Solar(s) Panel(s), wich choose?

[Gordon in Idaho]

Gordon (funny name),
Page 6 of THIS manual :
http://www.windynation.com/cm/P30L%2...0Manual_R1.pdf
says 40 amp fuses for all positive wires on a 30amp controller and that's what I went by. However, what you say makes since to me, although the Renogy manual does state that the fuse on the battery line should match the amp rating of the controller.
Maybe an expert can chime in here and explain this conflicting information?

Gordon

[Raz]

Originally Posted by gordon2

, I never exceeded 6.7 amps from the panel, so even a 10 amp would be fine.

That's what I would use. I'd put it between the controller output and the battery, on the positive wire, close to the battery. This protects the wires, etc. from high current from the battery in the event of a short. Raz

[gordon2]

Originally Posted by gordon2 ... I never exceeded 6.7 amps from the panel, so even a 10 amp would be fine.

Originally Posted by Raz

That's what I would use. I'd put it between the controller output and the battery, on the positive wire, close to the battery. This protects the wires, etc. from high current from the battery in the event of a short. Raz

Just to be clear, I am talking about 15 amp fuse (or 10) between a single 100 watt panel and the controller. The wiring is 10 gauge so i could use a higher rating except that the panels spec sheet calls for 15 - no doubt to protect the more delicate wiring in the panel. Renogy and other manufactures have more information about fusing for mutliple panels.

Elsewhere in the trailer's circuits different fuses are needed. Since my solar controller is basically wired in parallel with the converter (to the battery), the trailer's original wiring and fusing is intact*. Fusing is added as needed for the additional hardware.

* Not technically correct as I have upgraded from 10 g to 8 g wiring to the battery and put a better main fuse on the battery, but the methodology is unchanged for the original wring.

[gordon2]

Giles picked out a fine basic system IMHO and Renogy is a trusted brand.

I have just started using a 100 watt Renogy panel and I am pretty happy with the results so far, but a lot depends on your power usage and length of stay, weather, and on and on...

I also have the TriMetric meter and I think its a very good idea to have a battery usage meter. If you don't, how will you know how much power you have used or how much the solar has put back? The meter helps me get the most out of a modest system. For example, it tells me when the solar panel is collecting more energy that the charging and current level of use requires. This is the best time to use this otherwise "wasted" energy to charge cell phones, etc.

Also BTW, in the Amazon listing for the unit Giles bought.. you can see the panel spec sheet that says a MAX 15 amp fuse for the panel itself. Same as mine.

Giles, 20 feet of cable might be a bit much depending on the gauge. If you are mounting the panel on the camper try to keep the runs as short as possible. If making a portable rig, 14-15 feet of 10 gauge is about as far as you can go before the power loss becomes more of an impact than you would want. Plenty of charts on line to help you figure out what size wire to limit the power loss to 3% or so, which is the recommendation.

[Gilles]

Gordon, I downloaded and read the document Renogy seems very well explained.

If I have doubts for some editing, I have a friend electrician who will certainly be able to direct me there.

I give you details when I have received and installed the system.

Thank you,

[Byron Kinnaman]

Originally Posted by Gilles

Gordon, if I understand well, one 40 amp fuse on the positive before the controller and one 40 amp fuse on the positive after the controller...


Sent from my GT-P5210 using Fiberglass RV mobile app

I hope you have wire large enough to handle 40 amps. Your 20 amp trailer wiring will protect the 40 amp fuses. Look out for fire.

[Jon Vermilye]

Originally Posted by Byron Kinnaman

I hope you have wire large enough to handle 40 amps. Your 20 amp trailer wiring will protect the 40 amp fuses. Look out for fire.

That is an important consideration. While the panel & controller will never produce 40 amps, remember the fuse is also protecting against a short between the battery & the controller, i.e. 100's of amps available from the battery.

[Byron Kinnaman]

Originally Posted by Jon Vermilye

That is an important consideration. While the panel & controller will never produce 40 amps, remember the fuse is also protecting against a short between the battery & the controller, i.e. 100's of amps available from the battery.

Study Ohm's law a bit. Then the power law.
The danger is drawing current between the maximum the wire is supposed to handle and the fuse rating. For one thing the 40 amp fuse isn't going to blow at 40 amps. Fuses generally have a time associated with the current rating.
Let's play a little math game. 12 AWG wire rated for 20 amps. Now let's draw another 20 amps through that same wire. Let's sat the battery is connected so that it delivers the 12 volts. 12 X 20 = 240 watts of heat dissipated in that piece of wire. Now think how hot a 100 Incandescent light bulb gets, then that 2x+. That a whole lot of heat. enough to burn your trailer down.

[gordon2]

Well Jon and Byron have both highlighted the problem with the very basic instructions for the solar setups that have been provided. The instructions are good, but rather generic and don't necessarily take into account some important details.

May I suggest that you post some VERY extensive details on the planned installation? it is easier sometimes to find flaws with a plan than to explore every possible requirement or suggested method when doing something like this.

I would include details such as an overall listing of components with their layout and placement, wire gauge, length, fuse rating, etc.

I have found that there is a lot of knowledge on this forum.. if we can get it focused to your situation.

Basically, you want fuses to fail (blow) before so much current goes through any wires or other components that it damages then. Sounds simple and its pretty much is, given the proper planning.

[Byron Kinnaman]

A steadfast rule. Never fuse anything at a higher current rating than the wire is designed to handle. There's lots of charts that indicate the size of wire vs current. Fuse accordingly to be safe.

[steve dunham]

The current carrying capacity of a wire is determined by the AWG size of the wire ,whether copper or aluminum , the insulation rating ,applied voltage , number of conductors in a raceway - cable or - bundled or in free air ,ambient temperature , the load being served ,voltage drop and code limitations .etc etc etc. I have #6 AWG 90 deg C THWN copper wire going from my battery to my 100 watt solar panel controller .The #6 wire is fused at 7.5 AMPS not at the wires listed ampacity.

[Byron Kinnaman]

Originally Posted by steve dunham

The current carrying capacity of a wire is determined by the AWG size of the wire ,whether copper or aluminum , the insulation rating ,applied voltage , number of conductors in a raceway - cable or - bundled or in free air ,ambient temperature , the load being served ,voltage drop and code limitations .etc etc etc. I have #6 AWG 90 deg C THWN copper wire going from my battery to my 100 watt solar panel controller .The #6 wire is fused at 7.5 AMPS not at the wires listed ampacity.

There's just so many things wrong with this post that it take three pages of type to correct.

[Gilles]

I found this document in one of the links that someone from the group identified as reference.

After finding the amperage required at the end of fillage, one may have the right idea of the fuse size to use ...

Is good?

[gordon2]

Originally Posted by Byron Kinnaman

There's just so many things wrong with this post that it take three pages of type to correct.

Well then we understand if it takes a while to prepare the response.

I'll throw this diagram out there for comment, and for suggestions as to it's appropriateness for the OP. There is no fuse on the battery side of the solar controller, but it seems to me that the 20 amp for the main trailer wiring and the 30 amp for the solar controller side (which is all 8 AWG from battery to controller) will cover any eventuality. Or did I miss something.

(BTW, the 30 amp is a Blue Sea Systems post mounted fuse, right on the battery post with the required post mount. I really like these since there is no length of wire coming off the battery that is unfused. The original Scamp connection had a foot or so of wire before the first fuse.

[Raz]

Makes life easier

[steve dunham]

Originally Posted by Byron Kinnaman

There's just so many things wrong with this post that it take three pages of type to correct.

Please Byron ; ENLIGHTEN ME !! !!

[steve dunham]

Allowable ampacity of a #8 AWG wire copper or aluminum
#8 Copper 60 C insulation no more than 3 wires in a raceway = 40A
#8 Copper 90 c insulation no more than 3 wires in a raceway = 55A
#8 Alum 60 C insulation no more than 3 wires in a raceway = 35A
#8 Alum 90 C insulation no more than 3 wires in a raceway = 45A
#8 Copper 60 C insulation in free air = 60A
#8 Copper 90 C insulation in free air = 80A
4 to 6 conductors in a raceway or cable derate listed ampacity to 80%
7 to 9 conductors in a raceway or cable derate listed ampacity to 70%
See NEC Art 310.15((2)(a) and 310.15((2)(b) for correction factors for ambient temperature
The ampacity of a given conductor when sized to limit voltage drop is the maximum ampacity where the voltage drop does not exceed the maximum voltage drop allowed . IE; We often install runs of #6 or #4 Copper wire for parking lot lighting to limit voltage drop and the wires are fused at 20 amps.
The ampacity of a conductor is also limited to the temperature rating of the terminations IE ; Circuit breakers are rated for 75 deg C and are another limiting factor on ampacity.

Reference Art 310 of the NEC
I stand by my post !!

[redbarron55]

Always remember the fuse is chosen to protect the wire (and the stuff around it) and not the electrical device (so much).
If the device has a fault then the fuse will not make it all better.
The fuse rating should always be lower than the ampacity of the wire to prevent overheating.
The fuses should also be near the source of power so that a short circuit between that source and the fuse is unlikely. A short before the fuse is like it is not in the circuit at all.

[Gordon in Idaho]

I feel like I'm getting an education here, although it may be just enough knowledge to get me in trouble.
Thanks for the diagram, gordon2.
I just got off the phone with Renogy tech support, and was told that my 3 100w parallel panels can be protected with a single 25-30 amp fuse. At the risk of being annoying, I asked twice, to be sure.
So.....here's what I'm going to do: 25amp fuse on the solar feed, 30 amp on the battery line, and 30amp on the load line to the primary fuse block, where each branch circuit is fused according to draw. I understand wire resistance, and my 10awg runs are fairly short.
I'll see if I can share real world data from the field.
I hope my replies haven't added confusion to the discussion. I just try to share what I Think I know, and my education continues.

Gordon

[Uplander]

I must admit that after reading all the technical mambo-jumbo in this seemingly endless post any plans I ever had on adding a solar battery charging system to my trailer have been canceled FOREVER !!!