The short answer
For a diesel generator in a workshop, yard or camp, three numbers tell you most of what you need: is it running, how loaded is it, and is the starter battery healthy. A Shelly Pro 3EM on the output gives load and run hours; a Shelly Plus Uni measures the 12 V or 24 V starter battery directly on its 0–30 V input and reads the controller’s volt-free “running” contact. Both publish over MQTT, and InduQT warns when the battery dips lower on each crank or the load pattern changes.
- Run hours, starts and load on each phase
- Starter-battery health from the voltage dip on every crank
- An alert when the generator runs when it should not, or fails to
- What to buy
- Fit the sensors
- Turn on MQTT
- Set up the MQTT broker (once per plant)
- Check the readings with Claude before you connect anything
- Wire it to InduQT
- What InduQT does with it
What to buy
Load, voltage and energy on each phase of the generator output. Maker: Shelly. Maker’s page
Battery voltage on ANALOG IN (0–30 V); the controller’s running contact on IN1; powered from the same battery (9–28 V DC). Maker: Shelly. Maker’s page
Runs the MQTT broker and the InduQT bridge (skip it if you already built the gateway). Maker: Raspberry Pi. Maker’s page
Prices are typical street prices in US dollars when we wrote this, not quotes; buy from the maker or a local distributor. InduQT does not sell sensors and is not paid by any maker named here.
Fit the sensors
- Lock out the generator and disable auto-start.
- Fit the Pro 3EM clamps on the three output phases and its voltage inputs through fuses, in the generator’s output panel.
- Wire the Plus Uni: power from the starter battery (fused), ANALOG IN across the battery, IN1 to the controller’s volt-free “running” or “engine on” output.
- Restore and test-run: the meter shows load, the Uni shows the battery dropping during the crank and recovering.
Turn on MQTT
- Join the Shelly to the plant Wi-Fi with the Shelly app (or its own hotspot at 192.168.33.1).
- Open http://<device-ip> → Settings → MQTT and turn MQTT on. Server 192.168.1.20:1883, the sensors user and password.
- Client ID and topic prefix: factory/genset-1.
- Turn on “Generic status update over MQTT”. Save; the device reboots and starts publishing.
- Do the same on the Uni with the same topic prefix, factory/genset-1, so both appear as one machine. Set the Uni’s voltmeter report threshold to 0.1 V so it catches the crank dip.
You get factory/genset-1/status/em:0 (em_0.a_current, em_0.total_act_power …), status/voltmeter:100 (voltmeter_100.voltage, the battery) and status/input:0 (input_0.state, running).
Set up the MQTT broker (once per plant)
The sensors publish their readings to a broker: a small program that receives MQTT messages and hands them to whoever subscribes. Mosquitto is free and runs on a Raspberry Pi, an old PC or a small industrial box on the plant network. You need one per plant, not one per machine. If you already have a broker (Node-RED, Home Assistant, an IoT gateway), use it and skip this step.
# Raspberry Pi OS, Debian or Ubuntu
sudo apt update
sudo apt install -y mosquitto mosquitto-clients
# One user for the sensors and one read-only user for testing
sudo mosquitto_passwd -c /etc/mosquitto/passwd sensors
sudo mosquitto_passwd /etc/mosquitto/passwd viewer# /etc/mosquitto/conf.d/factory.conf
listener 1883
allow_anonymous false
password_file /etc/mosquitto/passwd
acl_file /etc/mosquitto/acl# /etc/mosquitto/acl
user sensors
topic readwrite factory/#
user viewer
topic read factory/## Mosquitto 2 wants these files readable only by its own user
sudo chown mosquitto: /etc/mosquitto/passwd /etc/mosquitto/acl
sudo chmod 0700 /etc/mosquitto/passwd /etc/mosquitto/acl
sudo systemctl restart mosquitto
sudo systemctl enable mosquitto
# Watch everything that arrives (Ctrl+C to stop)
mosquitto_sub -h localhost -u viewer -P 'viewer-password' -t 'factory/#' -vCheck the readings with Claude before you connect anything
Before the data goes anywhere, make sure the sensor is telling the truth. Record two minutes of messages to a file and ask Claude (or ChatGPT) to check them. This catches the usual first-day problems (a clamp on the wrong cable, a probe reading the room instead of the pipe, a sensor that only reports when something changes) while you are still standing at the generator.
# Record 2 minutes of messages to a file you can give Claude or ChatGPT
mosquitto_sub -h 192.168.1.20 -u viewer -P 'viewer-password' \
-t 'factory/#' -v -W 120 | while read -r line; do
echo "$(date -u +%Y-%m-%dT%H:%M:%SZ) $line"
done > sensor-sample.txt# Windows PowerShell, with Mosquitto installed from mosquitto.org
& "C:\Program Files\mosquitto\mosquitto_sub.exe" -h 192.168.1.20 -u viewer -P viewer-password `
-t "factory/#" -v -W 120 | ForEach-Object { "$(Get-Date -Format o) $_" } | Out-File sensor-sample.txtI've attached sensor-sample.txt: two minutes of MQTT messages from a sensor I just fitted to the generator.
Each line is: time, topic, payload.
Please check it for me:
1. List each topic and every numeric field in it, with the min, max and typical value.
2. Tell me whether the values are physically plausible for the generator. The battery should rest at about 12.6–13 V (or 25–26 V for 24 V) and dip during the crank, but not below about 9.6 V (19 V for 24 V). The three phase currents should be within about 20 % of each other under load. Tell me the lowest battery voltage during each crank and the load while running.
3. Point out gaps longer than 30 seconds, repeated identical values, or fields that are always 0.
4. Say which fields are worth sending to InduQT as signals and which I can ignore.
Answer in a short table, then a list of anything I should fix before I wire it up.Claude Code or Claude desktop with a terminal can run the mosquitto_sub command for you: ask it to "subscribe to factory/# on 192.168.1.20 as viewer for two minutes and check the readings". Either way the readings stay on your laptop: nothing is stored in InduQT until you wire it up in the next step.
Using a cloud broker (HiveMQ Cloud, EMQX Serverless or your own server with TLS) instead of one on the plant network? Add the free InduQT connector to Claude (https://claude.ai/directory/connectors/induqt) and Claude can listen to the broker for a few seconds itself:
Use InduQT to preview my MQTT broker before I connect it:
url mqtts://<your-cluster>.hivemq.cloud:8883, topic factory/#,
username viewer, password <viewer password>. Listen for 10 seconds.
Then tell me which topic level names the machine and which fields are numeric.Wire it to InduQT
Once the readings look right, send them to InduQT. The simplest way is a small bridge on the same Raspberry Pi: it listens to your broker and forwards every number to InduQT over HTTPS. It works on every InduQT plan, including the free one (up to 3 machines), and nothing on the plant network has to be opened to the internet.
- In Claude with the InduQT connector, paste the prompt below. Claude creates the site, the machine and a key that can only send readings to that site. (No Claude? Do the same in the InduQT app: Add machine with the same externalId, then Settings → API keys → a key with the ingest scope, limited to the site.)
- Copy the key Claude shows you. It is shown once.
- Start the bridge on the Raspberry Pi with that key.
- Ask Claude for the latest values, and set the normal bands.
Set up InduQT for this sensor:
1. Create a site called "Plant 1" (skip if it already exists).
2. Create a machine named "genset-1" with externalId "genset-1" and family "other".
3. Create an ingest key for the site called "Raspberry Pi bridge" and show it to me once.
After I start the bridge, I'll ask you to check the latest values. The signals will be em_0.*_current, em_0.total_act_power, voltmeter_100.voltage and input_0.state.python3 -m venv ~/induqt && source ~/induqt/bin/activate
pip install "paho-mqtt>=2.0" requests
export MQTT_HOST=localhost MQTT_USER=viewer MQTT_PASSWORD='viewer-password'
export MQTT_TOPICS='factory/#'
export INDUQT_API_KEY='iq_live_…' # the site key Claude or the app created for you
python3 induqt_bridge.pyinduqt_bridge.py (the whole bridge, about 120 lines)
#!/usr/bin/env python3
"""
induqt_bridge.py — forward MQTT sensor messages to InduQT.
Subscribes to your local broker, turns each message into numbers, and posts them
to the InduQT ingest API in batches. Works on every InduQT plan, including the free one,
and your broker never has to be reachable from the internet.
factory/<machine>/<anything> -> machine = <machine> (matched to the machine's externalId)
factory/pump-3/vibration {"vib_rms_x_g": 0.12} -> signal vib_rms_x_g
factory/comp-1/status/em:0 {"a_current": 12.4} -> signal em_0.a_current
(two or more levels after the machine: the last level names the group, so
two probes or two channels never overwrite each other)
{"temperature": {"tC": 41.2}} -> signal temperature.tC
factory/furnace-1/temp 21.7 -> signal temp (a bare number takes the last level)
pip install "paho-mqtt>=2.0" requests
"""
import json
import os
import re
import threading
import time
import paho.mqtt.client as mqtt
import requests
MQTT_HOST = os.environ.get("MQTT_HOST", "localhost")
MQTT_PORT = int(os.environ.get("MQTT_PORT", "1883"))
MQTT_USER = os.environ.get("MQTT_USER")
MQTT_PASSWORD = os.environ.get("MQTT_PASSWORD")
TOPICS = [t.strip() for t in os.environ.get("MQTT_TOPICS", "factory/#").split(",") if t.strip()]
MACHINE_LEVEL = int(os.environ.get("MACHINE_LEVEL", "1")) # factory/<machine>/... is level 1
SEND_EVERY = float(os.environ.get("SEND_EVERY", "10")) # seconds between posts
IGNORE = set(os.environ.get("IGNORE_FIELDS", "id,ts,time,timestamp,unixtime,Time").split(","))
INGEST_URL = os.environ.get("INDUQT_URL", "https://api.induqt.ai/v1/ingest")
API_KEY = os.environ["INDUQT_API_KEY"] # a site key from InduQT (Settings -> API keys)
BAD = re.compile(r"[^A-Za-z0-9_.\-]")
buffer, lock = [], threading.Lock()
def key(name):
return BAD.sub("_", name)[:64]
def numbers(prefix, value, out):
"""Collect every number in a JSON value; true/false become 1/0."""
if isinstance(value, bool):
out[key(prefix)] = 1 if value else 0
elif isinstance(value, (int, float)):
out[key(prefix)] = value
elif isinstance(value, str):
text = value.strip().lower()
if text in ("on", "true", "online"):
out[key(prefix)] = 1
elif text in ("off", "false", "offline"):
out[key(prefix)] = 0
else:
try:
out[key(prefix)] = float(text)
except ValueError:
pass
elif isinstance(value, dict):
for k, v in value.items():
if k not in IGNORE:
numbers(f"{prefix}.{k}" if prefix else k, v, out)
def on_connect(client, userdata, flags, reason_code, properties):
print(f"MQTT connected ({reason_code}); subscribing to {TOPICS}")
for t in TOPICS:
client.subscribe(t, qos=1)
def on_message(client, userdata, msg):
levels = msg.topic.split("/")
if len(levels) <= MACHINE_LEVEL:
return
machine = levels[MACHINE_LEVEL]
try:
payload = json.loads(msg.payload.decode("utf-8", "replace"))
except ValueError:
payload = msg.payload.decode("utf-8", "replace")
values = {}
group = levels[-1] if len(levels) - MACHINE_LEVEL > 2 else ""
if isinstance(payload, dict):
numbers(group, payload, values)
else:
numbers(levels[-1], payload, values)
if values:
with lock:
buffer.append({"machine": machine, "ts": int(time.time() * 1000), "values": values})
def sender():
while True:
time.sleep(SEND_EVERY)
with lock:
batch = buffer[:500]
if not batch:
continue
try:
r = requests.post(
INGEST_URL,
headers={"Authorization": f"Bearer {API_KEY}"},
json={"readings": batch, "autoCreate": True},
timeout=15,
)
if r.status_code < 300:
with lock:
del buffer[: len(batch)]
print(f"sent {len(batch)} readings: {r.json()}")
elif r.status_code in (400, 401, 403):
print(f"InduQT refused the batch ({r.status_code}): {r.text}")
with lock:
del buffer[: len(batch)] # fix the key or mapping; retrying will not help
else:
print(f"InduQT returned {r.status_code}; will retry")
except requests.RequestException as e:
print(f"network error, will retry: {e}")
with lock:
del buffer[:-5000] # keep at most ~5,000 readings while offline
client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2, client_id="induqt-bridge")
if MQTT_USER:
client.username_pw_set(MQTT_USER, MQTT_PASSWORD)
client.on_connect = on_connect
client.on_message = on_message
threading.Thread(target=sender, daemon=True).start()
client.connect(MQTT_HOST, MQTT_PORT, keepalive=60)
client.loop_forever()
Keep it running after a reboot (systemd)
# /etc/systemd/system/induqt-bridge.service — keeps the bridge running after a reboot
[Unit]
Description=MQTT to InduQT bridge
After=network-online.target mosquitto.service
[Service]
User=pi
EnvironmentFile=/home/pi/induqt-bridge.env
ExecStart=/home/pi/induqt/bin/python3 /home/pi/induqt_bridge.py
Restart=always
RestartSec=10
[Install]
WantedBy=multi-user.target
# then:
# sudo systemctl daemon-reload && sudo systemctl enable --now induqt-bridge
# journalctl -u induqt-bridge -fThe bridge treats the topic level after factory/ as the machine (it matches the machine's externalId and creates it if needed), turns every number in the message into a signal (nested fields become names like temperature.tC; when the topic has a group after the machine, such as Shelly's status/em:0, the group goes in front, as em_0.a_current, so two channels never overwrite each other; true/false and on/off become 1/0) and sends a batch every 10 seconds. It was run end to end on 2026-10-31 against Mosquitto 2 with Shelly Gen2, Theengs and plain-number messages. Prefer Node-RED? The same bridge as a Node-RED flow is on the gateway guide.
Show me the latest values InduQT has for genset-1.
Then set these normal bands so InduQT knows what "normal" looks like: voltmeter_100.voltage above 12.2 V at rest (24.4 V for a 24 V system).On the Plant Monitor plan InduQT can also subscribe to a broker directly. Point your sensors (or a Mosquitto bridge) at a cloud broker with TLS, then ask Claude to "create an MQTT connector for this broker, machine from topic level 1", or add it in the app under the site → Connect data → MQTT broker.
What InduQT does with it
- Tracks the lowest voltage on each crank and forecasts when it will fall below a safe start voltage.
- Counts starts and run hours for the service schedule.
- Flags a set that runs unloaded for long periods (wet stacking risk) or carries an unbalanced load.
Frequently asked questions
Can I use this on a wellsite or in a process area?
No. Hazardous areas need ATEX/IECEx certified equipment installed by certified people. Use your certified instruments there and bring the data out through the site’s control system or a certified gateway; InduQT can read OPC UA or MQTT from those.
Does the generator controller have the data already?
Modern controllers (Deep Sea, ComAp, Woodward …) often expose it over Modbus. If yours does, read it with the PLC/Modbus guide and skip the extra sensors.