Community Forums

AlanTerry · 04-06-2022, 12:44 PM

Hi Guy’s I have been learning a lot reading this and the Boondocking section here. I am using Hightecc Solar 200 watt 36 cell panels Vmpp 21.052V, Impp 8.50a, Voc 24.338V, Isc 9.87a. Due to where I am coming in from roof wire from combiner box is approx 40’. Using 8 awg stranded welding cooper wire. I am wiring 5 panels in series. I have found my Voc max = 146.01, max circuit current =15.3972 ( so I would use a 20 amp fuse between panels and solar controller?
Between Solar controller and batteries ( agm 6v 205 w 12 v wired series parallel)
What should fuse be? What are the calculations ?

Yhanks in advance?

DavidEM · 04-06-2022, 01:07 PM

There is no code that requires (or is it even necessary) to put any fuses between the solar panels and the controllers. The panels are considered a "self limiting current source". It can never, ever go above Isc.

There is a requirement to size the wires to handle the maximum current. But that is a very small bar. 14 gauge can handle the 9.87A Isc.

What you want to do is to size the wire so that you get a reasonably small voltage drop from the panels to the controller. Using 40' and an Isc of 9.87 and a maximum voltage drop of 0.5 V you need #8 wire and no fuses.

BTW five panels wired in series is rather dangerous IMO. 146 volts can kill you.

David

Dan-Dekalb · 04-06-2022, 01:25 PM

A couple of things to remember, you're talking about installing 1,000W of solar power. If you put them all in series, if any one single cell is shaded, it will drastically reduce the current flow and delivered power. A low sun causing the AC to shadow a few cells could cause your entire array to stop producing any significant energy. A tree overhead waving across a few cells will do the same thing.

The 2nd thing to remember: Most of us have been bit at one time or another in our lives by power coming from an outlet. That's AC power, and alternating current direction makes it easier to release your muscles. The same voltage in DC tends to contract the muscles and prevents you from letting it go. There are significant safety concerns you need to make sure are covered.

Ideally if you can, it would be better to run additional wires to the panels and try to keep operating voltage in the 48 volt range. I work on Telecom systems at these voltages, and while you still need to respect them, they are much more forgiving. What's more, if you can split them across 2 or 3 MPPT charge controllers, you'll optimize energy harvest on a per-group basis.

DavidEM · 04-06-2022, 02:37 PM

David

DavidEM · 04-06-2022, 02:42 PM

Five panels makes it difficult to wire them in series/parallel to a single controller. This keeps the voltage down to 48 or below but increases the current over all series wiring. You could wire four in series/parallel to one controller and wire the other panel to a smaller controller.

David

AlanTerry · 04-08-2022, 08:11 AM

David and Dan thanks for mentioning that my Voc max of 146.01 can kill me. Haven’t seen that mentioned in any Solar discussion. I still plan on wiring in Series though and plan to cover up my panels as well as add a breaker between my solar controller and panels, as well as a switch/ fuse between solar controller and the batteries to kill power before working on the system. So killing the power should protect me?

Persistent · 04-08-2022, 09:09 AM

Solar controller to battery does need a breaker or fuse. It will probably be a 12 volt circuit and will require a larger capacity cable and circuit breaker. It may be 12 volts at about 90 amps. 4 Gauge should be good for 4 feet.
(5 X 200) / 12 = 83.33

8 gauge wire can carry 45 to 55 amps, so a 50 amp fuse or circuit breaker in that 40' wire would work.

Older designed solar panels would stop working if even a portion of the panel was shaded. Older panels in series would stop the whole series from working in shade.

The shade sections of the panels would short the power from all the other sections or other panels in series.

Newer designs have diodes in the panels. The each section has a diode that prevents back flow of current.

hclarkx · 04-09-2022, 01:01 PM

Quote:

Originally Posted by AlanTerry

Hi Guy’s I have been learning a lot reading this and the Boondocking section here. I am using Hightecc Solar 200 watt 36 cell panels Vmpp 21.052V, Impp 8.50a, Voc 24.338V, Isc 9.87a. Due to where I am coming in from roof wire from combiner box is approx 40’. Using 8 awg stranded welding cooper wire. I am wiring 5 panels in series. I have found my Voc max = 146.01, max circuit current =15.3972 ( so I would use a 20 amp fuse between panels and solar controller?
Between Solar controller and batteries ( agm 6v 205 w 12 v wired series parallel)
What should fuse be? What are the calculations ?

Yhanks in advance?

Your instinct to put a fuse between the panels and the solar controller is good. Hundreds of watts flowing into a short inside the solar controller could create lot of heat and damage even beyond the solar controller. Unfortunately, it's not practical to size a fuse that will pass up to 8.5 amps of current and blow on 9.87 amps of short-circuit current (or less since the resistance to the short inside the solar controller might result in an even lower short-circuit current). So, it's not a perfect world. Some things we live with.

Your solar controller manual may instruct you to open a switch on the panel side of the controller before opening a switch between the solar controller and battery to shut down the solar system. And to switch the battery side first when booting up the solar controller. This makes it desirable to have both sides switched and labeled so the process is easy.

Ideally you could find a place for a sixth panel (you can't have too much solar) and group them in two sets of three series panels each with its own solar controller. Less hazardous voltages, higher reliability, more solar, better MPPT performance, etc.

DavidEM · 04-09-2022, 02:13 PM

Quote:

Originally Posted by AlanTerry

David and Dan thanks for mentioning that my Voc max of 146.01 can kill me. Haven’t seen that mentioned in any Solar discussion. I still plan on wiring in Series though and plan to cover up my panels as well as add a breaker between my solar controller and panels, as well as a switch/ fuse between solar controller and the batteries to kill power before working on the system. So killing the power should protect me?

No, it is the panels that are putting out the 146 volts, not the battery. When you touch the wire coming from the panels, it will shock you with 146 volts.

You would need to disconnect the 5 panels from each other to be safe.

David

vsheetz · 04-09-2022, 02:31 PM

Fyi -

As to whether to fuse and where a PV array depends on the array configuration and panel specifications.

At a minimum there should be service disconnect before the solar controller(s). I like to use a circuit breaker(s) for that disconnect.

Here's more details.

From the article.
...KEY TAKEAWAY: This means that if the Short Circuit Current of the entire solar array is GREATER than the Maximum Series Fuse Rating on the*solar panel*label, each parallel connected panel (or series string) must be fused...

https://www.explorist.life/how-to-fu...y-not-need-to/

vsheetz · 04-09-2022, 02:37 PM

Fuse for the wire size, size wire for the load.

In your case I see #8 from PV array to controller with about 10a current. So a 20a PV circuit breaker would do. Using a circuit breaker also serves as a service disconnect.

I don't see noted the wire size or controller size to battery bank. With 1000w PV and 12v battery bank I would expect maybe #4 wire and a 100a or so circuit breaker.

AlanTerry · 04-12-2022, 06:04 PM

thanks Hclarkx and vsheetz for your answers. I have not installed my solar yet but appreciate the responses.

Persistent · 04-13-2022, 06:43 AM

Quote:

Originally Posted by AlanTerry

David and Dan thanks for mentioning that my Voc max of 146.01 can kill me. Haven’t seen that mentioned in any Solar discussion. I still plan on wiring in Series though and plan to cover up my panels as well as add a breaker between my solar controller and panels, as well as a switch/ fuse between solar controller and the batteries to kill power before working on the system. So killing the power should protect me?

I see lots of good advice above.

For more complete instruction, always read and follow device manufacture's installation instructions and specifications.

Read solar panel installation instructions and specifications.

Read solar controller instructions for required input and output wiring requirements.

Get expert review from manufacture for large or unusual systems. Requirements for switches on input and output as well as fuses and circuit breakers may be different for different designs.

Typical RV solar installations are recommended to be 48 volts from the panels or less. Higher than that can result in catastrophic failure of batteries.

Drop-in Li battery BMS have had catastrophic fails when the solar controller fails while using high voltage. Lead acid batteries can also fail with serious results.

Please read this article for a better explanation.
Lithium Battery Systems
https://marinehowto.com/drop-in-life...ated-consumer/
It also contains a little info about solar that will be useful.

If you are going to use Li batteries, you should probably get advice from the Li battery manufacturer before you settle on a solar system with Li battery design. Different drop-in Li batteries have different requirements.

TacomaJoe · 04-13-2022, 08:38 AM

Two thoughts, what is the max voltage your controller can accept and have you factored the low temperature rating into the equation?

For the experts, where do you install a fuse between the controller and the battery. If the fuse is at the controller and there is a short between the fuse and the battery, there is no protection. Fuse both ends?