Are Tracer MPPT controllers (2215RN) actually better than PWM?

[LETitROLL]

Check out this thread http://www.solarpaneltalk.com/showth...344#post147344 for some speculation about a real life problem that may be caused by overpaneling an unsophisticated MPPT CC. Or may just be bad wiring.

Thanks for that, I have been reading and learning a little more since my last question. Funny to see your location, I was up at 4:00am but did not have time to read your response because I was in a hurry to start my 800 mile solo drive (all today) to my mothers house in the foothills near your location. All loaded up in the car, turn the key, starts for 1 sec. and dies, (fuel pump out). Now I am relaxing catching up on e-mail instead.
thanks

[inetdog]

Check out this thread http://www.solarpaneltalk.com/showth...344#post147344 for some speculation about a real life problem that may be caused by overpaneling an unsophisticated MPPT CC. Or may just be bad wiring.

[Bucho]

Thank you, after some more research and crunching some of the replies here, I think you have the right answer. Should be no problem with the better MPPT controllers that give you control via software/firmware over the output, but the cheap ones as always are on a case by case basis.
thanks

There is a fancier tracer that lists PV current limiting protection: http://www.amazon.com/EPsolar-Tracer...rge+controller

[LETitROLL]

I don't know, I've heard this:



But does it apply to the cheapest MPPT you could find *shrug*

Thank you, after some more research and crunching some of the replies here, I think you have the right answer. Should be no problem with the better MPPT controllers that give you control via software/firmware over the output, but the cheap ones as always are on a case by case basis.
thanks

[Bucho]

Thanks, so in that kind of mismatch situation would the charge controller do what it can (12v to battery at approx. 20 amp) or would some damage be done to some component?
thank you for your reply

I don't know, I've heard this:

If your CC is PWM, then no, you cannot over panel them by more than the manufacturer allows, probably 10% or so. The reason is that although the pulse width modulation can still regulate the average current to the battery, the peak current during the on pulse will be too high for the switching element(s) and they will fail.
If your CC is MPPT, most will just regulate to a lower power level than the MPPT point to keep the output amps down. You may be able to overpanel by a factor of two or more without problems.

But does it apply to the cheapest MPPT you could find *shrug*

[LETitROLL]

If you go with Flooded batteries, now you have to maintain them, and the manual of that tracer specifically states, do not put it near FLA batteries (they are going to vent).

Now that is good information, thank you for that, that is one thing I would not have known (until i read the manual), and then it would be too late.
thanks again

[LETitROLL]

That will allow you to use all of your panels, but you are spending a lot more on lead than you will need.

That is the part i am trying to figure out, I want to size the system more for production than storage because of the 90% rule (cloudy 90% of the time i will need it). We get stretches of 10 to 20 days sometimes without any direct sun, I don't want to spend 300 to 500 on batteries to capture and store that long term for the little bit i need. Also remember I only need 150-200 w/h once about every 10 days, not ever 2 days in a row. The amount that the panels produce when cloudy will get me by, and if I am correct wouldn't a 20% draw down of a 100ah RV batt = 20ah x 12v = 240 w/h?. Mostly I just want to make sure I don't damage anything when the sun does come out, if it will just float and waste the excess energy. Will a 10amp MPPT charge controller convert 24v 7a, to 12v 10a (rated max), or will it stay at 7a, or try and do 12v 14a and fry the output?
thanks

[paulcheung]

If going with Trojan batteries, The L16RE-B would be a better choice for Solar applications. True deep cycle and PSOC.

[mschulz]

wire 2 of these in series http://www.trojanbattery.com/product/j305e-ac/
that gets you a 12V 305Ah battery which could be charged at 39amps
you'll need a 40A MPPT though

That will allow you to use all of your panels, but you are spending a lot more on lead than you will need. If you go with Flooded batteries, now you have to maintain them, and the manual of that tracer specifically states, do not put it near FLA batteries (they are going to vent). Look more at the AGM if you are going to mount the CC close to the batteries.

[LETitROLL]

So here's the thing 470w at 12v is 39.2 amps. That's a lot more than the 20 amps this controllers rated for.

Also one needs to be aware of how quickly you can charge your battery. A rate of 1/8th the capacity is a pretty normal upper limit for FLA's, typically represented as C/8. Here's a tutorial: http://www.solarpaneltalk.com/showth...eries-Tutorial

C/8 for a 100ah battery is 12.5 amps it is not 39.2 amps

Thanks, so in that kind of mismatch situation would the charge controller do what it can (12v to battery at approx. 20 amp) or would some damage be done to some component? I realize it would waste alot of potential energy, In my case there will be substantial waste anyway since I only need 200 W/H once every 10 days or so, whatever system is in place will be sitting idle most of the time, and since batteries are the most costly/problematic part I don't want to increase that, I would only use one panel and keep the other for future expansion. The last factor is that I am only going to be using this in the winter months and I am in a very grey region (mild weather, but not that sunny), so I would like to size the system for my "expected conditions" during the 4 months or so of usage, not the year round average of 3.5 sun hours. The panels I have tested here appear to put out about 10 - 15% of their rated panel wattage when cloudy, so I was looking at 470w x .10 x sun hours = 150 to 200w range per day that I needed, I guess i just need to know how best to setup the rest of the system so that things don't go bad when the sun peeks out.
thank you for your reply

[thastinger]

wire 2 of these in series http://www.trojanbattery.com/product/j305e-ac/
that gets you a 12V 305Ah battery which could be charged at 39amps
you'll need a 40A MPPT though

[mschulz]

I just have a couple of 235w panels I picked up cheap, and want to play around at a off grid cabin I use, only need a couple hundred watt/hrs a day for a few lights, and radio, etc., my needs are small enough that to keep it simple I would rather run just 1 large 12v battery (100ah), and then I figured as long as it is a real MPPT at least I would get the full production of the panels, instead of losing 1/2 right off the top through the PWM because of stepping down from 24v to 12v.

thanks to all for the replies, it sounds like it is not too bad if I can pick one up for the right price.

I use the 40 AMP model on my cabin, same usage as you, (210Watt panels, 1 100AMP AGM) and it works great. I only use one of the two panels as it is plenty. My daily usage is 300 watt-hours (cell phone booster, ARB Fridge, and Phone and tablet charging). My battery is on float by noon. If I needed a bigger battery system, I would step up to a high quality CC, but I am just screwing around right now. Wish I had real battery temp monitoring like Morning Star and Midnite Solar.

[Bucho]

I just have a couple of 235w panels I picked up cheap, and want to play around at a off grid cabin I use, only need a couple hundred watt/hrs a day for a few lights, and radio, etc., my needs are small enough that to keep it simple I would rather run just 1 large 12v battery (100ah), and then I figured as long as it is a real MPPT at least I would get the full production of the panels, instead of losing 1/2 right off the top through the PWM because of stepping down from 24v to 12v.

thanks to all for the replies, it sounds like it is not too bad if I can pick one up for the right price.

So here's the thing 470w at 12v is 39.2 amps. That's a lot more than the 20 amps this controllers rated for.

Also one needs to be aware of how quickly you can charge your battery. A rate of 1/8th the capacity is a pretty normal upper limit for FLA's, typically represented as C/8. Here's a tutorial: http://www.solarpaneltalk.com/showth...eries-Tutorial

C/8 for a 100ah battery is 12.5 amps it is not 39.2 amps.

So you really shouldn't go buying any more parts yet, these are solvable problems but you need to figure out a system that will work together before you buy it.

[LETitROLL]

It is an MPPT controller, that doesn't necessarily mean it's a good choice. What do you have for a system?

I just have a couple of 235w panels I picked up cheap, and want to play around at a off grid cabin I use, only need a couple hundred watt/hrs a day for a few lights, and radio, etc., my needs are small enough that to keep it simple I would rather run just 1 large 12v battery (100ah), and then I figured as long as it is a real MPPT at least I would get the full production of the panels, instead of losing 1/2 right off the top through the PWM because of stepping down from 24v to 12v.

thanks to all for the replies, it sounds like it is not too bad if I can pick one up for the right price.

[thastinger]

It is a real MPPT CC, it just doesn't have a lot of bells and whistles as far as battery programs go.