System almost complete, but should I switch to 24 volt?

[joshjhayes]

I'm being indecisive and could use some advice. I have my panels mounted and wired in 2 series arrays (4x 415watt panels), I have a 3000 watt renogy inverter, and 2 litime 100ah tm batteries in parallel. 2x victron 100/50 controllers are en route.

So my conundrum is that the chargers won't get full wattage in perfect sun scenario and my wiring is 1/0. I don't anticipate using full inverter power for long periods of time hence I justified the small(ish) wire. I also figure in real world I'll be lucky to get full 100 amps out of the controllers and over panelling isn't a terrible thing. But if I switch to 24v that will solve those 2 "worries" Also, to switch to 24v would I need a 12v battery or would the system run directly off a step down converter? Can I keep cheap 12v battery and charge with a cheap mppt? Or is step down converter better?

I'm within return window with Amazon so I could return inverter and even downgrade to 100/30 controllers...

 

[Q-Dog]

If you want a 24 volt system you need a 24 volt inverter and 24 volt batteries. The Victron charge controllers can run at 12 or 24 volt.

 

[ericfx1984]

I would always suggest that you switch to 24 volt or higher even

You could definitely go higher than 3,000 Watts on a 12 volt system but realistically 12 volts is the upper practical limit of a 12 volt system

And 3000 Watts on 12 volts is probably above the abilities of most people to do it right

 

[kayakingphotos]

Have you calculated the open circuit voltage of two panels in series? The colder it is, the higher the open circuit voltage is.

It is quite likely that two in series will go over 100 volts in most of the United States at the coldest recorded temperature

 

[Pi Curio]

I'm being indecisive and could use some advice. I have my panels mounted and wired in 2 series arrays (4x 415watt panels), I have a 3000 watt renogy inverter, and 2 litime 100ah tm batteries in parallel. 2x victron 100/50 controllers are en route.

Your 415W panel's Voc is too high for comfort to be used as two in series with a 100V(Voc limit) MPPT.

With two twin 100/50 SCCs that's not a problem at all in your case. You can run the panels in parallel, two per MPPT. It will even improve partial shading performance if there's a shade near the array during the day.

Also, it's best to have a battery with the native system voltage, that is, if you have a 24V system then ideally your battery should be a 24V one.

So my conundrum is that the chargers won't get full wattage in perfect sun scenario and my wiring is 1/0. I don't anticipate using full inverter power for long periods of time hence I justified the small(ish) wire. I also figure in real world I'll be lucky to get full 100 amps out of the controllers and over panelling isn't a terrible thing. But if I switch to 24v that will solve those 2 "worries" Also, to switch to 24v would I need a 12v battery or would the system run directly off a step down converter? Can I keep cheap 12v battery and charge with a cheap mppt? Or is step down converter better?

If you have a 24V battery, your inverter needs to be a 24V one as well, and vice versa.

For a 3000W Inverter, I'd go with 24V. Roughly, 3000W/24V = 125A (Smaller cables/fuses or simply said easier to manage)

For 1660W(realistically a 1360W/85% of STC rating) of solar panels @24V system voltage, a 24V 250Ah ish battery would be ideal/minimal desired, and a good match for the 3000W inverter too.

However, you could start with a single 24V 100Ah battery as long you understand you probably won't be able to utilize the inverter fully. And add more 24V 100Ah batteries in parallel later.

Plus, depending on the battery you go with, if it's a single 24V 100Ah off-the-shelf one, you might want to consider tuning down the max charging Amps. A 0.2C is ideal for LFP in general.

I'm within return window with Amazon so I could return inverter and even downgrade to 100/30 controllers...

If you have no plans for further system expansion, you could go with two 100/30 SCCs.

But, if there's even the slightest chance you might want to expand the system further one day, 100/50 will make that possible.

 

[joshjhayes]

This was my first post, and the immediate responses have been awesome and very appreciated.

I plan to keep the (2) 12v 100 ah batteries regardless, just run in series if I switch to 24v. Is a mppt solar charger feasible or desirable to use with 24v battery as source and cheap 12v batt as destination (to run RV lights etc)? I'm thinking very cheap here as I don't care too much about the 12v SLA battery I already have that came with the RV. Or can I completely eliminate the 12v battery?

I was planning to turn off pv input on cold days to reduce risk of over voltage to controllers. But i don't know why I didn't consider running in parallel to eliminate the risk. Thanks again y'all.

 

[joshjhayes]

Have you calculated the open circuit voltage of two panels in series? The colder it is, the higher the open circuit voltage is.

It is quite likely that two in series will go over 100 volts in most of the United States at the coldest recorded temperature

47.8 + 47.8 = 95.6

How high could voltage spike on cold day? I saw video where victron controller throws a fault in this case. Is the controller self protected or would it be damaged?

 

[kayakingphotos]

I was planning to turn off pv input on cold days to reduce risk of over voltage to controllers. But i don't know why I didn't consider running in parallel to eliminate the risk. Thanks again y'all.

My quick calculation would be that if you had two in series, you would hit 100 volts open circuit at a temperature of 48 degrees. Kind of hard to just unplug them any time it gets to that temp. You would have them unplugged most of the year.

Running panels in parallel isn't the best option either. If the distance between your panels and charge controller is 75 feet, you need much bigger wire if you were running two in parallel instead of two in series. If you wanted to keep voltage drop to 3% or less, you would need to use 4 AWG wire for two in parallel while if you were using two in series, you could use 10 AWG wire.

Voltage Drop Calculator | Southwire

www.southwire.com

 

[rodrick]

47.8 + 47.8 = 95.6

How high could voltage spike on cold day? I saw video where victron controller throws a fault in this case. Is the controller self protected or would it be damaged?

Voltage kills controllers, on a cold day sub zero temperatures you could see 110 or more volts

the protection for the controller is properly setting up the panels making sure you don’t exceed the max voltage, victron controllers don’t have protection mode but do have a visual alarm just watch for the smoke

 

[Q-Dog]

Since you want to use Victron charge controllers, here is a calculator they offer to figure out what charge controllers will work best for your panels. Obviously it would have been better to do all of the math before you bought anything.

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

www.victronenergy.com

 

[joshjhayes]

Is a mppt solar charger feasible or desirable to use with 24v battery as source and cheap 12v batt as destination (to run RV lights etc)? I'm thinking very cheap here as I don't care too much about the 12v SLA battery I already have that came with the RV. Or can I completely eliminate the 12v battery?

 

[mikefitz]

have my panels mounted and wired in 2 series arrays (4x 415watt panels),

For a 12 volt system , two Victron 150/60, or if you decide to go 24 volts then a single 150/60. Its the high Voc of the panels that requires the 150 volt specification. If your AC requirements are modest then a 12v system will Integrate more easily with the RV circuits.
Things to consider.
The two LI time batteries are specified at 100 amps maxinum so that will limit the usuable power output of the inverter to around 2000 amps at either 12 or 124 volts.
With a 24 volt system you need a 24 to 12 converter, ( no 12v battery required)

https://www.amazon.com/Victron-Orion-12-70A-DC-DC-Converter/dp/B01BF5BQLA/ref=sr_1_1?crid=1YPE7CUCPUS7H&keywords=Victron%2B24%2Bdc%2Bto%2B12dc%2Bconverter&qid=1701616813&sprefix=victron%2B24%2Bdc%2Bto%2B12dc%2Bconverter%2Caps%2C205&sr=8-1&th=1

The existing RV charge systems are designed for 12v, for a 24 volt house battery new chargers will be needed.
You have a 12v inverter, for a 24 volt system this will need to be replaced.

 

[SamDeleted]

I'd say there's not much point in swapping to 24v now

 

[chrisski]

Also, to switch to 24v would I need a 12v battery or would the system run directly off a step down converter? Can I keep cheap 12v battery and charge with a cheap mppt? Or is step down converter better?

Depending on system requirements, you can run a step down converter for the 12 volt side.

IMO, a 24 volt 10 amp to a 12 volt 20 amp converter would work fine. The biggestDC load you are likely to see is the 120 watt DC heater blower fan.

I have slide outs, so I went with a 24 volt 35 amp to 12 volt 70 amp converter. My trailer emergency breakaway is powered by this converter also.

EDIT: Also, there is a max discharge rate for a lithium battery, and tow may not be enough for a 3000 watt inverter.

 

[joshjhayes]

Thanks for all the help. Decided to switch to 24v and ordered new inverter and 2 150/35 victron controllers.