Looking for a 40 amp MPPT solar charge controller

So, anyways, back to the OP.

How do other MPPT controllers in the 40a range compare to the Tracer 4215BN?

BFL13 wrote:
I say keep poking at it on paper but don't buy the MPPT yet. There might be more to the PWM and 24v route yet to be discovered! Keep your powder dry and all that. :)

I don't see 24v in my future. High amperage voltage converters are very expensive, and I do not intend on changing inverters anytime soon. And I already have 12v panels, so...

MPPT won't be 'til next fall, anyway.

Niner said,

"Why would panel V be pulled down to 13V? With PWM, you are interested in Isc in amps, or 8.5 amps per panel. You assume the battery can take that full 17 amps. Sometimes it can, if below 85 to 90% state of charge."

I'm not assuming anything. I know for a fact that my 430Ah bank can accept over 30a at 90% soc, at 14.8Vabs. Moreover, in winter, and do to my work schedule and where I sometimes have to park, gen charging from 5-6:30am may not always be an option. So I may very well have to use solar on a fairly heavily depleted bank, from morning 'til evening, when I can then fire up the gennie. And, there will be loads running, all the while.

As per the pwm pulling panel voltage down to 13v, this would indeed happen if my bank got down to 12v. So, 13v and 16a for the pwm. The mppt, however, could produce as much as 20a in such a situation, thus making up for the continual loads (heat pump, fans, fridge, etc.)

To add two more panels, it would cost about $340can. The Tracer 3215BN will cost about $275can., so no savings to be had going with more panels.

Now that's funny! I didn't do any calculation. I just stated what's wrong with the one I was reading.

As for cherry picking, you throwing that back at me? Got your feelings hurt? Have you been waiting to use that phrase? I didn't make the 5% up. As you know it from a white paper where they calculated gains from 10% down to zero percent. The average is 5%. That's in line with calculations and measurements I have taken.

As for the link, surface charge also kills mppt gains. That battery in the test has no surface charge. Gains will be higher. Are you cherry picking again?

12thgenusa wrote:
You would get a failing grade if that was an exam question.

Salvo said,

"When using mppt, temperature is a killer . You didn't account for it."

Actually, I did, indirectly, when I said,

"In hot conditions, as Vmp goes down, pwm efficiency would go up in comparison; and vice-versa."

The efficiencies on the chart are at conditions (25*C) favouring the mppt, of course. But the fact remains, there are conditions that favour mppt, and conditions that favour pwm. I plan to exploit both.

Hi Niner,

You have not allowed for the greater atmospheric path. On December 21st, in perfect solar conditions, I get 17 amp hours from 256 watts of panels during 8 hours of sunlight. In June I get over 100 amp-hours. My guess is that I'd need 5X the panel wattage for my location which is about 51 degrees latitude.

NinerBikes wrote:
with short days and northern lattitudes, you may need a factor of 2 or 3x the watts to amp hour ratio that most consider normal, ie 1 watt of panel to 1 amp hr of battery.

Salvo wrote:
You would get a failing grade if that was an exam question. When using mppt, temperature is a killer . You didn't account for it. At 1000W/m^2 irradiance, the panel will be fairly hot.

The math has been done many, many times. mppt should have about 5% advantage.

Well I would think you would earn a failing grade as well.

How hot is "fairly hot"? As you well know cell temp is dependent not only on irradiance but also ambient temp, wind speed and panel mounting. I am certain that my panel cell temp in Colorado even at only 5000' elevation is much lower than it would be in Arizona or SoCal at an equal irradiance of 1000 W/m^2.

You also know that the advantage of MPPT is not only dependent on cell temp, but also battery SOC and battery voltage and a corollary to that on how long the controller stays in bulk. MPPT has quite an advantage at lower SOC with corresponding lower battery voltage.

To cherry pick the worst possible scenario for MPPT then say the math is done and the advantage is only 5% is frankly irresponsible.

No doubt there are times then the advantage is only 5%, but to be fair if you are going to assert that, you also need to state the conditions under which that is true.

Did you view the link in a previous thread in which side-by-side tests were done using identical panels with different controllers? His results showed a better than 20% advantage for MPPT over week long testing. Granted his conditions were ideal for MPPT, but that's my point. There's no math that says MPPT has only a blanket 5% advantage for everyone everywhere.

You would get a failing grade if that was an exam question. When using mppt, temperature is a killer . You didn't account for it. At 1000W/m^2 irradiance, the panel will be fairly hot.

The math has been done many, many times. mppt should have about 5% advantage.

jrnymn7 wrote:
Concerning controller efficiencies, it seems to me,

With 280w (2x 140w) of 12v panels in series/mppt, if the mpp of the panels was found to be at 8a and 17v, that's 8a x 34v = 272w input. At 96% eff., that's 261w output. If the bank was at 12v ocv, and charging began at say 13v, that would produce 20a of charge current (261w / 13v).

With 280w parallel/pwm, if Isc was 8.5a, and panel voltage was pulled down to 13v, that would produce 17a of charge current (2x Isc); so 3a less than with mppt. Assuming the pwm operates with 100% eff., the input and output would both be 221w (17a x 13v). 221w / 272w of available power = 81.25% eff.

In hot conditions, as Vmp goes down, pwm efficiency would go up in comparison; and vice-versa.

I say keep poking at it on paper but don't buy the MPPT yet. There might be more to the PWM and 24v route yet to be discovered! Keep your powder dry and all that. :)

jrnymn7 wrote:
Concerning controller efficiencies, it seems to me,

With 280w (2x 140w) of 12v panels in series/mppt, if the mpp of the panels was found to be at 8a and 17v, that's 8a x 34v = 272w input. At 96% eff., that's 261w output. If the bank was at 12v ocv, and charging began at say 13v, that would produce 20a of charge current (261w / 13v).

With 280w parallel/pwm, if Isc was 8.5a, and panel voltage was pulled down to 13v, that would produce 17a of charge current (2x Isc); so 3a less than with mppt. Assuming the pwm operates with 100% eff., the input and output would both be 221w (17a x 13v). 221w / 272w of available power = 81.25% eff.

In hot conditions, as Vmp goes down, pwm efficiency would go up in comparison; and vice-versa.

Why would panel V be pulled down to 13V? With PWM, you are interested in Isc in amps, or 8.5 amps per panel. You assume the batterier can take that full 17 amps. Sometimes it can, if below 85 to 90% state of charge.

You are making this too complicated for winter time use in Canada, you're going to have short days, and need a generator to get the batteries back up to close to full charge.

Seriously, jrneyman, you are over thinking this. Go PWM and add another 140W panel, for 3 of them, and then pick whatever your heart desires for a charge controller.

If it's under 30 Amps at 12v, go PWM, if it's over or you have long runs of wire, go MPPT with 28V or more from the panels.

Or just buy the damn MPPT, experiment with it, and then get back to us on how it worked out, be the guinea pig.

Everything is a trade off, you can't have it all, so pick what's most important to you, make a decision, and spend wisely.

My decision was to have enough panel to stay in bulk charge, have a pwm controller that I can set at 15.0V for bulk, and since I know my unit just idle sucks 24 amp hours a day, I was sucking an amp an hour while dark, empty, or 14 to 16 amps in winter. Turn on lights fan, TV and of course the consumption increases. with short days and northern lattitudes, you may need a factor of 2 or 3x the watts to amp hour ratio that most consider normal, ie 1 watt of panel to 1 amp hr of battery.