Cheap LiFePO4 BMS?

[cuthound]

16 hours ago, nicknorman said:

The advantage of not including the MPPT is that some folk like to open their battery isolator when they leave the boat, to ensure they haven’t left anything on and I suppose for a slight element of safety (everything is disconnected). But by leaving the MPPT connected it means the batteries continue to be charged / kept topped up by the solar. Also eliminates the risk of damage to the MPPT from disconnecting the batteries when the MPPT is producing current.

I don’t see any advantage is a double pole isolator - each pole represents potential voltage drop and unreliability, so you have doubled both those!

 

I agree, in my previous career double pole isolators were used to stop the backfeeds on the neutral of the mains equipment caused by harmonics.  None of which apply to a DC circuit.

[jetzi]

13 hours ago, peterboat said:

That breaker is a bit large! 

I matched the breaker to my MPPT which is a 250V / 100A Victron SmartSolar. It's really an off switch rather than a breaker. I shan't be seeing current like that, I know, but I wanted to overspec it in case I add more panels.

 

2 hours ago, nicknorman said:

Bear in mind that the relay coil takes about 3A DC so you need push switches that can cope with that current. The last thing you want is for the contacts to weld themselves closed! I also notice that the Tyco has built in freewheel diodes which is great for protecting the buttons, but it also means each coil is polarity sensitive. If you get + and - the wrong way round, something will melt!

Thanks for the tip. I found it next to impossible to find momentary push switches that were rated in DC. I bought some that were rated in AC 3A 250V, AC 6A 125V. I know that DC is more onerous on the terminals - these might not be sufficient, I'll test them well before I install them as part of the system. Alternatively I'll can the idea.

[peterboat]

1 hour ago, ivan&alice said:

I matched the breaker to my MPPT which is a 250V / 100A Victron SmartSolar. It's really an off switch rather than a breaker. I shan't be seeing current like that, I know, but I wanted to overspec it in case I add more panels.

 

Thanks for the tip. I found it next to impossible to find momentary push switches that were rated in DC. I bought some that were rated in AC 3A 250V, AC 6A 125V. I know that DC is more onerous on the terminals - these might not be sufficient, I'll test them well before I install them as part of the system. Alternatively I'll can the idea.

The reason why I said it was mine has tripped which stopped the MPPT controller getting fried beyond the 3 fets, the controller is on it's way back from Spain along with a surge protector to stop it happening again. The first I knew about the problem was when I saw the breaker had tripped and would not reset 

[TheBiscuits]

On 25/05/2020 at 13:58, cuthound said:

 

I agree, in my previous career double pole isolators were used to stop the backfeeds on the neutral of the mains equipment caused by harmonics.  None of which apply to a DC circuit.

 

Wanna bet?

 

 

[nicknorman]

Snuck down to the boat to trial my alternator controller V2. Happy to say all instability issues resolved, I think it was a dodgy ground connection before (caused by Beta painting everything including the alternator B- stud!). Having set the switch to 100% SoC I was chuffed to see the regulated voltage drop from 14.4 to 13.5 when the Mastershunt SoC reading hit 100%.

 

One thing that is really noticeable is that the regulation is much “harder” than a normal analogue regulator. It holds 100% field current until the system voltage is very close to the regulated voltage, unlike an analogue one where the current starts to taper off 1/2 volt or more below the regulated voltage. The joys of a digital control loop!

 

When I’d connected it all up after lunch and with the SoC at about 85%, on starting the engine I got about 180A going into the batteries, which are still the Trojans (field current at 100%) and generally a much faster charge that with the alternator’s native regulator Because the battery voltage was being held at 14.4v and with battery sensing, rather than slowly creeping up to it and with machine sensing,

 

Which of course is good and bad, the bad being alternator cooking territory! But with the ability to set the max field current to say 50%, the beast can be tamed!

 

Circuit board v3 arrived back from China on Saturday but I didn’t have time to populate it yet. It adds the switch for slow or fast charge (limiting the field current, or not) and the interface for BMV battery monitor. I feel I am close to being able to permanently install the prototype, just need to mount the v3 board in a box! And the oled display will be nice.

Edited June 9, 2020 by nicknorman

[MoominPapa]

1 hour ago, nicknorman said:

One thing that is really noticeable is that the regulation is much “harder” than a normal analogue regulator. It holds 100% field current until the system voltage is very close to the regulated voltage, unlike an analogue one where the current starts to taper off 1/2 volt or more below the regulated voltage. The joys of a digital control loop!

I suspect that one of the reasons for the softer transfer function in an analogue regulator or to avoid instability - with a sharp edge, when the voltage limit is reached, the current drops and therefore the voltage does, so the current increases again, and oscillation occurs. A digital system can do better filtering and keep stability partly because is can retain state and implement hysteresis.

 

MP.

 

[Dr Bob]

10 hours ago, nicknorman said:

Snuck down to the boat to trial my alternator controller V2. Happy to say all instability issues resolved, I think it was a dodgy ground connection before (caused by Beta painting everything including the alternator B- stud!). Having set the switch to 100% SoC I was chuffed to see the regulated voltage drop from 14.4 to 13.5 when the Mastershunt SoC reading hit 100%.

 

One thing that is really noticeable is that the regulation is much “harder” than a normal analogue regulator. It holds 100% field current until the system voltage is very close to the regulated voltage, unlike an analogue one where the current starts to taper off 1/2 volt or more below the regulated voltage. The joys of a digital control loop!

 

When I’d connected it all up after lunch and with the SoC at about 85%, on starting the engine I got about 180A going into the batteries, which are still the Trojans (field current at 100%) and generally a much faster charge that with the alternator’s native regulator Because the battery voltage was being held at 14.4v and with battery sensing, rather than slowly creeping up to it and with machine sensing,

 

Which of course is good and bad, the bad being alternator cooking territory! But with the ability to set the max field current to say 50%, the beast can be tamed!

 

Circuit board v3 arrived back from China on Saturday but I didn’t have time to populate it yet. It adds the switch for slow or fast charge (limiting the field current, or not) and the interface for BMV battery monitor. I feel I am close to being able to permanently install the prototype, just need to mount the v3 board in a box! And the oled display will be nice.

Great progress, Nick.

How long did it take to get from 85 to 100% and how hot did the alternator get? I guess it must have been a while as the reducing tail current dug in......but then the alternator would have cooled?

Whats the plan to put some Lithiums on?

[nicknorman]

40 minutes ago, Dr Bob said:

Great progress, Nick.

How long did it take to get from 85 to 100% and how hot did the alternator get? I guess it must have been a while as the reducing tail current dug in......but then the alternator would have cooled?

Whats the plan to put some Lithiums on?

As always the last 5% took a long while, but it seemed much quicker between 85 and 95%

 

i haven’t mounted the temperature probe yet. There are a couple of issues to resolve, one being that I’m temporarily using the same digital sensor that I used on my glider project, it’s a little transistor shaped thing which I’ve encapsulated using heat shrink and glue from a hot glue gun, which melts at about 70C! I’ll need to assemble something using some higher temperature glue, silicone maybe.

 

And secondly the max permitted temperature for the device is 125C. We don’t want to run our alternators that hot, but it occurs to me that if I mount it directly on or just above the alternator, even if the outside of the alternator is say 90C, if the engine is stopped (hence no more alternator fan) the residual heat inside the bulk of the alternator is likely to exceed 125C which may damage the device. I therefore intend to mount the sensor so it is measuring the air temperature of the expelled cooling air, rather than the case temperature. Anyway, first step is to not use thermal glue!

 

What is good about the regulation curve is that when the microprocessor sends a target voltage, the regulator does its damnest to try to achieve it, unlike a conventional alternator whose regulator is vague and wooly. In other words, it can be precisely controlled.

 

i did mention getting some Lithiums to Jeff. He said “want do we need those for, their’s nothing wrong with the Trojans?”. And he is of course correct, but being a supportive husband once I’d explained he was encouraging me to get them. I’ll probably order some from China fairly soon, so as to get them before we leave the EU. Until I’ve got them I can’t really check out the integration between my BMS and alternator controller.

 

We will have a technical problem which is that the boat has tended to fly a bit left wing low since most of the storage is on the left. Now I am proposing to remove some heavy LA batteries and replace them with Li which are a fraction of the mass. And yes, the batteries live on the right! I’ll have to find some lead ballast or some such.

Edited June 10, 2020 by nicknorman

[nicknorman]

10 hours ago, MoominPapa said:

I suspect that one of the reasons for the softer transfer function in an analogue regulator or to avoid instability - with a sharp edge, when the voltage limit is reached, the current drops and therefore the voltage does, so the current increases again, and oscillation occurs. A digital system can do better filtering and keep stability partly because is can retain state and implement hysteresis.

 

MP.

 

Yes absolutely. In my helicopter career I flew the Super Puma Mk1, the Mk2 and the EC225 which was effectively the mk3.

 

Obviously regulating (governing) the rotor rpm of a helicopter is a critical thing, and not a simple control loop because to increase the engine power in response to an increased aerodynamic load, you have to spool up the gas turbines, which takes a while and has a very non-linear acceleration curve (very slow coming off idle, very fast near max rpm). And of course with a gas turbine, you can’t simply stuff lots of fuel in or take the fuel away - the former causes stalling and surging and melts the combustion chamber, the latter makes the flame go out. Ooops! You have to progressively increase or decrease the fuel, co-ordinated with the current turbine speed.

 

In the Mk1 this was handled by a hydromechanical engine control unit that controlled fuel flow, plus some simple analogue electronics to compare actual rotor rpm with desired rotor rpm and output a difference voltage to the hydromechanical unit, and to try to compensate for the very soft regulation. Then in the Mk2 the analogue electronics was replaced with digital, but still with a hydromechanical fuel control unit. The digital bit had virtually the same transfer function as the analogue had.

 

Both these suffered from a lot of “static droop” by which I mean a significant reduction in stabilised governed rotor rpm with a lot of aerodynamic load (collective control well up) vs that with little load. This was compensated for by a potentiometer on the collective that increased the datum rotor rpm as the collective was raised. All this meant that there was quite a big variation in rotor rpm with collective position. This “static droop” equates to the tailing off of alternator current long before regulated voltage is reached.

 

Then on the EC225 everything was digital, there was no hydromechanical fuel control unit, just a fuel metering valve controlled by a stepper motor. Rotor rpm was absolutely precise, 100% in the cruise regardless of max power or idle power. Not 100.5 or 99.5, but absolutely exactly 100%. Amazing to have such precise control without a hint of overshoot or instability. That is the power of digital control loops!

Edited June 10, 2020 by nicknorman

[MoominPapa]

3 hours ago, nicknorman said:

Then on the EC225 everything was digital, there was no hydromechanical fuel control unit, just a fuel metering valve controlled by a stepper motor. Rotor rpm was absolutely precise, 100% in the cruise regardless of max power or idle power. Not 100.5 or 99.5, but absolutely exactly 100%. Amazing to have such precise control without a hint of overshoot or instability. That is the power of digital control loops!

Indeed. Thanks for the interesting explanation. Out of interest, how fast does the control loop have to react? What's the ratio of steady-state rotor power to rotational kinetic energy of the rotor? If it takes 30s for the rotor to spin down at high collective (I assume that's large blade AOA and therefore large air-load?) then that's much easier to handle than  if it takes 5s.

 

MP.

 

 

[WotEver]

I used to spend a lot of time at Redhill Aerodrome in my youth, and it was the home of Bristows Helicopters. I recall one occasion where they wheeled a Jet Ranger out of the workshop and after running up the engines for a while started low-level manoeuvres at about 6ft off the ground. Suddenly there was a very large bang, followed by the helicopter sitting on the ground with a small cloud of smoke above it. I would imagine the pilot then had to go and change his trousers. At a guess I’d say one of the turbine fans broke up. 
 

 

Edited June 10, 2020 by WotEver
Add the last bit

[BEngo]

Cannot speak about the Puma, but if you lost the engine in either a Wasp or the Wessex Mk1 or Mk3 regardless of the rotor load, you needed to get the (collective pitch)  lever down damn quick or your rotor speed was gone, and not coming back.  Much less than 30 seconds to play with, probably about 2 or 3 seconds max.  Twin engined helos were much less demanding, depending on the mass and where you were.  Heavy, hovering at 40 ft over the water in a Seaking you needed to be wide awake if you lost one engine and wanted to fly away rather than ditch.

 

In normal operation, with a smooth pilot the  governor could keep up, but ham-fistedness would easily  produce  rotor speed droop and over torque warning noises in the earphones, both in single engine and two engine helicopters. 

 

 It is also possible to over pitch a helicopter  rotor, causing its drag, and hence power wants, to be greater than either the engine(s) can give or the gearbox can handle.  That is a fairly easy governor task though.

 

N

 

[nicknorman]

2 hours ago, MoominPapa said:

Indeed. Thanks for the interesting explanation. Out of interest, how fast does the control loop have to react? What's the ratio of steady-state rotor power to rotational kinetic energy of the rotor? If it takes 30s for the rotor to spin down at high collective (I assume that's large blade AOA and therefore large air-load?) then that's much easier to handle than  if it takes 5s.

 

MP.

The Super Puma family all had composite blades so very low inertia. If there was a double engine failure in the cruise, or second engine failure following the failure of the first, you had about 1.5 seconds to dump the collective otherwise the rotor rpm was unrecoverably low. It probably decayed at about 20% per second. But of course that was an extreme change from cruise power to zero power.

 

Although there are modest changes in power demand created by aerodynamic effects, moving the cyclic, turbulence etc, the greatest source of large power demands was pilot-initiated, ie operating the yaw pedals and in particular the collective. So it was second nature for pilots to try to make these control inputs in a smooth and progressive way, not least because those controls were very powerful - think of a difference between not much lift with the collective right down on the ground, vs 11 tonnes of lift with the collective 2/3rds of the way up.

 

The biggest limitation was the engine acceleration speed. The later engines were remarkably fast to spool up, under a second to go from cruise power to full power, but the old engines eg the Turmo on the original 1970s Puma, took 8 seconds to go from idle to full power. 8 seconds is a long time when the ground is rapidly approaching!

 

So I think it is fair to say that unless you moved the collective faster than the engine could be accelerated or decelerated (which was quite fast in the EC225) the rotor rpm remained pegged on its datum value. There was no additional lag, and certainly no overshoot, created by the control loop.

 

On the Super Puma mk1 there was an acceleration test which was carried out eg following and engine change, that was collective right down on the ground, to hovering, in 3 seconds (hovering in a helicopter uses much the same amount of power as fast cruise). The mk1 would have a little rpm droop during that process (mostly arising from slow acceleration at low engine rpm) but the 225 could do that without breaking a sweat. Zero overshoot.

 

[nicknorman]

1 hour ago, WotEver said:

I used to spend a lot of time at Redhill Aerodrome in my youth, and it was the home of Bristows Helicopters. I recall one occasion where they wheeled a Jet Ranger out of the workshop and after running up the engines for a while started low-level manoeuvres at about 6ft off the ground. Suddenly there was a very large bang, followed by the helicopter sitting on the ground with a small cloud of smoke above it. I would imagine the pilot then had to go and change his trousers. At a guess I’d say one of the turbine fans broke up. 
 

Well some sort of engine failure anyway!  The jet ranger had metal blades and a huge amount of rotor inertia so it was very forgiving in situations like that. It was said that you could do an engine off landing, lift back into the hover and yaw 90degress, settle back on the ground all before running out of rotor rpm.

 

I did my training at Redhill in 1980, on the Bell 47.

[nicknorman]

23 minutes ago, BEngo said:

Cannot speak about the Puma, but if you lost the engine in either a Wasp or the Wessex Mk1 or Mk3 regardless of the rotor load, you needed to get the (collective pitch)  lever down damn quick or your rotor speed was gone, and not coming back.  Much less than 30 seconds to play with, probably about 2 or 3 seconds max.  Twin engined helos were much less demanding, depending on the mass and where you were.  Heavy, hovering at 40 ft over the water in a Seaking you needed to be wide awake if you lost one engine and wanted to fly away rather than ditch.

 

In normal operation, with a smooth pilot the  governor could keep up, but ham-fistedness would easily  produce  rotor speed droop and over torque warning noises in the earphones, both in single engine and two engine helicopters. 

 

 It is also possible to over pitch a helicopter  rotor, causing its drag, and hence power wants, to be greater than either the engine(s) can give or the gearbox can handle.  That is a fairly easy governor task though.

 

N

 

The sea king I’m guessing was similar to the S61 in that you had “speed select” levers on the overhead panel, with which the pilot not flying could adjust the target rotor rpm to allow for the “static droop” I’ve been talking about. So you would push them forward a bit as the pilot lifted into the hover to set the hover rotor rpm (whatever that was) and tweak them differentially a bit to match the engine powers. Old fashioned hydromechanical fuel control unit!

[WotEver]

10 minutes ago, nicknorman said:

I did my training at Redhill in 1980

A few years after my time there. Was The Tiger Club still present at that time or had they moved to Shoreham by then?

[peterboat]

Reading all the above does make me wonder about the sorties carried out in NI in Pumas at very high speed and low altitude!

[nicknorman]

6 minutes ago, WotEver said:

A few years after my time there. Was The Tiger Club still present at that time or had they moved to Shoreham by then?

Yes they were still there, next door hangar I seem to recall.

[nicknorman]

5 minutes ago, peterboat said:

Reading all the above does make me wonder about the sorties carried out in NI in Pumas at very high speed and low altitude!

Ah yes but speed is your friend, you can convert speed into height (using the cyclic) and into rotor rpm (also using the cyclic). Low and slow is dangerous (but not if you are so low that it’s not far to flop onto the ground). Hence the “avoid curve”  (aka HV) graph in helicopter flight manuals which identifies a speed / height zone from which recovery from complete power loss isn’t possible (well, not without breaking it anyway).
http://www.copters.com/pilot/hvcurve.html

 

Low and fast only carries the risk of hitting something you hadn’t noticed.

 

Edited June 10, 2020 by nicknorman

[WotEver]

2 minutes ago, nicknorman said:

Yes they were still there, next door hangar I seem to recall.

Across the field iirc. First hangar on the left when you entered, and Bristows were on the far side. I did well over 100 (passenger) hours on Stampes and Tigers over the few years I was active there. My brother-in-law was club secretary. 

[nicknorman]

On 10/06/2020 at 08:30, Dr Bob said:

Great progress, Nick.

How long did it take to get from 85 to 100% and how hot did the alternator get? I guess it must have been a while as the reducing tail current dug in......but then the alternator would have cooled?

Whats the plan to put some Lithiums on?

Today I've been looking at temperatures. First issue is that after cruising for most of the day, the ambient temperature in the engine bay near the alternator is 40C, and that is with fairly low ambient temperatures and canal water temperature. So it is about 25C above ambient and that is with the engine running at canal speeds, not tidal river speeds! The engine is under boards at the back (trad stern) but it does have two hooded vents at the back, plus a vent into the engine room (ie the space above the boards) and is ultimately connected to the bilge / cabin under floor area), that also having hooded vents at the front.

So in terms of keeping the alternator cool, I really need to try to lower the engine bay temperature eg by having forced extraction from one of the external vents. Something I've been thinking about for a while, but I lost the necessary round tuit. And batteries are in that zone too, they can get pretty warm eg 35C.

 

Bearing in mind the maximum possible field current is just over 4A (field connected directly to battery+), today I set the max permitted field current to 3A. This means that the maximum output varies quite a bit with rpm at low rpm but at canal cruising rpm it could put out about 130A. After the batteries had fully charged and with the engine bay still hot, I put the 2kw electric kettle on to fully load the alternator via the inverter. I poked the temperature probe nearly inside the alternator cooling air outlets (being careful not to poke it into the fan!). The alternator is a double fan model, and the exit to the front fan didn't seem to get that hot, around 60C. However the exit from the rear fan (which takes in air past the diodes (and regulator, if there was one!) and on to the rear part of the windings, got up to about 90C.

 

Unfortunately I didn't bring my infrequent red thermometer so I couldn't test the casing temperature. It was certainly hot but definitely not over 100C, more like 80 I'd say.

 

So I take from that that the 175A alternator can probably run at 75% of its output without much exceeding 90C, and if I could get the engine bay ambient temperature down a bit that would help on hot days.

 

With the engine bay starting cold I think it could run at 100% output for say 1/2 hr without breaking into much of a sweat, that could put in 85Ah or so into Li batteries, then it might need to be throttled down a bit for any more charge, to say the 130A. Which is still a pretty fast charge, putting a day's worth of usage back in in around an hour.

 

 

Edited June 11, 2020 by nicknorman

[Keeping Up]

On our boat (cruiser stern) it made a huge difference when I installed a bilge-blower fan to take air in from outside and blow it into the engine bay near the alternator

[nicknorman]

4 minutes ago, Keeping Up said:

On our boat (cruiser stern) it made a huge difference when I installed a bilge-blower fan to take air in from outside and blow it into the engine bay near the alternator

Yes I need to do something like that, however I think mine needs to pull air from the engine bay into the outside. This will of course suck outside air in from the other vents. I think if I pumped outside air in, there would be some leakage of the slightly pressurised air that could result in engine bay air (and fumes, oily smells etc) getting into the engine room which is living space.

[nicknorman]

So next question - axial or centrifugal  bilge blower? I am inclined to think centrifugal because that is better at elevating pressure and the hooded vent that I propose to use as the air exhaust, doesn't have a particularly large x-sectional area. In other words I suspect the centrifugal might be better for forcing air out through the restricted vent. But I am just guessing!

[Keeping Up]

Just now, nicknorman said:

So next question - axial or centrifugal  bilge blower? I am inclined to think centrifugal because that is better at elevating pressure and the hooded vent that I propose to use as the air exhaust, doesn't have a particularly large x-sectional area. In other words I suspect the centrifugal might be better for forcing air out through the restricted vent. But I am just guessing!

No idea, I had a spare hole to use when I had the exhaust moved from one side to the other, and the bilge blower fitted with some trunking was perfect for it. It comes on with the ignition so I totally ignore it, and it made more than 10-15 degrees difference. Probably even better because it's directed at the alternator. Somehow I just don't instinctively feel that sucking is as effective as blowing - but I take yuor point about fumes etc; even with the cruiser stern there is a slight leakage through the electrical ducts etc into the rear cabin.