DON'T lock this thread, i want and need information so for those of you who want to come in here and have petty little bitch fights, PISS OFF!!!!
Based on the above information are the following conclusions correct? 1. The peak amps drawn by the starter motor in most cases is dictated by the CCA rating of the battery. 2. The amps drawn by a perfect short circuit in most cases is dictated by the CCA rating of the battery. If the above statements are correct then the missing piece from the puzzle is exactly how long the starter will draw peak amps. I suspect it is less than 0.5 seconds in which case the starter will not trip the circuit breaker in the following examples. The only way to be sure is to actually test the circuit breaker with your battery. Example 1. Red Top Optima 720 CCA and the Blue Sea 200A circuit breaker. (720A is %360 of the 200A circuit breaker). The circuit breaker will trip in just under a second at the CCA rating. Example 2. Standard Battery 500 CCA and the Blue Sea 200A circuit breaker. (500A is %250 of the 200A circuit breaker). The circuit breaker will take around 3 seconds to trip at the CCA rating.
Quoted from wiki Cold cranking amperes (CCA) is the amount of current a battery can provide at 0 °F (−18 °C). The rating is defined as the current a lead-acid battery at that temperature can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery). It is a more demanding test than those at higher temperatures. This is the most widely used cranking measurement for comparison purposes. 1. What determines the current draw on start up is the total resistance of the circuit you need to consider the resistance of positive cable from battery to starter, earth return cable, resistance of solenoid contacts, motor armature etc. The best way to find out is to measure it with a clamp meter. 2. Pretty much yes.
Thinking about it, I would think the short circuit current would actually be a lot higher than the cca rating. The battery would get extremely hot in a very short time and probably explode. It certainly wouldn't last 30seconds and still be okay.
Sorry if I'm posting to much guys I just find this subject interesting. So for the sake of cable selection and protection device selection I tested the current it took to start my zed with a Fluke 337 clamp meter. Inrush current was a consistent 265A and continuous cranking current was 120A. The meter measures in a 100ms time scale. Going with those numbers personally I would be using 25mm squared cable (rated at about 100A from memory) and a 150A fuse/circuit breaker.
Did you test a TT or NA? I expect a NA would be harder to crank than a TT due to the higher compression ratio. How long did the inrush current last? What was the CCA of the test battery?
It gets really funky and starts to take all sorts of things in to consideration and all are very important for that crazy small period right at the start. Engine temperature and condition are primary concerns and then there is a long list of modifications that could have a significant effect on the first instant. - we are all cleaver enough to work out the list for ourselves. If we all lived in Russia or some place where extremely cold conditions are common then I would bet we would see some really interesting results over winter compared to summer. (yes the battery will perform differently when cold also).
THIS, I can assure you happens. Spectacularly!!! My ears were ringing well into the next day and my cloths were destroyed............. E
considering a c/b will take longer to react than a fuse will it be safer to use a fuse instead? there has been a bit of talk lately about battery relocation and the use of fuses or c/b with the longer cables but it seems there is no definate answer on what to use. i know some people are saying "do it this way" but some people also have conflicting ideas, i just thought it would have been a more talked about subject.
In all seriousness if the installation is done correctly it does not need to be fused at all. Consider this as an option if you are seriously safety conscious: Run two power cables, one fused at say 80amps, this one will go to everything except the starer motor, the cable will only need to be capable of handling say 50amps continuous. (even this would be overkill) The second cable will run the starter BUT will have an old school Ford style starter relay in line so that there is only power to the rest of the cable when cranking the starter motor. I personally would consider a third cable much smaller and with only a 5 - 10 amp fuse to run the memory on the stereo and clock - only if you intend to do a lot of work on the car though.
dude that seems a bit full on plus my car doesn't have stereo, clock, interior lights or aircon so one big cable will do me. i think i will go for the big fuse route for simplicity and also because im a clumsy fella and am always shorting shit out. like Tassie said, he has seen and felt a battery explode and i'd prefer to have something that will react instantly rather than when its too late.
Actually thought a little more, you can still run the one cable to the front and just run a smaller fuse with the starter relay in parallel for when cranking - much simpler and fairly safe
I have tried to keep things as simple as possible... As already stated what determines how a protective device operates is the tripping curve, doesn't matter if its a C/B or a fuse. But generally a C/B is capable of operating much faster as it incorporates a magnetic trip. But either way both will be so fast in a short circuit situation its a non issue. What actually determines the speed of the trip is the size of the cable and the resistance of the short as higher short current means faster protective device operation. If you wanted to go by Australian and New Zealand standards using AS3000/AS3008 (the electricians bibles) as a basic guide using Ib<In<Iz (< = less than or equal to) for overload protection, Ib=maximum demand (amps) In=nominal current of protective device Iz=continuous current carrying capacity of the cable (Izx0.9 if using a HRC fuse) Going by the currents that I actually measured 120A continuous while cranking and not taking into account derating factors and assuming your using standard 75 degree rated cable you will require 35mm squared cable (150A) and a 150A C/B, I will ignore HRC fuse for simplicity as you would have to upsize the cable (doesn't matter if its a fuse or a C/B as long as it has a slow trip characteristic to take into account the inrush current of the starter motor) Ib<In<Iz = 120A<150A<150A = maximum demand < Circuit Breaker Rating < Current carrying capacity of the cable That is a perfectly safe installation. Clear as mud? Stick to making engines with massive horsepower Mungy.
I was thinking along the same lines. If it is a sealed "ignition protected" remote starter soleniod then you could probably mount it in the battery box http://bluesea.com/productline/8 The running/charge cable would need to be able to handle the max output of the alternator. The manual lists the alternator at > 80A at 5000 rpm. (pg EL-38 of the 1996 service manual) so around 80A would do the job. The big advantage of this method is that a much lower amp circuit breaker can be used which will be easier to trip with a small short. It is a annoying having to reset the clock and stereo settings very time you disconnect the battery. A third stereo circuit that includes the amp would be a good idea. Most amps are connected directly to the battery anyhow.
Why run 2 cables when you can run one with a simple fuse? But hey sure go ahead and waste your money.
Agreed one cable would be better as I suggested afterwards, you could run an 80amp fuse and a starter solenoid in parallel so you have the best of both worlds, nice safe minimal trip rating on the fuse and then no problem when cranking. Most light aircraft use a similar system in that the starter cable is always dead unless cranking. More than one way to skin a cat and I am sure there will be plenty of ideas on how it should be done - might pay to have a look at how Nissan wired Skylines etc and take this in to consideration when deciding on an approach. What say you fit a 150 amp fuse in there following the advice of some around here and one day by accident try to crank while it's in gear = pop! main fuse blown, car dead, stuck wherever you were unless you have some way to bypass or a spare fuse :rofl:
