nicknorman

February 12

38 minutes ago, IanD said:

I really don't understand why you've turned a simple question about whether a B2B -- used as being discussed for the Victron Orion XS, 12V LA to 12V LFP -- needs isolation into an argument about CANbus screening, throwing out assorted strawman and diversionary arguments in the process, some of them just plain wrong -- or at least, wrong as you stated them before backpedalling... 😉

To repeat the answer to the original question -- no, there's no advantage to having an isolated B2B except in rare and unusual circumstances, 12V LA to 12V LFP isn't one of these, isolation costs more and increases losses to no benefit.

As I explained several times, you made a blanket statement that was flawed. I was merely pointing that out. But I realise my mistake now, it is against the laws of the universe for you to have said anything even slightly wrong or over-generalised. Sorry about that.

45 minutes ago, Iain_S said:

Would 100A through 1 ohm not need 100V?

Yes, as I said in the next sentence!

February 12

Electricity is invisible and we are not able to smell it from this distance! In other words, the only option for resolving this is to take some measurements. You have a very large battery bank, perhaps the charging system has never worked and you have only now flattened the batteries. Or perhaps the charging did work but now doesn't.

You need to measure the voltage across the battery terminals with the engine running, to see if the problem is that it is not charging, or whether it is that the batteries are knackered ( the former is the more likely because it is unlikely, though not impossible, that the batteries are suddenly completely knackered).

What engine? What alternator arrangement? What is the behaviour of the alternator warning light(s) on the panel (should be on when you turn the ignition on, and go out after the engine starts)

One easy answer could be that the domestic battery isolator has either been turned off by accident, or is faulty (high resistance, melted plastic) and the 12v systems are being run directly from the alternator. What sort of battery isolator is installed and is it on? If it has a red plastic key it has probably melted and disconnected the batteries

February 12

Cite a narrowboat or other small boat that uses screened canbus cables?:

"My boat. Therefore that must mean that it is often used on boats."

Examples given of boats needing isolate gnd B2S:

"Yes but my boat doesn't do that so clearly it doesn't need to exist elsewhere"

It really is all about you!

February 12

Maybe you should get some sleep, it must be incredibly tiring to always be right about everything.

February 12

15 minutes ago, IanD said:

CANbus is differential but even so it's often screened on boats, because people will insist on doing things like running the cables right past things like SMPS that radiate a lot of switching noise. Yes I know that people like you and I wouldn't dream of doing this, in the same way we wouldn't run microphone/instrument cables on a stage right next to the mains cables, but that doesn't stop people doing this... 😞

The need for an isolated GND on B2B is still only true if the low rail is not 0V on the higher-voltage systems, which is not common -- for example my boat has 12V and 24V and 48V systems and all are ground-referred to 0V. If one GND is not the same voltage as the other then obviously you do need an isolated B2B, but I doubt that many boats are like this because it's asking for trouble with wiring -- because people think GND means GND and there's a temptation to connect them together... 😉

Mastervolt's own Masterbus/CANBUS cables are not screened. So I don't know where you are getting your "often screened on boats" from. How many boats with CANBUS are you aware of that use screened cable? Please cite them. And I don't mean eg naval warships! 120 ohm impedance and voltage differentials of several volts between hi and lo means that the chances of some SMPS radiating interferece that affects the data is effectively zero. More so (better than zero😁) if you use a twisted pair.

I am personally aware of 2 boats that use an isolated B2B, in both cases they are hybrids with 48v LA drive batteries and 24v engine electrics along with 2 B2Bs for charging the 48v bank from the engine alternator/battery. The upper one at least must be isolated.

February 12

8 minutes ago, magnetman said:

Threaded rod seems interesting as it is sort of formed like a natural heatsink.

Maybe a rod through a cylinder containing water.

What happens when the water has all steamed off?

February 12

17 minutes ago, IanD said:

Many CANbus systems are isolated, including some in Victron gear, to cope with large ground voltage differences in large systems. Many comms systems including CANbus are differential, but with transmitters at both ends you can't follow the usual "ground cable shield at TX, isolate at RX" recommendation because there are TX at both ends, so the cable shield has to connect to GND at both ends -- a completely isolated interface usually has a floating GND for the transceiver and internally uses optical/transformer isolation to get power and data to and from the equipment.

With CANBUS being a differential system, generally there is no need for cable screening. Certainly not for boat systems. At a pinch you can use a twisted pair but it's not necessary at the 250kB/s rate that Masterbus uses. In fact thinking about it, probably the only reason for Mastervolt including a ground in their connectors/cabling is because some of their devices need to receive power via the cable to run the CANBUS interface. But if I had been careless of thought I might have connected the gnd on the CANBUS system to the gnd on the BMS and Alternator controllers and that would have been a mistake.

21 minutes ago, IanD said:

None of which is anything to do with the question "does a B2B charger/DC-DC converter on a boat need isolated grounds?" -- to which the answer is, no it doesn't.

My point was that was too blanket a statement. Often no, but sometimes yes especially if there are systems at different supply voltages (eg 12v, 24v, 48v systems) which does sometimes happen on boats.

February 12

30 minutes ago, magnetman said:

This was an interesting comment on another forum in a thread about using LTO batteries as starter for a vehicle.

Obviously the internet is like liquorice and there are ultracrepidarians all over the place but the M6 rod thing did pique my interest and raise an eyebrow.

M6 is a thread not a diameter.

So presumably the suggestion is to somehow connect a length of ss M6 studding in the charge line from the alternator.

would this really do anything ?

If it might work then one could use ring crimps with 6mm holes and nyloc or binx nuts to clamp the wires to each end.

Extending the idea a little more one could have a 1m length of the said studding mounted onto Stauff clamps (nylon hydraulic hose clamps) and experiment with clamping one of the wires at different positions.

A variable resistor?

You have to consider the heat dissipated in the “resistor”. A short length of rod with resistance 1 ohm and 100A is going to dissipate 10kw! Apart from anything else, 1 ohm is far too much as it would drop 100v. More realistic would be 0.01ohm which would drop 1v at 100A. But that is still going to dissipate 100w and will get extremely hot. This is why a long wire is the preferred choice - the longer the wire the more scope for dissipating power without getting too hot.

February 12

1 hour ago, IanD said:

Why don't you leave off the ad hominem attacks and stick to the facts and good old Ohm's and Kirchoff's laws?

Diversion tactics here -- you weren't talking about small errors in the BMS voltages which can obviously happen with ground voltage drops if the BMS is remote, you were talking about large currents flowing in thin ground wires like CANbus and damaging/melting them -- which simply isn't going to happen with the voltage differences here, regardless of how large the currents in the thick wires are.

If you get a high resistance ground connection in a high current path then heating due to voltage drop will damage the connection/cable in that ground path, not any other thin non-isolated ground wires.

Draw out an equivalent circuit and put some realistic numbers in and this becomes obvious... 😉

You started the ad hominem attack, but of course when you do it, it doesn’t count. In your head.

As I said at the outset, under normal circumstances the stray found current would not be problematic for heating/damage/fire risk. However in the event of a poor or bad connection it could be significant. And of course you would only be one human error away from disaster - someone decides to disconnect the battery negative and then you are left with the thin wires and PCB tracks to pass the entire system current.

It is fundamentally bad design to create that sort of alternative current path gotcha. Same applies to alternative current paths created eg by a radio aerial earth connected to hull. It is probably not going to be an issue due to the differing current path resistances, but it could be under unusual circumstances.

And while I think of it, I had similar thoughts on the CANBUS interface. In the end I had 2 pads on the PCB, CANBUS ground and system ground. Because CANBUS is a differential system I decided that most likely it would not be necessary to connect the 2 grounds together and this has shown to be correct, so another alternative current path was eliminated. A good design engineer thinks about these things and tries to eliminate these sort of issues that lie only just below the surface of a correctly functioning and correctly operated system.

February 12

8 hours ago, IanD said:

You might want to bone up on Ohm's Law. Unless the voltage difference is huge -- which it won't be in the case you mentioned -- you won't get large currents flowing down thin wires because of their resistance.

😉

And there was me thinking you were some sort of design engineer! I did explain the consequences of the differing cable resistances. I also explained the potential for a bad connection to result in excessive current flowing in the thin wires / pcb tracks. What I didn’t explain was that the BMS measures cell voltages with a resolution of 1mV and an accuracy of a couple of mV and even a small current flowing through the BMS 0v wire to the cells is going to introduce a significant error. It would simply be bad design to create an alternative current path.

Actually I did think of connecting only the Tx and Rx VE.Direct wires but not the 0v, but decided this was a bit gash so used optoisolators instead.

February 11

7 minutes ago, IanD said:

Because in the general (non-boat) case there may be significant differences between the different grounds. Not usually an issue for boats though... 😉

Well in general terms it can be an issue. For example we have a BMV712 battery monitor. It is connected to 0v at the shunt. We also have a BMS. It is connected to 0v at the cells, so not quite the same place. Then there is a lead taking VE.Direct data from the BMV to the BMS, including a 0v line. So that immediately creates an alternative current path for the 0v current. Certainly the difference in cable sections (and hence resistance) between the battery 0v line (70mm^2) and the BMV data line (very thin) means that the dc current flowing through that thin wire, and thence through another thin wire between BMS and cell 0v, wont be much. But then again “not much” of 200A can still be a fair bit. But if you introduce some slightly corroded or bad connection in the 70mm^2 wire, you could end up with large currents flowing through the thin wires and much smoke and melting ensuing. So I used an optoisolator to ensure there wasn’t a secondary 0v current path.

February 11

40 minutes ago, David Mack said:

Is that the only difference between isolated and non-isolated? Since both the engine and domestic batteries have to be grounded to the boat shell anyway, then what's the point of separate ground connections on the B2B?

It allows you to charge a battery with a different negative potential. For example, you have a 12v alternator and starter battery. You have a 24v domestic system (2 x 12v batteries in series). You can use 2 B2Bs, one connected to the 0 and 12v points of the 24v battery as usual, and the isolated one’s negative connected to the 12v battery mid-point, and its positive to the 24v. Thus charging a 24v system from a 12v system.

February 11

1 hour ago, David Mack said:

Or even easier just to stick with lead acid batteries and established charging technology.

Only someone who has not had Li on their boat would say that.

February 11

3 minutes ago, Tony1 said:

Even with my limited understanding it seems clear that an alternator controller is the most efficient and elegant solution, but I don't know if its going to be cost effective for everyone.

Consider those unfortunates among us who have sub-40hp engines (such as my canaline 38), many with narrow V belt alternators that have quite modest current output (and I mean continuous output).

On top of the cost of the lithium batteries themselves, you're looking at perhaps £1200 to install one of these controllers on a domestic alternator, that can only put out say 45 amps safely on a continuous basis.

Its a lot of money to spend for such a modest output, And upgrading to a powerful alternator in some cases requires a crank upgrade to fit a poly V belt, so that adds maybe £250-300 for the alternator and maybe £500 for supply and fit of the crank upgrade. So perhaps another £800 on top of the £1200 for the Wakespeed controller?

And that's on top of the cost of the batteries themselves.

I suspect that to many folks with older or less powerful engines, it will appear just too high a cost- so its easy to see the appeal of this new victron unit for that group of people.

They can still achieve their max 45 amp charging rate, but for only £300 - and they can probably install it themselves and save money there too.

And if they have two alternators they can get a second B2B unit and get another 30-40 amps charge from their canaline 38 (if they're feeling a bit brave).

I totally agree its not the best way to solve the problem, but I reckon for for a certain segment of the boating population it will look like a decent cost effective option.

The biggest question in my mind for people pondering lithiums is- which of these charging setups will meet any potential future regulations...

Yes I get the cost thing and that was my point really - the intrinsic cost (component cost) of a fancy smart alternator regulator is less than £100 so it is a shame that they cost nearly 10 times that. The only reason why they do cost that much is because the manufacturer and the retailer both need to make a profit, and a lot of up-front man-hours go into software development, testing etc.

But there is a lot of “open source” stuff out there, people give freely of their time to create stuff and publish it on the internet, which eliminates most of the one-off costs above. So it’s a shame that this doesn’t happen for an alternator controller project. Well it did, as we know, but it then went commercial.

February 11

18 minutes ago, dmr said:

There is a fair bit of design effort involved, including bluetooth and writing good apps for iPhone and Android

Bluetooth is easy to implement at the regulator end. It’s is just a serial interface and a £3 BLE module from China, plus the software to compose the appropriate sentences. iPhone and Android App development is beyond my pay grade and probably harder work, but I question why a phone app is really necessary for a well designed alternator controller that “just works”. Yes very interesting to see the field current etc for the first 5 minutes, but after that what are you going to do with it? Ok maybe configuration too, but again that is a one-shot usage.

18 minutes ago, dmr said:

I disagree with you (dangerous 😀) on the current control loop, I think its better to do all the critical stuff yourself rather than using "black box" software in a controller chip which is really designed for automotive.

I disagree, obviously! An automotive chip is designed to quite a high standard, much higher than stuff for domestic use etc, and of course it will have been “field-tested” in millions of vehicles world wide. It has to be 100% robust and with several layers of fail-safe.

In using one, all one is doing is specifying the voltage to regulate to and the maximum field current, data which would normally have come from the vehicle’s ECU. In the event of the vehicle ECU ceasing communication with the chip (wire come off etc) the devices go into a failsafe mode, in the case of the one I use, a default voltage of 13.5v which is vehicle-safe but also of course is lithium-safe. There are separate hardware (ie not software dependant) protections within the chip eg a hardware over-voltage shutdown.

It would be a massive and pointless task to repeat all that design and testing work and I can see no reason other than masochism to follow that route!

February 10

All this shenanigans with trying to interface a LA alternator to Li by means of heavy current electronics, when the solution is to convert the alternator to Li-friendly charging. End of problem!

It is a shame that currently available alternator regulators are so expensive, but good to see the Zeus appearing. Maybe some other manufacturers will produce something, and with a bit more competition prices will drop. The crazy thing is that it can be done cheaply in terms of component cost, I think mine might be over £50 but certainly less than £100, and that is with CANBUS and a VE.Direct interface for the BMV712. All the extra cost is in the software development, testing etc. It would be good if there was another open source project such as the Wakespeed was originally, but with a better initial concept - the Wakespeed design was far too complicated in that it reinvented the wheel and all the regulation was done from scratch, whereas there are several digital automotive alternator control chips on the market for a few £ that mean 90% of the hard work is already done.

February 9

7 minutes ago, MtB said:

* Such a BMS will have a 'soft disconnect' feature to ramp down the alternator current slowly, and some sort of method of setting/adjusting/limiting the charging current.

Easy to say, not easy to achieve. It is easy to have a solid state switch that is either on or off, because in either state there is very little power dissipation.

But a switch half-on dissipates a huge amount of power as heat. So you need to add the sort of technology found in B2B converters. Switch mode buck converters. Which can be done, but at the sorts of currents involved is going to be very expensive and bulky.

All of which is why this would be a crazy way of doing it. The correct way to do it is to control the charge sources. Which is quite easy by comparison. No heavy current electronics required.

February 9

1 hour ago, mrsmelly said:

So after saying we would not have another dog at our age......the house has been empty without a dog and this poor eight year old sweetie needed rescuing. So after donating lots of beer money to rescue centre here she is, we must be daft lol

Old dogs flock together.

February 9

16 minutes ago, MtB said:

What do you mean by 'safe' anyway? It is a matter of degree. Nothing is truly 'safe'.

Very true. For example in the certification of airliners carrying hundreds of passengers at 35,000’, the certification requirement is not that the wings can never unexpectedly fall off resulting in everyone plummeting screaming to their deaths, rather it is that the probability of this happening is “extremely improbable” and they go on to put a number on it, 1 times 10 to the power -9. What the unit of that event is doesn’t seem to be specified - an hour, a flight maybe. So although a one in a thousand million sounds quite improbable, and you would be pretty unlucky if it were you, a lot of flying goes on around the world and so we can’t be too far off such an event becoming a near certainty.
And if a bad event could happen once in 1,000,000,000 flights that does not mean it will happen on the 1,000,000,000 flight, the laws of probability say it could happen on the first flight, or anywhere in between, or after..

February 9

9 minutes ago, MtB said:

So is it really the rôle of BSS to prevent people from installing systems which wear out and need periodic maintenance? To protect people from finan cial loss and/or their own stupidity?

I hold that the risk of a future cell failure in the LA battery is not a good enough reason to ban hybrid LFP/LA systems, if people want to install them in their boats.

The problem arises due to arse covering and not really understanding the detail. I would draw a likeness with installing a new gas appliance, as you know the overriding requirement is to install it in accordance with the manufacturer’s instructions. If for some reason you decide to install it in contravention to the installation instructions, even if it is completely safe, you face a severe uphill battle trying to convince a bureaucrat that it is safe despite the apparent contravention.

So it is with the various Li battery and cell manufacturers who state “do not mix with batteries of other chemistries”. Even though they probably mean to not mix with other Li chemistries, the statement is taken at face value by people who have no hands on experience.

February 8

12 minutes ago, Naughty Cal said:

We certainly don't live like cavemen on the van. That manages just fine with a single 100ah lithium battery.

Cavewoman then? But seriously, a van is a much smaller space and has less “stuff” than a modern narrowboat. I also have 100Ah in my caravan.
Camper vans tend not to be parked up “off grid” for several days or weeks - they either get driven or are on a site with hookup - as a generalisation.

On the boat we tend to use about 200Ah a day, although we are certainly not frugal.

February 8

57 minutes ago, MtB said:

Thanks. That's actually what I thought but didn't want to have people say I was overstating the case.

So spend £6,000 to get it exactly right or £350 to get it pretty close.

Hmmm.... now which option will the average tightwad boater think looks better value?

Not sure where the £350 comes from. I have 600Ah which cost around £1800. I guess £350 might get you the cheapest 100Ah battery but that is only any use if you wished you had been born as a caveman. People who are looking at Li probably have electrical demands greater than one rusty candle and a sink foot pump for water.

February 8

1 hour ago, MtB said:

I think this understates the case.

To bung a "Drop-in" LFP battery into an existing system as a hybrid and configure a long piece of wire to limit the charge current to protect the alternator can be done for £350 and an afternoon's work. Yes this is a fine ol' bodge but it brings most of the benefits of lithium batteries to yer average boater boating/living on a shoestring.

To do it 'properly' would firstly be way beyond the technical capability of yer average boater so they would be into having it done professionally. Yes? Which would cost what? I really have no idea but I'd imagine a quote from Ed Shiers would be several £k.

Lets guess £3k for a stand-alone LFP system with separate charge controller, cell protection and perhaps a new, appropriate alternator. A sum few boaters of modest means are going to spend especially when they can get nearly the same benefits for 10% of that price.

So in summary, the real-life reality for yer average boater is a choice between a slightly-less-than-techncally-perfect LFP/LA hybrid which works fine and doesn't bust the bank if it goes wrong, or nothing.

I think Ian's point is that your "works fine" needs to be defined. Do you mean works fine right now. In that case, yes. Do you mean will still work fine after 10 years of long summer cruising days with batteries already fully charged by solar? Well we don't know that, but the suspicion is it probably won't.

The difficuly with something with a projected life of well over 10 years, is that it takes a long time to discover that you have done something that in fact has reduced the expected life to half what it should be.

February 7

9 minutes ago, Midnight said:

Oh that's got me thinking. The pulley wheel on the original Iskra 95amp alternator on my Beta 43 was 80mm. The disastrous Mastervolt Alternator had a much larger pulley, probably 100mm. The Prestolite pulley was 60mm. Does this mean unless the pulley wheel is 80mm the rev counter will give a false reading?

Because there are so many possible combinations of pulley sizes on engines and alternators, just about every tacho can be adjusted to suit the pulley ratio - it wouldn't be economical to manufacture different tachos to suit all these combinations.

February 7

55 minutes ago, rusty69 said:

Don't tell us his name, you stupid boy!

It’s Pike.

Oops, shouldn’t have said that.

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