PWM or MPPT?

[earlvillestu]

I just took delivery of a 120W portable solar panel from SolarBlvd, which I will use to charge a single AGM Group 31 with an AH capacity of 105. We have a popup and are minimal electricity users, so I believe this will meet our needs.

The panel specs are Vmp 18.0, Imp 6.67, Voc 22.7, Ioc not specified. I plan to ditch the cheesy supplied controller and put a 3-stage adjacent to the battery.

My question is, would there be a significant benefit to buying an MPPT controller over a good PWM? I know that if I expand the number of panels in the future, there are benefits to MPPT, but assuming I'm planning to stay with the current setup, is it worth the substantial extra cost?

[NinerBikes]

BFL13 wrote:
You don't need a controller at all except when you are not there during the day.

Panel direct will gradually raise the battery voltage to 15v or so before dark, then it collapses back at dusk. With one battery you would get to 15 sooner in the day and then want to just disconnect for a while. But that is what the controller does for you, is hold the voltage at some limit like 14.4 till dark and it goes back down.

-You can keep that controller and use it
-You can go panel direct till batt voltage gets to 15v then apply the controller to do a Vabs at 14 (almost like an Iota converter! 🙂 )
-You can get a new controller that goes to 14.6 and holds there.

I had a LandStar 2024 that went to 14.6 and stayed there for two hours then dropped to 13.8v and stayed there till dark. They are about $40 instead of the $15 ones. I now have a $15 one that goes to 14.4 and stays there till dark. Works for me. (130w panel)

What model did you end up going with for 14.4 V and $15???

[earlvillestu]

Thanks for all your replies. I have ordered a 10 amp Steca controller.

I'd like to add a Trimetric meter and plan to do so eventually, but for now the DW - approved budget is spent.

[Old___Slow]

BFL13


I like your qualified assessment of batts, controllers and etc.

Right on, my good man. Keep the posts coming.

O&S
Floyd

[Shadow_Catcher]

This is one case where it is just not a good idea to cheap out, You have or will have a substantial investment in your 105AH AGM battery and to risk it with no controller or one that is likely to fail just does not make sense. Moringstar is well made world wide respected company as is Steca. No controller may work with a 25W panel but more than that...
The only way to accurately gauge the SOC (state of charge) is with a meter that measure the current going into and coming out of your battery through a shunt such as the Bogart Trimetirc or Vectron battery monitor. The little plug in battery meters are not accurate unless there is has been no current in or coming out for a couple of hours. The Vectron we have is set so that it displays the percent SOC. The simple panel meters particularly the analogue will be hard put to differentiate between 70% SOC at 12.32V and 50%SOC at 12.06V 50% is the magic number below which you do not want to go. See http://www.solar-electric.com/deep-cycle-battery-faq.html

[earlvillestu]

Good advice, Thank you. The panel specs I gave are from the pamphlet that came with the unit.

[NinerBikes]

earlvillestu wrote:
I just took delivery of a 120W portable solar panel from SolarBlvd, which I will use to charge a single AGM Group 31 with an AH capacity of 105. We have a popup and are minimal electricity users, so I believe this will meet our needs.

The panel specs are Vmp 18.0, Imp 6.67, Voc 22.7, Ioc not specified. I plan to ditch the cheesy supplied controller and put a 3-stage adjacent to the battery.

My question is, would there be a significant benefit to buying an MPPT controller over a good PWM? I know that if I expand the number of panels in the future, there are benefits to MPPT, but assuming I'm planning to stay with the current setup, is it worth the substantial extra cost?

http://www.solarblvd.com/Solar-Panels-&-Systems-12-Volt-Solar-Panels/c1_269/p2756/W-Solar-120-Watt-Foldable-12-Volt-Solar-Panel/product_info.html?osCsid=5bfff18c08bc1aef8f51655eae63fdba

Double check your figures, I get something different from what you are showing. VMP 17.2v and IMP 6.98 Amps. VOC 21.8v ISC 7.76 Amps


Stick with the PWM. There are other programmable PWM options like a WEN charge controller version 1.2 that now allow you to program additional "bulk" type voltage into your battery, for 12 to $15 on Ebay.

http://www.ebay.com/itm/Digital-PWM-10A-Solar-Charge-Controller-Regulator-12V-24V-Autoswitch-Solar-Panel-/171177553544?pt=LH_DefaultDomain_0&hash=item27dafa2e88

Just 2 weeks ago, at 34N, I ran some tests on mine, and had no trouble getting 6.33 to 6.56 amps measured, just pointing the panel and aiming it at the sun. Summer time is another matter, longer days, more chargeable hours... with the sun where it is now, I'd be lucky to get 30 to 35 Ah in a day. Sunlight hours are a lot longer after March 21st to Sept 23.

Get yourself one of those RV charger meters on Ebay for $12 to $15 from China, and set yourself up to be able to measure your charge per day. Your voltage in the morning, before the panels start to kick in charging, will tell you your state of charge. 12.0 to 12.1V is about 50%

[BFL13]

You don't need a controller at all except when you are not there during the day.

Panel direct will gradually raise the battery voltage to 15v or so before dark, then it collapses back at dusk. With one battery you would get to 15 sooner in the day and then want to just disconnect for a while. But that is what the controller does for you, is hold the voltage at some limit like 14.4 till dark and it goes back down.

-You can keep that controller and use it
-You can go panel direct till batt voltage gets to 15v then apply the controller to do a Vabs at 14 (almost like an Iota converter! 🙂 )
-You can get a new controller that goes to 14.6 and holds there.

I had a LandStar 2024 that went to 14.6 and stayed there for two hours then dropped to 13.8v and stayed there till dark. They are about $40 instead of the $15 ones. I now have a $15 one that goes to 14.4 and stays there till dark. Works for me. (130w panel)

[Shadow_Catcher]

I have a similar application, a teardrop with limited roof space. I went a different route with a 185W high voltage (70+V) panel which required an MPPT controller feeding a 150AH AGM.
A PMW will work well and I recommend the MorningStar SunSaver and if you are contemplating adding, get the 20A version (about $75), and if SB did not include that see if you can trade up.
Parts of this equation are conservation in the form of LED lights etc. and battery monitoring i.e. a Trimetric or Vectron (I chose the Vectron)

[earlvillestu]

The problem with the onboard controller is, as nearly as I can decipher from the Chenglish "User Manual," is that it bulk charges at 14V, whereas the battery manufacturer recommends 14.6.

[time2roll]

Not only would I stick with PWM I would use the controller provided.

If you expand the system then evaluate the panels/controller needed.

[BFL13]

A 120w panel usually has an Isc around 7.6a, so you can expect that with PWM when it is pointed at the sun, when the sun is high enough on a clear day.

The rule is to have a 20% margin over that in controller size for when you get more than rated amps (happens), so that means another 1.5a for 9.1 so a 10a controller should be ok.

There are dozens of 10 or 20a PWM controllers on ebay for under $20, and some have free shipping. they work just fine as several forum members have reported, including me.

MPPT with a 12v 120w panel will get you maybe another part of an amp above that 7.6. Don't even bother. 🙂

[mena661]

No benefit with using a MPPT in this case.

[JiminDenver]

In this instance I don't believe you would see enough benefit for the extra you would spend for a MPPT controller.