# Multiplus-II trips the AC-input MCB **URL:** \ **Category:** DIY\ **Tags:** multiplus\_2\_gx, domestic, beginner\ **Created:** [7 March 2025 19:01 UTC](https://community.victronenergy.com/t/multiplus-ii-trips-the-ac-input-mcb/24483 "2025-03-07T19:01:02Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![havoc](https://avatars.discourse-cdn.com/v4/letter/h/c5a1d2/32.png) [@havoc](https://community.victronenergy.com/u/havoc)\ **Post date:** [7 March 2025 19:01 UTC](https://community.victronenergy.com/t/multiplus-ii-trips-the-ac-input-mcb/24483/1 "2025-03-07T19:01:02Z")
Multiplus II GX. **No battery connected.** Cause trip of B16 MCB some seconds after switching on. L-N “polarity” OK. I don’t have a battery a home, just wanted to update firmware and get access for the settings. Theoretically some capacitor charging can cause this inrush or there is something else? I re-read the manual, no word, that energization without battery is prohibited. ---
**Author:** ![DuivertNL](https://dub1.discourse-cdn.com/victron/user_avatar/community.victronenergy.com/duivertnl/32/279_2.png) [@DuivertNL](https://community.victronenergy.com/u/DuivertNL)\ **Post date:** [7 March 2025 19:02 UTC](https://community.victronenergy.com/t/multiplus-ii-trips-the-ac-input-mcb/24483/2 "2025-03-07T19:02:57Z")
Its a battery based system, so you either have to connect a battery or a big enough DC powersupply You can not run on only ac ---
**Author:** ![havoc](https://avatars.discourse-cdn.com/v4/letter/h/c5a1d2/32.png) [@havoc](https://community.victronenergy.com/u/havoc)\ **Post date:** [7 March 2025 19:06 UTC](https://community.victronenergy.com/t/multiplus-ii-trips-the-ac-input-mcb/24483/3 "2025-03-07T19:06:18Z")
1. Can you explain why, what physics behind that? 2. What do you mean y big enough power supply? I have 0-30V 5A lab, should I try, or no chance? ---
**Author:** ![DuivertNL](https://dub1.discourse-cdn.com/victron/user_avatar/community.victronenergy.com/duivertnl/32/279_2.png) [@DuivertNL](https://community.victronenergy.com/u/DuivertNL)\ **Post date:** [7 March 2025 19:10 UTC](https://community.victronenergy.com/t/multiplus-ii-trips-the-ac-input-mcb/24483/4 "2025-03-07T19:10:15Z")
Its designed to run from battery like an normal inverter, it needs to start from dc, needs ro be configured and then its ready to connect to ac If its a 12/24v multiplus, you can use that at the right voltage setting, not on a 48v multiplus Inrush will be higher then 5A, but you can try, or either build a pre charge circuit ---
**Author:** ![pwfarnell](https://dub1.discourse-cdn.com/victron/user_avatar/community.victronenergy.com/pwfarnell/32/2341_2.png) [@pwfarnell](https://community.victronenergy.com/u/pwfarnell)\ **Post date:** [7 March 2025 20:15 UTC](https://community.victronenergy.com/t/multiplus-ii-trips-the-ac-input-mcb/24483/5 "2025-03-07T20:15:38Z")
There is a large capacitor bank on the DC input. You connect the ac, the unit checks the ac, decides it meets the required voltage and frequency, closes the input relays and then your ac goes high trying to charge these capacitors. ---
**Author:** ![MikeD](https://dub1.discourse-cdn.com/victron/user_avatar/community.victronenergy.com/miked/32/1522_2.png) [@MikeD](https://community.victronenergy.com/u/MikeD)\ **Post date:** [8 March 2025 04:32 UTC](https://community.victronenergy.com/t/multiplus-ii-trips-the-ac-input-mcb/24483/6 "2025-03-08T04:32:21Z")
Although not specifically prohibited in the manual, the wiring order is Battery firs, then AC. However, there is screen print on the front cover of the inverter specifically saying to connect the battery cables before applying AC power. ---
**Author:** ![havoc](https://avatars.discourse-cdn.com/v4/letter/h/c5a1d2/32.png) [@havoc](https://community.victronenergy.com/u/havoc)\ **Post date:** [8 March 2025 09:37 UTC](https://community.victronenergy.com/t/multiplus-ii-trips-the-ac-input-mcb/24483/7 "2025-03-08T09:37:28Z")
> [@MikeD](#): > > the wiring order is Battery firs, then AC. No, the order of paragraphs in manual doesn’t mean the order of connecting AC/DC. > [@MikeD](#): > > However, there is screen print on the front cover of the inverter specifically saying to connect the battery cables before applying AC power. There is no such text on the front cover. The text on the cover says: “Disconnect the supply before making or breaking the connection to the battery”. There is lot of funny recommendations in this manual like "Do not lift heavy objects unassisted ", but really necessary information is missing or nот clear. PS: Solution with 24V DC power supply instead of battery worked for me.