Mitsubishi MDS alarm 30 means over-regeneration — the regeneration detection level exceeded 100%: the regenerative resistor is overloaded. The drive integrates how hard the regen resistor is working; when the duty exceeds what the resistor can dissipate, alarm 30 trips before the resistor burns. It is the slow-cooking cousin of alarm 33 (overvoltage): 33 = the bus spiked NOW; 30 = the resistor has been over-worked over time. Mitsubishi's seven steps:
The seven steps, in prose
- Is the duty simply too high? If the machine's real regenerative load (frequent decel, heavy inertia, aggressive cycles) exceeds the fitted resistor's tolerable capacity → add/upgrade to the option regenerative resistor. A machine that grew a bigger chuck or faster cycle times can genuinely outgrow its resistor.
- Check the parameters — SV036 (servo) / SP032 (spindle): the regen-resistor type declared to the drive must match what is fitted. Wrong → correct it — a drive told it has a bigger resistor than reality under-protects; told smaller, it trips early. Classic after drive swaps and restores.
- External or built-in resistor? Determines the next check: external → step 5; built-in → step 4.
- Built-in: the P–D short wire. The jumper between the P and D terminals selects the internal resistor — not connected, disconnected, or contact-faulted → connect/reseat/replace. A missing P–D link after drive replacement is a textbook alarm 30 origin.
- External: the resistor wiring — incorrect connection → rewire per the diagram.
- The resistor and its cable themselves: disconnect and measure — resistor broken or resistance too high → replace the resistor; cable broken → replace the cable. An open regen path means every decel's energy has nowhere to go — expect alarm 33/overvoltage in the history too.
- Power supply voltage: above 253 V AC → review the supply. High mains leaves less regeneration headroom, working the resistor harder at every stop — the same night-time high-mains story as our alarm 33 guide. Voltage normal and everything above checked → the drive unit's regen control/detection is at fault — bench repair or exchange.
Tip: Alarm 30 clustering at specific jobs → duty (step 1): lengthen decel times or upgrade the resistor. After a drive swap → SV036/SP032 and the P–D jumper. With alarm 33 mixed in the history → the regen path is physically broken (step 6). And never ‘fix’ alarm 30 by declaring a bigger resistor in the parameter than is physically fitted — that converts a nuisance trip into a resistor fire.
Diagnosis checklist (in order)
- Which jobs trip it? Job-correlated → duty/resistor sizing.
- Verify SV036/SP032 against the fitted resistor.
- Built-in → check the P–D short wire; external → verify wiring.
- Measure the resistor and cable; replace as found.
- Measure mains: >253 V → fix the supply.
- All clear → drive unit regen circuit to the bench.
Related guides
- Mitsubishi MDS alarm 33 (overvoltage — the instantaneous cousin)
- Mitsubishi MDS alarm 10 (undervoltage)
- Mitsubishi M70/M80 alarm list
Alarm 30 tripping your cycles? JJ Automation sizes and supplies regenerative resistors, verifies regen configurations, and repairs MDS drive regen circuits at component level — on site in NCR. WhatsApp us or call +91 88022 12394.