4x100w panels in parallel - to fuse or not to fuse

[dsaint1884]

I have the Renogy 400w solar kit. The panels have:

15a max series fuse rating
Short Circuit Current (ISC) 5.21a

If I run the 4 panels in parallel I'd be up to 20.84a (5.21x4). If one of the panels shorts and the other three panels decide to take the path into that panel they would only be pushing 15.63a (5.21x3 good panels) right? So that 15.63 is right inline with the 15a max series fuse rating.

Their website seems a bit contradictory to me. It shows a diagram of the panels in parallel with a 10a fuse on just one panel (not sure what that does) but then also says 'if you choose to connect in parallel, you can use three pairs of Solar Y Branch Connectors to connect four panels in two by two, and then parallel again; do not use an in-line fuse in parallel circuits."

New 400 Watt 12 Volt Solar Premium Kit W/MPPT or REGO Solar Charge Controller

4* 100W Eclipse Monocrystalline Solar Panels totaling 400 Watt, 1* 40 Amp MPPT Charge Controller, 2* 20' Solar Extension Cables, 1* Solar Adapter Kit 9'' in length, and 4 Sets of Z brackets for Mounting

renogy.com

I suppose I could add in a 10a fuse on each positive line from the panel, beyond the short circuit current but enough to catch the 15.63 short circuit ratings, but is adding a fuse on each panel positive wire, 4 in total, really necessary?

 

[camelCase]

15.63 amps is greater than 15 amps. Sorry if I sound like a jerk but the rating is for 15 amps, not 15 amps and little bit more.

If you wired them 2s2p, then you would not run over the current limit and wouldn't need to fuse the panels.

 

[dsaint1884]

15.63 amps is greater than 15 amps. Sorry if I sound like a jerk but the rating is for 15 amps, not 15 amps and little bit more.

If you wired them 2s2p, then you would not run over the current limit and wouldn't need to fuse the panels.

Ha, not sounding like a jerk at all - just confirming the facts that I wasn't hoping to hear. The fact that their own website specifically says it's not required to have a fuse for parallel on this kit is what's throwing me off, but I hear what you're saying.

If I go 2s2p then it works for amps. It does take my open-circuit voltage from 24.3 (parallel) up to 48.6 (2s2p). I was hoping to keep the voltage lower because it seems like it would be a safer system, but maybe I'm just telling myself that about the voltage and I'm over thinking the safety factor between a parallel and 2s2p setup.

 

[sergea]

Ha, not sounding like a jerk at all - just confirming the facts that I wasn't hoping to hear. The fact that their own website specifically says it's not required to have a fuse for parallel on this kit is what's throwing me off, but I hear what you're saying.

If I go 2s2p then it works for amps. It does take my open-circuit voltage from 24.3 (parallel) up to 48.6 (2s2p). I was hoping to keep the voltage lower because it seems like it would be a safer system, but maybe I'm just telling myself that about the voltage and I'm over thinking the safety factor between a parallel and 2s2p setup.

use mc4 connector with embedded fuse if you want something simple.

 

[12VoltInstalls]

fact that their own website specifically says it's not required to have a fuse for parallel on this kit is what's throwing me off

Well that’s another example why I throw rocks at Renogy’s windows every chance I get. Their support stinks, and their directions aren’t too trustworthy either I guess.

 

[time2roll]

At this voltage and current level I would skip the fuses.

 

[dsaint1884]

Well that’s another example why I throw rocks at Renogy’s windows every chance I get

Sounds like you are in the fuse each panel camp since I'd be above 15amps. Instead of rocks I'll order a box of fuses and we can throw them as subtle hints until they update their website. :|

With the short-circuit current at 5.21 amps, would you fuse with the 10a inline connecter like they provided and has a bit of a buffer or go to 15a on the fuse, which is the max series fuse rating?

 

[dsaint1884]

use mc4 connector with embedded fuse if you want something simple.

Simple is good. Would you simply order some inline fuses for each panel then? They provide one 10a, so I'd need three more. Would you use a 10a fuse like they provided which is > than the short current at 5.21a or 15a fuse (the max series fuse rating)?

 

[12VoltInstalls]

Simple is good. Would you simply order some inline fuses for each panel then? They provide one 10a, so I'd need three more. Would you use a 10a fuse like they provided which is > than the short current at 5.21a or 15a fuse (the max series fuse rating)?

Would you use a 10a fuse like they provided which is > than the short current at 5.21a or 15a fuse (the max series fuse rating)?

When I was parallel I used 20A rated MC4 fuseholders with 8A fuses; and bought more 8A fuses for them. Never needed them.
15A is biggerish than 8A and your panels are a possible 5.5A at 18V each when it’s cold out.

 

[dsaint1884]

When I was parallel I used 20A rated MC4 fuseholders with 8A fuses; and bought more 8A fuses for them. Never needed them.
15A is biggerish than 8A and your panels are a possible 5.5A at 18V each when it’s cold out.

Ok, thank you. Helpful perspective. They included a 10a fuse, I'll go with 3 more of those and call it good. Keeps me below the max series fuse rating but over the possible 5+ amps the panels could ever generate in proper working order while in 4p. Thank you.

 

[camelCase]

Looking at that kit, it has an MPPT controller, so there's no reason at all to worry about the higher voltage of a 2s2p panel configuration. That's exactly what MPPT controllers are designed for - converting high voltage/low current from the panels into the optimum lower voltage/higher amperage for charging the batteries.

 

[dsaint1884]

Looking at that kit, it has an MPPT controller, so there's no reason at all to worry about the higher voltage of a 2s2p panel configuration. That's exactly what MPPT controllers are designed for - converting high voltage/low current from the panels into the optimum lower voltage/higher amperage for charging the batteries.

Thank you for taking the time to check that out and I agree the MPPT can handle it. Perhaps I'm mis-guided but when I hear about how there's different concerns for safety at 50v DC then I thought stepping up to a 2s2p system which produced higher voltage would increase risk on the solar side of the controller if I happen to touch a short or something. Moving the sytems from 24.3v Voc (4p) to 48.6 Voc (2s2p) seemed like a riskier setup. Maybe I'm over thinking it?

 

[camelCase]

To answer your question, I would say first of all, you should always avoid contact with any type of live current.

That said, OSHA requires safety precautions with DC current over 50 volts. Old fashioned telephone systems limited DC voltage to 48 volts as that was considered the max safe level (plus it was a convenient voltage for lead acid backup batteries). All that to say you're not significantly increasing electrocution risk by going from 24V to 48V.

 

[PVorBust]

Looking at that kit, it has an MPPT controller, so there's no reason at all to worry about the higher voltage of a 2s2p panel configuration. That's exactly what MPPT controllers are designed for - converting high voltage/low current from the panels into the optimum lower voltage/higher amperage for charging the batteries.

+1
Unless you really need low voltage, higher voltage has many benefits including thinner cable for the same loss and increased hours of useful output per day.

As for fuses, under what circumstances would a fuse in the PV feed blow?

 

[dsaint1884]

As for fuses, under what circumstances would a fuse in the PV feed blow?

I had read this which explained it to me:

How/When to Fuse a Solar Panel Array

This blog post is going to teach you how to determine when and if you need to add in-line fuses when designing a camper solar array. Sometimes you need to fuse your solar array, and

www.explorist.life

 

[12VoltInstalls]

ybe I'm over thinking it

Yes

concerns for safety at 50v DC then I thought stepping up to a 2s2p system which produced higher voltage would increase risk on the solar side of the controller if I happen to touch a short or something.

this is why you have disconnects

 

[dsaint1884]

this is why you have disconnects

By disconnects do you just mean a switch or a fuse that lets me isolate the PV from the MPPT connection/system if needed?

In my head I was thinking of the scenario where the positive and negative wires both have a short touching the van. If I touch the metal van then I'd be in the circuit. I'd rather discover those shorts at 24.3 volts than 48.6. Or in that scenario is the solar panel reaching it's short circuit current and voltage drops to zero?

 

[12VoltInstalls]

48.6.

That won’t likely kill your but depending on the chemistry of your skin sweat could provide varying degrees of…discomfort

 

[12VoltInstalls]

disconnects do you just mean a switch or a fuse that lets me isolate the PV from the MPPT connection/system if needed?

A double DC-rated breaker or properly rated dc switch

 

[dsaint1884]

A double breaker or properly rated dc switch

Something like this is what I had planned to use:

https://smile.amazon.com/dp/B000MMC914?psc=1&ref=ppx_yo2ov_dt_b_product_details

In 2s2p I'd be at 48.6Voc, and this switch is only rated for 48v max, so I'd need something with a higher rating, but conceptually it's just the way to disconnect the panels from the MPPT.