RX8inSTL

iTrader: (7)

So I went to start my car today after just doing a battery relocate to the trunk, well I ended up blowing the 100 amp fuse after the battery.

I used 0 gauge wire to the front of the car, it goes through the firewall right behind the AC inside the car and comes out where the washer fluid is. It goes under the rear passenger seat and up to the trunk.

I have 12.3 volts from the battery and also at the front of the car. Theres a 100 amp fuse right after the battery and in the front theres a distrobution block with a 100 amp fuse for the main line and a 60 amp fuse for both the EPS and also the line that goes to the fuse block in the engine bay.

When I was starting the car it cranked over but after that the fuse popped and no power.

If anyone has some advice on spots to check id appreciate it.

Heres some pics of how everything is set up.


In this first picture theres now a60 amp (blue) fuse for the fuse box wire. Not the 100 amp (yellow) pictured.

RX8inSTL

iTrader: (7)

Also ive checked all my grounds to see that they are good with a multimeter and they seem to be good.

Also just checked to see if my main line was messed up somewhere by taking out the battery and just connecting it up front with an extra run of wire and grounding to the engine bay. It still blew a fuse so it shouldnt be the line.

RX8inSTL

iTrader: (7)

For anyone interested I found what seems to be the problem. I did two things at the same time which didnt help the trouble shooting. But I believe it to be the first thing ill tell you more so than the second.

The rear fuse near the battery fuses were not a very good fit for the holder. I actually had to bend the fuse a little to make it fit. And even then it was super tight. I took that off and just ran the power wire to the main supply in the front at the distro block.

The other thing I did was put a 100 amp fuse in the line that goes to the Main fuse block. This fuse didnt blow before or after so idk if it was the cause or not.

Anyway ill be going to get a replacement fuse for the rear tomorrow and then ill see if it starts.

Rotaman

You will probably find that the 100amp main line fuse is too small, try around 250amp. Your starter motor could easily draw more then 100amps at start up, especially if it is cold weather.
A fuse will normally blow in two different ways, first way is slowly and the blown fuse element will look like it has just broken in half. The second is because of a direct short, and the fuse element will look like it has blown apart.
Also that earth terminal on your battery needs to be thrown in the rubbish bin and replaced, get a decent solid one like your positive terminal.
Also your earth grounding point on the suspension point there is not a good place to have the earth grounding. There is too much movement in that type of point and will quite likely cause a problem in time.
Find a solid mounting point say somewhere there is chassis steel and weld a mounting point there. Make sure there is no paint or anything else likely to cause a problem with good contact. Then coat it with some sort of metal protective spray that is conductive.
Also make sure your main power cables are protected from anything that is sharp or anything that could rub through the casing over time.
The worst areas for problems is where the cable comes through the firewall, the main cable must not be aloud to touch any metal in this area. In other words make sure it runs through a rubber grommet or something that will protect it.
The other main area is around seats. Make sure you run the main cable in some kind of conduit for protection around anything that is seat related.
One other thing, solder the terminal connections, on 0 gauge this means you will have to use a very big soldering iron, or a gas torch.
When you are dealing with 12V systems, every connection is critical, and a bad connection can lead to not enough Voltage getting to the starter. Also 12V systems draw large amounts of current, especially on startup.
The voltmeter should be reading over 12.5v if your battery is any good. Anything under 12v and it is fit for the rubbish bin.
The one good thing I can see, is that it looks like you have used good quality power cable, and you should not have any problem with getting enough current to your starter motor with 0 gauge cable.
Hope this is helpful.

RX8inSTL

iTrader: (7)

Thanks for the info. I will be doing a few things for sure like replacing that battery terminal, probably adding a seond groud, I may do the soldering tomorrow. Im not sure though about going to a 250amp fuse. Earlier tonight the car started with just using a 100amp fuse.

There is a grommet in the firewall and the back seats are rarely used so i dont see the wire having a problem there.

Rotaman

You keep using the 100amp fuse if you like, but one day when you are out in the country somewhere on a cold night, and you come to start your car, wait and see what happens. I suggest you best keep a spare fuse in your car.
You could put a 300 or 400 amp fuse in the main line, it does not really matter. That fuse is only there to blow if you have a main line direct short. In other words, it will blow only if that main power wire starts acting like a arc welder because of a short circuit. This will stop a fire happening.
If you understand how dangerous wiring a 12V system wrongly can be, you would be a lot more careful with how you wire things.
Sorry to be a bit blunt, but I've seen some very poorly wired setups over the years, by people who have no idea as to the dangers of the high currents that can be involved with 12V systems.
Have fun

Spin9k

1. Right there is one BIG (math) problem, surprised you didn't see it. You have a 100 amp fuse at the battery, that leads to a 100 amp + 60 amp fuse. So you're asking a 100 amp fuse to handle 160 amps? Guess what'll blow? Yup, the one that blew

But that's NOT correct even if you fix that... actually not the half of it....if you've ever looked at the car's wiring diagram that is. Then you'd realize that coming DIRECTLY off the positive side of the battery are the following fuse blocks:

1. 120 amps
2. 60 amps
3. 15 amps
4. 30 amps
5. 15 amps
6. 20 amps
plus alternator connection

...ummm .. get out you calculator and discover the total amperage for the fuse you are looking for in your setup at the battery.

...some other things...

2. You're measuring voltages at several points. That's fairly useless for troubleshooting. In fact, if you have ANY voltage drop in a static setup, you've got real problems there somewhere. What you want to do, and it pretty difficult without a power resistance bank to replace actual loads, is to measure VOLTAGE DROP when the system is maxed out handling current. Obviously the electric assist steering and starter are the big draws in the system, if that helps, you might get a friend to help you swinging on the steering, with the ignition disabled for short period while running the starter.

You need to check the voltage DROP is the result of amperage going thru a resistance. The resistance can come from poor connections, like the crimps at connectors, the fuse block connections, the battery clamps, and of course from the resistance of long lengths of wire (which you have from the trunk). 0/1 is certainly good enough one would think, but is there anywhere where you are using a short, smaller gauge in-line somewhere for convenience? Even a short link could cause an unacceptable voltage droip under high current use.

RX8inSTL

iTrader: (7)

Thanks for the responses from both of you, they defiently are helping out. I was just going with the 100 amp because it seemed like everyone else used that too but they didnt seem to be using distrobution block. So it looks like I need at least a 250 amp fuse right after the battery. All those things you listed out are actually around 270 but a 250 should be fine correct?

Spin9k

chances are. fuses protect from the worst case. the worst case for every system at the same time is unlikely.

RX8inSTL

iTrader: (7)

Well everything is pretty much buttoned up, I replaced the fuse after the battery with a 200 amp. All seems to be well now. Thank you guys.

Rotaman

Glad to hear that it all seems to be working ok now, hope you have managed to learn something from this.
have fun

Spin9k

Take note... your 100amp fuse at the engine fuse block is too small. I gave you the answers already. You need to look at the engine wiring diagram.

RX8inSTL

iTrader: (7)

hmm, throw a 120 amp on the wire for the fuse block and i guess I need to find out what size fuse the starter uses.

StealthTL

iTrader: (1)

Stock starter has no fuse.

9krpmrx8

iTrader: (46)

Glad you go it sorted. What kit did you use to secure the battery?

RX8inSTL

iTrader: (7)

Thanks stealth. 9k the battery tray is actually just a cheap thing from autozone. Its one thing ill be wanting to replace at some point because it isn't a tight fit for the battery.

Rotaman

For anyone else thats has or is looking at fitting there battery into the boot. Try and fit it up as close behind the back seat as possible. The further back in the car you fit it, the more centrifugal weight you are swinging about in corners. You need to get that swinging weight as close to centre of the car as possible.
I know the weight sits a little higher up behind the seat, but a little height in roll turns is got to be better then swinging weight by having the battery so far at the back of the car.
Anyway this is worth looking at.