Does this seem redundant to you

[tr8todd]

Lucas battery cut-off switch. Cool, but just one more thing to go wrong with the electrics in our TRs.

https://www.ebay.com/itm/Lucas-Original-B...r#ht_500wt_1330

 

[Darrell_Walker]

Notice they don't call it a "cut on" switch!

 

[TR3driver]

Required for many race tracks, though.

And not necessarily such a bad idea for a street-driven car. At least you'd be more likely to disconnect the battery when working on the car. Which I almost never do, even after one of the Stags tried to catch fire from a short in the steering column.

 

[angelfj1]

Lucas battery cut-off switch. Cool, but just one more thing to go wrong with the electrics in our TRs.

https://www.ebay.com/itm/Lucas-Original-B...r#ht_500wt_1330

No. Not really, I mean, not redundant since a switch capable of carrying full battery current (hundreds of amps at starting) has never been offered by ST or BL, at least not in a sports car. Some people add these as a cheap deterrent to theft. I don't see any reason why adding one would lower electrical system reliability. They are completely manual, just a simple pair of heavy contacts. I think they make good sense and could avert a disaster if Joe Lucas starts playing tricks.

P.S. Beware of cheap nock-offs from foreign lands. This one looks legit!

 

[justin_mercier]

That's actually a nice looking switch too... I might keep my eye on that myself to see if it goes cheap =) Right now it's only a few bucks more than the 7$ walmart ugly thing I've got attached to my battery.

 

[tr8todd]

Apparently I am the only one that sees the irony in a special part that makes Lucas electrics shut off---on purpose. For the record, a racing battery cutoff must have 4 posts to work. It needs to cut off all power to the engine even when the car is running, therefore you need two posts for the battery and two other posts to interrupt the alternator. A safety kill switch is no good after an accident if the engine keeps running off the alternator. The two pole design is only good for preventing battery drain during storage or for security reasons.

 

[TR3driver]

Apparently I am the only one that sees the irony in a special part that makes Lucas electrics shut off---on purpose.

Oh, you mean like a Lucas ignition switch to control a Lucas coil.

Actually, I think Lucas gets a bum rap. I have several Lucas items that are original to the car and still doing their job over 50 years later. Of course, now that I've bragged about it, no doubt something will break tomorrow!

<div class="ubbcode-block"><div class="ubbcode-header">Quote:] and two other posts to interrupt the alternator. [/QUOTE]
Assuming of course, that your race car has an alternator. Doesn't take much of a battery to run the ignition for an hour or two, and some folks don't like having the drag on the engine.

 

[dklawson]

Actually, I thought those switches or ones similar to them were used on the big Healeys. No... that's not TR or BL, but it is close to being BL.

Like Randall said, the 4-terminal switches like that are FIA approved parts for breaking the connection to the battery and dumping the alternator output to ground via a big dropping resistor. On my father-in-law's Formula-Vee we run on the battery alone and recharge the battery between runs. There are smaller power losses and fewer components to fail.

 

[70herald]

Actually, I think Lucas gets a bum rap.

AS if 50 year old Bosch parts on a VW never break down. Ignition switches come to mind....

 

[cheseroo]

For the record, a racing battery cutoff must have 4 posts to work. It needs to cut off all power to the engine even when the car is running, therefore you need two posts for the battery and two other posts to interrupt the alternator. A safety kill switch is no good after an accident if the engine keeps running off the alternator. The two pole design is only good for preventing battery drain during storage or for security reasons.

Not entirely true. We run a 2 pole on the Lemons RX7 because the alternator doesn't require a 4 pole. The Lemons Jag uses a 4 pole because the alternator does require it. The switches in both cars get tested in tech at every race (rev to 3k then dump the switch). The bigger set of poles is to cut power. The smaller 2nd set of poles is not to interrupt the alternator but to provide a place for the alternator to "bleed" off energy (the power it is creating) so that you don't smoke the diodes.

 

[TR3driver]

The smaller 2nd set of poles is not to interrupt the alternator

So, what keeps the alternator from self-exciting? I've only tried it a few times, but every car I've tried it on has kept on running just fine with the battery disconnected.

(Not advisable to try this, though, as the load dump that Rich mentioned can potentially drive enough voltage to pop diodes or even electrocute the person holding the battery cable.)

 

[tdskip]

The smaller 2nd set of poles is not to interrupt the alternator

So, what keeps the alternator from self-exciting? I've only tried it a few times, but every car I've tried it on has kept on running just fine with the battery disconnected.

(Not advisable to try this, though, as the load dump that Rich mentioned can potentially drive enough voltage to pop diodes or even electrocute the person holding the battery cable.)

Rich told me it was just magic and I shouldn't worry about it.

 

[Got_All_4]

NASA likes redundant systems. It it means more safety do it!

 

[dklawson]

The FIA switch I mentioned earlier actually has two big terminals and four small terminals.

The first two are the "big" main power disconnect.
The next two smaller terminals are for power going to the coil.
The third set are to "dump" the power from the alternator to earth. That's the pair that has the power resistor on it.

Rather than describe it in detail, please see the picture in the link below. (Sorry, I'm no good at embedding pictures in posts on this board).

https://media.turbosport.co.uk/2004/5/20045411162559398.gif