JugaarLife

Yes, it is a JP1, and you're about right with the revs. Also with the alternator pulley - I haven't actually measured it (I will), but probably closer to two and a half, I can't really run the engine now so I'm going back to this in the morning.

They are as you described in your first comment about them. The alternator one is a bit larger than 2", the engine one 10-12". I'm tired, I got lazy in my description. I realise that doesn't help, I will be more specific.

Yes, it is. Also, yes, you're right about the pulleys - they're massive, I'll abandon that train of thought. Doing so now...

Sooo...lamp now coming on, but not going off. It is a very low revving engine, though - I'm limited in how much I can crank it up. No guage but it's low. I'm guessing this particular model of alternator worked at some point with this engine, though. Although that is a guess. Another oddity....there is no negative cable on the Dynastart. It's bolted to the hull, but there isn't a negative back to the starter battery, which is where it gets it's power from.

Got terrible signal, thought I replied to this but can't see it. Apologies, my bad - both the starter negative and leisure negative connect to the bolt holding the alternator on, which is in turn connected to the hull. I'm sorry - my brain's getting fried!

Apologies, was away from the boat for a few days. No, the negative bus bar is connected to the leisure battery negative terminal. Which is not connected to the hull...

Which explains why I can eat a Chinese meal for three!!!?!

You've both been awesome. Going with that, I'll report back once I've got my hands on a good leisure battery.

Ooh, interesting! Never tried that, I'm going to give it a go! I love shallots. Never occured to me to try them with this. I shall!

Yes, is the answer to that one. It's on a plastic fitting, mounted on a wooden board.

Yes, this part makes sense. I wasn't hugely surprised it didn't work with the negative cables disconnected. Very helpful posts Tony Brooks and Nick Norman, thank you. I'll report back shortly! Appreciate your help. And yes, I'll gladly post a pic of the engine. Prewar Lister JP1.

Not directly to the engine block, no, but there is the heavy negative lead running via the alternator body (not a terminal on the alternator, but the big bolt at the top of the alternator, which does ultimately go to the engine block), to the leisure battery negative (and onto that earth bar). Would this be basically the same? Ahhhh....yes. Ok, so the alternator light does not work. It is powered by the leisure batteries. I don't actually have an ignition, she's hand crank with Dyna start, but this is starting to make a bit more sense. I'm going to try with healthy leisures. Thank you, Nick Norman, very much. My brain just became a tiny bit less baffled.

Fair assumption (I just double checked myself!) but no, it is indeed a Unipoint. Not heard of them before myself.

Yeah, I explained the whole thing terribly in my first post. I was tired and frustrated! Regret that slightly now! Also, this is all quite new to me, so I know I don't always use the correct terms. A better attempt - alternator wasn't charging, so I checked all cables and connections, using a multimeter, either checking resistance to see if the wiring was good, or in the case of the alternator, I wanted to see if the voltage was a) the same as the leisure battery while the engine was off and b) if there was any increase in voltage when the engine was running. Used a multimeter, negative probe on negative starter terminal, positive probe on positive alternator terminal. What I discovered was that when the engine is off, the voltage at the alternator positive terminal drops to less than 1V when the negative cables between starter and leisure batteries are connected. This is the same whether they are connected at the alternator body, or bypassing the alternator. I don't have a starter motor (have Dyna start/hand crank connected directly to the starter battery, there is not a negative wire between the Dyna start and alternator). The two large, negative cables between the starter battery and leisure batteries were connected at the body of the alternator, large bolt onto the engine block. If, however I do bypass the alternator, and have the negative cable from the starter running straight to the negative leisure terminal (and onto the earth bar from there), the starter battery will not power the Dyna start. Thank you, Nick Norman! That is useful info about the Sterling unit. I will try again with a healthy leisure. Back to the other point - voltage reading at the alternator positive terminal. The thing is, it IS showing more than 12V when those negative cables are disconnected, and almost nothing when they are connected. Could this also be simply because my leisures are dead? My god. I hope so!!!!!

"Where are you measuring the voltage? If the leisure negative is disconnected, there will be no voltage between leisure positive and the negative bus bar." I agree completely, this is exactly what's confusing me. I can see that the voltage from the starter battery is reaching the alternator positive terminal, but ONLY when I disconnect the negative cable between the starter and leisure batteries. Which makes no sense to me at all! "If the leisure bank is indeed dead flat, when the alternator tries to charge it, the voltage between alternator output and negative will be low." Yes, but the loss of voltage running to the alternator when negative cables are connected occurs when the engine is off. It's not the fact that the alternator isn't charging (I know it can't charge if it's not getting any voltage), it's the fact that it no longer gets voltage from the starter battery when the negative battery cables are connected. Apologies, it's difficult to explain this, because it's so damn odd!

" there are 2 meter probes, where are you putting both of them". Negative probe on starter negative terminal, positive probe on alternator positive terminal. "So for example if there was a really bad connection between alternator and the battery positive, when you put the meter on the alternator positive and the battery negative with the alternator negative disconnected, I might read 12.6v because the meter takes virtually zero current and no other current is flowing. But when you connect the alternator negative and make a circuit, the small current flowing into the alternator via the really bad (high resistance) connection causes all the voltage to be dropped and the meter now reads zero," I believe the connections are ok, as when I test the resistance (multimeter testing ohms, one probe at each connection) there are zero ohms. Correct me if I'm wrong here, though. "Another consideration is that an alternator needs field current to work, that current has to come from a battery in the first instance before the alternator becomes self-generating. If the battery is completely flat" I see what you're saying here, but that battery isn't completely flat, the multimeter (used as before) reads 12.6V on both the battery and positive terminal on the alternator. I did pop this in the original post. "Remember, you know what you are measuring but we can only know if you tell us precisely" Very fair point.

Here you go. I'm sorry, I don't know the correct symbols for everything but I hope that gives an idea. Disconnect the negative cables between the batteries and a multimeter (negative probe on starter negative, positive probe on alternator positive) reads the same voltage as the starter battery. Connect them and it reads almost zero. I think the controller part number is Pro Alt C, from what I can see on the casing. Tried to upload a photo but file was too big.

Thank you!

Anyone managed to perfect this? I've tried several times and the results have been rubbish, to be perfectly honest! Always ends up tasting like a poor version of the sauce in the polystyrene cup from the Chinese poured over everything, but from the Chinese you avoid rather than a good one (since I actually like that sauce!) Any delicious sweet and sour tips, send 'em this way! And in exchange I'll try and think of something I actually cook well...

Hi all, Hoping someone may point out an obvious thing I'm missing here. I have checked previous posts, couldn't find anything relating exactly to this problem, but happy to be redirected if I've missed it. I have just bought the boat, so as it stands everything is as it was when I picked her up. She has a Unipoint 12V 70amp alternator, running through a Sterling Digital to Alternator Battery Charger, max alternator size 80amp. Had a split charge relay on my previous boat, so I'm unfamiliar with this set up, although it looks to be logical. Alternator shows almost no voltage when the battery earth is connected. Disconnect the earth and 12.6V (or whatever the starter battery is at) shows. As soon as the earth is connected voltage drops to 0.4V (hence "almost nothing"). All of the above is when the engine is off, when running the alternator simply doesn't charge, but that's no surprise. I didn't install these electrics, so I'll just describe them as they are. I'm stating the obvious with some stuff but as I haven't yet found the fault I'll just whack it all in. The batteries are earthed to a standard earth bar. Sterling unit is earthed to the same via the leisure battery. The starter earth runs to the same via the alternator body and starter battery. If I bypass the alternator and go directly through the leisure battery (and so to the earth bar) the starter earth no longer functions as an earth. Battery does nothing at all when trying to start. Connect back through the body of the alternator and she starts fine, but then the alternator has no voltage. The earth for the starter functions only if it runs via the alternator body, nowhere else. There is what really, really looks like a negative terminal on the alternator (I do believe it is one), but if I connect the earth wires here, it doesn't work - as if it's an open circuit, as with bypassing the alternator. I have checked all connections and wiring between starter, leisure, Sterling unit and earth bar, and have found no resistance at all (ok, 0.1ohms at one point, I forget where now but this was so minimal I ignored it), the cabling appears to be in excellent condition. I feel like this could relate to the Sterling unit, but that's possibly because it's the unfamiliar component in the set up for me. I can't actually work out why it would be though, since everything still shares a common earth whether through the alternator or not. The circuit seems basically the same. I'm sure I've missed something blindingly obvious. My knowledge of electrics is fairly limited (sure it shows!), so I hope that's the case. Will be so happy to be put straight, as I'm stumped! The poor leisure batteries are unfortunately absolutely, absolutely flat. 4V or something. Not sure how long they've been like that for, so I'm not crazy hopeful about their future, but I'll pass under that low bridge when I come to it. Any advice gratefully received.