Lithium charging via large alternator ?

[MtB]

1 minute ago, peterboat said:

How many batteries do you have Mike? if its only a few a couple of cheap lcd gauges and rotary switches will do the job

 

I have an eight cell 200AH 24v pack. All the cell interconnects are stainless steel spot welded to the terminals so cannot be disconnected. Not that I see any need to. 

 

[Dr Bob]

11 hours ago, Mike the Boilerman said:

 

I need to try this and get to know my voltages. Having a cheap second hand set of cells its not a great disaster if I end up wrecking them, just very annoying. 

 

How does your comment square with received wisdom that 101% SoC can be achieved and batts wrecked with long term trickle charging (from say, solar) without the voltage ever rising to trip voltage? As explained by MP in post 66 above your post. 

 

10 hours ago, MoominPapa said:

Almost none. They have a terrifyingly small internal resistance.

 

 

Lots of different points here!!!!

The first one on estimating SoC from voltage. I do it all the time. See graph below. Plot of voltage (x axis) v Ahrs Out (y axis) -480Ahrs bank

At 13.30V my bank is pretty full. At 12.80V then I am 40% ish (give or take 10% which is not important). I find it very easy to estimate SoC charge from V and Ahrs used.

 

Next point-overcharging with Solar. If you set your auto disconnect at the right voltage then I think  you are safe. Problem here is I dont have much experience of being over 80% SoC as I have only been there when on shore power - not enough sun this summer - but .....I can extrapolate. In previous threads earlier in the year, I was being told I need to charge at 13.9V or 14.0V to get to 90% plus SoC. I am now finding that 13.50V is ok to get me to 80%. Now a word of caution, mine is a true hybrid with 600Ahrs+ of LAs and 480Ahr of Li's and the voltages may not mimic Simon's, Tom's and Peter's but maybe no more than 0.2V out (long story which I can explain later). The at rest voltage when almost full (97%...ie before the knee) is around 13.35 -13.40 volts. For every amp of charge current you get an increase of voltage of around 0.01V so with 10Amps charge you will see  a voltage increase of 0.1V. At 80% SoC, my voltage will be around 13.30V so if I charge at 10A it will be 13.40V or at 20A 13.50V.

Setting your auto disconnect at 13.50V should therefore catch any overcharge by solar. I use the relay on my BMV to do the auto disconnect and that relay voltage setting takes 15 secs to change via the bluetooth app. My disconnect is currently set at 13.7V.

Peter is saying it isnt a problem as a small charge current from solar when he is at 100% is ok.

@MoominPapa, what happens on your system when you have charged up to 85% via the alternator and then sat in the sun for the rest of the day with 20A going in from the solar? I guess your disconnect will trip as the 20A will raise the voltage to you trip point when you get in the knee? The real question is what about 5A of solar when you are up in the knee? Peter is saying that his MPPT will switch to float at 13.4V so that can not overcharge the Li Bank. Peter, when that happens, is there any charge current going in? I doubt it.

If the sun ever comes out again, and we plan to do a long day crusing, I will have a go and look at these voltages in detail. I am pretty sure though if I set my voltage disconnect on 13.5V then it just couldnt overcharge and let me get to 80% SoC easily on the alternator (that maybe 13.7V on everyone elses system).

 

Edited June 14, 2019 by Dr Bob

[Col_T]

With apologies for being an ignoramus, what is that spreadsheet and chart telling us, Dr. Bob? Column headings, at least, might be helpful.

 

[WotEver]

18 minutes ago, Dr Bob said:

I am pretty sure though if I set my voltage disconnect on 13.5V then it just couldnt overcharge

Plenty of evidence to the contrary, Bob. Here’s the first one I found, loads more if you keep looking:

http://liionbms.com/php/wp_cccv_charging.php

[peterboat]

22 minutes ago, Dr Bob said:

 

Lots of different points here!!!!

The first one on estimating SoC from voltage. I do it all the time. See graph below. Plot of voltage (x axis) v Ahrs Out (y axis) -480Ahrs bank

At 13.30V my bank is pretty full. At 12.80V then I am 40% ish (give or take 10% which is not important). I find it very easy to estimate SoC charge from V and Ahrs used.

 

Next point-overcharging with Solar. If you set your auto disconnect at the right voltage then I think  you are safe. Problem here is I dont have much experience of being over 80% SoC as I have only been there when on shore power - not enough sun this summer - but .....I can extrapolate. In previous threads earlier in the year, I was being told I need to charge at 13.9V or 14.0V to get to 90% plus SoC. I am now finding that 13.50V is ok to get me to 80%. Now a word of caution, mine is a true hybrid with 600Ahrs+ of LAs and 480Ahr of Li's and the voltages may not mimic Simon's, Tom's and Peter's but maybe no more than 0.2V out (long story which I can explain later). The at rest voltage when almost full (97%...ie before the knee) is around 13.35 -13.40 volts. For every amp of charge current you get an increase of voltage of around 0.01V so with 10Amps charge you will see  a voltage increase of 0.1V. At 80% SoC, my voltage will be around 13.30V so if I charge at 10A it will be 13.40V or at 20A 13.50V.

Setting your auto disconnect at 13.50V should therefore catch any overcharge by solar. I use the relay on my BMV to do the auto disconnect and that relay voltage setting takes 15 secs to change via the bluetooth app. My disconnect is currently set at 13.7V.

Peter is saying it isnt a problem as a small charge current from solar when he is at 100% is ok.

@MoominPapa, what happens on your system when you have charged up to 85% via the alternator and then sat in the sun for the rest of the day with 20A going in from the solar? I guess your disconnect will trip as the 20A will raise the voltage to you trip point when you get in the knee? The real question is what about 5A of solar when you are up in the knee? Peter is saying that his MPPT will switch to float at 13.4V so that can not overcharge the Li Bank. Peter, when that happens, is there any charge current going in? I doubt it.

If the sun ever comes out again, and we plan to do a long day crusing, I will have a go and look at these voltages in detail. I am pretty sure though if I set my voltage disconnect on 13.5V then it just couldnt overcharge and let me get to 80% SoC easily on the alternator (that maybe 13.7V on everyone elses system).

 

 

3 minutes ago, WotEver said:

Plenty of evidence to the contrary, Bob. Here’s the first one I found, loads more if you keep looking:

http://liionbms.com/php/wp_cccv_charging.php

I have the toilet fan running and the fridge freezer running all the time, and I have ckecked on the puter and can say that my controller is not charging when the 13.8 limit is reached, it immediately goes down to 13.6 float, the batteries will sit at 13.8 and then gradually drop as the power is used, if I turn the kettle on the amps go up and the charger starts charging again, until the batteries are 80% full. The system works for me and my batteries

[WotEver]

6 minutes ago, peterboat said:

I have the toilet fan running and the fridge freezer running all the time

And therein lies the difference. 

[MtB]

12 minutes ago, WotEver said:

Plenty of evidence to the contrary, Bob. Here’s the first one I found, loads more if you keep looking:

http://liionbms.com/php/wp_cccv_charging.php

 

Ah but there, the author is saying the overcharging problem only happens when the cells are out of balance.

 

That American bloke with the grating style of writing says even well balanced banks never stop charging even at lowish 'float' voltages IIRC, so extended periods on float still wreck lithiums even when 'safe' voltages are not exceeded. 

 

[Dr Bob]

6 minutes ago, Mike the Boilerman said:

 

Ah but there, the author is saying the overcharging problem only happens when the cells are out of balance.

 

That American bloke with the grating style of writing says even well balanced banks never stop charging even at lowish 'float' voltages IIRC, so extended periods on float still wreck lithiums even when 'safe' voltages are not exceeded. 

 

The big question is how many amps go into the Li bank at 99% charge (ie in the knee) when the MPPT switches from its 13.8V absorption to 13.4V float when there is reasonable sun and no current draw. I dont think we know the answer to that one.

I will try and answer it when a) I ever get over 90% and b) the sun shines.

I know I will be able to try it in July when we get back onto mains for a night or two.

 

I have forgotten all about cell balancing. They are exactly the same as when installed at start of March. I think cell balancing is only a problem if you are in the top or bottom of the capacity range.

[MtB]

12 minutes ago, Dr Bob said:

 

I have forgotten all about cell balancing. They are exactly the same as when installed at start of March. I think cell balancing is only a problem if you are in the top or bottom of the capacity range.

 

That is my view too, although variation in the SoC of the cells in series means the overall capacity of the bank is reduced as one needs to keep the lowest charge cell above its minimum safe SoC and the highest charged cell below its maximum. And this is where the danger lies if you just look at the bank as a whole. Individual cell monitoring is essential in my view if managing the bank manually.

 

Peterboat confirms what you find about cell balance - they stay where they are over long periods. WotEver argued a while back this cannot happen, but your and Peter's empirical evidence illustrates it can, and does. 

 

 

[MoominPapa]

1 hour ago, Dr Bob said:

@MoominPapa, what happens on your system when you have charged up to 85% via the alternator and then sat in the sun for the rest of the day with 20A going in from the solar? I guess your disconnect will trip as the 20A will raise the voltage to you trip point when you get in the knee? The real question is what about 5A of solar when you are up in the knee?

 

The charge will terminate when the AH-counted SOC goes a little bit positive (5Ah, from memory.)

 

MP.

 

[WotEver]

1 hour ago, Mike the Boilerman said:

Ah but there, the author is saying the overcharging problem only happens when the cells are out of balance.

Yes, he does, but others claim it happens whatever the balance state. As I said, it was simply the top of the list when I did a Google search. 

[WotEver]

45 minutes ago, Mike the Boilerman said:

Peterboat confirms what you find about cell balance - they stay where they are over long periods. WotEver argued a while back this cannot happen, but your and Peter's empirical evidence illustrates it can, and does.

The quality (and matching) of the cells has a direct bearing on how long it will take for an unbalance to become significant but whatever Bob and Peter state, it does and will happen, possibly over quite a long time frame. 

https://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing

[MtB]

13 minutes ago, WotEver said:

Yes, he does, but others claim it happens whatever the balance state. As I said, it was simply the top of the list when I did a Google search. 

 

Which is the reason I am wary about leaving my own lithiums on solar float for indeterminate lengths of time, as Dr Bob says I can.

 

I think I need to positively isolate the Li bank when I leave the boat. And have a way of doing it remotely if I forget. Or forget if I remembered. Or stuff like that....

 

 

 

[WotEver]

6 minutes ago, Mike the Boilerman said:

 

Which is the reason I am wary about leaving my own lithiums on solar float for indeterminate lengths of time, as Dr Bob says I can.

 

I think I need to positively isolate the Li bank when I leave the boat. And have a way of doing it remotely if I forget. Or forget if I remembered. Or stuff like that....

 

 

 

I completely agree. Peter covers this scenario by having a small constant load (fan and fridge freezer), Bob’s install includes a 600Ah LA bank in parallel, which might sufficiently absorb the small charging current itself, but I’m unsure about that. 

[MtB]

1 minute ago, WotEver said:

I completely agree. Peter covers this scenario by having a small constant load (fan and fridge freezer), Bob’s install includes a 600Ah LA bank in parallel, which might sufficiently absorb the small charging current itself, but I’m unsure about that. 

 

I need to actually connect the damned Li bank up and start using it, rather than just pontificating about it.... ?

 

 

[peterboat]

My drive batteries are sitting turned off at the moment they are 74% charged which is to high for long term storage but high enough to fully charge in a day, they have sat at that percentage and voltage for a couple of weeks self discharge just doesnt seem to happen

[WotEver]

44 minutes ago, peterboat said:

self discharge just doesnt seem to happen

I note that with all my Li-ion power tools. I can pick up a drill that hasn’t been used for a couple of months or more and simply use it. Completely different to NiCad. 

1 hour ago, Mike the Boilerman said:

 

I need to actually connect the damned Li bank up and start using it, rather than just pontificating about it.... ?

 

 

Then you can tell us all what happens...

[Dr Bob]

2 hours ago, Mike the Boilerman said:

 

Which is the reason I am wary about leaving my own lithiums on solar float for indeterminate lengths of time, as Dr Bob says I can.

 

 

 

 

 

No, I didnt say that. I said that you  are unlikely to overcharge if the MPPT goes to 13.4V float, and you should be ok for a day or maybe a week. A year ....defo not!

Most of the papers I have read say that capacity is compromised if you stay up at 100% for extended times...ie a year. Not a good idea to leave it full.

What I am saying is keep between 20 and 80% but in the event you go off and leave the solar on, then it will either not charge at a voltage of 13.4V (float) or it will auto disconnect if you set your disconnect at 13.5V and you are ok at 100% SoC for a week.

Which ever happens you are not going to wreck your bank if you go off and dont get back for a week.

If my system is anything to go by, you'll never see 100% unless you try hard.

@MoominPapa, how many times in the last 4 months have you been up over 90% without you trying to get there (to syncronise/reset etc)?

[Dr Bob]

3 hours ago, Mike the Boilerman said:

 

 Individual cell monitoring is essential in my view if managing the bank manually.

 

Peterboat confirms what you find about cell balance - they stay where they are over long periods. WotEver argued a while back this cannot happen, but your and Peter's empirical evidence illustrates it can, and does. 

 

 

I have a £20 ebay 4 cell monitoring device. I glance at it every day. It has a line for the delta....ie the diff between the voltage of the highest and lowest cell plus a votage for each cell. The delta is always between 20 and 60mv and varies dependent on depth of discharge/charge. Its been the same since early march. I used to look at it every hour at first. Once a day is enough now but to be honest, I dont need to do that.....and it has an alarm.

[Dr Bob]

4 hours ago, Col_T said:

With apologies for being an ignoramus, what is that spreadsheet and chart telling us, Dr. Bob? Column headings, at least, might be helpful.

 

Ignore the table. I was just wanting to post the graph....of voltage vs Ahrs out (ie a measure of SoC if you know the capacity....which I told you).

[MoominPapa]

45 minutes ago, Dr Bob said:

@MoominPapa, how many times in the last 4 months have you been up over 90% without you trying to get there (to syncronise/reset etc)?

Because we cooked up this mad scheme to boat the tidal Thames, then dash up to Boston and cross the wash, for much of that time we've been boating every day. The batteries have been getting to charge termination each day, so 100%, but actually 13.5v charge/13.34v open circuit - our charge thresholds are set not to stuff the last bit of capacity into the batteries, for cell longevity.  Since we boat during the day and switch  the engine off when the solar output is falling off and we have a fridge on all the time, the system has never had to do charge termination as a result of solar input. Graph of SOC (purple) and current (green) for the last nine weeks is below.

 

I have considered taking the batteries offline when the engine is running on alternate days, to reduce the average SOC, but have not actually done it.

 

MP.

 

 

 

[peterboat]

1 hour ago, Dr Bob said:

I have a £20 ebay 4 cell monitoring device. I glance at it every day. It has a line for the delta....ie the diff between the voltage of the highest and lowest cell plus a votage for each cell. The delta is always between 20 and 60mv and varies dependent on depth of discharge/charge. Its been the same since early march. I used to look at it every hour at first. Once a day is enough now but to be honest, I dont need to do that.....and it has an alarm.

 

3 hours ago, Mike the Boilerman said:

 

I need to actually connect the damned Li bank up and start using it, rather than just pontificating about it.... ?

 

 

 

16 minutes ago, MoominPapa said:

Because we cooked up this mad scheme to boat the tidal Thames, then dash up to Boston and cross the wash, for much of that time we've been boating every day. The batteries have been getting to charge termination each day, so 100%, but actually 13.5v charge/13.34v open circuit - our charge thresholds are set not to stuff the last bit of capacity into the batteries, for cell longevity.  Since we boat during the day and switch  the engine off when the solar output is falling off and we have a fridge on all the time, the system has never had to do charge termination as a result of solar input. Graph of SOC (purple) and current (green) for the last nine weeks is below.

 

I have considered taking the batteries offline when the engine is running on alternate days, to reduce the average SOC, but have not actually done it.

 

MP.

 

 

 

The problem is I am going on for a year now on the LifePo4s you have been on them for months along with Tom and Bex, we will still be having to say how good our systems are in another tens years!! Take up for our systems will be slow because people seem to read to much into experts on the tinternet!! We all seem to doing well because we have set our systems to 80% max and 20% min I am sure in the fullness of time we will all have our home brewed systems, because the commercial systems are just a ripoff! fingers crossed that a cheap system becomes available for the majority of boaters 

[Dr Bob]

4 hours ago, peterboat said:

 

 

The problem is I am going on for a year now on the LifePo4s you have been on them for months along with Tom and Bex, we will still be having to say how good our systems are in another tens years!! Take up for our systems will be slow because people seem to read to much into experts on the tinternet!! We all seem to doing well because we have set our systems to 80% max and 20% min I am sure in the fullness of time we will all have our home brewed systems, because the commercial systems are just a ripoff! fingers crossed that a cheap system becomes available for the majority of boaters 

Agreed.

 

5 hours ago, MoominPapa said:

Because we cooked up this mad scheme to boat the tidal Thames, then dash up to Boston and cross the wash, for much of that time we've been boating every day. The batteries have been getting to charge termination each day, so 100%, but actually 13.5v charge/13.34v open circuit - our charge thresholds are set not to stuff the last bit of capacity into the batteries, for cell longevity.  Since we boat during the day and switch  the engine off when the solar output is falling off and we have a fridge on all the time, the system has never had to do charge termination as a result of solar input. Graph of SOC (purple) and current (green) for the last nine weeks is below.

 

I have considered taking the batteries offline when the engine is running on alternate days, to reduce the average SOC, but have not actually done it.

 

MP.

 

 

 

 

Wow! Your SoCs are high!

Good to see the graph of voltage and SoC. Keep us posted.

[RLWP]

5 hours ago, peterboat said:

 

 

The problem is I am going on for a year now on the LifePo4s you have been on them for months along with Tom and Bex, we will still be having to say how good our systems are in another tens years!! 

 

I doubt it. Having spent some time on Melaleuca this is clearly the way to go.

[peterboat]

11 hours ago, RLWP said:

 

I doubt it. Having spent some time on Melaleuca this is clearly the way to go.

I hope you are correct, it seems at time that I am always defending my decision to go LifePo4 and always being told that they will go out of balance and destroy themselves! when in reality they dont