Modify "dumb" charger to do a storage charge

[Sacker]

Hello guys!

Situation:

a relative of mine, following my advice, keeps his battery on a storage voltage during weeks without use. I use a smart charger for that (from RC) but he only have the typical adapter supplied with the bike:

So he has to be watching the charge progress with the voltmeter and stop manually at the desired voltage.

Questions:

- If the charger puts a 42V output, if I add a DC - DC converter between it and the battery that takes the voltage down to 38V, it will work fine until the battery reaches the 38V and then will not charge more?

- Put an AC regulator at the source of the adapter and bring down the input voltage from 220V to something lower will bring the 42V output to a lower value?

I'm sorry if I'm saying stupid things non-stop because of my electronic ignorance ; /

 

[ZeroEm]

I am missing something are you charging up to a good storage voltage, or trying to keep it from draining down?
I have never worried about them draining unless connected to something and charging up you could just use a cheap timer and do a timed charge.
I have two batteries and the one not in use is connected to solar panels with a buck charger which I set the max voltage, to store my battery I just run it down to where I want it and disconnect from everything and forget it.

 

[Sacker]

I am missing something are you charging up to a good storage voltage, or trying to keep it from draining down?

I'm charging up to a good storage voltage (let's say 38V) to leave the battery there for a few weeks.

Problem is that the charger can't set the max voltage (can't set anything, it's just "plug and play"), so it always goes up to the maximum (42V)

you could just use a cheap timer and do a timed charge.

Well, not the option I had in mind but could work for sure : )

Thanks ZeroEm

 

[ZeroEm]

It's best to store them between 40% - 70% charge 38V is good. I don't stress over it unless it's over 80% or 4V per cell then I want to ride it down to a lower voltage. The time thing is the cheapest outside of just watching it and then there is spending money on a high end charger. I watch mine when using the cheap charger it will charge the cells to 4.225V in my pack that is 84.5V so I don't let it do a full charge.
Some one here did use a resistor to have the charger cut off early at a lower voltage if I find it, will let you know.

 

[eMark]

a relative of mine, following my advice, keeps his battery on a storage voltage during weeks without use.

Why not just ride the ebike and discharge the battery somewhere between 36v to 38v before storing the battery for a few weeks? If he doesn't have a DMM to test the voltage get one. You can buy a fairly inexpensive Digital Multi-Meter on Amazon with four choices ranging from $6.30 to the $11.38. The AstroAI AM33D Digital Multimeter comes with one 9V 6F22 Battery, 2-Test Leads and User Manual) ... https://www.amazon.com/dp/B0012VYKOS/ref=psdc_14244471_t3_B07VHC1NMC ... The $6.30 MN25 includes a protective rubber holster, 9V battery, and test leads.

In order for most BMSs to idle (discharge) balance any higher cell voltages to match any lower cell voltages a charger has to fully charge with charger left plugged in with green light still on (indicating full charge of 42v has been achieved) for at least a few hours to hopefully balance all the cells (say within 12mv of each other). The problem is that idle discharge balancing at the top end takes even way longer with an aging battery pack. Do you want to leave a charger plugged in for idle discharge balancing at the top end for up to 16 hours once a month?

The more a battery pack ages and the cells invariably become more unbalanced during use it can take days for a BMS to idle balance by discharging voltage of the higher fully charged cells to match the voltage of the lowest cell voltage. Chargers don't have anyway of knowing if all the cells are 4.2v when a 36v pack is fully charged to 42 volts. For example in a fully charged aging 42v pack some of the cells may be higher than 4.2v while other cells are lower than 4.2v for a combined total of 42v when full charge cut-off. The more a pack ages invariably the more likely the cells become unbalanced to the point that the BMS may not be able to balance the pack cells anymore. That's why i actually balance charge my 10S5P pack and don't use a BMS. A good reliable smart 10S BMS can cost $130.

Now i've got a question. When a pack is fully charged to where some to the unbalanced cells are over 4.2v and some under 4.2v for a average of 42v (when fully charged) will most reasonably priced BMSs still idle (discharge) balance the higher cell voltages even without the charger plugged in or does the charger have to remain plugged in with green light on for the BMS to balance the cells? I ask this because the distributor of my 10S4P 10A pack recommends that once a month the 2.5A charger be left plugged in for at least twelve hours after the fully charged green light comes on in order to balance the pack's cells ?

 

[amberwolf]

- If the charger puts a 42V output, if I add a DC - DC converter between it and the battery that takes the voltage down to 38V, it will work fine until the battery reaches the 38V and then will not charge more?

as long as the dc-dc is a non-hiccup-current-limited unit, like an led psu or lab psu (or charger) then yes. but if the dc-dc is like many of them are, it depends on the laod to limit current. in a battery, current has to be limited by the source, so they make an overload. most of them limit by shutting off untl the overload goes away, so they dont' work on batteries.

- Put an AC regulator at the source of the adapter and bring down the input voltage from 220V to something lower will bring the 42V output to a lower value?

that will rpobably just cause the charger to not function correctly or at all, if it's a cheap design, or it will do exactly what it already does if it's a good design.


the safest way to do it is to get a charger designed specifically for doing the lower voltage charge. either a regular battery charger, or an led psu, or lab psu, that are adjustable-voltage will work. meanwell hlg-60h-42a would be adjsutable down to 38v. one random example below
https://www.amazon.com/HLG-60H-42A-Meanwell-HLG-60H-MEAN-WELL/dp/B06XCHT699/ref=sr_1_1?keywords=meanwell+hlg-60h-42a&qid=1578525243&s=industrial&sr=1-1
there's probably even lower power versions, which will be cheaper.

if you want to risk it, there are a few threads on changing the voltage of these HP high power / hipower hi power chargers, using potentiometers inside them. but like anything else it's possible to damage during adjsutment, or disassembly / reassembly, and then you don't have a charger at all.

 

[crazyfrog]

I got beat to saying it but there’s a trim pot inside that charger that allows you to change the output voltage. You only need a electricians screwdriver(only the metal end exposed) and a multimeter to measure the output voltage as you adjust it.


Sent from my iPhone using Tapatalk

 

[Sacker]

wow, thank you guys for all the information. I learnt a lot!!

the safest way to do it is to get a charger designed specifically for doing the lower voltage charge. either a regular battery charger, or an led psu, or lab psu, that are adjustable-voltage will work

I searched and lab psu's are not as expensive as I thought! There are models where you can adjust up to 60V and the intensity, for a reasonable price. That's great!

 

[Sacker]

There's something I didn't had in mind with the "dumb" charger, the charging algorithms. The output of the charger measured with the multimeter (without anything connected) is equal to the "full charge" voltage, but once the battery is plugged, the "not that dumb" charger should do this, right? (I can't plug the multimeter to the charger and measure on this stage to see what happens by myself):

I mean, I can't just buy an adjustable PSU, plug it to the battery (discharged, let's say at 35V) and set 38V in the PSU. It must be an "intelligence" there constantly monitoring and raising the voltage as needed keeping the current constant.
Or I can just throw 38V to the battery and the BMS will do that work?

edit -> I found in a manual of a PSU that if you select an intensity value in the PSU, it adjust the voltage to match it. So I think that's enough "intelligence" to make the storage charge. But I'm curious to know the answers at the prior questions : >

 

[amberwolf]

There's something I didn't had in mind with the "dumb" charger, the charging algorithms. The output of the charger measured with the multimeter (without anything connected) is equal to the "full charge" voltage, but once the battery is plugged, the "not that dumb" charger should do this, right? (I can't plug the multimeter to the charger and measure on this stage to see what happens by myself):

basicaly with many chargers, and all of the adjustable psus (lab or led), you adjust the output voltage without the battery connected.

then the charger or psu adjusts the voltage automaticlaly to keep the current within the limit of the charger or psu.

if you use one iwth adjsutable current, too, then to set the current you have to start the charge, then ajdust current until it is at or below the limit you wish to use. it's best to do this when the batery is almost empty so the max current the charger / psu would ever produce on the batteyr will happen, so you can be sure of limting it correctly.

that way you don't end up with say a 20a psu left able to push 20a into a battery that should only be charged at 3a, etc.

fwiw, the bms doesn't adjsut anything, all it does it allow or disallow charge or discharge based on the cell voltages / etc. it is only there as a last-ditch safety device, and is not intended to regulate anything. that's up to the charger (or psu) and the controller on the bike.

 

[Sacker]

There's something I didn't had in mind with the "dumb" charger, the charging algorithms. The output of the charger measured with the multimeter (without anything connected) is equal to the "full charge" voltage, but once the battery is plugged, the "not that dumb" charger should do this, right? (I can't plug the multimeter to the charger and measure on this stage to see what happens by myself):

basicaly with many chargers, and all of the adjustable psus (lab or led), you adjust the output voltage without the battery connected.

then the charger or psu adjusts the voltage automaticlaly to keep the current within the limit of the charger or psu.

if you use one iwth adjsutable current, too, then to set the current you have to start the charge, then ajdust current until it is at or below the limit you wish to use. it's best to do this when the batery is almost empty so the max current the charger / psu would ever produce on the batteyr will happen, so you can be sure of limting it correctly.

that way you don't end up with say a 20a psu left able to push 20a into a battery that should only be charged at 3a, etc.

fwiw, the bms doesn't adjsut anything, all it does it allow or disallow charge or discharge based on the cell voltages / etc. it is only there as a last-ditch safety device, and is not intended to regulate anything. that's up to the charger (or psu) and the controller on the bike.

Thank you very much amberwolf, perfectly explained and clear :thumb: Always a pleasure to learn like this

 

[dogman dan]

Uhhh, you could put a timer on the charger. Lets say you know damn well a full charge takes hours. Set the timer for half that time.

Another real easy way, is to charge full, then take a short ride. One mile will take the sting out of full voltage for storage, and take only a few min.

Don't even consider storing a battery with a bms for months at half charge.. You'll have the bms kill it then.

 

[ZeroEm]

Just wondering, is it bad to slow charge a battery. 45 watt solar in winter taking 2 months to charge my battery to 80% with a buck charger.

 

[john61ct]

When a pack is fully charged to where some to the unbalanced cells are over 4.2v and some under 4.2v for a average of 42v (when fully charged) will most reasonably priced BMSs still idle (discharge) balance the higher cell voltages even without the charger plugged in or does the charger have to remain plugged in with green light on for the BMS to balance the cells?

Depends on the BMS.

There are many fundamentally different balancing methods used by various balancing devices.

Most BMS use passive resistance, top balancing only, aka the "bleeding" type balancing method.

"Idle" balancing is not a thing.

Most bleed-balancing BMS do the job very poorly, combining a very low sub-amp balance rate
with a non-adjustable start-balance setpoint, set way too high.

I recommend either avoiding such, only using its monitoring & LVC / HVC features, or maybe buy a "protective-only BMS" without any balancing feature

and use a better designed balancer for that purpose as needed.

Of course a pack of new top-notch cells treated well may be fine with a standard cheap bleed-balancing BMS for years.

But those recycling scrapped cells, mixing those from different batches etc will need a better balancer that uses a different algorithm

as do all banks eventually as they wear out.

A balancing charger is one solution, but many (most?) although much better, are plagued by the same issues outlined above.

What I look for in a balancer:

obviously, the ability to actually see the cell/group level voltages, ideally showing top/bottom/highest delta, and which are the weak cells being serviced

adjustable V setpoint where balancing starts
ideally, adjustable V delta where it stops, allowing the user to choose their (lower) charge termination point and let the balancing process start earlier, at say 85% SoC rather than waiting for a definition of 100% you shouldn't even be allowing your cells to get near in normal use

a decent balancing rate, 1A minimum, up to 6A would be nice for high-Ah cells, but in any case faster is better

ideally, the ability to balance without charging active
so able to use the balancer not just at the top but for bottom or middle balancing without needing to do the job manually.

 

[john61ct]

Just wondering, is it bad to slow charge a battery. 45 watt solar in winter taking 2 months to charge my battery to 80% with a buck charger.

Depends on the battery.

For lead chemistries, yes very bad, must be stored at 100% Full for longevity.

LI is the opposite, should be stored at a static low SoC%,

ideally only charged just before needed to service loads.

So not great either, but only harmful when sitting at the high SoC.

Give more specific info for more

 

[john61ct]

[ the bms doesn't adjsut anything, all it does it allow or disallow charge or discharge based on the cell voltages / etc. it is only there as a last-ditch safety device, and is not intended to regulate anything. that's up to the charger (or psu) and the controller on the bike.

Not always true. There are BMS that actually regulate the charger via CANbus or other comms protocol, specifying the voltage and current desired.

Ideally in a failsafe manner, so the charge message is sent every second, and the charger stops charging automatically when that signal has not been received for X seconds.

I agree that another redundant HVC device and/or timer control should be "supervising" for safety in this case.

 

[john61ct]

I can't plug the multimeter to the charger and measure on this stage to see what happens by myself

Sure you can just measure actual charging voltage **at the pack terminals**.

During Bulk / CC stage, the source (PSU, charger, DCDC converter, solar, alternator whatever) is "striving" to reach the Absorb setpoint, but is not in control, the battery is, resistance, SoC, CAR specs of the chemistry, Ah capacity all determine the "negotiated" V & A of the circuit.

Of course the source must be limiting the amps to a maximum **if** the battery is trying to draw higher current than is healthy, with high-CAR LI chemistries that is always the case.

Many cheap PSU / converters are not current-limiting, thus not suitable for use as chargers for LI batteries.

Once the Absorb / CV setpoint is reached, the source is just capping V to that, and amps start to drop, but again under the batteries "control" (resistance, SoC, CAR) not the charge regulator's.

That is **only** capping the voltage at this point.

But the next critical function, and **the** definition of a charger as opposed to a PSU is applying some algorithm to determine when the batt is 100% Full and terminating charge without the user having to do so manually.

Since an LI battery can burst into flames if charging goes on too long (or higher V or A), that part is critical.

If you don't need an Absorb / CV stage, then a simple HVC can provide this function.

All the above has little to do with getting to a mid-SoC storage voltage point.

If the batt is lower just charge up to that point, HVC is fine.

If higher, then discharge, LVC.

 

[john61ct]

Hello guys!

Situation:

a relative of mine, following my advice, keeps his battery on a storage voltage during weeks without use. I use a smart charger for that (from RC) but he only have the typical adapter supplied with the bike:

So he has to be watching the charge progress with the voltmeter and stop manually at the desired voltage.

Questions:

- If the charger puts a 42V output, if I add a DC - DC converter between it and the battery that takes the voltage down to 38V, it will work fine until the battery reaches the 38V and then will not charge more?

- Put an AC regulator at the source of the adapter and bring down the input voltage from 220V to something lower will bring the 42V output to a lower value?

I'm sorry if I'm saying stupid things non-stop because of my electronic ignorance ; /

A DCDC converter with lab-style current adjustment, is by definition current-limiting so yes would "work" to feed current at a lower CV setpoint.

except it won't have any charge termination function.

 

[eMark]

"Idle" balancing is not a thing.

Tongue-in-cheek from my RC flying days using those little stand alone (hand-held) dang blinkity-blink cheap resistance discharge balancers that take forever. Basically the same slow resistance discharge technique (bulk charger in idle when green light is on) with inexpensive BMSs. Now available for Lilo (same as Lipo blinkity-blink). Was $32 (when available) and then as expensive as an inexpensive BMS ... https://www.hobbytown.com/astro-flight-blinky-lithium-battery-balancer-ast106/p9704 ... just goes to show that some addicted RC guys will [apparently] pay whatever the price.

Most bleed-balancing BMS do the job very poorly, combining a very low sub-amp balance rate.

AGREE! The American distributor of my [Chinese-made] 36v 10S4P 10A battery recommends that once a month the 2.5A bulk charger remain plugged in for 16 hours (including charge time) after the green light comes on. To me this is a red flag indicating the questionable quality of the Chinese 18650 cells. Didn't have a choice as that's what came with my American made Liberty Adult eTrike.

That's the reason why i decided to build a Vruzend 10S5P 15A (30Q) pack that's wired so i can divide it into two 5S5P packs when balance charging with my 2-80W balance chargers as the pack ages (whether at first just to balance charge from 4.0v to 4.05v, or later IF or when necessary for bottom balance charge from 3.3v to 3.4v and/or at top with 2.5A bulk charger from 3.6v to 3.9v and then balance charge from 3.9v to 4.05v). Anyway looking forward to some interesting experimenting when warmer whether and snow free biking paths once again appear in Minnesota. That's why i decided to get the Vruzend kit as tinkering (good learning experiences) is my mddle name.

The safest way to do it is to get a charger designed specifically for doing the lower voltage charge. either a regular battery charger, or an led psu, or lab psu, that are adjustable-voltage will work. meanwell hlg-60h-42a would be adjsutable down to 38v. one random example below
https://www.amazon.com/HLG-60H-42A-Meanwell-HLG-60H-MEAN-WELL/dp/B06XCHT699/ref=sr_1_1?keywords=meanwell+hlg-60h-42a&qid=1578525243&s=industrial&sr=1-1

Walmart's price is $78.14 ... https://www.walmart.com/ip/MEAN-WELL-LED-driver-HLG-60H-42A-60-9W-42V-1-45A-adjustable-AC-DC-Power-Supply-with-PFC/515235352

I got beat to saying it but there’s a trim pot inside that charger that allows you to change the output voltage. You only need a electricians screwdriver(only the metal end exposed) and a multimeter to measure the output voltage as you adjust it.

THANKS GUYS as it's EXACTLY what i've been looking for with voltage output adjustment. Suggest using one of those plastic screwdrivers when adjusting a voltage pot (just in case you're not carefully careful). Can't beat the price at $32.50 :thumb:
Here's the detailed 7-spec datasheet ... https://www.mouser.com/datasheet/2/260/HLG-60H-spec-34051.pdf

 

[Ianhill]

For a cheap dumb charger id keep it simple and first adjust the pot on board to the voltage you want to storage charge to and check its resistance then adjust the pot till the charger cuts out at full charge and check what it reads again now you have the two values to set your charger to terminate at differing voltages.
Take the pot of the board and form a 2 way switch that brings in one or the other resistances so you can switch the charger to storage mode or full charge maybe add a 2 colour led to show an active indication to see the green light in your eye and know its going all the way but blue would mean storage only.

All this assumes your packs are using a bms ?

 

[john61ct]

If you do use a dumb PSU / converter etc, how do you ensure preventing overcharge?

Do not rely on the BMS for that routinely, only use it as a protective backup from when the device usually handling that function fails.

 

[Ianhill]

If you do use a dumb PSU / converter etc, how do you ensure preventing overcharge?

Do not rely on the BMS for that routinely, only use it as a protective backup from when the device usually handling that function fails.

By stopping the charge cycle at a ceritan voltage same as all my chargers do, I would remove the pot and use 2 resistances so I can easily have 2 voltage end points to choose from.

I'd never use a bms to choose an endpoint if that fails I'm then in runaway situation it's only a backup if the charger end point fails.

 

[john61ct]

By stopping the charge cycle at a ceritan voltage same as all my chargers do

I mean, specifically how?

You sit there watching V&A and manually flip a switch?

Talking PSU here, not proper chargers.

Not really "asking how" for myself, I've already explained, just hammering the point home for those that may not yet have grokked just how critical that specific issue is, when jury-rigging a DIY setup on a budget.

Boom bad!

 

[Ianhill]

By stopping the charge cycle at a ceritan voltage same as all my chargers do

I mean, specifically how?

You sit there watching V&A and manually flip a switch?

Talking PSU here, not proper chargers.

Not really "asking how" for myself, I've already explained, just hammering the point home for those that may not yet have grokked just how critical that specific issue is, when jury-rigging a DIY setup on a budget.

Boom bad!

Where not talking psu at all you are John check the thread title.
I've explained how to adapt a basic charger it's not cowboy to modify or does it make it any more dangerous that a stock unit from China.

Do you like me then John I think you may have an issue with how u seem to reply to me.

I know there's no current monitoring on a psu so I can not place a quick method on that system as it is dangerous without have a way of controlling both the volts and the current.

 

[john61ct]

The thread did diverge, and my Q you answered was about non chargers.

Sorry if I wasn't clear and no feelings involved nothing personal

peace