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Cheap LiFePO4 BMS?


jetzi

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6 minutes ago, nicknorman said:

temperature sensor (not a thermocouple, perleese!)

 

What other types of temperature sensor are there? Surely a thermocouple is quite well suited to the task. 

 

I know very little about electronics. You may have noticed :) 

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28 minutes ago, MtB said:

 

What other types of temperature sensor are there? Surely a thermocouple is quite well suited to the task. 

 

Bimetallic strips, sealed oil filled capsules, optical pyrometers, mercury or alcohol in glass thermometers, slump cones.......

 

 

The list is endlesd.

 

N

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34 minutes ago, MtB said:

 

What other types of temperature sensor are there? Surely a thermocouple is quite well suited to the task. 

 

I know very little about electronics. You may have noticed :) 

A thermocouple is a junction of 2 dissimilar metals, that creates a voltage which increases when heated. But in order to complete the circuit, the dissimilar metals have to be joined again somewhere else (in the sensing device). That junction also creates a voltage according to its temperature. This is normally called the “reference junction”. If the temperature at each end are the same, the voltage as the same an no current flows. So a thermocouple system measure the temperature difference between the sensor end and the reference end. Ideally one holds the reference end at a specific temperature, say zeroC. But if it is left at ambient temperature, accuracy is lost. Of course if the sensing end is in a flame at 1000C, it doesn’t matter too much if the reference junction is at zero or 20C, the error isn’t significant. But when you are trying to detect the difference between 0 and 5C, obviously it is.

 

Even with reference junction compensation, thermocouples are not great for measuring small differences in temperature, you just get a micro volt or two per degC and thus any noise picked up in the cable, any inaccuracy in the sensor etc is going to have a huge effect.

 

Many people would use a thermistor, this is a resistor whose resistance changes with temperature. You connect it to the sensing end and it’s resistance is measured by passing a small current through it.

 

But that is all so last century! Or the one before, even!

 

These days one uses a digital sensor where all the sensing and conversion to a digital format occurs in the sensor, which is the size of a small transistor. The standard communication protocol is One-Wire bus. Which surprisingly has at least two wires, maybe three! One wire for negative, one wire for data communication, and one optional wire for positive (3-5v). Transferring the data digitally means there is no loss of accuracy in the transmission process from resistive wiring, bad connections etc.

 

Also one can put numerous devices in parallel as they each have a unique address. So one pin on your BMS could have a dozen OneWire devices connected to it, one for each cell in say a 3P4S battery with the wiring daisychained.

Edited by nicknorman
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1 hour ago, jetzi said:

 

Ah yeah, you just left off the "h" before, as Nick said.

 

Still, 1.4kWh for a day is really really good (2.4kWh is a good day for me in summer!). The most I have got recently is 0.46kWh, that was middle of last week. I reckon your tilt is probably the thing that make the difference. have 1500W of panels but they are not on a tilt. I decided to rather just add more panels and leave them flat, my controller and roof still has capacity for 2 more panels which I think I might add since they are so inexpensive. But really I think to make a difference I should add at least a one axis lateral tilt.

 

To be fair, that was the best two days I had for a while, and after that I moved to a spot that's overlooked by a high bank and bushes etc on the south, so recently the panels have not been able to give much at all. 

 

But when the side of the boat faces south (ish), the tilting definitely makes a difference.

Just as an example, my front panels are laid out as a set of four in a square formation, and if I tilt the two that are on the south side, they obscure the panels on the north side- so for smaller panels in that configuration, tilting in autumn/winter doesnt seem to work well. 

 

The rear panels are a set of two larger units laid out lengthwise along the boat. So when they tilt to the side, nothing is thrown into shadow, and you see an immediate increase in yield of energy from them- as long as its sunny. 

If its overcast, as you'll know, the tilting is not as effective. 

 

But on that sunny day, about 2 weeks ago, the front panels (not tilted) collected about 700Wh, and the rear panels (tilted) collected twice that amount- and the two sets are rated very similarly (in watts).  

 

All that said, in the summer you get so much charge anyway that in early Sept when I put the rear panels on, I didnt even bother tilting. That approach might change now that I have my immersion heater hooked up to the batteries. So my plan next summer is to tilt if needed, so that I can heat the water with the extra energy I get from tilting. 

 

I can imagine that on a sunny summers day, with panels tilted to the south, I'll have the water heated by 10am, and the batteries topped up by midday. Even on poorer days they'll still do enough that I wont be running the engine just to do charging, or get waster to wash. You gotta love solar! 

 

 

 

 

 

Edited by Tony1
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Anyway back to low temperature charging, have a look at the Relion instructions here:

 

https://www.coastalclimatecontrol.com/images/PDF/ReLiON/Relion_Charging_Instructions_v3.pdf

 

To summarise the relevant bit:

 

LiFePO4 batteries can be safely charged between -20°C to 55°C (-4°F to 131°F). However, at temperatures below 0°C (32°F) the charge current must be reduced, until the temperature is >0oC (32oF), as follows:
1. 0°Cto-10°C(32°Fto14°F)chargeat0.1C(10%ofthebatterycapacity) 2. -10°C to -20°C (14°F to -4°F) charge at 0.05C (5% of the battery capacity)

 

 

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11 minutes ago, nicknorman said:

Anyway back to low temperature charging, have a look at the Relion instructions here:

 

https://www.coastalclimatecontrol.com/images/PDF/ReLiON/Relion_Charging_Instructions_v3.pdf

 

To summarise the relevant bit:

 

LiFePO4 batteries can be safely charged between -20°C to 55°C (-4°F to 131°F). However, at temperatures below 0°C (32°F) the charge current must be reduced, until the temperature is >0oC (32oF), as follows:
1. 0°Cto-10°C(32°Fto14°F)chargeat0.1C(10%ofthebatterycapacity) 2. -10°C to -20°C (14°F to -4°F) charge at 0.05C (5% of the battery capacity)

 

 

 

Thanks Nick, that's very useful to know.

From my viewpoint it means that even if I leave the boat for 2 weeks in Jan, and the (interior) battery cupboard goes to zero or below, I dont have to worry about a low level solar charge doing any damage.

 

 

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2 hours ago, MtB said:

Until this problem of prevention of charging below 0c is resolved, the "LFP for boats" industry cannot be regarded as mature. As you say, disconnecting the cells from the charging source as the temp approaches 0c is crude and inelegant. What really needs to happen is all the different charging sources on the market need to routinely monitor temp at the cells and turn themselves off at (just above) 0c. The emergency low temp disconnect in the BMS should be only a back-up for if/when the charge source fails to disconnect due to a fault.

I've never really fully agreed with the philosophy that all the charge sources (and load) have to be "smart". While it's definitely good to go "belt and braces", the only real reason for that is to add another layer of protection. If your "BMS" (using that term loosely to include the entire system, not just the "brain") has at least 1 and preferably 2 independent layers of temperature protection (plus added to that the human operator's common sense and understanding of the temperature limitations) then really I think it's enough.

 

Besides, we're not (yet) fast charging with super high amp boat recharge bays like EVs. We're mostly talking about a tiny (C/10?) trickle charge coming in from some winter sun at or around zero. If you are a liveaboard with decent alternator or generator output you might want to charge as fast as possible in the cold, but in those cases you need to apply common sense and a battery heater (backed up by the aforementioned low temp BMS charge cutoff).

 

1 hour ago, Tony1 said:

All that said, in the summer you get so much charge anyway that in early Sept when I put the rear panels on, I didnt even bother tilting. That approach might change now that I have my immersion heater hooked up to the batteries. So my plan next summer is to tilt if needed, so that I can heat the water with the extra energy I get from tilting. 

 

I can imagine that on a sunny summers day, with panels tilted to the south, I'll have the water heated by 10am, and the batteries topped up by midday. Even on poorer days they'll still do enough that I wont be running the engine just to do charging, or get waster to wash. You gotta love solar! 

Yeah, if you imagine the daily yield curve over the whole year, it forms a rough sine wave right. In my case, the peak between about April/May and about September/October yield is way more than I can use, and is truncated by the size of my battery, so tilting won't help at all for 6 months of the year. For 2-4 months of the year (March/April and October/November) the solar provided is "just enough" and could benefit from tilting sometimes (more panels would probably be almost as effective). Then for the last 2-4 months of the year (November to March) solar is basically useless and tilting would help a little, but never enough to rely on. So I figured that tilting is quite a lot of mechanical complication to add to your mount for only 2-4 months of benefit.

 

If you have a permanent mooring then it's different probably, but if you have to physically change the tilt all the time, honestly it's more faff than I can probably be bothered with. If it was automatic though, that would be different... and a fun project!

 

 

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4 minutes ago, jetzi said:

  

I've never really fully agreed with the philosophy that all the charge sources (and load) have to be "smart". While it's definitely good to go "belt and braces", the only real reason for that is to add another layer of protection. If your "BMS" (using that term loosely to include the entire system, not just the "brain") has at least 1 and preferably 2 independent layers of temperature protection (plus added to that the human operator's common sense and understanding of the temperature limitations) then really I think it's enough.

 


I rather disagree. Which is not surprising bearing in mind I’ve made my charge sources “smart”!

 

It is a standard concept to have a normal control system that takes into account all expected factors. And then to have an emergency “Oh shit” protection device that operates in the event of a failure of the normal system.

 

Consider an immersion heater in a calorifier. As well as the operator being able to switch it on and off, there is a thermostat that regulates the temperature. But there is also an “Oh shit!” over-temperature trip set at the maximum tolerable temperature. Fan heaters, central heating boilers etc etc all follow a similar design philosophy. I don’t see why Li charging should be any different. Ok the former things are protecting against damage due to heat, explosion and fire, but the Li thing is protecting you from severe damage to your wallet!

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28 minutes ago, jetzi said:

  

I've never really fully agreed with the philosophy that all the charge sources (and load) have to be "smart". While it's definitely good to go "belt and braces", the only real reason for that is to add another layer of protection. If your "BMS" (using that term loosely to include the entire system, not just the "brain") has at least 1 and preferably 2 independent layers of temperature protection (plus added to that the human operator's common sense and understanding of the temperature limitations) then really I think it's enough.

 

Besides, we're not (yet) fast charging with super high amp boat recharge bays like EVs. We're mostly talking about a tiny (C/10?) trickle charge coming in from some winter sun at or around zero. If you are a liveaboard with decent alternator or generator output you might want to charge as fast as possible in the cold, but in those cases you need to apply common sense and a battery heater (backed up by the aforementioned low temp BMS charge cutoff).

 

Yeah, if you imagine the daily yield curve over the whole year, it forms a rough sine wave right. In my case, the peak between about April/May and about September/October yield is way more than I can use, and is truncated by the size of my battery, so tilting won't help at all for 6 months of the year. For 2-4 months of the year (March/April and October/November) the solar provided is "just enough" and could benefit from tilting sometimes (more panels would probably be almost as effective). Then for the last 2-4 months of the year (November to March) solar is basically useless and tilting would help a little, but never enough to rely on. So I figured that tilting is quite a lot of mechanical complication to add to your mount for only 2-4 months of benefit.

 

If you have a permanent mooring then it's different probably, but if you have to physically change the tilt all the time, honestly it's more faff than I can probably be bothered with. If it was automatic though, that would be different... and a fun project!

 

 

 

I can see where you're coming from about the real-world benefits from tilting, and I did think a bit before I went for my tilting mounts. 

 

In my case, since I'm hoping to get water heated (at least warn enough to wash, so maybe 40 degrees) from the solar panels for maybe 4-6 months of the year, I feel I have an incentive for the extra hassle that it takes to tilt them. 

Because of that extra charge needed to heat water, I'll no longer always have more charge than I need, even in summer (my panels are rated at about 1.4kw in total).

On overcast summer days, or under trees, I might struggle to get the water warm, so there will be a benefit from tilting on some days and in certain situations, although I would certainly not attempt to say there was a clear cut case. 

 

I just fitted the tilting mounts without a great deal of thought, based on a hunch.

If I had done some detailed calculations, I might not have bothered to be honest- but overall, I am glad I did.  

You still have to drill holes in the roof for non-tilting mounts, and the wiring can be a faff either way, so what the tilting panels really cost me was an extra £150 or so, and I'm ok with that level of expense. 

 

Its an odd situation- I wouldn't try to argue in favour of them, but I'm glad I did go for them myself.

 

 

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3 hours ago, MtB said:

 

I'd long ago picked up this impression from reading the Nordkyn Design website. Nothing to do with water in the cells freezing as there is none, just that 0c happened to be the temperature ISTR him saying was the threshold to be avoided. The site had a major re-write a few months or a year ago (and all the previous stuff he published on lithiums was dumped) at which point IIRC he introduced the concept of electrode plating when charge rates exceed the rate the reaction can absorb it, so I think he has developed the point about low temp charging. Yes I can see it is unlikely there would be a sudden threshold and claiming 0c must be an oversimplification. 

 

I'll have a read of it again. 

You can charge LFP batteries below 0C but the maximum allowable charge rate drops off rapidly. Some batteries with manufacturer-supplied or inbuilt BMS allow this, for example the BYD batteries allow charging down to -10C but maximum current is heavily derated -- for example the LV3.5 (51.2V 70Ah) battery can be charged at 40A above +12C, 20A from +2C to +12C, 15A between -10C and +2C, and zero below -10C. Note that that's still 0.2C down to -10C...

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1 hour ago, jetzi said:

if you have to physically change the tilt all the time, honestly it's more faff than I can probably be bothered with. If it was automatic though, that would be different... and a fun project!

 

 

Usually useless though - most of the automatic tracking solar panel mounts use more electricity than they gain.  Quite a few people tried them when panel prices were a lot higher than they are now but most gave up.

 

If you fancy it as a fun project go for it, but adding an extra panel will cost less and give more power.

 

Manual tilt once moored works reasonably well if you need it, as long as you are moored in the correct orientation.

 

On a related topic, I had cheap amusement watching an automatic satellite dish on a boat a few months ago.  It spent about 10 minutes trying and failing to find the satellite before giving up and parking itself.  A quick glance at sky dishes mounted on nearby houses showed me that the enormous mill they had moored near was blocking direct line-of-sight between the boat and the satellite!

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1 hour ago, TheBiscuits said:

 

On a related topic, I had cheap amusement watching an automatic satellite dish on a boat a few months ago.  It spent about 10 minutes trying and failing to find the satellite before giving up and parking itself.  A quick glance at sky dishes mounted on nearby houses showed me that the enormous mill they had moored near was blocking direct line-of-sight between the boat and the satellite!


The people who had a Hudson built shortly after ours had all the gadgets including an automatic satellite lump on the roof. A day or two into their first cruise I got a phonecall and general whinge that the expensive satellite system wasn’t working. Eventually it transpired that they were moored in woodland and had no idea that the dish actually had to be able to “see” the satellite!

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19 hours ago, Tony1 said:

 

I can see where you're coming from about the real-world benefits from tilting, and I did think a bit before I went for my tilting mounts. 

 

In my case, since I'm hoping to get water heated (at least warn enough to wash, so maybe 40 degrees) from the solar panels for maybe 4-6 months of the year, I feel I have an incentive for the extra hassle that it takes to tilt them. 

Because of that extra charge needed to heat water, I'll no longer always have more charge than I need, even in summer (my panels are rated at about 1.4kw in total).

On overcast summer days, or under trees, I might struggle to get the water warm, so there will be a benefit from tilting on some days and in certain situations, although I would certainly not attempt to say there was a clear cut case. 

 

I just fitted the tilting mounts without a great deal of thought, based on a hunch.

If I had done some detailed calculations, I might not have bothered to be honest- but overall, I am glad I did.  

You still have to drill holes in the roof for non-tilting mounts, and the wiring can be a faff either way, so what the tilting panels really cost me was an extra £150 or so, and I'm ok with that level of expense. 

 

Its an odd situation- I wouldn't try to argue in favour of them, but I'm glad I did go for them myself.

 

 

Tilting panels give about 15% more power over the year (especially in summer) than flat-mounted ones -- you can view this as "free" if you're willing to put up with the extra height of tilting mounts, or that it's not worth it and flat-mounting closer to the roof is easier and more secure and looks less obtrusive -- either viewpoint is valid.

 

The difference will be bigger in the depths of winter when the sun is lower, maybe 30% or so -- but increasing power from 100% of sod-all to 130% of sod-all doesn't seem like much incentive...

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37 minutes ago, IanD said:

Tilting panels give about 15% more power over the year (especially in summer) than flat-mounted ones -- you can view this as "free" if you're willing to put up with the extra height of tilting mounts, or that it's not worth it and flat-mounting closer to the roof is easier and more secure and looks less obtrusive -- either viewpoint is valid.

 

The difference will be bigger in the depths of winter when the sun is lower, maybe 30% or so -- but increasing power from 100% of sod-all to 130% of sod-all doesn't seem like much incentive...

 

As I said, I'm not advocating tilting panels, but I have seen liveaboards out and about who swear by them, so I think the case for tilting depends on each boater's circumstances. 

 

There are lots of people who are more hard core and use less energy than I do (e.g. don't run a fridge), and who get enough extra power from their tilting that they can manage without running their engine for days and days, even in winter. 

It's all fairly marginal in winter as you say, and there are not a huge energy savings to be made in absolute terms, but for some liveaboards its the difference between running their engine to recharge, and not having to do that, on many days. 

There was one guy I parked next to at Whixall Moss in May, who said he had been there for several months waiting for engine parts after a catastrophic failure (yes, with the permission of CRT, to save anyone the bother of asking). 

I would imagine he wasn't using a fridge, and he was moored with the panels facing roughly south, but in his particular case the tilting was a life saver. He even had one panel hung vertically on the south side of the boat.

 

The thing is that although the gains are only 15% over a year (is that a fixed tilt btw?), my own experience over the last few months has been that on specific days, tilting can almost double the power yield. I've found this by recording the energy collected by my rear panels both before and after tilting, and also by comparing my permanently flat front panels with my similarly rated rear panels that tilt.  

 

I think the extra 100 or so quid for the tilting mounts will pay for itself, but only over a period of years- which to be fair is also the case with the lithium batteries and the solar panels.

But the economic case is not great in my own situation- its just a nice thing that on a number of days I've been able to collect enough power to not run the engine- to be fair, a fairly minor win, but I quite like it when it happens.  

 

The other thing in my case is that I'm looking to gain more from the panels in summer to heat water, and if tilting them in the mornings helps me to get hot water without having to run the engine for more months of the year, then it's another win. 

Only time will tell on that one- the immersion was connected to the batteries in mid-Oct, which was too late to be used for this year, but I'm hoping tilting will help me get solar hot water from around May to mid-Sept- as opposed to June to August only, if I dont tilt them. Again, not a big win, just nice to have.

 

 

Edited by Tony1
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25 minutes ago, Tony1 said:

 

As I said, I'm not advocating tilting panels, but I have seen liveaboards out and about who swear by them, so I think the case for tilting depends on each boater's circumstances. 

 

There are lots of people who are more hard core and use less energy than I do (e.g. don't run a fridge), and who get enough extra power from their tilting that they can manage without running their engine for days and days, even in winter. 

It's all fairly marginal in winter as you say, and there are not a huge energy savings to be made in absolute terms, but for some liveaboards its the difference between running their engine to recharge, and not having to do that, on many days. 

There was one guy I parked next to at Whixall Moss in May, who said he had been there for several months waiting for engine parts after a catastrophic failure (yes, with the permission of CRT, to save anyone the bother of asking). 

I would imagine he wasn't using a fridge, and he was moored with the panels facing roughly south, but in his particular case the tilting was a life saver. He even had one panel hung vertically on the south side of the boat.

 

The thing is that although the gains are only 15% over a year (is that a fixed tilt btw?), my own experience over the last few months has been that on specific days, tilting can almost double the power yield. I've found this by recording the energy collected by my rear panels both before and after tilting, and also by comparing my permanently flat front panels with my similarly rated rear panels that tilt.  

 

I think the extra 100 or so quid for the tilting mounts will pay for itself, but only over a period of years- which to be fair is also the case with the lithium batteries and the solar panels.

But the economic case is not great in my own situation- its just a nice thing that on a number of days I've been able to collect enough power to not run the engine- to be fair, a fairly minor win, but I quite like it when it happens.  

 

The other thing in my case is that I'm looking to gain more from the panels in summer to heat water, and if tilting them in the mornings helps me to get hot water without having to run the engine for more months of the year, then it's another win. 

Only time will tell on that one- the immersion was connected to the batteries in mid-Oct, which was too late to be used for this year, but I'm hoping tilting will help me get solar hot water from around May to mid-Sept- as opposed to June to August only, if I dont tilt them. Again, not a big win, just nice to have.

 

 

The 15% is for south-facing panels with fixed optimum tilt (35 degrees in the UK) -- actually, the exact figure is that flat panels give 84% of the yield of tilted, which means that tilting gives 19% more power over the year. On specific winter days in winter with a bright low sun the gain will be more than this, especially if you're willing to manually choose the best angle, but varying tilt even in winter gives very small gains (a few percent) compared to a fixed tilt -- the physics of how panels absorb light predicts this, and measurements on real panels confirm it. Also don't forget that especially in winter (or with no direct sun) more light comes from the sky as a whole not directly from the sun, and the yield for this is actually higher with flat panels.

 

As I said, it's a matter of choice whether people think the gains with tilting are worth the hassle, there's no right or wrong answer here... 😉

Edited by IanD
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44 minutes ago, IanD said:

The 15% is for south-facing panels with fixed optimum tilt (35 degrees in the UK) -- actually, the exact figure is that flat panels give 84% of the yield of tilted, which means that tilting gives 19% more power over the year. On specific winter days in winter with a bright low sun the gain will be more than this, especially if you're willing to manually choose the best angle, but varying tilt even in winter gives very small gains (a few percent) compared to a fixed tilt -- the physics of how panels absorb light predicts this, and measurements on real panels confirm it. Also don't forget that especially in winter (or with no direct sun) more light comes from the sky as a whole not directly from the sun, and the yield for this is actually higher with flat panels.

 

As I said, it's a matter of choice whether people think the gains with tilting are worth the hassle, there's no right or wrong answer here... 😉

 

I do agree about varying the tilt angle every hour or so, and I couldn't be arsed with that on any day of the year, except purely for testing and personal interest.

A single tilt to say 40 degrees seems to do the job for most of the day, in my case.

60 degrees would be even better apparently, but I'd need to devise a higher-lifting support, as the panels are so heavy. 

 

I should point out, in case anyone reading this is considering tilting mounts, that metre-wide panels such I chose (I think 1.8m long), are typically around 20kg or more, which is pretty heavy when you're hanging onto the side of the boat trying to lift it up one handed. 

Bear in mind that any kind of tilt-locking system involving half a dozen allen-head bolts or that needs precise two-handed operation is going to be tricky on those days when the lifting is done from the canal-facing side of the boat. 

And if the panel is more than say 80cm wide, its weight can present a bigger stress on the locking system. 

 

I gave up on using the intended locking system because of this.

What I do now is scuttle along the gunnels and get the side of the panel lifted up quickly with one hand, and then stick a short aluminium ladder under the edge of the panel with the other hand- whilst keeping one elbow against the rail in an attempt to hold myself in place.

All rather precarious, but preferable to the extra hassle of doing it when stood on the roof.

 

But prospective buyers should bear in mind that for the large high-yield panels, the tilting process is not always as quick and easy as it might appear, especially when done from the canal side of the boat, and if single-handed. 

 

Edited by Tony1
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9 minutes ago, Tony1 said:

 

I do agree about varying the tilt angle every hour or so, and I couldn't be arsed with that on any day of the year, except purely for testing and personal interest.

A single tilt to say 40 degrees seems to do the job for most of the day, in my case.

60 degrees would be even better apparently, but I'd need to devise a higher-lifting support, as the panels are so heavy. 

 

I should point out, in case anyone reading this is considering tilting mounts, that metre-wide panels such I chose (I think 1.8m long), are typically around 20kg or more, which is pretty heavy when you're hanging onto the side of the boat trying to lift it up one handed. 

Bear in mind that any kind of tilt-locking system involving half a dozen allen-head bolts or that needs precise two-handed operation is going to be tricky on those days when the lifting is done from the canal-facing side of the boat. 

And if the panel is more than say 80cm wide, its weight can present a bigger stress on the locking system. 

 

I gave up on using the intended locking system because of this.

What I do now is scuttle along the gunnels and get the side of the panel lifted up quickly with one hand, and then stick a short aluminium ladder under the edge of the panel with the other hand- whilst keeping one elbow against the rail in an attempt to hold myself in place.

All rather precarious, but preferable to the extra hassle of doing it when stood on the roof.

 

But people should bear in mind that the tilting process is not always as quick and easy as it might appear, especially if single-handed. 

 

People have the wrong idea if they think that accurate tilting of panels to within a few degrees makes any big difference, see plot below.

 

If you're going to tilt them, anywhere in the 30-40 degree range is fine.

 

Assuming they're south facing, which for a boat depends on which way the canal runs. If the canal runs N-S, flat-mounting is better than tilting...

 

Which is why that for a boat having tilting panels gains less (on average) than the theoretical 19% I quoted, unless you can always moor where the canal runs E-W...

 

 

solar panel angle.png

Edited by IanD
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18 minutes ago, IanD said:

People have the wrong idea if they think that accurate tilting of panels to within a few degrees makes any big difference, see plot below.

 

If you're going to tilt them, anywhere in the 30-40 degree range is fine.

 

Assuming they're south facing, which for a boat depends on which way the canal runs. If the canal runs N-S, flat-mounting is better than tilting...

 

Which is why that for a boat having tilting panels gains less (on average) than the theoretical 19% I quoted, unless you can always moor where the canal runs E-W...

 

 

solar panel angle.png

 

What I'm seeing with those who rely a lot on solar even in winter is that they'll seek out places where the panels can face roughly south.

But to be honest for the sake of the extra watts gained from that, there are many times I dont bother tilting at all. 

I'd rather stay on a nice mooring and maybe run the engine for a bit longer, than moor somewhere less nice for the sake of more solar. 

But each to their own, of course - I can imagine that sometimes people are working with such tight budgets that saving some fuel by gaining solar becomes a higher priority than finding a nice mooring.

 

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On 05/12/2021 at 09:14, Tony1 said:

 

I've never had a low temp thermometer in the engine bay, and I have no real idea how low the temp gets in below-zero weather,

 

Neither have I but a few years ago it got cold enough to turn the diesel in the bowl of the webasto filter into wax, This was just under the deck boards so well away from the canal water warmed baseplate. I think that waxing occurs around -10C melting of said wax doesn't occur easily till over 20C degrees which is how I found out trying to work out why the wabasto was sulking.

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2 minutes ago, Detling said:

Neither have I but a few years ago it got cold enough to turn the diesel in the bowl of the webasto filter into wax, This was just under the deck boards so well away from the canal water warmed baseplate. I think that waxing occurs around -10C melting of said wax doesn't occur easily till over 20C degrees which is how I found out trying to work out why the wabasto was sulking.

If your LFP batteries are sitting on the baseplate they're unlikely to ever have a low-temperature problem even in the coldest winters, the baseplate shouldn't ever get much below +4C which is the temperature where water reaches its maximum density and sinks.

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  • 4 weeks later...

Couple of things:

 

These are available from GWL (and elsewhere doubtless): AMETEK Magnetic Latching Contactor 12V 1200A Two other sizes available also.

 

Tesla owners manual now says this: “If your vehicle is equipped with an LFP Battery, Tesla recommends that you keep your charge limit set to 100%, even for daily use, and that you also fully charge to 100% at least once per week.” (Source: InsideEVs)

 

HNY.

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5 hours ago, Martin Nicholas said:

Couple of things:

 

These are available from GWL (and elsewhere doubtless): AMETEK Magnetic Latching Contactor 12V 1200A Two other sizes available also.

 

Tesla owners manual now says this: “If your vehicle is equipped with an LFP Battery, Tesla recommends that you keep your charge limit set to 100%, even for daily use, and that you also fully charge to 100% at least once per week.” (Source: InsideEVs)

 

HNY.

Of course we don't know what Tesla define as "0%" and "100%" as far as the user battery display is concerned. It's possible that to allow drivers to use as much capacity as often as possible without reducing the battery life, the "0%" seen by the user is actually 5% or 10% of the theoretical cell capacity, and the "100%" seen by the user is actually 90% or 95%. Othe LiFePO4 battery suppliers with built-in BMS do exactly this to prevent lifetime reduction, at the cost of some loss in capacity compared to the theoretical limit.

Edited by IanD
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I finally got around to writing the code for automatically top balancing the cells. The hardware only supports a maximum duration for any one cell of 37 minutes. I could of course repeatedly trigger it but since the discharge current is 1A or so, that is probably enough for routine small adjustments (ie a bit more than 1/2Ah) so I didn’t bother for the time being.

 

I charge at 14.3v which is an average of 3.575v per cell. If any cell gets to 3.6v, the balancing process is started. 3 cells vs the lowest cell, a discharge duration proportional to the differences. The oled display gets a little asterisk next to the cell being balanced whilst the mosfet drive is on. One cell at a time for thermal reasons.

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Great thread! That's 3 days I won't get back. :lol:

Seriously though, many thanks to all of you. - There's enough info here to get a good grounding on what's entailed. The convenience once over the initial pain of it all is definitely tempting.

 

I don't have much in the way of high wattage gadgets, but I do have a quite high powered PC which is used for music production and mixing, and powered 240v monitors + big screen which combined do use a fair bit of power for long stretches, maybe even 12-14 hours a day. I need to do a proper power audit but I'm fairly sure it'll be "quite a lot". I'm permanently on shore power due mainly to this, but I would very much like not to be trapped reliant on being in a marina just for that. A laptop simply will not do what I need - the batteries last 20 mins, the screen too small, the CPU heat generated is too much for a laptop - I've tried. And - one can't reliably mix using just headphones. It's just a hobby but it's my main hobby.

 

I've lived on a narrowboat for 5 years because I like it. No plans to change that until I get shovelled into an old peoples home.. :)

 

One question, maybe for Nick as I read he has one - would using my travelpower and 240V (80A IIRC) charger get around the many problems that seem to be associated with alternator charging? I have a 15 year old Beta43 and it already has one installed in addition to the starter and leisure bank alternators. It does seem like a pretty good thing but must have limitations. We were planning to install solar too. This is a long term aim as other work needs doing first not least of which is re-insulating the entire boat while living on it so plenty of time to plan. :(

Edited by Slow and Steady
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41 minutes ago, Slow and Steady said:

Great thread! That's 3 days I won't get back. :lol:

Seriously though, many thanks to all of you. - There's enough info here to get a good grounding on what's entailed. The convenience once over the initial pain of it all is definitely tempting.

 

I don't have much in the way of high wattage gadgets, but I do have a quite high powered PC which is used for music production and mixing, and powered 240v monitors + big screen which combined do use a fair bit of power for long stretches, maybe even 12-14 hours a day. I need to do a proper power audit but I'm fairly sure it'll be "quite a lot". I'm permanently on shore power due mainly to this, but I would very much like not to be trapped reliant on being in a marina just for that. A laptop simply will not do what I need - the batteries last 20 mins, the screen too small, the CPU heat generated is too much for a laptop - I've tried. And - one can't reliably mix using just headphones. It's just a hobby but it's my main hobby.

 

I've lived on a narrowboat for 5 years because I like it. No plans to change that until I get shovelled into an old peoples home.. :)

 

One question, maybe for Nick as I read he has one - would using my travelpower and 240V (80A IIRC) charger get around the many problems that seem to be associated with alternator charging? I have a 15 year old Beta43 and it already has one installed in addition to the starter and leisure bank alternators. It does seem like a pretty good thing but must have limitations. We were planning to install solar too. This is a long term aim as other work needs doing first not least of which is re-insulating the entire boat while living on it so plenty of time to plan. :(

On the travel power question, the whole issue of alternator overheating disappears if you are charging by Travelpower and a charger (assuming the leisure 12v alternator is disconnected or otherwise disabled). What may not be so easily addressed is control over the charger. Depending on the model of charger it may have a lithium mode but if not you would need to disable voltage temperature compensation. You would probably want to be able to adjust the charging voltages to suit. Of course it depends on how long you intend to cruise for but it might be an issue that a long cruise would hold the batteries at a high voltage for longer than desirable. On the other hand you might be able to configure the charger to go into a suitable float voltage that doesn’t push any more current into the batteries once they are charged. So many variables! But overall yes I think you would be starting from a better place than someone who just has a 12v alternator.

Edited by nicknorman
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