DIY: Battery Relo

wstar · 06-01-2009, 07:34 PM

So back on the breaker / disconnect ideas, this looks nice, as it accepts 1/0 wire directly: Lightning Audio LCB200 Larger than 100A total fuse rating Circuit Breakers Amplifier Installation Car Accessories and Installation Car Audio and Video - Sonic Electronix

200A sounds like it's probably plenty for the starter (yet still way way below short circuit current), but I really need to measure the current draw when starting my car to verify (with one of those clamp-on amp meters, I think I have an attachment for my multimeter for that around here somewhere). Looks like a decent solution though, and any time I'm working on something on the car that requires the battery be disconnected, I can just hit the manual trip button.

ChrisSlicks · 06-01-2009, 08:14 PM

I don't have specs on the starter but it could potentially pull over 300A, provided the battery can deliver that much.

wstar · 06-01-2009, 09:04 PM

Quote:

Originally Posted by ChrisSlicks

I don't have specs on the starter but it could potentially pull over 300A, provided the battery can deliver that much.

The service manual only quotes 'less than 110 amps' under unloaded conditions (like spinning it up on a bench), which isn't really helpful. In general, I'm not finding a whole lot of definitive data anywhere on the net about the cranking current of a starter motor when actually starting an engine. I suspect this lack of data is because the real answer is 'it varies a lot depending on conditions'.

I imagine if for some reason your engine was incapable of turning over (somehow seized up completely) that the starter motor stalling out against it would probably become damn near a short circuit and probably fry the battery. This is probably why the factory wiring on every car runs the starter wire separately without a fuse, whereas everything else on the car is fused.

I changed my mind about trusting a clamp meter before I even tried it, once I remembered that they only really measure AC amps, not DC amps, so it wouldn't really give any sort of accurate reading.

ChrisSlicks · 06-01-2009, 09:10 PM

Quote:

Originally Posted by wstar

I changed my mind about trusting a clamp meter before I even tried it, once I remembered that they only really measure AC amps, not DC amps, so it wouldn't really give any sort of accurate reading.

You can measure DC current with a clamp, the hall effect is still valid.
AC/DC Current Clamp

06-01-2009, 07:34 PM	#1 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3595	So back on the breaker / disconnect ideas, this looks nice, as it accepts 1/0 wire directly: Lightning Audio LCB200 Larger than 100A total fuse rating Circuit Breakers Amplifier Installation Car Accessories and Installation Car Audio and Video - Sonic Electronix 200A sounds like it's probably plenty for the starter (yet still way way below short circuit current), but I really need to measure the current draw when starting my car to verify (with one of those clamp-on amp meters, I think I have an attachment for my multimeter for that around here somewhere). Looks like a decent solution though, and any time I'm working on something on the car that requires the battery be disconnected, I can just hit the manual trip button. __________________ 7AT Track Car! Journal thread / Car setup details

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06-01-2009, 08:14 PM	#2 (permalink)
ChrisSlicks A True Z Fanatic Join Date: Mar 2009 Location: North East Posts: 6,203 Drives: 09 370Z Sport M6 Rep Power: 654	I don't have specs on the starter but it could potentially pull over 300A, provided the battery can deliver that much.