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MPPT vs PWM for single 190w panel?

LVLAaron

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Jul 16, 2021
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Just got my first camper. It has a 190watt 24v panel and a clumsy Go Power control panel that leaves a lot to be desired.

I have a Victron 75/15 w/ BT in my shop that not being used.

Would I benefit swapping in the Victron?
 
You don't need MPPT just because your battery is 12v.

With the Victron you'll get a benefit in information, but not charging speed.

This debate on PWM vs MPPT has been going on for years. Now if you want to wire your panels in series with higher voltage you can't with a PWM SCC, but for your system you'll see no charging benefit. With a simple 190 watt setup you will get no real benefit from MPPT. Theory yes, real no.

Our camper with a 170 watt GoPower panel also came with a GoPower SCC, but once we changed to a Victron 100/30 saw no difference in charging time. Except, Victron will tell you are 100% charged when it goes to float, whereas GoPower tells you are 100% full only when you are actually 100% full, so with the Victron you get a false reading making you believe your batteries are full. I've found others who have realized this flaw with Victron SCC's.

When not on the road our camper sits in a seasonal site eight-tenths of a mile from our condo. I play with the readings all the time. Last June I was at the camper when I watched the Victron go from absorption to float. At the exact time the monitor jumped to 100% full. I immediately disconnected the solar, waited five minutes, ran the water pump for perhaps 20 seconds and took my multimeter and measured the voltage. My batteries (lead acid SiO2) were somewhere between 90-95% full. I did this a year earlier with our AGM's and found the same scenario.

On the other hand if you want to check how your setup is working or have a potential problem you get history with Victron SCC units and even more history when you add a Victron 712 battery monitor. The two work together. Last January it quickly diagnosed our AGM failure and found the WFCO charger had decided to throw 21 volts to the batteries, destroying them. The WFCO charger is now disconnected and has been since last February when we got our new batteries. Don't miss it and don't need it. FYI, we don't have a DC-DC charger, and for our needs don't need one.

In all fairness, in the fall, winter, and spring our 170 watts was more than enough for us, but last June we added an additional 300 watts to our camper (465 watts when accounting for mixed panel loss), wired in parallel, to help with shading we get where we camp in Minnesota in the summer months.

We had the discretionary income, and had seen a previous battery failure so purchased our Victron 100/30 SCC and 712 BMV to better monitor the system, and it did show us the WFCO failure. So far our current batteries are running perfect, but the Victron system gives me lots of info that I don't need until something goes wrong.

If you have the discretionary income, love to watch electrical monitors, and play with your system, ditch your GoPower SCC, otherwise you're just fine.

OTOH, you already have the Victron controller, so why not install?

Enjoy,

Perry
 
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You don't need MPPT just because your battery is 12v.

With the Victron you'll get a benefit in information, but not charging speed.

This debate on PWM vs MPPT has been going on for years. Now if you want to wire your panels in series with higher voltage you can't with a PWM SCC, but for your system you'll see no charging benefit. With a simple 190 watt setup you will get no real benefit from MPPT. Theory yes, real no.

Our camper with a 170 watt GoPower panel also came with a GoPower SCC, but once we changed to a Victron 100/30 saw no difference in charging time. Except, Victron will tell you are 100% charged when it goes to float, whereas GoPower tells you are 100% full only when you are actually 100% full, so with the Victron you get a false reading making you believe your batteries are full. I've found others who have realized this flaw with Victron SCC's.

When not on the road our camper sits in a seasonal site eight-tenths of a mile from our condo. I play with the readings all the time. Last June I was at the camper when I watched the Victron go from absorption to float. At the exact time the monitor jumped to 100% full. I immediately disconnected the solar, waited five minutes, ran the water pump for perhaps 20 seconds and took my multimeter and measured the voltage. My batteries (lead acid SiO2) were somewhere between 90-95% full. I did this a year earlier with our AGM's and found the same scenario.

On the other hand if you want to check how your setup is working or have a potential problem you get history with Victron SCC units and even more history when you add a Victron 712 battery monitor. The two work together. Last January it quickly diagnosed our AGM failure and found the WFCO charger had decided to throw 21 volts to the batteries, destroying them. The WFCO charger is now disconnected and has been since last February when we got our new batteries. Don't miss it and don't need it. FYI, we don't have a DC-DC charger, and for our needs don't need one.

In all fairness, in the fall, winter, and spring our 170 watts was more than enough for us, but last June we added an additional 300 watts to our camper (465 watts when accounting for mixed panel loss), wired in parallel, to help with shading we get where we camp in Minnesota in the summer months.

We had the discretionary income, and had seen a previous battery failure so purchased our Victron 100/30 SCC and 712 BMV to better monitor the system, and it did show us the WFCO failure. So far our current batteries are running perfect, but the Victron system gives me lots of info that I don't need until something goes wrong.

If you have the discretionary income, love to watch electrical monitors, and play with your system, ditch your GoPower SCC, otherwise you're just fine.

OTOH, you already have the Victron controller, so why not install?

Enjoy,

Perry

Fair points. The Victron controller is MUCH nicer than the go-power "thing" - It has very little information and is not the least bit helpful. I'll put the Victron in, as I'll be moving to lithium batteries when the AGM's die anyway, so I'll need the flexibility.
 
The exact benefit in charting with MPPT versus PWM depends on the exact Voltage (Vmp) of the panel in question, versus your charging Voltage. The difference (e.g., 24.0 Volts - 14.4 Volts = 9.6 Volts) is left unused by a PWM controller, but will be utilized by a MPPT controller to create more charging current - cut down by about 5% inefficiency in the Conversion.

If your panel is 24.0 V(mp) and 190 watts, the current I(mp) would be about 7.91 Amps under standard test conditions. 7.91 Amps * 9.6 Volts = about 76 watts which the PWM controller must leave in the panels under near-perfect standard test conditions light levels, So the effective 'rated power' through the PWM is more like 114 watts. The MPPT can use all 190 watts going in, but wastes about 5% in converting to lower Voltage with more current. So you can get roughly 171 watts (under near-perfect conditions), an increase of 50% over the PWM configuration. (Your exact numbers might vary, of course).

That's advantageous, but only *if* your battery bank and loads wants to take it all in. If the PWM controller is already reaching float mode at 1 PM, then you don't really gain that much: You'll simply reach "float mode" at 11 AM instead, leaving the entire afternoon mostly unused. But the Victron is also vastly more programmable, to do exactly what you want when you want it. Even if you appear to be getting "near full" with the PWM controller, the "dumb" Go-Power is possibly going into float mode a bit too early. The Victron programming, and settable parameters, are vastly superior. It also gives you BT monitor capability, which is great to have.

I'd switch out the Go-Power and put in the Victron, for sure.
 
Are you sure it is a 24 volt panel with 60 or 72 cells? I am seeing 190w panels with 36 cells (4x9) and this would be a 12v panel even if the Voc is close to 24 volts. With the PWM you basically get the Isc rating and the battery voltage so maybe 126 watts max (9a x 14v). May get a bit more wattage out of MPPT, especially at the lower 13.4 volts where your LFP will spend most of its time.

If this is a 24v panel the Isc will be closer to 6 amps and that is all you get with PWM, 84 watts.
 
It does appear to be this panel


I have the Victron installed and full sun should happen in an hour or two from now.
 
That is a nominal 12v panel. Should get close to 9.45 amps with a PWM controller. Should get a few more amps from MPPT but maybe not enough to spend money on a controller to get it. Of course if you have an MPPT collecting dust on the bench, the battery should see at least 10% more power in all conditions.
 
Yep. Definitely had one collecting dust!
I have room to add a second panel and night do that in the spring.
 
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