Toyspeed.org.nz Message Board

by **Vertigo** » Sun Aug 05, 2012 2:21 pm

After battery relocation, the car was fine for a month or two, now it keeps blowing the 100A fuse I put in front of the battery positive. Seems to only happen on cranking, and it might have something to do with the battery being slightly discharged (from just trying to start the $&#$% thing). Im guessing theres a short. Any tips on how can I find it?

Thought I had posted this before I went to the car just now, ahaha, well Ive just tested continuity and resistance on my wiring and its a-ok. Also the engine block earths seem ok too.

Is 100A too small?

Website · by **Bling** » Sun Aug 05, 2012 2:33 pm

Have a read of the top sticky in car audio section. Should give you some ideas

by **jaypines** » Sun Aug 05, 2012 2:37 pm

did you put the 100a fuse to feed the starter as well? if so thats your problem. the 100A fuse should only be connected to the charging cable and other power feeds, not the B+ of the starter. HTH.

by **iOnic** » Sun Aug 05, 2012 3:21 pm

^ This - your main (big fat) starter cable is trying to draw current via the fuse and is blowing it. On the stock setup this cable isn't fused - it runs directly off the positive battery terminal.

by **Lloyd** » Sun Aug 05, 2012 3:28 pm

Used to just run one of these, a lot easier

by **Vertigo** » Sun Aug 05, 2012 3:29 pm

Lol. $&#$% noob mistake

Cheers guys

by **blindnz** » Sun Aug 05, 2012 11:55 pm

jaypines wrote:did you put the 100a fuse to feed the starter as well? if so thats your problem. the 100A fuse should only be connected to the charging cable and other power feeds, not the B+ of the starter. HTH.

Out of interest what sort of current would a starter draw? 200A?

by **jspec153** » Mon Aug 06, 2012 6:58 pm

iv never measured one but i depending on alot of things e.g. Gear reduction starter, Compression of motor etc. but i wouldnt think it would draw any more than that its only the initial crank at the start that would draw lots once its spinning as fast as it goes itl be a whole lot less current draw

by **jaypines** » Mon Aug 06, 2012 8:56 pm

blindnz wrote:Out of interest what sort of current would a starter draw? 200A?

depends on how much power or kW the starter have. common ones (petrol) i think are 1 - 1.5kW... so divide that by 12v (healthy battery) will give you roughly 85-120A and thats not having to factor in transient currents and tolerances.

by **blindnz** » Mon Aug 06, 2012 9:31 pm

yeah, I'm looking at fuse'ing my battery relocation was thinking 250A or 300A should be ok. 12V x 200A=2.4kW. Not sure what a rb30 starter woud draw though

by **KinLoud** » Mon Aug 06, 2012 9:52 pm

I've been using a 250 amp fuse between battery and starter/electrical system in my 4afe corolla for the last 3 months
http://www.jaycar.co.nz/productView.asp ... rm=KEYWORD
Hasn't blown yet with all the starting/stopping/running around I do.

Been doing this as research for what size fuse I will use in my racecar (4agte AA63 Carina.
Will see if a 125 amp fuse will survive reliably or blow... Guessing it won't be big enough from your experience

Ken

by **Vertigo** » Tue Aug 07, 2012 8:36 am

125 is definitely big enough once the car is running, its just that cranking requires a bit of juice, hence why it should bypass the low amp fuse.

by **allencr** » Tue Aug 07, 2012 6:07 pm

I can be wrong, but if no auto/truck/forklift/industrial engine/whatever manufacturer in the world fuses their starter cable - they just do a nice install - then I don't have a clue why you'd want to do it!

by **Lloyd** » Tue Aug 07, 2012 6:33 pm

Because the battery has been relocated

by **jaypines** » Tue Aug 07, 2012 6:52 pm

yeah just do a nice install... avoid sharp body works to avoid chafing and provide plenty of insulation/boot and insulated fixings... those BMWs and other euros that have battery in the boot have no fuse blocks going to their starter/alternator either.

by **Lloyd** » Tue Aug 07, 2012 7:36 pm

They tend to actually be well insulated though, and through solid plastic cable cases right up to a mount in the engine bay.

Much better than the likes of a 190E with a cable running out the drain bung for the boot (no grommet) and cable tied to the fuel lines to get it to the engine bay... I really hope that car caught fire one day

by **rollaholic** » Tue Aug 07, 2012 8:03 pm

using a massively over sized fuse is no answer. the fuse is supposed to be the weakest link...

by **Lloyd** » Tue Aug 07, 2012 8:10 pm

That is exactly the answer. If you're going to fuse anything then the point of it is to protect the wiring in the case of a short, or the component in the case of a failure that draws excessive current. If your starter cable from the battery gets shorted in a crash then I'm sure most people would rather the fuse blows than the cable turning into a heater that sets the car on fire.

by **blindnz** » Tue Aug 07, 2012 8:39 pm

rollaholic wrote:using a massively over sized fuse is no answer. the fuse is supposed to be the weakest link...

I plan on it being the weakest link. under normal conditions Ok. But the first to blow if it shorts.

by **sergei** » Tue Aug 07, 2012 9:12 pm

I use 150A slow fuse on 3SGTE no problems.
with 50mm^2 wire anything up to 350A continuous will be fine...

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Battery fuse keeps blowing (100A)

Battery fuse keeps blowing (100A)

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