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Cheap LiFePO4 BMS?


jetzi

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10 minutes ago, nicknorman said:

So as a rotor blade completes a circle in fast forward flight, it is twisted first one way then the other, to maintain constant lift all the way round so that the helicopter attitude remains constant.

It's amazing that they don't fall off ;)

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Just now, nicknorman said:

They do sometimes, which can spoil your day!

Nasty, noisy, unstable things... :D

 

As an aside, I was talking to a retired Navy copter pilot a few years ago who said they used to fly one of their craft in a complete loop in air displays. He said "We never used to tell the boss about the oil pressure warning light coming on half way through the manoeuvre".  I always wondered if that was a true story.

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39 minutes ago, WotEver said:

Nasty, noisy, unstable things... :D

 

As an aside, I was talking to a retired Navy copter pilot a few years ago who said they used to fly one of their craft in a complete loop in air displays. He said "We never used to tell the boss about the oil pressure warning light coming on half way through the manoeuvre".  I always wondered if that was a true story.

Probably true. The lynx with its rigid rotor head could be looped and rolled quite easily. A Sea King, probably not.

 

This will be the main gearbox oil pressure. Since the main gearbox is all roller / ball bearings (Seaking high speed shaft input bearing excepted) it is quite tolerant of short periods of no lubrication and ditto the other and equally important function of the gearbox oil, to carry heat away into an oil cooler. If the g gets below 0 at the top of the loop then the oil will fall away from the inlet and momentary loss of oil pressure will result. No big deal.

 

There is no particular need to get below zero g at the top of a loop, but I guess in a helicopter you are battling limited airspeed and a limited desire to pull a lot of g, so it probably is normal (I’ve never done a loop in a helicopter).

 

Zero or slightly negative g feels very alarming to the occupants but for the aircraft it means it doesn’t have to produce any lift - easy life! (provided you don’t have a teetering rotor head in which case it’s catastrophic!).

Edited by nicknorman
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The Naval Lynx could be barrel rolled, as could the Gazelle,  though neither had the manoeuvre in their Release to Service.  There was a bit of a tendency for the Lynx Central Warning Panel to light up  here and there as the aircraft became inverted but it sorted itself out on the way down again.  AFAIK there were no Naval Rotary wing aircraft that could be looped.  A big wingover, carefully flown, could be made to look like a loop from the right viewpoint.

 

It might be possible to loop an (Army) Apache, but I have never been in one of them.

 

N

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16 minutes ago, BEngo said:

The Naval Lynx could be barrel rolled, as could the Gazelle,  though neither had the manoeuvre in their Release to Service.  There was a bit of a tendency for the Lynx Central Warning Panel to light up  here and there as the aircraft became inverted but it sorted itself out on the way down again.  AFAIK there were no Naval Rotary wing aircraft that could be looped.  A big wingover, carefully flown, could be made to look like a loop from the right viewpoint.

 

It might be possible to loop an (Army) Apache, but I have never been in one of them.

 

N

I think it would be quite possible to loop a lynx, it’s just not an approved manoeuvre. There was a ruckus at the Eurocopter factory when a test pilot looped a customer’s brand new EC225 (11 tonne transport helicopter) in front of the CEO and the customer. It was his last day at work.

 

 

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1 hour ago, nicknorman said:

Zero or slightly negative g feels very alarming to the occupants...

I've flown inverted a few times.  It's quite disconcerting as one's frame of reference is the aircraft in which you're sat, so the first time it happened I was wondering why my arms suddenly wanted to fly above my head. I was more concerned about that than why the ground and sky had swapped places.

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2 hours ago, nicknorman said:

No sorry you are talking about the collective. So called because it changes the pitch on the blades collectively (ie all at once by the same amount).

 

The cyclic is the “joystick” that controls the attitude of the helicopter (pitch and bank). The attitude is affected by the attitude of the rotor disc (ie the imaginary disc around which the rotor tips fly). The lift from the rotors is perpendicular to the disc so if the disc is tilted forward, the helicopter pitches nose down and moves forwards. If the disc is tiled lateral, the helicopter banks and moves sideways (in forward flight this makes it turn).

 

So how to tilt the disc relative to the fuselage? Well it can’t just be forced because there is a lot of gyroscopic force and the consequence would that the fuselage tilted the wrong way whilst the disc remained fixed. So the disc has to be “flown” into a  new attitude. This is done by varying the pitch on each rotor blade as it goes through one revolution. So for example (and let’s take a clockwise- rotating disc) when you move the cyclic forwards to pitch nose down / move forwards, a rotor blade as it passes beyond the forward position will be twisted progressively to increase its angle, which makes it start to fly up. As it passes the 3 o’clock position this twist will be at a maximum and then decrease so that the angle is nominal at the 6 o’clock position but by now the blade is higher than it was. As it moves forward again the blade is progressively twisted the other way to decrease its angle so it starts to fly down, reaching a maximum reduced pitch at the 9 o’clock position before arriving at the 12 o’clock position at nominal angle but at a lower height. So the blade is flying high at the back and low at the front, ie the Rotor disc is now tilted forwards, the lifting force is inclined forwards and the helicopter pitches nose down and moves forwards.

 

So with the rotor blade pitch angle varying as it goes round in a circle, or a cycle if you will, what should we call the control? How about the cyclic?!

 

To spell it out, the cyclic controls blade pitch cyclically whereas the collective controls blade pitch collectively!

 

The is another issue which is that in forward flight (well, flight in any direction really) a rotor blade has different airspeed as it goes around a complete rotation. When the blade is moving into the relative wind (“wind” arising from both the actual wind and the motion of the helicopter) the speed of the air over the blade is greater compared to the when it is moving away from the relative wind. An aerofoil produces more lift as the air speed over it increases, so we have a situation where as the blades moves forward into the wind it produces more lift and starts to fly up, and as it moves away from the wind it produces less lift and starts to fly down. Thus the disc is tilted away from the direction of travel and the helicopter will pitch or roll away from it and want to go in the opposite direction. Not ideal!

 

So in forward flight the cyclic has to be moved forward somewhat so that the increased airflow over the rotor blade moving into wind is countered by it having a reduced angle, to give the same overall lift. Ditto the blade moving down wind has lsss airflow and so has to have more  pItch angle to produce the same lift. So as a rotor blade completes a circle in fast forward flight, it is twisted first one way then the other, to maintain constant lift all the way round so that the helicopter attitude remains constant.

Well I follow some of that, thank you I will have another look later ;)

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1 minute ago, tree monkey said:

Well I follow some of that, thank you I will have another look later ;)

Simply satisfy yourself that it's the stick-that-must-be-wiggled-constantly ;)

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2 hours ago, tree monkey said:

This I am happy with ;)

Another dodgy helicopter fact. The big nut that holds the rotor onto its shaft is called the "Jesus nut". Because if it comes undone, the next person you meet is Jesus.

 

(I bet this isn't really true. Nick?).

 

MP

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1 minute ago, MoominPapa said:

Another dodgy helicopter fact. The big nut that holds the rotor onto its shaft is called the "Jesus nut". Because if it comes undone, the next person you meet is Jesus.

 

(I bet this isn't really true. Nick?).

 

MP

I've heard this and love the idea but I suspect it's an urban myth 

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1 hour ago, MoominPapa said:

Another dodgy helicopter fact. The big nut that holds the rotor onto its shaft is called the "Jesus nut". Because if it comes undone, the next person you meet is Jesus.

 

(I bet this isn't really true. Nick?).

 

MP

It can be true if the helicopter has a teetering rotor head, eg Bell 206 jet ranger or Bell UH1  (Huey from the Vietnam war), Bell 212 etc. But larger helicopters with more than 2 blades have an articulated head /hub which doesn’t have a bit nut on top.

Edited by nicknorman
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The Wessex most certainly  did and thus I assume the whole 0 S58 family..  There was a big hydraulic contraption for tightening it up.  Then you had to rig it...

But of course, no helio copeter pilot was  actually expecting to meet Jesus.  They are all headed the other way??.

N

 

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Huzzah! I have version 1 of my new electrical system up and running. This consists of all domestic loads running from my LiFePO4 battery and it being charged by my solar - I've already put 840Wh into them already today which is crazy.

The wiring is a bit of an unholy mess. Before anyone mentions it I do have a board covering the battery terminals, I just removed it for the photo. I will be tidying everything up once the inverter (phase 2) and alternator charging (phase 3) are done.

I'm a little embarassed to share this pic for the rats nest of wires but here it is nonetheless:
 

lifepo.jpg.861f706e8bf966164136d230f0699ae8.jpg

 

 

Now, I equalised the cells before connecting everything up, and Jeremy said they were about 60% charged. But being that I don't have shore power nor a 3.2V battery charger (I have a 12V) I haven't been able to do a top balance. I plan to buy a 3.2V charger and book a night in a marina every few months to do a top balance (if anyone can recommend a 3.2V mains battery charger... that would be great!)

Given that I haven't done the top balance I am wondering if I should be worried about overcharging here, but as I understand it all this will mean is a potential loss in capacity as the charging is limited to the highest voltage cell.

My MPPT has been set to the default LiFePO4 settings (Absorption 14.2V, Float 13.5V). So far the stats on my MPPT are showing a max battery of 13.49V and a min of 13.13V today. I have read that the addition of Yttrium in our Winstons raises the fully charged voltage to 4.0V per cell, so I am not sure if I should be tweaking the MPPT settings. After some deliberation I decided Victron knows better than me.

 

I set the min voltage on my BMS to 3.1V per cell (the most conservative LFP setting it has) - if the voltage drops below this for 35 seconds a relay will shut down the load.


I set the max voltage on my BMS to 3.7V per cell (this is the second least conservative LFP setting it has). I have not wired the MPPT output through the disconnect relay, because I'm scared that if the BMS turns off the charge it's going to damage my MPPT - instead the MPPT is wired directly to the battery (via the isolator though). However, the Uemergency relay will kick in at 0.3V above this - 4.0V - and that will shut down both the MPPT and the load. At 4.0V (up to 16V on the battery) I think I have bigger problems than my MPPT getting damaged!

 

I also have two audible alarms.

 

My BMV712 obviously only detects voltage over the whole battery. It is set to go off for overvoltage at 15.2V (i.e. 3.8V per cell - kept this a bit pessimistic since the cells might be out of balance).  For undervoltage it goes off at 12.4V (i.e. 3.1V per cell, the same voltage at which the BMV is supposed to shut down the load).


My ISDT BG-8S I set a touch lower since it can detect individual cells, but unfortunately this doesn't have an overvoltage alarm (that I can find). The BG-8S is set to go off if any cell drops to 3.0V.

 

I'm waiting with baited breath to see what happens when the battery is "full". If I have all my settings correct, hopefully, the MPPT will shut down the charge before any alarms or any relays go off.

Edited by ivan&alice
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5 minutes ago, ivan&alice said:

Huzzah! I have version 1 of my new electrical system up and running. This consists of all domestic loads running from my LiFePO4 battery and it being charged by my solar - I've already put 840Wh into them already today which is crazy.

The wiring is a bit of an unholy mess. Before anyone mentions it I do have a board covering the battery terminals, I just removed it for the photo. I will be tidying everything up once the inverter (phase 2) and alternator charging (phase 3) are done.

I'm a little embarassed to share this pic for the rats nest of wires but here it is nonetheless:
 

lifepo.jpg.861f706e8bf966164136d230f0699ae8.jpg

 

 

Now, I equalised the cells before connecting everything up, and Jeremy said they were about 60% charged. But being that I don't have shore power nor a 3.2V battery charger (I have a 12V) I haven't been able to do a top balance. I plan to buy a 3.2V charger and book a night in a marina every few months to do a top balance (if anyone can recommend a 3.2V mains battery charger... that would be great!)

Given that I haven't done the top balance I am wondering if I should be worried about overcharging here, but as I understand it all this will mean is a potential loss in capacity as the charging is limited to the highest voltage cell.

My MPPT has been set to the default LiFePO4 settings (Absorption 14.2V, Float 13.5V). So far the stats on my MPPT are showing a max battery of 13.49V and a min of 13.13V today. I have read that the addition of Yttrium in our Winstons raises the fully charged voltage to 4.0V per cell, so I am not sure if I should be tweaking the MPPT settings. After some deliberation I decided Victron knows better than me.

 

I set the min voltage on my BMS to 3.1V per cell (the most conservative LFP setting it has) - if the voltage drops below this for 35 seconds a relay will shut down the load.


I set the max voltage on my BMS to 3.7V per cell (this is the second least conservative LFP setting it has). I have not wired the MPPT output through the disconnect relay, because I'm scared that if the BMS turns off the charge it's going to damage my MPPT - instead the MPPT is wired directly to the battery (via the isolator though). However, the Uemergency relay will kick in at 0.3V above this - 4.0V - and that will shut down both the MPPT and the load. At 4.0V (up to 16V on the battery) I think I have bigger problems than my MPPT getting damaged!

 

I also have two audible alarms.

 

My BMV712 obviously only detects voltage over the whole battery. It is set to go off for overvoltage at 15.2V (i.e. 3.8V per cell - kept this a bit pessimistic since the cells might be out of balance).  For undervoltage it goes off at 12.4V (i.e. 3.1V per cell, the same voltage at which the BMV is supposed to shut down the load).


My ISDT BG-8S I set a touch lower since it can detect individual cells, but unfortunately this doesn't have an overvoltage alarm (that I can find). The BG-8S is set to go off if any cell drops to 3.0V.

 

I'm waiting with baited breath to see what happens when the battery is "full". If I have all my settings correct, hopefully, the MPPT will shut down the charge before any alarms or any relays go off.

The mantra is 80% for a long life! Everyone I know that is using LifePo4s charges to 13.8-9 volts bulk I float at 13.4 which works for me.

The small loss of capacity is more than returned by a long and trouble free balanced life of the batteries 

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41 minutes ago, ivan&alice said:

 

My BMV712 obviously only detects voltage over the whole battery. It is set to go off for overvoltage at 15.2V (i.e. 3.8V per cell - kept this a bit pessimistic since the cells might be out of balance).  For undervoltage it goes off at 12.4V (i.e. 3.1V per cell, the same voltage at which the BMV is supposed to shut down the load).

 

All good but that 15.2V is a bit (lot) high.

If you intend to let them go to 100% (I only do this to balance them and reset the BMV sync) then I woul go a lot lower with the BMV top voltage. If you are charging at 30-40A max then I would be in the low 14.* V. Mine was set to 13.9V  for 80% but that had around 0.2V drop in the line so was really 14.1V. It all depends on what the BMV is going to do when it hits that voltage limit.

I started my balancing by taking power from an individual cell rather than charging it. RIg up a simple circuit with high wattage wire wound resistors - nice and cheap. I did then buy a lab power supply that does 8A at 3.6V but only ever used it once.

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20 minutes ago, Dr Bob said:

All good but that 15.2V is a bit (lot) high.

If you intend to let them go to 100% (I only do this to balance them and reset the BMV sync) then I woul go a lot lower with the BMV top voltage. If you are charging at 30-40A max then I would be in the low 14.* V. Mine was set to 13.9V  for 80% but that had around 0.2V drop in the line so was really 14.1V. It all depends on what the BMV is going to do when it hits that voltage limit.

The BMV is just an overvoltage alarm for the whole battery - IIRC your BMV drives a relay right? 14.1V divided by 4 cells is only 3.525V per cell, which seems too low given that "full" is supposedly 4.0V per cell, right?

I am not sure to what % SoC my MPPT is going to charge the batteries - the default settings on the MPPT for the LiFePO4 are an absorption voltage of 14.2V, float of 13.5V. What does this mean for % SoC?

 

  

20 minutes ago, Dr Bob said:

I started my balancing by taking power from an individual cell rather than charging it. RIg up a simple circuit with high wattage wire wound resistors - nice and cheap. I did then buy a lab power supply that does 8A at 3.6V but only ever used it once.

Won't this only work for bottom balancing though? If you try to top balance like this won't you have to overvoltage on some of the cells in order to come down?

If I can top balance this way, then the nice advantage to this, of course, is that I won't need to buy a charger or use mains!!

 

 

  

21 minutes ago, Dr Bob said:

If you are charging at 30-40A max then I would be in the low 14.* V.

My solar is currently charging at 55A so could be a bit higher than 40A. Also I'm so impressed with my solar yield that I'm strongly considering putting another 2 panels in series (taking my VOC up to 240V, which is the limit of my MPPT) so I could be charging at up to 100A in the future just from solar.

 

 

Edited by ivan&alice
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I have been keeping an eye on the voltage and it just reached 14.1V. One of the cells was almost at 3.9V so I decided to trip the breaker switch on the solar input (so glad I installed this). I've seen a record yield of 1.7kWh before I pulled the plug. 

 

After 15mins or so, the voltages have subsided a bit. My BG-8S is reporting the cells as follows:

 

1. 3.331V

2. 3.337V

3. 3.418V (this is the cell that almost reached 3.9

4. 3.321V

 

Cell 3 is clearly horribly out of balance. So I think I should at least "mid-balance" this cell down to 3.3ish volts - do you think I could use a 12V immersion heating element (in a bucket of water) for this purpose?

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9 minutes ago, ivan&alice said:

I have been keeping an eye on the voltage and it just reached 14.1V. One of the cells was almost at 3.9V so I decided to trip the breaker switch on the solar input (so glad I installed this). I've seen a record yield of 1.7kWh before I pulled the plug. 

 

After 15mins or so, the voltages have subsided a bit. My BG-8S is reporting the cells as follows:

 

1. 3.331V

2. 3.337V

3. 3.418V (this is the cell that almost reached 3.9

4. 3.321V

 

Cell 3 is clearly horribly out of balance. So I think I should at least "mid-balance" this cell down to 3.3ish volts - do you think I could use a 12V immersion heating element (in a bucket of water) for this purpose?

Yes, its a resistive load so will work just monitor closely, I though you had a BMS?

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1 minute ago, peterboat said:

Yes, its a resistive load so will work just monitor closely, I though you had a BMS?

Thanks, I will give this a try later today.

Depends what you mean by "BMS"! I have stopped using that term altogether. I have a cell monitoring board, which shuts down the load if any cell goes down to 3.1V (i.e. minimum of 12.4V for the battery). I am not using the overvoltage protect for the solar - because I don't want to damage my MPPT by abruptly disconnecting the battery. The board will shut down both load and MPPT if any cell reaches 4.0V.

 

This board does not do any active balancing, if that's what you're referring to. The BG-8S does have a balance function so I have flipped that on to see what happens, it does seem to have helped a little but given the size of my bank it seems unlikely that it's going to balance anything in my lifetime.

I think what's more important is that I adjust my MPPT charge voltage down (at least for now). What settings do you guys use for your solar charging of your LiFePOs?

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3 minutes ago, ivan&alice said:

Thanks, I will give this a try later today.

Depends what you mean by "BMS"! I have stopped using that term altogether. I have a cell monitoring board, which shuts down the load if any cell goes down to 3.1V (i.e. minimum of 12.4V for the battery). I am not using the overvoltage protect for the solar - because I don't want to damage my MPPT by abruptly disconnecting the battery. The board will shut down both load and MPPT if any cell reaches 4.0V.

 

This board does not do any active balancing, if that's what you're referring to. The BG-8S does have a balance function so I have flipped that on to see what happens, it does seem to have helped a little but given the size of my bank it seems unlikely that it's going to balance anything in my lifetime.

I think what's more important is that I adjust my MPPT charge voltage down (at least for now). What settings do you guys use for your solar charging of your LiFePOs?

13.9 bulk, 13.8 absorb and 13.4 float same in my electric truck  it allows for a bit of wander without a chance of doing damage.

Could you not put the cut off on the solar side of the controller? No date to it or the panels if something goes wrong 

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20 minutes ago, peterboat said:

Could you not put the cut off on the solar side of the controller? No date to it or the panels if something goes wrong 

That's a pretty good idea, and it did cross my mind. I would need to get a bistable relay that would be happy with the 160V (and possibly 240V) that is on the solar side.

But also, I will want to use the overvoltage relay for protection against my alternator, so I don't want to use that circuit for the PV because it will need to change in future.

 

24 minutes ago, peterboat said:

13.9 bulk, 13.8 absorb and 13.4 float

I can only seem to set Absorption and Float voltages - I'm not sure what "re-bulk voltage offset" is.

 

Would you recommend then that I change to 13.8 absorb and 13.4 float then? Remember I have the Winston Thundersky LiFeYPO4s from Jeremy, I gather these run at a little higher voltage than other LFP chemistries.

 

image.png.abaa204dbb43bd44a66259ed883ec988.png

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2 hours ago, ivan&alice said:

I have been keeping an eye on the voltage and it just reached 14.1V. One of the cells was almost at 3.9V so I decided to trip the breaker switch on the solar input (so glad I installed this). I've seen a record yield of 1.7kWh before I pulled the plug. 

 

After 15mins or so, the voltages have subsided a bit. My BG-8S is reporting the cells as follows:

 

1. 3.331V

2. 3.337V

3. 3.418V (this is the cell that almost reached 3.9

4. 3.321V

 

Cell 3 is clearly horribly out of balance. So I think I should at least "mid-balance" this cell down to 3.3ish volts - do you think I could use a 12V immersion heating element (in a bucket of water) for this purpose?

If your cell 3 reached 3.9V then you dont have the right settings for you BMS.

When any cell reaches 3.5V and you are charging at 30-40A (and certainly over), you need to be watching cell voltages by the minute.

 Take power out of cell 3. Maybe aim to get 10Ahrs out first then charge the whole bank again and watch the cell voltages. Repeat until cell 3 is not the highest cell.

To get 10Ahr out, you will need something that draws 10A at 3.3V. Not easy. I didnt think you could do it with a 12V element when I tried to do the sums. I built my own resistor circuit. My highest cell was 3.6V when the others were just getting to 3.4V and I had to take 20Ahrs out of the high cell to get it to balance. It took me around 4-5 hours.

As you charge, record the cell voltages every 5mins then every 1 min as they get to 100%.

Once you have finished your balancing, I would set the bulk voltage to 13.8 or 13.9V to keep safe.

The balancing circuit in the BG8S will be useless. It will do a max of 100ma - and only if cell voltage is high. You are looking at taking out 10A. You dont want to keep your cells at those high voltages for days on end.

Forget the yttrium in the cells. I have exactly the same cells as you and 13.9V is my limit. Never go over it.

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