Lifepo4 battery too cheap?

[IanD]

4 minutes ago, TheBiscuits said:

 

I quite agree, it just struck me as funny.

 

The real limit for solar on boats - as you are well aware - is available roof space for them.

 

Wallet depth is another consideration, but that can be spread out over time if needed, the roof size tends to stay fixed.

It was quite a good joke... 😉

 

By the time you include the real overall costs of the alternatives (generator, wear/servicing engine, fuel) solar is now the cheapest way of generating power onboard, and prices are still dropping while the alternatives are going up. DAMHIK...

Edited February 14, 2023 by IanD

[n-baj]

40 minutes ago, TheBiscuits said:

 

Just watch out that Renogy quote the output power of their B2B and Sterling quote the input power.

 

The Sterling 60A takes 60A from the charge source and delivers around 45A to the battery.  The Renogy 60A delivers 60A to the battery so takes 80-90A from the source.

 

It makes quite a difference if you're trying not to kill an alternator!

 

Both can be switched to half-power mode though, but if it's going to be used permanently, buy the smaller B2B!

 

I ended up going for a clearance Sterling - works fine but has a scratched case.

 

Also Renogy emailed me this morning to say they're having a sale this week.  It's of no interest to me, but if you have already decided on their product ...

I’ve read the manual for the b2b and it states the efficiency is 90% so figured on a 60A model it will be around 66A. As it happened I’ve experimented the other day by putting a 60-70A load on the alternator (110A) and it was heating up too much (90 deg c+) at around tick over so decided on the 40A model. I know it will cool down at higher revs but I don’t want to be in a flight of locks or going past a line of moored boats worrying about the temperature of the alternator. If the 40A charger takes less than 50A from the alternator then I’d be surprised if there’s still an overheating problem but I will email renology and get a confirmation on the input current.

 

37 minutes ago, IanD said:

If you're wanting to be able to run more than one normal domestic electrical appliance at a time then 200A maximum current (limited by the JBD BMS) isn't really enough, and anyway I wouldn't want to push a BMS/battery like this to their absolute maximum limit because they're never clear about how long this can be sustained for.

 

If you want to do this then instead of 2 parallel 12V batteries you'd be better using either 2 in series or the 24V 280Ah battery (where 200A is 4.8kW nominal) and something like a Victron Multiplus II 24/5000 inverter/charger -- high power inverters are cheaper at 24V anyway. But then you've got to deal with how to get the alternator to charge them...

 

Alternatively, lower your expectations of how much power you need... 😉

I don’t run more than 1 high power device as the inverter is 2.5kw. The washing machine is really the only necessary high power device I use. In winter I only use the inverter on moving day to do the laundry as the food is in nature’s fridge. Summer I use the electric kettle, microwave and toaster (not all at once!) simply to use the excess solar once the batts are fully charged. On cloudy days and in evenings I tend to use gas. I intend to carry on with this system with lithiums with the addition of having a 1kw immersion. You’re right it’s not good to run the bms right at the limit and if the kettle or washing machine runs the bms at the limit then I’d just get a lower power kettle and only use the washing machine when I’m moving like I do currently. 

[Tony1]

16 minutes ago, rusty69 said:

Yeah but every boat should have an amp clamp and IR thermometer anyway. How else are we going to measure the temperature of everything that moves, and most things that don't for a whole week after buying one.

 

Yes, the little laser pointing thing is quite addictive. I did develop a sudden interest in knowing the temperature of every object on the boat. 

 

But maybe the OP could borrow these items from a nearby boating friend, and save a few quid? 

 

 

[Jon57]

1 minute ago, Tony1 said:

 

Yes, the little laser pointing thing is quite addictive. I did develop a sudden interest in knowing the temperature of every object on the boat. 

 

But maybe the OP could borrow these items from a nearby boating friend, and save a few quid? 

 

 

£17at lidl atm 👍

[MtB]

5 minutes ago, Tony1 said:

Yes, the little laser pointing thing is quite addictive. I did develop a sudden interest in knowing the temperature of every object on the boat. 

 

 

 

And shockingly inaccurate in my experience, if you point them at something you already know the temperature of. 

 

Or maybe they have improved nowadays.

 

 

 

 

[TheBiscuits]

6 minutes ago, n-baj said:

The washing machine is really the only necessary high power device I use.

 

Feed it with hot water via a thermostatic mixer valve set to the wash temperature you desire.  The motor only uses a few hundred Watts, nearly all the power goes into heating the water.

[n-baj]

32 minutes ago, Tony1 said:

 

This is a very important point. 

 

I bought two Sterling B2Bs, but my smaller alternator can't even deliver 45 amps without overheating to above 100 degrees- which I thought was a bit too hot, given the normal running temp is less than 60 degrees. 

Luckily the Sterling has a half power mode, so I switched down to that and the B2B delivers about 30 amps, which the alternator can do without getting hot. 

My alternators are pretty low capability, and yours may well be able to put out larger current and still stay cool, but I would strongly recommend doing some testing before you spend a few hundred on a B2B. 

 

You need to find out how much current the alternator can put out and still stay under 100 degrees or so. When testing, run it for at least 20 mins- and bear in mind that a test in cold weather with the engine cover off wont closely reflect summer use. 

 

You can test out your alternators capacity by buying a 10 metre length of cable that is about 10mm square, and connecting the long cable between the lead acid battery and the lithium battery (or between the alternator and the lead acid, I'm not sure if it matters that much).

I think the main thing is limit what goes into the lithiums, and keep an eye on the alternator temp every few mins. They can overheat really quickly, so be very very careful).

The length of the cable will control how much current can pass through, so you can shorten the cable length in say 50cm steps. In this way you can test increasing levels of current, and find out when the alternator gets too hot.  Its a lot of faffing fitting new lugs on the cable ends every time you chop half a metre off it, but its worth knowing your alternator's capacity.

 

With this approach you can find out what your alternators safe limit is, and buy a B2B that delivers the right current. 

Or you could just carry on charging using a long length of cable- loads of people are charging lithiums in parallel just using 'long wire' method. 

 

With the money saved form buying a B2B, you could more panels and another MPPT, and that way you might get enough solar for hot water during the summer, so that you dont need to run the engine half so much anyway. I think 1000 watts would pretty much guarantee solar hot water for a few months in the summer, and would extend the number of months that you get enough solar for a fridge and lights etc.

I have 1400 watts of panels, and yesterday I got just over 1700Wh of power from the panels, so no engine running was needed. Today not so good, but you get the point.

 

This will mean buying a clamp meter (to measure how much current is going through a cable) and an infra red type thermometer to keep an eye on the alternator, but tbh there will be other costs anyway. Lengths of cable, lugs, a decent crimper to fit the lugs, the list does go on a bit.

 

ETA- just a thought. Also test the alternator temp at different rpm, just out of interest. 

I found that if I charged at say 1300rpm, the alternator was able to put out more current before it started to overheat. 

Knowing that, I then bought a second B2B of lower power, and in winter when doing a static charge moored up, I switch on the extra B2B and up the revs to 1300rpm, and I can charge a bit faster with more current from the alternator. 

(That's not a suggested approach btw, I think I had gotten B2B fever at that point)

 

 

 

 

 

Thanks Tony I’ve started experimenting last week with a clamp meter and thermometer and 60-70A is a few amps too far so wanting the continuous load to be less than 50A on a 110A alternator. I don’t anticipate overheating on that load but plan to try it when I run the engine and move on Thursday. I’ve tested at tick over or the min amount of revs needed to achieve the target output for worse case. If the alternator still doesn’t like continuous loading at <50% of the rated output then I’d be suprised.

[Tony1]

34 minutes ago, n-baj said:

 

 As it happened I’ve experimented the other day by putting a 60-70A load on the alternator (110A) and it was heating up too much (90 deg c+) at around tick over so decided on the 40A model. I know it will cool down at higher revs but I don’t want to be in a flight of locks or going past a line of moored boats worrying about the temperature of the alternator. If the 40A charger takes less than 50A from the alternator then I’d be surprised if there’s still an overheating problem but I will email renology and get a confirmation on the input current.

 

 

Aha, I see you're already au fait with the testing of the alternator. 

I had the same thought as you- I needed a charging setup that stayed cool at tickover in case of locks etc) 

But here's another thought- why not consider an alternator upgrade? 

If yours is a poly V type of belt (the thicker type) , you can probably get a 160 amp alternator for not much more cash than a B2B charger, and that would allow you to charge at 90 or 100 amps instead of 40 or 50amps. 

(You could still use the 'long wire' method to control the charging current, and save the cost of a B2B.)

It doesnt sound much, but in winter it means only running the engine for maybe an hour, as opposed to two hours or more with a lower charge current- so there's a saving on diesel, and on engine servicing costs due to less running hours. 

 

 

ETA- that was just a left field idea really- in your shoes, my preferred option would be to use the money on more solar, and use a long wire length to control charge current, but I would think that some kind of battery monitoring would also be advisable? And a way to stop the charging when the batteries reach say 13.9 volts  So the costs would start to mount up.

 

So I can see how a B2B does look a decent option as it manages the charging current/voltage, and will stop the charging at your chosen criteria, rather than relying on the battery's built in BMS, which should be considered an emergency/backup safety system, and never used in the day to day charging operations. 

 

 

Edited February 14, 2023 by Tony1

[MtB]

4 minutes ago, TheBiscuits said:

 

Feed it with hot water via a thermostatic mixer valve set to the wash temperature you desire.  The motor only uses a few hundred Watts, nearly all the power goes into heating the water.

 

Except when it starts up, when the current draw will be significantly higher than steady run speed AIUI.

 

[n-baj]

2 minutes ago, TheBiscuits said:

 

Feed it with hot water via a thermostatic mixer valve set to the wash temperature you desire.  The motor only uses a few hundred Watts, nearly all the power goes into heating the water.

It’s fed via the calorifer but I do set it at 40 deg c so it does use the element if the water isn’t quite at that temperature. I could use it on cold wash only but I’m including the washing machine because there’s a possibility of using it on sunny days and not have to run the engine and I can heat the water electrically using excess solar 🙂

[Tony1]

26 minutes ago, n-baj said:

Thanks Tony I’ve started experimenting last week with a clamp meter and thermometer and 60-70A is a few amps too far so wanting the continuous load to be less than 50A on a 110A alternator. I don’t anticipate overheating on that load but plan to try it when I run the engine and move on Thursday. I’ve tested at tick over or the min amount of revs needed to achieve the target output for worse case. If the alternator still doesn’t like continuous loading at <50% of the rated output then I’d be suprised.

 

Yes mine is not a great example and has poor charging capacity. In my case I have a 100 amp domestic alternator, but at tickover it will not put out more than about 45 amps without getting too hot- so a bit less than 50% of its official rating (I suppose in fairness, it was intended to work with lead acids).

Yours will probably be ok putting out 50% of its rated current for long periods, but definitely worth checking before splashing the cash. 

 

ETA- I did a lot of testing with my alternator at different current outputs,  and I found it reaches a point where just a few extra amps coming out started it overheating to above 100 degrees, so with mine there is a bit of a fine line that I had to stay within. 

If your chosen temp limit is less than 90 degrees, you might find even putting out 50% of its max current will be pushing it a bit. 

I hope you'll keep us updated- I have a morbid fascination with other people's alternators- largely out of jealousy I think.  

 

Edited February 14, 2023 by Tony1

[rusty69]

27 minutes ago, Tony1 said:

So I can see how a B2B does look a decent option as it manages the charging current/voltage, and will stop the charging at your chosen criteria, rather than relying on the battery's built in BMS, which should be considered an emergency/backup safety system, and never used in the day to day charging operations. 

Are you sure about that? It seems to be the preferred method recommended on certain facebook groups.

[n-baj]

5 minutes ago, Tony1 said:

 

Aha, I see you're already au fait with the testing of the alternator. 

I had the same thought as you- I needed a charging setup that stayed cool at tickover in case of locks etc) 

But here's another thought- why not consider an alternator upgrade? 

If yours is a poly V type of belt (the thicker type) , you can probably get a 160 amp alternator for not much more cash than a B2B charger, and that would allow you to charge at 90 or 100 amps instead of 40 or 50amps. 

(You could still use the 'long wire' method to control the charging current, and save the cost of a B2B.)

It doesnt sound much, but in winter it means only running the engine for maybe an hour, as opposed to two hours or more with a lower charge current- so there's a saving on diesel, and on engine servicing costs due to less running hours. 

 

 

 

No it’s not a poly v belt it’s a Barrus shire so 2 alternators (50A and 110A) each with its own thin belt so a bigger alternator might start to eat belts.

 

I prefer to go down the b2b route because I can set and control the output voltage into the lithiums and also in the event of the 110A alternator failing I can easily connect the 50A alternator and half the output of the B2B

 

Also I only use the engine if it has several jobs to do (electric generation, hot water for washing, moving, etc) if I only want the batteries charging I use the genny in the winter (80A charger) or if I want a shower I use the ebersplutter. I’d rather use devices costing hundreds to do those jobs rather than an engine costing many thousands but that’s just me. I find my 370w panel is fine in the summer although the mppt allows another panel on if I need another. on the odd occasion I need the batteries charging in the summer I run the engine and engage gear and maybe put a wash on if I’m going past a water point (I don’t run the genny in the summer months)

 

 

[Tony1]

9 minutes ago, rusty69 said:

Are you sure about that? It seems to be the preferred method recommended on certain facebook groups.

 

I think if the BMS criteria and limits are properly configurable, they might useful for day to day charging control, but the ones I've seen look a bit extreme. 

E.g. I've seen a few that only disconnect the battery at say 10v, which is very very low for daily usage really, probably corresponding to 1% SoC or similar. On a day to day basis you want to be cycling them between 20-80% (give or take 5% or so for individual preference), with maybe a bi-weekly excursion from say 100% down to 5 or 10% as a sort of limbering up exercise to stop them getting lazy). 

There is a whole range of advice about it, and it seems to change every year, but thats my own approach- at the moment anyway. 

The other concerns is the high voltage disconnect might be a bit too high, e.g. it might allow the batteries to charge to say 99% before it disconnects them- which again seems a bit much for day to day charging. 

Charging them with a charger that will go into float at say 14v is a good way to make sure the SoC and the voltage dont get too high on a daily basis. 

But to be fair, I am a complete amateur and maybe using rather outdated advice, there will be others hopefully who will provide more reliable info. 

Edited February 14, 2023 by Tony1

[n-baj]

32 minutes ago, Tony1 said:

 

Yes mine is not a great example and has poor charging capacity. In my case I have a 100 amp domestic alternator, but at tickover it will not put out more than about 45 amps without getting too hot- so a bit less than 50% of its official rating (I suppose in fairness, it was intended to work with lead acids).

Yours will probably be ok putting out 50% of its rated current for long periods, but definitely worth checking before splashing the cash. 

 

ETA- I did a lot of testing with my alternator at different current outputs,  and I found it reaches a point where just a few extra amps coming out started it overheating to above 100 degrees, so with mine there is a bit of a fine line that I had to stay within. 

If your chosen temp limit is less than 90 degrees, you might find even putting out 50% of its max current will be pushing it a bit. 

I hope you'll keep us updated- I have a morbid fascination with other people's alternators- largely out of jealousy I think.  

 

The 90 deg c limit is just what I’ve read what others consider a overheating alternator. Maybe it’s fine at 100 deg or 110 deg but I really don’t know the temp the alternator doesn’t like so I’m erring on the side of caution. I’ve measured where the stator coils are and that was 140 deg so figured that is too hot. They run at 50% efficiency I’ve read so if running at 900 watts for example it’s got to dissipate 900 watts of heat, almost one of them glowing bars on an electric fire!

 

I’ll keep you all updated. I’ve replied to your pm tony but I don’t know if it went through being a noob 

[Tony1]

13 minutes ago, n-baj said:

No it’s not a poly v belt it’s a Barrus shire so 2 alternators (50A and 110A) each with its own thin belt so a bigger alternator might start to eat belts.

 

I prefer to go down the b2b route because I can set and control the output voltage into the lithiums and also in the event of the 110A alternator failing I can easily connect the 50A alternator and half the output of the B2B

 

Also I only use the engine if it has several jobs to do (electric generation, hot water for washing, moving, etc) if I only want the batteries charging I use the genny in the winter (80A charger) or if I want a shower I use the ebersplutter. I’d rather use devices costing hundreds to do those jobs rather than an engine costing many thousands but that’s just me. I find my 370w panel is fine in the summer although the mppt allows another panel on if I need another. on the odd occasion I need the batteries charging in the summer I run the engine and engage gear and maybe put a wash on if I’m going past a water point (I don’t run the genny in the summer months)

 

 

 

I remember us chatting about the genny thing, and I do agree it makes a lot of sense to use an engine that costs £400 than use one that costs £8000.

I did consider a genny myself for this reason, but I can charge at 80 amps plus if needed, and so my engine charging runs are quite short, and they are only needed anyway between say mid-Nov and mid-Feb (so less than 100 days per year).

Outside that time window my solar starts to do the job most of the time, and by March I'm expecting solar hot water on some days. 

 

Apologies, I hadn't picked up that your approach for the engine charging is only for periodic use when washing machine is on etc. That does change things a bit really, and a B2B is a simple solution that you can fit yourself, and it will manage the voltage and current pretty well, 

 

 

 

[IanD]

26 minutes ago, rusty69 said:

Are you sure about that? It seems to be the preferred method recommended on certain facebook groups.

The problem with certain facebook groups -- and a lot of blogs on the subject -- is that people hack something dubious together (like badly thought out parallel LA/LFP) and go "Woo hoo, this was dead easy and works just great!"

 

Which it does, for a bit -- LFP won't fail dramatically if you discharge them down to 0% or less and up to 100% or more (or whatever limits the internal BMS does an emergency disconnect at), but for sure their lifetime will be reduced significantly, maybe drastically depending how tight the internal protection is. They're not designed to hit these charge limits as a matter of course, only in an emergency. If you take care over how you use the system to stop this happening then that's fine, but they're not idiot-proof -- and there are plenty of idiots out there who will just let these disconnections happen all the time, maybe even thinking this is "normal"... 😉

 

If the batteries then die after a year instead of the predicted 10 years, that's not the bloggers problem, they're long gone -- but it is for the poor boater whose expensive long-life lithium batteries are now dead... 😞

Edited February 14, 2023 by IanD

[Tony1]

5 minutes ago, n-baj said:

 

 I’ve replied to your pm tony but I don’t know if it went through 

 

 

Yes it did, and I appreciate the offer, but I've already explained that sex acts with gerbils just don't interest me

 

[n-baj]

6 minutes ago, Tony1 said:

 

Yes it did, and I appreciate the offer, but I've already explained that sex acts with gerbils just don't interest me

 

Will hamsters be okay?

[n-baj]

Okay after fun with gerbils I’ve tested the alternator today. I let everything warm up by subjecting the alternator to a load for a while, then set it so it produced about 50A for about an hour at tick over speed (about 900rpm) I chose this because the B2B charger quotes an efficiency of 90% so assume on a 40A output will take about 44A although I have emailed/raised a ticket with renology to confirm this.

 

the temps seems to plateau at 100 deg c on the main body and 120 deg c where the stator coil is. This is very worse case, usually the alternator will be spinning faster so will be running cooler. I’ve emailed Barrus Shire asking for max safe temperatures. I really don’t want to charge lower than 40A.

 

I’m planning to have a lead acid and alternator into the B2B charger then from the B2B into the interver/solar charger output/lithium batts so I’ve emailed the firm where I got the solar system from and asked if when the bms stops charging it will do any damage to the solar controller. The reply is;

 

“The controller is designed to work with lithium, and although there can be issues if batteries are disconnected while there is solar production, we haven't heard of any cases so far, related to BMSs shutting off charge acceptance and causing an issue. In any case, I would recommend you stick to the charge voltages as specified by the battery manufacturer, and this should avoid the BMS shutting down, as this is really a 'last resort' to avoid overcharging.”

 

I’ve read that as no reported issues when it stops accepting charge (but it’s still connected to the battery) but there’s issues when the bms shuts off the battery completely (equivalent to isolating a battery completely).

 

I’m not too au fait with lithium bms but is there 2 types of disconnect? e.g there’s normal ‘okay I’m 95% full or whatever I’ll stop accepting charge but allow discharge’ and then there’s the second emergency ‘NOOOO! the pack voltage is 16v I’m about to blow up isolate everything NOW!’?

 

Im guessing the controller will be fine at normal disconnect but will be unhappy at the second disconnect, if bms devices work like that?

[Tony1]

 

If I understand the setup right, I don't think you'll ever have a situation where the battery's internal BMS kicks in and disconnects it because the voltage is too high. 

The reason I say that is because you're using both a B2B and an MPPT to do the charging, and with both of those chargers you can set charging profiles so that they will go into float at say 14v (there might be a user defined profile you can set up). 

So the bulk charge voltage you set up on the charging profiles will be well below the high voltage cutoff limit that is set within the BMS. The internal BMS disconnect might not kick in until you get above 14.6v for example, or maybe higher. 

As soon as the battery voltage gets up high enough, the chargers will just go into float mode and basically stop the charging.

I have my float set to 13.15v, which means basically no charging is happening. 

With lithiums I personally dont think you need a float phase, you just bulk charge them, and then stop the charging at the correct point. 

The BMSs I've seen have fairly extreme limits, for both high voltage and low voltage disconnects- which was why I suggested that you don't want to use that feature in day to day management of charging- its an emergency backup thing.  

 

Could the MPPT or the B2B ever fail in some way that they just carry on charging, so that the voltage keeps on going up to dangerous levels? I think its really unlikely, but in that unlikely event, you still have the internal lithium BMS disconnect as the backup to save the batteries, . 

During my testing I accidentally physically disconnected the batteries from the MPPTs when they were charging, and I got away with it- there was no damage. But thats not to say its a safe to do. But it may be that its such an unlikely event you can take the chance, knowing that the worst thing that can happen is it ruins the MPPT, but the batteries are safe because of their internal BMS disconnect? 

I do have an automatic physical disconnect switch that is managed by a BMV712 in the event that the voltage gets too high, but I only did that because my batteries dont have an internal BMS high voltage disconnect- which yours already do.

Plus, all that stuff can start getting expensive, and in your case I might be tempted to rely on the charging units controlling the voltage safely. 

 

 

 

Edited February 16, 2023 by Tony1

[Tony1]

50 minutes ago, n-baj said:

Okay after fun with gerbils I’ve tested the alternator today. I let everything warm up by subjecting the alternator to a load for a while, then set it so it produced about 50A for about an hour at tick over speed (about 900rpm) I chose this because the B2B charger quotes an efficiency of 90% so assume on a 40A output will take about 44A although I have emailed/raised a ticket with renology to confirm this.

 

the temps seems to plateau at 100 deg c on the main body and 120 deg c where the stator coil is. This is very worse case, usually the alternator will be spinning faster so will be running cooler. I’ve emailed Barrus Shire asking for max safe temperatures. I really don’t want to charge lower than 40A.

 

 

If you can confirm the B2B never draws more than 45 amps that will help, but the lead acid may also take in some charge, especially during the first 10-15 minutes of charging, so I don't know if you can assume that the 45 amps for the B2B is the total current draw throughout the charging process....

But I understand that lead acid batteries rapidly build up a resistance to charging after the first 10-15 mins, that issue might not be a problem. You might see 60 amps total draw initially if the lead acid battery needs some charging, but maybe you'll only see that for 10 minutes, and then it might go down to a safer level.

 

I hate to say this because I've been there myself with limited capacity alternators, but it might that your alternator (at engine tickover) just cant put out more than 40amps without going above 100 degrees. 

When my engine is charging at tickover (which happens often during cruising), I limit the current draw to 30 amps from each alternator, by setting the B2Bs onto half power mode. But when moored up and charging, I can up the revs and safely draw more current from the alternators.

But I have a separate B2B and lead acid for each alternator, and its a fair bit of faff/expense tbh. Not recommended.

Maybe you can set the Renogy B2B to half power when cruising, in case it spends long periods at tickover etc, but when moored up you can run the engine at say 1300rpm to cool the alternator a bit, and in that scenario maybe switch it to full power?

This is why I suggested testing alternator temp vs output current at different rpm. 

 

 

Edited February 16, 2023 by Tony1

[n-baj]

Thanks Tony, I’m probably overthinking it re disconnect scenarios. I say that because the battery manufacturer as an example gives a bulk/absorption voltage as 14.4 and float as 13.8 and all I need to do is type those figures in the charging sources and every will be okay?

 

Although the B2B charger doesn’t have a float setting unless it knows it’s full and stops charging completely?

 

 

[rusty69]

42 minutes ago, n-baj said:

 

I’m not too au fait with lithium bms but is there 2 types of disconnect? e.g there’s normal ‘okay I’m 95% full or whatever I’ll stop accepting charge but allow discharge’ and then there’s the second emergency ‘NOOOO! the pack voltage is 16v I’m about to blow up isolate everything NOW!’?

I can't speak for all BMS types, but my one has user programmable settings that you can set an upper cell voltage disconnect, and an overall voltage disconnect. I believe if the BMS is activated that discharge can still take place as long as none of the discharge parameters have been triggered.

 

The solar controller(s), as well as an absorption and float voltage setting also have an over voltage disconnect and a charge limit.

 

I set my solar controller so that it goes into float well before the BMS cuts in. I am one of those that believe the BMS should not be used as a charge control device, but that the charging sources, if using a homebrew system should be set accordingly.

[Tony1]

11 minutes ago, n-baj said:

Thanks Tony, I’m probably overthinking it re disconnect scenarios. I say that because the battery manufacturer as an example gives a bulk/absorption voltage as 14.4 and float as 13.8 and all I need to do is type those figures in the charging sources and every will be okay?

 

Although the B2B charger doesn’t have a float setting unless it knows it’s full and stops charging completely?

 

 

 

Obviously I'm no expert and hopefully more knowledgeable folks will contribute soon, but I would say this:

 

I would not do a daily bulk charge at 14.4v, because that will result in your lithium getting up past 95% full on a day to day basis, and that seems a bit stressful for a daily regime. They say it is better to go up to maybe 80% or 85%, and some say 90%, for the daily charging. 

I found that a bulk charging voltage of 13.8 or 13.9v works well, because it gets you battery up to about 85%, and as the voltage goes over that level, the unit goes into float. 

But I wouldn't use a float of 13.8v either, that is more of a bulk charge voltage. 

I would set a float of 13.1 or 13.2, which means the charging effectively stops once your battery is about 85% full. 

 

ETA- sorry I didnt check your attachment pic. I see that there is only one voltage option there that might be suitable, which is 14v.

I think its a tad high, in that it will probably fill the battery to 90%, but we are not talking daily charging here- so that setting would be my choice if I couldn't pick 13.8 or 13.9v

 

 

 

 

 

 

 

 

 

 

Edited February 16, 2023 by Tony1