I have a 2005 Mini cooper that is going to be used as an emergency response vehicle. I plan on connecting a siren directly onto the battery as the siren system has 4 - 15amp lines which has the potential to draw up to 60 Amps. Based on my calculations I shouldn’t be using more then 30 Amps. I was wondering if anyone new the current draw by the car right now (stock) and the maximum available. Also I will be using a barrier spade terminal directly onto the battery, would you recommend I put an inline fuse onto each line or since the battery is already fused it wont be necessary to add those fuses?

Thanks,
Adam

 

Where and what value?
A fuse protects your car & you from a short-circuit.
I have seen wiring smoke and melt away to nothing (no more metal, no more insulator) when shorted with no fuse.

If you have a thin wire "protected" by a big fuse, the wire will melt before the fuse - if you are lucky. Or the wire will catch fire and take the car with it.
You would be best advised to protect each wire with an appropriate fuse.


No idea what stock current draw of the MINI is. Lighting is a big consumer (guessing 200W of lights) so is power steering (?W). I suppose if you have the HK upgrade and run the sound at max volume that could be a big current draw too.

 

A MC has a 120 amp alternator. A MCS, because of space limitations, can only fit a physically smaller 105 amp alternator in the space between the blower and the a/c compressor.

The electrical system of MINIs is very well thought out and in the case of the MCS, a bit unique. The MCS has two feeds from the battery in the trunk: an unfused cable that supplies power to the starter as well as a connection for the alternator, and a second feed fused at 200-250 amps for all other accessories. Both the MC and MCS have a fuse box under the dash with several large fuses ranging from 30 to 50 amps in addition to smaller fuses, the larger ones feeding the high current drawing accessories. Hidden from view underneath are four more fuses, three of which are 50 amps which feed groups of smaller fuses (consider these as 'branch circuits') plus one 100 amp fuse dedicated to the power steering pump. This pump represents the biggest power draw in the electrical system after the starting motor. However, maximum power draw is only seen when making tight parking lot maneuvers and turning the steering wheel hard against the stops.

Your best bet is to use the fuse box feed terminal as your source and fusing your siren with a 30-40 amp fuse immediately after the terminal. Intermittent use of the siren and the occasional peak draw will not overtax the system, and the battery will fill in for those occasional times that the alternator gets overwhelmed. Do not use the jump start terminal, since this is not fused at all (but is protected in a crash by a 'Battery Safety Terminal' with a tiny explosive charge that is fired by the airbag system to disconnnect the battery in a crash serious enough to set off the airbags).

Accessory power 'hogs' roughly in order from heaviest on down:

Power Steering Pump
Radiator Fan
Heater-A/C Fan
ABS Pump
Rear Defroster Grid
H/K System at Full Blast
Headlights
Running Lights