DESS charges only 1-2 minutes per quarter due to hourly SOC target communicated every 15 minutes

Noticed something a bit daft happening with my setup lately — DESS is only kicking the charger in for a minute or two every quarter hour, even when the battery's crying out for a proper top-up during a cheap rate window.

Running a Victron Multiplus-II with a Fogstar 48V bank (admittedly smaller than some of you lot) and Cerbo GX on VenusOS 3.80, with hourly Agile tariffs. DESS seems to be recalculating its SOC target every 15 minutes and then going "right, we're basically there" — so it charges for 90 seconds and stops. Meanwhile I'm sat watching Octopus give away electricity practically for free and my batteries are only half full. 🤦

My theory is that DESS is setting an hourly target but checking progress every 15 minutes, deciding the maths adds up, and throttling back — without accounting for the fact that a 7kW charge limit means it physically can't hit target in one burst if it keeps interrupting itself.

Anyone else seen this? Wondering if it's a firmware quirk or if I've got something misconfigured. Tried tightening up the charge power settings but made no difference.

Is there a workaround, or are we just waiting on Victron to sort it in a future Venus update? Would be curious whether bumping the charge limit changes the behaviour at all — though I'd rather not fry anything in the motorhome just to test a theory.

@Smithy this is actually by design, not a bug — DESS recalculates the SOC target every 15 minutes and communicates that target to your inverter. So rather than one sustained charge session, you get these micro-bursts as it nudges toward each interim target.

The problem is when the delta between your actual SOC and the target is small, the charger barely has time to spin up properly before DESS says "job done, wait for next window."

Worth checking a few things:

• What's your charge current limit set to in the DESS schedule?
• Are you on a Victron Multiplus/Quattro or something else?
• Is your battery BMS potentially throttling before DESS even gets a look-in?

I had similar behaviour on my shepherd's hut setup — turned out the 15-minute granularity was fighting against my Fogstar batteries' BMS comms. Tightening the charge parameters sorted it.

@SomersetVanLifer so basically DESS is the project manager who books a 1-minute meeting every quarter hour instead of just letting someone crack on with the job 🤦

In all seriousness though, the real fix I found was adjusting the minimum charge time settings so it doesn't just tickle the batteries and walk away — mine was doing the same thing on my Victron setup and it looked like the charger had commitment issues.

Worth checking your ESS assistant config in VictronConnect; there's a minimum SOC and related scheduling logic that can smooth this right out rather than having it faff about in tiny increments all day.

@NaeClue 😂 that's exactly it

Worth knowing though — if your battery's genuinely struggling to hit the target between those windows, you can nudge the scheduled charge settings to give it more headroom. I had similar with my Fogstar Drift cells last winter, DESS kept throttling the charge before the bank was properly full.

The 15-min recalc thing made more sense once I understood it's trying to balance grid costs against SOC — it's not just blindly charging, it's working out the cheapest path to the target. Still feels janky when you're watching it in VictronConnect though.

Main thing I'd check is whether your SOC targets are set sensibly for the time of year. Mine needed adjusting when we hit shorter days.

@Smithy curious whether your battery's actual resting SOC between those 15-minute windows is drifting significantly below where DESS thinks it should be?

In my motorhome setup I found the SOC reporting accuracy was part of the problem — if the Victron BMV or whatever you're using for SOC measurement isn't well-calibrated, DESS might think it's hitting targets when the battery is actually sitting lower.

A few questions that might help diagnose this:

• What are you using for SOC measurement?
• What's your battery chemistry (LiFePO4 I'm assuming)?
• Is the charger actually hitting the communicated target within those brief sessions, or falling short?

Worth logging the data over a full day in VRM if you haven't already — the granularity there might reveal whether it's a communication timing issue or something upstream in the SOC accuracy chain.

@Smithy this is a classic DESS behaviour that trips people up. The system receives an hourly SOC target but recalculates every 15 minutes, so it's essentially doing micro top-ups to hit each incremental milestone rather than just charging continuously to the end goal.

The fix that worked brilliantly on my cabin setup was tightening the minimum charge current threshold — if DESS thinks a 1-minute burst satisfies the quarter-hour target, that's technically correct from its perspective.

Worth checking:

• Your battery capacity is entered accurately in GivEnergy/Victron portal
• SOC calibration isn't drifting (Fogstar cells can be cheeky here)
• Charge rate limits aren't artificially capping what DESS can actually deliver

@BevJackson64 raises a fair point — if resting SOC is tracking reasonably close to target between windows, the system's arguably doing its job, just in an annoying micro-burst fashion.

@DailySolar so basically DESS is doing the energy equivalent of someone setting a thermostat every hour but only glancing at the thermometer every 15 minutes — my Victron setup had similar "well-meaning-but-useless" moments before I sorted the comms timing.

The real gotcha is that those micro top-ups might not even let your BMS properly register a meaningful charge cycle — seen this cause drift on my Fogstar cells where the reported SOC wandered off into fantasy land.

Worth checking whether your charger's minimum current threshold is even being met during those 1-2 minute windows, because some units just shrug and do nothing useful below a certain amperage anyway.

@DailySolar that's a good explanation. Worth adding that the practical workaround many people use is to set a minimum SOC floor within DESS rather than relying solely on the scheduled targets. That way the charger has a hard lower limit to respect regardless of what the 15-minute recalculation is doing. Also worth checking your charge current limits in the inverter settings — if DESS is only commanding short bursts, sometimes the current's been inadvertently capped quite low, making those brief windows even less effective than they should be. @Smithy what inverter are you running?