re-wiring question.....simple.
Discussion
im re-locating my battery this weekend....to the boot. i already have the correct length of power cable cut and crimped.....a few questions
im putting a battery isolator in ( std hella type) am i correct in thinking it would be best of in the earth side ( switching positives surely isnt good for my ecu !)
im also putting in a 200 maxi fuse....fuse connected to battery term, cable connected to fuse. this ok ???
and lastly, earths.....is earthing directly to the floorpan ok ???? then earth leads from the bulkhead to the engine/box.....i don't see any reason why not - anyone disagree.
thanks in advance
im putting a battery isolator in ( std hella type) am i correct in thinking it would be best of in the earth side ( switching positives surely isnt good for my ecu !)
im also putting in a 200 maxi fuse....fuse connected to battery term, cable connected to fuse. this ok ???
and lastly, earths.....is earthing directly to the floorpan ok ???? then earth leads from the bulkhead to the engine/box.....i don't see any reason why not - anyone disagree.
thanks in advance
Put the cut out switch in the positive line. shouldnt be any need to put a fuse in line unless you really are worried about shorting the cable out, in which case i would question the routing of the cable.
Earth to the floorpan is fine, just bare metal the area under the earth terminal before connecting up, then just a smear of vaseline or waxoyl over it when it is all tightened up
Earth to the floorpan is fine, just bare metal the area under the earth terminal before connecting up, then just a smear of vaseline or waxoyl over it when it is all tightened up
It won't make any difference which side of the battery you put the isolator into from the ECU's perspective.
Are you fitting the isolator just as a convenient way of disconnecting the battery when working on the car or storing it, or for stopping the engine in the event of an emergency on a track? If the latter then you must fit a proper FIA isolator, a normal isolator will not stop the engine if you have an alternator wired in.
Putting a fuse in-line with the starter motor is not a good idea, even if it has a high enough rating that it can take the current it will still cause additional voltage drop. You won't find many (any?) production cars with a fused starter motor, the maxi fuses are usualy used on the alternator to battery cable and the main feed to the permanent and ignition switched circuits and for any other high current consumers, e.g. electric power steering pump.
Are you fitting the isolator just as a convenient way of disconnecting the battery when working on the car or storing it, or for stopping the engine in the event of an emergency on a track? If the latter then you must fit a proper FIA isolator, a normal isolator will not stop the engine if you have an alternator wired in.
Putting a fuse in-line with the starter motor is not a good idea, even if it has a high enough rating that it can take the current it will still cause additional voltage drop. You won't find many (any?) production cars with a fused starter motor, the maxi fuses are usualy used on the alternator to battery cable and the main feed to the permanent and ignition switched circuits and for any other high current consumers, e.g. electric power steering pump.
K13 WJD said:
the isolator is just a way of cutting the battery off on track....isolator in boot, t-pull cable in dash.
200a maxi fuse........just in i have a shorting issue on track....
Just confirm, the supply to the starter motor does not go through the fuse? Also make sure that you are protecting the alternator not just the battery. A conventional approach is 1000A cable from battery direct to starter motor, 200A cable from alternator direct to starter motor, 200A cable from starter motor to fuse box/distribution panel with a 100A fusible link in line.200a maxi fuse........just in i have a shorting issue on track....
K13 WJD said:
my starter wont draw 200 amps...unless i start in in first with the brakes hard on !!!!!
I don't know what engine you've got, but many engines will easily exceed that. It's not normal to fuse the supply to the starter because it takes so much current that it will blow any sensible fuse.maybe they draw more than 200 a for ten milliseconds....but as i stated, slow blow.........p=iv rule....presuming 12 volts standing voltage.....200 amps means 2.4 kilowatts.....thats some starter motor......
put it this way. my transit 350 has the same fuse in the + line....and has done for 3 years.......and my mates mini bus has a 190a fusible link in the - line......which doesnt blow. ever.
put it this way. my transit 350 has the same fuse in the + line....and has done for 3 years.......and my mates mini bus has a 190a fusible link in the - line......which doesnt blow. ever.
K13 WJD said:
the isolator is just a way of cutting the battery off on track....isolator in boot, t-pull cable in dash.
In that case make sure you don't isolate it when the engine is running, unless you run a separate alternator cable back to the battery. The voltage transients seen during "load dump" events are huge, can easily be over 100v.K13 WJD said:
maybe they draw more than 200 a for ten milliseconds....but as i stated, slow blow.........p=iv rule....presuming 12 volts standing voltage.....200 amps means 2.4 kilowatts.....thats some starter motor......
put it this way. my transit 350 has the same fuse in the + line....and has done for 3 years.......and my mates mini bus has a 190a fusible link in the - line......which doesnt blow. ever.
The battery voltage will drop considerably under the load from the starter, it wouldn't be at all unusual to see it drop as low as 9V. I wouldn't be surprised to see a sustained current draw of 400A on a big engine and the peak current could be quite a bit higher. However, you'll soon find out whether the fuse is up to the job. I suggest you monitor the voltage drop across it and check whether it gets warm when you operate the starter. These big fuses tend to fail mechanically as well as electrically, and you may find that if it's near its limit it breaks down progressively before it finally lets go.put it this way. my transit 350 has the same fuse in the + line....and has done for 3 years.......and my mates mini bus has a 190a fusible link in the - line......which doesnt blow. ever.
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