Thinking about installing the Renogy 20 amp DC to DC charger

[Rob Culver]

Originally Posted by Wavery

That is exactly what you want. The controller is lowering the voltage from 32V (which is ~max output of the panel) to 14V which increases the panel amperage output from 6.7A to the maximum ~15A.

In order for a 30A controller to go past 15A, it would need higher voltage from the panel. Installing a 30A controller will not increase the amperage to the battery any higher unless you install a second panel.

The advantage that the MPPT controller gives you is that it will start charging your battery earlier and continue charging later in the day.

I have a 30A controller on my trailer with 640W of solar panels. I'll take a pic of the output of my setup when the Sun gets a little higher today.

Hi Wayne,
I agree that the MPPT controller, combined with the high voltage of the panel, and the high wattage, starts the battery charging earlier in the day and keeps it charging later in the day. With this 370 watt panel, I've already maxed out the 75/15 controller at 14.8 amps and 215 watts at 10:15 in the morning. And it stays maxed out all the way past 3:15 pm in the afternoon. So that's all good.

However, I have no doubt that my amperage in to the battery between 10:15 and 3:15 would go much higher than 15 and perhaps even 25 amps if the controller supported that and without having to add another panel.

What type of 30 amp controller are you using? Is it mounted in front of the sink? Does it require an extra ground wire for safety over and above the 4 positive and negative wires going to the panel and the battery? Thanks..

[ShrimpBurrito]

Originally Posted by Wavery

In order for a 30A controller to go past 15A, it would need higher voltage from the panel. Installing a 30A controller will not increase the amperage to the battery any higher unless you install a second panel.

Why do you say that, Wayne? Presuming he got the "ZNSHINE SOLAR" 370W panel, the max voltage is ~34V and max current is 10.8A. There's your 370W.

He recorded the voltage from the panel to be about 32V, which is nearly at the max, but was only getting 6.7A, which is ~4 amps shy of what it could be outputting. Why wasn't the panel putting out more current?

My thinking is that the controller is current-limiting, and will not allow more input current, because it can't do anything with it. If it allowed a higher current, it can't be added to the output, so it would have to dissipate that extra power as heat.

With a higher output rating, why would a 100/30 charger not allow for a higher input current, allowing that additional ~4 amps at 32V from the panel? (Of course, this presumes there is enough sun for the panel to generate that much power, and second, the battery is sufficiently discharged to take more than 15A.)

And yes, I use a 100/30 Victron controller. My scenario is a bit different though as I have three 100W panels in series, so the input voltage range tops out at 60-some volts. But that charger will turn on and start charging when the panel voltage is only slightly higher than the battery charge voltage. I can't remember exactly, but it's in the manual, I want to say 15 or 16 volts. So you don't need much voltage for the controller to start charging, at least when you're beyond a single 100W panel, which tops out around 21 volts.

(Side note: I may have missed any discussion on WHERE you install the controller, but why are you installing it under the sink, and not, perhaps, in the rear compartment next to the batteries? That's where I put mine, anyway.....)

Dave

[Wavery]

Originally Posted by ShrimpBurrito

Why do you say that, Wayne? Presuming he got the "ZNSHINE SOLAR" 370W panel, the max voltage is ~34V and max current is 10.8A. There's your 370W.

He recorded the voltage from the panel to be about 32V, which is nearly at the max, but was only getting 6.7A, which is ~4 amps shy of what it could be outputting. Why wasn't the panel putting out more current?

My thinking is that the controller is current-limiting, and will not allow more input current, because it can't do anything with it. If it allowed a higher current, it can't be added to the output, so it would have to dissipate that extra power as heat.

With a higher output rating, why would a 100/30 charger not allow for a higher input current, allowing that additional ~4 amps at 32V from the panel? (Of course, this presumes there is enough sun for the panel to generate that much power, and second, the battery is sufficiently discharged to take more than 15A.)

And yes, I use a 100/30 Victron controller. My scenario is a bit different though as I have three 100W panels in series, so the input voltage range tops out at 60-some volts. But that charger will turn on and start charging when the panel voltage is only slightly higher than the battery charge voltage. I can't remember exactly, but it's in the manual, I want to say 15 or 16 volts. So you don't need much voltage for the controller to start charging, at least when you're beyond a single 100W panel, which tops out around 21 volts.

(Side note: I may have missed any discussion on WHERE you install the controller, but why are you installing it under the sink, and not, perhaps, in the rear compartment next to the batteries? That's where I put mine, anyway.....)

Dave

Hi Dave,

He stated, "The panel is at about 32 volts and 6.7 amps and the battery is at about 14 volts and 14.9 amps." That means that the charge controller doubled the amount of amps that was coming from the panel to going into the battery. This is done by converting the 32V coming out of the panel to 14V (the setting for bulk battery charging) going into the battery. Chances are, the battery is close to fully charged at that point and will cut back to ~13.8V float charge.

When trying to calculate the amount of watts being produced by the panel and dividing that by either amps or volts, you are leaving out the conversion rate of the MPPT algorithm.

I agree with you about getting that charge controller out of the cabinet under the sink. I actually mounted mine (on all of my TrailManors except my current Elkmont) on the outside of the storage cabinet. It is protected from weather, both opened and closed. It's much easier to read and service, it stays a lot cooler. and is closer to the battery storage.

[Rob Culver]

Originally Posted by ShrimpBurrito

Why do you say that, Wayne? Presuming he got the "ZNSHINE SOLAR" 370W panel, the max voltage is ~34V and max current is 10.8A. There's your 370W.

He recorded the voltage from the panel to be about 32V, which is nearly at the max, but was only getting 6.7A, which is ~4 amps shy of what it could be outputting. Why wasn't the panel putting out more current?

My thinking is that the controller is current-limiting, and will not allow more input current, because it can't do anything with it. If it allowed a higher current, it can't be added to the output, so it would have to dissipate that extra power as heat.

With a higher output rating, why would a 100/30 charger not allow for a higher input current, allowing that additional ~4 amps at 32V from the panel? (Of course, this presumes there is enough sun for the panel to generate that much power, and second, the battery is sufficiently discharged to take more than 15A.)

And yes, I use a 100/30 Victron controller. My scenario is a bit different though as I have three 100W panels in series, so the input voltage range tops out at 60-some volts. But that charger will turn on and start charging when the panel voltage is only slightly higher than the battery charge voltage. I can't remember exactly, but it's in the manual, I want to say 15 or 16 volts. So you don't need much voltage for the controller to start charging, at least when you're beyond a single 100W panel, which tops out around 21 volts.

(Side note: I may have missed any discussion on WHERE you install the controller, but why are you installing it under the sink, and not, perhaps, in the rear compartment next to the batteries? That's where I put mine, anyway.....)

Dave

Thanks for that response Dave. The reason I put the 75/15 controller in front of the sink is that I was replacing the original PWM controller that was located there. In that way I wouldn't have to rewire anything. I just used the original 4 wires that were plugged in to the PWM controller and plugged them in to the new one.

[Rob Culver]

Originally Posted by Wavery

Hi Dave,

He stated, "The panel is at about 32 volts and 6.7 amps and the battery is at about 14 volts and 14.9 amps." That means that the charge controller doubled the amount of amps that was coming from the panel to going into the battery. This is done by converting the 32V coming out of the panel to 14V (the setting for bulk battery charging) going into the battery. Chances are, the battery is close to fully charged at that point and will cut back to ~13.8V float charge.

When trying to calculate the amount of watts being produced by the panel and dividing that by either amps or volts, you are leaving out the conversion rate of the MPPT algorithm.

I agree with you about getting that charge controller out of the cabinet under the sink. I actually mounted mine (on all of my TrailManors except my current Elkmont) on the outside of the storage cabinet. It is protected from weather, both opened and closed. It's much easier to read and service, it stays a lot cooler. and is closer to the battery storage.

Hello again Wayne,
My battery was nowhere near fully charged when it got limited at 15 amps. The battery continued to charge up for many hours at the 14 to 15 amp rate. Another indicator that 15 amps to the battery is a hard limit of that controller is that the Victron App allows you to set that amperage lower than 15 in one of the configuration menus but not higher. When I set it lower than 15, the controller pretty much instantly started delivering to the lower maximum.

[ShrimpBurrito]

Originally Posted by Wavery

Hi Dave,

He stated, "The panel is at about 32 volts and 6.7 amps and the battery is at about 14 volts and 14.9 amps." That means that the charge controller doubled the amount of amps that was coming from the panel to going into the battery. This is done by converting the 32V coming out of the panel to 14V (the setting for bulk battery charging) going into the battery. Chances are, the battery is close to fully charged at that point and will cut back to ~13.8V float charge.

When trying to calculate the amount of watts being produced by the panel and dividing that by either amps or volts, you are leaving out the conversion rate of the MPPT algorithm.

Hmmm....well, the manual says that "peak efficiency" is 98%. Not sure what "peak" means, but even if we assume it's only 90% efficient on average, he would only be losing 37 watts when the panel was producing its rated power. So if 370 watts were going in (which it's not, but arguably could be), 333 watts should be coming out, which, at 14 V, is ~24 amps.

But if you take his readings, he is losing much less than that.

32 V * 6.7 amps INPUT = 214.4 watts
14 V * 14.9 amps OUTPUT = 208.6 watts.

...which is 97.2% efficient, if those readings are accurate.

And since you have a 200Ah LiFePO4 battery, it will take as much current as any solar controller you put in there can give it until close to the end of the charging process. Even if it were 10-20% discharged, I think you can charge them at over 100 amps (maybe even 200 amps).

I went through this process when I installed my first solar array, which consisted of three 100W panels (in series, so 60-some volts input). I underestimated the efficiency of my solar panels, and found that my 100/20 controller was maxing out at 20 amps, but I wasn't getting the full rated power of the panels. It was close, but I was wondering if I could squeeze more power out of them, so I bought a 100/30 controller, and that got me 22-23 amps output.

But, that's just my experience, and I experimented with it due to Amazon's generous return policy. In the end though, I ended up keeping the small controller for our 2nd TM.....

Dave

[Rob Culver]

Originally Posted by ShrimpBurrito

Hmmm....well, the manual says that "peak efficiency" is 98%. Not sure what "peak" means, but even if we assume it's only 90% efficient on average, he would only be losing 37 watts when the panel was producing its rated power. So if 370 watts were going in (which it's not, but arguably could be), 333 watts should be coming out, which, at 14 V, is ~24 amps.

But if you take his readings, he is losing much less than that.

32 V * 6.7 amps INPUT = 214.4 watts
14 V * 14.9 amps OUTPUT = 208.6 watts.

...which is 97.2% efficient, if those readings are accurate.

And since you have a 200Ah LiFePO4 battery, it will take as much current as any solar controller you put in there can give it until close to the end of the charging process. Even if it were 10-20% discharged, I think you can charge them at over 100 amps (maybe even 200 amps).

I went through this process when I installed my first solar array, which consisted of three 100W panels (in series, so 60-some volts input). I underestimated the efficiency of my solar panels, and found that my 100/20 controller was maxing out at 20 amps, but I wasn't getting the full rated power of the panels. It was close, but I was wondering if I could squeeze more power out of them, so I bought a 100/30 controller, and that got me 22-23 amps output.

But, that's just my experience, and I experimented with it due to Amazon's generous return policy. In the end though, I ended up keeping the small controller for our 2nd TM.....

Dave

Thanks for sharing that story Dave. I haven't paid much attention to the efficiency of the controller but it is amazing how efficient the MPPT controllers are.

I did purchase the 370 watt znshine off of Craigslist for only $120. Was a little bit leery of buying a panel off of a guy from the back of his truck but Wayne's confidence in Craigslist in general pushed me to buy it. I figured even if it didn't work at all I'm only out $120. lol.

That's been a great deal as long as there's not a reliability issue later. Considering that it's already at 215 watts at 10:15 am, and I do the math it means they would be over 330 watts at peak or maybe more if not limited by the controller.

I too am taking advantage of Amazon's return policy an am returning my 250 watt panel which I had tried earlier which topped out at 165 watts. I know it's expected for manufacturers to exaggerate panel output but that was a bit too much of an exaggeration even though the price was Ok at $225.

Meanwhile, I'm so pleased with getting over 200 watts for over 5 hours in the day, not to mention that it starts up with a few watts even before direct sunlight hits, that I'm not even in a hurry to put in the 30 amp controller. But I'm sure I will.

[Rob Culver]

Originally Posted by Rob Culver

Thanks for sharing that story Dave. I haven't paid much attention to the efficiency of the controller but it is amazing how efficient the MPPT controllers are.

I did purchase the 370 watt znshine off of Craigslist for only $120. Was a little bit leery of buying a panel off of a guy from the back of his truck but Wayne's confidence in Craigslist in general pushed me to buy it. I figured even if it didn't work at all I'm only out $120. lol.

That's been a great deal as long as there's not a reliability issue later. Considering that it's already at 215 watts at 10:15 am, and I do the math it means they would be over 330 watts at peak or maybe more if not limited by the controller.

I too am taking advantage of Amazon's return policy an am returning my 250 watt panel which I had tried earlier which topped out at 165 watts. I know it's expected for manufacturers to exaggerate panel output but that was a bit too much of an exaggeration even though the price was Ok at $225.

Meanwhile, I'm so pleased with getting over 200 watts for over 5 hours in the day, not to mention that it starts up with a few watts even before direct sunlight hits, that I'm not even in a hurry to put in the 30 amp controller. But I'm sure I will.

Just to close the loop on this thread, I installed the Victron MPPT 100/30 controller and now I am able to go much higher than 15 amps in to my battery. For a few minutes at peak I even saw it go to 24.9 amps and 345 watts. Very exciting!

Thanks Wayne for the Craigslist suggestion and thanks Dave for weighing in on the thread. Looks like I'm very boondocking ready now!

[ShrimpBurrito]

That’s great news, Rob! Gotta love squeezing out that extra power!

Dave