Froggy

Ok, thanks, i was forgetting how badly blocked those vent grills at the rear were, we were quite shocked when we took the alternator off, it wasn't evident from the top and front when checking oil and water levels.

I'm guessing though that a blown diode might possibly indicate too large a load could have been imposed on the alternator at the time of failure by running too many high-demand appliances?

You are correct, belt had been slipping for a while on startup, it usually resolved after 5-10 minutes, i tended to have to readjust belt roughly once a month but hadn't got around to it that time. What can you see in the photos to indicate slippage, is it the way the backing has parted company in the second photo? Ok, well that's reassuring, i just wanted to cover all bases since the repair is costing about £160.

Ok, thanks. Profiles looked more or less identical although photos don't really show this, but old belt has been binned so can't double-check. New belt ran about 6 hours before alternator failure. Hopefully just coincidence, there were no obvious indications of belt slippage.

Latest update on this is that a diode was blown. Alternator is getting an extensive refurbishment in addition to the diode. Is it possible that fitting a belt that isn't an exact replacement could cause issues? The replacement belt was already on the boat but i did note the teeth were a little chunkier but just assumed it was due to wear on the older belt and/or different manufacturing tolerances. Both belts were as good as identical in terms of width and circumference. Taking a closer look at these close-ups now though there does seem to be a real difference in the profile of the teeth. The older belt is at the bottom in both photos.

Thanks for the suggestion but domestic alternator is now in for repair.

Tony, i am asking a lot of questions because i am a novice with electrics, but very inquisitive (and need to make a decision quickly since we are currently without power and have had to defer a fairly lengthy week's cruise until this is sorted). I appreciate all the advice you have given. No, we haven't done a power audit but our existing charging regime has kept us in good stead in the four years or so we've had the boat. The batteries still seem to hold their charge well about three years in and the belt has only been changed twice in over four years. The engine is probably only run on average for about 10 hours a week, apart from occasional longer cruises. We are normally very frugal with power consumption: the tv, fridge and vacuum are used very sparingly (the fridge is only used in very hot weather, mainly to cool drinks) and the microwave almost never; most of our lighting has been converted to led. I'm going to phone Barrus tomorrow to see if they can shed any light on the alternators that might have originally been fitted / recommended for this engine. Then I'll await the refurbisher's report and take it from there. I'll report back on how this pans out, and obviously the advice you and others have given will help guide my decisions.

The main predicament here is that we don't at this moment know the output of our dysfunctional alternator. If this can be ascertained we can try to source a similarly rated alternator, or have the existing one repaired. If we can't determine this the dilemma would be having to guess and ending up with an alternator with an inferior rating to the original. If you think a 50 amp alternator would efficiently drive a service battery bank i will bear that in mind.

It might be because the boat was originally fitted out as a six-berth hire boat. At the time it had four Trojan domestics and from memory (we still have the original manual) it still had a separate battery for the diesel heater, which was originally a Webasto.

The reason I'm questioning this is that the guy who diagnosed the alternator as being defective reckoned that 50 amps wouldn't be sufficient to charge a domestic bank. It would surely at least add to fuel consumption and engine wear on account of having to run the engine longer?

Yes, 4, with two alternators, afaik the lower alternator just charges the starter. When new the boat was fitted with four Trojan domestics, but the engine has been replaced with a different model in the meantime so it's possible that the original engine used two belts.

Please note I've corrected my post above and also replied to yours. The Eberspacher actually has its own battery but i think is charged from the same alternator that does the main leisure bank, i e. the alternator that has failed.

Yes. But i don't think it's on its own alternator. That's what I thought I'd been told when we bought the boat, it's probably faulty memory, the fact that when starting the engine after the alternator failed the voltage didn't change on our Eberspacher-specific volt guage suggests i was wrong. If we can't determine the amp rating of the faulty alternator and can't have it repaired do you think a 50 amp alternator would suffice for charging leisure batteries (currently about 240 ah from memory but ideally we would upgrade in the future to higher capacity). The downside of a low rated alternator would surely be longer charging time and hence greater fuel consumption and engine wear. I think that would be too much hassle since the starter and Eberspacher batteries are on the opposite side of the engine bay to the main leisure bank.

Yes, the alternator below only seems to charge the starter battery. I had been under the impression that it was charging the Eberspacher but i started the engine before removing the faulty one and no charge seemed to be going to the Eberspacher circuit.

Ok, thanks again for all your help. I'll post an update when we have it sorted. As things stand we don't even know the rating of the alternator we've removed so it might be a bit of a gamble. I can't find the exact model anywhere on the internet, I'm guessing it went out of production about 20 years ago. I think I'll phone Barrus tomorrow, they've been very helpful in the past on two occasions, i even got to talk to a guy who helped develop this particular engine model (1950).

Thanks Tony, your knowledge is much appreciated. Would that additional squeal/shredding only happen if a high demand was being placed on it by too many appliances being run whilst the engine was running? Certainly, before the last belt snapped (and it was at least three years old), the first sign that it needed tightening was what i assume was belt squeal that would then cease after about 5 minutes (except when the belt was very loose). So i guess that our first step is to find out what the failed alternator rating was, and hopefully the refurbisher can tell us this, and then try to either have it repaired or source something with a similar rating? If we can only source a higher amp replacement could we get away without belt squeal if we limit the demand on the current whilst the engine is running?

But if this is a 50 amp alternator and we opted, say, to replace with an 80 amp one, could that cause problems? For example, would it increase the likelihood of belt squeal/slippage? Or would the regulator compensate accordingly? We're not sure what exactly failed on the alternator at this point, we've been advised it's either the regulator or the coil winding. If the latter, could the coil winding have burned out because too high a demand was placed on it? With our 1500 inverter, we occasionally use a hoover rated at, i think, 1000w and a microwave, rated at 750w. The other high demand item is a 240v fridge, which we only use occasionally. These items aren't usually used at the same time but my other half said she was using the microwave at the same time as the fridge around the same time the alternator failed. Could it be that the coil burned out because too much demand was being placed on it, and if so, would it be better practice in future to run these items without the engine running and then charge the battery bank back up later? As mentioned earlier, after removing the alternator we discovered the vents were badly clogged so this could have contributed to overheating.

Ok, i've managed to edit the file sizes of the pictures i took in order to upload here. The alternator is a Mando brand, this is embossed into the casing at the back; however there is no other information visible regarding a serial number or amp rating. I'm taking this to a refurbishment company later today but your advice might help me make a decision as to whether to refurbish or replace it. There's one very similar on eBay rated at 50 amp. That might well be the rating for this one, but i've been led to believe that 50 amps would be insufficient to supply a service battery bank, and if this alternator is actually higher than 50 amps i certainly wouldn't want to downgrade. If this actually was 50 amps though, and we went for, say, an 80 or 90 amp alternative, would there be any downside to doing so? Our system includes a Victron inverter rated at 1500w.

Tin alternator? How very, very dare you! 😉 Yes, i can remember reading some criticism of that design a few years back, possibly on another thread i posted. It works well enough, although the belt needs tightening every few weeks, which may or may not be related - it could just be that the last belt was of poor quality.

Thanks, that might be useful at a later date but at the moment the alternator has been removed and both of the alternators plus the water pump work off the same belt.

Ok, thanks for all your help. It's easily checked re BSS i guess. The priority is to get our alternator refurbished or replaced prompto. We dont have any domestic power at all from battery bank now it's been disconnected. I'll keep you posted how things go and post a photo later if possible.

Ok, thanks for all your help. It's easily checked re BSS i guess. The priority is to get our alternator refurbished or replaced prompto. We dont have any domestic power at all from battery bank now it's been disconnected. I'll keep you posted how things go and post a photo later if possible.

Thanks Tony. Engine was built somtime in the 1990s i think (Barrus Shire 1950). Is it a BSS requirement in order to stop the risk of the boards above catching fire?

Thanks for your advice Tony, and everybody else. I'm unable to attach a photo from my phone at present - file size is too big, I'll have another go from my laptop as soon as i get a chance. I can confirm that the alternator is fecked and will probably go down the route you suggest of taking it to a local refurbisher. I think i know the reason too - rear ventilation grill was badly clogged with small strands of fibre that seem to have come from the insulation around the exhaust manifold (i think) and pipe. This insulation is falling apart, and looks as if it might be made of asbestos or something. How important is this insulation, and what's its main purpose? Is it simply to keep the temperature down in the engine bay?

Strewth, that's a bit drastic! 😃