weird electrical problem b230k
 

Hello,

I recently had a weird problem with myu 1987 volvo 740. it's the b230k engine.

So, was running ok, a little lumpy, so i decided to clean my carburetor, and while i was at it, gave the engine a bit of a de-grease, now i admit i didn't cover electrical components, but i was pretty careful when rinsing.

now, the interesting part; after cleaning was running a little lumpy, not ideal but i assumed it was just a bit of water affecting somewhere part of the ignition system, and as expected i warmed the engine up let it dry off, and he was running absolutely smooth as ever, better than ever before in fact the carb cleaner worked a treat. and i even drove around quite a bit later that day,

now we're on day 2, i get home from work and go to start my car (not driven since yesterday) and he's DEAD, i mean ABSOLUTELY no lights on the dash, absolutely nothing with the key, fully dead. open the bonnet there's a VERY VERY slight burning smell, but definitley there, tested the battery, and it has absolutely no charge at all, completely flat (doesnt even register anything on my tester) weirdly if i put the battery on charge it blows the fuse in my charger. seems like something has gone terribly wrong, i am not particularly mechanical, and i only do very minor work on my cars, and my knowledge is very limited.

at ma guess have i damaged my alternator or something?

regards -Matt

Does sound like it may be the alternator if the diode or rectifier pack has failed and allowed the battery to discharge through it. Chances are the battery may well be cooked as well, if there is no charge in it all then it probably will overload a battery charger. Try leaving it for a couple of days to see if it will recover before trying again.

Perceived wisdom is that a car battery will be fubared if it has discharged below 10 volts. This is because of sulphation which means that the plates will be covered with lead sulphate which will reduce the battery’s capacity to hold a charge even if you can persuade it to accept one.

In a deeply discharged state you will either need a very dumb (old) charger or a very clever new one featuring multiple cycles to try to regenerate the battery. One way or another you will need to include a period of controlled over-charging to try to shift some of the sulphate. You will not remove it all and the battery will be permanently diminished.

If the deep discharge took place over a short period of time then the battery has almost certainly overheated internally and has probably developed an internal short because the plates will have bent and touched each other. If you suspect this to be the case (your charger fusing is a clue, but not definitive evidence) don’t try to charge it. Consign it to your local recycling centre and buy a new one.

It's worth disconnecting (and insulating) the +ve lead from the alternator Matt and then try the charger again on it's lowest charge rate. As Forrest says, it may be the battery is FUBAR but there's a possibility that if the alternator has taken it down, you may get away with it.

However, a word of CAUTION!!! Disconnect the battery earth lead to start with as well, just in case it's not the alternator at fault and connect the charger to the battery without it being switched on. When you plug in/switch on the battery charger, try to be as far as possible from the battery, just in case it decides to go bang. If possible, wear eye protection and any other protective gear you can. Batteries aren't pretty when they explode and battery acid in the eyes is painful.

I'd still say it would be better to replace the battery though but before you do, make sure the alternator is disconnected. Connect the battery +ve lead first, place a rag over the replacement battery and gently connect the earth lead, making sure you can disconnect it quickly if there's a big "splash" of current (blue flash) as you connect. A little splash is normal as the central locking, interior lights and so on power up again but any more than a tiny little spark/splash disconnect immediately and report back and we'll work out what's dragging all the power.

FYI the rag above is an attempt to catch the battery acid if it does go bang, it may not work that well but better than nothing!

Good luck and let us know how it goes! ;) :D

so quick update, not had much free time, did just pop out to see if i could do anything, took the battery off, and connected to charger directly to the car terminals, the same thing happened, popped the fuse in the charger

assuming this is same- as having a completely dead battery, and it's drawing too much power and killing the fuse?

_Matt

Pretty much Matt but when i said disconnect the battery and connect the charger, i meant connect it to the battery! :rolleyes:

It sounds as if you have a fault on the car, whether it's the alternator or not is anybodys guess, you need to check all the earth straps to make sure you haven't broken them with the jetwash or whatever and disconnect the alternator output terminal (the big one with the red lead usually) before reconnecting any power source to it. That is simply to eliminate it as a possible source of the problem.

My Jeep battery went completely flat and my charger would not even touch it.
I put it on a bench power supply I have for electronics and let it charge for a day or two at 200mA.
After that it seemed to recover and after then charging it with my normal charger brought it back to life.

Drained battery
 

A fully drained battery hardly accepts any charge current, but it will not blow the fuse of the charger. Quite the opposite, there is hardly any current going through. You probably have a short circuit somewhere in your car, most likely in the alternator or starter motor circuit. Any deeper in the system all circuitry is behind fuses. A short circuit there would also blow a fuse in the fusebox.

By the way, a deeply drained battery hardly accepting any charging current is the reason that you best switch on as many power consumers as you have before disconnecting the jumpstart cables. Otherwise there might be a voltage surge because the alternator suddenly has to reduce its capacity to almost no load.

ok pretty certain ive found the problem

on a side note one of auxilary terminals had become dis-connected from it's crimp connector but i dont believe that's been the cause of this.

I borrowed a battery connected that one up, and i could hear a hissing noise and saw some small amount of smoke coming from the alternator, so that's pretty certainly my culprit. So sourcing a new one is next on the order!

I guess this is what I get and a good lesson, don't be lazy, always take just a minute to protext your electrical components whenever water is nearing your engine. I can't really imagine a worse outcome, now i need a new alternator and battery, lol. lesson learned!

thanks for the replies everyone. I will update as/when it's fixed too

Regards, Matt

After disconnecting the test battery, did you then disconnect the alternator and reconnect the test battery just to make sure everything else is ok Matt? :thinking: