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Cheap LiFePO4 BMS?


jetzi

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

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34 minutes ago, MtB said:

 

I disagree. 

 

1) I leave my fridge turned on when I'm not on the boat. This alone makes a "low cell" disconnect mandatory. Agreed the alarm perhaps falls into the 'nice to have' category but I think without the advance warning alarm, one only has to be left sitting in the dark unexpectedly once or twice, to begin to see it as essential.

 

2) Separate channels for load disconnect and charge disconnect are essential too. If you get say, a high cell disconnect you NEED the load circuit to stay connected or how will you discharge the battery to a safe level? Similarly with low voltage disconnect. You NEED the charging devices to remain connected to correct the low SoC.

 


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

 

In the event of a low voltage disconnect the BMS disables all its interfaces, display etc and goes to sleep, using well under a milliamp. When ready to charge, you start the engine - alternator is unpowered since leisure batteries are disconnected. You press a button on the BMS, the first thing it does is close the relay, which powers the alternator controller, then the BMS waits a few seconds before starting to check cell voltage again, meanwhile the alternator is now putting in 100A or so and the cell voltage is back up. 

Edited by nicknorman
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11 minutes ago, nicknorman said:

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

 

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

 

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

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3 minutes ago, jetzi said:

 

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

 

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

I can see that, for example, if you had solar, separate charge and load disconnects would be a good idea. But for our setup and usage, I couldn’t see any advantage.

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6 hours ago, MtB said:

 

I disagree. 

 

1) I leave my fridge turned on when I'm not on the boat. This alone makes a "low cell" disconnect mandatory. Agreed the alarm perhaps falls into the 'nice to have' category but I think without the advance warning alarm, one only has to be left sitting in the dark unexpectedly once or twice, to begin to see it as essential.

 

2) Separate channels for load disconnect and charge disconnect are essential too. If you get say, a high cell disconnect you NEED the load circuit to stay connected or how will you discharge the battery to a safe level? Similarly with low voltage disconnect. You NEED the charging devices to remain connected to correct the low SoC.

 

 

 

That's a pretty big 'as long as'. To rely on whole battery voltages one also needs the cells to be closely matched in capacity. If one top-balances, then the cells need to be close to each other in capacity or when fully discharged, one cell will get low first. It strikes me that a lot of users focus unnecessarily closely on balancing, possibly because it's an easy concept to grasp compared to some of the other more important things needed to be accounted for in designing a lithium battery installation.

 

 

 

 

 

If you stay in the 20-80% it makes no odds Mike 

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6 hours ago, nicknorman said:

I can see that, for example, if you had solar, separate charge and load disconnects would be a good idea. But for our setup and usage, I couldn’t see any advantage.

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

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28 minutes ago, peterboat said:

If you stay in the 20-80% it makes no odds Mike 

 

This is the way I'm thinking.

If I can beef up my capacity to 550Ah with another battery, it'll be easier to stay within the 30-80% SoC range, and there'll be very little chance of an individual cell ever being pushed too high or too low. 

At the moment I think my knee phase starts at about 86-88%, and I'd rather avoid that if possible. 

More capacity means I can stock up on charge when the sun is shining (or I'm out cruising for say 5 hours), but without letting the SoC get above 80%. 

 

 

 

 

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16 minutes ago, nicknorman said:

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

 

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

 

 

5 minutes ago, Tony1 said:

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

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

 

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

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10 minutes ago, jetzi said:

 

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

 

 

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

 

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

I have been doing the 20-80% for 4 years on both the boat and my pick up truck which is way harder on the batteries. No issues at the moment and the pickup like the boat is solar charged, though after the first couple of years I have given up plugging in the puter to check 

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22 minutes ago, jetzi said:

 

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

 

 

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

 

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

 

Yes this is my thinking. 

 

It would be quite difficult to set up a cell-level monitor and disconnect system, so I'm kind of stuck with doing these functions at battery level- in fact, on a routine basis, its monitored at the level of the entire bank. 

 

But given that the valences are capable of some degree of balancing, I feel the risks of one cell going seriously over-voltage are reduced, at least to some degree.

 

And to further reduce any risk, my thinking would be to stay within a quite conservative SoC range of say 20-80%. As you say, a cell would have to be badly out of balance to end up at a dangerously high voltage given these fairly gentle parameters.

 

Also, if one cell gets badly out of whack, there is an indicator light on the battery that changed from green to  red, so I'll get some warning, and I can check them with the PC.  

 

There's always the chance one  cell could go out of balance badly enough to get damaged by the charging process, but I will have done what I reasonably could to prevent it.

 

 

 

 

 

Edited by Tony1
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57 minutes ago, Tony1 said:

But given that the valences are capable of some degree of balancing, I feel the risks of one cell going seriously over-voltage are reduced, at least to some degree.

 

This is true, but highlights the two skools of lithium user on here. You, Peter and a few others are using Valence batts with factory built-in (and undocumented AIUI) BMS whereas I, Nick and a few others are using bare cells. In addition you Valences are LiFeMgPO4 not LiFePO4 (again AIUI) so you really are 'off piste' as far as applying LiFePO4 rules of management. And in addition in addition (!), I suspect your batts might comprise hundreds of little cells arranged in parallel/series grids, whereas I have eight whacking big individual cells the voltage of which I can measure individually. 

 

 

You don't have this option.

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1 hour ago, MtB said:

 

This is true, but highlights the two skools of lithium user on here. You, Peter and a few others are using Valence batts with factory built-in (and undocumented AIUI) BMS whereas I, Nick and a few others are using bare cells. In addition you Valences are LiFeMgPO4 not LiFePO4 (again AIUI) so you really are 'off piste' as far as applying LiFePO4 rules of management. And in addition in addition (!), I suspect your batts might comprise hundreds of little cells arranged in parallel/series grids, whereas I have eight whacking big individual cells the voltage of which I can measure individually. 

 

 

You don't have this option.


Although lots of cells in parallel, then in series, isn’t a problem because each set of paralleled cells are effectively 1 cell for monitoring purposes.

 

By the way, so far I haven’t seen any need to balance the cells again, there seems to be no tendency to go out of balance and I can’t see why there should be unless a cell goes defective. My BMS chip has the capability to drive balancing FETs/resistors but so far, due to feeling there is no need, I haven’t written the software to make it happen. Not sure I ever will.

Edited by nicknorman
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42 minutes ago, MtB said:

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

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

 

 

1 hour ago, MtB said:

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

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

 

1 hour ago, MtB said:

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

 

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

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3 minutes ago, jetzi said:

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

 

The Valence batteries have a built in Battery Monitoring System BMS.  If you want the full Battery Management System BMS you have to buy a complete new system from Valance that includes all the rest of the kit, and they deliberately refuse to supply it for secondhand batteries.

 

It's the confusion between the two meanings of BMS that throws people offtrack.

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5 minutes ago, TheBiscuits said:

 

The Valence batteries have a built in Battery Monitoring System BMS.  If you want the full Battery Management System BMS you have to buy a complete new system from Valance that includes all the rest of the kit, and they deliberately refuse to supply it for secondhand batteries.

 

It's the confusion between the two meanings of BMS that throws people offtrack.


One has to wonder WHY they won’t sell the management system? Sheer bloody-mindedness perhaps? But anyway this was the reason why I went for bare cells, one doesn’t want to get trapped in some IP dead end.

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1 minute ago, nicknorman said:


One has to wonder WHY they won’t sell the management system? Sheer bloody-mindedness perhaps? But anyway this was the reason why I went for bare cells, one doesn’t want to get trapped in some IP dead end.

 

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

 

If the company design and provide your whole system it will do what you need at a (high!) price.  If you buy used or abused batteries secondhand they simply won't support them or provide you with the extra kit they make.

 

It's a valid commercial decision to make, but most boaters are not prepared to pay the premium for an all singing all dancing fully guaranteed and supported battery system.  We'd rather bodge it on the cheap, so bare cells appeal to us more.  

 

And some of us buy half a dozen battery monitors and cobble them together ... ;)

 

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2 hours ago, MtB said:

 

This is true, but highlights the two skools of lithium user on here. You, Peter and a few others are using Valence batts with factory built-in (and undocumented AIUI) BMS whereas I, Nick and a few others are using bare cells. In addition you Valences are LiFeMgPO4 not LiFePO4 (again AIUI) so you really are 'off piste' as far as applying LiFePO4 rules of management. And in addition in addition (!), I suspect your batts might comprise hundreds of little cells arranged in parallel/series grids, whereas I have eight whacking big individual cells the voltage of which I can measure individually. 

 

 

You don't have this option.

You can fit a separate BMS  but why would I? I can check if something is going wrong if I want, indeed I used to but after never finding a problem it all seemed pointless. 

So this leads me to 20-80% rule if you follow it it doesn't matter because as Nick says the batteries really have to be out of balance to cause issues. 

58 minutes ago, jetzi said:

  

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

 

 

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

 

 

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

It does change the voltage 14.6 is maximum voltage I charge to 13.9, which is enough for me and others 

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34 minutes ago, TheBiscuits said:

 

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

 

If the company design and provide your whole system it will do what you need at a (high!) price.  If you buy used or abused batteries secondhand they simply won't support them or provide you with the extra kit they make.

 

It's a valid commercial decision to make, but most boaters are not prepared to pay the premium for an all singing all dancing fully guaranteed and supported battery system.  We'd rather bodge it on the cheap, so bare cells appeal to us more.  

 

And some of us buy half a dozen battery monitors and cobble them together ... ;)

 

When I bought mine I tried to get a LV master BMS not a chance, now of course it's a different company so who knows, but now I don't care as they work fine for me

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1 hour ago, TheBiscuits said:

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

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

 

1 hour ago, TheBiscuits said:

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

 

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

 

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

 

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

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9 hours ago, jetzi said:

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

 

 

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

 

 


the built in Valence BMS does balancing and keeps track of state of charge and allows one to view cell voltages. All of which is good, but with the lack of a disconnect system, only a small part of the requirement. I like to think that if I had them, I would have hacked the data stream and thus have access to the data electronically. But on the other hand, it is easier to start with a blank piece of paper than to try to hack and adapt someone else’s design.

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10 hours ago, jetzi said:

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

 

 

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

 

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

 

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

Made in America for the navy's minisubs originally does that give you a clue why they are well regarded?

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On 15/10/2021 at 22:59, jetzi said:

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

 

I've previously misunderstood the way fuelling works on these narrowboat engines. 

My understanding was that the amount of fuel used depends entirely on the position of the throttle.

So at idle, I had thought it always had the same amount of fuel to consume, regardless of what the alternator was trying to do. 

 

And if you push the throttle forward by a given amount, the amount of fuel consumed would always increase by a set amount. 

 

But you're saying here that the alternator itself can act in such a way that it causes more fuel to be consumed, regardless of the position of the throttle? 

 

My point in saying you might as well charge on the move was based on the idea that when cruising, you will use the throttle as required to drive and navigate the boat as per the route and the conditions.

I.e. the position of the throttle at the different points in your journey is dictated by how you decide to complete the journey.

And my understanding was that the fuel consumption during this journey was entirely controlled by the throttle positions during the cruise. 

 

But what you're saying is that the alternator can cause more fuel to be consumed at a given throttle position? 

I had no idea this was a thing that could happen, I must confess.

 

 

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12 hours ago, jetzi said:

  

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

 

I have the Valences and it also grates me when the "monitoring system", is described as a "management system".

 

Connect a bank to a laptop with the software, you can "monitor" everything to your hearts content, but there is no "management" going on.

 

In my experience, (backed up by the T6 forum), to use the balancing facility, a battery/bank needs to be connected to a computer with the software, and the computer must be on and awake.

 

The few times I have tried this for a few hours, the actual balancing that takes place is minimal. Maybe it would be effective if you could do it for several days. Peter says that he balanced his when he got them, and I think he has mentioned days, rather than hours. I'm not sure whether he has spoken about the need to have the computer on and awake.

 

With the valences, we are pretty much stuck with management at the battery level, and not at the cell level. A hands on approach is pretty much necessary when charging reaches a bit above the knee. If I am charging to 100%, I watch the software quite closely when the cells are approaching 3.6V/3.65V.

 

Having said that, 100% is only necessary when wanting to reset the monitor, (BMV712S in my case). Other than that, I tend to use between 80/90% and 20%.

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3 minutes ago, Tony1 said:

My understanding was that the amount of fuel used depends entirely on the position of the throttle.

 

No. It's much more sophisicated than that. The "throttle" (a misnomer - it isn't a throttle) is actually an "engine speed selector". There is a mechanical governor which increases the fuel injected if the engine is running slower than selected on the speed control, and vice versa.

 

So it you load the engine with an alternator, it slow down and more fuel gets injected to compensate.

 

 

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