Core answer: power-bank energy Wh=mAh×3.7V÷1000 — 20000mAh≈74Wh sits under the 100Wh flight limit; RAID 5 usable capacity=(disks−1)×disk size and survives one failure, RAID 10 halves capacity; CCTV daily storage GB = bitrate Mbps×10.55×channels (H.265 halves it); projector distance = throw ratio × image width — 100-inch 16:9 is 2.21m wide.
The power bank Wh ledger
Wh = mAh × 3.7 ÷ 1000 (cell voltage 3.7V):
| Label | Real energy | Flight |
|---|---|---|
| 10000mAh | 37Wh | ✓ no declaration |
| 20000mAh | 74Wh | ✓ no declaration |
| 30000mAh | 111Wh | airline approval |
| 50000mAh | 185Wh | ✗ banned |
Note “rated capacity” (5V output basis) runs ~30% below the label — a 20000mAh bank delivers about 12000-13000mAh to your phone.
RAID levels compared
| Level | Min disks | Usable | Tolerance | Fit |
|---|---|---|---|---|
| RAID 0 | 2 | 100% | none | speed scratch disks |
| RAID 1 | 2 | 50% | 1 disk | two-bay NAS |
| RAID 5 | 3 | (n−1)/n | 1 disk | mainstream NAS |
| RAID 6 | 4 | (n−2)/n | 2 disks | large arrays |
| RAID 10 | 4 | 50% | 1 per mirror | databases |
RAID is not backup — it covers hardware failure, not deletion, ransomware or fire.
Sizing CCTV storage
GB/day = Mbps × 86400 ÷ 8 ÷ 1024 ≈ Mbps × 10.55 per channel. An H.264 camera at 4Mbps writes ~43GB/day; H.265 halves it (~21GB). Disks deliver ~93% of label capacity after formatting.
Throw distance and image size
Throw ratio = distance ÷ image width:
- Standard 1.5-1.9:1 → 100-inch (2.21m wide) needs 3.3-4.2m
- Short throw 0.9-1.2:1 → 2.0-2.7m
- Ultra-short 0.25:1 → 0.55m from the wall
Ceiling mounts must respect lens offset — most units start the image below the lens axis, and flipping the projector flips the geometry.
Example: 8 cameras, 30 days
8 channels of H.265 at 2Mbps: daily = 2×10.55×8 ≈ 169GB; 30 days = 5.1TB; a 6TB disk ×0.93 = 5.6TB ✓. Switch to H.264 at equal quality and bitrate doubles → you would need 12TB class — an H.265 NVR halves your disk budget.
Example: where to mount a 100-inch setup
100-inch 16:9 width = 100×2.54×0.8716 ≈ 221cm. A 1.2:1 unit → distance = 1.2×2.21 ≈ 2.65m lens-to-screen; add body depth and cabling, so the room needs ≥3m clear. Otherwise drop to a 0.9:1 short throw (2.0m) or a 92-inch image.
Common pitfalls
- “Bigger mAh means more charges”: convert to Wh, then apply ~85% efficiency — a 20000mAh bank refills a 4000mAh phone about 3.5 times, not 5.
- “RAID 5 survives two dead disks”: one only; a second failure during the hours-long rebuild kills the array — use RAID 6/10 for big disks and important data.
- “Peak bitrate is enough for sizing”: multiply by channels and days, add 10%; motion-triggered recording saves 30-70% but never bet critical scenes on it.
- “Shorter throw is always better”: UST exposes every wall ripple as wavy lines — pair it with a proper ALR screen.