels and also looking at whether to run two series pairs in parallel or all four in parallel which would require heavier or redundant wiring to minimize loss.

I thought there was "Shunt" vs "Series" for "PWMs" where Series means doing Absorption with constant voltage and tapering amps. (like the LandStar eg)

Now it seems "PWM" came in after "Shunt" so "Shunt" is not PWM. So what do you call it to distinguish it from "MPPT"? But MPPT came in later on too. (After PWM -Series?) And once there was PWM you get PWM-Shunts that have FET switching? Gads!

Now we seem to call any controller with no buck converter in it, "PWM" and any controller with one, "MPPT" since it seems you always get the MPPT included when you get the buck converter.

So you can use the PWM Solar30 (and other 12/24 ones) with your 24v array if you also wire your 12v batts to be 24v. But you can use your MPPT 12/24 controller with 12 or 24v array and leave the batts 12v

Yes, Morningstar's algorithm was based on addressing two main issues... pulses per day and Vrr (voltage regulated reconnect). But they claim their's to be "real" pwm, whatever that means?

They also compared their pwm to the newest chargers on the market, which I have to presume is referring to switching technology, as opposed to linear? If they call it "series", I'm not sure what that means?

How far up in SOC you get is just to do with the array size, battery bank size, how far down to start with and how long the daylight is and how much you use during the day while trying to recharge at the same time. Can't see what type of controller you have matters.

The little shunt type seem like they would be good for float charging. Get the batts to 14.3v, quit, wait till the batts get back to 13.2 and goose them back up to 14.3 again. Plus the batts slide at night. Must make an average float voltage somewhere in the 13s.

"Interrupted" charging above 80% SOC might allow the batts to cool a bit between shots so more of the recharge AH goes into SOC and less into heat? Mex might have something on that. ( I don't!)

Edit: I read that Morningstar link. I think I caught that PWM and "Series" are not the same? Series seems to mean the controller spends less time on as SOC gets near to full. The ASC did that too but only claimed that was Low Frequency PWM. It did have FETs in it, so maybe Morningstar was talking about them with "others" just fiddling with FETs and not doing it as well as their own algorithm PWM does?

Obviously the old shunt type spends a lot of time not charging while the battery drifts back down to the low set point, so much of the day would be "wasted" That seems to be what they really mean by low "average" SOC, longer time at less than full means more sulfated etc. ( A float charger would be ok with that keeping the already full batt above 12.7 by going between 13.2 and 14.3)

So even some pwm's have over current protection. Nice.

That raises the question, though, how does the pwm clip amps? I'm guessing thru the same sort of modulation it does during abs? In that case, pwm does sometimes happen during bulk?

BFL, that was the whole debate, it seems. If the "reconnect voltage", or "low set point" was too low, that would decrease the rate of frequency of on/off. So some early (low frequency) pwm's spent too much time in 'off' and were unsuccessful at keeping Vbatt up, which is necessary for proper finish charging,(not to mention the lack of current going to the batteries). But apparently, the most important factors were number of pulses per day and the reconnect voltage. The promotion by Morningstar made claims that these type would only get the batteries up to 60% soc in a day... clearly a poorly calibrated controller, but perhaps not representative of all such type controllers, as they are still in use today.

With your Landstar, perhaps you could not see the voltage going up and down because it would be doing so at a rather high frequency... say 300x/sec.

http://pvdepot.com/media/pwm-solar-charge-controllers.pdf