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How Parkside X20V and 12V Tools Detect Battery Undervoltage via BMS and T/DS Pin

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User question

how parkside tools detect battery undervoltage ?

Artificial Intelligence Response

Direct answer to the question

  • In most Parkside X20V “Team” tools, the battery pack’s BMS monitors cell voltages and signals “undervoltage” to the tool over an auxiliary pin (often marked T/DS). The tool’s controller then shuts the motor off; the pack itself typically does not open a high‑current MOSFET for discharge cut‑off in the 20 V family. (positron96.gitlab.io)
  • On Parkside 12 V packs, users have verified a true pack‑side hard cutoff around 8.7 V (~2.9 V/cell), after which the battery resumes normal charging. (reddit.com)

Key points

  • Battery does the sensing; tool enforces the stop for 20 V class.
  • The T/DS pin behaves like a “health line”: normal = pulled down; fault (UV/OC) = floats, which the tool detects and stops. (positron96.gitlab.io)
  • “Smart” Bluetooth packs can expose discharge profiles in the app with different per‑cell limits (user‑reported). Thresholds vary by model and setting. (reddit.com)

Detailed problem analysis

  • Topology (20 V class):
    • Inside the battery: a small BMS monitors each series cell group. Instead of opening the discharge path, it asserts a fault via the T/DS pin. Internally, the pin is tied to pack negative through roughly a 10 kΩ thermistor and a transistor. In normal operation the transistor pulls the pin low; on undervoltage (and some other faults) the transistor turns off and the pin goes high‑impedance. (positron96.gitlab.io)
    • In the tool: the control PCB applies a pull‑up (e.g., ~5 V via ~10 kΩ) to that pin and measures its level. “Low” indicates OK; “float/high” indicates a fault → controller disables the PWM/drive and the tool stops. This gives a clean, fast “soft” cutoff without breaking the heavy current inside the battery pack. (positron96.gitlab.io)
    • Rationale: moving the actual cutoff action into the tool avoids stressing pack MOSFETs, reduces battery heat, and lets the tool shape its shutdown (e.g., braking, indicators). Community teardowns for Parkside 20 V commonly show no discharge MOSFETs, reinforcing this split of responsibility. (reddit.com)
  • Pins and naming seen in the field:
    • Parkside packs/chargers frequently expose extra contacts labeled T, CS/ID, and sometimes DS. Community reverse‑engineering has measured ≈12 kΩ from P− to CS and high megaohms to DS on some boards; CS is often used by chargers for identification/temperature, while DS/T is used to flag faults to tools. Exact functions can vary by generation. (alldatasheet.com)
  • Thresholds and behavior:
    • One carefully measured example (20 V class) reported the battery indicating over‑discharge to the tool at about 13 V (≈2.6 V/cell) on that specific pack. That is a BMS‑to‑tool alert threshold, not necessarily a physical pack cutoff. (positron96.gitlab.io)
    • By contrast, a 12 V Parkside pack has been user‑tested to open its own discharge path near 8.7 V (~2.9 V/cell), i.e., a true hard cutoff in the battery. (reddit.com)
  • Smart/Bluetooth variants:
    • Recent “Performance/Smart” batteries integrate Bluetooth and app profiles that users report as mapping to different per‑cell discharge limits (e.g., “Eco,” “Balanced,” “Performance/Expert” with progressively lower voltage cutoffs). Because this comes from user reports, treat values as indicative and model‑dependent. (reddit.com)

Current information and trends

  • Community documentation (2024–2025) shows continued use of the fault‑line approach on 20 V packs and periodic “blips” on the T pin (power‑saving polling) that external adapters must filter to avoid nuisance trips. (positron96.gitlab.io)
  • Smart packs are adding configurable discharge behavior and firmware‑updatable logic shared between battery and tool ecosystems, but exact per‑cell setpoints differ by firmware and app profile. (reddit.com)

Supporting explanations and details

  • How the T/DS pin communicates state:
    • Electrical model: Tool provides pull‑up (≈10 kΩ to 5 V). Battery provides ≈10 kΩ pull‑down when “OK.” The tool reads ≈2.5 V mid‑rail = OK. When the battery removes its pull‑down (fault), the line rises toward 5 V and the tool stops. Some packs momentarily release the pull‑down for housekeeping; tools (or external adapters) should add timing/hysteresis to ignore very short releases. (positron96.gitlab.io)
  • Why park the hard cutoff in the tool (20 V):
    • Eliminates high‑current MOSFET conduction losses/heat in the pack during normal use.
    • Lets the tool brake the motor gracefully and show a low‑battery indicator.
    • Still preserves cell safety because the BMS decides when “it’s time to stop,” and the tool enforces it. (reddit.com)
  • Variant note:
    • Different lines (e.g., 12 V vs 20 V, smart vs non‑smart) are not identical. Evidence suggests 12 V packs include a discharge MOSFET cutoff, while many 20 V rely on the tool to act on the BMS signal. (reddit.com)

Ethical and legal aspects

  • Bypassing undervoltage protection or faking the T/DS pin to keep a tool running risks deep discharging lithium‑ion cells, leading to capacity loss, internal damage, and potential safety hazards. Doing so can void warranties and may violate local safety regulations for electrical equipment. Always preserve the protection chain. (positron96.gitlab.io)

Practical guidelines

  • For diagnosis:
    • Under load, if the tool stops abruptly but the pack still measures a reasonable open‑circuit voltage, you likely hit the BMS undervoltage alert and the tool did the cutoff. Recharge and try again. (positron96.gitlab.io)
    • If building an external adapter (e.g., to power a non‑Parkside device), read the T/DS pin exactly as the tools do: provide a 10 kΩ pull‑up to 5 V and interpret ≈mid‑rail as OK and ≈5 V as fault. Add RC filtering (~hundreds of milliseconds) and hysteresis to avoid reacting to the pack’s momentary pin releases. (positron96.gitlab.io)
    • If you must implement your own UV cutoff for a 5‑series (20 V class) pack used outside the ecosystem, a conservative no‑load threshold near 16–17 V (3.2–3.4 V/cell) reduces the chance of cell imbalance driving a weak cell below safety during load peaks. This is a best‑practice guideline, as exact Parkside thresholds vary by pack and app profile. (reddit.com)

Possible disclaimers or additional notes

  • Model variance is real: PCB revisions and “Smart” vs “non‑Smart” packs differ. Treat numbers above as representative, not universal. When precision matters, instrument your exact pack. (positron96.gitlab.io)
  • Community sources are valuable but unofficial; where possible, confirm behavior on your hardware.

Suggestions for further research

  • Reverse‑engineer the DS/CS/ID lines with a logic analyzer across several tools to document protocol nuances (especially on Smart packs). (alldatasheet.com)
  • Characterize per‑cell thresholds across app profiles on multiple firmware versions to build a reliable table for designers integrating Parkside packs. (reddit.com)

Brief summary

  • Parkside’s 20 V ecosystem generally detects undervoltage in the battery (BMS) and signals it to the tool over the T/DS pin; the tool then stops the motor (“soft” cutoff). Some lines (notably 12 V) implement a true battery‑side hard cutoff. Exact thresholds and signaling details vary by pack generation and, for Smart packs, by app profile, so verify on the specific model before designing around it. (positron96.gitlab.io)

User question

what is stihl AS2 battery pinout and can it be replaced by a parkside X12V battery ?

Artificial Intelligence Response

Direct answer to the question

  • Short answer:
    • STIHL AS 2: 10.8 V (3‑series Li‑ion) pack used in the STIHL AS System (e.g., GTA 26, HSA 26, SEA 20). STIHL does not publish an official pinout. Community evidence indicates at least three terminals: battery +, battery −, and a single auxiliary/sense line used by the tool/charger for temperature/ID/enable. (stihlusa.com)
    • Parkside X12V: also a 3‑series (10.8–12.6 V) system, but with its own mechanical interface and “T/DS” auxiliary line conventions. (parkside-diy.com)
  • Can a Parkside X12V battery replace an AS 2?
    • Not directly. The packs are mechanically incompatible and their auxiliary/enable signaling is different. Even if the voltage class matches, the STIHL tool/charger expects the AS‑2‑specific sense/ID behavior and will typically refuse to run/charge without it. (stihlusa.com)

Detailed problem analysis

  • Electrical basics
    • STIHL AS 2 specifications (U.S. market as of Nov 6, 2025): 10.8 V rated (12.6 V max), 2.1 Ah, 28 Wh, 3 cells in series. These specs are consistently listed by STIHL dealers and show “Number of cells: 3.” (hutsoninc.com)
    • Parkside X12V is Parkside’s 3‑series “12 V Max” ecosystem; the battery BMS and connector are Parkside‑specific. (parkside-diy.com)
  • Pinout reality for AS 2
    • STIHL does not provide a public pin map for AS‑System batteries. Across STIHL platforms, an auxiliary line (variously used for NTC temperature sense and/or pack identification/handshake) is common. For higher‑end STIHL packs (e.g., AR series), documented community teardowns show explicit communication lines in addition to the power rails; smaller packs often implement a simpler single sense/ID line, but the principle is the same: the tool/charger looks for a valid condition on the auxiliary pin before enabling. This is why connecting only +/− often does not allow charging or operation. (eevblog.com)
    • Practically, the AS 2 presents at minimum: B+, B−, and a single auxiliary contact. The auxiliary line’s exact behavior (pure NTC vs. ID/enable logic) is not officially documented; different hardware revisions can differ.
  • Parkside X12V auxiliary line
    • Parkside X‑Team batteries expose a center “T/DS” pin that tools/chargers read. Community reverse‑engineering (primarily on X20V and related designs) shows this line being used as a “presence/health” signal (NTC/logic combination), not just a passive thermistor, and some chargers/tools won’t enable without it. While implementations vary by voltage family, the take‑home is the same: the auxiliary pin is brand‑specific. (reddit.com)
  • Why they don’t interchange
    • Mechanical: Completely different housings/locking rails; no physical fit. (parkside-diy.com)
    • Electrical signaling: The auxiliary pin on STIHL expects STIHL‑specific sense/ID behavior; Parkside’s T/DS line is not the same. A simple 3‑wire adapter (+/−/aux) commonly fails because the tool never “enables” without the expected response. (eevblog.com)
    • Platform design: STIHL chargers for AS batteries (AL 1/AL 5/AL 5‑2) implement battery diagnostics and temperature/function checks, again relying on the pack’s expected signaling. (stihlusa.com)

Current information and trends

  • Confirmed current specs (2025): AS 2 remains a 28 Wh, 10.8 V battery used across the AS System; dealer pages and STIHL charts are consistent. (stihlusa.com)
  • Industry trend: Manufacturers increasingly use auxiliary sense/ID (and sometimes authentication) between tools/chargers and packs, reducing cross‑brand interchangeability even when the nominal voltage matches. STIHL is among those using extra signaling; Parkside has also moved toward smarter “T/DS” implementations and even Bluetooth variants in other voltage classes. (eevblog.com)

Supporting explanations and details

  • Typical small tool‑pack interface
    • B+ and B−: main discharge/charge path.
    • Aux pin: can be an NTC to ground, an ID resistor, or a logic/one‑wire‑style line. The tool or charger often sources a small bias (for example 3.3–5 V through a resistor); it then checks the returned voltage/resistance to validate the battery and its temperature window. If validation fails, the output stage is disabled.
  • What you’ll see if you probe
    • With an AL‑series charger: between Aux and B− you may see a non‑zero bias and state‑dependent behavior (e.g., changes with temperature/fault). With only B+/B− applied, most STIHL chargers will not initiate charge. This pattern is well‑documented on larger STIHL packs and consistent with field reports on smaller ones. (eevblog.com)
  • Why “same voltage” isn’t enough
    • Even when both systems are 3S Li‑ion, differences in: pack over/under‑voltage policies, inrush management, allowable current, and aux‑line semantics can stop operation or, worse, disable protection.

Ethical and legal aspects

  • Safety and certification: Mixing brands via DIY adapters bypasses the original compliance envelope (UL/IEC 62133, tool‑system safety testing), shifting risk to the user. Faults can lead to overheating, fire, or charger damage. Using non‑approved packs typically voids warranties and may violate local product‑safety expectations. Use only manufacturer‑approved combinations. (stihlusa.com)

Practical guidelines

  • If your goal is simply to keep a GTA 26/HSA 26/SEA 20 running, the practical, safe route is an AS 2 replacement battery. U.S. dealer listings show wide availability; pricing and specs are uniform. (hartvillehardware.com)
  • If you are investigating the pinout for engineering/learning:
    • Identify B+ and B− on the pack with a DMM; confirm polarity and open‑circuit voltage ~10–12.6 V.
    • Measure the auxiliary contact vs. B− with and without the tool/charger engaged to see if there is a bias or signature.
    • Do not inject voltages into the aux line until you understand the native levels; use series resistors and a scope/logic analyzer to observe behavior.
    • Expect that reproducing STIHL’s enable/ID behavior may require an active emulator, not just a resistor. Evidence from other STIHL platforms supports this. (eevblog.com)
  • What will not be plug‑and‑play
    • A Parkside X12V battery, even with an adapter, because mechanical fit and aux‑line protocol do not match. (parkside-diy.com)

Possible disclaimers or additional notes

  • Incorrect claim to avoid: The AS 2 is not a 36 V pack; it is a 10.8 V (3‑cell) battery at 28 Wh. Multiple current dealer specs confirm this. (hutsoninc.com)
  • Hardware revisions: Minor changes in BMS firmware or resistor values can exist across production runs, so behavior of the aux line can vary slightly by pack/charger revision. (stihlusa.com)

Suggestions for further research

  • Community reverse‑engineering threads on STIHL battery interfaces (showing communication lines on other STIHL platforms) provide a good methodology and pitfalls to avoid. (eevblog.com)
  • If you plan to develop an emulator, capture aux‑line waveforms during normal insert/remove/charge/run cycles with the genuine AS 2 + AL 1/AL 5/AL 5‑2; then design a small MCU board to mimic the observed signature safely. (stihlusa.com)

Brief summary

  • The STIHL AS 2 is a 10.8 V, 3‑cell pack with at least three terminals: +, −, and an auxiliary sense/ID line; STIHL does not publish an official pinout. (hutsoninc.com)
  • Parkside X12V batteries are the same voltage class but use a different mechanical interface and auxiliary‑pin scheme; they are not a drop‑in replacement for STIHL AS 2 tools/chargers. For safety, performance, and compatibility, use the intended AS 2 battery with STIHL AS System tools. (parkside-diy.com)

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