Fuses selection for MSXIV

Power calculation

	nom Power	max Power	nom current discharge	max current discharge	nom current charge (drive)	max current charge (drive)	nom current charge (Idel)	max current charge (idel)
Battery			0	0	0	0	0	0
Charger Interface		3300	0		0	0	-21.82539683	-21.82539683
Motor 1	2000	5000	15.28350909	40.21976077	-15.28350909	-40.21976077	0	0
Motor 2	2000	5000	15.28350909	40.21976077	-15.28350909	-40.21976077	0	0
Solar	-592.5	-1185	0	0	-4.527739569	-9.055479138	-4.527739569	-9.055479138
Pre-charger				2.1	0	0	0	0
DC DC	36	278	0.275103164	2.124407764	0	0	0	0
motor controller		18446.4
motor controller		18446.4

		Total current	30.84212135	84.66392931	-35.09475776	-89.49500068	-26.35313639	-30.88087596

Fuse calculation

IEC ampacity (A/m2)	1.3	cyclic load	1.3	alt(min)	2500	alt(max)	2600	Kx	0.8
	current	Kt(min) (T=60C)	Kt(max) (T=60C)	Kt(max) (T=45C)	Wire diameter	Cross sectional area	100% cable area	% cable used	Ke	Kv	Ka(min)	Ka(max)	I(rating) max	I rating min	wire current rating	maxium fuse
Battery fuse	84.66392931	0.845	0.9		6.15	29.70572204	65.12609947	0.456126227	0.95	1	0.975	0.97	165.0368992	144.8198791	255	191.25	EXRAD-XLX-4X
Charger fuse	21.82539683	0.9	0.9	0.95	2.58826	5.261452847	16.78876679	0.313391264	0.91	1	0.975	0.97	42.07710975	38.9739229	73	54.75	Awg 8
Motor fuse 1	40.21976077	0.845	0.9		4.95	19.2442185	30.93827752	0.622019713	0.95	1	0.975	0.97	78.40109312	68.79695922	155	116.25	EXRAD-XLX-6X
Motor fuse 2	40.21976077	0.845	0.9		4.95	19.2442185	30.93827752	0.622019713	0.95	1	0.975	0.97	78.40109312	68.79695922	155	116.25	EXRAD-XLX-6X
Solar fuse	9.055479138	0.845	0.9		1.62814	2.081964757	6.965753183	0.298885806	0.9	1	0.975	0.97	18.63267312	16.35017067	32	24	Awg 14
Pre-charger fuse	2.1	0.845	0.9		1.02362	0.82293855	1.615384615	0.50943815	0.95	1	0.975	0.97	4.093567251	3.592105263	16	12	Awg 18
DC DC fuse	2.124407764	0.845	0.9		1.02362	0.82293855	1.634159818	0.503585109	0.95	1	0.975	0.97	4.141145739	3.633855386	16	12	Awg 18

Thermal derating (Kt)

Thermal connection derating (Ke)

Recomendation

	Fuse	current rating
battery fuse	XEV25-175	175
Charger fuse	XEV10-50	50
Motor fuse 1	XEV20-80	80
Motor fuse 2	XEV20-80	80
Solar fuse	XEV10-20	20
Pre-charger fuse	XEV10-5	5
DC DC fuse	XEV10-5	5

For the lower-current fuses (Solar, Pre-charger, DC-DC), we will be using the axial bolt-on type.

Power calculation excel doc

Fuse calculation excel doc

Alternate Sources for fuses (since COVID happened and Eaton was not going to sponsor for a while)

Note On Interrupting Rating:

Fuses on our HV system should be able to project against a short circuit condition on the cables they are connected to. So what's the short circuit current?

The max current available from our batteries will be at their highest voltage, since a short circuit is just a resistive load. Maximum condition calculations will assume that the external short is 0mOhm, and the only thing limiting the current is the battery's internal resistance. This is a reasonable estimation as it will ensure an adequate safety factor for our fuses. Since our modules are in series, we only need to do the calculation for 1 module.

Voltage: 4.2V

Internal Impedance (using AC since a short circuit is a transient event, and AC IR is lower than DC IR typically): 25mOhm (ish - rough value of what was observed)

Short circuit current per cell (Iscc) = 4.2/0.025 = 168A

Short circuit current per module = 168A * 25 cells = 4200A = 4.2kA.

So all of our fuses must be rated to break a minimum of around 4.2kA.