Can I Charge a Lith-ion Battery like this?

[bobsyleck]

I just built a 48V Lithium-ion Battery Pack (13S 18650 Cells) and was wondering if I can use my Lead Acid Battery Charger on this Pack? (non adjustable)
It does have a BMS Board attached with literature that claims to protect the Pack from 'Overcharging' as well as the obligatory 'Over Discharge' protection circuit so I'm thinking that maybe, just maybe, I can get away with it?
I'm thinking the 48v SLA Charger will provide enough voltage and that the BMS on the Lithium Pack will kick-in when the Pack has sufficient voltage - or will the Charger just keep on attempting to throw more juice at it? (Not good Obviously)
I notice too that the Charger will do a spasmodic 'Intelligent Charge' (i.e. top up the SlA's with a trickle charge) as the Battery nears its full potential, but that is something I'm willing to forfeit if i can use it on my Lithium Pack without damaging it?!!
I'm figuring the scenario will be that the 48V SLA Charger will not turn itself off automatically as per usual but that the BMS will refuse to accept further Charge beyond it's peak quota!?
p.s. I do realise that a 48V SLA Battery (what the Charger is designed for) takes a few more Volts to be Fully Charged than my Lithium-ion 48V

*I do also have a Lithium Charger rated for a 36V e-Bike - now redundant since my last bike was nicked.

 

[friendly1uk]

In a word, No.
The output will be too rough. It won't back off as you approach full. It will instead put bursts through intended to clean up the lead acid, that is more likely to light up lithium.

What 36v charger? We could look at turning that up, but it's probably better to just buy a proper one. about £25 iirc

 

[bobsyleck]

In that case I was wondering if there's some kind of Mod I can do to this 36V one I have lying around?

*See Pics and thanks for the reply/info
p.s. I just realised this is for Lithium Poly Batts

 

[bobsyleck]

Now I'm a little confused (again), *steep learning curve going on here!!
I just found this on the 'BATTERY UNIVERSITY' Site (quote): Lithium-ion

"Lithium-ion charges similarly to lead acid and you can also use the power supply but exercise extra caution. Check the full charge voltage, which is commonly 4.20V/cell, and set the threshold accordingly. Make certain that none of the cells connected in series exceeds this voltage. (The protection circuit in a commercial pack does this.) Full charge is reached when the cell(s) reach 4.20V/cell voltage and the current drops to 3 percent of the rated current, or has bottomed out and cannot go down further. Once fully charged, disconnect the battery. Never allow a cell to dwell at 4.20V for more than a few hours"

it also states - "The differences with Li-ion and Lead Acid is the absence of trickle or float charge at full charge.....the so-called lithium miracle charger that promises to prolong battery life and gain extra capacity with pulses and other gimmicks does not exist."

so according to that as long as I have a BMS insitu between the SLA Charger and my Lithium Batteries it should work!! More confusion
*The LA Charger will not go into intelligent Charging Mode (latter stages) as the lithium BMS (Over Charge safety Circuit) will/should stop the Charging Process before it approaches the threshold that the LA Charger is targeting - me thinks?!!

My BMS specs are 'Single overcharge protection voltage: 4.25V' which calculates at 55.25V (13S Pack) and the LA Charger I am proposing to use has a floating Voltage of 55V and an Equal Charging Voltage of 59V! if that makes any sense to anyone?

 

[friendly1uk]

If you had a transformer based charger of the right voltage and smooth output, which frankly don't exist, then yes you could get away with it to an extent. Your charger more likely spits at the battery, with an average flow rate being quoted. It's aiming to float the batteries at 55v by using 59v which would lead to excessive current flow when you should be using 54v. Thus flow would likely not drop to 3% and it's charging mistakes at the top of charge that tend to be the cause of most fires and degradation of your expensive cells.
The battery university is setting you up for a fire, because they are being theoretical. They have no idea what you have, and presume your charging naked with a volt meter and charger that don't really exist.

Your doing it properly. You have assembled a pack that sounds like it has all the right bits. Don't be misled by people that don't get it


There is a good chance your charger will be adjustable but i don't recognise it. It's quite small though. About 60w.

 

[dogman dan]

Ok, I'm a dumbass, I we all know that.

But If his lead charger is not overcharging his new lithium pack, he can use the lead charger in a pinch.

NOT recommended for permanent at all,, And only if the lead chargers voltage output is less than the 4.20 v maximum for his cells.

If his lithium pack needs 54.6v, and his lead charger puts out 58v, then he can't use it.

If his pack is 14s, needing 58.8v, chances are his lead charger only goes to 56v or so, and will only undercharge his pack.

But in the end. He NEEDS a new lithium charger, for the long run.

 

[bobsyleck]

thanks people - all info is good info



@friendly1uk, if indeed the SLA Charger gives an intermittent spurting/spitting charge throughout the cycle and not just at the very end then indeed there is gonna be a problem - however I only hear a brief cycling (on and off) right at the very end of the Charge (when attached to SLA Batteries), in the final minute or so, as if topping-up?!

p.s. ideally there'd be a simple mod I could do to my existing 36V Lithium charger? as I have quite a lot of spare electronic bits 'n bobs lying around - caps regulators etc.
p.p.s. just another thought but what if I could stick some kind of Voltage regulator (Buck Converter) on the output thus reducing the output of the SLA Charger from 59V to 54V ?

 

[friendly1uk]

So you own a voltmeter then?
The sla charger output has no need to be smooth. You have to presume it's rippling at switch-mode frequencies. SLA is very robust while lithium requires the uppermost degree of nannying. It's the fact it's unknown that's partly making it unsuitable.

I can't be the one that advises you to do something that sets you on fire. We are not talking 0.001% risk here. We are talking quite likely. If you set the voltage and smooth it up, your not going to just do it once are you. Just when would you get the £30 out that you need to. Just before you sell the bike? have a fire? kill your pack off?

If your competent then open up the lithium charger and fix that as a temporary measure. It can serve as a backup after you get something better.

A 48v 2.5A charger is £17 delivered from china through ebay.

 

[bobsyleck]

yep your right, not worth the risk - its off to ebay I go

But as China Post can be, well how shall I put it?, lengthy! here's my intermediate solution - I happen to have an iMax B6 Charger that can handle up to 6S (unfortunately not 13S thats really required), sooooo, I'm gonna mod the Battery Pack thus - making it detachable into 3S (x3) and a 4s via some xt60 Plugs, with appropriate Balance leads attached and just bypass the BMS for now; The iMax can do the balancing on its lonesome. The methods a bit more cumbersome as opposed to just plugging something in and sitting back but at least I'll be able to Charge the pack for the next few weeks.

thanks again friendly1uk, (and dogman dan), I guess sense prevailed in the end - on reflection I was kinda clutching at straws in my impatience
p.s. I'm not feeling enticed enough to just nip out & pay the local retailers exorbitant prices, I'll sit this one out.
p.p.s. I did eventually open up the 36V Lithium Charger hoping to see some kind of Voltage regulating POT (as after watching some YouTube Vids many do appear to have internal POTS for Voltage & Current adjustments), however mine had Nada, zilch, twas very plain and boring.

 

[dogman dan]

Once again, I typo,, I meant to say if the pack needs 56.4v, he can't use a lead or lithium charger that puts out 58v.

In simple terms, sure, you can use a lead charger temporarily if it undercharges the pack. But not if it will overcharge it.

 

[bobsyleck]

yes dogman dan I suppose it might be possible to use it for a very short time (the SLA Charger) as you suggest, and I've even spotted some Posts on the Web where people actually do that, but as 'friendly1uk' has already pointed out the Voltage output of the Charger aint very conducive and will probably not be very healthy for the Lithium Batteries, & as he also points out the risk of overheating and fire (due to overvoltage across the Battery Terminals) is very real too; Hence its a risk I've decided to avoid.

Apparently my SLA Charger puts out 54V from the getgo but as it reaches 70-80% Battery Charge State it will dish out a Floating Charge of 59V - not good.

Thanks for the contribution dogman dan, always insightful and welcomed (I've found a decent 'n Cheap Lithium Charger on eBay-China)