No affiliation and no idea of price, but I thought it a nice little product for off-gridders.
We are familiar with throttling PV inverters using frequency shifting so production marries consumption.
This little relay is geared up to turn on loads at higher frequencies raising consumption to match production.
It’s called a Catch Power solar relay, in case the link doesn’t work.
EDIT: Actually at AUS $ 357.50, they can keep it.
I couldn’t even understand how it operates…
Aaah I’ve seen at least two of these products in the past. Some are even a bit smarter, they use a kind of PWM control to increase power proportional to the frequency.
I had one support case where it didn’t work properly. It was installed at a site where the PV was DC-coupled. Interestingly, you can still use frequency control even without AC-coupled PV, and it’s how you are instructed to install these with a Victron system. You install the PV-inverter assistant, and then you configure your solar chargers to charge a little higher than the Multi. The Multi sees the higher voltage and increases the frequency in order to throttle some non-existent PV-inverter. The higher frequency then controls the “hot water” switch. At this particular site, the solar offset specified in the manual of the device wasn’t enough to get a proper frequency shift…
@plonkster,
No, this doesn’t with PWM, it drives are relay, with settable hysteresis and settable timers.
You can switch in whatever you want.
It has a host of other functions too, but that’s the one that interests me.
Although, this does sound interesting as well. My MPPTs ( Outbacks) have an inbuilt PWM output that can be used to siphon off high battery voltages.
Obviously being DC equipment there is no frequency functionality.
Can you still remember the name of these products?
Can you control these Outback MPPTs (on/off)??
I want to schedule loads…
You’ll have to be more specific as to the intended application.
Outbacks are expensive, I wouldn’t consider them just for this added functionality.
I invested in a fine grid-tie inverter but have had far too many setbacks and consequently it was never installed (Huge thanks to CoCT!)
Consequently I’m now doing a cheap ‘keep the lights on’ inverter installation with whatever I have lying around. My 1kVA double conversion UPS is being pressed into service with some flooded 200Ah batteries.
I have 4 x 350W PV panels for my hot water system. This caters handsomely for my hot water requirements so I want to use these to charge the batteries when the water is hot enough…
So you have Outbacks already?
I think you are looking for a cheap PWM charger.
An Outback is a full-blown MPPT with an extra auxiliary PWM output that could drive an SSR to a dump load if there was also wind generation that drove the battery voltage too high for example.
It is expensive and a completely different animal to a cheap PWM charger
Yes. MX-60
Sorry, I just saw your post after my edit. I’ll reply again.
I don’t think the PWM function will help in your situation, as it is set relative to the charging settings.
See “diversion” in the manual.
The Outback can certainly charge batteries, though, like a standard 150V MPPT.
The MPPT will only power on when the battery supply is present, and it powers on automatically.
Your model is older than my Flexmaxs, and I don’t think the settings are involatile for any great length of time. So I don’t know if switching it ON and OFF at the battery side is a practical solution.
If your PV DC voltage is <150V, the cheapest, albeit a nasty solution would be to have a contactor chopover on the PV side driven by the geyser thermostat. This could divert the PV power to the MPPT.
You should already be using a contactor driven by your thermostat as the thermostat is AC-rated and won’t break DC.
The Geyserwise system controls the DC fed to the geyser element via the MPPT by a control signal fed to the MPPT. See: https://www.geyserwise.com/products/pv-water-heating-systems/150l-pv-water-heating-system/
So I can use this to disable PV heating of the geyser…
Very good, it’ll be spec’d to do the job then.
Unfortunately, it does appear that your panels are dedicated to water heating. I doubt they entertain any warranty claim if you alter the design.
And if they are connected in series as per the diagram, that will rule out using the 150V Outback MPPT.
No. The PV panels are connected 2S2P.
Then at least, it is in the realm of possibility.
I’m feeling better already! 
I followed up with Outback and they eventually came back saying it can’t be done!
Are you familiar with these Outback MPPTs?
My one died on me possibly due to switching the PV on before the battery…
Anyway the PV input is sc so it looks like one or more FETs have failed.
But the design puzzles me. Is it a transformerless system perhaps using inductors rather than transformers??
If someone perhaps has a schematic/circuit diagram then they will be welcome to produce this to clarify my troubled mind…
Sorry, I can’t help you here.
The Outback MPPT’s use a non-isolated buck converter topology, so no transformers.