TECHNICAL

USB Bandwidth & PCIe Expansion for BoxPhone

Why devices fail to appear when you plug in too many — and how PCIe USB cards break through the limit

Sikrid Team2026-04-265 min read

Plugging BoxPhone into a single PC via USB tops out at roughly 2-3 boxes (50-60 devices) before USB controller bandwidth saturates and newly-plugged devices stop appearing. The fix is a PCIe USB expansion card — Sikrid sells one for 6,500 THB that supports 5 boxes (100 devices) per card.

Why a 30-Port USB Hub Isn't Enough

Most people assume “more USB ports = more devices supported”— but in reality, every port on your hubs and motherboard shares the same USB controller bandwidth.

Standard USB 3.0 controllers have hard bandwidth limits:

USB 3.0 (5 Gbps) ≈ 500 MB/s per controller
USB 3.1 Gen 2 (10 Gbps) ≈ 1.2 GB/s per controller
USB 3.2 (20 Gbps) ≈ 2.4 GB/s per controller

Consumer motherboards typically have only 1-2 USB controllers — and every visible port (8-12 rear panel + front panel + external hub) shares that same bandwidth.

As you plug in more devices, per-device bandwidth shrinks — until newly-plugged devices can't be enumerated by the OS because there is no bandwidth allocation left.

How to Check If USB Bandwidth Is Saturated

On Windows:

Open Device Manager
View menu → Devices by connection
Expand each USB Hub → right-click Properties → Advanced tab
Check Bandwidth utilization — close to 100% means saturated

Windows screen showing saturated USB bandwidth — the cause of devices failing to enumerate — Example Windows screen with saturated USB controller bandwidth — newly-plugged devices won't appear

Easy symptoms to spot:

Newly-plugged devices don't appear in adb devices
Device list in OS shows “Code 10” or “Insufficient resources”
Previously-working devices randomly drop when new ones are plugged in

The Fix: PCIe USB Expansion Card

To run more than 60 devices on a single PC you must add a USB controller via a PCIe slot — not by adding more USB hubs (hubs share the existing controller).

Specs to check:

Card bandwidth — at least 20 Gbps (USB 3.2 Gen 2x2)
PCIe slot interface — x4 or higher (x1 will bottleneck at ~1 GB/s)
Controller chip — stable Renesas / ASMedia chips, not no-name controllers
Power input — some cards require an additional Molex/SATA power connector

Sikrid PCIe USB Card

Price: 6,500 THB / card
Capacity: 5 boxes (100 devices) per card
Bandwidth: 20 Gbps controller, fully isolated from the motherboard
Tested with BoxPhone: passes 24-hour burn-in with 100 devices simultaneously before shipping

What to Know Before Buying a PCIe USB Card

Motherboard compatibility — at least 1-2 free PCIe slots, with no GPU conflict
Verify slot specs — must be PCIe x4 or higher (the motherboard manual will state this clearly)
PSU headroom — accommodate the controller chip plus power for devices connected through the card
Case airflow — the controller chip runs hot under load, and without airflow it will throttle
Driver compatibility — Windows 10/11 is plug-and-play for most cards; Linux may require manual driver compilation

Scaling Roadmap — When to Use What

Device Count	USB Solution	Notes
1-60 (1-3 boxes)	Motherboard USB	Sufficient — no additions needed
60-300 (3-15 boxes)	+ 1-3 PCIe USB cards	1 card = 5 boxes on a separate controller
300+ (15+ boxes)	Distribute across PCs + OTG mode	See OTG over LAN

Conclusion

USB controller bandwidth is the real ceiling on phone-farm scaling — not hub port count.

Always test first via Device Manager → Bandwidth utilization before concluding that you “can't add more devices.”

If saturated, add a controller via a PCIe USB card at 20 Gbps+ in a PCIe x4+ slot — Sikrid offers one for 6,500 THB supporting 5 boxes on a separate controller.

Past 300 devices on a single PC, switch to OTG mode over LAN instead.

FAQ

01Will a 200-baht USB hub solve this?+

No. External USB hubs plug into a motherboard port that uses the same controller — they share the same bandwidth pool. Hubs add port count, not bandwidth. The only fix is adding a controller via PCIe.

02Are cheap PCIe USB cards from Lazada good enough?+

Fine for home-office work, but not for 24/7 phone farms. Most use older ASMedia chips that overheat or have unstable drivers. For production, choose newer Renesas chipsets or the burn-in tested Sikrid card.

03My motherboard only has PCIe x1 slots — can I install the card there?+

Physically yes, but you'll bottleneck — PCIe x1 ≈ 1 GB/s, not enough for 100 devices. You need x4 or x8. Check the motherboard manual carefully — slots typically used for Wi-Fi cards or NVMe expansion are usually x1.

04Can I use two PCIe USB cards in the same PC?+

Yes, as long as you have a free PCIe x4 slot and sufficient PSU headroom. This lets you control 200+ devices on a single PC. Beyond that, splitting across multiple PCs or using OTG mode is recommended.

05Does Linux support the Sikrid PCIe USB card?+

Yes — Linux kernel 5.x and later includes xhci drivers compatible with standard controllers. Plug-and-play on most distros. Older Ubuntu LTS releases may require a kernel update.

06Does the card support Mac?+

Tower-style Mac Pros support it — but Mac Mini and iMac don't have PCIe slots and are not compatible. We recommend Windows/Linux for production phone farms because the driver ecosystem is much more complete.