Contactors and precharge

The main contactor is the switch between pack and inverter. Closing it onto an empty DC-link cap looks like a short. Contacts weld shut. You usually find out later, when it will not open.

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