Cheap LiFePO4 BMS?

[Tony1]

1 hour ago, nicknorman said:

I wasn't proposing to disconnect the Li batteries at the desired SoC, I was proposing to use the ignition connection on the B2B to turn off the B2B whilst leaving the batteries in circuit. But that would use the BMV's relay which is already in use for the low voltage disconnect. Hence my point about needing another BMV.

Unfortunately you can't use the SoC alarm as you propose, the set value can only be less than the clear value, so it can only be used as a low SoC alarm not a high SoC alarm.

 

I'd be happy to get another BMV if that will give me a high SoC charge switch-off function for the B2B, and I think that's worth looking into. 

 

The thing is, I'm not using the ignition option at the moment. I have the B2B set to come on as soon as the lead acid source battery voltage goes above 13.2v, which it does shortly after I start the engine.

I havent used the ignition cable option because the manual says that in this mode, the B2B will carry on charging until the source battery falls below 11.9v, which didnt seem a great idea- but in reality, that never seems to happen. If the engine is running the source battery always shows a decent voltage.

 

In terms of implementation of this idea, the manual says that the B2B will switch off if minus 4 volts comes down the wire from the ignition. So how would I make that voltage drop  happen in reaction to the BMV detecting a high SoC in the lithiums?  

 

 

Edited August 18, 2021 by Tony1

[nicknorman]

47 minutes ago, Tony1 said:

 

I'd be happy to get another BMV if that will give me a high SoC charge switch-off function for the B2B, and I think that's worth looking into. 

 

The thing is, I'm not using the ignition option at the moment. I have the B2B set to come on as soon as the lead acid source battery voltage goes above 13.2v, which it does shortly after I start the engine.

I havent used the ignition cable option because the manual says that in this mode, the B2B will carry on charging until the source battery falls below 11.9v, which didnt seem a great idea- but in reality, that never seems to happen. If the engine is running the source battery always shows a decent voltage.

 

In terms of implementation of this idea, the manual says that the B2B will switch off if minus 4 volts comes down the wire from the ignition. So how would I make that voltage drop  happen in reaction to the BMV detecting a high SoC in the lithiums?  

 

 

Maybe it depends on exactly which model B2B you have, and which mode. The one I’m looking at has “ignition feed activation (with automatic on/off)” which works when ignition input is on and voltage above 13.3v. It stops when voltage drops below 13.2v, or when the ignition turns off. So you would connect the ignition input to 12v via the BMV relay, default normally closed. It would then activate when the engine is running (voltage above 13.3) and stop when the voltage fell to 13.2v OR when the BMV relay operated (above specified SoC) and disconnected the 12v supply from the ignition input.

[Tony1]

9 minutes ago, nicknorman said:

Maybe it depends on exactly which model B2B you have, and which mode. The one I’m looking at has “ignition feed activation (with automatic on/off)” which works when ignition input is on and voltage above 13.3v. It stops when voltage drops below 13.2v, or when the ignition turns off. So you would connect the ignition input to 12v via the BMV relay, default normally closed. It would then activate when the engine is running (voltage above 13.3) and stop when the voltage fell to 13.2v OR when the BMV relay operated (above specified SoC) and disconnected the 12v supply from the ignition input.

 

Thanks a lot Nick. I don't know quite enough to put that idea into action, but I have found a good electrician who will be able to try it. 

 

My B2B is a Sterling BB1260, which either activates from an ignition voltage (when connected), or else relies on the source battery voltage to kick into action, but there is a complication.

 

If my cunning plan to wire both alternators to the starter battery works, I will get more charging current, and will probably put in a second BB1260, or maybe the 30 amp model.

On that note, there is a theory that the smaller 75 amp starter battery alternator might be contributing less charge than expected because it might also be involved in running the water pump. 

But either way, fingers crossed I will have two B2Bs to switch on and off, not one as I have now- so I'll see whether that all pans out before putting in a high SoC switch-off for the B2Bs. 

 

Am I right in thinking that I set the low SoC on the BMV to say 85%, but because the relay is closed, that means the system stays working as long as the SoC stays below 85%.

But when the SoC  gets to 85%, that will trigger the relay to switch to open, which will cause the required voltage to be sent to the B2B and disconnect it?

 

Could I also use a BEP motorised switch, that would open at 85% SoC, and thus disconnect the B2Bs? 

 

 

[nicknorman]

20 minutes ago, Tony1 said:

 

Thanks a lot Nick. I don't know quite enough to put that idea into action, but I have found a good electrician who will be able to try it. 

 

My B2B is a Sterling BB1260, which either activates from an ignition voltage (when connected), or else relies on the source battery voltage to kick into action, but there is a complication.

 

If my cunning plan to wire both alternators to the starter battery works, I will get more charging current, and will probably put in a second BB1260, or maybe the 30 amp model.

On that note, there is a theory that the smaller 75 amp starter battery alternator might be contributing less charge than expected because it might also be involved in running the water pump. 

But either way, fingers crossed I will have two B2Bs to switch on and off, not one as I have now- so I'll see whether that all pans out before putting in a high SoC switch-off for the B2Bs. 

 

Am I right in thinking that I set the low SoC on the BMV to say 85%, but because the relay is closed, that means the system stays working as long as the SoC stays below 85%.

But when the SoC  gets to 85%, that will trigger the relay to switch to open, which will cause the required voltage to be sent to the B2B and disconnect it?

 

Could I also use a BEP motorised switch, that would open at 85% SoC, and thus disconnect the B2Bs? 

3rd para: The BB1260 has the same behaviour that I described. Basically it works as your system currently does whenever there is 12v on the ignition input. Whenever the ignition input is disconnected, it will always turn off regardless of voltages present.

 

Water pump theory: bullshit.

 

If you have 2 B2Bs the ignition inputs can be wired together and controlled from the same thing (eg BMV relay).

4th para: yes.

 

5th para: yes you could, but why would you want to do that? Extra cost and complexity of another motorised switch when the B2Bs already have the necessary feature built in.

 

 

 

 

[peterboat]

4 hours ago, nicknorman said:

As you say, it depends on what you mean by "float". You are right that Li batteries should not be floated in the same way as LA batteries are. However if the float voltage is at or below the resting voltage of the battery at that SoC then no current flows into the battery so it has no idea whether it is being "floated" or not. The reason for putting my Li batteries on to float is so that if some large electrical load is turned on, eg electric kettle via the inverter, the current is supplied by the alternator not by the batteries. The regulator I'm using is very precise so the system voltage only has to be pulled down by about 0.1 - 0.2v to get full output from the alternator. So with the float voltage set at the battery resting voltage, no current flows into the batteries but when a significant load is applied that would pull the battery voltage down, most of the current is supplied by the alternator.

 

My only problem is that I can only set the regulated voltage in steps of 0.1v which is quite coarse because of the very low internal resistance of Li batteries. So I have to have the regulated voltage slightly below the resting voltage at the 3 selectable SoCs (50%, 80%, 100%) which means that with a small load (the fridge etc) the SoC will decline over time with the engine running. But the code flips it back to charge mode when the SoC has dropped 1% for the 50% and 80% SoCs so after a long day's boating the SoC should still be within 1% of the selected SoC.

For the 100% SoC I didn't want the batteries kept at 100%, so when it goes to float it will stay at float until the engine is switched off and on again or the switch is moved to one of the other settings and back to 100%. But the aim is mostly to hit 100% to synchronise the SoC meters and so it doesn't matter too much that after a long day's cruise, the SoC will have fallen below 100% due to the float voltage being below the 100% SoC rested voltage, in fact it's a good thing.

 

Out of interest I'm using 13.1v for the float for 50% SoC, 13.2v for 80% and 13.3 for 100%. This last is of course way below the 14.3v that the system voltage hits at 100% SoC but the voltage drops rapidly down to around 13.4v after just a few % of SoC is extracted, in the same way that the graph above shows the voltage rising rapidly just for the last few % of SoC during charge.

My float change is 13.4 and bulk is 13.8 with absorption at 13.6 this has worked well for years for me with no obvious distress from the batteries.

You are right about the batteries the work zone for them is 13.4 down to 12.8 volts 

Edited August 18, 2021 by peterboat

[Tony1]

1 hour ago, nicknorman said:

3rd para: The BB1260 has the same behaviour that I described. Basically it works as your system currently does whenever there is 12v on the ignition input. Whenever the ignition input is disconnected, it will always turn off regardless of voltages present.

 

Water pump theory: bullshit.

 

If you have 2 B2Bs the ignition inputs can be wired together and controlled from the same thing (eg BMV relay).

4th para: yes.

 

5th para: yes you could, but why would you want to do that? Extra cost and complexity of another motorised switch when the B2Bs already have the necessary feature built in.

 

 

 

 

 

Thanks again Nick, that's very much appreciated. 

So the only real additional cost to set up a high SoC 'prevention' is another BMV712 (and am I right in thinking it just needs the monitor thing, and not the shunt as well?)

 

I wont rush into this because I have the charging upgrade to do first, and there's no immediate prospect of any civilians using/abusing my boat for a few days without me present to supervise the batteries, so they are safe with the SoC being checked manually.

 

But if/when I feel I can trust someone enough to look after the boat well enough (perhaps whilst I travel for a few weeks), I will definitely need something to stop the SoC being held too high for too long- and especially given that the borrowers will be aboard at a time when there is lots of solar also flooding in (and even more so since I'm upgrading the solar).

Its easy to imagine that with 1.2kw of solar, in June and July on most days the batteries will get to 85% before lunch, and no further charging from engine or sun will be advisable (unless I fit a solar charge dump to power an immersion heater with the excess energy). 

 

My ideal solution would be to have both the solar and the B2Bs stopped from charging via the same control mechanism, once the SoC reaches 85%.

 

 

 

Edited August 18, 2021 by Tony1

[nicknorman]

The BMV uses the shunt for power and sensing current. It might be possible to connect 2 BMVs to 1 shunt using an RJ9 splitter, but I wouldn’t like to say whether this would have any effect on the accuracy of the BMV. Since you can’t buy a BMV without a shunt I think it would be better just to have the 2 shunts wired in series.

 

i’m not sure how you would stop the solar, you don’t want to disconnect the controller from the batteries, you want to disconnect the panels from the controller. The BEP switch has a maximum voltage of 32v and it’s likely your panels will exceed that. There may be a remotely operated switch for disconnecting panels but I’m not aware of one.

[Tony1]

5 hours ago, nicknorman said:

The BMV uses the shunt for power and sensing current. It might be possible to connect 2 BMVs to 1 shunt using an RJ9 splitter, but I wouldn’t like to say whether this would have any effect on the accuracy of the BMV. Since you can’t buy a BMV without a shunt I think it would be better just to have the 2 shunts wired in series.

 

i’m not sure how you would stop the solar, you don’t want to disconnect the controller from the batteries, you want to disconnect the panels from the controller. The BEP switch has a maximum voltage of 32v and it’s likely your panels will exceed that. There may be a remotely operated switch for disconnecting panels but I’m not aware of one.

 

Thanks Nick, I had no idea there was a 32v limit on those BEP switches. And as you say, I cant guarantee that the voltage coming in from the panels will be below that, so for the time being I'll just keep an eye on the SoC manually.   

 

 

[nicknorman]

7 minutes ago, Tony1 said:

 

Thanks Nick, I had no idea there was a 32v limit on those BEP switches. And as you say, I cant guarantee that the voltage coming in from the panels will be below that, so for the time being I'll just keep an eye on the SoC manually.   

 

The other thing to consider is that we are talking about 85% etc without any hard evidence. I do wonder if the thing to avoid is simply going up the knee, eg charging only to about 13.7v which will give 95% SoC or more, without stressing the batteries. Maybe. Who knows?

[Tony1]

2 minutes ago, nicknorman said:

The other thing to consider is that we are talking about 85% etc without any hard evidence. I do wonder if the thing to avoid is simply going up the knee, eg charging only to about 13.7v which will give 95% SoC or more, without stressing the batteries. Maybe. Who knows?

 

I guess all we can do for the time being is await more published info, evidence, and studies etc, and pick a level of apparent 'risk' that we each feel ok with. 

I have seen enough to convince me that for greater longevity (at least ten years seem a very realistic expected lifespan), its worth generally keeping the SoC between 25% and 85%, or even 80% if you want to be more careful (and you have the extra capacity to do that).  

 

At the moment its no an issue for me, but if I ramp up the charging to say 100 amps, and also double the panels, there could be times when I get 170 amps of charge, and then I'll have to watch things more carefully.

 

Will Prowse has done an interesting video on this. Not sure how extensive his evidence is, but its an interesting watch. 

 

 

 

 

 

[IanD]

51 minutes ago, nicknorman said:

The other thing to consider is that we are talking about 85% etc without any hard evidence. I do wonder if the thing to avoid is simply going up the knee, eg charging only to about 13.7v which will give 95% SoC or more, without stressing the batteries. Maybe. Who knows?

There has been some research published about LiFePO4 battery life vs. max/min SoC. IIRC the key at the top end was to not go up the rising voltage knee shown on Nick's curves because this is where the internal chemistry starts to change, which suggests that even 90%-95%/13.6V(3.4V/cell) is fine, and you can stay there forever (e.g. on "float" if that's what your charger calls it). What they definitely do *not* like is being taken up to 100% SoC (14.4V/3.6V/cell) and kept there for any length of time (e.g. by "floating" at this voltage), so again what Nick does is absolutely fine.

 

Like Nick said, the only real reason to ever go to 100% is to do top balancing at 14.4V/3.6V/cell, and this should be for a short period before letting the cells/float voltage to drop back to 13.6V/3.4V/cell.

 

At the bottom end, if you follow the same principle discharging down to 10% SoC (12.4V or 3.1V/cell) should also be fine -- again, it's going below this where the voltage starts to plummet that reduces battery life.

 

In between these limits (10%-90%/95% SoC) the exact SoC has little effect on total battery life -- yes you get more cycles with a narrower range but also less energy per cycle, the product of the two stays pretty constant. Just as an example, if you used 10%-90% (80% range) and got a lifetime of 3000 cycles, you might expect 30%-70% (40% range) to give 6000 cycles -- in both cases the product (total energy over lifetime) is roughly the same, but you have to recharge twice as often (by half as much) in the second case. Not exactly true, but close enough that it's a good rule-of-thumb. Not surprising when you consider the same total amount of chemicals/ions are being moved backwards and forwards in both cases. Unless you charge/discharge at very high rates when this falls over, but all boat applications are fractional-charge (<C, usually <0.5C, often 0.25C or lower which is 4 hours charge/discharge for 100%).

 

[the Will Prowse video shows this to some extent, other papers or manufacturers data show this too]

 

This is why LiFePO4 are so easy to use once you have a proper BMS installed -- so long as you stay away from the very bottom and top of the SoC range for normal use, what you do in between makes little difference to lifetime. Even occasional excursions down to 0% and up to 100% won't cause any damage or reduce the lifetime so long as you only do this occasionally.

Edited August 19, 2021 by IanD

[nicknorman]

31 minutes ago, Tony1 said:

 

I guess all we can do for the time being is await more published info, evidence, and studies etc, and pick a level of apparent 'risk' that we each feel ok with. 

I have seen enough to convince me that for greater longevity (at least ten years seem a very realistic expected lifespan), its worth generally keeping the SoC between 25% and 85%, or even 80% if you want to be more careful (and you have the extra capacity to do that).  

 

At the moment its no an issue for me, but if I ramp up the charging to say 100 amps, and also double the panels, there could be times when I get 170 amps of charge, and then I'll have to watch things more carefully.

 

Will Prowse has done an interesting video on this. Not sure how extensive his evidence is, but its an interesting watch. 

 

 

 

 

 

The only thing with that video is that much of the data is not about LiFePO4. So once again we are just guessing, but I am inclined to agree with IanD’s guesses!

In my case I am still mentally struggling with the concept of keeping the SoC symmetrically  around 50%. I’m sitting here now cruising with the SoC on 80% and I am just desperate to flick the switch and have it go up to 100%. But so far this holiday the minimum SoC has been 60% so I need to try harder to force myself to have a lower SoC! Old habits die hard!

Edited August 19, 2021 by nicknorman

[Tony1]

33 minutes ago, IanD said:

There has been some research published about LiFePO4 battery life vs. max/min SoC. IIRC the key at the top end was to not go up the rising voltage knee shown on Nick's curves because this is where the internal chemistry starts to change, which suggests that even 90%-95%/13.6V(3.4V/cell) is fine, and you can stay there forever (e.g. on "float" if that's what your charger calls it). What they definitely do *not* like is being taken up to 100% SoC (14.4V/3.6V/cell) and kept there for any length of time (e.g. by "floating" at this voltage), so again what Nick does is absolutely fine.

 

Like Nick said, the only real reason to ever go to 100% is to do top balancing at 14.4V/3.6V/cell, and this should be for a short period before letting the cells/float voltage to drop back to 13.6V/3.4V/cell.

 

At the bottom end, if you follow the same principle discharging down to 10% SoC (12.4V or 3.1V/cell) should also be fine -- again, it's going below this where the voltage starts to plummet that reduces battery life.

 

In between these limits (10%-90%/95% SoC) the exact SoC has little effect on total battery life -- yes you get more cycles with a narrower range but also less energy per cycle, the product of the two stays pretty constant. Just as an example, if you used 10%-90% (80% range) and got a lifetime of 3000 cycles, you might expect 30%-70% (40% range) to give 6000 cycles -- in both cases the product (total energy over lifetime) is roughly the same, but you have to recharge twice as often (by half as much) in the second case. Not exactly true, but close enough that it's a good rule-of-thumb. Not surprising when you consider the same total amount of chemicals/ions are being moved backwards and forwards in both cases. Unless you charge/discharge at very high rates when this falls over, but all boat applications are fractional-chage (<C, usually <0.5C).

 

[the Will Prowse video shows this to some extent, other papers or manufacturers data show this too]

 

This is why LiFePO4 are so easy to use once you have a proper BMS installed -- so long as you stay away from the very bottom and top of the SoC range, what you do in between makes little difference to lifetime.

 

 

I also have a psychological issue to bear in mind (one of several, to be fair).

Will says the charge cycle should ideally be focused around 50% as its central point, but I unconsciously feel that a higher SoC is better, and I find myself reluctant to let the SoC go too far below 50%, whereas for more longevity I should be letting them go down to 30-40% and occasionally more.   

 

ETA- just seen Nick's post explaining the same issue! 

Perhaps we need some kind of low-SoC aversion therapy! 

 

There is a grain of common sense behind these feelings though. If I wake up one morning with the SoC at 35% and I find that for some reason my charging system is buggered, a higher SoC would give me that bit of extra buffer charge in reserve, and more time to sort something out before I run out of juice altogether. 

It sort of feels safer to have a bit of contingency charge, but its not ideal for the batteries. 

 

 

Edited August 19, 2021 by Tony1

[IanD]

45 minutes ago, Tony1 said:

 

 

I also have a psychological issue to bear in mind (one of several, to be fair).

Will says the charge cycle should ideally be focused around 50% as its central point, but I unconsciously feel that a higher SoC is better, and I find myself reluctant to let the SoC go too far below 50%, whereas for more longevity I should be letting them go down to 30-40% and occasionally more.   

 

ETA- just seen Nick's post explaining the same issue! 

Perhaps we need some kind of low-SoC aversion therapy! 

 

There is a grain of common sense behind these feelings though. If I wake up one morning with the SoC at 35% and I find that for some reason my charging system is buggered, a higher SoC would give me that bit of extra buffer charge in reserve, and more time to sort something out before I run out of juice altogether. 

It sort of feels safer to have a bit of contingency charge, but its not ideal for the batteries. 

 

 

As far as the batteries themselves are concerned, I don't think they give a fig how they're used between 10% and 90% SoC -- and this is what a lot of manufacturers recommend. The total energy in/out over lifetime is what matter not the number of cycles as such, and some LiFePO4 manufacturers actually rate their battery lifetime like this e.g. 47.5MWh for a 15.4kWh BYD LVL battery.

 

It's more related to where you get the power from to charge them and how often you want to do this. If you're mixing solar and generator and you know you're going to have plenty of sun tomorrow, it doesn't make sense to burn (expensive, noisy) generator fuel to get 90% SoC because there won't be any space to fit the (free) solar charge the next day. Equally you don't want to run down close to 10% SoC during the day and then be forced to run the generator to stop the batteries hitting 0% overnight.

 

OTOH if you're also using the generator to give you free hot water via a calorifier, there's no point cycling the batteries between 10% and 90% by running the generator for several hours every 2 or 3 days and having to do something else (burn more fuel?) to get daily hot water -- you'd be better off running the generator every day for an hour or so to get hot water, which probably means only cycling the batteries over a 30% range or so. Unless it's summer and solar can give you all the power you need, then no generator at all (except for an electric boat cruising every day).

 

In other words battery lifetime no longer determines how you manage charging and SoC, you can do whatever suits you for other reasons. LiFePO4 has a huge advantage over LA because of this 😉

Edited August 19, 2021 by IanD

[nicknorman]

I was very very naughty this morning. We have Jeff’s parents on board which uses 2 x more hot water, 2 x more dishes to wash up etc. So the pudding dishes and glasses from last night were dirty this morning, but I knew there wouldn’t be any hot water left so …I put the immersion heater on for an hour! Very naughty and against all forum protocols. But the batteries gave me a shrug and the SoC still about 60% at the end of that, and plenty of hot water for the washing up. By mid morning they were back at 80% and alternator in float.

[Tony1]

1 hour ago, nicknorman said:

I was very very naughty this morning. We have Jeff’s parents on board which uses 2 x more hot water, 2 x more dishes to wash up etc. So the pudding dishes and glasses from last night were dirty this morning, but I knew there wouldn’t be any hot water left so …I put the immersion heater on for an hour! Very naughty and against all forum protocols. But the batteries gave me a shrug and the SoC still about 60% at the end of that, and plenty of hot water for the washing up. By mid morning they were back at 80% and alternator in float.

 

Running an immersion heater from the batteries? 

I daresay not even Caligula was ever so decadent 😀

 

[TheBiscuits]

1 hour ago, nicknorman said:

I put the immersion heater on for an hour! Very naughty and against all forum protocols.

 

I added a thyristor to mine, so I can choose what voltage to feed it and hence tune the power it's using.

 

My solar controller also toggles a relay when it's got "spare" capacity so any "waste sunshine" goes to heat water.  I just need to turn it up or down a bit depending on how grey a day it is.

[Tony1]

10 minutes ago, TheBiscuits said:

 

I added a thyristor to mine, so I can choose what voltage to feed it and hence tune the power it's using.

 

My solar controller also toggles a relay when it's got "spare" capacity so any "waste sunshine" goes to heat water.  I just need to turn it up or down a bit depending on how grey a day it is.

 

After I've added some extra panels I'm going to put in a system that will use solar charge to heat the water. 

 

I didnt even know this was 'a thing' until I saw the video below:

My thinking is that with 1.3kw of solar, I'll have hot water most of the day during the summer months, and warmish water (warm enough to wash anyway) for most of Spring and Autumn. 

I want to put in a manual switch to direct the solar charge either to the batteries or to the immersion heater. My thinking for keeping it manual is that if I know its going to be sunny all day, I might as well get the water hot first, and top up the batteries later. 

 

Its far too easy to let one's strict hygeinic standards slip when living afloat. Personally I make sure I get a wash every 6 months whether I need it or not.

 

 

 

 

[nicknorman]

This 3D printing lark is a bit addictive! I decided to design and print an entire lid for my BMS complete with integral OLED display mounting and accurate cut-outs for the connectors, countersunk holes and a support for the push button actuator. Took 4 hours to print but you can just let it get on with it.

 

 

 

[peterboat]

2 minutes ago, nicknorman said:

This 3D printing lark is a bit addictive! I decided to design and print an entire lid for my BMS complete with integral OLED display mounting and accurate cut-outs for the connectors, countersunk holes and a support for the push button actuator. Took 4 hours to print but you can just let it get on with it.

 

 

 

Very nice Nick, a friend of mine is having loads of hassle with his REC BMS, he has a 16s system and the supplier allegedly top balanced the Winston thundersky batteries when dispatched, but real imbalance happens on cell balancing! Up to that point all is well (balancing starts at 3.45 volts per cell) after that things go wrong. 

I honestly think that they haven't been top balanced so a variable charger has been ordered fingers crossed, I will report next week what's happening 

[nicknorman]

18 minutes ago, peterboat said:

Very nice Nick, a friend of mine is having loads of hassle with his REC BMS, he has a 16s system and the supplier allegedly top balanced the Winston thundersky batteries when dispatched, but real imbalance happens on cell balancing! Up to that point all is well (balancing starts at 3.45 volts per cell) after that things go wrong. 

I honestly think that they haven't been top balanced so a variable charger has been ordered fingers crossed, I will report next week what's happening 

Just had a look at the REC manual, one good idea they have is the pre-charge device that softly charges up inverter input capacitors etc prior to the contactor turning on. On the other hand, I hope my emergency disconnect never operates so maybe it doesn’t matter!

 

As to the balancing, it doesn’t look like it could dissipate much power, if you have 3 watts per cell and up to 15 cells being balanced. With reasonable cells, once balanced it doesn’t seem as though they need frequent re-balancing anyway.

[peterboat]

50 minutes ago, nicknorman said:

Just had a look at the REC manual, one good idea they have is the pre-charge device that softly charges up inverter input capacitors etc prior to the contactor turning on. On the other hand, I hope my emergency disconnect never operates so maybe it doesn’t matter!

 

As to the balancing, it doesn’t look like it could dissipate much power, if you have 3 watts per cell and up to 15 cells being balanced. With reasonable cells, once balanced it doesn’t seem as though they need frequent re-balancing anyway.

It also controls the victron inverter charger solar controller! And I know it does because I watched it at play 😊

When its trying to balance the cells it drops the solar right down, it's a biggish system at 4P 16c and the solar is 6kw as well!

The charger will be there tomorrow so top balancing should sort it out, it's a shame that the supplier didn't do it properly. 

[nicknorman]

3 minutes ago, peterboat said:

It also controls the victron inverter charger solar controller! And I know it does because I watched it at play 😊

When its trying to balance the cells it drops the solar right down, it's a biggish system at 4P 16c and the solar is 6kw as well!

The charger will be there tomorrow so top balancing should sort it out, it's a shame that the supplier didn't do it properly. 

Mine controls the Mastervolt combi. But I had to reverse engineer the CANBUS protocols, the good thing about Victron is that they go to a lot of trouble to publise their various protocols. If and when our Mastervolt Combi eventually dies I think I might switch to Victron.

[Tony1]

3 hours ago, nicknorman said:

This 3D printing lark is a bit addictive! I decided to design and print an entire lid for my BMS complete with integral OLED display mounting and accurate cut-outs for the connectors, countersunk holes and a support for the push button actuator. Took 4 hours to print but you can just let it get on with it.

 

 

 

 

I met a really nice chap on the Shroppie last year, who was right into this 3D printing thing, and was producing all manner of bits and bobs for friends/boaters. 

At the time I considered it an amusing toy, and he did say it used a lot of power , but clearly this has some serious potential.... 

 

In other news, the excellent Ed Shiers of Four Counties marine is visiting this week, with the primary objective of determining whether I can get a tune from my two rather work-shy alternators. He is one of very few marine electricians who has a lot of hands on experience with the issues involved in charging lithiums, so I'm finally confident that I will get a solution to my poor charging performance one way or the other- even if it means a new alternator. 

 

 

[nicknorman]

1 minute ago, Tony1 said:

 

I met a really nice chap on the Shroppie last year, who was right into this 3D printing thing, and was producing all manner of bits and bobs for friends/boaters. 

At the time I considered it an amusing toy, and he did say it used a lot of power , but clearly this has some serious potential.... 

 

In other news, the excellent Ed Shiers of Four Counties marine is visiting this week, with the primary objective of determining whether I can get a tune from my two rather work-shy alternators. He is one of very few marine electricians who has a lot of hands on experience with the issues involved in charging lithiums, so I'm finally confident that I will get a solution to my poor charging performance one way or the other- even if it means a new alternator. 

This is one reason why I’d never want to live on a boat full time - not enough room for all my toys!

 

Ed is a top bloke, if anyone can sort out your electrics he can. Let us know what he says/does.