Jump to content

Lithium battery abuse


TheBiscuits

Featured Posts

3 minutes ago, Alan de Enfield said:

 

Surely 'maximum' means that it is OK to do that (example 70mph maximum on a motorway ?) and you can do 'the maximum' continuously.

The motorway signs do not say you should drive at 65mph - but - you can occasionally creep it up to 70 mph.

 

Good point. If Alistair want's to run his LFPs at 4.00v that's up to him, but best not to suggest to everyone else its fine when it isn't.

Link to comment
Share on other sites

17 minutes ago, Alistair1357 said:

I can't understand pigheadedness - the term "maximum" is what is you're missing MtB. None of your replies include that. You choose to ignore it. 

The problem arose because you said “recommended” and “maximum” in the same phrase. 4v per cell is the absolute maximum beyond which immediate severe damage will occur. The recommended charge voltage is 3.65v/cell. It is incorrect and misleading to conflate these two pieces of information and say the the maximum recommended voltage is 4v.

 

It comes back to the concept of having a normal operating range, and an absolute maximum rating. Something which is commonplace in electronic specifications and elsewhere. Hence the fact that normal and best practice is to have systems that keep the operating voltage within the normal range, and a separate system which will come into play in the event of a control system failure such that the absolute maximum rating is about to be exceeded. What I call my “emergency disconnect” system.

7 minutes ago, Alan de Enfield said:

 

Surely 'maximum' means that it is OK to do that (example 70mph maximum on a motorway ?) and you can do 'the maximum' continuously.

The motorway signs do not say you should drive at 65mph - but - you can occasionally creep it up to 70 mph.

No, not in this context.

Edited by nicknorman
Link to comment
Share on other sites

12 hours ago, nicknorman said:

Obviously I agree with the general point of having at least 2 levels of safety. I just want to pick up on your point above. One cannot correlate charge voltage with SoC. If you charge very slowly, 13.8v will get you to about 99% SoC. If you charge very fast, when you hit 13.8v maybe you are as low as 80% but I think it would have to be very fast as in 1C. Our alternator in slow charge mode gives about 95A into the 600Ah, ie about C/6. It takes a long time for the voltage to get over 13.6 and by the time it is 13.8v the SoC is about 95%. So (depending on how fast you charge) I suspect that actually you are charging to quite a lot more than 80% if you charge until the voltage hits 13.8v.

 

Just on the safety point are there actually many examples of LiFePO4 cells going on fire/exploding or whatever? I thought the general feeling was that they were pretty stable and robust compared to other chemistries and the danger was more to the wallet than to life and limb.

Fully agree with your comments on correlating charge voltage with SoC. I frequently charge at 90A with my 2 B2B's and 45A with one  B2B's. The voltage when I terminate is very different. My 13.8V target is with the 90A charge so the 45A would be 13.6-13.7A.  In my posts I do reinforce the point that peeps need to work out their own voltages. My 80-90% target is a point before the amps start dropping more quickly and hence well before the voltage knee. My biggest worry here is Mark saying its fine to charge to 95-99% (ie less than 100%) and peeps who dont understand accepting that fact.

 

I am not aware of examples of thermal runaway in LiFePO4 in the real world but we test them and they do fail. Of course the chemistry is safer and there is less energy density but internal shorts via defects/dendrites etc can trigger runaways. It is interesting in our work supporting the EU inititive of transporting Li cells on passenger planes, the relevant bodies made no differentiation between LiFePO4 and Li-ion cells (ie the regulations on transport will be the same from both). It's also interesting that all this air transport work is assuming the cells in transport are not on charge!!!! The relevant bodies see the risk of thermal runaway on just charged batteries rather than during the charging process. I dont know where the legislation will end up but may be set so the batteries will have to be less than 30% charged and in approved 'safe' packaging boxes. Also, we dont hear about many Li-ion batteries causing problems, likely as most vendors have well designed safety systems.

Link to comment
Share on other sites

It’s a bit like the anti-Vaxxers/ other conspiracy theorists who ignore the overwhelming majority of information and data, and fixate on one piece of information that taken out of context seems to suit them, which they manipulate and misrepresent to make their case.

3 minutes ago, Dr Bob said:

Fully agree with your comments on correlating charge voltage with SoC. I frequently charge at 90A with my 2 B2B's and 45A with one  B2B's. The voltage when I terminate is very different. My 13.8V target is with the 90A charge so the 45A would be 13.6-13.7A.  In my posts I do reinforce the point that peeps need to work out their own voltages. My 80-90% target is a point before the amps start dropping more quickly and hence well before the voltage knee. My biggest worry here is Mark saying its fine to charge to 95-99% (ie less than 100%) and peeps who dont understand accepting that fact.

 

I am not aware of examples of thermal runaway in LiFePO4 in the real world but we test them and they do fail. Of course the chemistry is safer and there is less energy density but internal shorts via defects/dendrites etc can trigger runaways. It is interesting in our work supporting the EU inititive of transporting Li cells on passenger planes, the relevant bodies made no differentiation between LiFePO4 and Li-ion cells (ie the regulations on transport will be the same from both). It's also interesting that all this air transport work is assuming the cells in transport are not on charge!!!! The relevant bodies see the risk of thermal runaway on just charged batteries rather than during the charging process. I dont know where the legislation will end up but may be set so the batteries will have to be less than 30% charged and in approved 'safe' packaging boxes. Also, we dont hear about many Li-ion batteries causing problems, likely as most vendors have well designed safety systems.

Fair enough but on your last point, there are plenty of cases of cheap devices with Li-ion batteries going on fire. Hover boards seem popular for that!

  • Greenie 1
Link to comment
Share on other sites

6 minutes ago, nicknorman said:

It is incorrect and misleading to conflate these two pieces of information and say the the maximum recommended voltage is 4v.

I think you are further confusing the issue. My term "Recommended maximum voltage" and your term "maximum recommended voltage" are not the same terms. You are misquoting me, as well.

Link to comment
Share on other sites

3 hours ago, Alistair1357 said:

I don't know where 14V comes into a "dangerous" zone in the case of my Winston cells - The supplier recommends a maximum charge of 4V per cell which is 16V if I understand maths correctly? 

 

https://files.gwl.eu/inc/_doc/attach/StoItem/3861/ThunderSky-Winston-LIFEPO4-100Ah-WIDE-Datasheet.pdf

 

Certainly not. This is the problem on this thread. Peeps (including Alistair) do not understand the basics here.

 

The 16V is not what the supplier is recommending/talking about/referring to. You are totally ignoring cell balance. If the bank was fully in balance, yes you could have 16V but that will NOT be the case. Once you get in the voltage knee then you are likely to have a wide range of voltages. In a vendor sourced system than  they may have a reasonable balance so maybe 4.0V, 3.9V, 3.6V 3.6V - so a total of 15.1V but in a homebrew system you could be at 4.0V on one cell and the other 3 not even at 3.5V - total 14.5V max. You could then be driving that high cell to destruction. That is the issue about homebrew systems.

Too many peeps on here think of a high level cell voltage and multiply by 4. WRONG.

So Alistar.....you do not understand correctly!

  • Greenie 1
Link to comment
Share on other sites

I'm not arguing with you, Dr. Bob - My post was an enquiry. If your recommendation is 14V based on addition of cell values rather than multiplication of cell values, I understand your concerns.

 

What I didn't state, and perhaps I should have, is that my BMS controls both individual cell voltages and pack voltages - any anomaly in either results in protection. So, I have my cells set at 3.75V and my 8S pack at 30V - either limits a dangerous situation. And as Nick has pointed out my chemistry includes yttrium, so my limits may not apply to other LifePO batteries. 

Link to comment
Share on other sites

On 15/02/2022 at 00:39, TheBiscuits said:

 

Having just disturbed the moths in my wallet for lithium batteries, I have been idly wondering about @Dr Bob's "top up tank" theory that got shot down on the forum a while back.  It's probably a geek version of buyer's remorse!

 

The disparaged concept was simple enough: stick a medium sized LiFePO4 battery in parallel with your existing lead acids and let it keep the charge up at (not ideal) float voltage.

 

Lots of the experts said it was a bad idea at the time, but Sterling Power are selling a range of LiFePO4 12v nominal batteries with onboard BMS units that will handle high/low voltage/temperature/current disconnect/reconnect.

 

The smallest battery in the range - 20Ah - has the BMS but not the bluetooth link.  Charging profile as recommended by Sterling is 14.4v bulk/absorption, 13.8v float, no equalisation, no desulphation.

 

If you don't add a battery-to-battery charger between these and the alternator the warranty is void.  This is quite important on the 200Ah/£1000+ batteries, but the 20Ah version retails at £90 ....

 

Does this alter the thinking of the real Electrical Engineers?  What actually happens electrically if I take a tired but not broken bank of 4 x 110ah lead acid batteries - fairly much a standard narrowboat setup -  and add one or two of these small, cheap lithiums to it in parallel with no other hardware in the mix?

 

  1. Will the lithium discharge and charge first? 
  2. Will there be enough power in the small battery to "top up" via parallel equalisation that expensive and painful last 5% on a lead acid bank? 
  3. Would this allow a boater on a tight budget to ignore the warranty and just abuse the battery, while keeping their Lead Acid bank at a much healthier voltage?

 

I don't know the answers, I'm asking for thoughts.  And possibly guinea pigs ...

 

1.Will the lithium discharge and charge first?

 
I'm not sure.
 
2.Will there be enough power in the small battery to "top up" via parallel equalisation that expensive and painful last 5% on a lead acid bank?
 
I'm far from certain.

3.Would this allow a boater on a tight budget to ignore the warranty and just abuse the battery, while keeping their Lead Acid bank at a much healthier voltage?
 
I like abusing my lead acids.
 
 
Psssst. Did Dr Bob confirm his theory was indeed practical? I was going to read his reply, but it was far too long, and my concentration span i
 
  • Greenie 1
  • Haha 2
Link to comment
Share on other sites

21 minutes ago, rusty69 said:
Psssst. Did Dr Bob confirm his theory was indeed practical? I was going to read his reply, but it was far too long, and my concentration span i
 

In summary, it will work if:

- the Li bank is big enough for 24 hrs use ie 100Ahrs likely - if not you deplete your LA's so sulphation issues

- you spend money on some levels of redundancy (or have control of charge sources ie alternator controler/solar charger), but audible alarms are cheap.

 

That is for the 'top up' type hybrid system. Not to be confused by my parallel hybrid system (400Ahrs of LA and 400 Ahrs of Li) which is now tried and tested for nearly 4 years. It cost me circa £1500 to install. It will last at least another 4 years (maybe a lot more) which when you include the cost saving in reduced running the engine (fuel and servicing) is a big saving over replacing 400-500 Ahrs of LA's every 4 years.....but you need to understand how to homebrew a system. It's not obvious from this thread that the average level of knowledge is high enough to have a reasonable level of safety.

 

  • Happy 1
Link to comment
Share on other sites

39 minutes ago, Alistair1357 said:

I'm not arguing with you, Dr. Bob - My post was an enquiry. If your recommendation is 14V based on addition of cell values rather than multiplication of cell values, I understand your concerns.

 

What I didn't state, and perhaps I should have, is that my BMS controls both individual cell voltages and pack voltages - any anomaly in either results in protection. So, I have my cells set at 3.75V and my 8S pack at 30V - either limits a dangerous situation. And as Nick has pointed out my chemistry includes yttrium, so my limits may not apply to other LifePO batteries. 

I have never ever recommended 14.0V. That to me is too high at my 90A charging rate. I disconnect at 13.8V with the emergency cut off at 13.9V to give me lee-way if my cells ever drift out of balance (which I do look at monthly).

I have Winston cells so also have yttrium in.

 

What is the point of going over 80% SoC? If its about capacity then put bigger cells in. If newbies cant afford the investment then stick to LA's.

Link to comment
Share on other sites

47 minutes ago, rusty69 said:

1.Will the lithium discharge and charge first?

 
I'm not sure.
 
2.Will there be enough power in the small battery to "top up" via parallel equalisation that expensive and painful last 5% on a lead acid bank?
 
I'm far from certain.

3.Would this allow a boater on a tight budget to ignore the warranty and just abuse the battery, while keeping their Lead Acid bank at a much healthier voltage?
 
I like abusing my lead acids.
 
 
Psssst. Did Dr Bob confirm his theory was indeed practical? I was going to read his reply, but it was far too long, and my concentration span i
 

Welcome back

  • Love 1
Link to comment
Share on other sites

1 hour ago, Alistair1357 said:

I think you are further confusing the issue. My term "Recommended maximum voltage" and your term "maximum recommended voltage" are not the same terms. You are misquoting me, as well.

Whichever way around you put the words, you are still misrepresenting what the manufacturer is saying. Where they mention 4v, the word “recommended” is not used in the same phrase.

Link to comment
Share on other sites

 
As the thread title is about Lithium abuse, and as I am likely to soon be abusing mine, perhaps through ignorance rather than intent, I would like to ask the assembled experts this.
 
I have 28 cells (Thundersky), connected as a nominal 12V bank, It has a cheapy chinese BMS (JBD/Overkill type). The BMS monitors and 'protects' cell voltage and overall bank voltage, but only of the 4 parallel connected cells. 
 
So, what is the likely hood of the BMS protecting the overall pack in the event of one or more of the parallel connected cells going over 4 V?
 
I assume, being connected in parallel they should all be of a similar voltage  and a lot will depend on what charge and disconnect values I have set.
  • Greenie 1
Link to comment
Share on other sites

30 minutes ago, rusty69 said:
So, what is the likely hood of the BMS protecting the overall pack in the event of one or more of the parallel connected cells going over 4 V?
 

 

 

It is not possible for one of the four cells connected in parallel to go over 4.00V. They are all held at the same voltage because they are in parallel. So your BMS will see that voltage and disconnect at 3.65V, unless you have been fiddling  with the settings. 

 

Welcome back by the way! 

 

 

Edited by MtB
Clarify a point.
  • Greenie 1
Link to comment
Share on other sites

7 minutes ago, MtB said:

 

 

It is not possible for one of the four cells connected in parallel to go over 4.00V. They are all held at the same voltage because they are in parallel. So your BMS will see that voltage and disconnect at 3.65V, unless you have been fiddling  with the settings. 

 

Welcome back by the way! 

 

 

Well, that's kinda what I figured, but if one of them is faulty due to some internal short or summit, will the other pull it down, or will the BMS see the faulty one and disconnect the lot?

 

PS. Of course I've been fiddling with the settings. It seems rude not to.

Link to comment
Share on other sites

7 minutes ago, rusty69 said:

Well, that's kinda what I figured, but if one of them is faulty due to some internal short or summit, will the other pull it down

 

Yes.

 

But high cell voltage is not what happens if a cell goes faulty. A cell voltage like 4.00 will only originate from a charging source. 

 

Bear in mind I no nuffern about any of this...

 

 

 

Edited by MtB
Clarify a point.
Link to comment
Share on other sites

23 minutes ago, MtB said:

 

Yes.

 

But high cell voltage is not what happens if a cell goes faulty. A cell voltage like 4.00 will only originate from a charging source. 

 

Bear in mind I no nuffern about any of this...

 

 

If an individual cell goes wonky, then one effect will be the capacity of that cell is likely to be different to the other 6 you have in parallel  which will bring down the capacity of the 'large 7 cell' unit. When you charge, then the 4 large cells will likely go well out of balance. Here's where I am at my pay grade limit - but would anticipate that 7 cell unit will hit the voltage knee first and likely overcharge if you charge to your normal voltage. I'm sure Nick will have the right answer.

Link to comment
Share on other sites

2 hours ago, rusty69 said:
I like abusing my lead acids.
Psssst. Did Dr Bob confirm his theory was indeed practical? I was going to read his reply, but it was far too long, and my concentration span i
 

 

BTW.......

Wot are you doin' here?

I've only been let out as @TheBiscuits was casting nasturtiums at my theories and there's rumours of a noodle conspiracy being reported.

Link to comment
Share on other sites

9 minutes ago, Dr Bob said:

 

BTW.......

Wot are you doin' here?

I've only been let out as @TheBiscuits was casting nasturtiums at my theories and there's rumours of a noodle conspiracy being reported.

 

Someone told me there was to be an auction of boating merchandise on one of the forums. On closer inspection, I noticed it was just Aunty Waitrose selling off her usual c̶h̶e̶a̶p̶ ̶t̶a̶t̶ high quality merchandise.

 

To be fair to Monsieur biscuits though. Has anyone confirmed the 'Dr Bob theory' apart from a certain Dr Bob? Not that I am casting nasturthingies on the good Dr you understand. I have heard some people think he is a muppet, but not me, noooooo, not me.

  • Greenie 1
Link to comment
Share on other sites

6 minutes ago, rusty69 said:

To be fair to Monsieur biscuits though. Has anyone confirmed the 'Dr Bob theory' apart from a certain Dr Bob? Not that I am casting nasturthingies on the good Dr you understand. I have heard some people think he is a muppet, but not me, noooooo, not me.

...ah but he has got a duck!

  • Haha 1
Link to comment
Share on other sites

12 minutes ago, rusty69 said:

To be fair to Monsieur biscuits though. Has anyone confirmed the 'Dr Bob theory' apart from a certain Dr Bob?

 

May I prevail upon you to refresh my memory?

 

What is this "Dr Bob theory" of which you write, exactly? I wonder if Dr Bob knows anything about it....

Link to comment
Share on other sites

Just now, MtB said:

 

May I prevail upon you to refresh my memory?

 

What is this "Dr Bob theory" of which you write, exactly? I wonder if Dr Bob knows anything about it....

 

No, I'm sorry. You may not. I have no idea what it is. May I point you in the direction of a certain @Dr Bob, or perhaps even @TheBiscuits. I was merely quoting that a theory may or may not have been allured to, but perhaps only confirmed to work by the very person who may or may not have floated the idea in the first place.

That, to me, does not seem a very scientific procedure.

 

I only came here to bid on the mr grumpy mug in the auction, but I fear it may be out of my price range.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.