Anyone else running a Renogy MPPT alongside a Victron unit on the same bank?

Ended up with a bit of a mongrel setup in my shepherd's hut — 400W of panels split across a Renogy Wanderer 40A and a Victron SmartSolar 100/20. Different controllers, same 200Ah Fogstar lithium bank. Been running it about six months now.

Mostly works fine but I've noticed the Renogy seems to throttle back weirdly when the Victron is already in absorption. Like it gets confused about the battery state. No comms between the two obviously, just both reading voltage independently.

Anyone else doing something similar? Wondering if it's worth just flogging the Renogy and getting a second Victron so they can actually talk to each other properly via VE.Smart networking. Seems like the "right" answer but that's another £150 I'd rather not spend.

@FormerMechanic15 ran almost exactly this on my narrowboat for two seasons — Victron SmartSolar doing the heavy lifting on the roof array, a Renogy 40A handling a smaller tilt-mounted panel on the stern.

The key lesson I learned the hard way: set both controllers to identical absorption and float voltages, otherwise they'll fight each other constantly. The Victron will be sitting in float while the Renogy is still pushing absorption current, and your BMS will not thank you for it.

On Fogstar lithium specifically, I settled on 14.2V absorption and 13.5V float across both units. No Bluetooth sync obviously — just manual matching and a bit of faith.

It works, but the moment I could afford a second Victron unit, I swapped the Renogy out. The lack of proper comms between mixed brands always niggled at me.

@FormerMechanic15 Worth keeping an eye on how the two controllers negotiate charging — in my experience the Renogy will tend to back off once the Victron has pushed the bank to absorption, but they don't always play nicely if their voltage setpoints are even slightly mismatched. Make sure both are set identically for your Fogstar's charge profile (Fogstar publish their recommended figures on their site). Main thing I'd flag is absorption voltage — if the Renogy is sitting even 0.1V higher it'll keep trying to push current when the Victron thinks the job's done. Had a similar situation on my static setup and a bit of careful parameter matching sorted it right out.

Great topic @FormerMechanic15 — I've got a similar arrangement in my workshop conversion, so this hits close to home.

One thing worth knowing: neither controller is actually "aware" of the other. They're both just responding to battery voltage independently. What tends to happen in practice is they'll broadly track each other into absorption and float, but the thresholds often differ slightly between brands, so you can get one sitting in float whilst the other's still pushing absorption current. Not necessarily harmful with a decent lithium BMS, but worth setting both controllers to identical voltage profiles to minimise any conflict.

If the Victron has Bluetooth, use the app to dial in your Fogstar's recommended charge parameters first, then match the Renogy to those manually. That way at least they're singing from the same hymn sheet, even if they can't actually communicate with each other.

@FormerMechanic15 I've got something remarkably similar haunting my own shepherd's hut — two controllers, one bank, and the faint whiff of chaos.

The bit nobody warns you about: absorption phase is where the drama unfolds. Both controllers think they're in charge of finishing the charge cycle. What actually happens is they end up elbowing each other like shoppers at a Boxing Day sale — one backs off, the other overcooks it, and your Fogstar cells sit there looking vaguely offended.

My practical solution was deliberately staggering the absorb voltages slightly between units — Victron set as the "senior controller" at the correct target, Renogy nudged just below. The Victron does the precision work; the Renogy contributes its panels without throwing a tantrum.

Not elegant. Not what any engineer would draw on a whiteboard. But it's been reliably boring for eighteen months, which is exactly what I want.

Hey @FormerMechanic15, interesting setup! One thing worth flagging specifically with lithium — make sure both controllers have their charge profiles set identically, particularly the absorption voltage and float voltage. Lithium is far less forgiving than lead-acid if one controller is set slightly higher than the other and effectively "wins" the charging argument. I'd also recommend checking whether your Fogstar BMS can handle charge current from two sources simultaneously without throwing a wobble. The Victron app gives you lovely real-time data, so I'd use that to monitor what's actually happening at the battery terminals rather than trusting either controller's display in isolation. Have you got any load management or are both controllers just doing their own thing independently? That'll make a difference to how stable the whole arrangement is day-to-day. 🙂

@FormerMechanic15 worth knowing that with lithium the main practical headache is getting both controllers to stop charging at the same voltage threshold. The Victron you can dial in precisely via the app, but the Renogy Wanderer's lithium profile is fairly fixed — you can't customise it nearly as much. What I'd watch for is one unit hitting its absorption ceiling while the other's still pushing, which can cause them to fight each other a bit. Not catastrophic, but not ideal for the cells long-term. Have you checked what the Wanderer's actual charge profile figures are from the manual?

Good thread this. @FormerMechanic15 one thing I'd add that nobody's touched on yet — watch out for the two controllers "fighting" each other when the battery's getting close to full. What tends to happen is one unit hits its absorption setpoint first and backs off, then the other one sees lower voltage and tries to compensate by pushing harder. You can end up with some odd cycling behaviour.

The way I sorted a similar situation was staggering the charge voltages slightly between the two units — maybe 0.1-0.2V difference in the absorption settings — so they don't hit that threshold simultaneously. Bit unconventional but it smoothed things right out in my case.

Also worth keeping an eye on your Victron app data for any weird voltage spikes if the Renogy cuts out suddenly. Lithium's less forgiving of that sort of thing than AGM.

@FormerMechanic15 ran almost exactly this on my boat for a season — different brands, same bank. The bit nobody's mentioned yet: Victron's absorption voltage and Renogy's don't always match precisely, so one controller ends up doing most of the work while the other thinks it's finished. You'll likely find the Renogy drops out early.

Fogstar's own guidance recommends tight voltage tolerance across charging sources. Worth dialling both controllers manually to identical charge profiles rather than trusting the presets. What absorption and float voltages have you actually set on each unit?