Dodgy alternator?

[Relfy]

This is narrowboat electrics but in theory its the same - 12V - except for an extra wire cos of the no-earth bit, so I wonder if you electrical-whizzes could give me some advice?

My batteries have been flat a couple of times when i get home (live on the boat) lately, so I've had to jump start the boat engine via a spare battery. I took the batteries (one starter and two house) to a friend with a tester-thingy last weekend and they are fine.

However, although this worked the last couple of times, I left the motor running for nearly 2 hours last night and it made no difference to my own batteries whatsoever - still flat.

1.) I dont really know why the batteries should be flat when i get home. Nothing is left on, so is there possibly something draining them?

2.) If it hasn't charged with 2 hours running time (normally an hour a day or so does it), does this mean something is up with my alternator? If so, can you fix alternators or is it a case of buying a new one? I think I need a bigger one anyway, mine is quite diddy.

I look forward to some 'light being shed' on this topic. Teehee. Sorry.

[alex_holden]

If the battery flattens itself in a day when it's not connected to anything at all, that means it's disintegrated internally. If it only flattens itself when it's connected to the boat electrics, that probably means something is consuming power. Is there an ignition light connected up to one of the alternator terminals, and if so does it go off when the engine's running? When you leave it running, is it idling fairly fast? What voltage do you get across the battery when the engine is running?

[Packedup]

Of course, if the alternator is toast it could have failed in a way that allows the battery to drain back through it - So it might be struggling to charge when running, then sapping any charge present when not.

[Relfy]

Investigated last night - the alternator is putting out zilch. (Btw, I do recommend the 12-Volt bible for boats by Miner K. Brotherton - its revealing all sorts of mysteries to me - car and boat!)
I reckon it must have been on its way out but still doing something the last couple of times I ran the engine, but now is dead. The batteries are fine according to chap who tested them for me last weekend - perhaps they just charged enough the last couple of times for an evening of light/water pump and that was it.
I'm going to swop the alternator around for another one tomorrow and see if that fixes the problem, otherwise I suppose I better investigate the wiring.... not easy on a boat!
Thanks for the advice

[Relfy]

For anyone who's interested in how this developed, (electrics by the bodger of bodgers), this is how it went...

The original alternator was definitely dead and was going to cost quite a bit to recondition, so I found another alternator, a bit bigger but not too big for the engine to turn over, so better for the job really! It also had the right connections on the back. £20. Bargain.

So I fitted it to the boat, but struggled to get the ignition light to work. Didn't worry too much though as I continued to have good light in the boat for a week, running the engine every other day for a couple of hours. But when I went to start the engine after that week - nothing.

Hmm. More prodding with a voltmeter. There is charge coming out of the alternator along the ignition wire. Difficult to get at the charging wire so assumed there is charge there too. Batteries fine aswell - well they must have been holding the charge all that time and tested fine too. Is it perhaps the relay? Someone has put a loop onto it, implying it perhaps wasn't working right before - good I spotted that though as now I know I'm drawing from all three batteries when using lights etc., not just the 2 house batteries as previously thought... yes, look at that! When I put the charger on the starter battery my lights go bright! So, maybe the relay is also bust enough that it isn't letting charge through from the alternator? Hmm.

To rule it out for good, I went and got my 2nd alternator tested. Its fine. The interesting bit was where the guy said YOU HAVE TO HAVE A SECOND CHARGE LEAVING THE ALTERNATOR TO EXCITE THE DIODES TO LET THE MAIN CHARGE THROUGH. I didn't know that.

Aha. So its that ignition light thats the problem. So I bought a new bulb unit and replaced it... nice and cheap, problem solved - it lit! and then it stayed lit....

Scratched head for a while. Why is that happening? alternator's fine, got a new ingition light unit... is it still not charging for some reason? the relay? or maybe some dodgy wiring along the way? Then I had a little thought. The light goes out when the leccy to the ignition light is balanced by that charging, so maybe as its a bigger alternator its putting out a bigger current and I should try a bigger bulb? Scrounged a bigger bulb from someone, stuck it on with tape and hey-presto the light goes on when not charging and goes out when charging. Just as it should.



I'm pretty sure now, the problem is solved, but will see what happens after another week! (Hopefully not a boat fire )

[Axolotl]

I also have a narrowboat, and you do learn a lot about electrics quite fast when your life (i.e. heating, water pumping, lighting and fridge) depend on it, especially in winter .

I had the ignition light-bulb thing too at one stage. It has to be just right or you get no charge or the light doesn't go out at all. Mine needed a size (wattage) no-one stocks any more, so when I finally got one, I got two (if you see what I mean).

However, you can wire the alternator up using a relay to work the ignition light bulb instead of just the "balanced" circuit, then the size of the bulb doesn't matter. Just don't ask me how.

I've seen it done, but wouldn't know where to start. Maybe a friendly electrician could rewire it for you and mean you're not dependent on that ignition light bulb?

[Relfy]

Yes - have to say I'm completely and utterly worn out but its all good learning-experience! Next year hopefully all my teething-troubles will be ironed out...

My fridge and water heater are actually gas, although no point in water-heating with no electric to pump it there of course... The fridge is pretty cack, so I'm going to try and switch to propane (butane for some reason atm) and see if that helps (don't worry I'll get a corgi person to do that for me), otherwise I'll stick a plug on it and put it on mains as soon as we have it... we've been digging up the car park and laying cables the past month or so, as in, all of us boaties and the sea cadets, me included, aswell as fixing the boat electrics and the car... No wonder I've been getting sore throats, flu etc.
Now I'm sorted for 12V though, thats the main thing. If I ever get round to it I'll draw a wiring diagram for the boat and go about replacing it... I've already found lots of wierd/not very good things. One piece of wire with 2 joins within 2 inches!! lol. And several randomly waiving naked ends that are probably giving me a nicely corroded hull. It all looks a bit old and brittle so wont do any harm to redo it once I'm an expert. ;) I'll definitely think about your relay system then - or before if this bulb blows and I cant find another!
My heating is solely solid fuel stove - but it heats up Wilma's 30' in no time atall so I am comfortable and not falling over everything and causing huge fire-risks with tea-lights either anymore.

Its such a great community life though isn't it?! Every weekend I wake up there is laughing and whistling and chatter going on outside and I feel so lucky and can't wait to get out of bed.

[Axolotl]

Try and get a copy of Ed Sherman and Miner Brotherton's "12 Volt Bible for boats", it gives a lot of useful stuff, even though some of it is for tupperware boats. Currently £9.74 at Tesco books (or is that an advert?)

It'll help you unravel your current (excuse the pun) electrical "knitting".

[Relfy]

Try and get a copy of Ed Sherman and Miner Brotherton's "12 Volt Bible for boats",

See 4th post down. It is a brill book! (although my version is a little bit old, its been v helpful!)