Thanks for those links, Kurt and Kris. Very helpful.
PlanB wrote:Some thorny issues with these boxes on just what to disconnect & when, sometimes I worry we over think the why? So I just take the Leaf for a spin then I feel better.
So you reckon I should just take MeXy for a spin. Hmm, I think it's about time I drew up a complete schematic, in case there's something else I'm overlooking.
As much as I love MeXy's "exquisitely intricate mess of copper and iron, all twisted and interwoven" (Richard Feynman's eloquent description
of an induction motor/generator), I'm glad they are becoming less popular as domestic loads direct-on-line, since they play hell with relay contacts opening under load. Not so common in fridges and washing machines now, but still used on water pumps.
The annoying thing is that these relays will never be required to open if everything else is working properly, and yet they have to be spec'd to cope with operating every few minutes for days on end without welding, in case no one is home when something goes wrong.
The PIP-4048MS all-in-one inverter/charger/MPPT is convenient for running a PI control loop that uses serial comms to control charging, without having to worry whether it's from PV or genset. It's a pity they won't let us raise the inverter cut-off above 48 volts so we could do the same with discharging. But even if they did, the all-in-one nature of it forces the backup relays for load-disconnect and source-disconnect to be on the AC side (LV), whereas if the inverter was separate from the chargers, they could be contactors on the DC side (ELV).
Hmm. A thought. So that I don't have to worry so much about the AC relays welding their contacts:
Give the BMS control over the battery-isolation contactor too. If it has turned off the AC load relay, and the lowest-cell voltage is still falling, then it can drop out the battery contactor (an EV200). Likewise, if it has turned off both the AC genset relay and the DC PV array contactor (with their coils in parallel), and the highest-cell voltage is still rising, then it can drop out the battery contactor.
Fortunately this doesn't require a third relay-control output from the IMU. The battery contactor's coil can be powered by a diode-OR from the source and load relay-control outputs. Only if the BMS turns both of them off (or you hit the emergency stop) will the battery contactor go off.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).