Batteries not charging as expected

[Tony Brooks]

33 minutes ago, DShK said:

Indeed it is lithium charging, and the drop of course varies with current. I believe it was pushing about 60 amps when it dropped 0.3. If it is indeed just the sum of multiple connections, is it then an acceptable solution to up the max charging voltage to compensate?

 

I can't see why not, as long as you ensure whatever you are using to measure the "new" voltage is accurate. However, if charging LAs then as the current dropped the maximum voltage would rise so may cause problems.

[DShK]

23 minutes ago, Tony Brooks said:

 

I can't see why not, as long as you ensure whatever you are using to measure the "new" voltage is accurate. However, if charging LAs then as the current dropped the maximum voltage would rise so may cause problems.

 

Ah, is this a problem either way? The voltage drop increases with current, so if they are being trickle charged (say by solar on an overcast day), then they could in theory be pushed beyond the safe voltage. I guess this could be externally disconnected before it got to that point.

[Tony Brooks]

1 hour ago, DShK said:

 

Ah, is this a problem either way? The voltage drop increases with current, so if they are being trickle charged (say by solar on an overcast day), then they could in theory be pushed beyond the safe voltage. I guess this could be externally disconnected before it got to that point.

 

This is why @nicknorman has, I think, a home brew charge controller for his lithiums to do just that. However, I don't think a 0.3 volt drop would make a significant impact on the time to fully charged on a lithium battery bank. (Out of my comfort zone here, so may be wrong.)

 

In any case, if you only upped the bulk and absorption voltage (to use LA terms) and left the float voltage low, I don't think there would be any damage. this assumes that you have a fully programmable solar controller.

Edited May 19, 2023 by Tony Brooks

[rusty69]

4 minutes ago, Tony Brooks said:

 

This is why @nicknorman has, I think, a home brew charge controller for his lithiums to do just that. However, I don't think a 0.3 volt drop would make a significant impact on the time to fully charged on a lithium battery bank. (Out of my comfort zone here, so may be wrong.)

 

In any case, if you only upped the bulk and absorption voltage (to use LA terms) and left the float voltage low, I don't think there would be any damage. this assumes that you have a fully programmable solar controller.

That is effectively what I have done too, as I have a difference in battery voltage and mppt voltage. You must also consider the duration time, and alter it from the LA setting to something much lower. 

[DShK]

So I read a bunch more of Nordkyn design you'll be happy to know @MtB. I thought I had a read a bunch of it but I wasn't aware that there were multiple articles. I read the charging one and found it very interesting.

 

My understanding now is that charge should be terminated based on a "tail" current which depends on what the ""absorption"" voltage is set to. I also understand that these batteries will continue to charge even if at a "float" voltage. I knew they didn't like to be kept at 100% but I wasn't aware of this overcharging.

 

I also am aware of the "memory effect" but I get the feeling this is a bit contentious.

 

I have engaged sterling and they are repeatedly telling me that regardless of what I think, their batteries last years with the Daly high voltage disconnecting. I have told them that hitting 15V on a cell, potentially every day, is not good. And if I set the charge voltage low enough to avoid this (13.8-13.9V) I will get very slow charge times. They also think that there are "multiple schools of thought" on proper lithium charging and safety.

 

They have offered to take them back to look at them, I am hoping they will do something (replace a cell, top charge them, replace them altogether) but I am not hopeful considering their insistence that the batteries will last the warranty (I want more than 5 years out of them...). Not sure how I will keep my DC electrics going without the batteries, I guess I could wire them to the starter and leave it on a shoreline.

 

On the plus side, I have set up a raspberry pi as a venus device to get my victron units talking, and get access to node-red. This system allows the solar charge controller to get the battery voltage from the shunt (rather than it's own reading) so it will compensate for voltage drop! Very useful. I will be looking to use node-red to terminate charge when the batteries hit 100% (as measured by the shunt, which can calibrate with tail current - I am not sure how I would reliably terminate based on current readings, given all the variables in play).

[Tony Brooks]

This may not be true because I am not heavily into lithiums, but my understanding is that tail current is not as indicative of being fully charged as t is on lead acids. Please double-check that your understanding is correct. I happily await being told that I'm wrong.

[IanD]

8 minutes ago, DShK said:

So I read a bunch more of Nordkyn design you'll be happy to know @MtB. I thought I had a read a bunch of it but I wasn't aware that there were multiple articles. I read the charging one and found it very interesting.

 

My understanding now is that charge should be terminated based on a "tail" current which depends on what the ""absorption"" voltage is set to. I also understand that these batteries will continue to charge even if at a "float" voltage. I knew they didn't like to be kept at 100% but I wasn't aware of this overcharging.

 

I also am aware of the "memory effect" but I get the feeling this is a bit contentious.

 

I have engaged sterling and they are repeatedly telling me that regardless of what I think, their batteries last years with the Daly high voltage disconnecting. I have told them that hitting 15V on a cell, potentially every day, is not good. And if I set the charge voltage low enough to avoid this (13.8-13.9V) I will get very slow charge times. They also think that there are "multiple schools of thought" on proper lithium charging and safety.

 

They have offered to take them back to look at them, I am hoping they will do something (replace a cell, top charge them, replace them altogether) but I am not hopeful considering their insistence that the batteries will last the warranty (I want more than 5 years out of them...). Not sure how I will keep my DC electrics going without the batteries, I guess I could wire them to the starter and leave it on a shoreline.

 

On the plus side, I have set up a raspberry pi as a venus device to get my victron units talking, and get access to node-red. This system allows the solar charge controller to get the battery voltage from the shunt (rather than it's own reading) so it will compensate for voltage drop! Very useful. I will be looking to use node-red to terminate charge when the batteries hit 100% (as measured by the shunt, which can calibrate with tail current - I am not sure how I would reliably terminate based on current readings, given all the variables in play).

 

There is also a lot of of good information on the marinehowto website, for example:

https://marinehowto.com/drop-in-lifepo4-be-an-educated-consumer/

https://marinehowto.com/lifepo4-batteries-on-boats/

https://marinehowto.com/li-ion-be-careful-what-you-read-believe/

https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/

5 minutes ago, Tony Brooks said:

This may not be true because I am not heavily into lithiums, but my understanding is that tail current is not as indicative of being fully charged as t is on lead acids. Please double-check that your understanding is correct. I happily await being told that I'm wrong.

Voltage and SoC (from an appropriate BMS) are more appropriate than tail current -- the key is to *stop charging* when the cells hit the upper voltage limit, typically 3.45V/cell, and not keep pushing any more current in which will cause the voltage to rise rapidly.

[DShK]

7 minutes ago, Tony Brooks said:

This may not be true because I am not heavily into lithiums, but my understanding is that tail current is not as indicative of being fully charged as t is on lead acids. Please double-check that your understanding is correct. I happily await being told that I'm wrong.

This is just what it says here. https://nordkyndesign.com/charging-marine-lithium-battery-banks/ There seems to be differing opinions, a lot of people seem to go on voltage alone. But my understanding is that you can get lithium fully charged at any voltage above, I think 13.6V (Or there abouts). It just takes longer. So using voltage alone doesn't seem like a good source. This website seems like a particularly reputable source of info.

 

 

2 minutes ago, IanD said:

 

There is also a lot of of good information on the marinehowto website, for example:

https://marinehowto.com/drop-in-lifepo4-be-an-educated-consumer/

https://marinehowto.com/lifepo4-batteries-on-boats/

https://marinehowto.com/li-ion-be-careful-what-you-read-believe/

https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/

I'll give those a read, thanks!

[TheBiscuits]

17 minutes ago, DShK said:

I have engaged sterling and they are repeatedly telling me that regardless of what I think, their batteries last years with the Daly high voltage disconnecting. I have told them that hitting 15V on a cell, potentially every day, is not good. And if I set the charge voltage low enough to avoid this (13.8-13.9V) I will get very slow charge times.

 

Have you considered that Sterling might be correct?  Recommended charge voltage for their LiFePo4 batteries is 14.4V, if the charging pushes a cell too high the BMS will disconnect the charging circuit.

 

All the recommendations for only charging at 13.8V come from those people with bare cells who don't have a proper BMS disconnect or those who don't trust the BMS.  And @Tony1 who has half a BMS but not the charge disconnect bit.

 

How are you getting your lithiums up to 15V? 

Is that what the BMS is reporting or another voltmeter elsewhere? 

Is the charging mosfet not switched off before that voltage?  You'll need to use the app to check this, there's no externally visible indication.

[Tony Brooks]

21 minutes ago, IanD said:

Voltage and SoC (from an appropriate BMS) are more appropriate than tail current -- the key is to *stop charging* when the cells hit the upper voltage limit, typically 3.45V/cell, and not keep pushing any more current in which will cause the voltage to rise rapidly.

 

That was my understanding.

[Tony1]

2 minutes ago, TheBiscuits said:

 

Have you considered that Sterling might be correct?  Recommended charge voltage for their LiFePo4 batteries is 14.4V, if the charging pushes a cell too high the BMS will disconnect the charging circuit.

 

All the recommendations for only charging at 13.8V come from those people with bare cells who don't have a proper BMS disconnect or those who don't trust the BMS.  And @Tony1 who has half a BMS but not the charge disconnect bit.

 

How are you getting your lithiums up to 15V? 

Is that what the BMS is reporting or another voltmeter elsewhere? 

Is the charging mosfet not switched off before that voltage?  You'll need to use the app to check this, there's no externally visible indication.

 

You rang, m'lud? 

Not to be pedantic old fruit, but one feels obliged to point out that one does actually have a high voltage disconnect, although sadly not built into the cells as I would like. 

 

I use a BMV712 to control a Victron Battery Protect unit. I currently have it set to 14.7v, and if the battery voltage goes above that, the relay in the BMV712 will trigger the battery protect unit to physically disconnect the main charging cable that runs into the batteries. Rather cleverly (at least to me), this setup leaves the loads connected, so the battery is able to discharge. 

 

The emergency low voltage disconnect is a similar thing, but uses a BEP switch to disconnect the loads- because rather stupidly, the Battery Protect unit, although primarily intended as a low voltage disconnect, does not work with an inverter connected to the batteries.

But when that activates, only the loads are disconnected. The chargers remain connected, and the battery can get itself back up to a decent voltage pretty sharpish. 

 

Its a right old palaver of a thing, but it does work. 

 

 

[DShK]

35 minutes ago, TheBiscuits said:

 

Have you considered that Sterling might be correct?  Recommended charge voltage for their LiFePo4 batteries is 14.4V, if the charging pushes a cell too high the BMS will disconnect the charging circuit.

 

All the recommendations for only charging at 13.8V come from those people with bare cells who don't have a proper BMS disconnect or those who don't trust the BMS.  And @Tony1 who has half a BMS but not the charge disconnect bit.

 

How are you getting your lithiums up to 15V? 

Is that what the BMS is reporting or another voltmeter elsewhere? 

Is the charging mosfet not switched off before that voltage?  You'll need to use the app to check this, there's no externally visible indication.

 

47 minutes ago, IanD said:

 

There is also a lot of of good information on the marinehowto website, for example:

https://marinehowto.com/drop-in-lifepo4-be-an-educated-consumer/

https://marinehowto.com/lifepo4-batteries-on-boats/

https://marinehowto.com/li-ion-be-careful-what-you-read-believe/

https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/

Voltage and SoC (from an appropriate BMS) are more appropriate than tail current -- the key is to *stop charging* when the cells hit the upper voltage limit, typically 3.45V/cell, and not keep pushing any more current in which will cause the voltage to rise rapidly.

 

Missed the second part - the SoC from the Daly BMS is next to useless. I have seen it jump from 70% to 100%, and one battery read 60% while the other 100%.

When one cell hits 3.75V, the lowest cell value I get is 3.36V - so not quite fully charged. My concern is that my understanding is you don't really want to be using the BMS to disconnect charging, it's a safety feature. So I would want to set the charge voltage to a lower value to avoid this happening, as I have no output from the BMS to read cell voltages. Hence, I get a low charge speed (it will charge to full even at a lower voltage, is my understanding - hence the "tail current")

 

Most of my arguement here comes from the nordkyn design recommendation of tail current. I also don't want to be hitting 15V and letting the BMS disconnect. So to avoid that I have to set my charge voltage to a lower value - and so how do I then tell when I am fully charged other than something like a tail current?

 

35 minutes ago, TheBiscuits said:

 

Have you considered that Sterling might be correct?  Recommended charge voltage for their LiFePo4 batteries is 14.4V, if the charging pushes a cell too high the BMS will disconnect the charging circuit.

 

All the recommendations for only charging at 13.8V come from those people with bare cells who don't have a proper BMS disconnect or those who don't trust the BMS.  And @Tony1 who has half a BMS but not the charge disconnect bit.

 

How are you getting your lithiums up to 15V? 

Is that what the BMS is reporting or another voltmeter elsewhere? 

Is the charging mosfet not switched off before that voltage?  You'll need to use the app to check this, there's no externally visible indication.

 

It's not a recommendation I've had to charge at 13.8V. I set my chargers to 14.2V. The combined cell voltage hits about 14V, and the BMS disconnects charging at one cell has hit the high volt ceiling (3.75V). My understanding is the BMS should be used as a backup safety feature? I don't know how such a tiny bit of kit could be safely regularly disconnecting such high amps.

 

24 minutes ago, Tony1 said:

 

You rang, m'lud? 

Not to be pedantic old fruit, but one feels obliged to point out that one does actually have a high voltage disconnect, although sadly not built into the cells as I would like. 

 

I use a BMV712 to control a Victron Battery Protect unit. I currently have it set to 14.7v, and if the battery voltage goes above that, the relay in the BMV712 will trigger the battery protect unit to physically disconnect the main charging cable that runs into the batteries. Rather cleverly (at least to me), this setup leaves the loads connected, so the battery is able to discharge. 

 

The emergency low voltage disconnect is a similar thing, but uses a BEP switch to disconnect the loads- because rather stupidly, the Battery Protect unit, although primarily intended as a low voltage disconnect, does not work with an inverter connected to the batteries.

But when that activates, only the loads are disconnected. The chargers remain connected, and the battery can get itself back up to a decent voltage pretty sharpish. 

 

Its a right old palaver of a thing, but it does work. 

 

 

 

I planned to have a BEP switch controlled by a relay as a second line of defence (first - correct charger settings, second - relay disconnect, third - BMS).

Edited June 1, 2023 by DShK

[TheBiscuits]

11 minutes ago, DShK said:

I don't know how such a tiny bit of kit could be safely regularly disconnecting such high amps.

 

I'd recommend not trusting your battery charger, your solar controller or your alternator either then.  They all switch high currents on and off all the time!

 

Hint: it's solid state electronics, it's not a switch contact inside the box ...

 

The issue you might want to avoid with relying on the BMS is that it can break your alternator if you don't have either a suppression device or a lead acid battery connected to it.  Alternators don't like being disconnected from batteries when running.

[rusty69]

16 minutes ago, DShK said:

I planned to have a BEP switch controlled by a relay as a second line of defence (first - correct charger settings, second - relay disconnect, third - BMS).

Exactly how I have implemented it. Though many people on a popular Facebook page use the BMS as a charge control device, apparently with no problems. 

[DShK]

11 minutes ago, TheBiscuits said:

 

I'd recommend not trusting your battery charger, your solar controller or your alternator either then.  They all switch high currents on and off all the time!

 

Hint: it's solid state electronics, it's not a switch contact inside the box ...

 

The issue you might want to avoid with relying on the BMS is that it can break your alternator if you don't have either a suppression device or a lead acid battery connected to it.  Alternators don't like being disconnected from batteries when running.

 

Fair point! I didn't think about solid state electronics doing the switching. Yeah, my alternator charges the starter, and then I have a sterling b2b charger pulling from the starter. So that's all good.

 

7 minutes ago, rusty69 said:

Exactly how I have implemented it. Though many people on a popular Facebook page use the BMS as a charge control device, apparently with no problems. 

There does seem to be a lot of conflicting info out there. My concern is that how many longer term data points do we have? (10 years or so). I also don't want a fairly cheapo bit of chinese tech being the primary line of defense against my home burning down....

[Tony1]

28 minutes ago, DShK said:

 

Most of my arguement here comes from the nordkyn design recommendation of tail current. I also don't want to be hitting 15V and letting the BMS disconnect. So to avoid that I have to set my charge voltage to a lower value - and so how do I then tell when I am fully charged other than something like a tail current?

 

I planned to have a BEP switch controlled by a relay as a second line of defence (first - correct charger settings, second - relay disconnect, third - BMS).

 

I think most people rely a charger voltage setting to keep their batteries safe from high voltages, and to be fair you don't hear stories of disasters from that.

And most people have built in BMSs in their batteries too, which is their second line of defence, as an 'emergency' disconnect.

I change my MPPT settings as the seasons change, but if I set the charging voltage at about 14.4v my MPPTs and B2Bs will all go into float well before the battery voltage gets dangerously high. And I'm no expert, but 15v sounds very high. 

 

But I don't think you'd want your batteries getting full on a daily basis. You'd maybe want to charge them to 80-90% day to day, with the occasional full 100% charge. So what you need to know is- what is the right charge setting that will get the batteries somewhere between 80 and 90% full?

And it seems the answer is not straightforward. 

 

I think it was Nick Norman who explained that if you charge at high amps, the batteries will reach their charge voltage quicker than if you charge at low amps. So if you charge at low amps, the batteries get more full before the chargers go into float mode.  

 

E.g. if I charge at say 100 amps, with a charge voltage set to 14.4v, my batteries will get to about 75% full before the chargers go into float. 

But if I charge at 20amps, and the same charge voltage setting of 14.4v, my batteries will get up to about 90% SoC and higher before the chargers go into float (float is set at 12.7v, so float means they effectively stop charging).

 

If you have enough battery capacity, it probably doesnt matter if you only get to 75% SoC on a day to day basis, as long you give them a full charge every couple of  weeks. 

But if the SoC is something you are keen to keep a closer eye on, a BMV712 might do a good job of that, You mentioned you are considering a BEP switch anyway to act as a high voltage disconnect, so I think you'll need a BMV712 anyway, to manage that switch. 

 

As Mr Biscuits said, there is a risk to the alternator with any of these charging/ high voltage disconnects.

Hopefully some more expert and knowledgeable people will chip in with better knowledge and info than I have.  

 

 

Edited June 1, 2023 by Tony1

[rusty69]

7 minutes ago, DShK said:

 

Fair point! I didn't think about solid state electronics doing the switching. Yeah, my alternator charges the starter, and then I have a sterling b2b charger pulling from the starter. So that's all good.

 

There does seem to be a lot of conflicting info out there. My concern is that how many longer term data points do we have? (10 years or so). I also don't want a fairly cheapo bit of chinese tech being the primary line of defense against my home burning down....

Most of the early adopters on here made home brew systems in the early days. Some, much more involved than others. Think nick Norman, moominpapa. Others like Dr Bob and much later myself adopted simpler belt and braces methods. As BMS technology has become more widespread,more relied on and ultimately better, perhaps there is enough data out there to suggest that a BMS alone is enough. 

 

From my point of view, and whilst learning, I am happy to have the other protection in the system. Only more time will tell if it's overkill or not. 

 

As Mr biscuits, and others implied, you already rely on things like solar charge controllers to terminate charge at the correct time. 

 

All this, of course, flies in the face of the oft quoted nordkyn and marine know how websites, which I suspect the majority of lithium adopters have never even read. 

Edited June 1, 2023 by rusty69

[DShK]

1 minute ago, Tony1 said:

 

I think most people rely a charger voltage setting to keep their batteries safe from high voltages, and to be fair you don't hear stories of disasters from that.

And most people have built in BMSs in their batteries too, which is their second line of defence, as an 'emergency' disconnect.

I change my MPPT settings as the seasons change, but if I set the charging voltage at about 14.4v my MPPTs and B2Bs will all go into float well before the battery voltage gets dangerously high. And I'm no expert, but 15v sounds very high. 

 

But I don't think you'd want your batteries getting full on a daily basis. You'd maybe want to charge them to 80-90% day to day, with the occasional full 100% charge. So what you need to know is- what is the right charge setting that will get the batteries somewhere between 80 and 90% full?

And it seems the answer is not straightforward. 

 

I think it was Nick Norman who explained that if you charge at high amps, the batteries will reach their charge voltage quicker than if you charge at low amps. So if you charge at low amps, the batteries get more full before the chargers go into float mode.  

 

E.g. if I charge at say 100 amps, with a charge voltage set to 14.4v, my batteries will get to about 75% full before the chargers go into float. 

But if I charge at 20amps, and the same charge voltage setting of 14.4v, my batteries will get up to about 90% SoC and higher before the chargers go into float (float is set at 12.7v, so float means they effectively stop charging).

 

If you have enough battery capacity, it probably doesnt matter if you only get to 75% SoC on a day to day basis, as long you give them a full charge every couple of  weeks. 

But if the SoC is something you are keen to keep a closer eye on, a BMV712 might do a good job of that, You mentioned you are considering a BEP switch anyway to act as a high voltage disconnect, so I think you'll need a BMV712 anyway, to manage that switch. 

 

Hopefully some more expert and knowledgeable people will chip in with better knowledge and info than I have.  

 

 

 

I do indeed have a BMV-712!

 

None of my chargers have ever gone into float because they either get switched off by the bms disconnect, or they take an age to charge due to the low voltage. Not that float is good for lithium, afaik..

 

My understanding is that charging to less than 100%, to the same point every day, will cause a "memory" effect which will degrade the battery capacity. I've seen a forum post contest this, so I don't know how true that is. At the moment, my batteries aren't getting fully charged just a random amount from the solar each day, so no harm done. But when the sun is bright they will get fully charged - and I either need to switch them off before 100% in a random location (might be able to do with the raspberry pi) or properly fully charge them. It's interesting to note that sterling told me on the phone there is no problem leaving them at 100%. 

[Tony1]

3 minutes ago, DShK said:

 

I do indeed have a BMV-712!

 

None of my chargers have ever gone into float because they either get switched off by the bms disconnect, or they take an age to charge due to the low voltage. Not that float is good for lithium, afaik..

 

My understanding is that charging to less than 100%, to the same point every day, will cause a "memory" effect which will degrade the battery capacity. I've seen a forum post contest this, so I don't know how true that is. At the moment, my batteries aren't getting fully charged just a random amount from the solar each day, so no harm done. But when the sun is bright they will get fully charged - and I either need to switch them off before 100% in a random location (might be able to do with the raspberry pi) or properly fully charge them. It's interesting to note that sterling told me on the phone there is no problem leaving them at 100%. 

 

I do vary things a bit, so that I dont get the batteries to the same SoC every day, as I've seen that memory effect come into play. I also try to let them run down to at least 30% or lower once a week, again to avoid too much memory effect. 

 

Now I'm no expert on these matters, I must say that, but it does seem odd that the battery's internal BMS is coming into play on an almost daily basis (I think you said it disconnects the batteries when they get up to 15volts? )

If you've set the MPPTs bulk charging voltage at 14.2v, surely they should be going into float (or stopping their charge) before the voltage gets up to the 15v that triggers the BMS? My MPPTs and B2Bs both go into float at about 14.6 or 14.7v, with a bulk charge setting of 14.4v. 

 

(And I realised that float is not appropriate for lithiums, but many charger units still insist that you put in a float value when you set up a custom charging profile- so I set mine to float at 12.7v, which means they effectively stop any charging when they go into float)

 

The issue I can see with relying on the internal BMS disconnect as a day-to-day voltage limit/control is that when the BMS kicks in and disconnects, it also disconnects the loads, right? So does that mean you lose all power from the batteries? And if so, how long does it take before the internal BMS reconnects the batteries, and what do you do for power in the meantime? 

 

 

 

 

[DShK]

2 minutes ago, Tony1 said:

 

I do vary things a bit, so that I dont get the batteries to the same SoC every day, as I've seen that memory effect come into play. I also try to let them run down to at least 30% or lower once a week, again to avoid too much memory effect. 

 

Now I'm no expert on these matters, I must say that, but it does seem odd that the battery's internal BMS is coming into play on an almost daily basis (I think you said it disconnects the batteries when they get up to 15volts? )

If you've set the MPPTs bulk charging voltage at 14.2v, surely they should be going into float (or stopping their charge) before the voltage gets up to the 15v that triggers the BMS? My MPPTs and B2Bs both go into float at about 14.6 or 14.7v, with a bulk charge setting of 14.4v. 

 

(And I realised that float is not appropriate for lithiums, but many charger units still insist that you put in a float value when you set up a custom charging profile- so I set mine to float at 12.7v, which means they effectively stop any charging when they go into float)

 

The issue I can see with relying on the internal BMS disconnect as a day-to-day voltage limit/control is that when the BMS kicks in and disconnects, it also disconnects the loads, right? So does that mean you lose all power from the batteries? And if so, how long does it take before the internal BMS reconnects the batteries, and what do you do for power in the meantime? 

 

 

 

 

 

It's not 15V, I've just said that poorly - it's 15V equivalent for the problem cells. So the whole battery hits 14V, but one cell is at 3.75V (which would be 15V if all the cells hit this level). As the overall voltage only ever hits 14V, no chargers can go into "float" at 14.2V. 

 

It only disconnects the charging, so that's not a problem. And it reconnects them when the voltage gets pulled down (so, whenever the MPPT stops fully supply loads, for example).

[Tony1]

3 minutes ago, DShK said:

 

It's not 15V, I've just said that poorly - it's 15V equivalent for the problem cells. So the whole battery hits 14V, but one cell is at 3.75V (which would be 15V if all the cells hit this level). As the overall voltage only ever hits 14V, no chargers can go into "float" at 14.2V. 

 

It only disconnects the charging, so that's not a problem. And it reconnects them when the voltage gets pulled down (so, whenever the MPPT stops fully supply loads, for example).

 

Apologies, I skim read and misunderstood the issue. 

I wonder if it might be worth trying to balance the cells?

 

 

[DShK]

25 minutes ago, rusty69 said:

Most of the early adopters on here made home brew systems in the early days. Some, much more involved than others. Think nick Norman, moominpapa. Others like Dr Bob and much later myself adopted simpler belt and braces methods. As BMS technology has become more widespread,more relied on and ultimately better, perhaps there is enough data out there to suggest that a BMS alone is enough. 

 

From my point of view, and whilst learning, I am happy to have the other protection in the system. Only more time will tell if it's overkill or not. 

 

As Mr biscuits, and others implied, you already rely on things like solar charge controllers to terminate charge at the correct time. 

 

All this, of course, flies in the face of the oft quoted nordkyn and marine know how websites, which I suspect the majority of lithium adopters have never even read. 

Even if it is alone enough, often hitting 3.75V (and being kept there) on a cell seems like a recipe for disaster. You can reprogram the Daly, but a lower cutoff voltage surely means the other cells are not getting charged fully (and thus experiencing a memory effect?)

 

And you're not wrong about relying on chargers - but it's about having multiple lines of defence. A LA battery gasses or chucks acid everywhere if things go wrong. With Lithium there is the potential for fire. And I saw a video of a boat getting set on fire recently - they really burn very very quickly. I have been in a housefire before, one thing I will never forget is how powerful and overwhelming the smoke is, if a fire happens it's not a good situation to find yourself in!

Just now, Tony1 said:

 

Apologies, I skim read and misunderstood the issue. 

I wonder if it might be worth trying to balance the cells?

 

 

I would, but the batteries are sealed and opening them would void the warranty. The passive balancer in the daly seems useless.

[rusty69]

7 minutes ago, DShK said:

37 minutes ago, rusty69 said:

Even if it is alone enough, often hitting 3.75V (and being kept there) on a cell seems like a recipe for disaster. You can reprogram the Daly, but a lower cutoff voltage surely means the other cells are not getting charged fully (and thus experiencing a memory effect?)

3.75 V seems very high to me. What is the cell voltage disconnect value set to?

[DShK]

2 minutes ago, rusty69 said:

3.75 V seems very high to me. What is the cell voltage disconnect value set to?

3.75V, it can be changed in the Daly with the password. My concern is going lower than this, the imbalance means the other cells are not charged. With a 0.3V+ imbalance, to me it looks like they could be nowhere near fully charged if max charge is set to something more sensible like 3.65V.

 

 

[Tony1]

2 minutes ago, DShK said:

Even if it is alone enough, often hitting 3.75V (and being kept there) on a cell seems like a recipe for disaster. You can reprogram the Daly, but a lower cutoff voltage surely means the other cells are not getting charged fully (and thus experiencing a memory effect?)

 

And you're not wrong about relying on chargers - but it's about having multiple lines of defence. A LA battery gasses or chucks acid everywhere if things go wrong. With Lithium there is the potential for fire. And I saw a video of a boat getting set on fire recently - they really burn very very quickly. I have been in a housefire before, one thing I will never forget is how powerful and overwhelming the smoke is, if a fire happens it's not a good situation to find yourself in!

I would, but the batteries are sealed and opening them would void the warranty. The passive balancer in the daly seems useless.

 

I'd be disappointed if had newish lithiums with that kind of spread between the cells, especially as it is causing some complications with managing the charging. I'd be wondering if there might be a warranty issue. 

 

But one approach I take, which I didnt mention earlier, is that for the day to day management of the charging, I use a third BMV712 which specifically monitors the SoC.

I use the 'Low SoC' function on the BMV712 (but I use it in reverse, so to speak), and I set the relay in the BMV to switch at 80 or 90% SoC depending on circumstances. The tiny control wire runs from the BMV to the 'remote BMS' input port that is present on my MPPTS and my B2Bs. If its a Sterling B2B you have, it will have a BMS input port. 

So you can use that control wire from the BMV712 to remotely switch off the B2B when the batteries reach a set SoC, and to switch it back on again when the SoC falls to the set level.  

 

Someone was asking about this SoC monitor setup in a thread a while back, and with Nicks help I was able to explain how I had it set up.