Volts and Amps

[SpottyDog5]

Dear collective.....
I looking to fit a battery isolator on my old Norton, I'm trying to fit the smallest (physically)one I can find.
The one I'm looking at is 100 amps at 24 volts continuous 500 amps for 5 seconds.
The Norton has an electric starter that pulls around 100 amps and is 12 volts.
What is the learned opinion of forum, is this suitable ?
Thanks in advance.
PS, sorry if I have posted in the wrong forum.

 

[Playtime]

The voltage (24V DC) is largely irrelevant - it's the current that matters and you are just on the max continuous rating. However, up to 5 times that is allowed for up to 5 seconds.

It should be fine, assuming you don't regularly need to crank for more than 5 seconds!

 

[macd]

I suspect it's the wrong forum, but what the hell.

I can't answer your question with authority, although it sounds like the isolator is at least as much up to the job as Norton's starter motor. But I can tell you you're lucky you've only got volts and amps to worry about. One of Norton's first prototype starter systems for the Commando 850 (I assume that's what we're discussing) was powered by...you won't believe this but it's true...shotgun cartridges. Such a system was quite commonplace aeons ago on piston-engined aircraft. Norton test-riders used to joke about riders wearing bandoliers of cartridges, falling off, and sliding down the road like Catherine wheels.

Norton soon ditched this explosive system and bought hundreds of Prestolite starter motors, which proved unable to crank over the 850 twin at sufficient speed. They eventually ended up in the T160 Triumph.

 

[lw395]

My experience with RIBs etc leads me to believe that battery isolators mostly fail because they are badly made and/or exposed to damp, rather than being rated too low.

Top tip is to make sure it's possible to put both leads on one terminal as a 'get you home' measure, and always carry the spanner to do this.

What Norton is it?

 

[SpottyDog5]

Thanks for the help Guys, this is the aftermarket starter that I have fitted :
http://www.britcycle.com/products/064791B.htm, it works great, usually starts her from cold fine
I have an inline 100amp blade fuse (the biggest they make)and occasionally this blows if I turn her over too long from a long period of standing, it also wet sumps so its pumping the oil back as well as the added resistance of the cold oil...
I put the fuse in there in case the starter relay stuck (happened once before, now replaced, no problem since) I like the idea of disconnecting the battery quickly should this happen again.
Now having read the spec on the motor a bit more, its easy to see why it blows a100 amp fuse

"Draws about 300 amps stall, 200-266 normal starting current, 120 amps once engine is turning.
Voltage depression at battery during current surge, 9.41-9.77v typical"
Btw she is an 1975 Mk 3 Commando

 

[charles_reed]

I suspect it's the wrong forum, but what the hell.

I can't answer your question with authority, although it sounds like the isolator is at least as much up to the job as Norton's starter motor. But I can tell you you're lucky you've only got volts and amps to worry about. One of Norton's first prototype starter systems for the Commando 850 (I assume that's what we're discussing) was powered by...you won't believe this but it's true...shotgun cartridges. Such a system was quite commonplace aeons ago on piston-engined aircraft. Norton test-riders used to joke about riders wearing bandoliers of cartridges, falling off, and sliding down the road like Catherine wheels.

Norton soon ditched this explosive system and bought hundreds of Prestolite starter motors, which proved unable to crank over the 850 twin at sufficient speed. They eventually ended up in the T160 Triumph.

That was also the method of cold starting the Field Marshall diesel tractor:- a 5 litre single cylinder 2-stroke with an enormous external flywheel beloved, in the 50s and 60s, of farm contractors. At tickover all dissolved into multiple images...

 

[SpottyDog5]

My old farther in law used to work at Marshall's of Gainsbough, used to love going to the agricultural shows and hearing his "inside knowledge" stories.