Discharge

General Requirements

EV4.9.1 If a discharge circuit is required to meet EV6.1.5, it must be designed to handle the maximum TS voltage permanently.

After three subsequent discharges within 15s in total, the discharge time specified in EV6.1.5 may be exceeded. Full discharging functionality must be given after a reasonable time with a deactivated discharge circuit.

EV4.9.2 The discharge circuit must be wired in a way that it is always active whenever the shutdown circuit is open. Furthermore, the discharge circuit must be fail-safe such that it still discharges the intermediate circuit capacitors if the HVD has been opened or the TS accumulator is disconnected.

EV4.9.3 Fusing of the discharge main current path is prohibited.

EV6.1.5 If the shutdown circuit is opened, the TS must be shut down by opening all AIRs and the voltage in the TS must drop to below 60VDC and 50VACRMS in less than five seconds. All accumulator current flow must stop immediately.

SRR

Definitions/Meaning

Although our vehicles inverter contains its own discharge circuit, the FSG rules demands that the vehicle will have its own discharge circuit to discharge all the intermediate circuit capacitors (the circuit is connected to the inverter + and - poles) in a way that the HV in the vehicle side of the AIR's will drop to below 60V DC in less than 5 seconds after opening the AIR's.

Last year 2022

In 2022 we used a discharge circuit that uses a relay and two MOSFET's logic to discharge the inverter capacitors through a 1Kohms resistor (rated for 100W) when the SDC is opened.

the Discharge unit acts as completely passive unit, unless it reads the HIGH from the shutdown circuits it is always on discharge mode.

because the Discharge circuit based on transistors, as a safety feature, in case of faulty transistors, the transistors would behave as shorted circuit resulting the discharge function whatsoever.

The full schematics and BOM of the 2022's discharge circuit is presented in our drive:

https://drive.google.com/drive/folders/1PVwCn0_dHeWnd95FvIOfRuZv4PX5ZB-2

Last Year (2022):

last year we used A TE Connectivity HSC1001K2K1.2KOhms resistor rated for 100 W which we got as a free sample from TE connectivity (https://www.te.com/usa-en/product-1-1625999-1.html).

One disadvantage is that it quite big and requires a big HV enclosure together with the Discharge PCB.

The calculated discharge time for 1.2KOhms is 2.91 seconds with initial power of 170 watts across the resistor. This resistor is rated for only 100W but according to the datasheet it can withstand a power overload according to the following graph:

Which means the resistor should be ok with discharging our inverter.

The resistor dimensions are:

M = 87.5mm

N = 47.5mm

P = 26mm

Price: we have several units in our workshop and therefore no need to purchace it.

PDR

:Discharge Resistors

The discharge circuit from the 2022 vehicle has been tested and we found that the logic is working well, this year we want to try to optimize the discharge resistors selection to save space and weight.

Option B:

Another suggested option is using 2 TT WDBR7 150 Ohm resistor connected in series. These resistors are flat card shaped and can save space.

2 150 ohms resistors (in series) will provide a discharge time of 0.75 sec with initial power of 342W for each resistor (684W total), the resistors are rated for 280 watts each, but can withstand high power for short times according to the following graph:

Dimensions:

W = 101.6mm

L = 152.4mm

T = 1.5mm

Weight: 181gr

Note that using those resistors requires a heatsink.

CDR

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