Pinout help needed: Repurposing HP P411 Cache Module / Supercap logic?

[wayigo8873]

Hello everyone,

I’m currently working on a hardware salvage project and I’ve hit a wall regarding some proprietary power connectors. I figured this would be the best place to ask since I usually just lurk here for the schematic breakdowns.

I recently rescued an HP Smart Array P411 SAS-SATA controller from an e-waste pile. I’m trying to use it for a home lab setup, but the card is missing the "Flash Backed Write Cache" (FBWC) supercapacitor pack. Without that power source, the card disables the write cache, which absolutely kills the throughput performance. I really hate seeing perfectly good silicon go to the landfill just because of a missing battery, so I’m attempting to "MacGyver" a solution.

My specific technical question revolves around the voltage regulation on the daughterboard. There is a small proprietary header connecting the cache module to the capacitor pack. I want to wire in a generic supercap bank or an external DC source, but I can't find a datasheet for the pinout. I’ve probed the pins with my multimeter while the system is live, but the readings are fluctuating, likely because the controller is polling for a "battery present" signal.

I remember spending a whole week once trying to bypass a Lenovo fan whitelist by flashing a custom BIOS, so I know these proprietary checks can be a massive headache if you don't get the handshake right.

Has anyone here ever reverse-engineered the power circuit on these older Smart Array cards? I’m curious if there is a specific resistance value or logic high/low signal on a sense pin that tells the controller the "battery" is healthy, or if I simply need to supply a clean 5.4V to the main rail?

Thanks in advance for any insights!

 

[olivia_49]

Those HP FBWC packs aren’t just batteries, they have a control board that tells the RAID card the pack is present and healthy. Supplying 5–6 V alone won’t enable write cache because the card expects that handshake. The usual fix is to reuse the PCB from a dead FBWC pack and hook your own supercaps to it.

 

[furnacewheat]

Hello everyone,

I’m currently working on a hardware salvage project and I’ve hit a wall regarding some proprietary power connectors. I figured this would be the best place to ask since I usually just lurk here for the schematic breakdowns.

I recently rescued an HP Smart Array P411 SAS-SATA controller snow rider from an e-waste pile. I’m trying to use it for a home lab setup, but the card is missing the "Flash Backed Write Cache" (FBWC) supercapacitor pack. Without that power source, the card disables the write cache, which absolutely kills the throughput performance. I really hate seeing perfectly good silicon go to the landfill just because of a missing battery, so I’m attempting to "MacGyver" a solution.

My specific technical question revolves around the voltage regulation on the daughterboard. There is a small proprietary header connecting the cache module to the capacitor pack. I want to wire in a generic supercap bank or an external DC source, but I can't find a datasheet for the pinout. I’ve probed the pins with my multimeter while the system is live, but the readings are fluctuating, likely because the controller is polling for a "battery present" signal.

I remember spending a whole week once trying to bypass a Lenovo fan whitelist by flashing a custom BIOS, so I know these proprietary checks can be a massive headache if you don't get the handshake right.

Has anyone here ever reverse-engineered the power circuit on these older Smart Array cards? I’m curious if there is a specific resistance value or logic high/low signal on a sense pin that tells the controller the "battery" is healthy, or if I simply need to supply a clean 5.4V to the main rail?

Thanks in advance for any insights!

You’re right to suspect a handshake — it’s not just a voltage issue. The P411 FBWC uses sense/ID pins for battery presence and health, so supplying 5.4–6 V alone won’t enable write cache. The controller actively polls those pins. Easiest route is salvaging a dead FBWC pack and replicating the resistor network or reusing its PCB; otherwise it’ll require proper reverse-engineering with a scope.

 

[jj_parkar95]

You’re on the right track on the P411, the FBWC isn’t just a power source; it also performs a health/ID handshake with the controller. Simply supplying 5.4 V usually isn’t enough, as the card expects a valid sense/ID signal (often via an SMBus/I²C-style line or resistor ID) to enable write cache. Most successful mods either reuse an original HP FBWC board with replaced supercaps or fully reverse-engineer the daughterboard logic; bypassing it cleanly is possible but nontrivial.

 

[tanzeel]

On the HP Smart Array P411, the FBWC supercap pack isn’t just a dumb battery feeding voltage. HP built in a handshake + health-check loop between the capacitor pack and the controller. That’s why your multimeter readings are unstable — the card actively polls for:

• Presence detection
• Charge state
• Temperature / fault status (on some revisions)

From what people have found while reverse-engineering similar P410/P411 cards:

• The main rail is around 5.3–5.4V, but simply injecting clean voltage usually does not enable write cache
• One pin acts as a sense / ID line, typically pulled through a specific resistance range
• Another pin reports “battery OK” logic high once charge thresholds are met
• If those signals aren’t correct, the firmware hard-disables FBWC regardless of supplied power

In other words: supplying voltage alone won’t satisfy the controller. You’d need to replicate the signaling, not just the energy storage.

A few realistic options:

• Salvage an original HP supercap pack (even dead cells sometimes still provide correct ID signaling)
• Find the exact pinout + resistor values from archived forums or server refurb communities (some diagrams exist but are revision-specific)
• Flash modified firmware (very risky, and success rate is low on Smart Array cards)
• Accept write-through mode and use it as a lab RAID controller without cache

Unfortunately, HP locked these down harder than Lenovo fan whitelists — you’re not imagining the pain.

Totally unrelated, but funny how troubleshooting proprietary hardware feels a lot like drywall repair colorado springs jobs: the damage looks simple on the surface, but the real problem is always hidden behind the wall