Cyrix-Li-ct Without Vicron BMS

Running a Cyrix-Li-ct in my static with non-Victron lithium here — the relay needs a proper charge/load disconnect signal or it just sits there confused like me in a B&Q electrical aisle.

The thing is, Victron designed that unit expecting its own BMS to pull the remote pin low when things go pear-shaped. Without that handshake, you're essentially relying on your third-party BMS having a suitable load disconnect output (usually a dry contact or open-collector signal) that you can wire to the Cyrix remote terminal instead.

My setup uses Fogstar Drift cells with a Daly BMS — the Daly's charge MOSFET output isn't a clean signal for this job straight out of the box, but with a small relay in between it works a treat. Bit of faff, mind.

Few things worth checking before you commit:

• Does your BMS have a dedicated alarm/remote output rather than just cutting the discharge line?
• What voltage logic does the Cyrix expect on that pin? (It's looking for the line to drop, not rise)
• Are you using it for combiner duty between starter and house bank, or purely as an isolation switch?

Anyone else bodged a third-party BMS signal into a Cyrix-Li-ct successfully? Particularly curious if anyone's got a Victron SmartShunt or Cerbo GX acting as the middleman to translate BMS comms into something the Cyrix respects — feels like the tidier long-term solution once you're further down the Victron rabbit hole.

@PanelRob the "load disconnect" signal is the bit that catches people out. The Cyrix-Li-ct needs an allow-to-charge and allow-to-discharge signal, and most non-Victron BMS units only give you a simple relay output rather than the voltage-level signal Victron expects.

What BMS are you running? If it's got a dry relay output for charge/discharge protection, you can use that to pull the Cyrix control line low — but you need to check the logic levels match, otherwise you're back to confused-in-B&Q territory.

On my boat setup I ended up using a small relay board to translate the BMS output into something the Cyrix would actually act on. Worked a treat once wired correctly. Fogstar lithiums have a decent BMS with proper relay contacts which made this much simpler.

What's your actual BMS model?

@PanelRob my non-Victron BMS had a dry contact relay output which I just wired into the Cyrix-Li-ct's H terminal — bodged it in about 20 minutes between cups of tea and it's been solid ever since in the garden office setup.

@PanelRob worth flagging that the Cyrix-Li-ct specifically wants a high-side signal (typically 12V) on that H terminal to allow combining — so if your third-party BMS only pulls a line low on fault, you'll need a small relay to invert that logic. Caught me out when I first wired up the emergency backup in the motorhome.

Also check what voltage your BMS outputs on its protection signal — some cheaper units only manage 3.3V logic which isn't reliably enough to trigger the Cyrix. A simple transistor circuit or a decent relay module from Amazon sorted mine for about £3.

What BMS are you actually running? Knowing the specific output type would help narrow it down properly.

@MrBodge73 dry contact into H works until your BMS opens that relay mid-charge and the Cyrix sees the voltage collapse as a "disconnect" signal — then you're in a fun little loop of the relay chattering itself to death like a hyperactive woodpecker.

What actually sorts it: if your BMS only has a dry contact output, you need a small relay board to convert that to a proper 12V high-side signal referenced to your house battery positive. I used a basic 12V SPDT relay module (couple of quid on Amazon) in my static van setup — BMS dry contact drives the coil, switched 12V feeds the Cyrix H terminal.

Victron's own wiring diagram for non-Victron BMS integration covers exactly this — it's buried in the Cyrix-Li-ct manual appendix, naturally.

@Rob1963 had exactly that drama with my shepherd's hut Fogstar battery — BMS threw a wobble mid-charge, Cyrix dropped out, and suddenly my fridge thought it was 1987 again.

Solved it by adding a small latching delay circuit (basic 555 timer job) so a momentary BMS hiccup doesn't immediately yank the H signal — buys you a few seconds before the Cyrix actually disconnects.

Not glamorous, but neither is rewiring everything at midnight because your BMS sneezed.