Hi folks,
I’ve got a Stream Engine 1-2kW hydro turbine in an off-grid house in Scotland which outputs around 80-100V DC when loaded, and up to 250-300V when unloaded. I’ve got two Victron Quattro inverter/chargers, a bunch of BYD Premium LV “48V” (more like 53-55V) batteries, and a Cerbo GX interfacing between the BMS and the inverters.
At present the turbine is connected to the DC bus via a HCON-2KW-48 wind turbine controller / lead acid charger. This has the nice property that, should the batteries become charged above a certain voltage, the charger incrementally adds resistive dump load to the turbine using PWM to regulate the turbine speed and voltage, eventually directly connecting the turbine to the dump load should the voltage go above a certain level.
However, this charger is for lead acid batteries so using it on the lithium battery system isn’t great - it doesn’t interface to the Victron system or the BMS at all, so it doesn’t respond to any charge voltage/current parameters from the BMS. This seems pretty unsafe for unattended operation; we’ve had problems with BMS and battery failures which have led to the DC power failing, which leaves the HCON-2KW-48 unit unpowered, so it doesn’t apply the dump load, and the turbine then spins unchecked for prolonged periods of time, damaging bearings and risking mechanical failure, vibration, leaks, etc.
I’d like to connect the turbine to the Victron system properly via something like a SmartSolar MPPT 150/35 which will be able to connect to the Cerbo via the VE.Direct connection, making the charge parameters responsive to the BMS, and also I can make use of the programmable relay to drive the turbine valve open and closed in response to voltage or state of charge. This works in the happy case that the system is sufficiently loaded to keep the turbine within the <100V range, but should the BMS lower the charge current to 0, the turbine will be unloaded and the voltage spike.
My original plan was just to put in an over-spec’d MPPT which would be able to handle the unloaded voltage from the turbine, so I grabbed a 250V MPPT in August, but when I got to the house and measured the unloaded voltage as way over 250V, this gets into 450V / 5+kW units which are a really expensive way to do what I’m trying to do.
Does anyone have any bright ideas? Do you know of any (ideally not too expensive) bit of kit which can do the incrementally adding a resistive dump load in response to voltage (eg add resistance between 100 and 150V), and then divert to the dump load should it exceed the Victron’s safe 150V input parameters? I did consider a voltage triggered relay, but taking an accelerating unloaded turbine to a suddenly very loaded one seems equally/more likely to make something break than just allowing it to spin unloaded for a period of time.
Thanks,
Rob