Unexpectant disadvantage converting from 12v to 48v??

[Blakes]

I live full time offgrid on Storm Mountain CO while building my log cabin.

Been running the following 12v system with great luck: 8 Renogy 200ah AGMs in parallel, 40amp Renogy controller, 2000w Renogy inverter/charger and 9 100w Renogy panels in parallel. The batteries are less than 6 months old, but the rest of those components are about 3 years old. This system worked great and full sun days (even in winter) it would get down to about 12.4v.

On a whim, I recently saw that Renogy has the 48v 3500w controller/inverter, so I bought it. I got it wired up yesterday. The batteries are in 2 parallel strings with 4 in series. I wired up 12, 100w panels and now have 2 parallel strings of 6 panels in series.

Today was a full sun day. I monitored the controller during full sun and it said the panels were ~125 volts and the max input amps I saw was around 8.

Now the batteries are sitting at 49.7v.

What gives? I'm running 2 more panels that I was two days ago. I'm gonna have to run the generator tonight. Had I left my existing 12v system alone, the batteries would have floated most of the day and i would not have to run the generator tonight.

Do I need more panels or??

 

[JoeHam]

Power is power so you should be fine regardless if you were before.

Remember that if you ran your 12v system at 100 amps that is the same as running your 48v system at 25 amps.

 

[MichaelK]

Something is wrong here. First, can you describe how you connected and started up the inverter? Did you connect the batteries or the solar panels first?

If you connected the panels before the batteries, the unit might have gotten "confused" by the higher then expected voltage? What I would do tomorrow morning, is do a complete shutdown, disconnecting the solar strings, and including disconnecting the batteries, then boot up the unit again on battery power only.

Only after the unit has properly booted up, then reconnect the solar input. Monitor the battery voltage just before, and again after you reconnect the solar panels. At 8-9am though, don't expect to see more than 5-6A coming off the panels. A fairly depleted battery should charge at about 52V, only raising to 57-59V when approaching full charge.

I would go into the charger settings and see what the charging volts is set to? A 48V string of your batteries would like to be charged at 57.6-59.2V. By noon though, I would expect your panels to be putting out (1200W/52V bulk charging) X 0.85lossfactor =19.6A. If the batteries are actually charging, then you won't see that amperage though. If you connect a heavy load at noon, say a 1500W toaster oven, you should see the maximal the panels can put out while the oven is on.

If you can do that, and then get back to us with the numbers you see, we might be able to help you solve your problem.

 

[Hedges]

... and 9 100w Renogy panels in parallel.

I wired up 12, 100w panels and now have 2 parallel strings of 6 panels in series.

Vmp is probably 17V, so expect 102V
Voc probably 21V, so 126V

48V 3500W Solar Inverter Charger

Renogy's 3500W 48V Solar Inverter Charger combines solar charging, AC/generator battery charging, and battery inverting into one convenient solution. Free shipping

www.renogy.com

"

Algorithm: MPPT

MPPT Voltage Range: 60 ~ 115V

"
"Max PV Input Voltage: 150V (145V recommended)"

You see OK there.

Today was a full sun day. I monitored the controller during full sun and it said the panels were ~125 volts

Near Voc? Double-check my Voc calculation, suggests no current draw.

Today was a full sun day. I monitored the controller during full sun and it said the panels were ~125 volts and the max input amps I saw was around 8.

Is that 8A from PV (1000W) or into battery (400W)?

Either way, should be charging. Unless that is discharge not charge current.

 

[Blakes]

Something is wrong here. First, can you describe how you connected and started up the inverter? Did you connect the batteries or the solar panels first?

If you connected the panels before the batteries, the unit might have gotten "confused" by the higher then expected voltage? What I would do tomorrow morning, is do a complete shutdown, disconnecting the solar strings, and including disconnecting the batteries, then boot up the unit again on battery power only.

Only after the unit has properly booted up, then reconnect the solar input. Monitor the battery voltage just before, and again after you reconnect the solar panels. At 8-9am though, don't expect to see more than 5-6A coming off the panels. A fairly depleted battery should charge at about 52V, only raising to 57-59V when approaching full charge.

I would go into the charger settings and see what the charging volts is set to? A 48V string of your batteries would like to be charged at 57.6-59.2V. By noon though, I would expect your panels to be putting out (1200W/52V bulk charging) X 0.85lossfactor =19.6A. If the batteries are actually charging, then you won't see that amperage though. If you connect a heavy load at noon, say a 1500W toaster oven, you should see the maximal the panels can put out while the oven is on.

If you can do that, and then get back to us with the numbers you see, we might be able to help you solve your problem.

Thanks man

I definitely understand at least some basics...I always (always) connect the batteries first.

I WFH, so I'm here all day looking at this thing. Right now (at 7:30am) the sun is coming up. I went outside and disconnected both parallels strings and checked VoC (is that correct) by simply plugging the volt meter into the mc4 cables. Both strings are at ~122V DC right now.

I'm a bit confused as to which menu item displays how much power is going from the panels to the batteries.

The display says my batteries are half charged and the panels are charging now. This is after running the 2000w generator last night (inverter set for 5amp charging rate). It only hold 1 gallon of gas, so the generator only ran for around 3 hours or so.

 

[Blakes]

Ok so continuing troubleshooting this thing.

Earlier this morning the panels themselves were at ~122 VoC (at the panels).

Then I flipped through the screens on the unit and found the PV input voltage was at 61 and output was 1.8amps. I was like 'huh' why is the input voltage at only 61....

I disconnected the mc4 connectors from the combiners that I have at the box (parallel) and tested each one. Both pairs were at ~125v. Interestingly enough, I tested voltage at the inverter PV input. 6.1v DC (with nothing connected to PV input).

I connected the mc4 connectors and now the inverter says PV input voltage is 112v and making 2amps. Maybe the connection wasn't good at the combiners?

Seems good now.

 

[A.Justice]

I could be misunderstanding what's going on, but is it possible that the higher voltage makes the amperage lower, and you just aren't used to the new numbers?

For example, if you have 900w @ 12 volt, it's 75 amps, and the controller would show 75a going in. If you have 900w @ 48 volt, it's ~19 amps. It's the same amount of power going in to the batteries, but the increase in voltage means that the amperage stays lower.

 

[Hedges]

I connected the mc4 connectors and now the inverter says PV input voltage is 112v and making 2amps. Maybe the connection wasn't good at the combiners?

Seems good now.

Only good if battery charge is near full, in absorption phase not bulk phase.

112V is half way between what I estimated for PV string (6s) Vmp and Voc
Your 125 Voc measurement is very close to my 126 Voc estimate
Double-check what Vmp should be according to label.
I think at 112V it is getting a fraction of the power it should.
Drawing 2A is 20% of what you should get with two strings of 100W panels (about 5A Imp each)

 

[Blakes]

The angle of the sun right now is coming in at a bad angle to the panels, but 125v 7.9amp is what the inverter says.

Is that about right?

 

[Hedges]

7.9A sounds OK, because panels are probably 5A each and 2 strings in parallel.
I don't understand 125V at 7.9A because it was 125Voc at zero amps.

125V x 7.9A = 988W, perfectly good for 12x 100W (STC) rated panels.

Maybe it's just higher Voc on a cold morning.
Seems like good performance now.

Since you suspected flaky connections in combiner box, you could check with DMM across connections or use an IR thermometer.
Keep checking the monitor, see if it goes back to unexpected behavior.

 

[HRTKD]

7.9A sounds OK, because panels are probably 5A each and 2 strings in parallel.
I don't understand 125V at 7.9A because it was 125Voc at zero amps.

125V x 7.9A = 988W, perfectly good for 12x 100W (STC) rated panels.

Maybe it's just higher Voc on a cold morning.
Seems like good performance now.

Since you suspected flaky connections in combiner box, you could check with DMM across connections or use an IR thermometer.
Keep checking the monitor, see if it goes back to unexpected behavior.

Isn't it 7.9 amps @ 48v on the output side?

 

[Blakes]

I am thinking about increasing voltage by adding another panel in each series string.

That should put me somewhere in the 140v range.

so that would be two sets of 7 100w panels in series.

It's still right now under full sun saying ~125v PV in and 8amps

 

[JoeHam]

If your MPPT max input is 150v don’t put 140v on it in Colorado.

A cold day will likely smoke it.

 

[TomC4306]

According to the Midnite Solar calculator you should be getting at the Mppt output around 57.6 volts at 20.8 amps. Charging around 100 Ah with 5 hours of good sun. The input to the Mppt (from panels) should be about 102v at 11.4 amps. assumes 6s2p Renogy 100w panels. I think you have a bad connection somewhere on the solar side.

 

[Forbisher]

I am thinking about increasing voltage by adding another panel in each series string.

That should put me somewhere in the 140v range.

so that would be two sets of 7 100w panels in series.

It's still right now under full sun saying ~125v PV in and 8amps

Most Renogy panels are 21.x Voc so 7 in Series is 147V not 140V

 

[Blakes]

Thanks for all the help. This is my first time dealing with 48v and this brand new renogy 3500w controller/inverter.

6s2p of renogy 12v 100w panels is all this controller can handle. 7s2p causes a fault even in low sun.

I'm up to 6s3p now. All the compact mono panels. This seems to work OK. Still building the rack out of unistruts.

Also have the BT-2 module and the app is worthless.

I don't like the way this thing deals with ac input from a generator. I've played with all the different modes and settings. It seems to favor ac power and runs everything off that ac input and also tries to charge the batteries. Cuts out a lot with my yamaha ef2000is and even the 7200w yamha industrial generator.

Overall I have mixed feelings about my jump to 48v. I've spent a lot of money and even gotten a bunch of new panels and I honestly feel like my old 12v system with 8 100w panels was just about as good.

I have more that needs to be done though.

 

[RStone13]

The angle of the sun right now is coming in at a bad angle to the panels, but 125v 7.9amp is what the inverter says.

Is that about right?

125v *7.9a=987.5watts You said you are using 12- 100w (1,200w) panels, looks good to me

 

[Yurtdweller]

I am still at 12v, so not sure how much good this comparison is, but otherwise, very similar kit. 8x100watt 12v panels, 2kw inverter on 12v 100ah lifepo4 battery, Renogy Rover cc, and my system top record is 45 amps, which would, of course, equal 11.25 amps at 48 volts. Obviously, this exceeded Rover parameters, but it was during the Texas snowstorm big freeze we just had, so low temps and snow reflection probably boosted everything a bit. Your system should be capable of producing 16amps@48v, depending on cc, of course.

 

[ewishki]

Thanks for all the help. This is my first time dealing with 48v and this brand new renogy 3500w controller/inverter.

6s2p of renogy 12v 100w panels is all this controller can handle. 7s2p causes a fault even in low sun.

I'm up to 6s3p now. All the compact mono panels. This seems to work OK. Still building the rack out of unistruts.

Also have the BT-2 module and the app is worthless.

I don't like the way this thing deals with ac input from a generator. I've played with all the different modes and settings. It seems to favor ac power and runs everything off that ac input and also tries to charge the batteries. Cuts out a lot with my yamaha ef2000is and even the 7200w yamha industrial generator.

Overall I have mixed feelings about my jump to 48v. I've spent a lot of money and even gotten a bunch of new panels and I honestly feel like my old 12v system with 8 100w panels was just about as good.

I have more that needs to be done though.

It might be just the Renogy unit being buggy. Will had issues with it and didn't like it on his YouTube review of it. I wanted one also because they list it as marine. To my knowledge it is the only marine rated all in one. I have avoided it because of Will's experience with it. MPP told me they have a marine rated one coming out in a couple months. I am kind of stuck as I cannot wait a couple months because I need to get the system up and running for a passage through Indonesia in July. I was considering still trying to use the Renogy solution but after reading your thread now I am back to wanting to avoid it.

 

[Blakes]

I don't know if my problem is the 8, 200ah renogy agm batteries, or their 48v controller/inverter.

I'm up to 4P6S of panels now. 2.4kw

I will admit that we've had an usually snowy season that is now turning to rain, so more clouds than usual.

But I still think that my old setup with 10 6v Duracell gold cart batteries, 8 12v 100w renogy panels and 40amp renogy controller and 2000w inverter was just about as good as my setup is now.