nicknorman

“You set an rpm above which the field current is unlimited, and below which you get 20% of max field current (or less).” my sentence above not clear (too late to edit), I should have said: You set an rpm above which the field current is unlimited, and set another (lower) rpm below which field current is limited to a maximum of 20%.

I think it can never be categoric because someone might eg have an insurance policy become due for renewal half way through the process, and forget/fail to do so. Or cancel a policy that is paid for monthly etc etc. There has to be some degree of trust.

If I wanted my boat moved, that is something I would check before committing. Do you put your professional liability insurance details on your webpage?

The Alpha Pro III is quite good, only trouble is it doesn't measure current or SoC so you can't terminate charge based on SoC or tail current. If you add in a Mastershunt then it does all that, but at quite a cost. So overall Wakespeed is probably best value. The "slow engine" mode is in fact small engine mode. It reduces the maximum field current at low rpm. The mechanical load from the alternator is roughly proportional to the field current. You set an rpm above which the field curent is unlimited, and below which you get 20% of max field current (or less). So you get a sliding scale of max field current as the rpm increases from idle to some reasonable speed that you specify. Which is very good. Not to protect the alternator but to protect the belt and avoid a heavy load on the engine at idle. Although of course you need the right interface to configure it from a laptop over Masterbus. As to your question about Sterling doing something similar, if you mean a B2B then no, it doesn't know the engine rpm.

I think we have come to the conclusion that he is OK, or better. But one has to bear in mind that there are a lot of scammers out there and his initial posts were a bit vague, no website, seemingly dodgy address, several potential red flags. So folk were just being cautious. IMO prising the information out of him and perhaps prompting him to set up a website, is to his long term benefit. And he also showed reasonable patience and didn't behave like a sulky teenager as so many do these days. So all of that is to his credit and helps his reputation. And he got 10 pages of free advertising!

Nice website!

Yes holding charge could be it. MtB missed out on that one! But it isn't quite as simple as that because when we are in the marina on shore power, the Combi is set to the "holding voltage" but when we turn stuff on in the boat, the charger supplies the juice rather than it coming from the batteries. And ditto when we are cruising after the batteries have reached the target SoC, the alternator remains available to supply any additional loads from the boat. So "holds" the SoC but also powers the loads.

Left moored on a lock landing by the looks of things, probably an irate boater dun it.

Well I think that float charge and trickle charge are not the same thing. When we had LAs, the Combi was permanently connected to shore power when we were away from the boat, voltage set to 13.25v. When I got back to the boat, current into the batteries was to all intents and purposes zero. That is floating - no current flowing either way. Same for Lis now. Whereas trickle charge is a low current slow charge.

Yes. I suppose my main point is to say that charging to some desired SoC less than 100% is not easily done by setting a specific charge voltage.

This is true, but then 2000KWH is quite a lot! As to 48KWH, you also have to factor in running the car or your proportion of the bus and train, popping off to the Med for a summer holiday, energy used by the hospital you might have to visit occasionally, your share of the pub's heating bill, the energy expended in getting your food to you (and a bit of energy expended in getting your poop disposed of) etc etc. Doesn't bear thinking about when it's all added up, which is why we are doomed.

Charging a typical boat battery of say 200-300Ah at 40A will mean it is about 99% charged by the time the voltage gets to 14.0v. When you stop the voltage will drop back to 13.4v or so. So when you start again surely it will go back to trying to achieve 14v? And when it does so, now the SoC will be 99.5% or some such. I would say that when you get to 13.8v at a moderate rate of charge, you are something north of 95%SoC. Well, that is how mine behave anyway. Bear in mind that holding 13.8v will eventually give you 99.9% SoC, so the charge current as a proportion of the capacity is an important factor in these sorts of discussions. Once it gets above 13.6v it is getting close to the knee and probably about 90%. Maybe it depends on where you are measuring the voltage - I am measuring it at the cell terminals, not upstream of the charge wiring. We normally charge at around 95A but it is a 600Ah bank so not that dissimilar relationship between current and capacity to you.

These things must be designed by people that have never owned a boat!

well to be fair there is a BMS inside the Valence, BMS being Battery Monitoring not Battery Management. In other words there is no disconnect. But there is balancing and SoC tracking. Interesting video on the guts of a Valence though!

That was exactly my problem when we first got the boat, with the tumble drier on (steady 2kw draw) from the travelpower, it really dipped the rpm and made the engine struggle at tickover passing moored boat, belt squeaking a bit. I considered some kind of idle-upping device but never got around to it. Now I use the travelpower going into the Combi with the current limit set at 4A (AC) and use "power asssit" for the rest which comes from the inverter mode of the combi. The alternator is only putting out 75A or so, the remaining 1/4 kw coming from the batteries. Which helps, but still rather slow. At least the load is shared between the two belts. Of course it would be fine if I ran the tumble drier only from the inverter, fed by the alternator and the batteries, but that means running the inverter fairly close to its max for an hour or so, not sure if that is the best idea long term. Just had a look at the MC-618 data sheet, even that fairly new regulator doesn't seem to do it well. The "Small engine mode" just reduces the field current across the rpm range, whereas what you want is only to reduce it at low rpm. It looks like the Wakespeed or the Alpha Pro III are the only ones that do it properly!

Which Balmar do you have, the MC-618? If so I’m surprised that halving the field current isn’t enough. Depends on engine and alternator size, I suppose. We lose about 50rpm between in gear idle not charging, and ditto charging at 1/2 field current which is not too bad. I did up the idle speed slightly so it is at the minimum of 850 under load, and 900 not under load.

He has a LA connected to the alternator. The B2Bs pump current from the LA to the Li, and can be switched off. The solar is connected to the Li and can be switched off. So there is no LA directly in parallel with the Li, but it is in there somewhere. And I have no idea why I am answering his question for him.

I normally leave the alternator controller on 1/2 charge rate (half of maximum field current) which gives 75A at idle and about 95A cruising at 1300rpm. On the fast charge setting, I get 180A or so initially but I’ve set a temperature limit of 90C and at that it settles on about 125A, depending on temperature. 90C is probably over cautious but then again 125A is plenty and if I want more I can turn on the travelpower and get another 60A or so from the Combi. The 125A is at 1300rpm, at lower rpms the max field current is reduced to avoid a heavly load on engine/belt/pulleys at low rpm. Between 5C and zero C the voltage decreases such that at zero and below, there is very little charge current. The batteries are mounted in the engine bay (modern trad stern) so the engine warms it fairly quickly and I also have some heating mats under the batteries. But even in very cold weather when we’ve been away from the unheated boat, I have rarely seen less than 5C and never less than zero. Edit - just checked my code, below 5C only 1/2 charge rate (1/6th C) and below 1C only the 50% SoC float voltage (ie the voltage that would give no charge current at around 50% SoC). Maybe not quite rigorous enough if the batteries are very low and very cold when the engine is started, I might need to add something to deal with that. But in practice, the SoC is floated at around 50% by the Combi when we are away from the boat so it SHOULDN'T be a problem. But it could be...

This could be done, of course. However you are starting from a premise that I question. Li cycle life seems to be based on the total Ah that can be extracted over the life of the battery. So for example you could have 5000 cycles at 50% DoD, or 2500 cycles at 100% DoD. The total Ah extracted being the same. Therefore if you force cycles on a Li battery unnecessarily, you are shortening its life unnecessarily. There is some evidence that failing to cycle Li batteries over a long period of time can generate some sort of “memory effect” but it is reversible. And I suspect quite difficult to generate. So on balance I think that supplying domestic needs from generated power (solar, or alternator on a long cruise) whilst holding a fairly high but not too high SoC is better than one charge and continuous discharge. Of course the ideal for a long day’s cruise would be to retain a mid SoC for most of the day, and then charge in the afternoon such that one reaches a fairly high SoC just as one ties up. I can do that to some extent but it does require a degree of clairvoyance to know when one is going to tie up. And remembering to do it!

I think you have just volunteered to invent the appropriate term!

In my opinion 13.8v is much too high a voltage for floating. Just look at a chart of voltage vs SoC for Li. As I said earlier, 13.4 gives you 99%. So that would be the absolute maximum float voltage for me. But since holding an Li at full charge is a bad idea, I’d consider 13.3v the max float voltage. You have to bear in mind that the people who say 13.8v don’t make the cells, they buy cells from china and package them up with a BMS etc. they are the same people that recommend charging at 14.6v. Ignore!

Well I have to say that we do float the Li. When we are away from the boat the Combi voltage is set precisely to give around 50% SoC. There is some continuous drain from the GSM transceiver (50mA ) and the Empirbus (10mA or so) plus a mA or so for the BMS. Not a lot but it is about 1.5Ah a day. If we were to be away for several months it could add up… I also float the Li when we are cruising, the alternator goes to a float voltage that matches the natural voltage of the Li at one of the specified SoCs (normally 80%) such that no current flows in or out. The advantage being that the alternator will supply up to full output to power a heavy inverter load such as the electric kettle, tumble drier etc. I did have a design problem in that I can only set the alternator target voltage to a resolution of 0.1v so I had to aim slightly low. This means that the battery will slowly discharge under normal loads (fridge, lights, chargers etc), and once it has dropped 1% the alternator will go back to charge mode and put that 1% back in. So there is an element of slight discharges followed by charges. Whilst this doesn’t seem to be ideal, in fact I think that because as soon as we tie up on goes the 2kw kettle, the air fryer etc etc, the batteries get a good discharge before the next day’s cruising and so I think a few hours of dodging around 80-79-80% doesn’t matter. I think it would be different if we had solar and were not using the boat.

One of the problems with Li is that you can’t easily charge to some desired SoC such as 90% by means of controlling the voltage. A voltage as low as 13.4v will get you to 99% eventually. It will just take longer than charging at 14.6v. So if for example you charge at 14.0v all the time you are out on a day’s cruise, then you will still be 99.9%SoC and you will still have been holding the battery there for hours, which is not good. If the charger uses timing to switch from bulk to float or off, then you have a problem if you stop for lunch and then restart with batteries already at 99%. All of which is why I use the BMV712 SoC to control charging - having of course synchronised it at 100% from time to time. I can’t see any other way of doing it.

There’s 3 bridges closed at various times on the Coventry, so it’s closed to through navigation for a month. I do get email notifications and do tend to skim through them, but I’m pretty sure I didn’t get 3 navigation closures on the Cov. Nor even one.

It does depend on the charge rate. The issue revolves around pushing more current into the battery than the normal chemical reaction rate can accommodate. One should be able to charge at 1C (current = capacity) at 5 degrees. By zero only 1/2C and below that, maximum current reduces fairly quickly. So it isn’t like something in the battery is turning to ice, it is a reduction in allowable charge rate as the temperature decreases. At the sorts of rates most people charge narrowboat Li, chances are 0 or a bit below is fine.