Cheap LiFePO4 BMS?

[nicknorman]

Hardware Version 3 of my alternator controller now installed “properly”. It has an OLED display (why not, they are under £4!).

 

3 screens showing:

Charge rate, mode (ie charge or float), target and actual SoC

Actual field (rotor) current and current limit, set and actual voltage

Alternator Rpm, battery current, alternator temperature and SoC (again)

 

Also added a galvanically isolated interface for VE-Direct ie to a BMV 700 series monitor (not tested because I don’t have a BMV battery monitor yet!). I ditched the emergency field isolation relay as not needed due to several layers of other protections.

 

Unfortunately in a rush to cut the aperture for the display in the lid of the box - hand held dremmel - so that looks pretty bad! 

 

On top are the two switches, one for charge rate (slow or fast) which limits the field current to about 1/2, or not. The other switch to select the SoC at which it goes to float voltage (50%, 80% or 100%).

 

The actual SoC of course is coming from the Mastershunt over CANbus, ditto the battery current (I_Bat on the display). The latter has a lot of smoothing (long time constant) done within the Mastershunt, so when you see the I_bat parameter winding up or down fairly slowly it is “lying”. Unfortunately nothing I can do about that.

 

In order for me to be allowed to fit it, Jeff says it must have personality hence the startup message...

 

First video is me starting the engine with the rate switch set to slow. Gives around 85A. Then I flick the switch to fast and you can see the field current ramping up to 4A (nearly maximum) fairly slowly, under the influence of the LRC (Load Response Control). If it snapped straight up to 4A there would be a big mechanical shock load. Battery charge current goes up to 175A and more, with the field current pegged at max even though the actual voltage is only 0.3v below target. It fair rams the current in - with the conventional regulator I would have been getting 120A and falling rapidly.

 

Second video taken shortly afterwards shows the actual SoC reaching the target SoC and it switching to float mode (13.3v for the time being). I’d set it to 80% just to prove it works, obviously this switch is only useful for Li batteries, for the time being with our lead acid batteries I’ll always want it on 100%.

 

 

 

 

 

 

[peterboat]

31 minutes ago, nicknorman said:

Hardware Version 3 of my alternator controller now installed “properly”. It has an OLED display (why not, they are under £4!).

 

3 screens showing:

Charge rate, mode (ie charge or float), target and actual SoC

Actual field (rotor) current and current limit, set and actual voltage

Alternator Rpm, battery current, alternator temperature and SoC (again)

 

Also added a galvanically isolated interface for VE-Direct ie to a BMV 700 series monitor (not tested because I don’t have a BMV battery monitor yet!). I ditched the emergency field isolation relay as not needed due to several layers of other protections.

 

Unfortunately in a rush to cut the aperture for the display in the lid of the box - hand held dremmel - so that looks pretty bad! 

 

On top are the two switches, one for charge rate (slow or fast) which limits the field current to about 1/2, or not. The other switch to select the SoC at which it goes to float voltage (50%, 80% or 100%).

 

The actual SoC of course is coming from the Mastershunt over CANbus, ditto the battery current (I_Bat on the display). The latter has a lot of smoothing (long time constant) done within the Mastershunt, so when you see the I_bat parameter winding up or down fairly slowly it is “lying”. Unfortunately nothing I can do about that.

 

In order for me to be allowed to fit it, Jeff says it must have personality hence the startup message...

 

First video is me starting the engine with the rate switch set to slow. Gives around 85A. Then I flick the switch to fast and you can see the field current ramping up to 4A (nearly maximum) fairly slowly, under the influence of the LRC (Load Response Control). If it snapped straight up to 4A there would be a big mechanical shock load. Battery charge current goes up to 175A and more, with the field current pegged at max even though the actual voltage is only 0.3v below target. It fair rams the current in - with the conventional regulator I would have been getting 120A and falling rapidly.

 

Second video taken shortly afterwards shows the actual SoC reaching the target SoC and it switching to float mode (13.3v for the time being). I’d set it to 80% just to prove it works, obviously this switch is only useful for Li batteries, for the time being with our lead acid batteries I’ll always want it on 100%.

 

 

 

 

 

 

Very good nick shame about the tractor being parked next to you  ?

[cuthound]

33 minutes ago, nicknorman said:

Hardware Version 3 of my alternator controller now installed “properly”. It has an OLED display (why not, they are under £4!).

 

3 screens showing:

Charge rate, mode (ie charge or float), target and actual SoC

Actual field (rotor) current and current limit, set and actual voltage

Alternator Rpm, battery current, alternator temperature and SoC (again)

 

Also added a galvanically isolated interface for VE-Direct ie to a BMV 700 series monitor (not tested because I don’t have a BMV battery monitor yet!). I ditched the emergency field isolation relay as not needed due to several layers of other protections.

 

Unfortunately in a rush to cut the aperture for the display in the lid of the box - hand held dremmel - so that looks pretty bad! 

 

On top are the two switches, one for charge rate (slow or fast) which limits the field current to about 1/2, or not. The other switch to select the SoC at which it goes to float voltage (50%, 80% or 100%).

 

The actual SoC of course is coming from the Mastershunt over CANbus, ditto the battery current (I_Bat on the display). The latter has a lot of smoothing (long time constant) done within the Mastershunt, so when you see the I_bat parameter winding up or down fairly slowly it is “lying”. Unfortunately nothing I can do about that.

 

In order for me to be allowed to fit it, Jeff says it must have personality hence the startup message...

 

First video is me starting the engine with the rate switch set to slow. Gives around 85A. Then I flick the switch to fast and you can see the field current ramping up to 4A (nearly maximum) fairly slowly, under the influence of the LRC (Load Response Control). If it snapped straight up to 4A there would be a big mechanical shock load. Battery charge current goes up to 175A and more, with the field current pegged at max even though the actual voltage is only 0.3v below target. It fair rams the current in - with the conventional regulator I would have been getting 120A and falling rapidly.

 

Second video taken shortly afterwards shows the actual SoC reaching the target SoC and it switching to float mode (13.3v for the time being). I’d set it to 80% just to prove it works, obviously this switch is only useful for Li batteries, for the time being with our lead acid batteries I’ll always want it on 100%.

 

 

 

 

 

 

 

Hopefully the 4800rpm displayed is the alternator speed and not your engine tickover speed? ???

[peterboat]

1 minute ago, cuthound said:

 

Hopefully the 4800rpm displayed is the alternator speed and not your engine tickover speed? ???

No its the tractor parked next to him 

[nicknorman]

2 minutes ago, peterboat said:

Very good nick shame about the tractor being parked next to you  ?

Well it is a kubota!

[peterboat]

Just now, nicknorman said:

Well it is a kubota!

Probably the best industrial engine in the world 

[nicknorman]

2 minutes ago, cuthound said:

 

Hopefully the 4800rpm displayed is the alternator speed and not your engine tickover speed? ???

Yes! Although you’ve reminded me that the chip is set up for a 5 pole alternator and mine is 6 pole, so I need to multiply the rpm by 5/6

[Dr Bob]

39 minutes ago, nicknorman said:

Yes! Although you’ve reminded me that the chip is set up for a 5 pole alternator and mine is 6 pole, so I need to multiply the rpm by 5/6

Well done Nick. This looks really good.

[nicknorman]

It’s interesting to be able to observe the field current. Maximum field current being limited by the resistance of the rotor, is about 4.2A on my alternator when it’s cool. I was playing with things yesterday with hot engine bay (fast cruising on the Severn) and with the tumble drier on (2kw) with the Travelpower turned off, so the 2kw was being supplied from the alternator via inverter. Very quickly I noticed that although the duty cycle was 100% (ie rotor effectively connected across the supply) the rotor current was now only about 3.5A. Presumably due to the temperature coefficient of the resistance of the windings. So that seems to be a “self regulation” mechanism whereby the alternator output is naturally reduced as it heats up, due to increased rotor resistance.

Edited July 17, 2020 by nicknorman

[Dr Bob]

29 minutes ago, nicknorman said:

It’s interesting to be able to observe the field current. Maximum field current being limited by the resistance of the rotor, is about 4.2A on my alternator when it’s cool. I was playing with things yesterday with hot engine bay (fast cruising on the Severn) and with the tumble drier on (2kw) with the Travelpower turned off, so the 2kw was being supplied from the alternator via inverter. Very quickly I noticed that although the duty cycle was 100% (ie rotor effectively connected across the supply) the rotor current was now only about 3.5A. Presumably due to the temperature coefficient of the resistance of the windings. So that seems to be a “self regulation” mechanism whereby the alternator output is naturally reduced as it heats up, due to increased rotor resistance.

That's useful info Nick. 

What was the difference in Amps out of the alternator and what sort of temperature were you seeing on the alternator?

[nicknorman]

4 minutes ago, Dr Bob said:

That's useful info Nick. 

What was the difference in Amps out of the alternator and what sort of temperature were you seeing on the alternator?

Difficult to be precise because I don’t have a direct measure of alternator output. I can see current in/out of batteries and in/ out of Combi, but not what is going into the boat. That said, even with the fridge on and various phones / iPads plugged into 12v charging points, I doubt the latter would be more than 5 - 10A during the day. With that caveat I’d say the max output, which is actually 185A or so when cold, was down to about 165A. Of course there isn’t a linear relationship between rotor current and magnetic field, especially as saturation of the iron core is approached.
 

As to temperature, the question is, temperature where? The alternator has 2 fans, one just cools the windings and one pulls air past the diodes etc and also cools the other side of the windings. I’ve mounted the sensor in the exhaust flow from the latter fan with the assumption that the semiconductors are the weak point. That one was at around 85C but climbing. I didn’t want to leave it on too long and anyway if it got to 90C my regulator would switch to “hot” mode and halve the field current. I did remember to bring my infrequent red thermometer and I could see 125C or so on the other end. That may sound hot but it’s just copper, so not that hot really especially if you recall that the alternator spec allows for an AMBIENT temperature of up to 100C.

 

The other consideration is that we were running the engine at 1600 rpm on the river, as opposed to the more normal 1300 that it would be on canals, and that of course improves the throughput of cooling air.
 

Engine bay temperature was 50C so definitely room for improvement there!

[Dr Bob]

33 minutes ago, nicknorman said:

Difficult to be precise because I don’t have a direct measure of alternator output. I can see current in/out of batteries and in/ out of Combi, but not what is going into the boat. That said, even with the fridge on and various phones / iPads plugged into 12v charging points, I doubt the latter would be more than 5 - 10A during the day. With that caveat I’d say the max output, which is actually 185A or so when cold, was down to about 165A. Of course there isn’t a linear relationship between rotor current and magnetic field, especially as saturation of the iron core is approached.
 

As to temperature, the question is, temperature where? The alternator has 2 fans, one just cools the windings and one pulls air past the diodes etc and also cools the other side of the windings. I’ve mounted the sensor in the exhaust flow from the latter fan with the assumption that the semiconductors are the weak point. That one was at around 85C but climbing. I didn’t want to leave it on too long and anyway if it got to 90C my regulator would switch to “hot” mode and halve the field current. I did remember to bring my infrequent red thermometer and I could see 125C or so on the other end. That may sound hot but it’s just copper, so not that hot really especially if you recall that the alternator spec allows for an AMBIENT temperature of up to 100C.

 

The other consideration is that we were running the engine at 1600 rpm on the river, as opposed to the more normal 1300 that it would be on canals, and that of course improves the throughput of cooling air.
 

Engine bay temperature was 50C so definitely room for improvement there!

OK, thanks Nick. The temp info is really useful.

[MoominPapa]

2 hours ago, nicknorman said:

It’s interesting to be able to observe the field current. Maximum field current being limited by the resistance of the rotor, is about 4.2A on my alternator when it’s cool. I was playing with things yesterday with hot engine bay (fast cruising on the Severn) and with the tumble drier on (2kw) with the Travelpower turned off, so the 2kw was being supplied from the alternator via inverter. Very quickly I noticed that although the duty cycle was 100% (ie rotor effectively connected across the supply) the rotor current was now only about 3.5A. Presumably due to the temperature coefficient of the resistance of the windings. So that seems to be a “self regulation” mechanism whereby the alternator output is naturally reduced as it heats up, due to increased rotor resistance.

Yes. I suspect the same effect explains why my 70A alternator becomes a 60A alternator when it's been running for a while.

 

Your controller looks good (apart from the dremelling!) don't forget that the OLED displays suffer from burn-in, so you need some sort of screen saver.

 

Do you store parameter logs?

 

MP.

[nicknorman]

33 minutes ago, MoominPapa said:

Yes. I suspect the same effect explains why my 70A alternator becomes a 60A alternator when it's been running for a while.

 

Your controller looks good (apart from the dremelling!) don't forget that the OLED displays suffer from burn-in, so you need some sort of screen saver.

 

Do you store parameter logs?

 

MP.

The OLED display is only on when the ignition is on. The controller has an input from the Beta warning light wire (which is no longer connected to D+), which it controls by means of a MOSFET and there is a flag coming over LIN that is “mechanical failure” ie the alternator isn’t going round. So when that flag is active and no voltage / current on the warning light wire (the ignition is switched off), the device goes to sleep and as part of that, the display is switched off. The port pin is set to interrupt on low to high transition so when the ignition is turned on again the device wakes up and the first instruction after the ISR clears the interrupt flag, is Reset(); and of course part of the initialisation code is to activate the display.

 

No I’m not logging anything, I could do so via the serial port I suppose.

[jetzi]

I installed my 3kVA Victron inverter today. My heating element came in handy again as a way to charge the capacitors while connecting it up. Was very satisfying to see our test toaster and hair dryer come to life on the boat for the first time (apart from a little shore power we had while getting our boat blacked last year, we've not had any 240V power before).

 

When I ran the washing machine, my BG-8S cell voltage low alarms went off. I'd set this to 3.1V so not too alarming. My BMV alarm went off at 12.4V - this was set to 12.4V (3.1V per cell average). Then a minute or two later the BMS board cut my load relay - which was set to 3.1V (the most conservative setting). I was watching the cell voltages and they were generally over 3V each but would occasionally dip into the high 2.9s.

 

Unfortunately, resetting the BMS board didn't seem to turn on the relays again like it was supposed to. I had to manually connect the relay circuits to turn them back on. Possibly I've set it up or wired it incorrectly. I'm going to look into it more tomorrow.

 

These aren't extremely heavy loads and my battery was nearly fully charged - is it expected that a washing machine could drop the voltage of my lithium bank from 13.4V to 12.1V? When the load eases up, it returns to 13.4V. In any case, I set the low voltage cut to 2.9V on the BMS and completed the washing machine cycle, so perhaps I just need to set my alarms to a more realistic voltage. I really just wanted to test them all, so mostly today was a good success

[MoominPapa]

23 minutes ago, ivan&alice said:

I installed my 3kVA Victron inverter today. My heating element came in handy again as a way to charge the capacitors while connecting it up. Was very satisfying to see our test toaster and hair dryer come to life on the boat for the first time (apart from a little shore power we had while getting our boat blacked last year, we've not had any 240V power before).

 

When I ran the washing machine, my BG-8S cell voltage low alarms went off. I'd set this to 3.1V so not too alarming. My BMV alarm went off at 12.4V - this was set to 12.4V (3.1V per cell average). Then a minute or two later the BMS board cut my load relay - which was set to 3.1V (the most conservative setting). I was watching the cell voltages and they were generally over 3V each but would occasionally dip into the high 2.9s.

 

Unfortunately, resetting the BMS board didn't seem to turn on the relays again like it was supposed to. I had to manually connect the relay circuits to turn them back on. Possibly I've set it up or wired it incorrectly. I'm going to look into it more tomorrow.

 

These aren't extremely heavy loads and my battery was nearly fully charged - is it expected that a washing machine could drop the voltage of my lithium bank from 13.4V to 12.1V? When the load eases up, it returns to 13.4V. In any case, I set the low voltage cut to 2.9V on the BMS and completed the washing machine cycle, so perhaps I just need to set my alarms to a more realistic voltage. I really just wanted to test them all, so mostly today was a good success

That sounds like a large voltage drop, but you don't say what load the washing machine is applying. Does the Victron inverter tell you what the DC current is? For comparison, our 480Ah bank of Winston 160Ah cells will drop to maybe 12.6v or 12.7v at the terminals with a 100A discharge when well charged. The per-cell immediate cutoff is set to 2.9v and we've never got close to that tripping.

 

MP.

 

[peterboat]

29 minutes ago, ivan&alice said:

I installed my 3kVA Victron inverter today. My heating element came in handy again as a way to charge the capacitors while connecting it up. Was very satisfying to see our test toaster and hair dryer come to life on the boat for the first time (apart from a little shore power we had while getting our boat blacked last year, we've not had any 240V power before).

 

When I ran the washing machine, my BG-8S cell voltage low alarms went off. I'd set this to 3.1V so not too alarming. My BMV alarm went off at 12.4V - this was set to 12.4V (3.1V per cell average). Then a minute or two later the BMS board cut my load relay - which was set to 3.1V (the most conservative setting). I was watching the cell voltages and they were generally over 3V each but would occasionally dip into the high 2.9s.

 

Unfortunately, resetting the BMS board didn't seem to turn on the relays again like it was supposed to. I had to manually connect the relay circuits to turn them back on. Possibly I've set it up or wired it incorrectly. I'm going to look into it more tomorrow.

 

These aren't extremely heavy loads and my battery was nearly fully charged - is it expected that a washing machine could drop the voltage of my lithium bank from 13.4V to 12.1V? When the load eases up, it returns to 13.4V. In any case, I set the low voltage cut to 2.9V on the BMS and completed the washing machine cycle, so perhaps I just need to set my alarms to a more realistic voltage. I really just wanted to test them all, so mostly today was a good success

Never had an issue if its showing 13.4 v it will drop to 13.1 with washer/dishwasher/kettle on at the end of the heat cycle 

[jetzi]

Oh dear. This suggests to me that the cells are a bit knackered?

9 minutes ago, MoominPapa said:

you don't say what load the washing machine is applying. Does the Victron inverter tell you what the DC current is?

I don't know what load the washing machine is applying but it should be much less than 100A. The inverter doesn't tell me what the current is, but I can try again tomorrow and test with my clamp meter.

[TheBiscuits]

2 minutes ago, ivan&alice said:

Oh dear. This suggests to me that the cells are a bit knackered?

I don't know what load the washing machine is applying but it should be much less than 100A. The inverter doesn't tell me what the current is, but I can try again tomorrow and test with my clamp meter.

What is the power rating of the washing machine on the label?

 

Nearly all of this rating will be the heater element, so either pick a cooler wash or feed the machine hot water.

 

 If it's a 2kw machine it will be pulling more like 200A from the batteries.  Was your engine running at 1500 rpm when you tried this?

[BEngo]

A washing machine heater of, say 1.7 kW is going to want about 170 A into the inverter, so much more than you expect.

One of the LiFe downsides is they don't readily deliver high current like an LA.

N

[Dr Bob]

6 minutes ago, TheBiscuits said:

What is the power rating of the washing machine on the label?

 

Nearly all of this rating will be the heater element, so either pick a cooler wash or feed the machine hot water.

 

 If it's a 2kw machine it will be pulling more like 200A from the batteries.  Was your engine running at 1500 rpm when you tried this?

On our old boat, the washing machine was rated at 2.3 KW so that would be pulling nearly 200A. It always tripped our 2000VA multiplus if we did a 30 C wash. We always did a cold wash when not on shore power.

My 480Ahr thunderskys dropped to circa 12.4V on applying 150A load when half full ish (13.1V rested).

What was the balance like down the bottom end? You say the cells got down to the high 2.9Vs. Was this all the cells or just one or two? It could be that there is one or two lower capacity cells.

Even with Li's, I would always run the engine if I was going to pull 150A for any length of time.

[jetzi]

3 minutes ago, TheBiscuits said:

What is the power rating of the washing machine on the label?

 

Nearly all of this rating will be the heater element, so either pick a cooler wash or feed the machine hot water.

 

 If it's a 2kw machine it will be pulling more like 200A from the batteries.  Was your engine running at 1500 rpm when you tried this?

Wash was cold, a 15min test run. This washing machine has a "true cold wash" button that allows you to turn off the heating element entirely. Washing machines don't get specified in a nice "this many watts" label because they vary so much depending on what they are doing; they get specified in "this many kWh per year" which is an infuriating measurement.. But in various other threads we've discussed this washing machine and the general consensus was it uses around 500W. 1000W is less than 100A.

My domestic battery is completely isolated from the engine for the time being. I'm expecting this battery to be able to put out 200A. Is this unreasonable?

 

[MoominPapa]

Just did a test for confirmation, hairdryer on max. 140A discharge, battery about 80% full, no cell below 3.17v, so your numbers look low.

 

MP.

 

[jetzi]

  

3 minutes ago, Dr Bob said:

My 480Ahr thunderskys dropped to circa 12.4V on applying 150A load when half full ish (13.1V rested).

What was the balance like down the bottom end? You say the cells got down to the high 2.9Vs. Was this all the cells or just one or two? It could be that there is one or two lower capacity cells.

Even with Li's, I would always run the engine if I was going to pull 150A for any length of time.

I have 640Ah of them which should also improve the current rating, right?

 

I haven't run the battery down much at all - the BMV says 23Ah. So I can't really say what the balance was like on the bottom. While under load from the inverter the voltage was bouncing around all over the place, but the cells were around 3.0 to 3.1, and occasionally would dip into the high 2.9s.

 

As I say the system is isolated from my alternator until I can do something clever with it. So running the engine is not an option.

 

I'm still very much testing (the washing machine didn't have any washing in it) so I'm more trying to discover the limits than look for a solution right now.

But today's testing is suggesting to me that the cells are on the weak side for putting out current. I'll put the ammeter on it to see what

 

6 minutes ago, MoominPapa said:

Just did a test for confirmation, hairdryer on max. 140A discharge, battery about 80% full, no cell below 3.17v, so your numbers look low.

Thanks for that. Are the cells in danger to drop below 3.0V when they are sufficiently charged? This isn't the same as undervoltage due to being flat, right?

 

[MoominPapa]

4 minutes ago, ivan&alice said:

  

 

Thanks for that. Are the cells in danger to drop below 3.0V when they are sufficiently charged? This isn't the same as undervoltage due to being flat, right?

 

3.0v is a pretty conservative limit. I use 2.9v, and I've seen 2.65v quoted. The fact remains that well charged LiFePO4 cells should not be dropping that far on quite small discharges. How sure are you of their SoC?

 

MP.