Contactors and precharge

You close the main onto an empty inverter. It sounds like nothing. A week later the car will not shut off, or it will not start, because the contacts welded shut on that first slam. You find out late.

Precharge first

Altran’s design guide: HV inverters have a large DC-link cap. Architecture is main +, main −, and a precharge contactor plus series resistor in parallel with main +. Sequence: close main negative, close precharge, charge through the resistor, close main positive, open precharge.

Thunderstruck FAQ: the controller uses a precharge circuit to charge its capacitors before the main closes — not to force the contactor just to “get it going.” Their VCU debug guide: do not force the main without precharge.

None of the three main-contactor datasheets print a required ohm value for a generic conversion. Altran’s 900 V / 8 mF / 1 s example is their example. Thunderstruck’s 50 Ω / 100 W kit is that SKU. ZEVA’s 48 Ω / 200 Ω are that module. Do not treat any of those as the number for your cap bank.

Parts people actually buy

Catalog: https://evengineeringlab.com/parts

TE KILOVAC EV200AAANA — TE catalog section 5-1773450-5: 12–900 VDC, 500 A typical continuous at 85 °C with 400 mcm. Built-in economizer (A coil, 9–36 VDC), 1.7 W hold at 12 V. Max make 650 A to avoid weld. Capacitive-make curves assume the controller is already at 80% min / 90% nominal precharge. Thunderstruck sells that P/N.

Altran AEV250 — Ver E (readable): 12–900 VDC, 500 A continuous at 85 °C, 1 Form X. Capacitive make: 50,000 cycles at 90% precharge, 50 cycles at 80% min. The Oct-2024 PDF is the file the catalog cites; Ver E is the sheet you can actually read those cells on. EV West AEV250-M. Shop “4000 A max” is not on Ver E.

Sensata Gigavac GV200 — Avertronics-hosted Sensata sheet: 500+ A, 12–800 VDC, Form X. “Applications with capacitors will require a pre-charge circuit.” Current-carry chart at 85 °C terminal rise: 400 A max on 4/0, 350 A on 2/0. The 500 A figure is the series headline, not that chart. ampREVOLT stocks MA / PA / QA coil options.

What people get stuck on

Close the main, then throw the disconnect, and you skipped precharge. DIYEC sticky (https://www.diyelectriccar.com/threads/precharge-what-is-it-why-do-i-need-it-how-do-i-do-it.25419/): that reintroduces the inrush. Check the controller for resistor size. That thread’s numbers (a 120 V bulb, 750 Ω, 10 kΩ) are that thread’s numbers.

Welded EV200s show up for sale. Do not reuse one. They are sealed and will reweld. https://www.diyelectriccar.com/threads/reusing-a-welded-contactor.92857/

A timer that closes the main whether precharge happened or not is the other failure. Close on voltage, not a blind timeout. https://www.diyelectriccar.com/threads/pre-charge-control-a-thought.91050/

OpenInverter SDU thread ohms (23 / 25 / 40 / 50 / “30–100”) are those packs. https://openinverter.org/forum/viewtopic.php?t=1652 An OEM HV junction box is not a drop-in precharge. https://www.diyelectriccar.com/threads/split-battery-packs-module-connections-to-bms-satellites.211968/

Sources

• https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=5-1773450-5_sec7_EV200A&DocType=CS&DocLang=English
• https://www.thunderstruck-ev.com/main-contactor-economized.html
• https://evwest.com/support/AEV250_Spec_Sheet_Ver_E.pdf
• https://www.altranmagnetics.com/dc-precharge-circuit-for-hybrid-and-electric-vehicles-design-guide/
• https://www.avertronics.com/upload-files/pdf/Sensata-Technologies/sensata-gigavac-gv200-series-open-contactors-datasheet.pdf
• https://www.thunderstruck-ev.com/faq.html