Short in alternator loom, 100A fuse blows

[bongovi]

Hi Bongo crew. It's been a while!

She's been off the road for a good while, in need of a weld to suspension bits, and general rust treatment.

In that time the dead leisure meant the solar didn't raise the LB enough to flip over to the starter, so that died too. Borrowed a donor batt to get the engine running and did the classic reverse polarity dingdong mistake. Wondered why the headlights were coming on for a good 20-30 seconds... In that time obviously something else went.

Cut to two new batts in hand (LB+SB), connecting the starter and bam, 100A main fuse blows. Try a few more times, disconnecting things as I go, down to 2x100A fuses left... I'd better stop now.

Checked continuity in the dash fuse box (among others, all fine) and find the Engine and "Meter" (speedometer, lower left blue 15A fuses next to each other) are shorting. Disconnect the alternator supply and see the continuity has gone between SB pos and neg leads. So that's the issue. Take off the lead directly under the 100A fuse and confirm that's the one feeding the alternator.

Now, does anyone know what's best for next steps? Alternator itself could be shorting, loom could have melted somewhere in reverse polarity battery mistake, and still the mystery of why the "Meter" fuse socket gives a short signal. Although the last one's not such an issue if there's no short at the SB leads when alternator disconnected, right?

Thanks and a happy sunny Saturday to all.

[g8dhe]

Normally its the diode block in the alternator that is damaged and then shorts out the feed to the 100 Amp fuse. Normally quite a quick fix if you have a suitable alternator/starter repair shop local to you, mine was just 24 hours can't remember the cost but a lot cheaper than a replacement alternator.

[bongovi]

Normally its the diode block in the alternator that is damaged and then shorts out the feed to the 100 Amp fuse. Normally quite a quick fix if you have a suitable alternator/starter repair shop local to you, mine was just 24 hours can't remember the cost but a lot cheaper than a replacement alternator.

Thanks a lot for this. I didn't follow up because I hadn't looked at the Bongo since the troubleshooting! Back at it now, I might just swap out the alternator because I can't find a repair person (East Mids) online. I'm guessing they are those people you know or you don't!

Hopefully that sorts it out. Might have damaged something in the solar circuit too - I get 20v across the panel leads coming in to the controller but as soon as it's attached I just get the batt voltage. Have set it correctly to B3, flooded/wet, and have reset several times AND replaced with a new unit (the cheap blue ones based on W88 design). Wondering if it's something in the van, even though the only connection the LB has to the vehicle is the negative/grounding on the batt I connected. Not actually sure if that's required now.

[bongovi]

I ended up replacing the alternator as I couldn't very easily find an alternator repair shop. I'm sure there will be plenty around the Midlands, but the alt wasn't super expensive. Just an expensive error!

Still having issues getting solar to charge, I don't know if I fried something somewhere when I dumped all that current back through the system.

But project still slowly crawling forward, should have it all back on track by spring/summer.

Big thanks as ever to @g8dhe and all those reading.

[g8dhe]

If the solar panel controller (what type make/model ?) is seeing the battery voltage then your connections are fine. If the display shows charger current or panel current as being several hundred milliamps or greater then it might just be lack of sunlight at present! Normally the chargers won't switch on at all unless they see 12v or 24v from the battery in order to avoid problems and they also current limit so unless its an old PWM (Pulse Width Modulated) type then it should be OK, the older PWM styles are a lot less robust! All the modern controllers are MPPT style (Max Power Point Tracking) which are a lot more efficient and more suited to our climate!