Battery charging basics

rick_p

100 W
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Feb 16, 2021
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I looked through the FAQs on this site and did some general searching on the web. I found lots of threads with similar questions but not close enough to trust the answers are applicable to my situations. I have two basic questions.

1. Is the charger's ability to detect when the battery has reached full charge and stop charging the only difference between a charger designed to charge a battery versus one that was designed to provide constant power to a device? If so, does the battery's BMS prevent over charging if charger doesn't have the detection capability?

2. The next question I have is, I have a charger intended for use with a scooter (Lithium Ion battery) that puts out 42 volts 1 amp. It has the correct tip (fit and polarity) to fit a 48 volt (Lithium Ion battery) I have. What, if any, harm might come to the battery if I used this charger to charge it? If it is safe (harmless) to use it to charge the battery, I presume it will never fully charge the battery, is that in and of itself bad for the battery aside from any other concerns?
 
rick_p said:
1. Is the charger's ability to detect when the battery has reached full charge and stop charging the only difference between a charger designed to charge a battery versus one that was designed to provide constant power to a device?
Mostly, yes, as long as "one that was designed to provide constant power to a device" means a CC/CV PSU (like the meanwell HLG or ELG LED PSUs, etc) that limits current by reducing voltage to maintain constant current, rather than one that limits current by hiccuping, or shutting off output until the overload goes away.

If "one that was designed to provide constant power to a device" means a random wallwart / AC adapter from some device, then no, those are unlikely to be CC/CV and won't safely charge a battery (some of them may not even *have* current limiting and will try to supply whatever is asked of them till they catch fire or otherwise fail).

If so, does the battery's BMS prevent over charging if charger doesn't have the detection capability?
It should...but don't rely on this, and make sure the full voltage of the charger or PSU is not enough more than the battery's full charge to allow it to ever overcharge. (don't use a 60v PSU on a 13s 48v battery ;) ) Same thing applies to chargers...if their voltage is too high, they won't shut off at "full charge" for the *battery* because they are trying to fill it up to what they're rated at, rather than what the *battery* needs. (they just detect that current drops below a certain point and turn off the output; that's all).

2. The next question I have is, I have a charger intended for use with a scooter (Lithium Ion battery) that puts out 42 volts 1 amp. It has the correct tip (fit and polarity) to fit a 48 volt (Lithium Ion battery) I have. What, if any, harm might come to the battery if I used this charger to charge it? If it is safe (harmless) to use it to charge the battery, I presume it will never fully charge the battery, is that in and of itself bad for the battery aside from any other concerns?
No direct harm...but it won't balance the battery, as that requires a voltage high enough to make the BMS start that process, which only typically happens near or at full charge. So if it's like most ebike or scooter batteries, it will get farther out of balance every time it is used and not fully charged.

Since 42v is pretty close to empty for a 48v battery, then it could get pretty far out of balance pretty quickly.

It also wont' have much capacity, and will perform like a mostly empty battery. If, for example, normally you'd get 10 miles out of it, at only 42v full charge it'll probably be a mile or less, and it wont' be able to provide as much power, and may even cut out above some throttle level.

Your controller may not even operate (turn on but not activate the motor) at that voltage, if it's a 48v controller and it has a high enough LVC.
 
Those are the BEST answers ever. I sure hope search engines return this page for similarly searched questions because this answers my questions and a whole lot more. No, I can't use a wall wart charger that wasn't meant for charging batteries, it needs to be a charger that limits current by reducing voltage to maintain constant current. And although it won't damage the battery, charging a battery with a charger who's output is a lower voltage rating than that of the battery, is going to result in very poor performance, possibly to the point of being unusable if the cells get too far out of balance, even if the charger is a proper battery charger. Thank you so much for these replies!!
 
I have another basic battery charging question. Do LiFePO4 batteries require a special charger? When I say special, what I mean is, can you use the same charger designed for Lithium Ion batteries, or is there a difference between the way the two chemistries need to be charged?
 
rick_p said:
The next question I have is, I have a charger intended for use with a scooter (Lithium Ion battery) that puts out 42 volts 1 amp. It has the correct tip (fit and polarity) to fit a 48 volt (Lithium Ion battery) I have. What, if any, harm might come to the battery if I used this charger to charge it? If it is safe (harmless) to use it to charge the battery, I presume it will never fully charge the battery, is that in and of itself bad for the battery aside from any other concerns?

amberwolf said:
No direct harm...but it won't balance the battery, as that requires a voltage high enough to make the BMS start that process, which only typically happens near or at full charge. So if it's like most ebike or scooter batteries, it will get farther out of balance every time it is used and not fully charged.
The follow up question I have about a charging LiFePO4 batteries is somewhat related to the previous question about having a charger intended for use with a scooter that has a Lithium Ion battery because I recently picked up a new (pretty old but not very used) bike and I "might" need to order a charger for it depending on the answer to the LiFePO4 question.

The bike is an iZip E3VIBE that came with two batteries. The original owner sold it because they left it out in the rain with the charger plugged in, and needless to say, the charger fried. The on/off switch at the throttle didn't work either, so the bike appeared totally dead, batteries and all.

However, I think the batteries are OK though, I removed them from the bike and both had a little charge on them, so dismantled the throttle to have a look at the switch, I couldn't see anything obvious so I removed the switch and dismantled it too. I found corrosion inside but there was no sign of short-circuiting and the springs were fine, so I cleaned up the corrosion and reassembled everything, and sure enough, the bike turned on so I took it for a ride. The bike is super comfortable, I'm really impressed with it, it will be great for my wife to ride with me.

The batteries are 24V LiFePO4 batteries and by coincidence my daughter has a 24 volt scooter, which has a 24 volt 1.8 amp charger. The specs are almost identical to the specs of the fried original. However, the batteries have stickers on then that read "Requires special charger" so I'm afraid to use the scooter charger until I find out if LiFePO4 batteries require a different charger or not due to the chemistry difference?
 
I’m going to answer my own question here because I found this post:

https://endless-sphere.com/forums/viewtopic.php?t=102134

Where someone asked a different question but in the responses my question is answered as well...

There is a difference between a charger designed for lithium ion batteries and one designed for LiFePO4 batteries. A charger designed for lithium ion might overcharge a LiFePO4 battery a little, which has a potential for danger but at the very least will shorten the life of the battery if used repeatedly.
 
rick_p said:
I’m going to answer my own question here because I found this post:

https://endless-sphere.com/forums/viewtopic.php?t=102134

Where someone asked a different question but in the responses my question is answered as well...

There is a difference between a charger designed for lithium ion batteries and one designed for LiFePO4 batteries. A charger designed for lithium ion might overcharge a LiFePO4 battery a little, which has a potential for danger but at the very least will shorten the life of the battery if used repeatedly.

thats just wrong. lithium chargers are not designed for any chemistry despite their marketing label. the only thing that matters is the set voltage. the charger has no clue about the chemistry nor does it care. that a certain voltage matches a certain battery chemistry is just for marketing purposes and for the less savy consumer to see if they have the right voltage charger.

charging SLA batteries and NIMH cells for example is actually tricky to charge well. lithium is stupidly simple by comparison.
 
flippy said:
thats just wrong. lithium chargers are not designed for any chemistry despite their marketing label. the only thing that matters is the set voltage. the charger has no clue about the chemistry nor does it care. that a certain voltage matches a certain battery chemistry is just for marketing purposes and for the less savy consumer to see if they have the right voltage charger.

charging SLA batteries and NIMH cells for example is actually tricky to charge well. lithium is stupidly simple by comparison.
That explains a lot, and is excellent news because after reading that thread and then reposting what I understood from it here, I searched for the exact model [ hp0060w(l2) ] of the original charger, which I hadn’t done before, and I was thoroughly confused when I found that it has been mostly used/sold as a charger for electric wheelchairs, with no mention of the chemistry of the batteries, but oftentimes it was stated to be a lithium ion charger. The replacement chargers were ridiculously expensive, I’m guessing just because they can get away with it due to it being for a wheelchair. I wasn’t able to find a single reference of it being used/sold for an ebike at all, let alone mine, which I thought was odd, I guess this bike wasn’t very popular.

At any rate, since the only thing that matters is the set voltage, then finding a suitable aftermarket charger ought to be easy, there are lots of reasonably priced 24 volt 2amp chargers that have the correct XLR connector with the correct polarity on the pins.

I do have two questions though, according to the label, my charger’s set voltage is DC OUTPUT: +24V 2A
Some chargers I see for sale have the exact same specs, but underneath that it also has: CHARGING: 29.4V MAX
Mine doesn’t have that, should I avoid a charger that says that?

And lastly, what actual voltage reading should I expect to get from my 24 volt battery after it is finished charging?
 
see, this is what makes everything comfusing for everybody. marketing over standards.

ignore the "marketed" voltage and actually look at the numbers on the battery.

a regular li-ion battery at "24V" means its usually a 7S battery pack (7*3.6=25.2V) and peak (fully charged) is 7*4.2=29.4V
but as you see the NOMINAL voltage is NOT 24V, its 25.2V. wich makes it a LOT more confusing because if you have lifepo4 cells it would be 8*3.2=25.6V NOMINAL with a fully charged voltage of 8*3.65=29.2V.

see how quickly and confusing it can get if manufacturers start obvuscating what you actually have? just look at power tools and the half dozen ways they advertise a simple 18V 5S battery, you will see every voltage between 18~21V on the makreting and printed on the batteries just to have 1 more then the competition, because 1 mroe is better, despite it being the exact same 5S battery setup.

ps: a mean well SP-100-27 would suit your battery well. you can just cut the wire of the 48V charger you already have and hook it up to the terminal. set the correct voltage and you are off. and SP-75-27 would also do the trick if you dont need to charge as fast. slower = better.
 
flippy said:
If you have lifepo4 cells it would be 8*3.2=25.6V NOMINAL with a fully charged voltage of 8*3.65=29.2V.
I do have a LiFePO4 battery, I will check the fully charged voltage as soon as I get my hands on a charger.

flippy said:
ps: a mean well SP-100-27 would suit your battery well. you can just cut the wire of the 48V charger you already have and hook it up to the terminal. set the correct voltage and you are off. and SP-75-27 would also do the trick if you dont need to charge as fast. slower = better.
Thanks for the recommendation, I really appreciate that. However, this isn't my only bike and those are a little on the expensive side for this particular bike. I'll probably buy one of those that are similar in nature to the one the bike came with. Hence the reason I asked the following question, which I would very much appreciate your advice on...

According to the label on my charger, it has a set voltage of DC OUTPUT: +24V 2A
Some chargers I see have the same exact output specs, but underneath that it also has: CHARGING: 29.4V MAX
A charger like that has a max charging output of .2V higher than what my battery should hold when fully charged, is that OK to use?
 
For lifepo4 you can slighty overcharge them if the current is low enough. So yes.
 
I have a related question. For a battery without BMS of nominal 3.6v li-ion cells and a generic bulk charger, when does the taper to the CV phase generally start? Very near the fully charged 4.2v/cell, or sooner? As flippy stated above the charger has "no clue" what it's connected to, and is just a fixed watt generator in the CC phase?
 
Barncat said:
I have a related question. For a battery without BMS of nominal 3.6v li-ion cells and a generic bulk charger, when does the taper to the CV phase generally start? Very near the fully charged 4.2v/cell, or sooner? As flippy stated above the charger has "no clue" what it's connected to, and is just a fixed watt generator in the CC phase?

that is impossible to say. if you charge with 50mA you will never see a CV stage.

the harder and faster you charge the sooner you hit CV. many high power DC chargers for cars will hit CV well into the low 70% range.

that there is a bms or not has no impact on the charging process. the bms only does something if somethig goes wrong. its a protection device, not a control device. it can only stop/pause the charging by simply cutting the input off, it does not control it. it simply shuts the door.
 
For a few years, one manufacturer called 14S lithium-Ion battery packs 50V. After the Bafang mid drives began growing in popularity, they were often used with 14S, and many began labeling the packs 52V. EGO-brand lawn tools call 14S 56V, and I think Echo calls them 58V. So which is it, and what charger can charge them?

The specs from the manufacturer say that each cell can be charged to 4.2V per cell maximum. Later, we found out that the pack life can be doubled (or more) if charged to only 4.1V per cell. The nominal "average" voltage from full to empty is 3.7V, and they really shouldn't be discharged below 3.0V, with 3.3V being a good target. Sooo...3.3V to 4.1V per cell.

For 14S, that would be setting the low voltage cutoff at 46.2V, and the pack would be fully charged at 57.4V (*nominal average is 51.8V).

LiFePO4 is a nominal 3.2V (*instead of 3.7V). I've read it can be charged to 3.65V per cell, but as we learned before, do not store lithium at max volts, therefore running LiFePO4 in the flat middle of its curve would be 3.0V-3.4V

When a lithium-Ion or a LiFePO4 pack are advertised as a "12V replacement", they are two different voltages. That's why they need a special charger, not because if the chemistry.

3S Lion is_______12.3V
4S LiFePO4 is___13.6V
4S LIon is_______16.4V

My car jump-starter box is 16V max (4S Lion), no BMS. The alternator only goes as high as 14V, so that's it's voltage when I use it.
 
This post is not necessarily related to the "related question" by Barncat or the replies from flippy or spinningmagnets, I'm just reporting back the results of charging my "24 volt" LiFePO4 batteries with a 24 volt 1.8 amp scooter charger.

Both batteries charged to 27 volts, give or take a small fraction of a volt. I assume this is when the charger detected the batteries had reached full charge. The charger got a little warmer than I might have expected, but it's possible I was just paying closer attention to it than I normally would.

I'm adding the following pictures and information about the batteries just in case it adds anything to the conversation.

One of the two batteries doesn't have a specification sticker on it, so the Ah is unknown but it is marked 24 volts next to the charging port. It only has one pack inside it, which appears to have 16 cells total.

small-battery.jpg

A close up of one cell.

small-battery-cell.jpg

I found it odd that there is no fuse in this battery, even though the case clearly came designed to have one.

small-battery-no-fuse.jpg

The other of the two batteries has a specification sticker on it, and says that it's rated at 9.6 Ah. It has two packs inside and it appears that there are 12 cells in each pack.

large-battery.jpg

A close up of one cell.

large-battery-cell.jpg

A close up of the sticker. I find it interesting that on the line where is gives the model, it has (RMB-Li RealForce), which left me wondering if that stood for lithium ion, but I looked it up and the cells are definitely LiFePO4.

large-battery-sticker.jpg
 
Just one more observation and one more question, since OP's thread is battery charging basics and primarily about charger/ battery compatibility.

My question a few posts back was actually not specific enough upon rereading. I should have said 20s5p battery on an 84V 3A bulk charger for example... as it happens the current does stay right at nominal 3A until very close to 4.2V/cell as measured by clamp meter. Common knowledge to the experienced I imagine.

I have a just completed 15s5p 225A rated battery that i don't have a specific or adjustable charger for yet that needs to be charged to just over 4V/cell for testing with a 60V rated Flipsky 6.6 vesc. I don't know yet how conservative that rating is... it would be nice if it could handle 61.5v, or the full 63.

Based on what I've read and pieced together, i could use the 84V 3A CC /CV charger without damaging the 15s pack, so long as you monitor it closely and UNPLUG IT AT 60V. Correct? Not advisable but it'll be at least a week to get something else.
 
Barncat said:
I have a just completed 15s5p 225A rated battery that i don't have a specific or adjustable charger for yet that needs to be charged to just over 4V/cell for testing with a 60V rated Flipsky 6.6 vesc. I don't know yet how conservative that rating is... it would be nice if it could handle 61.5v, or the full 63.

I don't know much about batteries, but I do know quite a lot about ESCs and would advise against this. 60V is the MOSFET rating, at which they start to break down and leak current. The avalanche voltage which will instantly destroy it is a few volts more (typical 125V for a100V fet so maybe 75V for yours, but consider regen, switching spikes... Really I wouldn't run that ESC above 12s. There's a good chance the standard firmware will immediately over voltage and turn off anyway.

Regarding the battery charging, I use a 13s charger in series with a lab PSU (dps5020) that allows me to generate any voltage and still use the 13s cutoff if I'm charging something funny/above 13s. E.g. 14s means set the DPS to 4.2V and put in series with 13s charger.
 
Code:
#define HW_LIM_VIN				6.0, 57.0

This line in the VESC setup says it'll turn off if you go over 57V. :!:
 
Hey mx- thanks for your insight on the vesc and charger setup. A bit to digest there as I'm still learning that unit and got sidetracked with refining my battery. Still waiting for another part...

Worst case I wreck the vesc and am out 140 bucks and have to find something else. Or perhaps better yet swap in a higher power unit now... locked into 15s5p.

I apologize to OP for veering off topic and will curtail any further posts in this thread.
 
There has been a lot of good information shared in this post's thread, and I have learned a hell of a lot, but despite all of that I can still say that I'm not absolutely sure about a few important things. I'm going to make a few statements about what I think I have learned and hopefully get some feedback on what I have correct and what I don't.

You can charge a LiFePo4 battery with same charger intended for Lithium Ion batteries as long as the charger is rated for the same "nominal" voltage, despite the fact that the two batteries will have slightly different fully charged voltages. Both Lithium types are compatible with the CC + CV algorithm employed by generic red light, green light chargers. Note that most batteries that are labeled with common voltages like 12V, 24V, 36V, 48V, etc are rarely, if ever those exact voltages when fully charged, they will be somewhat higher, and how much higher depends on the series configuration and the Lithium type used.

On the other hand, you should not charge any type of a Lithium battery with a charger designed for charging sealed lead acid (SLA) batteries, or vice versa because the charging algorithm is wrong in both cases, and in each case you will not only not charge efficiently, you will likely damage your battery. With that said, I read an article that said it's OK to use a constant current charger intended for SLA batteries to charge a Lithium battery if the current is low enough. Proceed at your own risk though!!
 
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