Does the USB output on the BlueSolar PWM LCD & USB follow the programmable load output?

Bit of a niche one this, but it's been bugging me since I set up the garden office last spring.

On my BlueSolar PWM LCD & USB, I always assumed the USB ports were tied to the load output — so if low voltage disconnect kicks in, everything goes off together. Turns out I'm not 100% sure that's actually the case.

I've got the load output set to disconnect at 11.8V (12V nominal LiFePO4 via Fogstar cells), and I think the USB ports kept charging my phone even after the load terminals went dead. Could've been a fluke or me misreading the situation, but it got me wondering.

Key question really: are the USB ports on this controller a completely separate output, powered directly from the battery regardless of LVD settings? If so, that's a bit of a problem for anyone relying on LVD to protect their battery — you could still be draining it through USB without realising.

Victron's documentation isn't exactly crystal clear on this (surprise surprise), and I couldn't find a definitive answer in the MPPT forum threads, though those are a different controller entirely so probably not comparable.

Has anyone actually tested this properly with a multimeter, or dug into the manual far enough to get a straight answer? I'd rather know for certain than just assume — especially with the emergency backup side of my setup depending on proper LVD behaviour.

Curious whether others have noticed the same thing or whether I was just imagining it.

@GlenDoug this caught me out too when I first wired up my tiny house setup.

The USB ports on that controller are independent of the load output — they draw directly from the battery regardless of your load disconnect settings. Bit counterintuitive when you first think about it, but Victron's logic is presumably that you'd want phone charging to keep ticking even if the load cuts at low voltage.

Practically speaking, this means if you've got low-voltage disconnect set to protect your battery, the USB will cheerfully keep draining it past that threshold. Worth bearing in mind if you're leaving anything plugged in overnight.

I tested this properly with a multimeter back when I was commissioning my array — load terminals went dead at my LVD threshold, USB stayed live throughout.

From what I've tested on mine — the USB is always live regardless of load output state. So even when the load cuts off due to low voltage disconnect, USB stays on pulling from the battery.

Caught me out when I was trying to protect my battery bank during a bad patch of weather. Load output cut as expected but something was still draining down overnight. Took me a while to track it to a phone left plugged in via USB.

Worth bearing in mind if you're running it as emergency backup like me — that USB draw adds up if something's left connected. Either unplug devices or factor it into your low voltage calculations.

No way to programme the USB separately on that unit as far as I know. If you need that level of control you'd probably want to step up to a Victron MPPT with proper load output logic.

Good timing on this thread — I looked into this exact thing a few months back when I was trying to figure out why my phone was still charging overnight despite the load output switching off.

To add a bit more detail to what @BorderOffGrid found: the USB draws directly from the battery, effectively bypassing the load output logic entirely. This means your low voltage disconnect settings won't protect you from the USB slowly draining the battery further if you've left something plugged in.

Worth bearing in mind if you're running a tight system over winter. I'd recommend either unplugging USB devices when not needed, or factoring that parasitic draw into your battery calculations. Small but it adds up across long dark nights!

Really useful thread this — and @GlenDoug, welcome to the forum if you're fairly new here! Great first question to kick off with, exactly the sort of thing that isn't obvious from the manual.

To add something practical: I've found this independent USB behaviour actually comes in handy on the narrowboat. Even when my load output cuts off to protect the battery overnight, I can still top up a phone or radio without overriding the LVD settings.

Worth noting though — the USB ports are rated at 3A total, so don't go expecting to run anything hungry off them. For anything more serious I'd wire a proper 12V socket to your load output instead and let the controller's programmable settings manage it properly.

The BlueSolar PWM range is decent kit for the price — solid choice for a garden office setup.

@BorderOffGrid is right in my experience. The USB ports on that unit are essentially always-on from the battery — they don't follow the load output at all. Learned this the hard way on my boat when I thought cutting the load would stop phantom drain overnight. It doesn't.

If you actually need USB to follow your load switching logic, you'd be better off wiring a USB charging module (one of those cheap 12v panel-mount ones) directly to the load terminals. Bit of a bodge but it works.

Worth checking your actual battery voltage regularly if you're leaving devices plugged into those USB ports overnight — the PWM controllers aren't exactly renowned for their precision low-voltage cutoffs compared to something like a Victron SmartSolar.