Key Technical Specifications

Parameter	Specification
Part Number	8700700-006
Model Designation	SQ-300I Microcontroller
Input Voltage	100-240 VAC, 50/60Hz
Controller Type	Microprocessor-based ESP controller
Primary Function	SCR firing control, spark rate regulation, voltage optimization
Application	Electrostatic Precipitator (ESP) high-voltage power supply control
Mounting	DIN-rail or panel-mount enclosure
OEM	Babcock & Wilcox (B&W)

 

Product Introduction

If you’re running a coal-fired boiler, a cement kiln, or a sinter plant with B&W electrostatic precipitators, you already know the pain of hunting for a replacement ESP controller. The B&W SQ-300I (8700700-006) is the microcontroller that sits at the heart of B&W’s electrostatic precipitator power supply system. It doesn’t just turn the voltage on — it constantly adjusts the SCR firing angle to maximize collection efficiency while managing spark rates. Too many sparks, and you’re wasting energy and eroding the plates. Too few, and your particulate emissions creep above permit limits.Engineers keep these units in stock because when they fail, the entire ESP field goes dark. The 8700700-006 revision handles 100-240 VAC input, which means it plays nice with global power systems. I’ve pulled these out of cabinets that have been running since the late ’90s. The microprocessor holds up, but the electrolytic caps on the power supply side are usually the first thing to go. If you’re swapping one in, check the firmware version against your existing units — mismatched firmware between fields can cause inconsistent spark detection thresholds.

Quality SOP & Tech Pitfalls

The Lab Report (SOP):Every unit goes through a five-step verification before it leaves our bench:

1. Visual and Counterfeit Inspection — We check the enclosure for heat damage, verify the B&W label and part number stamping, and inspect the PCB for capacitor swelling or burn marks around the SCR driver section.
2. Live Test on ESP Simulator — We power the unit at 120 VAC and 240 VAC, verify the microcontroller boots, and confirm the SCR gate pulse output responds correctly to simulated spark events.
3. Insulation Resistance Check — Megger test on the high-voltage sensing input circuit to rule out degraded isolation.
4. Firmware Version Logging — We record the firmware revision and cross-check it against the OEM compatibility matrix. Mismatched firmware is the #1 cause of “it works on the bench but not in the field” complaints.
5. Anti-Static Sealing — Unit is bagged in ESD-safe packaging with desiccant and a test report.

The Engineer’s Warning (Pitfalls):Two things will bite you with this controller:

• Firmware mismatch between fields. If you’re replacing a single controller in a multi-field ESP, the new unit’s firmware must match the existing controllers. Different firmware revisions can interpret spark rates differently, causing one field to run at a different voltage than the others. I once watched a plant spend three days chasing a “faulty transformer” before realizing Field 3’s new controller had newer firmware and was backing off voltage 15% earlier than the rest.
• Not photographing the DIP switch or parameter settings. The SQ-300I stores operating parameters (spark rate target, back-off angle, ramp rate) in non-volatile memory, but some installations use external jumpers or DIP switches for mode selection. Pull the old unit, take a photo of every switch position, and replicate it exactly on the replacement. Guessing gets you a tripped breaker.

 

Installation & Configuration Guide

Estimated swap time: 30 minutes (if you took photos beforehand).

1. Pre-Installation (⚠️ Safety First)
   • De-energize the ESP power supply and lock out/tag out the 120/240 VAC control circuit.
   • Wait at least 5 minutes for capacitor discharge in the T/R set rectifier.
   • Take a photo of the existing controller’s front panel settings, DIP switches, and wiring terminals. This step prevents 90% of post-swap headaches.
2. Removal
   • Label every wire at the terminal block with tape and a marker. Don’t trust the wire colors.
   • Release the DIN-rail clip or remove the mounting screws.
   • Slide the controller out carefully — don’t yank the wiring harness.
3. Installation
   • Copy all DIP switch and jumper settings from the old unit to the new unit before applying power. Double-check. Then check again.
   • Seat the new controller on the DIN rail and verify it’s fully engaged.
   • Reconnect labeled wires to the matching terminals. Torque terminal screws to spec (typically 0.5-0.6 N·m for these block sizes).
4. Power-On & Testing
   • Restore control power. Verify the controller boots — the display or LEDs should light within 5 seconds.
   • Check that the displayed parameters match your recorded settings.
   • Run a manual spark test (if available) to confirm the SCR firing output is functional.
   • Gradually ramp the ESP voltage while monitoring spark rate. Adjust the back-off angle if the unit is sparking too aggressively.
   • Download or verify the control program if your system uses external configuration software.

Compatible Replacement Models

• ✅ Drop-in Replacement: B&W SQ-300I 8700700-006 — Identical part number. Same firmware baseline. No reconfiguration needed if DIP switches are copied. Expect a premium price due to obsolescence.
• ⚠️ Software Compatible: B&W SQ-300I 8700700-004 (SCR Firing Module variant) — Same hardware platform, but the -004 revision is listed as a firing module rather than a full microcontroller. May require parameter reconfiguration and firmware verification. Budget 1-2 hours for commissioning.
• ❌ Hardware Mod Required: Third-party “universal” ESP controllers — These will require rewiring the SCR gate drive circuit, reconfiguring the spark sensing input, and potentially replacing the T/R set interface. Only attempt this during a full ESP retrofit, not as an emergency swap.

 

Frequently Asked Questions (FAQ)

Can I hot-swap this controller while the ESP is running?
No. The SQ-300I controls the SCR firing directly. Removing it while the T/R set is energized will cause an immediate loss of voltage to that field and may trigger a fault on the rectifier. Always de-energize the control circuit first.Is the 8700700-006 the same as the 8700700-004?
Not exactly. The -006 is listed as the microcontroller, while the -004 is listed as an SCR firing module. They share the same SQ-300I platform, but the -006 is the full controller. If you’re replacing a -006, stick with the -006 unless B&W engineering approves a cross.What’s the typical failure mode on these?
Electrolytic capacitors on the internal power supply. After 15-20 years, they dry out and the controller either won’t boot or resets intermittently. If your unit is rebooting randomly, that’s your culprit. The microprocessor itself is surprisingly durable.Does this work on 50Hz systems?
Yes. The spec lists 100-240 VAC at 50/60Hz. It’s rated for global use.How do I know if the firmware is compatible?
Check the firmware revision on the existing controller’s display or through the configuration software. Match it on the replacement. If you can’t match it, contact B&W technical support for a firmware upgrade path — don’t guess.Is this unit still manufactured by B&W?
No. The SQ-300I series is obsolete. Supply comes from new surplus stock or verified used units. If you’re planning a long-term operation, consider evaluating a full ESP control retrofit rather than stocking obsolete spares indefinitely.