PWM or MMPT?

[creativepart]

I have a modest solar install - three 100 Watt panels on my RV's roof. The initial setup with only one 100w panel came from the factory as an OEM Option and I added two more 100w panels later. The house batteries are 4-12v 100aH AGM true deep cycle. I have a 2000w Magnum inverter.

With the factory install I received a ZAMP 30-Amp PWM solar charge controller.

As currently configured the system handles my needs well and does keep my house batteries charged fully even during a storage period of 1 to 2 months.

We don't boondock or dry camp very much. But when we do, we run a residential fridge, TVs, Rokus, routers, chargers, etc.

I know that I just said it's meeting my needs, but I feel like I'm wasting power with the PWM charge controller because of how MPPT controllers are more efficient.

I'm being crazy right? The difference is minor and I don't really need more efficiency based on how I'm using this admittedly modest system anyway. Right?

Sometimes I get fixated on a thing, read all about it, and want to buy equipment to have the best system I can have. (Don't ask about my stereo setup at home.)

[PJStough]

If you decide to upgrade to a MPPT controller to gain a few more amp hours, I would also rewire the panels in series, to gain a few more amp hours by raising the voltage to the controller there by reducing voltage loss from the panels to the controller.

[creativepart]

The factory installed a complete Zamp system. So, along with the one 100w panel they installed the Zamp 3-port junction box on the roof. Since only one panel was plugged into the junction box I used the other two unused ports when I added my two new panels.

So, I'd either have to get rid of that junction box or modify it. I'll have to consider that.

I do know that MPPT are more efficient when the panel voltage is higher than the battery voltage - at least I think I know that.

If wired in series don't I have to worry that one shaded panel will degrade the power in all of the 3 panels?

[Sbrownstein]

I think you will find that MPPT is better than PWM on installations that are much larger. On 300 to 600 watt systems, the difference is minimal. The biggest advantage to MPPT is that it allows panels to be wired in series, producing higher voltages and lower currents and smaller wire can be used. It would also allow you to use grid tied panels that have much higher voltages than 18 volts. If you do neither of these things, it ain't worth it!

[creativepart]

Originally Posted by Sbrownstein

I think you will find that MPPT is better than PWM on installations that are much larger.

I hate to admit it, but this is what I was hoping someone would tell me.

[twinboat]

Run your batteries down the 12.3 volts, and then go out on a sunny day and measure the voltage before and after the controller.

If you see more then 14 volts, that energy is being wasted with a PWM controller.

Series wiring can be done with the panel connectors. Plug them in, one to the next and the last two ends go to the combiner box.

[Knightab]

Originally Posted by creativepart

I have a modest solar install - three 100 Watt panels on my RV's roof. The initial setup with only one 100w panel came from the factory as an OEM Option and I added two more 100w panels later. The house batteries are 4-12v 100aH AGM true deep cycle. I have a 2000w Magnum inverter.

With the factory install I received a ZAMP 30-Amp PWM solar charge controller.

As currently configured the system handles my needs well and does keep my house batteries charged fully even during a storage period of 1 to 2 months.

We don't boondock or dry camp very much. But when we do, we run a residential fridge, TVs, Rokus, routers, chargers, etc.

I know that I just said it's meeting my needs, but I feel like I'm wasting power with the PWM charge controller because of how MPPT controllers are more efficient.

I'm being crazy right? The difference is minor and I don't really need more efficiency based on how I'm using this admittedly modest system anyway. Right?

Sometimes I get fixated on a thing, read all about it, and want to buy equipment to have the best system I can have. (Don't ask about my stereo setup at home.)

From most I have read it seems the difference is you can gain 10-15% using MPPT. I changed mine from PWM because I have the same affliction as you lol. Thus my change to lithium batteries.

[Knightab]

Originally Posted by twinboat

Run your batteries down the 12.3 volts, and then go out on a sunny day and measure the voltage before and after the controller.

If you see more then 14 volts, that energy is being wasted with a PWM controller.

Series wiring can be done with the panel connectors. Plug them in, one to the next and the last two ends go to the combiner box.

I have seen my controller showing solar voltage coming into it at 19+ volts

[PbdBlue]

If you were starting from scratch I'd definitely go MPPT but since you already have a PWM it's probably not worth it. In my experience the MPPT will get you about 20% improvement. In your case I'd guess maybe 3 amps more. Is it worth the expense and hassle of rewiring? Only you can decide that.

[Soppy]

Solar panels produce their rated power between 18-20 volts . The current is almost constant from short circuit to the rated voltage. A 100w solar panel will produce about 5 amps of current . With 3 solar panels and a PWM controller your system will charge your battery bank at a maximum of 15 amps , regardless of the battery voltage , till the charge control starts to regulate . So if your batteries are at 12 volts , you will only get 180 watts of charging power (12volts x 15amps).
If you install a MPPT controller in the same system , the MPPT controller will allow the panels to operate at their maximum power point voltage about 19 volts. The current will still be a total of 15 amps. But through the "magic" of the controller your batteries will be charging at 285 watts (19 volts x 15 amps) or close to 24 amps . As the battery voltage increases , the current will decrease . If the batteries reach 15 volts, the charge current will be only 19amps. The values will be a little less due to the efficiency of the controller.

[creativepart]

Originally Posted by Knightab

I changed mine from PWM because I have the same affliction as you lol. Thus my change to lithium batteries.

See, now, you had to go and mention Lithium Batteries didn't you. Shame on you.

[Knightab]

Originally Posted by creativepart

See, now, you had to go and mention Lithium Batteries didn't you. Shame on you.

LOL, yes but we both knew it was coming. I am realllllllly happy with the Lipo battery. Never have to worry about if it is fully charged before using it, can pump power into it at any time, no memory, 80% usage no damage and most of all the constant voltage while inverting. That was the deal breaker for me. Our AGM's of 400 ah would drop the voltage low enough to kick out the inverter, with the Lipo it just pumps the voltage and blasts right through! Didnt want to spend that much for a battery but the advantages is greatly worth it, plus the cycles you get out of them make it a hands down upgrade. A shadow of shame will be cast upon you if you dont upgrade, dont let down your obsessed brothers! lol
PS: I am using a 200 AH lipo now, it provides almost as much as my 400AH of AGM'S and in a much less space. it is 19x6.6x9.5" beats the snot out of my 2 huge 8D's So I gained storage space with comes at a premium in our coach. Oh did I mention you can put them ANYWHERE! No acid no gassing and they love inside the coach in unused places otherwise. One key factor is you cant charge them if they are at freezing or below, you can use them but not charge. I just put a holding tank heating pad under mine.

[Sbrownstein]

Originally Posted by Soppy

Solar panels produce their rated power between 18-20 volts . The current is almost constant from short circuit to the rated voltage. A 100w solar panel will produce about 5 amps of current . With 3 solar panels and a PWM controller your system will charge your battery bank at a maximum of 15 amps , regardless of the battery voltage , till the charge control starts to regulate . So if your batteries are at 12 volts , you will only get 180 watts of charging power (12volts x 15amps).
If you install a MPPT controller in the same system , the MPPT controller will allow the panels to operate at their maximum power point voltage about 19 volts. The current will still be a total of 15 amps. But through the "magic" of the controller your batteries will be charging at 285 watts (19 volts x 15 amps) or close to 24 amps . As the battery voltage increases , the current will decrease . If the batteries reach 15 volts, the charge current will be only 19amps. The values will be a little less due to the efficiency of the controller.

Well, there is a gain with MPPT, but not that much at this system size. First off, you aren't going to charge any flooded cell at 12 volts, both controllers will push at least 13.5 to 14 volts into a discharged bank. That would be 210 watts for the PWM controller when you really care...i.e. low SOC. If we assume that the maximum power point for the panels is something like 19 volts as you say, the MPPT can "theoretically" push 285, but the efficiency of MPPT controllers isn't 100%, so say 85%, which would get you only 242. Now, an extra 32 watts isn't nothing, but you really should give the MPPT controller a higher voltage to work using series connected panels to get the best improvement. Then you have the shading issue.

MPPT is essential in kilowatt grid tied systems since currents and wire size get too high for PWM. At 200-300 watts its a toss-up. I use the Bogart SC-2030 since it cooperates with my Trimetric and offers remote sensing of battery voltage and excellent SOC control, eliminating the concern of wire size to the battery bank.

[creativepart]

My Zamp controller is a 5-stage PWM that can handle up to ~500watts of cells. It is adjustable by battery type and even includes a Lithium setting.

Here's what it looks like: