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Discussion Starter #1
I recently installed a small Odyssey battery and an on/off switch in the trunk of my GTV and ran 4/0 cable to the starter. Seems like it would be a good idea to have a fuse between the positive cable end and the switch in case there was ever a rub-thru or break in the positive cable insulation.

Any suggestions as to the amp rating of the fuse?

The starter is a 1.1 hp version from a series 4 spider.

Thanks,
 

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But Mad North-Northwest
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A starter pulls a metric buttload of amps. Several hundred easily. As far as I know it's not really feasible to fuse the positive cable to the starter.

So make really, really sure the cable is well insulated and there is good protection anywhere it passes through or rubs against the body...
 

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Discussion Starter #3
Thanks Tom, No sharp metal edges are touching the cable and lots of insulated clips were used to keep it snug to the underside, so not too worried about it shorting out - the fuse just seems like a good precaution. Would this be unfeasible due to the high current draw?
 

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Would this be unfeasible due to the high current draw?
Yea, I think that's what Gubi said. When manufacturers locate the battery in the trunk, they never put a fuse in the "+" connection. E.g., the later Alfa spiders.

Honestly if you did cobble up some sort of a high-current fuse, that component would probably just add to the likelihood of creating a short.
 

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But Mad North-Northwest
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Yeah, it's not impossible, just not easy or practical. The starter can pull a lot of amps.

I mean, if you search around you can find 12V fuses in 200A or whatever. But they're pretty big, and as Jay said you're probably more at risk from shorts or connection problems from hooking up the fuse itself.

Seems like if you really wanted one someone would make a big-asz fuse that just pops onto the + terminal, but I'm not seeing one doing a search.
 

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Some guy here is an electrical engineer. For sure he could tell you the correct amp and type fuse needed.
Or, you could use the one that other car makers use on their Bat.+ cable.
 

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My Honda cars have fusible links on the positive terminal of their batteries. As does the diesel truck that I drive for work.

On one of my Alfa GTV 2000s I installed a 100 amp rated marine circuit breaker (CB187P-100). The breaker is mounted on the battery tray which is mounted in the trunk. Approximately 1.6 meters of 2 awg battery cable runs between the breaker and the starter. The starter drew 98 to 101 amps when the outside air temperature was 20 C and the engine had 2100 miles on it since a rebuild. A Ferret battery tester was used to measure the current draw of the starter (it is a "1.1 hp" Bosch starter). This circuit has been in the car and operational for the last 6 or so years (~18,000 miles). Voltage drop on the battery cable to starter was 0.04 volts. The quality of the connection between battery terminal lugs and the cable strongly influence the voltage drop.

BTW, this design did get the approval of an electrical engineer (P.E.) who designs battery back-up systems for server farms. I questioned the use of 2 awg cable but he said that the load carrying capacities listed in the handbooks are very, very conservative. (handbooks says that for "chassis wiring" a 2 awg is rated for 180 amps. while a 4/0 awg is rated at 381.)

It does seem appropriate to mention that YMMV.

Bob
 

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Locked rotor current draw can exceed 500 amps. The only fuses I know of that may work would be these available from McMaster (and other sources too I presume). Scroll down to Lift Truck fuses.
 

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I'd use a midi fuse holder and midi fuse... That's my exact plan as I'm moving my battery very soon.

They come in a few styles depending on brand but here's a pretty generic one. Insulated case that bolts/screws down. With well crimped [Google 'hex crimping'] or soldered lines I can't see this being a new short risk. Small and unobtrusive.
Cost less than 2 pound on a site image I was going to use [messy water marks over the image and this image has the fuses pictured].

Most automotive electrical places have them.

Just while I googled the image I seen 200amp fuses. It wouldn't surprise me if they come bigger.
 

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Locked rotor current draw can exceed 500 amps. The only fuses I know of that may work would be these available from McMaster (and other sources too I presume). Scroll down to Lift Truck fuses.
That is why a 200 amp is best.
The fuse is supposed to blow before any damage is done to the wireing or components.
 

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I've been using this battery terminal sold by McMaster-Carr here in the U.S. with success:

Quick Solder Style—Made of tin-plated copper.
Applying heat to the flux and solder mixture creates a metallic bond nearly twice as strong as crimping or compression connections.

Papajam, I am confused, are you recommending not trying to fuse the positive side of the battery, or that it can't be done?

The only evidence I have is that my circuit (see above) is working and that the Eaton circuit breaker does trip when I try to draw more than 101 amps through it (it is rated for 100). Is the fact that it does not trip when I start the car with the 1.1 hp starter mean that the starter is not drawing 500 amps? Or is the breaker perhaps a "slow blow" type. Plus the Ferret battery tester connected to the circuit per the manufacturer's recommendations measured the starter drawing 98 amps when power was applied to the starter.

Bob
 

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Discussion Starter #14
Well after rigging a temporary switch for the backup lights today, I had some time to install the trial fuse set up you'll see in the photos. So far, so good during the 1st drive of the season.

The fuse is a Balkamp AMG 200 amp, $6.99 usd at NAPA stores. I bought 2.

Haven't checked the current draw yet, but will do so and report the reading when I have a test meter in a few days. Seems the real test will be in colder weather when the starter works harder.

Thanks to all who've replied so far.
 

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Cool, looks like a ANL fuse? Being the Larger version of a midi fuse.
If you ever run into vibration and the fuse breaking, as it looks like a pretty rigid mounting with the fuse supporting weight (viewing images on my mobile), then you can get holders similar to midi for those too.

Keep us updated on the fuse, not sure what size I'll run for a 3lt v6 yet. Likely buy a couple sizes and just start at 200a, keeping a spanner in car to change it should I get stuck.
 

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I found this last night while looking at the difference between mega fuses and ANL fuses. Worth a read and offers insight into why a 'smaller' amp fuse might last with a starter motor.

FUSES

"This graph lets you see the estimated time that it might take for an ANL type fuse to open. The data used to create the graph was found on the Bussmann web site. You can see that it would take as much as 10 seconds to blow at double its rated current flow but it would only take approximately 0.1 seconds to blow it if 1000 amps of current passed through the 100 amp fuse. If your amplifiers would intermittently draw 200 amps, the fuse probably would not blow. If they drew 200 amps for more than 10 seconds, the fuse would likely blow. If the wire was shorted to ground, the current flow would be extremely high (probably more than 1000 amps) and the fuse would blow almost instantly."
 

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A technical rep. for Eaton Industries just got back to me about why one of their 100 amp. marine breakers works with a starter motor that might have a short circuit current draw of upwards of 500 amps. (See my earlier post.)

He said this breaker is a "time-delay sized for inductive circuits". This morning I installed a 60 amp. version of the same breaker in place of a 100 amp. The car started just fine- breaker didn't trip.

The same tech rep. recommended not sizing a breaker or fuse for the short circuit load of the starter, that is, do not use a 500 amp. or even a 200 amp. breaker/fuse but instead use a fuse that will protect the components, wire insulation etc. in the circuit. That makes sense.

Bob
 
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