Another Lithium battery thread

[dmr]

I would like an alternator controller a bit like my Adverc but able to do equalisation without its up-down cycle, and also to limit maximum current to eliminate belt slip and to prevent working the alternator flay out. Lithium banks will have other requirements.

Hall effect "current transformers" are very cheap now so it should be feasible to provide current sensing on a controller. This would be a lovely open source project !!!!!

Rather than trying to do everything for everyone I would propose a standardised bit of hardware then those with unusual or new needs could write or customise the software themselves.

 

However, I have a fair bit of experience of producing one off bits of instrumentation and these things often sink or swim depending upon the quality of physical construction such as enclosures, circuit board mounting and choice of connectors. Would need to care using a DIY system to control an alternator, potential for very expensive failures!

 

...............Dave

[Robbo]

22 minutes ago, Dr Bob said:

14.6V charge and a 13.8V float?? Surely not?

Looking at the install doc, they use a battery to battery charger to charge the lifepo4's from the alternator/starter battery.

[Tony Brooks]

2 hours ago, nicknorman said:

I would guess at around 5A max. Whilst I am quite familiar with the theory, I have never actually taken the regulator off an alternator. However as you say, it is just a matter of snipping the wire, taking the ends out to a switch and making sure the joins are well protected. How hard can it be?

 

Maybe one of the alternator experts will be along at some point to verify what I’m saying!

 

Anyway, fitting a switch to cut of the alternator isn’t the best way to deal with things. After you have switched off the alternator field current, any current required by the boat (lights, fridge etc) will come from the batteries which will slowly discharge. And the alternator warning light will be on, along with the audio alarm. So that would have to be dealt with as well.

Depends so much on design. Earlyish Paris-Rhone machines with a separate brush box would be easy but things like the A127 and Bosch machines mount the brush holders on the regulator so you would need to get inside the regulator. It also depends how electricity is conveyed from the field diodes (assuming the common 9 diode machine) to the regulator. If any cable is used then you could break into that but if its just a spring blade contact its much harder unless you bend the blade and solder cables between the blade and its contact point on the regulator. I suspect that is the easiest way on the A127s but you may have to cut the spring blade down. Still if you are into Andrinos and usch like it should be a doddle

[Tom and Bex]

6 hours ago, Dr Bob said:

Does this mean that if the alternator gets to 14.0v it is only 80% charged on your system? If so I probably would not need additional alternator regulation. Also if right, how do you then get it up to 100% every 4-6 weeks to synchronise the BMV? Do you increase the volatage on the alternator regulator?

As voltage rises (very slowly!) during bulk charge, then when it hits 14.0v that equates to approx 80% soc. Continuing charging at 14.0v (absorption) until current drops to say 4% gets you to 100%. If you continue to charge at 14.0v (or any voltage that allows current to continue to flow into batteries) you will overcharge them, regardless of what that voltage is. 

 

5 hours ago, nicknorman said:

T&B has offered me the source code of which he has a copy, I’ll see if he also has a schematic...

 Yes should do, will try to get them over to you later. 

 

6 hours ago, Robbo said:

this BMS looks interesting that may be of interest to us here as it basically looks like you can just use your own sourced cells.

http://www.rec-bms.com

I liked this when looking at BMS options, but cost put me off in the end. 

 

2 hours ago, dmr said:

You could switch off an alternator by switching off the field current but this would involve changes within the alternator which might be fairly easy or very difficult depending upon the alternator. Fitting an external alternator controller (like an Adverc) and disabling the internal regulator would make switching off the alternator a whole lot easier.

 

Can only speak from my experience of A127 alternator, but found it relatively easy to disable internal reg and connect wire for external reg. Although brush holder is built into reg, I believe to disable with a switch, there is a wire running to spade terminal on reg which you could cut into, maybe @Sir Nibble could confirm? 

 

2 hours ago, dmr said:

Nicks point is interesting, once alternator is turned off then if you are running the engine (cruising!!!) then its silly to be running off the batteries, need a system to make enough volts to run the loads but not charge the batteries...this is essentially what a float mode is trying to do but not sure how that works with lithiums.

Is it that big a problem running from the batteries when fully charged? Doesn't do them any good to sit at 100% for too long, and shouldn't affect overall life much if they dropped to say 80% by end of day, then a bit more overnight. With lithiums you really do need to completely rethink your ideas on battery usage and charging, and forget about everything you learnt re lead acid batteries!

 

1 hour ago, dmr said:

I would like an alternator controller a bit like my Adverc but able to do equalisation without its up-down cycle, and also to limit maximum current to eliminate belt slip and to prevent working the alternator flay out.

That's exactly what our arduino controller can do if set up for lead acid instead of lithium. Has an input to enable equalization mode if set up for it. Connects to an existing shunt to measure current flow into batteries. 

 

A quick note re lithium charging voltages, we started with charging at 13.8v, but found we weren't able to make best use of lithiums ability to accept quick charge, so settled for 14.0v as a good compromise. That's still only 3.5v per cell if well balanced, which is well within the safe charging voltages. Just a personal decision though, we were slightly disappointed at first charging at 13.8v.

 

[nicknorman]

1 hour ago, dmr said:

However, I have a fair bit of experience of producing one off bits of instrumentation and these things often sink or swim depending upon the quality of physical construction such as enclosures, circuit board mounting and choice of connectors. Would need to care using a DIY system to control an alternator, potential for very expensive failures!

 

...............Dave

HaHa you obviously have some real design experience! Yes designing the clever bits is easy. Making it human and environment-proof is a lot harder!

[peterboat]

3 minutes ago, Tom and Bex said:

As voltage rises (very slowly!) during bulk charge, then when it hits 14.0v that equates to approx 80% soc. Continuing charging at 14.0v (absorption) until current drops to say 4% gets you to 100%. If you continue to charge at 14.0v (or any voltage that allows current to continue to flow into batteries) you will overcharge them, regardless of what that voltage is. 

 

 Yes should do, will try to get them over to you later. 

 

I liked this when looking at BMS options, but cost put me off in the end. 

 

Can only speak from my experience of A127 alternator, but found it relatively easy to disable internal reg and connect wire for external reg. Although brush holder is built into reg, I believe to disable with a switch, there is a wire running to spade terminal on reg which you could cut into, maybe @Sir Nibble could confirm? 

 

Is it that big a problem running from the batteries when fully charged? Doesn't do them any good to sit at 100% for too long, and shouldn't affect overall life much if they dropped to say 80% by end of day, then a bit more overnight. With lithiums you really do need to completely rethink your ideas on battery usage and charging, and forget about everything you learnt re lead acid batteries!

 

That's exactly what our arduino controller can do if set up for lead acid instead of lithium. Has an input to enable equalization mode if set up for it. Connects to an existing shunt to measure current flow into batteries. 

 

A quick note re lithium charging voltages, we started with charging at 13.8v, but found we weren't able to make best use of lithiums ability to accept quick charge, so settled for 14.0v as a good compromise. That's still only 3.5v per cell if well balanced, which is well within the safe charging voltages. Just a personal decision though, we were slightly disappointed at first charging at 13.8v.

 

I understand your disappointment with 13.8 volts however the shortening of a batteries life by going up to 100% soon makes me smile. I believe the excepted, charging to max, loses cycles over a LifePo4s life, and seeing both GM and Tesla do this for reliability reasons reinforces for me its the right decision. I can also say that early Nissan leafs  are having battery changes because percentage of charge is dropping below 75%, and I know of nobody that restricts charging on electric cars, so can only conclude that 80% is good for my pocket

[dmr]

27 minutes ago, Tom and Bex said:

As voltage rises (very slowly!) during bulk charge, then when it hits 14.0v that equates to approx 80% soc. Continuing charging at 14.0v (absorption) until current drops to say 4% gets you to 100%. If you continue to charge at 14.0v (or any voltage that allows current to continue to flow into batteries) you will overcharge them, regardless of what that voltage is. 

 

 Yes should do, will try to get them over to you later. 

 

I liked this when looking at BMS options, but cost put me off in the end. 

 

Can only speak from my experience of A127 alternator, but found it relatively easy to disable internal reg and connect wire for external reg. Although brush holder is built into reg, I believe to disable with a switch, there is a wire running to spade terminal on reg which you could cut into, maybe @Sir Nibble could confirm? 

 

Is it that big a problem running from the batteries when fully charged? Doesn't do them any good to sit at 100% for too long, and shouldn't affect overall life much if they dropped to say 80% by end of day, then a bit more overnight. With lithiums you really do need to completely rethink your ideas on battery usage and charging, and forget about everything you learnt re lead acid batteries!

 

That's exactly what our arduino controller can do if set up for lead acid instead of lithium. Has an input to enable equalization mode if set up for it. Connects to an existing shunt to measure current flow into batteries. 

 

A quick note re lithium charging voltages, we started with charging at 13.8v, but found we weren't able to make best use of lithiums ability to accept quick charge, so settled for 14.0v as a good compromise. That's still only 3.5v per cell if well balanced, which is well within the safe charging voltages. Just a personal decision though, we were slightly disappointed at first charging at 13.8v.

 

Ooooh   can you tell me more about your Arduino controller, either here or PM, did you buy it or did you make it yourself????

 

Yes, its easy to disable the internal regulator to use an external one (its easy to destroy things with a Dremmel ?), I did try to say this, retaining the internal regulator and getting access to turn it on and off is the potentially harder bit.

 

We are in the habit of leaving quite a lot of stuff turned on, so if we did a long days cruising and the batteries were discharging for most of that time I would be unhappy, especially if the next day or two were going to be none moving days. I suppose this is another variable...charge to 80% most times,but optionally charge to 100% if you want to go a long time before recharging????

 

........Dave

 

..............Dave

[nicknorman]

19 minutes ago, peterboat said:

I understand your disappointment with 13.8 volts however the shortening of a batteries life by going up to 100% soon makes me smile. I believe the excepted, charging to max, loses cycles over a LifePo4s life, and seeing both GM and Tesla do this for reliability reasons reinforces for me its the right decision. I can also say that early Nissan leafs  are having battery changes because percentage of charge is dropping below 75%, and I know of nobody that restricts charging on electric cars, so can only conclude that 80% is good for my pocket

However I suggest (admittedly having zero practical experience, unlike you) that if you limit charging voltage to 13.8v, although you won’t go above 80%, it will take quite a long time to get there since the current will tail off as 80% is approached. No idea how significant this is in practice, but clearly one major advantage of Lithiums - avoiding running a genny endlessly with little current going in - is lessened. Whereas charging at a higher voltage then stopping or reducing the voltage at 80% SoC will mean younreach 80% more quickly. At the expense of additional complication, of course.

3 minutes ago, dmr said:

Ooooh   can you tell me more about your Arduino controller, either here or PM, did you buy it or did you make it yourself????

 

Yes, its easy to disable the internal regulator to use an external one (its easy to destroy things with a Dremmel ?), I did try to say this, retaining the internal regulator and getting access to turn it on and off is the potentially harder bit.

 

We are in the habit of leaving quite a lot of stuff turned on, so if we did a long days cruising and the batteries were discharging for most of that time I would be unhappy, especially if the next day or two were going to be none moving days. I suppose this is another variable...charge to 80% most times,but optionally charge to 100% if you want to go a long time before recharging????

 

........Dave

 

..............Dave

You need to read the earlier part of the thread and T&B’s original thread on the subject! But anyway, it is here, though now sadly gone commercial...

 

http://arduinoalternatorregulator.blogspot.com/

[dmr]

13 minutes ago, nicknorman said:

However I suggest (admittedly having zero practical experience, unlike you) that if you limit charging voltage to 13.8v, although you won’t go above 80%, it will take quite a long time to get there since the current will tail off as 80% is approached. No idea how significant this is in practice, but clearly one major advantage of Lithiums - avoiding running a genny endlessly with little current going in - is lessened. Whereas charging at a higher voltage then stopping or reducing the voltage at 80% SoC will mean younreach 80% more quickly. At the expense of additional complication, of course.

You need to read the earlier part of the thread and T&B’s original thread on the subject! But anyway, it is here, though now sadly gone commercial...

 

http://arduinoalternatorregulator.blogspot.com/

Ive just had a look at that, thanks, that's a lot of functionality to squash into that little bit of Arduino memory!

 

............Daves

[TheBiscuits]

23 minutes ago, nicknorman said:

You need to read the earlier part of the thread and T&B’s original thread on the subject! But anyway, it is here, though now sadly gone commercial...

 

http://arduinoalternatorregulator.blogspot.com/

Except you can't just unilaterally decide to close GPL'd software.  He only needs to provide the source code to anyone he distributes the binaries to, but he has the binaries as public download without the corresponding source download.  He is breaking the terms of the GPL on all the libraries he is using in the software, which is a bad idea for a commercial product.

[Robbo]

5 minutes ago, TheBiscuits said:

Except you can't just unilaterally decide to close GPL'd software.  He only needs to provide the source code to anyone he distributes the binaries to, but he has the binaries as public download without the corresponding source download.  He is breaking the terms of the GPL on all the libraries he is using in the software, which is a bad idea for a commercial product.

Was it under the GPL license?

[dmr]

7 minutes ago, TheBiscuits said:

Except you can't just unilaterally decide to close GPL'd software.  He only needs to provide the source code to anyone he distributes the binaries to, but he has the binaries as public download without the corresponding source download.  He is breaking the terms of the GPL on all the libraries he is using in the software, which is a bad idea for a commercial product.

I hadn't really thought of that, I would think its frowned upon to make an open source project commercial, or was it just a private hobby project where he chose to publish his code??? The arduino is only a little thing so its no big deal to write your own version of any libraries which should get round any licence limitations, Ive done a couple myself though in my case it was to save memory rather than to get round copyright.

 

..............Dave

[TheBiscuits]

8 minutes ago, Robbo said:

Was it under the GPL license?

GPL 3 originally - his binary download on github still contains a copy of the GPL.

https://github.com/AlternatorRegulator/

3 minutes ago, dmr said:

I hadn't really thought of that, I would think its frowned upon to make an open source project commercial, or was it just a private hobby project where he chose to publish his code???

Making a GPL project commercial is not frowned upon at all as long as you comply with the licence terms.  Just closing the source to a project that uses other GPL software is very frowned upon.

  

"Free as in speech, not free as in beer."

[Robbo]

13 minutes ago, dmr said:

I hadn't really thought of that, I would think its frowned upon to make an open source project commercia

Most open source projects are commercial and are done by commercial companies.   Most “smart” hardware now would have some open source in it.

[nicknorman]

1 hour ago, dmr said:

Ive just had a look at that, thanks, that's a lot of functionality to squash into that little bit of Arduino memory!

 

............Daves

Depends which Arduino and how efficiently the code is written and compiled I suppose. But I would have thought 32k programme and 2k ram would be plenty. My project has used just over 1/2 the 28k programme memory on the PIC so far, and a lot of that is the routines for the I2C and one-wire interfaces to the 3 pressure sensors and 1 temperature sensor, and dealing with the weirdness of their driving requirements and processing/calculating their outputs into hPa and deg C. The actual main loop and interrupt service routines are pretty small.

 

I'm not an Arduino officianado - the concept of "sketches" irritates me slightly! Why not just call them programmes? And it is a bastardised version of C isn't it?, why not just call it C with libraries!

Yes it is very accessible for people who can't really programme, but for anything serious I don't really want a pre-made board which basically just has the processor pins taken out to connections. Better to make a board up oneself and then you don't need the great big DIL packaged processor!

 

OK Yes I admit it, I am a PIC fan!

[dmr]

6 minutes ago, nicknorman said:

Depends which Arduino and how efficiently the code is written and compiled I suppose. But I would have thought 32k programme and 2k ram would be plenty. My project has used just over 1/2 the 28k programme memory on the PIC so far, and a lot of that is the routines for the I2C and one-wire interfaces to the 3 pressure sensors and 1 temperature sensor, and dealing with the weirdness of their driving requirements and processing/calculating their outputs into hPa and deg C. The actual main loop and interrupt service routines are pretty small.

 

I'm not an Arduino officianado - the concept of "sketches" irritates me slightly! Why not just call them programmes? And it is a bastardised version of C isn't it?, why not just call it C with libraries!

Yes it is very accessible for people who can't really programme, but for anything serious I don't really want a pre-made board which basically just has the processor pins taken out to connections. Better to make a board up oneself and then you don't need the great big DIL packaged processor!

 

OK Yes I admit it, I am a PIC fan!

Yes, I fully shared your dismay at the term "sketches". I believe Arduino was aimed at non programmers and somebody thought this term might be less scary to the creative-arty types. But then they chose to standardise on "C" which is just about the scariest techy language you can get (assembler excepted). I would have thought a version of Basic or even Python would have been better....but then C is better for hardware related stuff.  I note that the bloke who does Basic for Android etc has done a Basic for Arduino, but I have not played with it.

 

Making PCB's is hard work so I think the Arduino concept is good, its instant electronics/software gratification!  Looking at the www most people plug them into those plastic breadboard things. They really are the work of the devil, especially for high speed stuff.

 

I used a library do drive one of those lovely little OLED graphics displays and the code plus the character set used up nearly all the memory.

 

....and programmes (programs) don't exist anymore, they are Apps now ?

 

and yes, I'm a bit of a fan of these things too, trouble is my specialty these days is audio capture and signal processing and they just haven't quite got the power for that.

 

................Dave

[nicknorman]

1 hour ago, dmr said:

Yes, I fully shared your dismay at the term "sketches". I believe Arduino was aimed at non programmers and somebody thought this term might be less scary to the creative-arty types. But then they chose to standardise on "C" which is just about the scariest techy language you can get (assembler excepted). I would have thought a version of Basic or even Python would have been better....but then C is better for hardware related stuff.  I note that the bloke who does Basic for Android etc has done a Basic for Arduino, but I have not played with it.

 

Making PCB's is hard work so I think the Arduino concept is good, its instant electronics/software gratification!  Looking at the www most people plug them into those plastic breadboard things. They really are the work of the devil, especially for high speed stuff.

 

I used a library do drive one of those lovely little OLED graphics displays and the code plus the character set used up nearly all the memory.

 

....and programmes (programs) don't exist anymore, they are Apps now ?

 

and yes, I'm a bit of a fan of these things too, trouble is my specialty these days is audio capture and signal processing and they just haven't quite got the power for that.

 

................Dave

On the subject of making PCBs, whilst I can and do make quite good single sided boards thanks to the joys of modern inkjet printers, double sided boards with vias and solder mask are a bit beyond me! However there is a company called Elecrow in China that will make me 10 double sided boards (100mm x 100mm) with all the trimmings for $5. Yup, five US dollars, or $0.5 each. Of course if you want it quick, there is another $26 for express shipping but if you don't mind waiting a month or so, the shipping is $8 via ordinary airmail. With the expensive shipping, turnaround will be about a week - 10 days. I have yet to try them but they seem to have a good reputation. Been spending tonight finalising the pcb design so should be ready to try soon. It will be mostly surface mount. This is one of the pressure sensors I am using, 8 pads underneath it. But with solder paste and a hot air rework station I had instant success soldering one to a test PCB I'd made. Just need strong glasses and a steady hand to position it! The sensor outputs pressure from 200 to 1200 hPa with a 24bit AtoD, uses a milliamp at 3v, has I2C interface and all for under £3.

[peterboat]

4 hours ago, nicknorman said:

However I suggest (admittedly having zero practical experience, unlike you) that if you limit charging voltage to 13.8v, although you won’t go above 80%, it will take quite a long time to get there since the current will tail off as 80% is approached. No idea how significant this is in practice, but clearly one major advantage of Lithiums - avoiding running a genny endlessly with little current going in - is lessened. Whereas charging at a higher voltage then stopping or reducing the voltage at 80% SoC will mean younreach 80% more quickly. At the expense of additional complication, of course.

 

 

I dont know Nick, as all my charging in summer is done by solar, and I see big amps going in and then it just drops to 1-2 amps before shutting off altogether, the controller then drops to 13.6 volts, which is a setting for gel batteries. When i have completely finished my conversion, I will customise the settings on the midnite, but until then its safe and secure on what it is.

In the spring I will have all 3.6k watts working on the solar so I will let you know how it all works then.

Remember that my system is a 24 volt system but I convert it to 12 volts so its easier to understand for narrowboaters who have this

[Tom and Bex]

7 hours ago, peterboat said:

I understand your disappointment with 13.8 volts however the shortening of a batteries life by going up to 100% soon makes me smile. I believe the excepted, charging to max, loses cycles over a LifePo4s life, and seeing both GM and Tesla do this for reliability reasons reinforces for me its the right decision. I can also say that early Nissan leafs  are having battery changes because percentage of charge is dropping below 75%, and I know of nobody that restricts charging on electric cars, so can only conclude that 80% is good for my pocket

Except I only rarely charge to 100%. Usually operate in the 30-80% range. As Nick says, you can get to 80% quicker by charging to 14.0v and then stopping charge. We'll just have to see how long these cells last, I guess.

 

I think it's still a learning curve for the manufactures as well if you look at how their recommendations on voltages have changed over the years, but remember, our market sector is insignificant to them, so no research into our usage rarely takes place. 

 

7 hours ago, dmr said:

Ooooh   can you tell me more about your Arduino controller, either here or PM, did you buy it or did you make it yourself????

 

Yes, its easy to disable the internal regulator to use an external one (its easy to destroy things with a Dremmel ?), I did try to say this, retaining the internal regulator and getting access to turn it on and off is the potentially harder bit.

 

We are in the habit of leaving quite a lot of stuff turned on, so if we did a long days cruising and the batteries were discharging for most of that time I would be unhappy, especially if the next day or two were going to be none moving days. I suppose this is another variable...charge to 80% most times,but optionally charge to 100% if you want to go a long time before recharging????

 

........Dave

 

..............Dave

I'm quite good at destroying things even without a dremmel! As to deciding when to stop charging, our setup will charge to 100% if left to it's own devices, and then switch to "float", except it monitors current, and tried to keep it as close to 0A as possible (but due to failsafe max voltage, in reality discharges to low 90's% before stabilising which suits us fine). Again, all fully customisable. We also have a switch to force "float" mode at any time, often used to stop charging at 80-90% when on extended cruising. "Float" mode is also activated automatically if temp drops to freezing at the batteries. 

 

I think Nick's answered most of your other questions already. If you PM me your email I'll send the files on to you as well (and anyone else who's interested). To be honest, this is all a bit (lot!) out of my comfort zone! Just glad to have something that works well, and is programmable to my exact needs. 

 

 

Edited January 8, 2019 by Tom and Bex
Spelling

[MoominPapa]

A quick report on progress with the Moomin-BMS. State-of-charge based on coulomb-counting is now functional, as is charge and discharge disconnect. The 3.5Ah test battery had its first full charge and full discharge cycle yesterday evening. The load bank pulls just over three amps, which is roughly C. Limiting the charge voltage to 14.0 gives a charge current of around 2/3 C That's 14.0v at the bench power supply. At the battery it's a bit lower due to the weedy wiring and connections in my test setup. For the next run I'll take the cell voltage up to 14.0.

 

These cells do have an amazing ability to accept charge. The charge current was very stable right 'till the end, which was kind of nerve-wracking as I had no idea  what  the initial state-of-charge was, and therefore when the end would be.

 

MP.

 

 

[nicknorman]

8 minutes ago, MoominPapa said:

A quick report on progress with the Moomin-BMS. State-of-charge based on coulomb-counting is now functional, as is charge and discharge disconnect. The 3.5Ah test battery had its first full charge and full discharge cycle yesterday evening. The load bank pulls just over three amps, which is roughly C. Limiting the charge voltage to 14.0 gives a charge current of around 2/3 C That's 14.0v at the bench power supply. At the battery it's a bit lower due to the weedy wiring and connections in my test setup. For the next run I'll take the cell voltage up to 14.0.

 

These cells do have an amazing ability to accept charge. The charge current was very stable right 'till the end, which was kind of nerve-wracking as I had no idea  what  the initial state-of-charge was, and therefore when the end would be.

 

MP.

 

I can't remember what SoC a steady 14v equates to, is it close to 100%?

 

It would be interesting to find out whether, for those people who want to charge only to 80% for reasons of cycle life, charging at 13.8v results in the same initial high current and rapid fall off of current as 80% SoC is reached.

10 hours ago, peterboat said:

I dont know Nick, as all my charging in summer is done by solar, and I see big amps going in and then it just drops to 1-2 amps before shutting off altogether, the controller then drops to 13.6 volts, which is a setting for gel batteries. When i have completely finished my conversion, I will customise the settings on the midnite, but until then its safe and secure on what it is.

In the spring I will have all 3.6k watts working on the solar so I will let you know how it all works then.

Remember that my system is a 24 volt system but I convert it to 12 volts so its easier to understand for narrowboaters who have this

Yes it is a lot easier if you don't have an alternator to deal with!

[Tacet]

12 hours ago, nicknorman said:

.

Expect some sadness in your life in 2019.......

[Dr Bob]

Ok, this thread is working well to help me map out the way forward. I think I have a reasonable handle on charging and what to do with the alternator now.

Let me ask another question.

If we go back to my original post and look at the diagram suggested by Eric (Eric of the blog on SLA/LiFePo hybrid systems), the hybrid system is designed so the SLA stops any technical issues if the Lithium bank is disconnected in an emergency. I am attracted to this system as all I need to do is put a lithium circuit in place (with auto disconnect on high/low voltage) and a manual disconnect ...and move the BMV712 to the Li circuit. I am wondering how many SLAs to leave in place ...ie I could leave all 6 *110Ahr in place inititally. Under normal operation how would this work.

Let's start in the evening in January with the Li and SLA's with no load and no charge....with the Li's at 75%. Voltage on the Li bank will be 13.0V+ so providing a trickle charge to the SLA which will have some 'internal' discharge (ie the SLA bank is fully charged and would be at 12.7V at rest). I now turn on the inverter and with the fridge and TV on etc, I am taking 10A. I assume from what Eric said that would all come out of the Lithium bank as the voltage drop in the bank is minimal (assume say 360Ahr of LiFePo capacity). I operate overnight like this so by morning the Li's have gone down from 75% SoC to say 40%. At 40% SoC, the lithium voltage is still over 13.0V (????) so the SLA's are still at 100%. Morning comes, I start the engine and the Li's charge back up to a target of 80% . Charge is then switched off and the SLA's are still at 100%.

This sounds like the SLAs will always be full. Yes they will take power out of the Li's to cover their self discharge but in principle, there will be little cycling in the SLA's. The only time the SLA's would go down in SoC is if the Li's drop to a voltage <12.8V but by that time I would have taken action.

Is this thinking correct?

If so I would be tempted into just leaving my SLA's in place and piggy backing the Li system - maybe putting my old BMV501 monitor on the total system and the BMV712 on the Li only circuit

 

[MoominPapa]

1 hour ago, nicknorman said:

I can't remember what SoC a steady 14v equates to, is it close to 100%?

 

It would be interesting to find out whether, for those people who want to charge only to 80% for reasons of cycle life, charging at 13.8v results in the same initial high current and rapid fall off of current as 80% SoC is reached.

Yes it is a lot easier if you don't have an alternator to deal with!

My 14.0V was under heavy charge, so tells you much more about the charge current than the SOC. and don't forget that this was a 3.5Ah pack, being charged at almost 1C. At the fractional-C charge rates likely with a domestic bank and alternator, I doubt the voltage will reach anywhere near 13.8 until the SOC is pretty high. My next test is a long charge at current limited to  half an amp, which equates to the 0.15C I'll get from a 70A alternator into my 480Ah bank, I need to let the logging subsystem sorted first though: the charge curve will be useful, and I'm not going to sit there for 7 hours manually noting data.

 

I'd expect the difference between doing CV at 13.8 and CV at 14.0 to be that the CV state is reached earlier, and the current fall-off will be more gradual. It will still get  to 100% but take a little longer.

 

MP.

 

ETA. Interesting problem with the 500mA charge scenario. The balancing shunts are sized for the full size system. and divert 200mA around up to three of the cells in the four-cell series string. That has quite a big effect on the small test battery being charged at 500mA!

 

 

 

 

Edited January 8, 2019 by MoominPapa

[Johny London]

I have been thinking whether I could add lithiums in addition to the LA's, partly because it's a new thing and I'm 100% dependant on my power, as a liveaboard. My idea was to use a bank selector switch. The idea of just paralleling sounds interesting though. Yet it seems rather inelegant..

 

On another note, all this messing around with extra cabling, switches and fuses - (and protection devices) all adds significant cost, and the resulting "home brew" lithiums only being able to give 50-60% of their capacity makes me wonder whether an off the shelf solution could be the way forward. After checking the "battleborn" website, they seem to have everything covered including internal disconnect protection - true drop in replacements and you can use 100% of the capacity (though they do quote much lower cycles probably due to this. But even 3000 cycles is still 8-9 years.

https://www.solar-electric.com/lib/wind-sun/Battleborn_BB10012_specifications.pdf

Just another way to go... if you can get them.