Forge Power Kit — 500 W Modified-Sine Inverter (SG3525)

Every stocked part for the Forge reference design: SG3525 + LM358 driver board, six IRF3205 MOSFETs with their gate resistors and pull-downs, drain snubbers, bulk capacitors, low-battery relay and voltage sensor, PC817 feedback opto, blower fan, fuses and prototyping board.

Kit contents

• 1 × SG3525 with LM358 inverter driver board (PW-3056)
• 6 × IRF3205 MOSFET, 55 V 110 A (CMP-2715)
• 6 × 10 Ω resistor — one in series with each MOSFET gate (stops paralleled FETs oscillating) (CMP-1970)
• 6 × 10 kΩ resistor — gate-to-source pull-down on each MOSFET (keeps it off if the board is unplugged) (CMP-1967)
• 2 × 100 Ω resistor + 2 × CBB22 0.15 µF 630 V film capacitor — RC snubber, one per bank, drain to centre tap (CMP-1952, CMP-2520)
• 4 × 1000 µF 50 V electrolytic (CMP-1944)
• 1 × 5 V 1-channel relay (low-battery interlock) (MDL-2301)
• 1 × Voltage sensor module (battery, for the interlock) (PW-3215)
• 1 × 12 V 5015 blower fan (EM-1995)
• 1 × Fuse assortment kit (PW-2658)
• 1 × Dotted veroboard 12×18 cm (PRT-2587)
• 1 × PC817 optocoupler (feedback isolation) (CMP-2896)

Not included

• Transformer: 500 VA laminated, 9-0-9 V (or 10-0-10 V) centre-tapped primary to 230 V. Not 12-0-12: the feedback can only shorten the pulse, so a 12-0-12 primary sags to about 190 V once the battery is down to 10.5 V on load. Any transformer shop will wind it.
• 2 × 1.5KE36A TVS diodes, one per bank, drain to source (cathode on the drain). They clamp the turn-off spike under the IRF3205's 55 V rating. We're adding them to stock; until then buy them locally.
• 60 A fuse and holder, 10 AWG cable, heatsink, case and socket.

12 V only. On a 24 V battery the push-pull puts about 58 V on each drain before any spike, over the IRF3205's 55 V. For 24 V use IRFP4468 MOSFETs, 1.5KE68A clamps, a 24 V transformer, and an L7812 to feed the driver board.

The full build guide — block diagram, wiring, why-these-parts, gotchas and safety — is the modified-sine-inverter-sg3525-500w reference design in Forge: forge.microscale.net/design (ask for it by name). Print the enclosure with Forge Prototype.