Monitoring lithium batteries

[MtB]

16 hours ago, Robbo said:

It looks like You can use the BMV with alarm output to disconnect the 12/200, if this disconnects the load as well (I don’t know if it does) and you use this then you can use the BMV to disconnect a relay (like one of Victrons).  This is how the other victron BMS’s do it (the BMS is connected to the relay to disconnect the alternator)

 

The other BMS’s that Victron have basically just turn off/on devices via “alarm outputs”, this then either turns off/on chargers/MTTPs/alternators or loads.  A BMV can do the same with its alarm output to what ever you set it to do.

 

basically the yellow cAbles from the BMS are the “alarm” outputs to control the loads/chargers.  Victron have just releSe a mini BMS which I think doesn’t have the bus to the combi so if you don’t need that have a look at that one.

 

 

Anything involving lots of Victron products always seems to be unnecessarily complicated, and therefore unnecessarily expensive. 

 

For a start, my boat has no 240Vac. And there are other things in this diagram that strike me as irrelevant and unnecessary when designing a lithium battery system layout. A lot of lily-guilding going on in the above diagram in my personal opinion. 

 

 

[nicknorman]

9 hours ago, peterboat said:

Yes you do like gadgets, but why bother? I take it everything is off in the boat when you moor it up in the marina? if so make sure that batteries are at 60% when you leave and 2 months later they will be the same of that I can assure you I have 10 sat around just like that. When you fire the boat up the batteries will be up to 13.8 in no time at all. Its the kiss principle and it really works Jame has been doing it for well over a year with total success, John and I under a year and apart from my solar panel fault all is working well

No, stuff is still on when we leave the boat. The Empirbus uses a small amount of power  even with its virtual master switch off, and the GSM remote is also permanently on - takes a few 10s of mA IIRC. So after several months the batteries would be getting low and sulphation would be building. Of course with LiFePO4 one doesn’t have to worry about sulphation and perhaps an alternative strategy of not leaving the boat on shore power would be appropriate - we are rarely away for more than a month even in winter.

 

Then again our entire boat electrics (lights, pumps etc) runs on CANBUS, software and MOSFETS so if anyone is going have a complicated hi-tech system it will be me! But I promise not to promote the idea to the technologically challenged!

[MtB]

22 minutes ago, nicknorman said:

Of course with LiFePO4 one doesn’t have to worry about sulphation

 

No but something LiFePO4 do suffer from like LA batts I've only just seen commented on is surface charge. Not related directly to your post of course, but worth pointing out as I mostly read people saying you can charge them as fast as you like. This is not strictly true according to one well informed web author I read recently. You can stuff more AH into them if you charge them slower than faster, apparently. Or at least if you charge them at breakneck speed then allow them to rest, the terminal voltage will fall a little and some more charge will be accepted, if I understand the author correctly. 

 

Will fish around later and seef I can find the page where he says this, or words to this effect. 

[nicknorman]

1 minute ago, Mike the Boilerman said:

 

No but something LiFePO4 do suffer from like LA batts I've only just seen commented on is surface charge. Not related directly to your post of course, but worth pointing out as I mostly read people saying you can charge them as fast as you like. This is not strictly true according to one well informed web author I read recently. You can stuff more AH into them if you charge them slower than faster, apparently. Or at least if you charge them at breakneck speed then allow them to rest, the terminal voltage will fall a little and some more charge will be accepted, if I understand the author correctly. 

 

Will fish around later and seef I can find the page where he says this, or words to this effect. 

No I think what you say is known to be correct. You can quickly get to around 80%, if you want to get to 100% without exceeding max voltage you have to slow the charge. But since there is no actual need to get to 100% this isn’t really an issue unless you are desperate to get maximum charge in. Once again, we have to remember the new paradigm whereby there is no merit in getting the batteries to 100%.

[MtB]

5 minutes ago, nicknorman said:

No I think what you say is known to be correct. You can quickly get to around 80%, if you want to get to 100% without exceeding max voltage you have to slow the charge. But since there is no actual need to get to 100% this isn’t really an issue unless you are desperate to get maximum charge in. Once again, we have to remember the new paradigm whereby there is no merit in getting the batteries to 100%.

 

Yes good, thanks for confirming. 

 

I just posted it to add to the body of forum knowledge as it is a point not widely understood. 

 

There IS merit in charging to 100& or close however. If you only charge to 80% you need to buy a bank 25% bigger and therefore 25% more expensive!

 

[TheBiscuits]

7 minutes ago, nicknorman said:

we have to remember the new paradigm whereby there is no merit in getting the batteries to 100%.

Mike has that one covered. 

[peterboat]

12 minutes ago, Mike the Boilerman said:

 

No but something LiFePO4 do suffer from like LA batts I've only just seen commented on is surface charge. Not related directly to your post of course, but worth pointing out as I mostly read people saying you can charge them as fast as you like. This is not strictly true according to one well informed web author I read recently. You can stuff more AH into them if you charge them slower than faster, apparently. Or at least if you charge them at breakneck speed then allow them to rest, the terminal voltage will fall a little and some more charge will be accepted, if I understand the author correctly. 

 

Will fish around later and seef I can find the page where he says this, or words to this effect. 

All true, which is why fast charging on cars is limited to 80%. But on normal charging, ie overnight you can put in 100%. Vauxhall Amperas have a 16kw battery pack, but only use just over 10 kw, and that is why some of their cars have over 400k on their original battery pack!!

[MtB]

I notice a few more second hand ex-electric car batteries coming on the market now. A bloke in Byfleet Surrey has quite a few for sale on ebay.

 

A trend I can only imagine accelerating as more electric cars get sold, then scrapped accident-damaged.

 

https://www.ebay.co.uk/sch/boatronicsuk/m.html?item=273566354547&rt=nc&_trksid=p2047675.l2562

 

These in particular look interesting, but I'm not convinced they are LiFePO4 as they come from a BYD car, and the BYD website says they use some other sort of battery I've never heard of. 

 

https://www.ebay.co.uk/itm/LiFePo4-3-3v-200Ah-Battery-Cell-ev-project-home-storage-for-solar-wind-power/273566354547?hash=item3fb1d34c73:g:guMAAOSwo3Fb8WZX:rk:1:pf:0 

 

 

Edited November 29, 2018 by Mike the Boilerman
missing words

[Robbo]

1 hour ago, Mike the Boilerman said:

 

 

Anything involving lots of Victron products always seems to be unnecessarily complicated, and therefore unnecessarily expensive. 

 

For a start, my boat has no 240Vac. And there are other things in this diagram that strike me as irrelevant and unnecessary when designing a lithium battery system layout. A lot of lily-guilding going on in the above diagram in my personal opinion. 

 

 

Half the stuff on that diagram most of us already have.   Lots of us have a Victron Inverter/Charger and a split charge relay, alternator, starter battery.   The only thing extra in that diagram is the BMS and relay for the loads!    The diagram for the BMS12/200 is even simpler as it's basically just a replacement of a split charge relay!

[MtB]

2 minutes ago, Robbo said:

 The only thing extra in that diagram is the BMS and relay for the loads! 

 

In which case how is disconnection of the alternator on high voltage handled? 

 

 

[Robbo]

1 minute ago, Mike the Boilerman said:

 

In which case how is disconnection of the alternator on high voltage handled? 

 

 

The BMS turns the relay off.   The yellow cables in the diagram are the BMS "alarm" outputs, to turn off loads/chargers.    This BMS has uses canbus to talk the Inverter/Charger - if you didn't have this then the miniBMS is similar but with out the bus to the Inverter/Charger.    You would use one of the outputs to turn the charger (like MPPT) off.

Edited November 29, 2018 by Robbo

[eid]

1 minute ago, Robbo said:

The BMS turns the relay off.

At what voltage?

[Robbo]

5 minutes ago, eid said:

At what voltage?

Cell>4V or temperature (red): charge disconnect output low because of imminent cell over voltage or over temperature. -

Cell>2,8V (blue): load disconnect output high. Load disconnect output low when off, due to imminent cell under voltage (Vcell≤2,8V).

[nicknorman]

27 minutes ago, Mike the Boilerman said:

 

Yes good, thanks for confirming. 

 

I just posted it to add to the body of forum knowledge as it is a point not widely understood. 

 

There IS merit in charging to 100& or close however. If you only charge to 80% you need to buy a bank 25% bigger and therefore 25% more expensive!

 

Well let’s look at this carefully. Firstly, charging only to 80% SoC increases battery life. So although you need to spend more initially, in the long term you probably don’t. That of course only works if you are a committed long term boater. If you are a fly-by-night “let’s just do the trendy boaty  thing for a few years then move on to something else” type, then very long battery life isn’t a bonus.

 

Secondly provided you can cope with the energy available from an 80% SoC battery between charges, it isn’t a problem. Yes you will need to run the genny more often (eg every 2 days instead of every 3) but the overall genny running time will be less, because all genny running time will be fast charging time.

 

But if I were designing it I’d probably have a system where the user can easily set the terminal SoC. Yes normally 80% but if a prolonged stay in one spot is anticipated, upping that to 100% by pressing a button would be optimal - if technically more complicated. I think one of those programmable arduino-based alternator regulators could easily do that.

 

Anyway your maths is a bit iffy as most people don’t go below 20%. So with an 80% to 20% range you get 60% usable. With a 100% to 20% range you get 80% usable. To get 60% up to 80% you need to add 33% capacity!

Edited November 29, 2018 by nicknorman

[MtB]

13 minutes ago, Robbo said:

The BMS turns the relay off. 

 

And wrecks the alternator?

[Robbo]

1 minute ago, Mike the Boilerman said:

 

And wrecks the alternator?

The alternator is connected to the starter battery so no, and if your alternator is providing over 16v, something is already wrong!

 

 

Edited November 29, 2018 by Robbo

[nicknorman]

2 minutes ago, Mike the Boilerman said:

 

And wrecks the alternator?

Of course the best way to turn the alternator off is to interrupt the field/rotor current, not to isolate the B+ connection.

 

but better still to lower the alternator regulated voltage until current flowing into the battery falls to zero. Then the alternator continues to supply any boat loads.

Edited November 29, 2018 by nicknorman

[MtB]

1 minute ago, nicknorman said:

Of course the best way to turn the alternator off is to interrupt the field/rotor current, not to isolate the B+ connection.

 

Yes I always thought this too, and wondered why it isn't the preferred way to do it. 

[nicknorman]

Just now, Mike the Boilerman said:

 

Yes I always thought this too, and wondered why it isn't the preferred way to do it. 

Well in part I suppose because it involves tinkering with the guts of the alternator. Not hard though.

[MtB]

Just now, nicknorman said:

Well in part I suppose because it involves tinkering with the guts of the alternator. Not hard though.

 

And it may not be reliable, given my 24v Leece Neville will self-excite. 

(Despite it not being supposed to!)

[nicknorman]

1 minute ago, Mike the Boilerman said:

 

And it may not be reliable, given my 24v Leece Neville will self-excite. 

(Despite it not being supposed to!)

Depend what you mean by self excite. If the rotor is still connected to the field diodes, even with the ignition off it can self excite in a “virtuous circle” whereby a a tiny bit of residual magnetism causes a tiny bit of induced power,  is fed through the field diodes to the rotor to increase the magnetism etc etc. But if you disconnect the field diodes from the rotor, that “virtuous circle” can’t happen. Yes there may still be a tiny bit of generated power (depending on residual magnetism) but I doubt it would be enough to worry about especially if there was even a very small bit of electrical load from the boat.

[MtB]

6 minutes ago, nicknorman said:

Depend what you mean by self excite. If the rotor is still connected to the field diodes, even with the ignition off it can self excite in a “virtuous circle” whereby a a tiny bit of residual magnetism causes a tiny bit of induced power,  is fed through the field diodes to the rotor to increase the magnetism etc etc. But if you disconnect the field diodes from the rotor, that “virtuous circle” can’t happen. Yes there may still be a tiny bit of generated power (depending on residual magnetism) but I doubt it would be enough to worry about especially if there was even a very small bit of electrical load from the boat.

 

The former I reckon. 

 

I have a switch to turn the field ON and if I forget to switch it ON, the alternator still loads up the engine and delivers full rated output once engine revs get up to about 250rpm. Annoying as the boat won't go very fast when it does this!

[Robbo]

26 minutes ago, Mike the Boilerman said:

 

Yes I always thought this too, and wondered why it isn't the preferred way to do it. 

If you have a voltage sensitive relay you’ll find that just cutting the link between the battery banks when the voltage is above a certain level is already done.

[Tom and Bex]

I think this thread demonstrates the range of options available from the very basic with owner doing the monitoring and taking any action necessary, to the complex fully integrated (expensive!) systems from the likes of Victron and Mastervolt etc. I suspect most real life systems fall somewhere between these 2 extremes (as does ours).

 

Our 2nd hand cells came from http://www.ev-support.co.uk and we paid £600 for 8 Thundersky 160ah cells. Those ones MTB linked to above look like good value if they are as they say they are. 

 

If anyone interested is in the Lapworth area, I'd be happy to show them our system and talk it through with them. 

[peterboat]

2 hours ago, Mike the Boilerman said:

I notice a few more second hand ex-electric car batteries coming on the market now. A bloke in Byfleet Surrey has quite a few for sale on ebay.

 

A trend I can only imagine accelerating as more electric cars get sold, then scrapped accident-damaged.

 

https://www.ebay.co.uk/sch/boatronicsuk/m.html?item=273566354547&rt=nc&_trksid=p2047675.l2562

 

These in particular look interesting, but I'm not convinced they are LiFePO4 as they come from a BYD car, and the BYD website says they use some other sort of battery I've never heard of. 

 

https://www.ebay.co.uk/itm/LiFePo4-3-3v-200Ah-Battery-Cell-ev-project-home-storage-for-solar-wind-power/273566354547?hash=item3fb1d34c73:g:guMAAOSwo3Fb8WZX:rk:1:pf:0 

 

 

Mike buy 8 of those to sort out your battery problems for ever!!