nicknorman

Yes for long term ie weeks, months etc it is better to use a voltage of around 13.2v which keeps the batteries nearly fully charged but minimises “positive plate corrosion” which can shorten the life of a battery left on charge for long periods. In your case, float at 13.8 would be a better option since you are only there for a few days.

As I explained, the propensity to slip is related to the load on the alternator which is related to the size and state of charge of the battery. So it seems that the pulley that was slipping badly, is now spinning ok despite being worn and polished, as the load is minimal. The one that was previously not loaded and hence not polished and worn from extensive slipping, is for the time being working better. Did you tighten the belt at the same time? Anyway, I would get a new belt and stay on top of keeping it correctly tensioned. Clean off the black dust. If it recurs this indicates the belt is slipping.

No. My point was that the reported voltage was too low to be explained away by a fully functional alternator being pulled down by low batteries. The reported voltage indicates something is wrong. Quite possibly belt slip.

From your description I’d say slightly over tightened. Twisting 90 degrees is a fair way to assess but only using moderate force. If you say “I can just twist it 90 degrees using maximum force” then that is too much. Put it another way, it needs to be just tight enough to avoid slippage, but not more. So back it off until it just squeals under max load at low rpm, then tighten slightly. Then note how much force is required to twist 90 degrees for future reference.

I disagree. OP reported 12.8v which is too low for a reasonable size of alternator. Yes of course low batteries will reduce the alternator voltage, but not by anything like that much. Mid to high 13s would be reasonable.

The other option would be to restore the Travelpower and use it to run a battery charger.

Yes it could just be a loose belt. You can try tightening but it may be worn. V belts are designed to contact the V shaped sides of the pulleys. If the belt or the pulleys get too worn, the bottom of the Vbelt can contact the bottom of the pulley and so there is no force on the V sides (which have a much better contact area). So even if you tighten it correctly, it can still slip. Have a close look at the bottom of the V on the pulley - if it is shiny, this indicates the belt has been bottoming out on it due to being too worn. New belt required. This design of alternator drive with 2 alternators on 1 belt (and a water pump) is not a great design as the “wrap” (% of the pulley in contact with the belt) isn’t great and it can be a bit marginal at the best of times even with belt and pulley in good condition.

It would be an interesting test and shouldn’t cause a problem, but don’t disconnect anything with the engine running. But see my post about belt slip, it could just cause the other alternator to slip on the worn belt when it is loaded up by the flat domestic batteries. Only one way to find out! Edit: actually I’m not clear what you would be swapping. Are you going to end up swapping which alternator feeds which battery by this swap? Or just swapping the alternator and battery combination between domestic and leisure supplies? If the former, good test. If the latter, not sure what it would achieve.

I’m a bit confused about your setup as the photos aren’t great. I think there are 2 alternators run by one V belt? Is one for the leisure batteries and one for the engine battery? And there is a polyvee belt in the picture, what is that for? Anyway, I would say that the leisure alternator is most likely knackered BUT as was mentioned, there is a lot of black dust which is indicative of belt slip. Can you rotate the leisure battery alternator pulley without the engine turning? If so it is slipping too much and probably the belt is worn to the point it’s not gripping due to being bottomed out in the pulley. It is worth bearing in mind that the propensity for the belt to slip depends on the electrical load on the alternator. Starting the engine uses probably less than 1 amp hour which is rapidly replaced and hence the load and propensity to slip on the engine alternator is minimal. By contrast low leisure batteries can take the full output of the alternator, maximum electrical and hence maximum mechanical load and hence could just be permanently slipping.

No that isn’t suitable for measuring any significant current, and you have to disconnect wires and insert the probes in series. A good way to blow the meter, or at least its fuse! The clamp meter MtB mentioned is the easiest way to measure current from alternators etc, you just clip it over the wire and hey presto! Or you can still get the slightly cheaper Uni-t ut203. As I routinely say on here, electricity is invisible and so without adequate test equipment, we and you are just guessing. Lots of time is spent on guessing and false actions, when the solution is a £40 meter! Does not compute!

BMF I think - British Marine Federation

However that is exactly what happened to our boat after 10 years. I thought the calorifier had split, but I finally traced it to the immersion threads. I replaced the fibre washer, but it still leaked. I then applied PTFE tape to the threads. This fixed the problem. However it’s worth bearing in mind that the seal is/should be the fibre washer. The PTFE tape helped primarily because it lubricated the threads and allowed me to tighten the immersion more - well, it went further round for the same force, crushing the fibre washer more. It felt quite different with the tape on the threads, a nice sliding of metal on metal gradually getting tighter, rather than jerky catching unlubricated metal on metal.

We were trying to ignore it.

Calorifier can of course be heated by 3 sources (at least), the engine - which is "free", an electric immersion heater (if you have shore power or a genny) or by whatever you use for central heating (diesel, gas or solid fuel stove). Instant gas water heater is a solution that doesn't require any electricity or engine running or diesel, and you only heat what you need, but the downside is a fairly slow flow rate making winter showers a bit miserable.

When you say “the fan moves freely by hand” do you mean with the belt taken off, or as it is now? You should not be able to move the fan if the belt is on, otherwise it is far too loose. Just because you can see the fan rotating doesn’t mean the belt isn’t slipping madly and the fan turning at 1/4 speed.

I wasn’t quite clear from the above whether the engine was completely cold when you turned on the isolator and checked for alternator warming. The test would be to start off with a completely cold engine, since the alternator is only going to get slightly warm from back flowing current. If it is already warm, you probably aren’t going to notice the difference. As usual we are up against the fact that electricity is invisible! Without proper test /measuring equipment it is very difficult to now what is going on. And yet adequate test equipment is so cheap! I would recommend getting a multimeter that includes a DC current clamp-meter (be careful, lots only do ac current). The Uni-t UT203 is the old favourite from ebay, used to be £30, now seems to be £40 (that’s inflation for you!) eg https://www.ebay.co.uk/itm/334520176779 You can clip the meter around a cable, eg the battery to alternator cable, and see if there is any current flowing. Or clip it on elsewhere in the hunt for where the current is going. Takes seconds! It is not super accurate as it works on magnetic field, you need 1/2 amp or so at least. But in the context of boat electrics, it is very useful.

The devil is in the detail. At a high current, provided the gate drive voltage is adequate, there is fairly low power dissipation. Obviously you would choose MOSFETS that have sufficiently low Rds(on) (on resistance) to keep power dissipation to a safe limit at max rated current - and taking regard for the relevant temperature range. When the MOSFET is off, there is no significant current and thus no power dissipation. Bearing in mind power = V*I, you can see that when on we have lots of I but no (very little) V, and when off we have lots of V but no I. But half on we have quite a lot of V and I and thus a very large power dissipation. So it is important to drive the MOSFET hard and fast to pass through this "partially on" phase as quickly as possible. Bearing in mind the actual semiconductor junction is very small and its thermal capacity is very low. Then we have the possibility of avalanche breakdown, which occurs when Vds is too high. No problem you say, we are using MOSFETS rated at 25v and the system voltage is never more than 14.6v. Except that we have to take into account inductance. Even a wire leading from a cell to the BMS board has some inductance, and the wires leading from the alternator to the battery, a lot more. The property of inductance is to resist rates of change of current, by creating an opposing voltage. V = LdI/dt. So with a fast dI/dt, which you need to avoid the power dissipation problem, you can generate a momentary transient voltage that exceeds the MOSFET rating. By "momentary" we are talking a few microseconds. "But I have a LA battery in parallel" you say. Yes, but again we have inductance in the wires and the battery will take more than a few microseconds to absorb the transient as a result. Well you did ask! So to answer your question, if the system is properly designed the MOSFETs won't be degraded by high current switching. If it is not properly designed, each time the MOSFETs switch off there could be a transient that takes the MOSFET into avalanche just for a few microseconds. And each excursion into avalanche takes a little bit of life away.

I'm not quite sure exactly what you mean by "pull over the other side" - in the vid he just seems to struggle to come alongside on the intended side. This is caused by hitting reverse too hard - water is pushed forwards and pushes the boat away from the wall. Come in more in the centre of the lock and turn towards the wall, swing the back in just before it hits at the front, and hit reverse when you have momentum carrying you towards the side. If you come in slowly, you need less reverse and the effect is less. He was going downhill, if you were going uphill and had problems with the "pull over to the other side" when the lock is filling, it is because you started out on the wrong side! Normally the Severn lock keeps tell you which side to go if there is just the one boat, such that the water flow from the paddles keeps you on that side. Mind you, with the advent of volockies, maybe that is no longer SOP.

The BMS switches are not mechanical, they are MOSFETs (transistors if you like) so there is no concept of mechanically wearing out. More ageing will occur from high charge and discharge currents than from switching on and off. Not dinosaurs IMO, just cautious based on decades of engineering experience that says a single point of failure shouldn't cause a catastrophe. That said, it is interesting that they mention the BMS is configured to be used as a hybrid system. I think traditionally, battery manufacturers have set the BMS limits on charge and discharge to be the absolute limit, in order to maximise the claimed capacity. The "dinosaurs" were concerned that taking the cells routinely up to the limit for "just not quite doing serious damage" was a bad thing. But of course there is nothing to stop a manufacturer from moving the BMS settings to more conservative values and thus one doesn't routinely approach and only just dodge the "death to Lithiums" conditions. This is what these folk have done, and same applies to Fogstar who have set fairly conservative limits in their BMS. Downside of that is if you want to use the battery in a "proper" system whereby charging is properly controlled and the BMS shutoff is considered the last resort protection - instead of the charging system controlling the charging, the battery BMS might decide to jump in first and thus the concept of "last resort protection" is nullified. The other thing to mention about the website is no mention of alternator overheating. I guess that doesn't concern them too much because their battery won't be damaged, but it is interesting they have not mentioned the slightly dodgy tactic of the "long wire".

It is inadvisable to run the engine and then disconnect the battery. Alternator damage may ensue. from your description it does sound as though the alternator is faulty. The voltage should rise to around 14v straight away, assuming you rev the engine a bit. If the alternator warning light is on, this means something is wrong and it is not charging. Probably a diode issue. If your battery is going flat with the isolator in the on position, but not in the off position, one explanation could be failed diodes in the alternator that allow the battery to discharge back into the alternator. You can check for this by turning on the isolator, not starting the engine, and then after 15 mins or so feel the alternator. If it has become slightly warm to the touch, it definitely points to failed diodes.

I did. There is a sounder on the BMS board that makes a fairly piercing shriek! BMS board is in the "engine room" area, ie close to the engine panel etc so it should be reasonably audible when driving the boat. As disconnect approaches, it starts to beep with increasingly long beeps until finally it sounds continuously for a few seconds and then disconnects. In the mean time of course it has sent an "imminent disconnect" message to the alternator controller which, if the engine is running, goes to a zero current voltage.

I was trying to be polite, you’ve blown it now!

Sorry, I had temporarily forgotten that my and your senses of humour are not compatible.

What exactly are the requirements? Anyone of engineering competence designing a warning system would not rely on the recipient having a phone, a phone that is on, a phone not selected to “silent” mode, a phone that has a non-flat battery and a phone that is currently running the relevant App.