High (250V) Maximum Voltage Ratings?

[John Frum]

So I seem to be a bit confused at the moment. Looking at charge controllers and I've noticed that Victron has controllers that are rated up to 250V "Maximum PV open circuit voltage". My main question is, is this high voltage rating for large Solar systems that are all wired in Series? I was planning on wiring my panels in parallel to keep the voltage at 12V. Is one method better than another?

What is the benefit of keeping your panel voltage at 12 volts?

 

[tmckenna]

What is the benefit of keeping your panel voltage at 12 volts?

Well I guess previously I was under the assumption that the simplest wiring setup would just be a bunch of 12V panels wired in parallel, the victrons 250V rating made me question exactly that.

 

[tmckenna]

In the Victron schematic, I see positive wire connecting LFP battery, starter battery, alternator, inverter.
Negative of LFP battery goes through BMS.
(Some systems might have negative or chassis tied, common, but not this one)

If you connected a DC load directly from LFP to chassis, it would bypass BMS.
Orion is shown as an isolation circuit which instead provides a positive connection that can be controlled, disconnecting load from LFP if necessary.

Note "Other DC Load" with positive and negative connections that you could use without needing Orion. That has negative isolated fro chassis.

Out of curiosity what kind of device would fall into the generic "DC Loads" category (without the Orion involved) and which would fall into the "DC Loads with minus connected to chassis" category (with Orion involved)?

 

[Hedges]

Out of curiosity what kind of device would fall into the generic "DC Loads" category (without the Orion involved) and which would fall into the "DC Loads with minus connected to chassis" category (with Orion involved)?

DC load with minus connected to chassis would include anything built that way, like typical automotive accessories. Driving lights and car stereos often have negative attached to their mounting bolts, for instance.

If a device has separate negative wire, just check with a meter that it isn't also connected to frame. If isolated, it could be used without Orion.

 

[the_colorist]

I paid close to $1000 for my 250/100.

Ouch, so 'spenive. These days they aren't quite that high depending on who a person is able to buy from/get a discount. And the BlueSolar models (non-BT) are cheaper yet than their SmartSolar brethren but only go up to 150V. BT is generally not needed if you have a GX device.

Out of curiosity why would I need that if the GX has battery Voltage and percentage displayed.

The 702 is a great way to monitor FLA and pretty much any battery (including Lithium) that doesn't have a CAN bus interface. And it will improve the life and performance of the system via DVCC. If you're using a CAN-enabled battery or BMS however, you generally don't need the BMV-702. The reason for this is that the BMS monitors the voltage and current of the pack and transmits that information to the GX device (Cerbo/Venus etc). Not to contradict anyone, just expanding on options.

If you do need to monitor voltage/current and you have GX device, the SmartShunt can be a cheaper alternative to the BMV.

Well I guess previously I was under the assumption that the simplest wiring setup would just be a bunch of 12V panels wired in parallel, the victrons 250V rating made me question exactly that.

Is this is an automotive conversion/installation? If you need to go 12V and you're looking to operate around 1000W of panels that might vary in performance/shading, a cheaper option that will also improve performance might be to use multiple smaller controllers such as the BlueSolar 75/15. Assuming 200-220W panels. One controller per panel. Around $89 ea at PKYS. 5 would come to around ~$450 and get you around 1,100W @12V.

If this is a ground mount array or an array that is unlikely to see variable shading, a larger controller might be more appropriate. I would personally avoid the 250V models for a 12V bank. The larger disparity between input and output voltages, the lower the efficiency. And the cost per watt jumps considerably between the 150V models and the 250V models. A recommendation might be 1x 100/30A and 1x 100/50A. Will get you around 1,140W @ 12V. If you buy from PKYS, you could be looking at around ~$500.

Another advantage of the smaller controllers (75/15 etc) is they have an automotive fuse built-in. Saves some $ and hassle adding one.

 

[the_colorist]

I just realized when I scanned the thread I didn't see you said 7x 200W.

So you're looking at 7 of the 75/15. $623

OR

2 of the 100/50A. $590

 

[tmckenna]

I just realized when I scanned the thread I didn't see you said 7x 200W.

So you're looking at 7 of the 75/15. $623

OR

2 of the 100/50A. $590

Thank you for the detailed replied. This setup would be on a camper/RV. I'm not necessarily dead set on 7 200W panels, but I'd like to get as close to 1500w as I can. Really just looking for the most cost efficient way to setup a good performing system around 1500w max output. I understand that because I can't adjust the angle as the sun moves that I'll rarely see max output but just in general Id like to be around that 1500 number.

 

[the_colorist]

Makes sense. If you can go for some higher wattage panels that will fit, you'll likely get more power per sq ft. How wide/long is the camper/rv? Or at least the area you would like to place the panels in?

 

[Hedges]

Summer when sun is nearly direct overhead you will get maximum output.
But off season, off angle, production will be much lower.
If you installed even half as much PV but did a seasonal tilt it would produce more power under those conditions.
Portable panels hung off the side would be one way. A single panel on the side would produce more than a covered rooftop for some seasons and latitudes.
If you have an estimate of power needs vs. season you can plan better.

 

[tmckenna]

Summer when sun is nearly direct overhead you will get maximum output.
But off season, off angle, production will be much lower.
If you installed even half as much PV but did a seasonal tilt it would produce more power under those conditions.
Portable panels hung off the side would be one way. A single panel on the side would produce more than a covered rooftop for some seasons and latitudes.
If you have an estimate of power needs vs. season you can plan better.

Id be using it mostly in the summer. The main application would be beach camping here on long island.

 

[tmckenna]

Makes sense. If you can go for some higher wattage panels that will fit, you'll likely get more power per sq ft. How wide/long is the camper/rv? Or at least the area you would like to place the panels in?

When its finished the room of the camper will be something like 28'x8'

 

[Deleted member 23531]

RV-style panels generate about 180-190W/m^2, so 28' x 8' is plenty of space and could generate something around 3.6kW, unless I made some huge math mistake.

If you already bought a Victron MPPT 250|100, then you could do 6x24V panels in series but definitely not 7x (since Voc ~40V). That would be cutting it pretty close at 240V nominal and slightly higher in cold but sunny weather. A safer wiring option would be 2 parallel groups of 4 = 8 panels which would keep the voltage at 160V nominally and the PV current pretty low still. As an example I recently ordered 210W 60-cell panels which are designed for 24V systems; it's 33.9V at Pmax and roughly 40Voc at 25degC. If you get bigger (2 m^2) panels you could need fewer of them, since you have the space. The ones I ordered are a bit over 1 m^2 (65" x 27").

The problem with your plan, however, is that 100A is not enough if you insist on a 12V battery. As an example 7 * 210W / 12V = 122.5A. You should use a 24V battery and then you're all set with your MPPT 250|100 as the max charge current would be less than 100A.

 

[Hedges]

If you already bought a Victron MPPT 250|100, then you could do 6x24V panels in series but definitely not 7x (since Voc ~40V). That would be cutting it pretty close at 240V nominal and slightly higher in cold but sunny weather. A safer wiring option would be 2 parallel groups of 4 = 8 panels which would keep the voltage at 160V nominally and the PV current pretty low still. As an example I recently ordered 210W 60-cell panels which are designed for 24V systems; it's 33.9V at Pmax and roughly 40Voc at 25degC.

Pretty close? Too close.
40V x 6 = 240V
What's the temperature coefficient of voltage for the panels, maybe -0.4%/degree?
Compared to 25 degrees C, 15 degrees C would be -10 degrees.
-10 x -0.4% = +4%
240V x 1.04 = 250V, already at the limit.
If temperature one morning was below 15 degrees C it would go over voltage.

Use maximum 5 of those panels in series.
As you say, if 8 total then groups of 4 is good. 4s2p.

To keep it simple or if you don't have complete specs for the panel, assume Voc can be 20% higher than shown on label.
40V x 1.2 = 48V
5 x 48V = 240V, safely below 250V
6 x 48V = 288V, above 250V so not OK for that charge controller.

 

[Deleted member 23531]

Yeah, that would be a problem: the temperature coefficient is 90mV/degC or about half what you estimated but still it would go over 250V with 6 panels. I think OP should do 4s2p.