Theo

Just rereading the thread, I noticed that I had not replied to this post from nicknorman. The 14.4V is read off the SmartGuage which is connected directly to the battery terminals. I believe the batteries to be pretty well knackered. I have had them living aboard for 3 years and 4 years not living aboard being looked after by the solar panels but for a period they were abused at the boatyard by being left without the solar panels connected. So they don't owe me much and I should really be thinking of replacing them.

It's not working at the moment so I have unshipped it, taken it home and am investigating. I think that it's the flame sensor plus some stiffness of the air blower from lack of use over a lengthy period. I can't buy any more gaskets. Mikuni have stopped making spares and MV Heating in Eastliegh have none left. Not necessarily a problem I can create my own from some 2mm gasket paper. I got this news from the nice man at MV Heating who told me that the replacement for the MX40 is an MV MX50 which they will mount on the same plate that the MX40 was mounted on if I send it off to them, cost £595 + VAT plus carriage. Question: is the MV MX50 a good buy? My inclination is to have a go with the old one and see if I can get it going for a few more years (months? weeks? not at all?) Opinions/advice will be gratefully read. N

Please be aware that one of the lasting benefits of this forum is the fact that there are many and various tangents that have been explored. The advice offered is usually good, often brilliant and always free. If you understand and can work with this you will have a very rewarding experience. Nick

Coming late to the discussion: Blue hydrogen is made from natural gas and is effectively a fossil fuel. Hydrogen made using elecricity from renewable energy of whatever variety is Green.

Absolutely not. As soon as you get lift from the cill on the bottom of the boat the stability is all shot to hell and the boat tips over to one side or the other. This could be mitigated if you managed to get to the forward end of the cill and then the boat would be like sitting in a drydock. The problem then, if you have not already submerged the bow, is that the boat could easily slip off. Please don't try this. You could always try a staircase where you could sit the boat down on the invert. Nice and level. But then you have the possibility of damaging the bottom of the boat by putting lots of wieight on a small pointy object. N

I suppose that makes a happy conclusion to the didscussion. I have, I hope, a non-slipping alternator belt, a bit more knowledge about the way that alternators work and the continued knowledge that there is seemingly endless help to be got from CWF. Thanks for all the contributions. Nick

"It’s to do with the regulation curve of an alternator’s rather basic regulator. The current supplied by an alternator is related (inversely) to the terminal voltage. So if we presume for example that the regulated voltage is 14.4v, at 14.4v it is producing no current. At 14.39v it is producing maybe 1% of its output. At 14.3 maybe 10%. At 14.2v maybe 25% You have to get right down to perhaps 13.7v before it is producing 100% of its output. (Figures made up, but the principle is right)." I have quoted the bit from nicknorman's post that I can't get me head around. Lets forget that we are using an alternator for a moment. If we were to use a true constant voltage source where the voltage is entirely independent of the current drawn, then the current delivered at, say 14.4V, would be entirely dependent upon what the battery bank would accept. Now take the case of nicknorman's alternator. The battery bank is at 14.4V so the current delivered is zero as controlled by the alternator electronics. Now let's say that some charge is drawn from the bank so that its voltage drops to 14.39. In the case stated by nn the alternator immediately delivers its 1% which, with a 70A alternator is 0.7A or a 140A alternator is 1.4A. If we take the load drawn out of the equation by assuming that it is switched off the moment that the voltage drops to 14.39V then the alternator will continue to charge the battery until the voltage reaches 14.40V and then stops. Ah! It is becoming clear what nn is saying even as I am typing the reply. What he means (and says clearly) is that, assuming the same alternator controller characteristics, a 140A alternator will charge the battery more quickly even at the low tail currents. My old alternator is a Bosch to which I fitted an adjustable controller. I originally found that it would charge reasonably rapidly at the beginning of the day's cruising but the current would drop off far to early. I got around this with an Adverc which made a huge difference... Thanks, nicknorman. I believe that I now understand but will not be fitting a bigger alternator because of the issues of fitting new pulleys etc. I will live with what I have. (And keep the belt tensioned properly.)

But at safe voltages you can only put so much current into the battery bank. At 80% charge and 14.4V my nominal 810AH (very old) battery bank is only accepting in the region of 18A. This will, of course be due to surface charge, but can such chemistry be overcome by lots of electronics? I am using an Adverc, and very excellent it is too, but I can't see how I would manage to keep my alternator working flat out any more than it is now.

I would be really interested in your reasoning. N

Ah, yes, but as I said it almost never produces anything like 90A. Thought! 🗯️ Perhaps it is a 90A alternator. After all it did only produce 85A when the soc was 25%.

I would guess that it's about that size. There is the added pully on the crankshaft. It's a small one and is used for the pelt drive to the raw water pump. Edited to add: An extension to the maths will show that the force on the drive belt to the alternator does not change as the pulley size on the alternator changes. I find that quite interesting. N

I should add that there is good and simple mathematics behind the advice to run the alternator fast: Power output of the alternator at any instant = VI. Power input ( just a bit more than power input) = Torque (in N-m) x angular velocity (radians/second) So for a given power input increasing the angular velocity (think RPM) the torque will reduce. So running the engine faster will reduce the force on the alternator belt. However running the engine faster means that it is wasting more power in overcoming friction so you will use more fuel. That's why I run the engine as slowly as possible consistent with maximum current. N

That, to me, seems like a really horrible person telling him lies to mislead him. Mind you, he should have bouhg some maps!

Thanks for all the useful advice. All the advice had already been followed except Tracy D'Arth's "There should be about 10mm maximum deflection on the longest run between pulleys with firm thumb pressure." It is embarassing to admit that I had not got it tight enough. I had been testing the tension on the shortest length from the water pump to the alternator (Theodora has a BMC 1.5) The longest length is from the alternator to the crank shaft. Tightening it with a little assistance of the jemmy should have done the trick but I can't test it properly until tomorrow when we will have run the batteries down a bit. David said "Have you always had a 70amp alternator, or is it a recent more powerful replacement? I replaced the original 35 amp alternator on Helvetiia with a bigger 70 amp one, still using the original 10 x 1050 belt, and experienced a lot of squealing under load. After tolerating it for a while, I arranged for Jonathon Hewitt at UCC to open out the crankshaft pulley V groove, fit a wider alternator pulley, and fit a 13.5 x 1050 belt - problem solved. " Actually, the alternator might be 100A. I fitted a new one when we first had Theodora. The old one, the original Lucas, IIRC, was not working at all when we bought the boat. And in my ignorance I thought that a bigger alternator had to be better. A few years later I got around to fitting an ammeter in the alternator output. What a worthwhile investment! I have never seen the output go higher than 85A and that was when we collected the poor old boat from where they had been painted. The soc (Smartguage) was reading 25%. I never let it go below 50% normally and usually get concerened when we approach 60%. I rarely charge the batteries with the engine when moored but when I do I run the engine just fast enough to give maximum current. I observe from the alternator current that at the beginning of the day the alternator output might go as high as 45A, falling back to 25A within five or ten minutes and gradually reducing over the rest of the day's cruising. Who needs a high paowered alternator? N

I have had a squealy alternator belt three times in the course of a three week trip with few running hours (often less than 4 hours per day. Each time I have tightened it a boit more. The belt was new at the beginning of the trip so I would expect to have to retighten it once after the initial tightening, but three times seems a bit excessive. It is a 10mm x 1005mm belt in the correct pulley width. This morning the battery soc was down to about 70% and as soon as the split charge relay connected the domestics the alternator delivered about 55A. Its a 70A alternator. As the battery voltage built up and the current delivered by the alternator reduced to about 40A the squealing stopped. What I don't want to do is to overtighten the belt. I was told years ago that the alternator would stand lots of lateral force on the bearings but not so the water pump. So I want to keep the tension as low as I can consistent with not shredding the alternator belt and scattering bits of black dust over the engine. Advice please? Nick