13s charger for low SOC charging

Vbruun

Vbruun

100 W
Joined
Sep 26, 2019
Messages
294
Hello

I recently posted about which vendor I should buy a battery from on aliexpress. The answers were honestly a bit dsicouraging, so I decided to build it with help from a friend.

It will be a 13s7p battery made from samsung 29E cells spotwelded together and regulated by an LTT BMS.

The reason i have gone to such great lengts is that I would like this battery to last me a good while, so naturally I want to be able to have a charger that allows me to adjust the SOC on the battery, when I charge and discharge it.

The ones I can find all seem very expensive, which surprises me a bit. Which ones do you use ?
 
While in use 47-48V, charging 53-54V

You need adjustability, Grin Satiator is a great charger.

You may be able to find direct from Ali, a "48V LI" (or LiPo) charger with a switch lets you select say 90% Full as opposed to 100%.

Otherwise maybe with an accessible voltage trimpot.

By "charger" I mean autostop.

Otherwise, you could make do with any adjustable "lab style" or telecom/industrial PSU or "DC-DC converter" with that voltage range, but

you will need to monitor V & A in order to manually stop charging when you get to your desired setpoints.

If you are regularly stopping at low SoC, make sure the device you use for balancing is compatible with your usage, some only start balancing up at the very top, and take a very long time if not used frequently.
 
But thats almost as much as my whole battery!

I need something significantly cheaper ;)
 
Could I possibly use something like this

https://www.ebay.com/itm/400W-DC-DC-Step-up-Boost-Voltage-Converter-Constant-Current-Power-Supply-Module/183843982240?epid=2304200649&_trkparms=ispr%3D1&hash=item2acdf48ba0:g:MusAAOSwMTRc~xW8&enc=AQAEAAACQBPxNw%2BVj6nta7CKEs3N0qVROxtY8UXMErzCyF%2ByrACO6CSNwgK0yo69%2F4EJX4pAnHAsFETZysRYMZtfB1s584Nq6XNOABSc6%2BwbAAXk9w%2B8K6ucA%2F40fEpz03wbsYa7ovEqtr6GDjMydDoH%2FC4R%2Be1BHv0AjiP4Bi%2FiKlXLI5GFvLy6FGzxnM49RIfLDUKd%2FxsDmoclheMhQptLaz55nB%2B%2FcqVbvmiTUSWGylEi1HTJec8liyfVib8DOLpPf2YtNTmKBRhLosocvd63QjR9KT6PX6avMEu8nZYrq%2Fn28MlIqyusfbhMLXGWkueCeA5tt7JkHxKYdxL8Y%2BYuvWOSsd4iX82GTpGr%2Ba5u%2BzvamAsf7kjDtjxmGMXSpxebSrDhMNGneeQpz0Mx8GvKbNskgrlpEV7jKkGlDZQXHc18ol2t3Z%2FGXIpx8unwzt7xd3LrtVSADb0P4%2BDOyhMir7htffS3IOPZK8Q6gSmV62I3lchYI8IC8b%2FRFCSgZDUIqMu3a2NIHNVGcJ9LBoyyI8N30fvof1Pt9eNdY6T3OkQkNSW%2Fz93RJYh9qOQgusJ7y6XiPVY28wYqm%2BpgwOPEnZ0RgOME%2FMpKtuBwwTgXH83b7rX90sV9DqeIkU%2Fh5j7e2iPggqS8m%2Fpc22Agdy%2BHk7%2F9HHctuM%2FgBTHWIgaQ3xqUQ1nT4ClCGLoepRTzVwClZ76Vem5PBXYraaJT0Q6waVvjIFwg7Vf27W%2FRGOGzEzLwcampd65dBCUUeq%2FuGeszcTbgnw%3D%3D&checksum=1838439822409090c1ca14bc4ac49179d6f03d8d54d2&enc=AQAEAAACQBPxNw%2BVj6nta7CKEs3N0qVROxtY8UXMErzCyF%2ByrACO6CSNwgK0yo69%2F4EJX4pAnHAsFETZysRYMZtfB1s584Nq6XNOABSc6%2BwbAAXk9w%2B8K6ucA%2F40fEpz03wbsYa7ovEqtr6GDjMydDoH%2FC4R%2Be1BHv0AjiP4Bi%2FiKlXLI5GFvLy6FGzxnM49RIfLDUKd%2FxsDmoclheMhQptLaz55nB%2B%2FcqVbvmiTUSWGylEi1HTJec8liyfVib8DOLpPf2YtNTmKBRhLosocvd63QjR9KT6PX6avMEu8nZYrq%2Fn28MlIqyusfbhMLXGWkueCeA5tt7JkHxKYdxL8Y%2BYuvWOSsd4iX82GTpGr%2Ba5u%2BzvamAsf7kjDtjxmGMXSpxebSrDhMNGneeQpz0Mx8GvKbNskgrlpEV7jKkGlDZQXHc18ol2t3Z%2FGXIpx8unwzt7xd3LrtVSADb0P4%2BDOyhMir7htffS3IOPZK8Q6gSmV62I3lchYI8IC8b%2FRFCSgZDUIqMu3a2NIHNVGcJ9LBoyyI8N30fvof1Pt9eNdY6T3OkQkNSW%2Fz93RJYh9qOQgusJ7y6XiPVY28wYqm%2BpgwOPEnZ0RgOME%2FMpKtuBwwTgXH83b7rX90sV9DqeIkU%2Fh5j7e2iPggqS8m%2Fpc22Agdy%2BHk7%2F9HHctuM%2FgBTHWIgaQ3xqUQ1nT4ClCGLoepRTzVwClZ76Vem5PBXYraaJT0Q6waVvjIFwg7Vf27W%2FRGOGzEzLwcampd65dBCUUeq%2FuGeszcTbgnw%3D%3D&checksum=1838439822409090c1ca14bc4ac49179d6f03d8d54d2

and an old computer PSU?
 
Current limiting is a must.

Of course a good charging system costs money!

Ex-industrial / telecom / server room gear can be excellent value bought secondhand, but a steep learning curve.

Cheap chinese gear can be very inconsistent, buy plenty of spares, and realize their actual capacity (without burning out) may be only a small fraction of what they're rated for.

Get a good ammeter and DMM as well, never trust the meters built-in to charge sources.

And remember, if it isn't a charger, it won't auto stop, you need to add an HVC or timer circuit, or sit there watching it.

Saving a little money's not worth burning down the house. . .
 
Another strategy is to use RC Hobby chargers, easily available new off the shelf, lots of choices, automatically balance, many can do discharge / capacity testing, show resistance etc.

Need to build the pack to suit, 6S + 7S in series with balance leads brought out.

If you can go to 14S then 2* 7S.

Hook up in series for use, break that connection for while charging.
 
What I'm looking for, is a solution that can be plugged in by my gf. For that reason alone, RC Chargers are out of the question.

My best bet right now seems to be getting a standard charger and turning down the voltage as much as possible using the built-in trim pod.

However, I'm not done exploring the DC-DC step-up converter as I still can't see why it isn't suitable.
Can you educate med om auto stop? Do purpose-built Chargers turn off when the voltage reaches a certain point?
 
Luna sells their "advanced" chargers with a 3 position selector for 80, 90 and 100% charge points.

https://lunacycle.com/luna-charger-48v-advanced-300w-ebike-charger/

There are probably other sellers of a similar (or identical minus the logo) charger but that's the one that came to mind.

Many of the cheaper chargers also have a pot inside that can adjust the termination voltage, though I don't know which ones specifically. A forum search on here will yield some more detail.

Many of the ones that don't have a pot installed for this can be modded to have one put in place of a resistor, a pretty simple job if you have basic soldering skills.

DMM = Digital Multimeter
 
I am actually really interested in that Luna Charger, but I can't find it from another vendor and shipping to DK from US is outrageous :(
 
If you are going to under charge your battery for longer life, you need a bms that will balance under 4.2v (like 4.1v or 4v).

At what voltage will your bms balance?

:D :bolt:
 
Vbruun said:
What I'm looking for, is a solution that can be plugged in by my gf
Click to expand...
I don't understand, is she subnormal or something?

If she is not willing to learn the basics of volts, amps, temperature etc the she should not be messing with this stuff.

Especially if inside a building where people live, very dangerous, if mishandled can easily burn the place down.

There is no "standard charger" that makes this stuff foolproof, a knowledgeable person paying attention to each charge cycle is important, even using a Grin Satiator or equivalent.

> However, I'm not done exploring the DC-DC step-up converter as I still can't see why it isn't suitable.

I didn't say not suitable, but now you seem to be saying that.

Not all chargers autostop, sounds like you definitely need one that does.

> turn off when the voltage reaches a certain point?

That would be a minimum, pretty crude algorithm.

Voltage then trailing amps, or using a timer circuit.

Getting right to exact 100% full is not so important. Stopping so a fire doesn't start is of course critical.

And as stated a few times now, your setpoint must be compatible with whatever you're using to get the cells or groups balanced properly.

 
Vbruun said:
I want to be able to have a charger that allows me to adjust the SOC on the battery, when I charge and discharge it.
Click to expand...
The charger cannot adjust the SOC during discharge.

The BMS, if it is programmable, can stop discharge at a certain level. Most of them are not programmable and typically only stop discharge when the cells reach the absolute minumum safe voltage level (LVC), completely empty, usually about 2.8v per cell. (controllers usually have an LVC higher than that, at the pack-level equivalent of 3-3.3v per cell).


So to really do what you want, you will need a BMS that is programmable, and you will need to set it up each time to whatever different voltage, etc, that you want the cells to balance at, whenever you want to change what SOC you're charging or discharging to.

If the BMS is reliable, with adjustable top and bottom cutoffs (HVC, LVC), then you don't have to adjust the charger voltage at all, just the BMS HVC, to prevent the pack from charging higher than you want it to. Just make sure the charger does not have a voltage higher than the max normal full voltage of the pack.


You *can* just use an adjustable-voltage charger to stop charging at a certain pack level below the full point, where the BMS balances, but it doesn't have a way to stop at a certain cell level--only the BMS can do that. (unless i'ts an RC charger with individual sense/balance wires hooked up to the cell groups).

So the pack doesn't necessarily stay balanced (definitely won't as it ages significantly, or when it's discharged all the way to empty a lot), unless the BMS is *also* adjustable to balance it at the lower voltage.

At first that won't matter, but it will gradually get out of balance, which will decrease the total capacity available to the lowest-capacity (lowest "full" voltage) cell group's capacity.




Now, if you really just want an adustable-voltage charger, to shut off at whatever pack-level HVC you've decided on, and don't care about the other stuff at cell-level, then you can use a number of things, including those mentioned already in this thread.

I use Meanwell LED PSUs in the HLG series, because they're adjsutable voltage *and* current, and work on 120vac or 220vac input, and are sealed and potted, so can be mounted on the bike without worrying about vibration, shock, weather, etc. I use the HLG-600H-54A, whcih means it's 600w output at up to 54v and is Adjustable. (the non-A versions are not adjustable!) The four I have so far actually go a bit higher, to almost 58v, and 12A, for around 700w of output.

If you don't need that fast a charge, they make them down to less than 100w IIRC, which wil be lighter and smaller. The adjustments are little screwdriver-turned pots under rubber caps (to keep water out), so you'd need to measure with a multimeter (DMM) while adjusting before hooking up to the battery, to verify the final output voltage whenever you adjust them.
 
e-beach said:
If you are going to under charge your battery for longer life, you need a bms that will balance under 4.2v (like 4.1v or 4v).

At what voltage will your bms balance?

:D :bolt:
Click to expand...

I have the LTT BMS and as far as I can tell, It will balance from 3,8v/cell and onwards, but this is adjustable.

john61ct said:
Vbruun said:
What I'm looking for, is a solution that can be plugged in by my gf
Click to expand...
I don't understand, is she subnormal or something?

If she is not willing to learn the basics of volts, amps, temperature etc the she should not be messing with this stuff.

Especially if inside a building where people live, very dangerous, if mishandled can easily burn the place down.

There is no "standard charger" that makes this stuff foolproof, a knowledgeable person paying attention to each charge cycle is important, even using a Grin Satiator or equivalent.

> However, I'm not done exploring the DC-DC step-up converter as I still can't see why it isn't suitable.

I didn't say not suitable, but now you seem to be saying that.

Not all chargers autostop, sounds like you definitely need one that does.

> turn off when the voltage reaches a certain point?

That would be a minimum, pretty crude algorithm.

Voltage then trailing amps, or using a timer circuit.

Getting right to exact 100% full is not so important. Stopping so a fire doesn't start is of course critical.

And as stated a few times now, your setpoint must be compatible with whatever you're using to get the cells or groups balanced properly.
Click to expand...

Hi

First of all, I didn't intend to offend you, I think it might have come off in that way?

My girlfriend is not subnormal, but she is not interested in this kind of stuff. I am not interested in having to monitor each charge either. And when that is said, I respectfully disagree with yours statement that lithium batteries can't be safe when not actively monitored by a person - that's what we have computers for! I have a lot of lithium powered devices including e-bikes which i know most people don't monitor in the slightest when they use them, and still they don't burn their houses down.

I will now explain how i understand the lithium charging cycle and then someone can maybe tell me where/if i'm wrong?

First part - constant current. The cells are fed a voltage based on the current that flows when the charger is hooked up

Second part - constant voltage. The cells are fed a constant voltage as soon as the current drops below the target. The cells are then held at this voltage by the charger until no more current is flowing and then the charger indicates that charging is done.

Third part - balancing. This has got more to do with the BMS, but it is required that the cells are held at a constant voltage by the charger.
 
amberwolf said:
Vbruun said:
I want to be able to have a charger that allows me to adjust the SOC on the battery, when I charge and discharge it.
Click to expand...
The charger cannot adjust the SOC during discharge.

The BMS, if it is programmable, can stop discharge at a certain level. Most of them are not programmable and typically only stop discharge when the cells reach the absolute minumum safe voltage level (LVC), completely empty, usually about 2.8v per cell. (controllers usually have an LVC higher than that, at the pack-level equivalent of 3-3.3v per cell).


So to really do what you want, you will need a BMS that is programmable, and you will need to set it up each time to whatever different voltage, etc, that you want the cells to balance at, whenever you want to change what SOC you're charging or discharging to.

If the BMS is reliable, with adjustable top and bottom cutoffs (HVC, LVC), then you don't have to adjust the charger voltage at all, just the BMS HVC, to prevent the pack from charging higher than you want it to. Just make sure the charger does not have a voltage higher than the max normal full voltage of the pack.


You *can* just use an adjustable-voltage charger to stop charging at a certain pack level below the full point, where the BMS balances, but it doesn't have a way to stop at a certain cell level--only the BMS can do that. (unless i'ts an RC charger with individual sense/balance wires hooked up to the cell groups).

So the pack doesn't necessarily stay balanced (definitely won't as it ages significantly, or when it's discharged all the way to empty a lot), unless the BMS is *also* adjustable to balance it at the lower voltage.

At first that won't matter, but it will gradually get out of balance, which will decrease the total capacity available to the lowest-capacity (lowest "full" voltage) cell group's capacity.




Now, if you really just want an adustable-voltage charger, to shut off at whatever pack-level HVC you've decided on, and don't care about the other stuff at cell-level, then you can use a number of things, including those mentioned already in this thread.

I use Meanwell LED PSUs in the HLG series, because they're adjsutable voltage *and* current, and work on 120vac or 220vac input, and are sealed and potted, so can be mounted on the bike without worrying about vibration, shock, weather, etc. I use the HLG-600H-54A, whcih means it's 600w output at up to 54v and is Adjustable. (the non-A versions are not adjustable!) The four I have so far actually go a bit higher, to almost 58v, and 12A, for around 700w of output.

If you don't need that fast a charge, they make them down to less than 100w IIRC, which wil be lighter and smaller. The adjustments are little screwdriver-turned pots under rubber caps (to keep water out), so you'd need to measure with a multimeter (DMM) while adjusting before hooking up to the battery, to verify the final output voltage whenever you adjust them.
Click to expand...

Alright, so as I Stated in my previous post, I actually do have a BMS that does All the tvinges, you state here.

You suggest, I just manage the SOC via the BMS. I have also thought about that, but as far as I know, it won't balance my pack if I use the hvc in such a way. Is that correct?
 
And to All. Sorry for the short replies. It just takes it's toll om me to process All this new information.

My plan ATM is as follows:

I already have 48v Brick Charger from UPP. I Will use this until I have another solution, which might well be to bring it to my local hackerspace and have a knowledgeable person help me modify the output voltage in one way or another.

I have also bought the board that I linked to from aliexpress. I Will use that if plan A doesn't Work.

Right now, I am not convinced that I can manage this via the hvc in my BMS, but I might be persuaded ;)
 
Vbruun said:
Alright, so as I Stated in my previous post, I actually do have a BMS that does All the tvinges, you state here.

You suggest, I just manage the SOC via the BMS. I have also thought about that, but as far as I know, it won't balance my pack if I use the hvc in such a way. Is that correct?
Click to expand...
No idea what that particular BMS can do, you would have to check it's manual to find out.

But if it is programmable for balance voltage point, you should just need to set the balance point to something appropriate for whatever you set the HVC to.

If it can't have both of those set appropriately at the same time, it's not a very useful BMS for what you want to do with it. ;)
 
Vbruun said:
I already have 48v Brick Charger from UPP. I Will use this until I have another solution, which might well be to bring it to my local hackerspace and have a knowledgeable person help me modify the output voltage in one way or another.
Click to expand...
If it helps, there are a number of threads about various chargers, and adjusting their output voltage. I would do a search by topic/title for both the words
'
charge*
volt*

at the same time, as at least some of those threads will come up in that search.

adjust*
volt*

may also come up with them.

Right now, I am not convinced that I can manage this via the hvc in my BMS, but I might be persuaded ;)
Click to expand...
You can experiment with it's settings while manually monitoring cell-level voltages to determine if it does or does not work, both during charge and discharge. It's not something that we should persuade you of, but rather something you would want to test for yourself and make sure it can work for you the way you want. ;)

Keep in mind that if you want to make it simple for her, you'd probably have to set the system up how you want it, verify it does what you want, both during charge and discharge, and then leave it so she can just plug it in and walk away, and then come back and unplug and ride.

(this is why that even though I don't use BMS/etc on my own packs, the pack I put on my brother's trike has a BMS, with a standard charger built into the trike, so he can just do exactly that. It also has a Cycle Analyst to monitor pack usage and whatnot, but that is for me so I can diagnose problems if they occur, as well as to give him a speedometer and a kind of battery meter (that I have to reset periodically, because it usually takes a little bit more charge Ah than it provides in discharge Ah, so it doesnt' completely zero out at charge time)).




If the BMS is a good design and well-manufactured, with the right settings available, it will do what you want.

If it is like most common BMSes and not all that well-made or designed, then it's just as reliable (or not) as those common ones.

(which have a number of common design problems, like not detecting cell voltages below some level below it's LVC point, so it can't tell either that cell sense wires are disconnected, *or* that cells are really really dead, and just allows charge and discharge anyway, which really destroys those cells if they werent' already, and even causes fire risks. )
 
amberwolf said:
Vbruun said:
Alright, so as I Stated in my previous post, I actually do have a BMS that does All the tvinges, you state here.

You suggest, I just manage the SOC via the BMS. I have also thought about that, but as far as I know, it won't balance my pack if I use the hvc in such a way. Is that correct?
Click to expand...
No idea what that particular BMS can do, you would have to check it's manual to find out.

But if it is programmable for balance voltage point, you should just need to set the balance point to something appropriate for whatever you set the HVC to.

If it can't have both of those set appropriately at the same time, it's not a very useful BMS for what you want to do with it. ;)
Click to expand...

This is something I don't really ubderstand fully: does a BMS have to be plugged into a Charger to balance the cells? Or is that not neccesary?

Because the balance voltage point is programmable.

I guess we have reached the conclusion that I should really just build the battery and test our hypotheses. I'm really looking forward to doing some experimenting!
 
IMO BMS function is for last-ditch failsafe layer of protection to prevent destruction of the battery, when (not if) the higher user-level equipment fails, like controller, chargers etc.

The only exception function being balancing, but then many protective BMS are sold without that, and IMO most do that job very poorly.

Dedicated balancing gear, or just doing it manually, or using balancing charger gear are all often better options for that function.

You also need to be prepared to spot your BMS failing pretty quickly, and replace with a new one; the cheap ones IMO often cause more battery failures than they prevent.

Some people spend many hundreds on top-notch BMS, and there one would have higher expectations.

But otherwise, I would not rely on the BMS to control routine daily charging, unless another HVC was acting as the failsafe.

Pack level voltage setpoint should be fine to trigger charge termination, as long as it is set well below the stressful maker-spec maximum, and you (the human regulator) are verifying proper balance is being maintained, regularly running to completiion.

Those that are not interested in the nitty gritty details of this stuff will end up spending a lot more on their bike per year, battery packs and good chargers are often worth more than the rest of the bike build. How the packs are cared for will have a huge impact on how long their useful lifespan.
 
Vbruun said:
> turn off when the voltage reaches a certain point?

That would be a minimum, pretty crude algorithm.

Voltage then trailing amps, or using a timer circuit.

Getting right to exact 100% full is not so important. Stopping so a fire doesn't start is of course critical.

And as stated a few times now, your setpoint must be compatible with whatever you're using to get the cells or groups balanced properly.
Click to expand...
First of all, I didn't intend to offend you, I think it might have come off in that way?
Click to expand...
Not at all, none meant nor taken.

If charging is at a healthy slow C-rate, stopping at CC is fine, no need for CV to get the cells to top SoC.

But balancing may require many hours, or even days sometimes held at Full voltage, with IMO stupidly designed BMS, hence the reco to use different gear for that, sitting at Full is bad for longevity.

Holding voltage just above a low start-balance setpoint, and feeding just enough current for the balance function, is another way to avoid stressing the pack, but that takes specialist gear.

If you are allowing unattended charging, then redundancy is extra important, as you know all electronics do fail eventually, and fires caused by LI charging are increasingly common, and impossible to extinguish, really should be done outside the living space, out in a back shed.
 
all non-smart/programmable bms have a balance voltage above 4.2V so that wont work in most cases.
 
flippy said:
all non-smart/programmable bms have a balance voltage above 4.2V so that wont work in most cases.
Click to expand...


Yeah but mine is a smart BMS ;)
 
And there are many alternative options to ensure good balancing, if you're "stuck" with a stoopid BMS just disable the balancing by staying below the start-balance setpoint.
 
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