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Can you put in too many amps when the volts never go up?

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A coulomb meter cannot measure the self-discharge of the battery so after some time needs to be reset when the battery is full or discharged.
 
Don't confuse Amps and Amp-hours. Take this in the kindest way, but a lot of the way you are using some your terms - amps, coulomb meter, amp meter, etc. suggest a learning opportunity.

BMS AH readings are not very accurate.

What meter are you using? Use a quality shunt meter, like a Victron Smartshunt if you want an accurate measurement.
Like I said. I am using the juntek to measure how many amps I have used and have left.
 
I am using the juntek to measure how many amp-hours I have used and have left.
FIFY

amps is a rate
amp-hours is a quantity based on a rate for a time period

Using 20 amps for 2 hours is 40 amp hours.
Using 20 amps for 5 hours is 100 amp hours.

A 200 amp hour battery can provide 20 amps for 10 hours.
A 200 amp hour battery can provide 40 amps for 5 hours.

Just trying to help. Cannot tell if I've had too much coffee or not enough...
Using the correct units helps comprehension and communication (and reduces errors).
 
I'm not up to speed on that Coulomb counter, but labeeman may be correct. Most of them will get out of sync somewhat over time and the pack must be charged to 100% occasionally to get it back in sync.
Even the Victron recommends doing a full charge once in a while to re-sync.

Hopefully now that you have done that you will be good to go for a while.

P.S. .... Glad you've got it working for you.
 
Thanks Bob.
I didn't want to do a full charge more than once every 6 months or so though.
Oh well. Now I know it is not accurate. Might go back to using the voltage as a fuel gauge instead again LOL.
 
I'm not up to speed on that Coulomb counter, but labeeman may be correct. Most of them will get out of sync somewhat over time and the pack must be charged to 100% occasionally to get it back in sync.
Even the Victron recommends doing a full charge once in a while to re-sync.
I have a JunTek and yes it needs to be synced every now and then. But as far as counting coulombs I feel it's very accurate and there are YouTube videos that will confirm the accuracy. In fact I recently received another one for my other battery but I haven't installed it yet. The JunTek needs to be set up properly to begin with. I have attached the quick start guide. JunTek has more detailed instructions on YouTube.
 

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Like I said. I am using the juntek to measure how many amps I have used and have left.
You are confusing Amps and Amp-hours. The sentence above should be:

Like I said. I am using the juntek to measure how many amp hours I have used and have left.

I think you have confused some of the responders who are miss-understanding your question.

Coulomb counters are not perfect. They need to be synced to 100% periodically. They won't account for self discharge, power consumed by the BMS, and many don't account for charge efficiency. In short, it is not surprising that the meter reads 100% before the battery is fully charged.
 
Lithium cells do not have a memory.
If you search out research papers on the topic you will find a memory effect can exist where the cells are short cycled. Taking the cell through a full charge cycle removes the effect, but required more energy than a normal charge cycle. This is one of many reports on the effect,

Mike
 
Might go back to using the voltage as a fuel gauge instead again LOL.
This actually works fairly well if you have plenty of battery and don't need to squeeze every bit out of it.
You will get a feel for it after a bit. I use 13.3v as "pretty full" and 13.0v and "getting low". Most of the amp hours will reside in this range. 13.0v will be about 25% "reserve".
 
You are confusing Amps and Amp-hours. The sentence above should be:



I think you have confused some of the responders who are miss-understanding your question.

Coulomb counters are not perfect. They need to be synced to 100% periodically. They won't account for self discharge, power consumed by the BMS, and many don't account for charge efficiency. In short, it is not surprising that the meter reads 100% before the battery is fully charged.
Ok it is off. Fair enough. But by 70 or 80 amps?
I call that a fail of the juntek myself.
Thanks for the insight. :)
 
If you search out research papers on the topic you will find a memory effect can exist where the cells are short cycled. Taking the cell through a full charge cycle removes the effect, but required more energy than a normal charge cycle. This is one of many reports on the effect,

Mike
Ah heck. Really? I had hoped we were done with that craziness.
Thanks for the link. I will read it.
 
Ugh - I thought we were done with that too. Note that the test is done basically by "short cycling" during regenerative braking processes in EV's and then failing to charge fully when back in the garage.

Ie, this scenario is liking taking out 2ah from your 300ah bank, recharging with 2ah, braking again - ad infinitum.

Another scenario is once again "short cycling" near the bottom of discharge. Ie, having your 300ah bank discharged to 95%, and only recharging 10% back in - rinse and repeat.

Moral: Don't treat your bank as if it was a regenerative braking system. Or, don't put a 5 watt solar panel on your heavily discharged 300ah bank, and cycle it like that. :)
 
If you search out research papers on the topic you will find a memory effect can exist where the cells are short cycled. Taking the cell through a full charge cycle removes the effect, but required more energy than a normal charge cycle. This is one of many reports on the effect,

Mike
Wow, ok that is crazy stuff. And extremely significant to me as I use my batteries for my mobility scooter.
Dang it all to heck.

Thanks again for the info. I hate it but at least now I have a heads up.
The partly significant part for me is that letting it rest a period of time can fix the problem. Sadly they do not say how long to let it rest for though.
I might be ok though as I sometimes do not use it for 2 or 3 days at a time.
I just "might" escape the problem :)

Anyhow, again, thank you for this information. :)
 
If you search out research papers on the topic you will find a memory effect can exist where the cells are short cycled. Taking the cell through a full charge cycle removes the effect, but required more energy than a normal charge cycle. This is one of many reports on the effect,

Mike

OK -- we should all agree to burn this paper -- i had to study this for one of my courses and honestly -- its best just to never read it .... most of us are using LiFePO4 and the paper is on Lithium ION and certain types and uses ...

also -- for the OP -- I'm not sure why you don't want to charge your batteries to 100% more than every 6 months ... nothing wrong with blasting it and shaking the cobwebs off it often ... LiFePO4 loves being pushed -- or at least thats what I tell myself ... but top balancing allows me to synch my meters often ... so I noprmally run my batteries between 87-90% and every 2 weeks max it out ...
 
OK -- we should all agree to burn this paper -- i had to study this for one of my courses and honestly -- its best just to never read it .... most of us are using LiFePO4 and the paper is on Lithium ION and certain types and uses ...

also -- for the OP -- I'm not sure why you don't want to charge your batteries to 100% more than every 6 months ... nothing wrong with blasting it and shaking the cobwebs off it often ... LiFePO4 loves being pushed -- or at least thats what I tell myself ... but top balancing allows me to synch my meters often ... so I noprmally run my batteries between 87-90% and every 2 weeks max it out ...
Ok thanks for the insight to that paper for one. :)

As for why I don't let'er rip is simple.
Because of covid they gave the disabled and seniors a bit of a bonus and I used that to get the batteries that I have. The opportunity will probably never come again.
As it is I spent $1,200 on the cells and that was almost ten percent of my annual income.
I want these cells to last for a couple of decades. Everything points to using them between 20 and 80% and only top balancing once a year.
I have them compressed according to specs as well.

So if they last me 20 years [going down to 80% functional] then I will be happy. By then I will hopefully be dead and done with this worlds nonsense. And if not. Maybe batteries will be affordable for people like myself. Although my family is long lived. So I probably have at least 30 or 40 more years.

So that is why I don't "max it out".
I simply can not afford it. And might never be able to afford it again in what is left of my lifetime.

Anyhow, I tried to keep this short. I hope this helps you to better understand how precious these 8 cells are to me. Without them. I don't travel, or go out for a coffee with a friend, or shopping, or to a park or much of anything to do with going outside actually.

Ok enough of this.
Thanks for the insight once again. :)
 
If you search out research papers on the topic you will find a memory effect can exist where the cells are short cycled. Taking the cell through a full charge cycle removes the effect, but required more energy than a normal charge cycle. This is one of many reports on the effect,

Mike
Consequences of the memory effect for electric and hybrid vehicles

The memory effect and its associated abnormal working voltage deviation have now been confirmed for one of the most common materials used as the positive electrode in lithium-ion batteries, lithium-iron phosphate (LiFePO4). With lithium-iron phosphate, the voltage remains practically unchanged over a large range of the state of charge. This means that even a small anomaly in the operating voltage could be misinterpreted as a major change in the state of charge. Or, to put it another way: when the state of charge is determined from the voltage a large error can be caused by a small deviation in the voltage. The existence of a memory effect is particularly relevant in the context of the anticipated steps towards using lithium-ion batteries in the electric mobility sector. In hybrid cars in particular, the effect can arise during the many cycles of charging/discharging that occur during their normal operation. In such vehicles, the battery is partially recharged during each braking operation by the engine running in a generator mode. It is in turn discharged, and usually only partially, to assist the engine during acceleration phases. The numerous successive cycles of partial charging and discharging lead to individual small memory effects adding up to a large memory effect, as this new study demonstrates. This leads to an error in the estimate of the current state of charge of the battery, in cases where the state of charge is calculated by software on the basis of the current value of the voltage.
very interesting, thank you!

it seems like this is something that could be practically engineered around for those who want absolute unforgiving accuracy.

for example, a Time To Empty or Time To Full meter could be informed by each individual cell temperature, individual cell voltage, stored history of shunt, amps flowing… etc…

if any cells become colder/warmer to the point of having a significantly different effective internal resistance, then the Time To Empty meter should actually reduce the estimated kWh remaining accordingly.

if an active thermal management system is being used, then it could be activated to force all the cells to a uniform temperature and therefore internal resistance, assuming equal usage and aging characteristic (unrealistic but an approximation)

the activating of the thermal management system will require power usage itself, and the specific heat capacity of the entire battery pack limits rate of temperature change.

if the amount of usable energy returned from changing the temperature/resistance of the battery is more than the amount needed to cool the battery material, then it’s a clear runtime win.

it’s best practice to regulate the temperature of the cells, but that’s rather complicated and with LiFePO4 chemistry it is easier to just keep it near room temperature and stay below 0.5C charge and 2C discharge, or whatever data sheet says, whichever is lower.

i believe applying a high voltage to a cell that’s cold, in order to force a fast charge, will probably damage it (reduce future ability to return Ampere hours input from charging)

gonna shamelessly plug this resource: https://diysolarforum.com/resources/general-lifepo4-degradation-vs-temperature.172/

BD81519C-17C7-428E-B31E-D4C752D8D6CF.jpeg
Figure 2. Discharge profiles for cells: No. 17 (30 °C, -5 °C). (a) This panel shows the long-term cycling (with a C-rate of 1 C and a temperature of -5 °C). (b) This panel shows the reference cycling (with a C-rate of 0.3 C and a temperature of 25 °C). This figure has been modified from Ruiz et al.39.
so cycling at 1C at -5 deg C is bad for life.
cycling at 1C at 30 deg C is significantly less bad for ability to hold charge afterwards.

they tested sooooo many combinations..
notes to help:
Tc= temperature of cell during charge
Td= temperature of cell during discharge
CRref= usable capacity after test in % of original
1625890929213.jpeg

i’m still learning and probably made a lot of mistakes, hopefully this helps about “too many amps possible?” line of inquiry

1625891540941.jpeg
basically it depends on temperature of charge and discharge among other stuff
 
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Too many amps all at once or over time? All at once would be determined by cell capacity and specifications. Over time the voltage will top out and the BMS will cut you off. I am with GW66... no reason to baby these things. They work for me, I don't work for them.
 
Too many amps all at once or over time? All at once would be determined by cell capacity and specifications. Over time the voltage will top out and the BMS will cut you off. I am with GW66... no reason to baby these things. They work for me, I don't work for them.
If I had your money then I would. But I don't so I don't. :)
 
Too many amps all at once or over time? All at once would be determined by cell capacity and specifications. Over time the voltage will top out and the BMS will cut you off. I am with GW66... no reason to baby these things. They work for me, I don't work for them.
Of course you and GW are right... :) It seems people forget if a cell with specs of 2000 cycles is cycled every day at the full C rate it will last apx. 5.5 years and still have 80% capacity left. How many do this? Many including myself keep the SOC between the knees which will increase cell life. Of course temps need to be taken into consideration. Most likely the cells will degrade due to aging before anything else.

My cells are used with a UPS so I float them at just less than 3.4 volts. I have let them float at this voltage for apx. 5 months and when I tested capacity a few weeks ago there was no loss. While I don't recommend this, and many won't float continuously anyways because they cycle their cells much more often than I do, it's my belief the newer prismatic cells will last a long time under most conditions if not abused, longer then some think. I will continue to float my cells at just less than 3.4 volts and will report occasionally on any capacity loss.

As for the paper regarding the "memory effect", I found it interesting. But I burned that paper shortly after I read it and never looked back. It's not anything any of us have to be concerned about.
 
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