Spoel van irrigatiekraan aansluiten op loaduitgang smartsolar 75/15

Been meaning to ask about this for a while so might as well stick it here.

I've got a Victron SmartSolar 75/15 on my static caravan and I want to use the load output to switch a 12V solenoid valve for a basic water feed setup. Nothing fancy — just one valve, not three like some setups I've seen discussed elsewhere.

My concern is the back-EMF spike when the solenoid coil de-energises. I know you're supposed to put a flyback/freewheel diode across the coil to protect the load output from those voltage spikes, but I want to make sure I'm doing it right before I fry anything.

A few questions:

• Which diode rating is sensible for a 12V solenoid drawing maybe 500mA? A 1N4007 seems overkill but it's what I've got lying around — is that fine?
• Does the 75/15's load output have any built-in protection, or is it basically bare?
• Has anyone actually run solenoid valves directly off a SmartSolar load output long-term without issues?

I'm also wondering whether the load output's low voltage disconnect would interfere with timed irrigation logic if I'm running it through a separate timer relay. Don't want the LVD kicking in mid-cycle and messing things up.

Got a Fogstar 100Ah LiFePO4 on the caravan so the battery side is solid — it's just this solenoid switching I'm unsure about.

Anyone done something similar on a boat or static setup? Feels like it should be simple but I don't want to assume.

@BayTim the load output on the 75/15 is rated at 15A continuous, but that's not the main concern with solenoid valves.

The issue is inductive kick — when the solenoid de-energises, it produces a voltage spike that can damage the MPPT's load output FETs over time. Victron's own documentation is a bit woolly on this.

What I'd do:

• Wire a flyback diode (1N4007 is fine) across the solenoid terminals, cathode toward positive
• Or better yet, use the load output to trigger a relay, which then switches the solenoid — keeps inductive nastiness well away from the SmartSolar

I've done exactly this on my shepherd's hut setup where I'm switching a 12V pump. The relay approach is cleaner and means you're not stressing the controller's output stage.

What's the solenoid's current draw? That'll determine whether a relay is strictly necessary or just advisable.

@SomersetVanLifer is right to flag that. The real issue with inductive loads like solenoid valves is the flyback spike when the coil de-energises — it can cause havoc with the MPPT's load output over time.

Had something similar on my boat with a bilge pump relay. What saved me was wiring a flyback diode (1N4007 does the job, costs pennies) across the solenoid coil terminals. Suppresses the voltage spike before it ever reaches the SmartSolar.

Also worth checking your solenoid's inrush current — some valves pull 3-4x their rated current at startup, brief but real. The 75/15 can handle momentary peaks, but worth knowing your numbers before assuming it's fine.

A cheap inline fuse between the load output and the valve is good practice too.

Has anyone actually done this on their setup and measured the spike? I'm curious whether a simple flyback diode across the solenoid terminals is sufficient protection, or whether you'd want a proper snubber circuit.

Also — does triggering the load output through the VictronConnect app introduce any complications here? I'm thinking specifically about the streetlight or BatteryLife modes and whether they'd interfere with timed irrigation logic.

What solenoid are you actually using @BayTim — is it a standard 12V latching or non-latching type? That makes a difference to how much current draw you're dealing with on the inrush side.

@VE_Boats yeah I did exactly this on my shepherd's hut irrigation setup last summer. Chucked a 1N4007 diode across the solenoid terminals (cathode to positive) and called it a day. Zero issues since, and the 75/15 hasn't complained once.

Total cost: about 12p from eBay 😂

Honestly the flyback diode is the move — dead simple fix and protects your MPPT from getting fried. I'd also recommend wiring a small blade fuse inline on the load output just as extra insurance, though technically the 75/15 handles that itself.

@BayTim just make sure your solenoid coil resistance gives you a sensible steady-state current draw — most 12V irrigation solenoids are well under 1A anyway, so you're miles within the 15A limit.