Bulk Charging LiPo at greater than 4.2 volts per cell

[NeilP]

No that title has got your attention, I do not intend to actually let my cells go above 4.2.or even 4.1 -4.15 but...a thread that I cant find now was askign about an intelligent bulk charger, that charged till say 4.0 volt per cell (storage voltage) the previous day then did a timed top up to..4.15- ..what ever you use as final charge..just before riding.

As I cn at fidn that thread, i thought I would start a new thread, with what that thread brought up in my mind.

For all I know, the 'Fast Charge - non balance" setting on a Icharge / Hyperion etc al ready do theis.

As all of us that bulk charge know..as the cells come up to voltage, the current reduces, so the last part of the charge can take longer than the first section.

The usual way to set up a bulk charge setup is to set the open circuit voltage to what you want the final pack voltage to be. But this results in an early taper off of charge current as pack voltage increases.

When I am bulk charging a pack in the workshop, with my string of PC supplies and a Meanwell as final voltage and current limiter, I often ramp up the output voltage of the charger, as the current decreases, so as to keep the charge current high..2C or so...while all the time keeping an eye on all cell voltages with a string of Battery medics/celllogs.

I still do not let the individual cell voltages go above by final voltage.4.15, but the charger is now effectively at a much greater open ircuit voltage than final pack voltage.

The charge coltage has to be reduced again as cell volts come up to required level...4.15 volts, but this does make for a quicker charge.


I just wondered about doing this and if any one else did similar...I can't see an issue with it as long as final cell voltages are not exceeded, but was just putting it forward to see what other think.

If the chap who was thinking about the 'Intelegent bulk charger reads this, maybe it could be incorporated in the programming of his system?...or in to Fechers cc/cv boards ...version 3 ?

 

[dogman dan]

Well you did make me look.

One thing bothers me about bulk charging. That is, bulk charging with no hvc board.

I do bulk charge all the time, using an RC charger hooked to a pile of paralelled packs, on the non balancing charge setting. But as the charge finishes up, it still slows down considerably, and creeps up to the final charge voltage of 4.2v. If I select fast charge, it stops at about 4.19v or maybe 4.18, but it still slows down to about 5 amps for the last bit, and skips that very last 2 amp or less portion of the charging cycle. I feel this is safe, particularly while packs are still behaving nicely and not getting .1v or more out of balance every cycle. Still do it in a flame resistant fireplace hearth, cuz I'm a fraidy cat.

But do you get that slower last few minuites of the charge with your setup? Does it matter if you terminate at 4.15v? My charger doesn't slow down till it's above that anyway. So presumably you could rock on at 10 or 20 amps, whatever your charger does, right to 4.15v.

I like the idea of using the bms battery chargers for bulk charging, because presumably they would ramp down the amps a bit towards the end.

But the idea of a power supply taking a pack right to 4.2v per cell at a high amp rate sounds like it could be tricky when the packs get older and start to have differing capacities.

 

[NeilP]

Well you did make me look.

One thing bothers me about bulk charging. That is, bulk charging with no hvc board. .

Never used one. I just monitor regularly. I did build one up from TPpacks, but it is jsut too inconvienent, because I ahve to remove the pack to charger each night

I do bulk charge all the time, using an RC charger hooked to a pile of paralelled packs, on the non balancing charge setting. But as the charge finishes up, it still slows down considerably, and creeps up to the final charge voltage of 4.2v. If I select fast charge, it stops at about 4.19v or maybe 4.18, but it still slows down to about 5 amps for the last bit, and skips that very last 2 amp or less portion of the charging cycle. I feel this is safe, particularly while packs are still behaving nicely and not getting .

Yes as I suspected, I have not tried the Fast charge setting on my RC charger, but suspected it did pretty much that, but obvioulsy with these RC chargers, as soo as you disconnect the pack to measuer the open circuit charger voltage, it cuts out, so measuring open circuit voltage is not possible.

But do you get that slower last few minuites of the charge with your setup? .Does it matter if you terminate at 4.15v?

Well, no, because if I see the current dropping I crank the volts up a bit more manually.

Does it matter if you terminate at 4.15v?

as opposed to ??

So presumably you could rock on at 10 or 20 amps, whatever your charger does, right to 4.15v.

Yep that is what I do. But this is not soemthing I do every day, or even every week, It is just if I happen to be in the workshop with a low battery and I want to charge it before going home or going out later

But the idea of a power supply taking a pack right to 4.2v per cell at a high amp rate sounds like it could be tricky when the packs get older and start to have differing capacities.

not sure it I would purposely go as far as 4.2 at high current ..or at any time. Highest I have knowingly gone is 4.18 as a balance charge with the iCharger

 

[Ykick]

My current limited 10A MW setup is adjusted to 4.15V/cell but current doesn't taper off much until around 4.1V/cell. If terminated at that point maybe 200-400mAh loss of capacity? That's good enough for me in a hurry (fast charge) as opposed to another hour trickling top charge. I fail to see much point in what you're attempting to accomplish?

I also did some temperature graphs and learned heat increases significantly even under low rate charge little above 4V/cell. I figure that can't be good for longevity so quick charge is fine by me most of the time.

A few users have shared how they've charged RC Lipo to 4.35V/cell when needing maximum capacity for one off rides but that's a carefully monitored and occasional situation. Personally, I simply add more capacity and keep V/cell gentle.

 

[NeilP]

I fail to see much point in what you're attempting to accomplish?

Not necessarily trying to accomplish anything, it is jsut a comment on what I have been doing when I occassionally charge the bike in the workshop.

I suppose I could say that the reason I have been doing it is to get it up to 4.15 volts a bit quicker. not to get more capacity in it. Just that when I see the cells at 3.9 volts or so, and the current is now down from 20 amps, down to 10 or so, I can easily get the charge current back up to 20 amps again, then as the cells approach 4.12 or so, I can start dialing the current down a bit.

I suppose it is just going for a longer CC portion of charge.

I really wanted to post this in the thread I first referred to but can't find it now. The bloke was asking about making intiligent bulk charger, and my thought was that if this was going to be a fancy programable charger...seem to remember C++ being mentioned.
So if it was going to be programable, then doing it this way, with cell voltage monitoring, and true CC charging up to a closer end point would give faster charging at the end. His idea seemed to be charge to storage voltage when first geting home , and not charging to full voltage...then doing the top off charge jsut before riding. But as we know this top off charge often takes as long due to the trickle current when the open circuit voltage is the same as battery final voltage. If this was an intiligent charge build, then the CC phase could be kept going longer..so have a quicker top off charge in the morning.
Now you mention temperature, maybe this system he wanted to build could include temp monitioring too, rather like the iCharger and others.

My reason for posting was really to prompt coments such as yours

 

[Ykick]

It's a good topic to discuss and look for elusive answers. For whatever reason my 10A rate MW holds right there until the very final top charge. Current begins to drop noticeably around 4V/cell but still 80% at 4.1V/cell, it hits 50% current at 4.13V/cell but from that point to 4.15V/cell drops like a rock. I de-rate everything (my MW's can do 13-14A but keep 'em trimmed back to 10A) so perhaps my chargers behave differently than what you're experiencing?

My modest testing revealed a minimal increase of a few degrees but it was always very consistent rise above 4V/cell at practically any charge rate I used. I don't think temperature sensing would be that useful for ensuring longevity although it could be an additional safety warning feature? In that vane, pressure sensors may also offer some alarm type protection for puffing cells? IMO, physical deformation (puffing) is likely responsible for majority of RC Lipo fires due to shorting tabs.

 

[NeilP]

I don't think temperature sensing would be that useful for ensuring longevity although it could be an additional safety warning feature? .

Yes, that was more my thought on it, not so much as a charge reg, safety function was my thought.

The Meanwell I have in my PC supply string is a 1volt unit, so it is good for 29 -30 amps. The PC supplies I have are all good uyp to about 25 amps. I have 10 or 12 PC supplies, plus more to convert. Would liek to run them all on the 5 volt line, for higher current . but this string is only everused for charging random selection of cells, so I just plug or unplug as m,any as I need to get whatever voltage I need then tune with the Menawell. It is jsut a rats nest of wires and supplies on the bench. Would like to make it up in a box, switch in/out, warning lamps etc, but all to much work and expense for no real gain.

 

[dogman dan]

Interesting that the meanwell does taper off the current some as it reaches the top.

But it's still not so clear to me, is that the meanwell doing that, or is it because it's getting harder to get power to flow into the cells.?

I just assumed a meanwell, or a computer ps or such would just slam current into the packs right up to the moment you pulled it off the charger, or had an hvc disconnect. Some of you folks that understand this stuff better than I must feel a lot more confident. I think I'll always be a bit of a noob with electronics, and be happier using an RC charger. Even though I still bulk charge with it.

 

[NeilP]

Interesting that the meanwell does taper off the current some as it reaches the top.

But it's still not so clear to me, is that the meanwell doing that, .

Not s much the meanwell doing it it is just what happens. When the voltage difference between pack and charger becomes less, then current reduces.

it is like having two tanks connected from the bottom with a pipe with a tap on it

Start with one tank full and the other empty. Now open the tap, water will flow fast down the pipe to start with, but as the level between the two tanks gets closer the rate of flow will get slower

 

[Ykick]

Interesting that the meanwell does taper off the current some as it reaches the top.

Just dawned on me 'might not have as much to do with MW as it does Fetcher's mini current limiter outfitted to my SP MW's? For my setup, battery's 95% full by the time it begins to taper but the last 2% can often take as long as it did to reach 95%.

 

[lazarus2405]

I like the idea of using the bms battery chargers for bulk charging, because presumably they would ramp down the amps a bit towards the end.

I bulk charge with a small alloy shell "400w" charger from BMS Battery. Inside there are three trim pots, one for the current limit, one for the open circuit voltage, and one for charge termination (as in, it ends charging, shuts off the fan, and turns on a green LED when the charge current drops below a certain threshold). The current will begin to fall off as you leave the CC portion and enter the CV portion of the charge, but as you reach your final desired voltage the current doesn't exactly reach zero, only approximately. How long that final portion of the charge is "supposed" to take is up to you - do you care to let it keep running at 0.1a of current for another hour? Probably not. So that charge termination takes place when that current is close enough for your tastes.

I suppose it is just going for a longer CC portion of charge.

Back to my charger, it's set to run at 5.5a up to 4.15v/cell and terminate when that current drops off to 0.5a. If I wanted to accomplish what you're suggesting, I would use that third pot in my charger to raise the cut off, maybe to 2.0a, or 3a or something higher. In my case I would do that with that third pot in my BMSBattery charger. That would mean the charge would terminate pretty soon after the end of the CC part of the charge. You'd then could increase the open-circuit voltage to, say 4.17v/cell or 4.2v or 4.23v or whatever would be appropriate for the pack, so that when the current reached your cutoff the cell resting voltage would be right where you wanted it.

I don't know if you're doing your charge termination with the Meanwell or with your eyeball. I think one of Fechter's limiter boards might have had that feature?

The reason some of you are seeing the current roll off relatively late in the charge is because your battery has a low internal resistance. Nothing to do with your meanwells. V=IR, so I=V/R. If you have a high current with a low voltage (in this case, the difference between your pack's voltage at that moment and your charger's open-circuit voltage), R must be low. The same reasoning suggests you'll want to be cautious with how much you increase your open-circuit voltage if you have nice low-resistance cells. I wouldn't feel comfortable charging at 2C at >4.15v.

 

[NeilP]

You'd then could increase the open-circuit voltage to, say 4.17v/cell or 4.2v or 4.23v or whatever would be appropriate for the pack, so that when the current reached your cutoff the cell resting voltage would be right where you wanted it. .

I think at latter in the charge when I 'up' the voltage I am looking at a much higher open circuit voltage per cell...Just today with an 8 s2P pack I made up to run a little SLA powered e-scooter...the open circuit voltage when I disconected once the cells had reached 4.15, was something like 48 volts...so 6 volts per cell. but whiel the pack was connected, and current was flowing , cell voltage never got above 4.15. While the cell volts were below 4.15 volts...say still down at 4.12, I did have the voltage of the charger set higher, and as the voltage of the cells approached 4.15, I reduced the voltage manually

I don't know if you're doing your charge termination with the Meanwell or with your eyeball. I think one of Fechter's limiter boards might have had that feature?

eyeball and cell log buzzer and manual shut off. Fetchers boards do not I thin ramp up the voltage, they just reduce it to keep current down. I do not thing they bring voltage up

 

[nechaus]

sometimes I bulk charge with out balancing, but atm i mostly use x2 400 watt turnigys and x1 1000 watt icharger, i have a 84 volt 11 amp charger to (bulk charger). i use that when my packs are well balanced and i use that when i have all my chargers running and need to charge another 20s pack.. however i will be using this bulk charger with my new BMS that im getting from founding power. i actually plan to keep the bike on charge all the time when im not using it but all cells will only go up to 4.18 volts

 

[Alan B]

The Hyperion 1420i pretty much does this already. It cranks up the voltage / current until something hits a max, either the input current, output current, battery voltage or output power (550 watts). This way the losses in the charging leads, etc are not slowing down the charge. The balance leads are used to read back voltages, and there is no current in them (when not balancing) so they read more accurately. They also periodically shut off the charge and "check" everything to get a reading with no current flowing.

One problem with the Meanwell power supplies used as chargers is that every resistance in the output circuit is slowing down the charging - the terminals, leads, current sensor, etc. So the current drops off earlier at the end of the charge cycle.