Non combustible backing board

Sheetrock with a backer board behind.

There is a metal company in downtown Denver that keeps a good sized inventory of scraps and cast-offs. I picked up a 18"x8' piece of diamond plate aluminum last year that was perfect for replacing a torn skirt on my RV trailer. They even made the length-wise cut for me and put a 90° bend at the end. I did pay for both of those add-on services. But they did a far better job than I could have. It really was outstanding! They had a lot of aluminum plate in the "scrap" yard.

Altitude Steel in Denver. Their website is minimal. You wouldn't find out much about them from it. Fortunately, a co-worker took me with him when he was buying items from the scrap yard by the pound.

Not inexpensive but here are fiberglass panels that are fire retardant. 1/4 in thick, 24" x 24" in black is $128. A thinner sheet could be epoxied to plywood.
(ePlastics.com)

Can't see any epoxy or other plastic product as "fire retardant"

Per their website:

G9 G10 FR4 GLASS EPOXY SHEET

G10 and FR4 glass cloth reinforced epoxy natural is typically a yellowish to light green color. The most versatile all-around laminate grades are continuous glass woven fabric impregnated with an epoxy resin binder. Epoxy resins are among the most versatile and widely used plastics in the electronics field, primarily because water absorption is virtually nil, rendering it an outstanding insulator.

Beyond its electrical insulating properties, epoxy resins exhibit great dimensional stability (shrinkage is usually less than 1 percent) and superior adhesive properties. G10/FR4 has extremely high mechanical strength, good dielectric loss properties, and good electric strength properties, both wet and dry.

The main difference between NEMA Grades G10 and FR4 is that FR4 is a fire retardant grade of G10. Therefore, FR4 can be safely substituted where G10 is called for, while G10 can never be substituted where FR4 is called for. G10 and FR4 Certifies to Mil-I-24768/27 GEE-F.
--
From a couple of minutes of research Mil-I-24768 further points to ASTM D 229 (link)

I couldn't see if the FR4 laminate is considered Class 0 or Class 1. This is not my field of expertise but it seems to indicate that it can withstand an 860 deg C. arc for at least 10 minutes before catching fire. It appears that the test may be on 1/2 in thick material.

A quick look through the Glasliner product (the brand available through Home Depot) doesn't show anything close to 1/2" thickness. I extracted the table below from their Glasliner Brochure.

I'm a bit confused about the difference between their Class A and Class C products. Except for flame spread and smoke generation they are very similar. Nonetheless, 430° C is really hot! At 806° F, there's plenty of other things in my trailer that are going to ignite before the FRP panel. I have leftover FRP that I think I'll use on the panel I'm mounting my components on.

researching a bit more:
ASTM E-84 is Surface Burning Characteristics of Building Materials

A score of 200 means the material flame spreads 200% further in 10 minutes than the reference material 1/2" thick select red oak. A score of 25 means only 25% of the flame spread. So if you have a class C material, you may be better off with wood. It also appears that there is fire resistant plywood available that rates as Class A.


(link)

bpal, thanks for the information. Based on that, it sounds like once the material catches fire, it spreads quickly. Quicker than wood, by 200%. Still, it has to catch fire first and 430° C seems like a very high threshold.

Considering that the entire bathroom ceiling is made of the FRP material that I would use behind my components, I'm not too concerned.

I reckon the best protection against fire is doing the job properly. The backing board doesn’t really make any difference.
Good quality components, specced correctly with wire (in conduit) and fuses sized & placed correctly. All connections greased (or locktite), nipped up tight then checked and double checked.

Good safety management comes from focusing on the proven causes of danger

How about a sheet of perforated steel. Fireproof, easy mounting (holes are already drilled) and improved heat characteristics (both improved airflow and conduction).


A 2' x 4' sheet of 20 gauge steel is $59. I would install Nutserts every place I wanted to mount something.

I’d rather have the (low) combustsbility of plywood than the conductiveness of steel or aluminium. That sounds like a lot more problems

20 gauge steel is incredibly thin.

snoobler said:

20 gauge steel is incredibly thin.

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Have to secure it with lots of fasteners to avoid vibration noise. You are not going to tear it with the weight of solar equipment. Especially since a more likely size to use is 2' x 2'.

For the plywood battery compartment I'm putting together, I will use plywood. I am considering painting it with some heat resistant paint, like you would put on an exhaust gas manifold, which mine gets up to 1600°F. I may try POR15. I don't know if that will help, but it will make me sleep better.

chrisski said:

For the plywood battery compartment I'm putting together, I will use plywood. I am considering painting it with some heat resistant paint, like you would put on an exhaust gas manifold, which mine gets up to 1600°F. I may try POR15. I don't know if that will help, but it will make me sleep better.

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That should be fine. Plain plywood should be fine. I was thinking more about improving airflow to improve longevity of the electronics. The cooler you can keep electronics, the longer it is going to last.

HaldorEE said:

That should be fine. Plain plywood should be fine. I was thinking more about improving airflow to improve longevity of the electronics. The cooler you can keep electronics, the longer it is going to last.

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That is something that worries me for the battery compartment I'm Building. I have 4 lead acid golf cart batteries that I will have two 2" vents in the top, and a third two inch vent in the bottom for air circulation. Outside that battery compartment is where my inverter and charge controller will be, and in AZ, its pretty hot in the summer. Not sure what to do to keep those two devices cool.

chrisski said:

For the plywood battery compartment I'm putting together, I will use plywood. I am considering painting it with some heat resistant paint, like you would put on an exhaust gas manifold, which mine gets up to 1600°F. I may try POR15. I don't know if that will help, but it will make me sleep better.

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Paints that are used on exhaust have to be cured with heat. I don't think you want to heat up you plywood that much. I painted the exhaust on a '91 Ford Ranger. That was a series of steps to get it cured right. That was a good 10 years ago. Maybe thinks have changed since then. Maybe caliper paint won't require the heat cure.

chrisski said:

That is something that worries me for the battery compartment I'm Building. I have 4 lead acid golf cart batteries that I will have two 2" vents in the top, and a third two inch vent in the bottom for air circulation. Outside that battery compartment is where my inverter and charge controller will be, and in AZ, its pretty hot in the summer. Not sure what to do to keep those two devices cool.

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I would add ventilation fans and rout the exhaust to the outside of the vehicle.

I am building a LiNMC battery pack and can't have any air ventilation (this chemistry vents with fire).

I am building the battery into a 40 MM grenade ammo can. For cooling I am attaching copper sheets to the cells then mounting copper, server class heat sinks to the copper sheets through holes cut in each side of the ammo can. Each heat sink will have its own thermostat controlled blower fan.

The ammo can will be completely airtight when I am done, and I am hopeful that I have provided adequate thermal management. I will be instrumenting the pack so I will know if I need to add more cooling capacity.

Ultimately I can reduce the charge/discharge rate if that is what is required to keep the battery temp under control. That is one of the advantages to using all Victron electronics. Pretty much everything is completely configurable.

PS I am in Phoenix so I am very concerned about overheating the battery also.

Ampster said:

I just use plywood or OSB on my garage walls because it is easier to attach sub panels and small devices to it. I do give it a coat of grey latex paint to give it an industrial look.

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Your comment about the industrial look caught my eye and I wanted to do something like that, however I can’t seem to find any gray latex paint at HD/Lowes. All I found is a gray primer. What do you use? And do you prime first?

AC/DC said:

All I found is a gray primer. What do you use? And do you prime first?

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Yes in some cases I primed but for interior surfaces it is not as important. HD and Lowes can mix a gray color of your choice. They typically stock few actual colors.