kWhikVault-1 (Gen-1)
This provides the details to ‘Vault-1’ in the first (publication worthy IMO) PowerVault lines of builds.
A PowerVault is a weather-resistant chest that provides for safe electrical usage outside the confines of a sheltering building. More details about the vault design in general is in PowerVault Gen-1
Vault-1 is actually one of the newest vault design versions in generation-1: it was rebuilt after Vault-4 and Vault-5 design reworks. It is also a pretty simple and complete all-in-one vault, so the core ideas of the vault build are all present.
Table of Contents
System Overview
Vault-1 is a simple 12V system with a 1200W inverter, a 100Ah LiFePo4 battery, a 100/20 MPPT, several AC power outs, and several monitors and controls (DC shunt, AC energy meter/switch, temperature probe, Victron Cerbo, etc.)
Core Structural Aspects
A Vault is structurally based on Truck “Tool Boxes”. Vault-1 is an aluminum 17”x18”x30” (depth-height-width) Underbody Tool Box and specifically this product: Arksen 192928026887
To transform the Tool Box into a Vault we need to:
- Frame the inside
- Frame the outside
- Connect between the two
Framing the inside
Framing the inside when there is no insulation involves:
- Providing a floor
- Providing walls for the inside structure (for Vault-1 a single full-span shelf)
- Providing support for the outside frame
The inside framing is done mostly with 3/4” plywood. Backerboard for the components is a separate aspect and is done with HexPly so the framing can be more basic.
The floor is solid plywood to help rise up the base to the lower lip edge. This subfloor is also a reasonable place to put insulation (under the plywood) as both a temperature and moisture barrier against the cold ground that the vault could be resting on. In most cases references to insulation will be to XPS although a fully-insulated vault (e.g. Vault-4) uses other materials as well.
The walls are also solid 3/4” plywood to provide strength for the outside frame and also suitable shelf support on the inside.
Framing the outside
The outside is primarily framed with ‘rails’: either redwood or cedar planks that will be bolted with 3/8” bolts through the aluminum to the inside. The advantage of using rails is:
- Readily accessible and less-expensive weather-resistant materials
- The inside wall becomes the primary stencil/template for the system and ‘disagreements’ (misalignments) can be avoided. A rail only has two holes, so it is easy to have the two rails agree with the inside wall frame.
- Esthetically fairly attractive and sturdy
Connecting the inside to the outside
The build uses stencils to have the basic dimensions ‘carved’ onto the other pieces, but this stenciling is progressive and ultimately the inner wall becomes the ‘statement of truth’ that will be applied to tool box and the outer rails.
The most important aspect for this is to make sure the precision on the truth is sufficient for aligning and cutting (drilling) other pieces. This precision goes from:
- 1/8” ‘Narwhal’ pilots
- 1/4” ‘Arbor’ pilots
- Actual holes sized for purpose
‘Narwhal’ pilots are used for anything that needs a fairly precise pilot, especially Forstner bits. They are also used for sanity checks since having a misplaced 1/8” hole is easily rectified and commonly consumed by the final actual hole.
‘Arbor’ pilots are the official pilots for the hole saws, which are used extensively for conduit fittings and providing space around the fitting.
The Stencil and Build
The critical positioning to get right for all vault builds are the structural 3/8” tie-bolts going through the side walls. These need to be spaced from the edge and projections/penetrations to prevent collisions and be structurally robust. The internal obstacles include the floor, any insulation, shelving locations, and penetration fittings. And as mentions, the bolts must have sufficient edge distance on the inner framing wall and outer rails for both grip and material strength. Combining that with build tolerances give the following example wall-template jig for the ‘electrical box’ side of a 17x18 [this is just an old example… schematic for a real version to follow].
Ringed holes are for penetrations and fittings. Other holes are for structural use including the four corner 3/8” tie-bolts. This earlier generation of template uses 1/4” pilots only but that caused issues with Forstner and similar precision bits.
Getting a bit ahead, the following is the current generation schematic for the complete Vault-1. This will be explained in the subsequent sections.
Base Tool Box dimensions
The 17x18x30 toolbox has a ‘neck’ to enable sealing the front door and the dimensions provided are for the outside of the box. To handle these aspects and provide tolerance for fitting pieces of wood/xps/etc. a half inch is removed from top, a side (shown as ‘right’ but really shared by both sides), and the front. An additional inch is removed from the front for the neck. So the inside dimensions are 15.5” deep, 16.5” high, and 29.5” wide.
The following basic diagram shows the view from the left, center(front), center (top), and right side of the box. Aqua (‘aa’) represents the claimed dimensions and Yellow (‘yw’) are the buffer spaces.
Subfloors and Inner Walls
A subfloor of 1.5” XPS is used to provide some amount of insulation from the ground and also to help lift the insides up to the height of the neck (about 2” up). Vault-1 has no serious insulation, but this subfloor will be an integral part of insulating Vault-4 and similar R-value vaults.
Showing the subfloor in lime (‘li’) spanning the whole bottom. It can also be broken into two pieces (side-to-side) if fitting it through the neck or laying it down proves imposible given the dimensions. A second subfloor is placed on top of it, so any gaps will be cross-covered by that.
Inner Walls
The side inner walls shown in brown (‘bn’) are fastened to the tool box side wall. They sit ‘on top’ of this subfloor and pin it into place from above (along with gravity). This relationship is part of the insulation model where the side insulation will match the dimensions of the side inner walls, providing a continuous insulation box and minimal thermal bridging.
The inner walls are only 1/2” thick but they are pinned against the aluminum side walls with rails on the opposing side, so their structural strength is considerably stronger than the 1/2” thickness would indicate. But in acknowledgement of their limited pull-out and shear strength for fasteners, inner shelves are not attached directly to the 1/2” inner walls. Instead, any load fasteners are attached to 3/4” plywood that strengthens that inner walls.
The thickness of the inner wall was optimized to enable side-wall insulation to be present without the functional inner dimensions being overly reduced.
Subfloor-2
The second subfloor shown in purple (‘pu’) is 1/2” plywood and sits inside the inner walls. It is basically just another plank, but there are optional (but likely useful) carve-outs in the corners that are to make sure the tie-bolt nuts and washers are easily accessible. The carve out is small enough that it does not interfere with usable space, especially if there is a HexPly floor on top of the Subfloor.
Outer Rails and Tie-Bolts
The outside of the vault uses horizontal rails shown in green (‘gn’) made of ~2” redwood or cedar boards (nominal 3”, actual approximately 2 3/8”) that span the same depth as the inner walls.
Tie-Bolts
The Tie-Bolts shown in red (‘re’) connect the outside rails to the inside walls, sandwiching the tool box between them. These are positioned 3” from each edge:
- To avoid internal obstacles like flooring and insulation
- To provide a line that other penetrations can work with
- To make sure the structural strength (e.g. pull-out or pull-through) is sufficient for both bolts and washers
- To help align the spacing of other penetrations and the electrical box
It is possible to tweak these numbers as needed given the clearance for the 3/8” bolts don’t need to be this large, but it produces esoteric variations that won’t work with other builds (especially Vault-4 that is very tight).
Note that the shown ‘re’ blocks include space for heads, nuts, and washers and are not the bolt diameter.
As can be seen with this last diagram, the Subfloor-2 and the Tie-Bolts (including the clearance space) would collide if Subfloor-2 did not have the carve-outs.
Inner Fittings and Penetrations
The Inner Fittings (e.g. Myers Hubs) shown in pink (‘pk’) span from outside the vault through the inner wall. The dimensions of these are for 3/4” conduit for Vault-1, but the fittings have multiple dimensions to support the penetration through the tool box and the necessary space for access to the nut on the inside. This combined with needing multiple pilots makes this one of the more complicated drillings involved.
Fortunately by using rails on the outside with sufficient clearance, the rails are not involved. And by using the inner wall as the main template, as soon as it is in place, the tool box wall is piloted with the corresponding hole location.
Penetrations
The actual penetrations required for the tie-bolts and fittings are shown in orange (‘oe’) and should be made to allow the bolt or fitting to cleanly enter the holes with sufficient clearance that alignment is not difficult and excess gaps are not present. For the 3/8” bolt, using 25/64” or 13/32” holes is recommended. The fitting requires ~1/16” space around its outer penetrating dimension.
The tie-bolts should be providing no shearing force directly and alignment does not need to be precise for shelving and hanging on the inside and outside. The tie-bolts are just used to compress the rail to the inner wall, which provides a very large area (many square inches) of friction to prevent sliding. The vault is also not meant to be lifted by the sides, but instead by straps, palett, or other support beneath it.
