EG4 100a charge controller and JK inverter BMS

Has anyone actually got one of these combinations running smoothly in a motorhome setup? I've been looking at pairing an EG4 100A MPPT with a JK BMS-controlled lithium bank and I'm struggling to find decent real-world info on how well they communicate.

My main concern is whether the EG4 will properly respect the charge parameters coming from the JK BMS via CAN or RS485. On paper it should work, but I've read a few threads elsewhere suggesting the handshake can be temperamental depending on firmware versions.

A few specific things I'd love to know:

• Which protocol are you using — CAN or RS485, and which cable pinout worked?
• Did you have to manually configure charge voltages on the EG4 side, or does the BMS take full control?
• Any issues with the EG4 cutting in and out when the BMS sends charge suspend signals?

For context, I'm running a 200Ah 16S LiFePO4 pack in my motorhome. Previously had a Victron SmartSolar which handled everything beautifully, but the EG4 was considerably cheaper and the 100A rating is attractive for my roof space.

I appreciate Victron's ecosystem is hard to beat for integration, but I don't necessarily want to spend Victron money if the EG4 can do the job reliably. Has anyone switched over from Victron and actually been happy with it long-term?

Would be good to hear from anyone who's been running this combination for more than a few months rather than just initial impressions.

Hey @IanStevens, yes I've got almost exactly this running in my converted Sprinter. The key thing most guides miss is setting the EG4's charge profile to user-defined rather than lithium, then manually entering the voltage parameters your JK BMS gives you. My JK is set to cut at 56.8V (14S pack) and I've matched the EG4's absorption accordingly with a small buffer underneath.

The communication side is where it gets fiddly - are you planning to use the RS485 link or just letting the BMS handle protection independently? I went standalone BMS with no direct comms to the controller and it's been rock solid for eight months now. Happy to share my exact settings if you let me know your cell count and pack voltage. What capacity are you building?

@IanStevens the EG4 doesn't natively "speak" to the JK BMS so you'll need to set your charge params manually — lithium profile, absorption around 3.45V/cell, float at 3.35V, and for the love of all things 12V disable the equalization cycle or you'll be having a very bad day with your cells.

Been running a similar bodge in my shepherd's hut on Fogstar Drift cells — the JK BMS is doing the heavy lifting on cell-level protection anyway, so the controller just needs to not actively fight it.

Victron would talk to it properly via DVCC but that's a different budget conversation entirely.

@IanStevens ran almost this exact combination on my last motorhome build before switching to a full Victron ecosystem. @CamperCarl is right about the manual parameters — what caught me out initially was the EG4's absorption stage sitting too long and confusing the JK's cell balancing routine.

Couple of things worth knowing:

• Set absorption time to around 20 minutes max rather than letting it calculate automatically
• The JK BMS charge disconnect won't actually protect you from the MPPT briefly re-engaging — add a proper Victron Battery Protect or equivalent on the charge line
• Keep your bulk voltage at 3.45V per cell (27.6V for 8S) rather than pushing to 3.55V — the JK will thank you

The combo does work reliably once dialled in. Just needs patience with the initial parameter setup.

@CamperCarl is right about the manual params — been down this exact rabbit hole in my motorhome and the EG4's absorption voltage wants to live at 3.45V/cell (27.6V for 8S) or you'll cook your top cells while the BMS sits there lying to you about balance.

The JK's UART comms won't talk to the EG4 directly, so treat the BMS as your last line of defence, not your charge controller. Set conservative limits in the EG4 first, let the JK handle emergencies only.

One thing nobody mentions: the EG4 100A can be a bit twitchy on the absorption timeout — shorten it from default, otherwise it'll hammer a full bank unnecessarily.

Fogstar Drift cells are forgiving enough that small misconfiguration won't kill you immediately, but tighter chemistry cells won't be so charitable.

@IanStevens worth noting the JK BMS has a built-in active balancer which makes a big difference with lithium banks — mine ran noticeably better once I stopped fighting it and just let the BMS do its thing rather than relying on the controller to manage everything perfectly.

Also check your cable sizing between the BMS and controller. I had a nightmare voltage drop issue on my backup setup that had me chasing phantom problems for weeks before I realised it was just a dodgy crimp on an undersized run.

What cell chemistry are you running? LiFePO4 or something else? Makes a difference to the absorption voltage you'll want to plug into the EG4 manually since @CamperCarl and @FormerCop have already covered that side of things.