so on friday my day started with a dead battery, called out the green flag and they tested my battery and confirmed i needed it replaced, so i replaced it and drove to work and almost got there before the battery died, all the lights on the dash were up and although the engine was still running, i had no throttle control or electrical control over anything... called the green flag again, turns out the alternator was shot and my other battery was probably alright.

sooo today i fitted my nice new alternator at a cost of £152 took me about 45 mins which i was quite impressed with, untill i started it up and the battery light was up on the dash, grrr. so after a long time trying to figure out what had gone wrong i finally discovered the main fuses on top of the battery and the 140amp fuse off the alternator had blown and melted and burnt the inside of the plastic box.

i cant get that fuse from anywhere untill friday so untill then i have connected 2 fairly thick bits of wire to a 100amp spade fuse which is the biggest i could find. its running and getting me about but the cable is getting extremely hot and has actually melted the whole of the spade fuse and half of the sleeve on the wire.

i cant work out why it would be drawing so much power through it, the car is completley standard with no electrical mods at all. what sort of current shoud be coming through there when the engine is running and how would i go about testing it?? i have got a multi meter now so i can test it. i just dont want it to catch fire through me missing something or not checking something.

any help would be great.

thankyou

if this is posted in the wrong area or would be more beneficial in a different area please move it. thanks

You didn't say which model car but a typical diesel has an alternator of around 90A and the load from the glow plugs are typically 80A (which are supplied ultimately from the alternator even with a charged battery). Petrol cars have alternators of around 60A.

Industrial flag ended fuses are designed to be cooled by their mounting arrangement so having an under-size cable attached in free air will make the fuse hot.

You may have another load (or a fault) taking a large current and the best way to check is with a clip-on d.c. ammeter. A multimeter will not normally have a means of reading large d.c. currents.

Most garages and battery places have the correct instrument.

Replacing the fuse box/fuses is just treating the symptom. I suspect that the cause of your problem is a high resistance in the crimped connector on the main feed wire from the alternator to the fuse box. You will need to replace the loom from the alternator to the fusebox and the damaged fuse box to sort it out. I think that these parts will cost around £75 and should be a reasonable DIY job.

sorry, its an octavia vrs. so petroel 1.8 turbo engine.

i have now removed the cable with the fuse on it as getting it to stay connected was a nightmare and i kept having to pull over and tweak the connection. i have now run 2 shor pieces of insulated wire where the fuse would be hopefully these wont get hot and if they do i will be able to tell from the sleve.

one of my friends is an electrician, its likley that he will have a way of reading dc current?? what should i be looking for? i have just got my battery tester through today and tested my old battery after a full charge. perfect working order so a waste of a new battery :(

how will replacing the cable from the alternator to the fuse change anything?? there is only the one cable that delivers power, if there was a fault would it not be most likley of the other side of the fuse with too much power being drawn or could it just be that the old alternator peaked and sent a lot of power before finally packing up.

thanks for the help, really appriciated.

Same happened to my octavia last week.

And as fordfan fan has said, high resistance in the crimped connector. Trip to the local dealer, swopped £37 for an alternator loom (in stock item ) and 20min fitting job back at the house. Connected in to the battery direct until pay day allows for the purchase of the fuse board, £70 quote :(

whats the need to replace the wire though?? the nut head on the end is a bit brown but from what i can see there is no damage to the wire, i dont understand why i would need to replace it??

I use to have similar problem with my fan fuse on the fuse box over the battery. Thank GOD I found it and fix it before it melted all the plastic fuse box. If you do a search over the internet you will find a lot of pics of VW, SEAT, melted fuse box

The way I fix it was to use a separated aftermaket fuse holder for that fan fuse. Maybe you can do the same and use a aftermarket fuse holder and a ATC Maxi Fuse

Also you can use/adapt a PAL type fuse

In places like does that install hi end car radio amplifers or other electronic shop you can find these aftermartket hi amp fuse holder.

Good luck,

Isaac

Edited 16 December, 200916 yr by Turbo_Boss

how will replacing the cable from the alternator to the fuse change anything?? there is only the one cable that delivers power, if there was a fault would it not be most likley of the other side of the fuse with too much power being drawn or could it just be that the old alternator peaked and sent a lot of power before finally packing up.

thanks for the help, really appriciated.

You need to think in terms of supply to the battery, rather than the current draw from it. The main supply cable from the alternator which can supply in the region of 90 amps when the electrical demand is high, develops a fault wherein it develops a high resistance at its crimped connector where it joins the fuse box. In trying to put alot of current through it alot of heat builds up and melts the fuse box. Hence replacing the cable will sort it. I have noticed that the replacement cables have a better crimped joint, so it may have been a problem that has been noted by the manufacturer and redressed.

You can get your friend to check it by taking resistance measurements along the cable.

hi there, had the same problem on Friday, gradually lost electrical systems one by one! Called out RAC who did a temp repair, 20 miles later same again, this time on A12 and it was minus four degrees!!!

Anyway the guy from the local garage had a look and said that it was the fuse box on top of the battery shorting out! Having read this forum I am not convinced. Is it worth getting the loom and alternator cable replaced as well as the melted fuse box? Was already concerned that it was just the symptoms being treated!

I am guessing this is a known problem??

Driving a Octavia 2003 Blueline btw

Thanks for any advice

Edited 10 January, 201016 yr by clonw1

Anyway the guy from the local garage had a look and said that it was the fuse box on top of the battery shorting out! Having read this forum I am not convinced. Is it worth getting the loom and alternator cable replaced as well as the melted fuse box? Was already concerned that it was just the symptoms being treated!

If you check some VW and SEAT forums, you will find that many people has suffer melted fuse box. I also experienced that problem but catch the problem before the damage was bigguer.

in my case the problem was that the A/C FAN has a internal short and this was making the fuse to over heat.

I dont know what or were is exactly the damage on your fuse box but if you can check it and found were the problem started, then you can find what fuse is the one that beguin to over heat and cause the damage. Then, check what circuit is protecting that fuse and check that part............... As I toll you above, in my case was the FAN and eaven that it was working it was causing the fuse to overheat. I change the FAN, and cure the problem.

What I mean is, if you dont trace the problem and cure it, if you put a new fuse box, is going to fail again.

Here is a pic of my fuse box when I catch the problem on time before it damage the complete the fuse box

Doing a search, I found this pic on a SEAT forum.

Good luck,

Isaac

Edited 10 January, 201016 yr by Turbo_Boss

You need to think in terms of supply to the battery, rather than the current draw from it. The main supply cable from the alternator which can supply in the region of 90 amps when the electrical demand is high, develops a fault wherein it develops a high resistance at its crimped connector where it joins the fuse box. In trying to put alot of current through it alot of heat builds up and melts the fuse box. Hence replacing the cable will sort it. I have noticed that the replacement cables have a better crimped joint, so it may have been a problem that has been noted by the manufacturer and redressed.

You can get your friend to check it by taking resistance measurements along the cable.

I have just replaced the alternator loom on my 53 plate TDI as I noticed (after burning my finger) that the connector on top of the fust box was getting hot. Inspection in the daylight showed that the copper cable had gone black and oxidized due to the heat.

The new cable appears to be heavier than the old one that I removed too.

Obviously this is a different fault to the one described here with melting fuses, but a not uncommon fault either.

thanks guys - I think EXAUDISI is close to it. The coonection at the end of the altrnator cable had melted, as did the next terminal along after the termporary repair. Something is causing the alternator cable to short out and overheat. I will get him to do a thorough analysis, although thinking back, I think the heating was a little cooler than normal - will get him to start there!

Thanks, and any more assistance will be appreciated.

I don't think that the alternator cable shorts out, it just gets a high resistance between the cable and the terminal and then gets very hot. Fortunately, thanks to Briskoda I spotted this before it got too far along. As I mentioned, the new cable was a heavier duty item than the old one, so perhaps the original fit item just isn't up to the job once the battery starts to get a bit older and the alternator has to start charging harder for longer?

thanks guys - I think EXAUDISI is close to it. The coonection at the end of the altrnator cable had melted, as did the next terminal along after the termporary repair. Something is causing the alternator cable to short out and overheat. I will get him to do a thorough analysis, although thinking back, I think the heating was a little cooler than normal - will get him to start there!

Thanks, and any more assistance will be appreciated.

Get the alternator cable to battery loom replaced.

I have seen those systems caused by loose or not fully tightened nuts on the fuse box cables above battery, this is also been seen as members stated on the VW forums for same reason

The other reason is also bad alternator cable due to the terminal creating high resistance, which again members have stated. This cable is around £35 from any Seat,VW or skoda dealer.

I found this on a AUDI forum how a member fix his problem without buying a new fuse box.

Isaac

Edited 10 January, 201016 yr by Turbo_Boss