voltage drop under load (maybe a simple question?)

[pellicle]

Hi

I recently purchased an eScooter which has a 13Ah 48V pack (18650 13 parallel bundles of 6). When "fully charged" by the plug in charger it seems to sit at around 53 or so volts and settle to 528 or so volts after a few minutes.

My question is in trying to estimate load on the battery by observing V in use (it has a prominent easy to read voltage LED display and that voltage has good agreement with my Fluke DMM when I test across the battery terminals.

The motor is 1000W and under load (steep hill ~9 degrees) voltage drops to about 45V but recovers quickly (on the flat) to 48 or so (reasonably fresh off the charger).

From this is it possible to calculate / estimate (approximately) what the amount of amps being drawn is?

Thanks

 

[flat tire]

You could guess if you knew the internal resistance but what I would do is get a cycle analyst w/ shunt then the scooter will be more empowered with trip computer and accurate consumption.

 

[pellicle]

:thumb:
Good idea

 

[kcuf]

54.6v is 48v 13s top charge

if measurements correct

pack is not fully charging

 

[DogDipstick]

I drop about a volt ( 1v ) when pulling 20 amps @ 58v. 15 Ah Lipo NMC pack. To know the amps used you need to know more than the voltage droop and the capacity.

 

[pellicle]

54.6v is 48v 13s top charge
...
pack is not fully charging

understood, I calculate it undercharging to a bit over 4V per cell, which as I read on battery university is actually good for battery longevity

 

[AngryBob]

While that is true, it is incomplete on an important matter. Search on the terms "BMS" and "balancing".

The difference between 53 and 54.6 is 1.6 V. Now, that could be evenly spread out over the whole battery. However, much more common is for that difference to be concentrated in one group. That single group will contain dramatically less energy than all the other groups. When under load, that single group will fall much farther and much faster than the rest, dragging the whole battery with it. The voltage will also rebound VERY quickly after the load is removed.

A new battery which does not charge to full voltage is a strong indicator of a serious defect, which will likely get a lot worse. It should, in fact, be sufficient to force a warranty replacement, which you should investigate because such a defect can destroy the battery as a whole, making it totally worthless. It is also the most expensive single component in the whole rig.

Talk to the company first, but they will often tell you to leave the charger connected for an extended period of time. If it will not charge to full voltage, get it replaced ASAP.

Something else to look at is a "discharge curve". The relationship between voltage and stored energy is NOT linear, it is a complex curve. For instance, there is a huge and dramatic difference between the stored energy between 4.2 and 4.0, and 4.0 and 3.8. The first drop happens fairly quickly, the second takes much longer. A cell at 2.6 V, which is what you likely have, will drop voltage very far, very fast, as it has virtually no stored energy at all and is generally considered to be dangerously low, not just dangerous to cell and pack longevity and function but a very real safety issue. I would not park this vehicle within 50 feet of anything flammable.

The odds of it actually bursting into flame are fairly low, but fire is a very bad thing. I don't play Russian Roulette even if the gun has 12 cylinders. Or a hundred.

 

[pellicle]

While that is true, it is incomplete on an important matter. Search on the terms "BMS" and "balancing".

yep, I have a basic grasp of those concepts ... I used to be an electronics tech, but back then our remote gear was NiMH or Gel-cell 12V ... so different animals.

I have some experience with Lithium and understand the discharge curve.

The difference between 53 and 54.6 is 1.6 V. Now, that could be evenly spread out over the whole battery. However, much more common is for that difference to be concentrated in one group. That single group will contain dramatically less energy than all the other groups. When under load, that single group will fall much farther and much faster than the rest, dragging the whole battery with it. The voltage will also rebound VERY quickly after the load is removed.

rebound isn't "very quick" but then is hard to know when talking qualitatively rather than quantitatively ...

A new battery which does not charge to full voltage is a strong indicator of a serious defect, which will likely get a lot worse.

actually it did charge to 54.6 on the first day if anything I've been taking it off the charge if I wander by and see that its 53 or something.

The article on battery university suggests that shallow usages are not harmful to Lithium.

Thanks, I'll follow up in the other thread on that specific question

 

[AngryBob]

When "fully charged" by the plug in charger it seems to sit at around 53

 

[pellicle]

When "fully charged" by the plug in charger it seems to sit at around 53

if you're quoting me please note the use of the preceeding word "around" and the lack of decimal places: meaning I did not report with precision. And that was after some time of settling (maybe 20 min)

 

[AngryBob]

Look, if you want to argue, fix it yourself.

Fully Charged does NOT mean you pulled the plug out before the charge was completed. That is what you did. What you DID, does not match what you said.

I really hope your house does not burn to the ground.

I also hope that if you see a rolling doughnut on your way to work, you know what to do.

 

[flat tire]

I think what Bob is trying to say is to make sure your BMS has a chance to do its balance routine even though you're wisely topping off below max voltage. You should manually verify your individual cell group voltages to make sure they're balanced.

 

[pellicle]

Hi

... BMS has a chance to do its balance routine even though you're wisely topping off below max voltage. You should manually verify your individual cell group voltages to make sure they're balanced.

I don't believe that this system has a BMS, there's no evidence of it.

Because its all sealed I can't actually get in to measure each cell group.

As I mentioned I was under the impression from reading on Battery University that (with a new pack like it is) that unbalancing came from running it too low not from shallow cycling it.

Two articles came to mind:
https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

From table 4
Charge level *(V/cell) | Discharge cycles | Available stored energy **
4.00 | 1,200–2,000 | 70–75%
and from https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

Simple Guidelines for Charging Lithium-based Batteries
Turn off the device or disconnect the load on charge to allow the current to drop unhindered during saturation. A parasitic load confuses the charger.
Charge at a moderate temperature. Do not charge at freezing temperature. (See BU-410: Charging at High and Low Temperatures)
Lithium-ion does not need to be fully charged; a partial charge is better.
Not all chargers apply a full topping charge and the battery may not be fully charged when the “ready” signal appears; a 100 percent charge on a fuel gauge may be a lie.
Discontinue using charger and/or battery if the battery gets excessively warm.
Apply some charge to an empty battery before storing (40–50 percent SoC is ideal). (See BU-702: How to Store Batteries.)

Thanks for your points. I appreciate that Bob is just being true to his screen name.

 

[pellicle]

Look, if you want to argue, fix it yourself.

I'm not aruging I'm clarifying ... and I haven't asked you to fix anything only explain something

 

[AngryBob]

First, what "evidence", exactly, do you expect to see that a BMS is present? A six foot tall, ten foot wide, blinking neon sign, perhaps? Virtually all commercially sold lithium vehicle power packs will have a BMS. Seriously, on what basis do you conclude there is no BMS?

Yes, you have "clarified" that you do not understand the term "fully charged", and also do not grasp the concept of scale or the diameter of a fingertip. For scale, you gave me the dimensions of a box that is not fully shown in the pic. Useless. Can you see your fingertip from where you are? You have multiple cells well on their way to melting their way thru the plastic case.

Read SpinningMagnets comments on the overheating thread. This is an experienced individual who agrees you may be looking at a VERY serious problem.

The information you are getting from the articles is dangerously incomplete, and the conclusions you have drawn from it are inaccurate. Read every troubleshooting thread on this website for the last 5 years and then get back to me with what you have learned. For starters, many, many batteries are DELIVERED in a severely unbalanced state. Your charging method does ZERO balancing, at all.

There are MULTIPLE indicators of a possible unbalanced condition, full charge voltage being one, severe overheating being another, and there are MULTIPLE paths to reaching an unbalanced state, undetectable minor cell defects being just one. Meaning you can follow all the correct procedures and still get badly unbalanced.

Also, this is what it looks like when I am making a major effort to be nice, polite, and cordial.

When somebody is risking burning their bleeping house to the ground and disregards obvious indicators of serious danger and blows it off because of some bleeping egghead article which is more theoretical than real-world practical I tend to get just a tad aggravated. When they also fail to answer simple, straightforward, direct questions and give misleading answers because they don't know that they don't know, it gets a bit worse.

But ANGRY? No, this is not angry. Not yet.

 

[pellicle]

First, what "evidence", exactly, do you expect to see that a BMS is present? A six foot tall, ten foot wide, blinking neon sign, perhaps? Virtually all commercially sold lithium vehicle power packs will have a BMS. Seriously, on what basis do you conclude there is no BMS?

well I can't be certain without cutting the battery pack apart, but I'd expected to see something like the board for it, but perhaps its fully internal. I'm new to this in some ways and so perhaps you could cut me a little slack? Maybe even tell me what to look for or make helpful suggestions?

but seriously I think your slant and choice of words is rather more rough than needed and you turn to being impatient and yelling even in your second post to me. I've got back with data and corrections, so I don't really understand why you're treating me this way, its far from civil or courteous.

To be honest I think I'd just prefer you ignore my questions here and don't reply if you wish to continue being so angry.
(and if you think you haven't been angry yet, then I submit what you call angry is actually abusive)

Also, this is what it looks like when I am making a major effort to be nice, polite, and cordial.

and thank you for that effort.

When they also fail to answer simple, straightforward, direct questions and give misleading answers because they don't know that they don't know,

so far I have done my best to answer your questions and explain why I answered as I did when you said it was insufficient, so your accusation is not based in much.

 

[flat tire]

Cut open the shrinkwrap on that battery and show us what's inside. Won't hurt it you can tape back up. Don't get butthurt about Bob he has a working brain so you would do well to listen.

 

[pellicle]

Hi

Cut open the shrinkwrap on that battery and show us what's inside. Won't hurt it you can tape back up.

thats a good suggestion, but I'm concerned about warranty. I've been engaging the seller and he's been quite friendly about this.

my plan next (which I forgot to add above) is to make it easy to quick remove the belly pan (I'll duct tape it on) and go for a hill climb. Then after an amount of time will quickly pull that off and inspect the entire insides with my thermal camera.

Don't get butthurt about Bob he has a working brain so you would do well to listen.

LOL ... thanks, and I have actually taken his points seriously ... I've been on many internet fora since NNTP was "all there was" and have met people who are quick to be painful just like him. I'm in my 50's now so I'm actually at a point where if the advice comes with a bit of vinegar I don't mind, but when it gets too close to being abusive I just block them. My view is I go to these places to ask questions and help where I am able, I don't come here to find an outlet for my anger or to pick fights.

Anyway, thanks for the advice

 

[AngryBob]

There are not just one, but multiple, indicators that you are currently at significant risk of coming home to the smoking ashes of what used to be your home. At minimum, the most expensive single component of your recent purchase is already degraded and devalued. The entire device is at risk of total destruction.

When someone remarks on a rapid oxidation reduction reaction, do they politely wait to catch your attention and then whisper, or do they scream "FIRE!" as loudly as possible? Do you have a personal preference here? If you encounter someone who appears to disregard the risk or not understand what it means, do you walk away, or do whatever you deem necessary to impress upon them the gravity of the situation? If they say, well look here, there is a magazine article which says that fire is not really all that bad, might you find that somewhat aggravating? In such a situation, do you actually give a crap what their opinion of your actions might happen to be?

Severe and unusual voltage drop for a new battery. Complete charge with corrective balancing rarely or never performed. Clear and obvious evidence of major overheating on multiple cells. A device often paid for by insurance and not by the actual user. A user base which is frequently elderly and regularly preyed upon by some vendors who may lack a scruple or two. A major one of which I happen to be personally familiar with, along with their business practices.

My suggestion at this point would be to disconnect the battery, move it at least 50 feet away from anything flammable, put it in a large bucket, cover it with sand, then contact the company and demand a replacement battery under warranty. Take a picture of the melt marks on the battery with something like a penny in the picture for scale, that should be all the proof that is required.

If they refuse to do so, get a ticket or incident number and get that and the company contact information to me, I will get you that replacement battery. I will not be polite or kind or courteous or anything remotely resembling these concepts, but that defective merchandise will be replaced. Obtaining such warranty replacements is something I have done many, many times in my professional life, in a completely different business. My success rate is extremely high. It is based solely on identifying absolute proof of product defect, which I believe you have.

There are, of course, numerous optional courses of action which you may choose to follow. By all means, see what the battery university folks have to say. Keep some marshmallows handy.

 

[pellicle]

Hi

... Take a picture of the melt marks on the battery with something like a penny in the picture for scale, that should be all the proof that is required.

thanks for your post, the above is exactly what I've just done this morning.

Also, I'm in Australia, so we may have different (sometimes better sometimes worse) laws. The seller has been dealing with this in a genuine way, and I've reported to him the advices I've recieved here (although have not told him where) and have said that I've kept this discrete so far.

I'm down in Brisbane (my job is currently here) and the scooter is up in the countryside where I live out on the veranda. So (apart from everything else) I simply can't get to it as its over 200Km from me.

BTW, this is the sort of scooter:

although that's the 500W single motor version and the one that's giving me issues is the 1000W dual motor version which I bought on Friday.

Thanks for your suggestions.

Actually if it goes up in smoke I just hope I have a phone on me to record it, cos that would be a hoot on youtube and give the seller the heebie-jeebies (which they should already have if they had a clue but don't).

 

[AngryBob]

Holy crap, you are in Australia! Turn the unit upside down immediately!

I assumed you were an old fart with a mobility scooter. That was incorrect. My mistake, I do make them occassionally. Not often, but it does happen.

Making the seller aware that getting those heebies and jeebies is a very real possibility is often a useful method for getting defective merchandise replaced.

Remember that the guy on the phone is well paid and well trained to NOT hand out replacement parts, and that makes them the enemy. DEFEAT is an event that occurs in the mind of your opponent.

 

[pellicle]

Hi

Holy crap, you are in Australia! Turn the unit upside down immediately!

I always use those chargers upside down to account for that (I've got ex-perience

I assumed you were an old fart with a mobility scooter. That was incorrect.

only partially, I am an old fart (55)

Making the seller aware that getting those heebies and jeebies is a very real possibility is often a useful method for getting defective merchandise replaced.

I have been doing exactly that ... and there is no "guy on the phone" who's well paid, I'm dealing directly with the owner of the business (and if you've ever run a business you know the staff are often paid better than the owner )

 

[AngryBob]

i have run my own business for almost 20 years with no staff, I can relate.

You may need to turn both the charger and the scooter upside down.

55 ain't old, ya pup, you're still snappin your whipper.

If they have seen the picture, what is their excuse for not having already shipped the new battery?

 

[pellicle]

If they have seen the picture, what is their excuse for not having already shipped the new battery?

dunno, but I'll be sending them this photo of a scooter fire from Singapore (different brand to mine, but I'm sure it'll drive the point home

https://www.todayonline.com/singapore/fire-bukit-batok-flat-1-victim-critical-condition-2-others-taken-hospital

I did say to them on Monday that because I'm down in Brisbane (where my work contract is) and can't be home till the weekend (to get the scooter) that there was no point in them doing much till then. I'll be doing a better pull down on the weekend as well as some thermal camera explorations of the battery in case the "marks" only happened when it was run (briefly) on unrestricted mode; which normally can not be accessed unless you know the "magic method", but was bloody turned on by default!

I shall keep posting to this thread.

Also (FWIW) I identified that part of the reason I was confused about charging voltages was that the 8.8Ah battery on my 500W scoot (which I keep in Brisbane) charges to the lower voltage. It could be the charger (its a basic chinese one showing 54.6V 2A on it. Both chargers have the same thing written on them, but I'll take the other charger up with me on the weekend and do some comparisons and also test actual battery voltage with my Fluke) DMM rather than rely on the reported V of the handlebar controller. I've tested the battery V on the 500W model against the controller and it was in agreement with my DMM.

 

[dogman dan]

Assumimg you pull 1000w, divide that by the voltage under load and you get amps. That comes out 22 amps, which is the amp limiting setting of many controllers that are called 20 amps controllers.

But once rolling, up that hill, you will not pull that full 22 amps. Betcha you pull about 18 amps up the hill. Your controller could be higher, 25 or even 30 amps, but at decent speed it will tend to pull at least 5 amps less, or more if the speed goes up like on the flat. 12-15 amps of load on the flat I bet.

You can confirm all this with a CA, or cheaper DC wattmeter. More info is always good in my book.


As for the sag, its a lot, but unfortunately typical for a lot of ebikes and scooters.

As for the undercharging, it might be trying to charge full, but can't because it's out of balance. (Assuming your charger puts out 54.6v) Charge, let sit half an hour, unplug, and then try to charge again. Repeat this many times, 10 or more times if you continue to see any improvement each time. If the charger will not start after the battery sits a half hour, ride a very short ride to get it to restart. Each time, any overcharged cells should be discharging some, allowing the less full cells to get a bit fuller each time.


One damaged, and or just weak cell in that pack can cost you a half volt of charge at full. If the battery is cheap, this is typical. Balances fine, but never at full charge. This is also true of all older packs. They simply cannot get to that full 56.4v, except when the charger is on. Soon as they get full and the charger current gets cut off, you lose a volt or two. So if you keep trying to force it to balance and it just won't improve ever, then you just have a weak cell or two in there.