Modifying CT Import/Export Readings - Dimplex Free-E

I have Dimplex Free-E solar diverter, but these is no way to set the export headroom to prevent it drawing below a set export reading (e.g. 200W). It seems to always aim for 0 but invariably ends up importing slightly.

I’ve tried adjusting the reading with different resistor values across the CT but this seems to cause more of a yoyo-ing effect (although I could do more experimentation).

I was wondering if it was possible to put a diode and resistor in one direction across the CT so that it under-reads the export level? This would hopefully cause it to ramp down aggressively when it sees import, but be less aggressive or be prevented from using up the reduced export reading?

Welcome, Ben, to the OEM forum.

I don’t know what’s inside your diverter, but I’d be prepared to say that neither of your ideas ever had the slightest chance of working. Lowering the value of the c.t. burden would decrease the sensitivity of the c.t. so increase the current it needed to see to read the same value - i.e. the opposite to what you wanted. Half-wave rectifying the c.t. output would dramatically distort the waveform, reduce the rms value and do much the same thing, albeit less predictably.

If you’re up for a steep learning curve, look at the ‘Learn’ section here to see how we measure power and determine its direction, and then look at Robin Emley’s “Mk2 PV Router” website, download one of his sketches and look at how it works and how he does the same thing - but as an option. In normal use, his diverter can and does exactly balance the dump load. I’m prepared to believe that your diverter works in much the same way. I think the only way you’d change yours, if it’s not a setting that’s accessible by you as a user or by their “authorised” techie or installer, is to rewrite the software for it.

In our experience, most commercial diverters behave exactly as you describe. If you want a Mk2 PV Router, he’ll be re-opening his shop later this week.

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Although not mentioned in the manual, so I don’t know what it really does, (and mine tracks closely, so I haven’t tried changing it to observe any effect) my Free-E has a Load Diversion adjustment in Advanced Settings.

I found reference to that in an aus manual. It just manually sets it to run at x% of load regardless of what the CT is stating. Maybe for troubleshooting or something?

Unfortunately, mine stopped working anyway. It just seems to run the immersion at full whack regardless of the CT reading. The unit doesn’t think it is active, the screen is blue and no fan kicked in so suspect a component has failed.

I’m afraid it sounds like that. If you’re up for a challenge, you could try all the normal fault-finding techniques, otherwise I’d recommend (of course) the open-source solution, because you have at the minimum all the information about how it works and details of all the parts you’d need to repair it should it ever fail.

A quick look suspect it might be this transformer, which seems like a few quid to replace so might try swapping it out.

Sorry to hear that and good luck with trying to fix it.

I was going to build a mk2 pv router but got a tip-off to the Free-E at a bargain price and it’s been OK after some initial problems which were fixed under warranty.