How load balancing works, amp by amp.

The balancer is built around one rule: the site never goes over its connection. Everything else follows from it.

Why a site needs it

A site’s connection to the grid has a limit. If everything on the site draws more than that limit, the main breaker trips and the whole site goes dark.

Without load balancing, you either install only as many chargers as the connection can carry at full power, or you pay for a bigger connection. With it, the chargers share whatever the rest of the site isn’t using, so more of them fit on the same connection.

The rules ChargeIT never breaks

• Never over the limit. Every allocation is checked against the connection before it is sent. Not even for seconds.
• Cuts before raises. Power is taken back from chargers first and given out after, so a change never adds up to more than the site has.
• Never below the minimum. A car is never run below 6 A, the lowest current AC charging works at.
• Admission at 0 A. A new car waits at 0 A until there is room for it to charge properly, instead of squeezing everyone below the minimum.
• Fails safe. If no meter reading arrives for 30 seconds, the balancer drops to its safety plan instead of guessing.

How the headroom is worked out

Headroom is the connection limit minus what the rest of the site is using, phase by phase. ChargeIT shares the headroom between the cars that are charging: each car up to its own maximum, the rest shared between the others.

A worked example

One phase of an 80 A connection, with three cars plugged in: car 1 and car 3 can take up to 32 A, car 2 up to 16 A. The values are illustrative.

• At 34 A, the 46 A of headroom is shared three ways.
• When the building rises to 50 A, every car is cut to 10 A before anything else happens.
• At 64 A, three cars would each get about 5 A, below the minimum. So two cars charge at 8 A and the third waits at 0 A.
• At 20 A there is plenty of room. Car 2 is capped at its own 16 A, and the rest is shared between cars 1 and 3.

Site meters

In dynamic mode, an edge gateway reads the site meter over Modbus and sends the readings to ChargeIT. The register maps of these meters are checked against each meter’s documentation:

• Eastron SDM630, SDM230, SDM120 and SDM72D-M
• Carlo Gavazzi EM340 and EM24

What the chargers need

The balancing runs in the ChargeIT cloud and reaches the chargers through standard OCPP smart charging, so nothing proprietary runs in the charger. The charger needs firmware that supports OCPP charging profiles.

AC and DC chargers can share one site: AC chargers are balanced in amps, DC chargers by the power they report.