[Cheap LiFePO4 BMS?]

Small update, I'm making reasonable progress with the Arduino based BMS.

It's reading my four voltages and the MOSFETs are driving the Tyco relay effectively. I still feel a few months away from an install though. "Productionising" this into a full system that doesn't have wobbly connections, is physically robust and stable, and has all 4 relays / 8 MOSFETs as well as all the other good stuff I have planned is going to be quite something, you can see how tangled the wiring is already.

 

A bigger problem is that the voltage readings don't seem to be stable. They will be fine for a while, then all of a sudden they start misbehaving, I think it might just be a wobbly connection. See the below log of my serial monitor.
 

Cell 0: 3.30  Cell 1: 3.30  Cell 2: 3.18  Cell 3: 3.32  
Cell 0: 3.30  Cell 1: 3.30  Cell 2: 3.18  Cell 3: 3.32  
Cell 0: 3.34  Cell 1: 3.30  Cell 2: 3.16  Cell 3: 3.32  
Cell 0: 6.90  Cell 1: -0.30  Cell 2: 3.18  Cell 3: 3.34  
Cell 0: 5.88  Cell 1: 0.74  Cell 2: 3.16  Cell 3: 3.34  
Cell 0: 7.48  Cell 1: -0.88  Cell 2: 3.18  Cell 3: 3.32  
Cell 0: 3.34  Cell 1: 3.26  Cell 2: 3.18  Cell 3: 3.34  
Cell 0: 3.96  Cell 1: 2.66  Cell 2: 3.16  Cell 3: 3.34  
Cell 0: 3.28  Cell 1: 3.30  Cell 2: 3.18  Cell 3: 3.34  
Cell 0: 3.28  Cell 1: 3.30  Cell 2: 3.18  Cell 3: 3.34  
Cell 0: 3.28  Cell 1: 3.30  Cell 2: 3.18  Cell 3: 3.34  

 

The voltages seem fairly accurate but there's enough play to concern me, and I think I may need to upgrade from the Uno to a microcontroller that has a higher than 10bit analogue/digital converter resolution.

 

[Bugsworth Basin visitor moorings]

Oh thank you! Is there a "day rate" for this donation or is it discretionary?

[Bugsworth Basin visitor moorings]

Anyone know what the situation is, are there cart visitors moorings in Bugsworth basin? How long can you stay, is there usually space, is it safe? Where are they, in the middle / lower arm or just anywhere along there?

 

I gather that much of the upper peak forest is too shallow to moor at the banks, so wouldn't like to get to the end and not have anywhere to moor...

 

Thank you!

[Diesel Prices]

I haven't been following since the fuel crisis - what's a good price for diesel per litre in this climate? Some places that are listed as 70p /litre (which I'd consider a good price) on the spreadsheet are now around 90p. Is that the new good price?

 

 

Its a great effort so not knocking it, but unfortunately the spreadsheet is kind of too out of date to give that sort of overall picture.

 

I know some folks get red diesel delivered but seeing as I can only store around 250 litres I'm guessing this isn't an option for me.

[C&RT's most useless signs and money wasted]

If I wasn't morally opposed to the blue signs, it actually sounds like a job I'd love. A large portion of your time on the waterways, spending time on the towpath, traveling to remote areas... Sounds pretty much like what I'm doing anyway!

 

Anyways, as frustrating, wasteful and inefficient as it is, I feel like we have to just accept this as a consequence of our waterways being funded by taxpayers and donations.

[Cheap LiFePO4 BMS?]

2 hours ago, nicknorman said:

For the 4th cell, it’s voltage, say up to 14.8v will have to be mapped onto the 4.096v, although I’m going to keep it mathematically simple by saying let’s use 4.096v/cell ie the max is 16.384v (4:1 mapping). Now the resolution is 16mV per cell and there will be at least 1 lsb of jitter), which is getting too much for the likes of balancing. But as I said, still ok for low and high alarms. There is no direct correlation between the AtoD output and the cell voltage, you need to know the cell voltages of the previous 3 cells to work it out, all of which can introduce further errors from lsb jitter etc.

Thanks for spelling it out, that makes total sense, that was also why I hoped I could use the voltage sensors like a "permanently attached multimeter" across each cell only. If I was to use a microcontroller with a 12 bit AtoD then I would end up with the 4mV you suggested for the 1st cell using the 10 bit. But I think I'm going to start with the Uno and see how I feel later.

 

 

 

2 hours ago, nicknorman said:

The normal way to do it would be to use an analogue multiplexer, which would charge up a tiny capacitor across the cell, and then switch both ends of the capacitor so it would be across analogue ground and the A2D input. Thus each cell voltage is mapped onto a 0 to 4.096v A2D input range. But that is quite complicated to achieve and why I used a dedicated chip that does all that for me, giving me a resolution of 1.2 mV on all cells.

I don't understand this bit, so I think this is beyond me for the time being. Going to keep it simple for now and get it working even if the resolution is too low.

 

 

2 hours ago, nicknorman said:

Other points: fuses. No particular opinion but every extra connection and item you add is a potential source of failure  so it should be kept simple unless the addition “brings something to the party”. You will be pissed off if after years  you finally have a genuine over or undervoltage event and the Tyco fails to open because the fuse blew last year, or the connections are corroded!

That's a really good point that I hadn't considered, one fuse for all relays make some sense. Perhaps I should add a "blown fuse LED warning" that will alert me in this case.

 

 

2 hours ago, nicknorman said:

Temperature sensor. Yes that’s how it’s wired but when done that way, the minimum reading is 2C. Maybe that is good enough.

I'm not sure why it would be so low, the sensor is rated from -55 to 150 degrees centigrade, but I'll look into this more as I suspect it's to do with the mapping of voltage to temperature.

 

 

2 hours ago, nicknorman said:

I don’t quite understand the bit about the thermostat, but the important point is not to leave an input floating (thermostat contact open) as it’s value is then undefined and could be anything.

 

I see - thanks yes, I will use a pull down resistor then on the analogue input to ensure that it is not floating when the contact is open.

Basically I was just trying to put across that I'm using an external digital thermostat and hooking it into the BMS with the (currently unused) relay. The digital thermostat came with the immersion element I bought (which has a 600W 12V element and a 1kW 240V element). That relay is supposed to turn on the 12V immersion heater element but the current is rated far too low (10A I think) so I never used it, but I still installed it because it's nice to see the temperature display. Just thought it was an easy way to know whether or not to keep putting dump energy into the calorifier or not.

[Cheap LiFePO4 BMS?]

3 hours ago, nicknorman said:

Quite a lot to say about that!

Thanks for putting me straight Nick! Luckily no comments on the MOSFETs or the switching, which is the bit that I was really thinking about. The rest I kind of chucked in to get an idea of what components I still needed to buy.

 

 

 

3 hours ago, nicknorman said:

I don’t think there is a need to fuse every coil of every Tyco relay.

 

I bought a bumper bag of fuses and holders and already built this part when I first installed. I figured that if I did fuse each coil individually, it would make it easier to see which relays and coils have a problem. Do you think that it's unwise to do this?

 

 

 

3 hours ago, nicknorman said:

But you do need to fuse the connections to each cell

Done.

 

 

 

 

3 hours ago, nicknorman said:

those arduino “voltage sensors” are just potential dividers. And Gnd and - are connected together. You have therefore wired dead shorts across the cells! All the GND connections must be connected to battery -.

You're dead right, I could in fact make my own here with a pair of resistors (which is how my experimental 1-cell voltmeter is working) but the prebuilt modules are so cheap and have nice screw terminals on them so will just make the installation easier. I have corrected the diagram. The 1, 1+2, 1+2+3, 1+2+3+4 sensors is exactly how much current per-cell monitoring is wired (ISDT-BG8S and the non-functional GWL CPM board).
 

 

 

3 hours ago, nicknorman said:

severely reducing resolution and accuracy.

 

That's a concern for me. Why does it reduce resolution and accuracy - because the accuracy of any cell is only as good as the weakest link? Or because of the sensitivity of the Arduino? I used an Uno because that's what I have, and the analog/digital converters are 10bit. I could get a different board like a ESP32 which has 12bit analog/digital converters, but I figured that 10bit would be good enough - maybe I should look into this more. It's no good relying on this system if it can't be accurate to at least 0.01V.

 

I'm taking pains to improve the accuracy with the addition of the LM4040 voltage reference, but since it only provides 4.096V do you think this is too far away to be accurate?

 

 

 

 

3 hours ago, nicknorman said:

Battery temperature sensor need a pull-up to analog ref. I think, as far as I’m aware an analog input can’t measure resistance directly, only voltage. But in any case I’d use a one-wire digital sensor eg DS1822

 

I've corrected it, didn't put any thought into that at all, just picked the symbol from the diagram maker and stuck it in anyhow! I have a LM35 transistor for this, I have corrected the diagram how I believe it should be connected, do I still need a pull-up / pull-down resistor?


 

3 hours ago, nicknorman said:

Calorifier thermostat needs a pull down resistor unless this can be set up in the IO configuration, which I doubt.

Corrected, currently I'm just using the digital thermostat as a thermometer so I know when I can start my shower, the relay is currently unused. I will take the signal from the arduino output then I think it doesn't need a resistor.

 

 

Here's the updated diagram:

 

[Cheap LiFePO4 BMS?]

I've drawn out a diagram of my plan for the Arduino-based BMS to try to identify the bits I still need to obtain. I have most of it lying around already from little experiments, going to order the other bits now.

 

The MOSFETs I've settled on are these: https://uk.rs-online.com/web/p/mosfets/6887175

They turn on at Vgsth = 1-3V (Vgs max=16V), so the Arduino must be able to drive them at 3.3V. They rated at 86A continuous / 340 pulse so they should be more than good enough to handle the Tycos. The maximum drain/source voltage is 55V, which should be able to handle any surges or fluctuations. The Rds(on) is only 8mΩ which also seems very low. They're marketed as "Automotive MOSFETs" which also makes me feel confident in my choice.

 

I'm sure this will need some tweaking and experimentation, but I thought I'd share what I have in mind so far anyway. Will update again in 3 weeks once I have it running!

 

 

[Cheap LiFePO4 BMS?]

1 hour ago, TheBiscuits said:

The Valence batteries have a built in Battery Monitoring System BMS.

What does that comprise exactly? A red led that lights up if the voltage of any cell goes above or below a preset threshold? Or is there more to it than that?

 

1 hour ago, TheBiscuits said:

Would you guarantee secondhand batteries of unknown provenance?  I wouldn't.

 

Does selling the BMS imply a guarantee though? Can they not just say "here's the BMS, but use at own risk unless you bought the battery directly from us?"

 

And with all these second hand valences, are there not second hand BMSes around as well? Or are these batteries all from much larger banks, usually?

 

I must be missing something because the valences are so highly regarded, but without meaning to criticise them, I fail to really see how they are different from bare cells. The protections that most of us have gone to lengths to build seem to be equally needed (which it isn't really, you could just have bare cells and a voltmeter and manually charge and discharge them).

[Cheap LiFePO4 BMS?]

  

42 minutes ago, MtB said:

You, Peter and a few others are using Valence batts with factory built-in (and undocumented AIUI) BMS

It kinds of grates me that whatever electronics are in the Valences is described as a "BMS", As far as I understand the Valence BMS doesn't include any of the 5 BMS "essential features" you mentioned nor the 2 extras that I want (apart from - it seems - a cell voltage alarm in the form of a warning light?). I fear that it might lead people to expect too much from what seems to be a balancer.

 

 

1 hour ago, MtB said:

Valences are LiFeMgPO4 not LiFePO4 (again AIUI) so you really are 'off piste' as far as applying LiFePO4 rules of management.

I have Winston Thunderskys which have Yttrium added (LiFeYPO4) and they say that it makes then more stable and slightly widens the allowable voltage. I expect the Valences' magnesium has a similar effect so assuming it's not just a gimmick it might actually make them a bit safer as well.

 

1 hour ago, MtB said:

I suspect your batts might comprise hundreds of little cells arranged in parallel/series grids, whereas I have eight whacking big individual cells the voltage of which I can measure individually. 

 

As I understand it, once you put the cells in parallel they effectively become one cell, so I'm not sure it would make any difference.

[C&RT's most useless signs and money wasted]

2 hours ago, ditchcrawler said:

Please can I have an E Type in showroom condition complete with insurance, I can afford the road tax myself

 

E types for everyone paid for by the public. The government spending will stimulate the economy. Anyways it is hardly fair that only the very lucky - or people who have worked their whole life, saving and forgoing other pleasures - can have a nice car. It makes sense that the public should pay for my car anyway, because the gongoozlers like to see a road with nice cars on it! 😁

 

[Cheap LiFePO4 BMS?]

16 minutes ago, nicknorman said:

Oh and I meant to say, what about a Combi which is both a load and a charge source?

 

Then its not possible, which is an extra reason to use separate chargers and inverter rather than a combi

 

 

5 minutes ago, Tony1 said:

If I can beef up my capacity to 550Ah with another battery, it'll be easier to stay within the 30-80% SoC range

The 30%-80% range will certainly be easier in the sense that you have more capacity before you run out. But won't you still have the same issue with 30% or 80% SoC being an average across the battery, with any one cell being out of range?

 

Granted, in any case, for a 12V battery charged to 80% to be overcharging one cell, that cell would have to be at least 27% out of balance ((73+73+73+100)/4 = 80) which is pretty dramatic, especially if your Valence battery has some sort of reliable internal balancing going on.

[Cheap LiFePO4 BMS?]

11 minutes ago, nicknorman said:

In the end I didn’t go for separate load and charge disconnects. I took the view that both over and under voltage events were extremely unlikely and certainly not part of normal operation. I suppose a low voltage event is probably human error, a high voltage event is equipment fault, so the former is far more likely. My charging devices both have awareness of individual cell voltages.

 

But if you do have separate load and charge disconnects, the system can be self-healing which is nice.

 

But yes I think that was a big shift in perspective from me in the journey of the last 86 pages, seeing the disconnects as emergencies and having the charge sources themselves be smart enough to know whether they should be charging the battery (at least on a whole-battery voltage level).

[C&RT's most useless signs and money wasted]

8 minutes ago, MtB said:

At the moment, a boat twice the width and therefore twice the size, only pays 20% more.  

 

Yeah, I really don't see this being fair, especially since widebeams (even slightly wide) can't share locks, can't breast up when mooring, and likely cause disproportionate wear on infrastructure. Paying per square metre (like you do on the Norfolk Broads) seems appropriate, more in line with "user pays" since they are "using" more of the canal, dead easy to calculate, and is actually a reasonably good proxy for boat value anyway, so no need to get into the debate about whether broke homeless people in inner cities should have their floating housing subsidised by leisure boaters (and the general public).

And as a plus, I have a narrowbeam, so I'm alright Jack!

[Cheap LiFePO4 BMS?]

Yes, I've changed my mind and I agree with you. The alarm by itself is not sufficient, there are any number of reasons you might miss the alarm even if you liveaboard (someone else on your boat doesn't know what it means, or you pop out to a shop or to do a lock, or you are listening to loud TV, or you sleep through it). Disconnect on a per-cell basis should be considered essential and the minimum requirement for a BMS. I think the temperature cutoff could be considered optional though, especially if you keep your batteries in the cabin and are aware of the limitation.

[C&RT's most useless signs and money wasted]

23 minutes ago, Higgs said:

Why should anything else matter, but the space used? 

 

Everyone should be able to do everything, whether they can afford it or not.

[Cheap LiFePO4 BMS?]

  

16 minutes ago, Tony1 said:

two different types of cell will probably charge at different rates, and the valences might reach 100% SoC long before the 200Ah unit does, etc. It just seems fraught with issues. 

This is definitely the case, in fact two of the exact same type of cells reach 100% at different rates. That's why per-cell monitoring is essential, you can't rely on the overall battery voltage.

 

19 minutes ago, Tony1 said:

The essential protection is there already with my disconnect systems, but it would nice to have some balancing functions as well. 

 

I really feel (and think the general consensus among posters here is) that automatic balancing is very non-essential to the point of being of of no real use. The main reason for balancing is to get more capacity out of your bank, and also it makes the setup a little safer because if the cells are well-balanced the whole-battery-voltage disconnect is less likely to exceed the range of any individual cell (which also then allows you to be less conservative with your charge range). But my experience is that the cells don't really get out of balance anyway, I think most of us are reporting the same. It's just not so much of a problem in our relatively low-current environments with our conservative charging ranges.

 

29 minutes ago, MtB said:

I'd second jetzi's question. Which BMSs do you have in mind, because I can't find any that have all the basic functions needed. 

 

The basic essential functions in my opinion are:

 

Separate charge disconnect on any individual cell voltage rising above a value the user can set

Separate load disconnect on any individual cell voltage falling below a value the user can set

Pre-disconnect advance warning (e.g. audio alarm) at user settable values

Charge disconnect at low temp (e.g. 0 degrees C)

High current capacity (say 150A) so use of relays is not required

 

Anyone building such a BMS will surely sell millions!

 

That's a good list and what I'm aiming for - plus I want to add a load dump and an automatic battery heater for when you try to charge below 0 degrees (I have these things at the moment but they're manual). But if we're talking about a bare minimum, I think the only really essential thing is a per-cell alarm (preferably disconnect). And as Tony is finding it's possible (albeit risky) to only use the whole-battery disconnect, as long as your cells are balanced and you aren't aggressive with the high/low SoCs.

 

There's a whole other topic though which is on charge regulation (especially on your alternators) - currently I'm relying on my LA dump battery to pick up the slack from an emergency charge disconnect.

[C&RT's most useless signs and money wasted]

  

6 minutes ago, MtB said:

Re-balancing the fee structure might be a better way forward. Base license fees on boat value, like Council Tax on houses perhaps. Mr and Mrs Moneybags with their £150k or £250k new builds who could easily afford £10k or £15k a year would then start contributing proportionally. It does seem iniquitous to me that a young couple in an old 60ft ex hire boat they paid £18k for, have to pay nearly the same licrense as a widebeam worth ten times as much and taking up almost twice as much canal 'real estate'. 

 

It's definitely one approach that could work. Whether it does becomes a question of left- vs right-leaning economics. I take a generally pessimistic view of these kinds of suggestions because they tend to create inefficiencies and perverse incentives that sometimes aren't obvious at first. For example, perhaps an annual boat valuation becomes a racket that ends up increasing costs for boaters without actually providing funds to upkeep the canals. Or perhaps boaters are disincentivised to maintain their boats to a high standard in order to reduce their value, leading to more accidents, environmental hazards or visual disappeal. Or perhaps the income projections for the switch cause boat buying and building behaviour to change (fewer people buy the expensive boats the new scheme plans to make money from) and the total income doesn't actually increase. Or, maybe, just maybe, government/cart come up with a really good scheme that doesn't cost much to administrate, is fair and well supported by the boating community, and brings in significantly more money to pay for the waterways - but looking at their past record, I am skeptical. Though it's unpopular, I tend to lean towards the most efficient and equitable system being "user pays".

 

 

10 minutes ago, Higgs said:

The cost of a boat should have no bearing on its licencing value. I can understand the equation of size (footprint). 

 

Why not?

 

 

17 minutes ago, TheBiscuits said:

I disagree.  Boaters are the Mickey and Minnie characters for CRT's Disneyland - we are the entertainment.

 

I think this is correct up to a point, but to a much smaller degree than boaters like to think. I agree that boaters-as-entertainment justifies SOME public expenditure to fund our hobby/housing, but not to the degree of subsidisation that it does today.

[Cheap LiFePO4 BMS?]

12 hours ago, Tony1 said:

Even adding the price of s BMS and a battery case, its still a fantastic price.

Nowadays I'm ok with the idea of building the battery myself, and adding an off the shelf BMS unit- there are some very good and configurable ones available these days. 

 

What BMS do you have in mind? This whole thread is pretty much about how an off-the-shelf BMS unit is not really available! But admittedly I haven't looked for a long time.

 

I think it isn't helped by the fact that BMS can refer to a very wide range of things - but as Tom and Bex said -

12 hours ago, Tom and Bex said:

Minium would be ability to monitor individual cell voltages, and ideally control systems (or loud alarm) based on those.

- really the only thing that's essential is a way to disconnect the battery on per-cell under/over voltage event (even if that way is just a loud alarm that prompts you to flip the battery disconnect).

 

The main problem I ran into is that the relays in these devices can generally only handle low currents.

[Quiet moorings on the Huddersfield Narrow?]

19 minutes ago, Mac of Cygnet said:

Are you hoping to catch some fish, then? 

 

Given the lack of water in the canal, probably don't need baited breath, you can just wade into the mud and pick them up!

[Calor Gas currently not supplying new fills]

I did consider lugging them back to the boat but I already have my two 13kg cylinders. Really you'd need a car (preferably a 4x4) to go and fetch them, just thought if someone is really struggling to find the cylinders they might be interested. Disclaimer though, I don't know if they are in working order (or if that matters). DM me if you want them and I can give you GPS coordinates.

[C&RT's most useless signs and money wasted]

28 minutes ago, Grassman said:

I think that the raising of the public's awareness is not so much about attracting donations but more to do with trying to secure future part funding from the government which I believe is currently around £50m per annum. It's up for review soon, and given the fact that when CRT was set up in 2012 the government said it wanted it to eventually be self funding (like the National Trust they said),  CRT are having to do their utmost to justify future government financial support by plugging their cause. Hence all their spiel about well being and canals for all etc. 

 

True, it's not only direct voluntary donations, there are also the "donations" the public makes via the govmt grant.

 

 

  

21 minutes ago, Grassman said:

90+ percent of canal users are using their towpaths free of charge and not paying a penny towards their upkeep? It's crazy that CRT should have to fight so hard and waste so much money on signs and other 'awareness' measures. Our canals provide an amenity for people to enjoy and should therefore always have a significant contribution from either local or national government. 

 

I know towpath improvements is sometimes funded by local authorities or the likes of Sustrans, but mostly it's CRT who have to bear the cost of the upkeep and maintenance.

While I do agree with you, the vast majority of visitors to the waterways (cyclists, amblers and ramblers) have no need for the waters to be easily navigable with services. Yes there are the gongoozlers but boats if anything inconvenience these groups.

 

Cart is in the difficult position of needing the majority public to justify/raise funding, but with the minority boaters needing the lions share of the money. That's why I think boaters should support at least a modest increase to license fees. We've had the conversation before that raising boat licenses high enough for boaters to actually pay their own way would price many off the canals, which is unfortunate, but I feel we have to strike a more reasonable compromise if the canals are going to remain navigable for the next 100 years.

[Calor Gas currently not supplying new fills]

Just now, mrsmelly said:

Are they owned by calor or any of its subsidiarys?

 

They are branded Calor cylinders yes

[Calor Gas currently not supplying new fills]

Not sure if finding empty cylinders is still a problem, but I came across 3 Calor cylinders flytipped with some other stuff at the top of a rough road in south West Yorkshire. Think there are 2x 13kg and 1 larger one. They appear to be in OK condition, not sure if they are fillable, but I should think the condition is Calor's problem once you've returned them. Are these junk or could they be useful to anyone?

[Cheap LiFePO4 BMS?]

2 hours ago, Tony1 said:

What I'm saying is that you're going cruising anyway, right? So the diesel is going to be used up anyway, for that purpose. 

So why not get the extra (and free) benefit of doing the battery charging whilst you're on the move?

After all, your system is capable of delivering a very large charge even in an hour's cruise. 

The energy has to come from somewhere, the alternator will increase fuel consumption if it is charging your battery. It's actually quite easy to demonstrate this if you are able to turn your alternators on and off, my engine (granted it's a small Beta 38) audibly labours if I turn on the alternators while it's running at low revs. I hear a similar argument when people treat electricity as free while the motor is running. Any amps that are going to domestic loads are amps that aren't going into your batteries. The situation can be a bit different with LAs and their low charge rate but generally speaking your LiFePOs can absorb as much as your alternators can provide.