The YYI-2 is a generic low-voltage DC current monitor with a programmable relay output. It can display current and switch its relay when current crosses thresholds you set, making it useful for noncritical experiments such as detecting a motor load or triggering an alarm. It is not a certified overcurrent protector, and its wiring, supply-voltage variants, and relay ratings are not consistently documented. Before connecting one, verify the exact board’s terminals and test whether its sensing path shares a ground with its power input.
What the YYI-2 does
The YYI-2 is sold under descriptions including “DC current detection module,” “overcurrent protection relay module,” and “motor stall protection board.” Those names describe possible uses, not a formal product standard. Its electronics monitor current in a DC circuit, compare the reading with one or two setpoints, and operate an onboard relay according to a selected mode. Product descriptions and documentation identify a 0–10 A DC measurement range, a digital display, I1 and I2 thresholds, and a current-error adjustment. Mantech datasheet · Lonten Tech product page
It may be useful for detecting a motor starting, stopping, or drawing unusually high current; controlling an alarm input; or signaling that a load has disconnected. Whether it is suitable depends on the particular board revision and installation. The available listings do not establish a consistent manufacturer or universal terminal diagram.
Reported specifications—and what they mean
| Item | Reported value | Qualification |
|---|---|---|
| Measurement range | 0–10 A DC | Repeated in listings and product documentation; verify the specific board. |
| Display increment or claimed accuracy | 0.01 A (10 mA) | This may describe the display or setting increment; it is not a guaranteed ±10 mA accuracy specification. |
| Standby current | Approximately 20 mA | Reported by product descriptions; the actual module may differ. |
| Supply voltage | Listings describe 5 V, 12 V, and 24 V versions; some claim 5–24 V or 7–30 V | Seller claims conflict. Treat versions as potentially different boards, not interchangeable options. |
| Relay switching rating | 5 A or up to 10 A DC, depending on the listing | Conflicting claims; assume no more than 5 A unless reliable documentation for the exact revision supports otherwise, and derate for the load. |
| Contacts | Commonly COM, NO, and NC | Confirm markings on the actual board before wiring. |
Sources: Mantech datasheet, Lonten Tech product page, and Newegg listing.
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A 10 mA display step does not establish measurement accuracy across the range, near zero, at different temperatures, or with pulsed and noisy loads. The product material does not provide a traceable tolerance, temperature specification, or validated response to switching noise. If a threshold matters, compare the display with a trusted meter under the actual load conditions.
How the P-11 through P-52 modes behave
The documentation describes ten modes in five pairs. In each pair, the second mode is intended to latch the relay until module power is removed; confirm behavior on your board before relying on it. The English descriptions are translated and may be ambiguous, so test the relay with a safe, low-voltage indicator before connecting a load.
| Mode | Relay behavior described |
|---|---|
| P-11 | Activates above I1; releases when current falls below I1. |
| P-12 | Activates above I1 and remains active until module power is removed. |
| P-21 | Activates above I2; releases when current falls below I1. |
| P-22 | Activates above I2 and remains active until module power is removed. |
| P-31 | Activates below I1; releases when current rises above I2. |
| P-32 | Activates below I1 and remains active until module power is removed. |
| P-41 | Activates between I1 and I2; releases outside that range. |
| P-42 | Activates between I1 and I2 and latches. |
| P-51 | Activates below I1 or above I2; releases when current is between them. |
| P-52 | Activates below I1 or above I2 and latches. |
These behaviors are reported in the Mantech documentation and Lonten Tech product page. “Above” and “below” refer to the configured thresholds; check how the board treats a reading exactly at a threshold.
Programming I1, I2, and the operating mode
Published instructions describe three buttons, commonly marked K1, K2, and K3. Button mapping and firmware may vary, so use the board’s own markings and verify the result rather than assuming every revision behaves identically.
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- Power the board from the correct DC supply for its specific version.
- Press and hold K1 for more than one second to enter setup. The display should show a mode such as P-11.
- Use K2 and K3 to select the desired program, following the control mapping for the board.
- Press K1 to move to I1, then adjust the threshold with K2 and K3.
- Press K1 again to reach I2 and set it if the selected mode uses it.
- Press K1 to return to the current display and standby operation. Test the relay’s response at safe currents.
The instructions say a short K1 press is ignored or avoided to reduce accidental triggering. In standby, holding K2 or K3 is described as adjusting the displayed-current error. Treat this as offset calibration, not a substitute for a calibrated instrument: compare against a trusted meter, and check more than one current if accuracy matters. Mantech instructions
Wiring: keep power, sensing, and relay contacts separate
The board has three distinct electrical functions: its DC power terminals run the display and control electronics; the sensing path carries the current being monitored; and COM, NO, and NC are relay contacts used as a switched output. Labels and internal connections are not consistent enough to infer a universal pinout from the YYI-2 name. Do not wire from a generic diagram unless it matches the exact board revision in front of you.
A current-sensing element ordinarily has to be in series with the conductor being measured. But one documented YYI-2 revision showed continuity between a sensing negative and module DC negative. That is user-measured evidence for one board, not proof that all revisions share the same topology. If you assume the sensing terminals are an isolated, floating inline input, you can create a short instead of a valid measurement circuit. All About Circuits discussion
Verify the actual board before applying power
- Photograph both sides of the PCB and the terminal labels. Identify the exact supply variant from the board and seller documentation.
- With the board unpowered and disconnected, use a multimeter’s continuity mode to check whether sensing negative connects to DC−, whether sensing positive connects to DC+, and whether either sensing terminal connects to relay contacts.
- Map the relay’s COM, NO, and NC contacts from the board markings or reliable documentation; do not assume contact state from terminal position.
- Use a current-limited bench supply and a low-risk test load first. Fit an appropriate fuse close to the supply.
- Once operating, check voltage drop across the sensing path and confirm the displayed current against a trusted meter.
Continuity tests can reveal a shared electrical reference, but they do not establish a safe load rating or complete pinout. If the connections remain unclear, do not connect the board to vehicle wiring or valuable equipment.
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Why a fuse can blow in an automotive installation
In one reported car-alarm installation, a user routed a fused siren supply through sensing terminals while also using the same fuse tap to power the module and a GPS tracker. The user reported an immediate blown fuse and continuity between a sensing negative and module ground. The discussion attributed the failure to wiring that effectively connected supply positive to ground, and the user later reported success after changing the arrangement. This is a single board and installation report, not a universal YYI-2 circuit. All About Circuits discussion
- A shared ground can make a sensing terminal non-floating, so connecting it as though it were an isolated ammeter input can short the supply.
- A fuse tap may place module power in parallel with, or directly across, the intended sensing path.
- Depending on the wiring, the board’s own roughly 20 mA standby draw may be included in the measured current.
- Never assume the board is automotive-qualified: transient, reverse-polarity, temperature, and vibration specifications are not established in the available product material.
When it can work—and when it is the wrong protection device
Motor load or stall indication
A motor’s current often rises under heavy load or stall, so an upper threshold can provide an indication or control signal. Set the threshold above normal startup current, which may be higher than running current. Test across the expected load and temperature conditions. Do not assume the onboard relay can interrupt the motor safely; it may be more appropriate to use the YYI-2 output to control a properly rated contactor or MOSFET stage.
Alarm or event trigger
A user in the cited automotive discussion reported a roughly 0.3 A increase when an alarm sounded and used the relay to simulate a GPS tracker SOS-button press. That example shows a possible use, not a guaranteed sensitivity or a universal wiring recipe. Vehicle voltage, pulsed siren current, shared loads, battery state, and wiring resistance can affect a threshold. Confirm whether the receiving input expects a dry contact, a pull-to-ground signal, or a particular voltage before connecting relay contacts.
Undercurrent or load-disconnect detection
Modes P-31 and P-32 are described as activating below I1 and releasing above I2, which may suit detecting a stopped pump, fan, lamp, or motor that has ceased drawing current. Test the transition and latching behavior with the actual load before making it part of an unattended system.
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Overcurrent protection
The YYI-2 can display a reading and change relay state around a threshold, but the available material does not establish certified protective behavior, a fail-safe state, overload response, or a reliable relay rating across revisions. Do not use it instead of a correctly sized fuse or circuit breaker where fault-current protection or fire safety is involved.
Relay limits, failure behavior, and safety checks
Listings conflict between a 5 A and 10 A DC relay claim. Until documentation for the exact revision proves otherwise, treat 5 A as an upper claimed figure, not a target operating current. Motor startup surges and inductive loads such as solenoids are harder on DC contacts than resistive loads; DC arcs do not benefit from the natural zero crossing that helps extinguish AC arcs. Derate for the load and use a better-rated external switching device when needed.
The available documents do not establish what happens if module power is lost, the sensing input is disconnected, current exceeds 10 A, the supply sags, the relay welds, or the control electronics fail. They also do not provide thermal derating curves, enclosure guidance, PCB trace ratings, or transient specifications. Do not rely on an assumed default relay state for a safety-critical function.
- Fuse the supply appropriately and keep the fuse close to the source.
- Verify polarity, supply voltage, sensing direction, and terminal continuity before connection.
- Keep mains AC off this low-voltage DC module.
- Test startup surges, normal operating current, threshold transitions, and power-loss behavior with a noncritical setup.
- Use an independent protective device where a fault could cause injury, fire, or equipment damage.
Troubleshooting common problems
The fuse blows immediately
Disconnect power and remove the load. Recheck the terminal identities, polarity, fuse-tap orientation, and continuity between sensing terminals and module ground. A sensing terminal that shares a rail with DC− must not be treated as an isolated input. Map the circuit with a meter before retrying. A reported YYI-2 wiring fault
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The display works but current is wrong or stays at zero
- Confirm current actually flows through the sensing path in series with the load.
- Check whether the load is connected in parallel or to the wrong terminal.
- Check whether the display is showing the module’s own supply current rather than the intended load.
- Consider zero-offset calibration, low practical sensitivity, or a pulsed/noisy load.
The relay switches at the wrong threshold
Confirm the selected mode uses the threshold you changed, that I1 and I2 are set as intended, and that the relay is not latched. Recheck the reading against a trusted meter and verify whether the load current hovers or jumps around the setpoint. Also confirm whether you are using NO or NC contacts as intended.
The relay chatters
If current hovers near a trip point, the relay may repeatedly change state. Where the mode supports it, use separated I1 and I2 thresholds so activation and release occur at different currents. A latching mode can retain a fault state but requires power removal to reset according to the documentation. External filtering, timing, or a better-suited controller may be needed for unstable loads.
The board overheats
Check for excessive current, high relay-contact stress, an incorrect supply voltage or polarity, and transients from motors or solenoids. Stop using the board if it becomes hot; the available specifications do not provide thermal limits or derating guidance.
When to choose another approach
| Alternative | Better fit when | Trade-off |
|---|---|---|
| Shunt resistor with a monitor | You need a more explicit current path, better measurement documentation, or telemetry. | May need a separate display, controller, or relay driver. |
| Hall-effect current sensor | Galvanic isolation or low insertion loss matters. | May cost more and require signal conditioning or a separate controller. |
| Industrial current-sensing relay | You need published ratings, support, enclosure options, or a more dependable installation specification. | Generally costs more than a generic board. |
| Fuse or circuit breaker | You need basic short-circuit and overcurrent protection. | Does not provide the YYI-2’s display and programmable current-based relay logic. |
| Microcontroller plus current sensor | You need logging, delays, communications, or custom logic. | Adds firmware and system-design complexity. |
| MOSFET or solid-state power controller | The load must switch frequently or without relay contact wear. | Requires appropriate current and voltage ratings, heat management, transient protection, and fault handling. |
What to verify before buying
- The exact supply-voltage variant; do not assume a 12 V board accepts 24 V because another listing advertises a broad range.
- Clear photos of both PCB sides, terminal labels, and markings for the specific revision being sold.
- The sensing topology and whether its terminals share a reference with module power.
- A documented DC contact rating for the actual load type, not merely an unspecific “10 A” headline.
- Whether the thresholds, latched modes, and button sequence match the documentation supplied with that board.
- A practical return option if the seller cannot confirm the pinout or variant.
Marketplace availability and prices vary by seller and region. One Lonten Tech page lists several voltage variants but marks the product sold out; a Newegg marketplace listing is sold by a third-party seller, while Electronics Katrangi Trading lists it for its regional market. Those listings are not evidence of a consistent first-party manufacturer or universal support. Lonten Tech · Newegg · Electronics Katrangi Trading
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