Current draw from the battery to the starter of E36

[Franky goes]

I'm retrofiting the race car with a cut-off switch and a cable from the battery to the front post located in the engine bay just ahead of the DME access.

The plan is to use the OMP 6 pole switch sold everywhere :
https://www.pegasusautoracing.com/do...ocID=TECH00109

The instructions show the rating of the large pole as 100 continuous amps and the secondary pole as 5 amps if I remember correctly.

The large pole is straight forward with the alternator rated at 80 amps making this the highest continuous current in the case of the alternator recharging a dead battery. I don't have a dead battery on hand to measure the current to the battery in such a situation but I suspect it will not be the full 80 amps since the alternator also has to run the car in that situation... If someone has measured the current in the large wire I am curious to find out the figure.
I measured it when the starter is activated to start the car in 60 degree weather and the draw is approximately 20 amps which I find low and makes me second guess my amp meter.

The secondary pole shows continuous currents between 0 and 2 amps with short peaks at 4 amps.

So the switch design is sound.
I would like to find out the maximum current draw in the large wire to the battery if someone has measured it.
In the mean time I am looking for a drained battery and will update when I can test it.

Thanks.

[NeilM]

A starter can draw 200 amps, sometimes more under adverse circumstances. To me that suggests running only the starter's solenoid wire through the new disconnect, but leaving its power cable directly connected to the battery feed (from the trunk, assuming your battery is still in the trunk).

That said, I don't race prep cars. There may be safety regulations or best practices on the subject that I don't and wouldn't know about.

Neil

[olemiss540]

Not sure your concern. That kill switch is rated (per pegasus): 100 Amps continuous duty and 500 Amps peak current.

There should be nothing bypassing the kill switch running to the battery. The kill switch is fed with a single cable back to the battery and on an e36 has the cable that runs from the kill switch output (has a split wired into the facotry wire) to run to both the alternator and starter.

The kill switch also has a ground wired with a resistor to short the alternator to ground in case of residual power and then has a feed to take your main wire (12ga or whatever) to the fuse panel. This main fuse panel wire feed will power the entire system including the starter switch/button which will feed the starter signal.

[NeilM]

Not sure your concern. That kill switch is rated (per pegasus): [COLOR=#000000][FONT=Verdana]100 Amps continuous duty and 500 Amps peak current.

And there's the missing information needed: 500 amps peak is plenty to handle the starter's short-time load..

Neil

[Franky goes]

Thanks.
The current draw says 20 amps on my gauge. It is probably too cheap to read a very short burst when the starter engages.
I'm still curious about the amperage going to the battery when being rechargeed by the Alternator.

I don't have a concern. i'm curious to know where the current goes and when and at what intensity.

[olemiss540]

I am going to guess it is 120 amps or 140 amps depending on which model alternator you are using. Also think there may be an 80 amp alternator but that's just a wing shot.

[NeilM]

The stock E36 alternator is 80A. There's also an available 140A version, but I don't know that it was ever used for production, or if it was, why. Unless you have banks of 60's era Cibié Super Oscar rally lights, or some giant thumpa-thumpa stereo system, the stock 80A is plenty adequate.

Neil