Lithium Batteries installation

[IanD]

5 minutes ago, nicknorman said:

Bored with pointless arguing with someone who is not capable of ever being even slightly wrong.

 

Still waiting for you to point out exactly what I said that was factually wrong instead of just waffling though -- after all I've done it for your post, the least you can do is return the compliment... 😉

 

As always I've even offered straight out to own up to being wrong if you do, which kind of blows a hole in your argument, doesn't it?

[dmr]

I think you both need to look back at some old threads and study the Gibbo arguments, they were really good, facts and insults are fine but where is the entertainment factor? 😀

I had to isolate between my laptop and the speakers as they run on different 12 volt circuits and so have slightly different and noisy ground levels. I started off with an audio transformer but now do it with an optical cable. I could use Bluetooth but I like wires.

[nicknorman]

43 minutes ago, dmr said:

I think you both need to look back at some old threads and study the Gibbo arguments, they were really good, facts and insults are fine but where is the entertainment factor? 😀

I had to isolate between my laptop and the speakers as they run on different 12 volt circuits and so have slightly different and noisy ground levels. I started off with an audio transformer but now do it with an optical cable. I could use Bluetooth but I like wires.

 

The thing with Gibbo was that he was actually wrong about quite a lot of stuff, but he said what he said with such dogmatism, repetitiveness and conviction (DRC) that the forumerati believed it all as gospel and he created a whole new post-truth. IanD still has some way to go in the DRC stakes, although it has to be said he is trying hard. Or maybe just trying?

 

1 hour ago, IanD said:

 

As always I've even offered straight out to own up to being wrong if you do, which kind of blows a hole in your argument, doesn't it?

 

That is irrational as we can't both be wrong.

Edited February 12 by nicknorman

[dmr]

1 hour ago, nicknorman said:

 

That is irrational as we can't both be wrong.

Not sure about that, you can't both be right but I think it is possible that you are both wrong?

[TheBiscuits]

6 hours ago, dmr said:

I think it is possible that you are both wrong?

 

You're channelling Oliver Cromwell again ... bowel trouble is it?

 

[IanD]

13 hours ago, nicknorman said:

 

The thing with Gibbo was that he was actually wrong about quite a lot of stuff, but he said what he said with such dogmatism, repetitiveness and conviction (DRC) that the forumerati believed it all as gospel and he created a whole new post-truth. IanD still has some way to go in the DRC stakes, although it has to be said he is trying hard. Or maybe just trying?

 

That is irrational as we can't both be wrong.

No, it's perfectly rational -- I can be wrong about one thing (e.g. CANbus shielding), you can be wrong about another (e.g. CANbus melting).

 

Still playing the ad hominem card, I see?

 

I notice you're carefully avoiding mentioning your scaremongering posts about melting thin comms cable wires with massive currents through them due to huge ground voltage differences, perhaps because you've now realised they were just plain wrong -- the differences can't be bigger than a few hundred millivolts without melting the high-current connection, even if this happened the currents through the CANbus ground connection would be small and non-damaging -- and since you say that they don't have a ground connection anyway, no current would flow at all 🙂

 

Care to own up to being wrong on this? If not, your accusations of me refusing to admit I'm wrong (and ad hominem snipes) are exposed for what they are -- projection of your own behaviour.

 

Which in case you don't know, is what Donald Trump does -- accuses other people of doing things (e.g. lying, namecalling, cheating) that he does himself, because he can't believe that other people wouldn't be as mendacious as he is.

 

P.S. As pointed out by another poster, you seem determined to turn this into a personal vendetta about irrelevancies rather than return to the subject -- which was how to charge a 12V LFP from a12V LA/alternator, in case you've forgotten...

[nicknorman]

3 hours ago, IanD said:

No, it's perfectly rational -- I can be wrong about one thing (e.g. CANbus shielding), you can be wrong about another (e.g. CANbus melting).

 

Still playing the ad hominem card, I see?

 

I notice you're carefully avoiding mentioning your scaremongering posts about melting thin comms cable wires with massive currents through them due to huge ground voltage differences, perhaps because you've now realised they were just plain wrong -- the differences can't be bigger than a few hundred millivolts without melting the high-current connection, even if this happened the currents through the CANbus ground connection would be small and non-damaging -- and since you say that they don't have a ground connection anyway, no current would flow at all 🙂

 

Care to own up to being wrong on this? If not, your accusations of me refusing to admit I'm wrong (and ad hominem snipes) are exposed for what they are -- projection of your own behaviour.

 

Which in case you don't know, is what Donald Trump does -- accuses other people of doing things (e.g. lying, namecalling, cheating) that he does himself, because he can't believe that other people wouldn't be as mendacious as he is.

 

P.S. As pointed out by another poster, you seem determined to turn this into a personal vendetta about irrelevancies rather than return to the subject -- which was how to charge a 12V LFP from a12V LA/alternator, in case you've forgotten...

You are getting quite excited! Maybe a lie down in a dark room?

 

As I have repeatedly said and you repeatedly ignored (so I really have no idea why I’m bothering) when there are alternative ground paths this can lead to problems. In the case of current divided between two alternative paths, one beefy, one weedy, the current is of course divided in proportion to the resistances of the two paths. So if the resistance of the beefy path increases, the current in the weedy part increases. The beefy part generates heat, the weedy part generates heat. The excess temperature reached depends on the ability to dissipate that heat and the rate of temperature change depends on the thermal mass. When there are varying resistances along the weedy path, the generation of heat will vary accordingly. So if you consider let’s say a 1mm^2 conductor from the BMV to the BMS, and a 1mm^2 conductor from BMS to battery negative you might think there is even heat dissipation along the route. But somewhere inside the BMS linking the two conductors there is a short and very thin PCB track - after all, the designer consider it a “signal wire” and knows that the return current from the data lines is miniscule. So now we have most of the circuit resistance (most of the generated heat) confined to a very small pcb track with very poor ability to dissipate heat.

 

But as I also said, the main issue is when there is a disconnect in the beefy battery negative line. Maybe someone decided to change the batteries - “disconnect the negative first” someone once told them. They would expect this to de-power the domestic electrics, but instead all the current is now routing through the thin wire. Disaster waiting to happen.

 

Anyway, I’ve got to go now, I am just putting together my bid for President of USA.

[IanD]

22 minutes ago, nicknorman said:

You are getting quite excited! Maybe a lie down in a dark room?

 

As I have repeatedly said and you repeatedly ignored (so I really have no idea why I’m bothering) when there are alternative ground paths this can lead to problems. In the case of current divided between two alternative paths, one beefy, one weedy, the current is of course divided in proportion to the resistances of the two paths. So if the resistance of the beefy path increases, the current in the weedy part increases. The beefy part generates heat, the weedy part generates heat. The excess temperature reached depends on the ability to dissipate that heat and the rate of temperature change depends on the thermal mass. When there are varying resistances along the weedy path, the generation of heat will vary accordingly. So if you consider let’s say a 1mm^2 conductor from the BMV to the BMS, and a 1mm^2 conductor from BMS to battery negative you might think there is even heat dissipation along the route. But somewhere inside the BMS linking the two conductors there is a short and very thin PCB track - after all, the designer consider it a “signal wire” and knows that the return current from the data lines is miniscule. So now we have most of the circuit resistance (most of the generated heat) confined to a very small pcb track with very poor ability to dissipate heat.

 

But as I also said, the main issue is when there is a disconnect in the beefy battery negative line. Maybe someone decided to change the batteries - “disconnect the negative first” someone once told them. They would expect this to de-power the domestic electrics, but instead all the current is now routing through the thin wire. Disaster waiting to happen.

 

Anyway, I’ve got to go now, I am just putting together my bid for President of USA.

 

I'm not getting excited, just tired of you evading questions you don't want to answer, misrepresenting what you said, and pretending things can happen when they can't... 🙂

 

I'm not ignoring what you're saying, the numbers simply don't add up given the likely maximum voltage drop across a poor high-current ground connection (a few hundred mV) without it destroying itself -- this is the maximum voltage driving ground currents in any other cable or connection. Due to series resistance (thin wires, remember) the current this would cause down any CANbus or similar cable with a ground connection will be small, certainly not enough to damage it. And then you tell me that these cables don't have a shield/ground connection anyway, which means that no current will flow at all -- the data lines are high impedance at DC so there will be no current in any PCB tracks.

 

If you disconnect a battery negative and try and power the entire boat through a thin wire -- in effect, putting 12V across it -- then undoubtedly something will go phut. Though how this can happen in a CANbus cable without a ground connection beats me -- so please do explain... 🙂

[nicknorman]

26 minutes ago, IanD said:

 

I'm not getting excited, just tired of you evading questions you don't want to answer, misrepresenting what you said, and pretending things can happen when they can't... 🙂

 

I'm not ignoring what you're saying, the numbers simply don't add up given the likely maximum voltage drop across a poor high-current ground connection (a few hundred mV) without it destroying itself -- this is the maximum voltage driving ground currents in any other cable or connection. Due to series resistance (thin wires, remember) the current this would cause down any CANbus or similar cable with a ground connection will be small, certainly not enough to damage it. And then you tell me that these cables don't have a shield/ground connection anyway, which means that no current will flow at all -- the data lines are high impedance at DC so there will be no current in any PCB tracks.

 

If you disconnect a battery negative and try and power the entire boat through a thin wire -- in effect, putting 12V across it -- then undoubtedly something will go phut. Though how this can happen in a CANbus cable without a ground connection beats me -- so please do explain... 🙂

 

You haven't been following the topic very well, have you. I started the issue talking about the VE.Direct connection. Maybe you don't know what that is? It is a 3.3v TTL level RS232 duplex connection between the BMV 712 battery monitor and something else, in this case my BMS. That cable, being single ended data, quite long and fairly low voltages, is screened with the screen acting as the 0v line. So there would be a direct ground connection to the BMS had I not decided to go for an optoisolator at the interface with the BMS.

Then I went on to mention the CANBUS and how I had decided not to connect the ground at all because it wasn't necessary and would again create an alternative ground current path.

You have focussed on the CANBUS not having a ground path because I decided not to connect it. Congratulations, you remembered that bit!  But I don't think you see the point. Neither does the VE.Direct have a ground connection, thanks to the way it is designed. Otherwise known as having an isolated ground in each case. Which was why I mentioned it by way of illustration - sometimes having an isolated ground is necessary even on a narrowboat. Do you get it now? (probably not).

Edited February 13 by nicknorman

[IanD]

1 hour ago, nicknorman said:

 

You haven't been following the topic very well, have you. I started the issue talking about the VE.Direct connection. Maybe you don't know what that is? It is a 3.3v TTL level RS232 duplex connection between the BMV 712 battery monitor and something else, in this case my BMS. That cable, being single ended data, quite long and fairly low voltages, is screened with the screen acting as the 0v line. So there would be a direct ground connection to the BMS had I not decided to go for an optoisolator at the interface with the BMS.

Then I went on to mention the CANBUS and how I had decided not to connect the ground at all because it wasn't necessary and would again create an alternative ground current path.

You have focussed on the CANBUS not having a ground path because I decided not to connect it. Congratulations, you remembered that bit!  But I don't think you see the point. Neither does the VE.Direct have a ground connection, thanks to the way it is designed. Otherwise known as having an isolated ground in each case. Which was why I mentioned it by way of illustration - sometimes having an isolated ground is necessary even on a narrowboat. Do you get it now? (probably not).

 

I do get it, because it's obvious -- in spite of your repeated sniping to assert your superiority, you're not the only one who understands basic electrical principles -- or even advanced ones. If you want a ground noise/shielding/screening/current loop challenge you should try dealing with having to get 1000A from an SMPS into a massive switch/router chip with a few millivolts of voltage drop, all sitting right next to sensitive analogue circuits with 100fs of jitter and 50GHz bandwidth.

 

[now I expect you'll come back and accuse me of bragging -- trust me, if I wanted to do that there's a load more stuff I could chuck out, but you're the one who started the "I know better than you" p*ssing-up-the-wall contest]

 

But all this is not what you said earlier, is it? With no ground connection through any data cables, there's no risk of them or the PCB tracks they connect to smoking and melting, is there? And even if there was a ground connection, a poor high-resistance high-current connection is extremely unlikely to result in enough voltage drop or current to damage the "thin wire", isn't it? All of which is what you said, and all of which is wrong, as Georg Ohm and Gustav Kirchoff would be well aware 🙂

 

If you actually answered these questions -- and did what you accused me of not doing, admitting when you're wrong -- instead of trying to change the subject then maybe this discussion could get back on a more sensible basis instead of degenerating into yet another p*ssing contest.

 

But please, if you're going to bother replying, leave out the sniping and veiled insults and stick to the facts -- and without trying diversion tactics yet again... 😉

 

BTW I went and looked up some actual numbers for you -- shielded data cables are recommended to be grounded at both ends so long as the voltage difference between the grounds is less than 1V rms (this is aimed at mains systems, to prevent ground loops), so they'll be perfectly happy with that and certainly not smoke or melt. If you have a 1V drop in a poor ground connection carrying 200A (5mohms -- your number not mine) then it might well burst into flames since it will dissipate 200W, but the shielded data cable (and the PCB it connects to) will still be perfectly happy, it might carry an amp or two of current down the shield -- and an unshielded one won't even notice. Numbers matter... 😉

 

Back on topic, isolated grounds are necessary only in cases they're actually *needed*. A 12V B2B as discussed is not one of these cases, and neither are most other ones on narrowboats -- with rare exceptions like the 24V/48V one you quoted, because there are very few boats like that out there, and for sure this wouldn't apply to anyone who was asking questions about B2B for 12V LA to drop-in 12V LFP on this thread.

 

 

Edited February 13 by IanD
numbers added

[Guest]

46 minutes ago, IanD said:

[now I expect you'll come back and accuse me of bragging -- trust me, if I wanted to do that there's a load more stuff I could chuck out, but you're the one who started the "I know better than you" p*ssing-up-the-wall contest]

 

I wonder if it's mere coincidence that most of these nowadays seem to involve you........

 

Has you boat sunk? You don't seem to use it much.

[GUMPY]

A while back didn't someone on here have a problem with his diesel heater whilst running heavy loads with the master switch ( fitted in the -ve ) switched off🤔

 

Return path was through the heater circuit board and the exhaust to the hull then via the -ve hull bond back to the battery 😱

[IanD]

34 minutes ago, GUMPY said:

A while back didn't someone on here have a problem with his diesel heater whilst running heavy loads with the master switch ( fitted in the -ve ) switched off🤔

 

Return path was through the heater circuit board and the exhaust to the hull then via the -ve hull bond back to the battery 😱

 

Of course it's always possible to devise cases where this happens -- which is a damn good reason never to split the grounds by doing something silly like putting the master switch in them, which can lead to all sorts of horrible (and expensive) consequences. I've spent a lot of my engineering career dealing with issues like grounding, and whether to split/segment or isolate grounds (including analogue and digital, or TX and RX), and separating them usually causes more trouble than it's worth -- there are cases where it's necessary, but you need to be *really* careful about how any return currents -- AC and DC -- get from one to the other, and how and where they're connected -- and these return/parasitic paths can be hard to spot, they can be hidden inside the circuit/equipment.

 

If the things you're connecting are a long way apart (I've dealt with up to 10km or so...) and have separate incoming supply/ground then isolation can be needed due to possible ground voltage differences. If you're dealing with one system without such separation -- like most boats -- then it's not only not needed, it risks unintended consequences if things go wrong -- like the case you gave. But in either case you do have to take care about where all the ground currents flow, especially the high current ones... 😉

Edited February 13 by IanD

[Guest]

18 minutes ago, GUMPY said:

A while back didn't someone on here have a problem with his diesel heater whilst running heavy loads with the master switch ( fitted in the -ve ) switched off🤔

 

Return path was through the heater circuit board and the exhaust to the hull then via the -ve hull bond back to the battery 😱

 

Why would anybody be daft enough to switch the -ve side?

 

Presumably it wasn't done intentionally?

[Alan de Enfield]

8 minutes ago, MJG said:

 

Why would anybody be daft enough to switch the -ve side?

 

Presumably it wasn't done intentionally?

 

Many years ago it was the recommended method on boats (certainly ditchy boats)

[IanD]

1 minute ago, Alan de Enfield said:

 

Many years ago it was the recommended method on boats (certainly ditchy boats)

 

Presumably before boats had the kind of interconnected electrical equipment that many have nowadays... 😉

[Alan de Enfield]

Just now, IanD said:

 

Presumably before boats had the kind of interconnected electrical equipment that many have nowadays... 😉

 

It was probably a hang-over from when cars had a positive ground.

Cars finally changed to negative ground in the 70's when electronics became more common - apparently electronics are not overly keen on a positive ground.

[IanD]

31 minutes ago, Alan de Enfield said:

 

It was probably a hang-over from when cars had a positive ground.

Cars finally changed to negative ground in the 70's when electronics became more common - apparently electronics are not overly keen on a positive ground.

https://mgaguru.com/mgtech/electric/et098.htm

 

A whole set of reasons, partly technical, partly historical, partly commercial.

 

The electronics themselves wouldn't really care *if* they were designed that way (0V as positive rail with -ve power supply), but the convention was to use positive supplies internally with 0V grounded because it made things like getting signals in and out and having lower internal regulated supply voltages easier (NPN transistors much preferred to PNP), and so that pushed cars the same way. Most alternators were also designed with negative ground, which had the same effect.

Edited February 13 by IanD

[magnetman]

300 Ohm resistor? 

 

 

[GUMPY]

1 hour ago, MJG said:

 

Why would anybody be daft enough to switch the -ve side?

 

 

Because at one time the CofC / BSS only permitted one battery isolator so it was the only way of isolating domestics and starter battery's with one switch. There were no double pole high current switches available then.

 

There are probably still quite a few boats that are wired that way.

 

 

1 hour ago, Alan de Enfield said:

It was probably a hang-over from when cars had a positive ground.

 

No

See above for the reason.

 

 

 

Edited February 13 by GUMPY
Add CR

[magnetman]

I remember the heady days of the C of C when it was all rather voluntary. 

[jonathanA]

I don't think it's anything as esoteric. Just simple cost!  easier and cheaper to put one isolator in the common neg to isolate both banks.  (In simpler times !)

 

Eta I'm not advocating it just saying  why it was done in the past before some numpty jumps in, has a go at me and tells us all why it's a bad idea. 

Edited February 13 by jonathanA

[magnetman]

Isolator switch

 

 

 

[MtB]

1 minute ago, magnetman said:

Single use isolator switch

 

 

 

 

FTFY!

 

 

[nicknorman]

Generally the advice from here for disconnecting a battery, is to disconnect the negative first. This is because if you touch the hull with the spanner, it doesn't matter. If you disconnect the positive first and touch the hull, you have a molten spanner. Once the negative is disconnected you can remove the postive connection and if the spanner touches the hull, nothing happens.

 

 

5 hours ago, IanD said:

 

I do get it, because it's obvious -- in spite of your repeated sniping to assert your superiority, you're not the only one who understands basic electrical principles -- or even advanced ones. If you want a ground noise/shielding/screening/current loop challenge you should try dealing with having to get 1000A from an SMPS into a massive switch/router chip with a few millivolts of voltage drop, all sitting right next to sensitive analogue circuits with 100fs of jitter and 50GHz bandwidth.

 

[now I expect you'll come back and accuse me of bragging -- trust me, if I wanted to do that there's a load more stuff I could chuck out, but you're the one who started the "I know better than you" p*ssing-up-the-wall contest]

 

 

 

You really should write a book. After all, you have designed almost everything from the entire Apollo moon landing software (which lets face it was pretty simple!) to the latest AI systems that can recognise a face from orbit. And everything in between. It would be fascinating, although rather long.

Although I do curse you when I find that on my iPhone the ringer volume and the alarm volume are inseparable. What were you thinking of when you designed that bit?

5 hours ago, IanD said:

 

But all this is not what you said earlier, is it? With no ground connection through any data cables, there's no risk of them or the PCB tracks they connect to smoking and melting, is there? And even if there was a ground connection, a poor high-resistance high-current connection is extremely unlikely to result in enough voltage drop or current to damage the "thin wire", isn't it? All of which is what you said, and all of which is wrong, as Georg Ohm and Gustav Kirchoff would be well aware 🙂

 

This is exactly what I said earlier.  To paraphrase "just as well I decided not to have any ground connections through any data cables as there would be a risk of harm to them or the PCB tracks (or the BMS accuracy) if I had done."

Having a ground connection would be the default, not having a ground connection was the result of considering the alternative current paths issue. This is the incredibly basic point of logic that you don't seem to get. Perhaps you are a badly trained AI after all?

By your logic, I avoided a problem with alternative ground paths by not having an alternative ground connection, therefore the potential issue of alternative ground connections doesn't exist. Ever. At all.

Does not compute. Back to the training data for you! Oh and forget the ad hominem attack thing, that only applies to humans.

Edited February 13 by nicknorman