Plausible to build custom variable voltage Lion charger?

Batteries, Chargers, and Battery Management Systems.
progrock   100 W

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Plausible to build custom variable voltage Lion charger?

Post by progrock » Oct 19 2017 11:46pm

I've been wondering why there are practically no variable voltage chargers for ebikes, all I can find is the Cycle Satiator (Which I admit, seems like a really nice charger, a little pricey, but with no competition, well worth it I suppose). But why are these not common by now?

It seems like it should be easy enough to take your standard DC power supply (ie. a 12v or 24v Meanwell, or similar... so commonly used for powering LED lighting, 3D printers, etc.) and a Boost converter (a quick search came up with this variable voltage and variable current DC boost https://www.aliexpress.com/item/B900W-I ... 29270.html)... this should be capable of providing a variable charger that could charge a pack to your chosen voltage.

I clearly must be missing something, if it was this easy, I couldn't imagine it not being done more often... So what am I missing?

To be clear, while I might be a bit out of practice, I do hold a degree in electrical engineering, so I'm far from ignorant on the subject. What I am trying to understand is what is special about these Lion chargers. If all it needs to do is provide a constant voltage, and enough amps, that really shouldn't be that hard to accomplish. I could see it might be good to be able to control the output amperage (primarily due to charging slower is supposed to be healthier for the battery)... tho from my understanding, most chargers have a set voltage, and a max amperage, but the reason why devices don't blow up when being charged by a charger that is capable of providing significantly larger amps than it need, is that the device only takes the amps it needs. One of the most basic laws in electronics, Ohm's law, V=I*R explains that a bit... if a voltage is constant from a charger, the amps a device is provided from a charger is dependent on the resistance the device 'produces'. Of course this also explains why providing the wrong voltage to a device is so dangerous. I'm still trying to understand whats so different about the Lion chargers used for ebikes, and the like. In fact, it seems like a charger would be pretty easy... unlike a computer or other complex electrical device that needs a very stable voltage to be able to send accurate electrical signals, it would seem that a very steady voltage wouldn't even be necessary in this case. Of course you want the final charge to be somewhat accurate to what you set, but it seems like it wouldn't matter that much in the process of charging.

Anyway, if anyone can explain what I am missing (preferably someone how actually understands their answer). Like I said, I may be out of practice, but I do hold a degree in Electrical Engineering... and while I don't expect the answer to be in the form of complex differential equations... I will be able to understand a complex/technical answer.

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fechter   100 GW

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Re: Plausible to build custom variable voltage Lion charger?

Post by fechter » Oct 20 2017 12:12am

A typical Meanwell supply does have a voltage adjustment and can be used as a charger if the current limit is set low enough so it doesn't overheat.
The thing a "real" charger does is to shut down when the current reaches some preset level (usually about 10% of the limit current. With a Meanwell the current will gradually taper down to near zero and hold the voltage there until manually turned off. If you forget to turn it off, keeping the voltage on is detrimental to the cells.
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Re: Plausible to build custom variable voltage Lion charger?

Post by progrock » Oct 20 2017 1:01am

Ahh, auto shutoff... yes, something I forgot to add to the equation. I suppose that would indeed add some complexity, though still far from enough IMO for there not to be a few dozen Variable chargers like the Cycle Satiator to be on the market. But thank you for adding that to the list of required features.

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Re: Plausible to build custom variable voltage Lion charger?

Post by danielrlee » Oct 20 2017 1:07am

fechter wrote:With a Meanwell the current will gradually taper down to near zero and hold the voltage there until manually turned off. If you forget to turn it off, keeping the voltage on is detrimental to the cells.
Could you please explain how leaving a power supply connected to a battery at the end of charge is detrimental, even though zero current is flowing, the voltage remains stable and doesn't increase? Thanks.

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Re: Plausible to build custom variable voltage Lion charger?

Post by fechter » Oct 20 2017 1:36am

danielrlee wrote:
Could you please explain how leaving a power supply connected to a battery at the end of charge is detrimental, even though zero current is flowing, the voltage remains stable and doesn't increase? Thanks.
It may just be urban myth, but everyone says that. If there is any kind of fault in the cell, like high self discharge, then I could see it making a difference. If the charger is set to a safe voltage, like 4.1v/cell, then I don't think it would hurt them. With many devices like phones and laptops, the charge voltage is set on the high side to allow for faster charging.
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Re: Plausible to build custom variable voltage Lion charger?

Post by danielrlee » Oct 20 2017 1:52am

fechter wrote:
danielrlee wrote:
Could you please explain how leaving a power supply connected to a battery at the end of charge is detrimental, even though zero current is flowing, the voltage remains stable and doesn't increase? Thanks.
It may just be urban myth, but everyone says that. If there is any kind of fault in the cell, like high self discharge, then I could see it making a difference. If the charger is set to a safe voltage, like 4.1v/cell, then I don't think it would hurt them. With many devices like phones and laptops, the charge voltage is set on the high side to allow for faster charging.
Thanks for your response.

I had always been of the opinion that the theory is a fallacy, caused by a misunderstanding of "trickle charging", but am always prepared to listen to someone as knowledgeable as yourself.

Charging a lithium battery with a CV will always cause the current to taper to zero, but with a true trickle charge, current continues to flow and that causes the voltage to continue to rise.

It is something I hear argued from time to time, but I have never heard compelling evidence to back the claim up. Without further information, I will assume that your first point hit the nail on the head and it is indeed an urban myth.

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Re: Plausible to build custom variable voltage Lion charger?

Post by amberwolf » Oct 20 2017 4:25am

progrock wrote:It seems like it should be easy enough to take your standard DC power supply (ie. a 12v or 24v Meanwell, or similar... so commonly used for powering LED lighting, 3D printers, etc.) and a Boost converter (a quick search came up with this variable voltage and variable current DC boost https://www.aliexpress.com/item/B900W-I ... 29270.html)... this should be capable of providing a variable charger that could charge a pack to your chosen voltage.
There's a lot of adjustable-voltage current-limiiting power supplies that by themselves, with no other components, can be chargers.

I've used a number of Sorenson lab power supplies (Lab PSU); they're adjustable voltage and adjustable current. These are less than portable, though.

Meanwell (and others) make various CC/CV PSUs, often for powering LED lighting and arrays and signs, that are also adjustable voltage and adjustable current.

I use the Meanwell HLG-600H-54A. (these are sealed and potted except for the adjustment points, so ideal for mounting on a bike or vehicle, but they're heavier and more expensive).

There are also open-frame and/or non-potted versions, but these aren't really suitable for putting on a bike or carrying around as the components are vulnerable to vibration damage and weather.

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Re: Plausible to build custom variable voltage Lion charger?

Post by billvon » Oct 20 2017 1:06pm

danielrlee wrote:Could you please explain how leaving a power supply connected to a battery at the end of charge is detrimental, even though zero current is flowing, the voltage remains stable and doesn't increase? Thanks.
Worst case for lithium ion batteries is maximum voltage at maximum temperature. They will degrade very fast under those conditions. (Which is why batteries are shipped at a ~50% state of charge.)

When you terminate charge, a lithium ion battery will droop from 4.2 to 4.1 or 4.0 volts. That's somewhat safer to store them at. But by far the best is to store them partially charged i.e. ride home and don't charge the battery until the next time you need it.
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Re: Plausible to build custom variable voltage Lion charger?

Post by danielrlee » Oct 20 2017 1:36pm

billvon wrote:
danielrlee wrote:Could you please explain how leaving a power supply connected to a battery at the end of charge is detrimental, even though zero current is flowing, the voltage remains stable and doesn't increase? Thanks.
Worst case for lithium ion batteries is maximum voltage at maximum temperature. They will degrade very fast under those conditions. (Which is why batteries are shipped at a ~50% state of charge.)

When you terminate charge, a lithium ion battery will droop from 4.2 to 4.1 or 4.0 volts. That's somewhat safer to store them at. But by far the best is to store them partially charged i.e. ride home and don't charge the battery until the next time you need it.
Although most of what you say is true (except that healthy cells shouldn't self discharge as you state), it doesn't directly address the matter of leaving a charger connected to a battery once the current has tapered to zero.

IMO, there is zero difference between a standalone fully charged battery and one that still has a charger connected at end-of-charge.

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Re: Plausible to build custom variable voltage Lion charger?

Post by DrkAngel » Oct 21 2017 6:27am

.
...
See - Meanwell Mega-Mod 30-54V adjust 0-5A adjust

Also ...
I have toyed with the idea of an adjustable low amp disconnect for charger.
An adjustable spring tension vs an electromagnet powered by charge line voltage seems viable, though hardcore old school.
My concern was not so much maintenance current but more the charge time and life enhancements of charging at 4.20V but discontinuing when actual cell voltage attained ~4.10V.
Charge time could be notably reduced, by hours, ... the common final trickle charge is prolonged and inefficient.
4.10V is nearly universally accepted as prolonging battery life 200% with a modest 10%, initial, capacity restriction.
At worst, if component fails, charge will complete at oem rated 4.20V ...

I have not seen any data determining ... but reasonably assume(?), charged voltage (internal) rather than charging voltage (external) is the major detriment to battery life.
Last edited by DrkAngel on Oct 21 2017 4:18pm, edited 3 times in total.
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Re: Plausible to build custom variable voltage Lion charger?

Post by 999zip999 » Oct 21 2017 8:44am

Yes the meanwells don't shut off and has different effects on different chemistry I wouldn't worry as much with lifepo4 . 18650 most chemistry's a little more concern. HobbyKing discount lipo packs very concerned. You can always make a close quess with a timer. Also what do you set your end voltage to. Better not set to full end voltage.

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Re: Plausible to build custom variable voltage Lion charger?

Post by flippy » Oct 21 2017 5:03pm

the problem with keeping cells on the charger is that it forces the cell to keep 4.2v. something the cell does not want to do. keeping cells at 4.2v for extended periods kills them slowly.

this is not a issue if you keep them at 4.05v, then you can keep them floating on the charger until the cows come home.
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Re: Plausible to build custom variable voltage Lion charger?

Post by Buk___ » Oct 21 2017 5:22pm

danielrlee wrote:IMO, there is zero difference between a standalone fully charged battery and one that still has a charger connected at end-of-charge.
Two words:dendrite formation?

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Re: Plausible to build custom variable voltage Lion charger?

Post by 999zip999 » Oct 21 2017 5:42pm

When you charge to 4.2v and take them off for 24hr. What do they rest at ? Yes your brand new Samsung 25r or lg h2 or a quality new cell

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Re: Plausible to build custom variable voltage Lion charger?

Post by wineboyrider » Oct 21 2017 8:31pm

My meanwell HLG charges at 10 amps so I can charge my pack to full by the time I get a cup of coffee. Usually, charge my 12s 16ah pack with about 30 minutes worth of juice. Of course I monitor voltage with cell logs and occasionally balance charge.
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Re: Plausible to build custom variable voltage Lion charger?

Post by DrkAngel » Oct 21 2017 9:08pm

A "boost converter" seems an unnecessary layer of complexity.
Meanwell, or meanwells can provide nearly any voltage and/or amperage.

What voltages-amperages do you need?

13s -20s 54-84V 500w CC\CV charger might be great ...
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Re: Plausible to build custom variable voltage Lion charger?

Post by tanstaafl » Oct 21 2017 11:50pm

My IMax 6s seems to do everything needed. Now if they'd just make a 24s RC charger... (I'd buy one) It would be nice to have one that does variable voltages, balancing, testing, etc.

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Re: Plausible to build custom variable voltage Lion charger?

Post by DrkAngel » Oct 22 2017 8:19am

RC Turnigy TQ4 4x6S Lithium Polymer Battery Pack Charger - $77.49

Not sure if will charge while in series or if, most likely, require separation.

Image

Requires 200w ~ 12V power supply
Computer power supply?
or
Dell DA-2 12V 18A -info
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Re: Plausible to build custom variable voltage Lion charger?

Post by DrkAngel » Oct 22 2017 9:36pm

DrkAngel wrote: My concern was not so much maintenance current but more the charge time and life enhancements of charging at 4.20V but discontinuing when actual cell voltage attained ~4.10V.
Charge time could be notably reduced, by hours, ... the common final trickle charge is prolonged and inefficient.
4.10V is nearly universally accepted as prolonging battery life 200% with a modest 10%, initial, capacity restriction.
At worst, if component fails, charge will complete at oem rated 4.20V ...

I have not seen any data determining ... but reasonably assume(?), charged voltage (internal) rather than charging voltage (external) is the major detriment to battery life.
Chaarge time.jpg
Chaarge time.jpg (26.63 KiB) Viewed 1344 times
.5C charge rate = 3.0 hours -50% charge might take 1 hour, then 2 hours of taper charge
1.0C charge rate = 2.5 hours - 50% charge might take 0.5 hours, then 2 hours of taper charge
The CV portion of charge, as the current tapers down to nothing, take the majority of charge time.

Charging at higher voltage (4.20V), with a lower attained voltage (4.10V), could reduce charge time considerably!
1Amp cutoff? might provide desired voltage differential?
Trial and error to determine for different individual battery.
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Re: Plausible to build custom variable voltage Lion charger?

Post by flippy » Oct 23 2017 12:03am

if you want short charge times you should get a more powerful charger that is limited by what current the battery can handle. when the current tapers off too about 0.3A per cell you are at about 4.1v at rest.

this does not work for high cell count packs above 10kg or so as you would need a 4+kW charger at that point. i personally use a 3.2kW charger for fast charging and that still takes 2 hours from empty with a 4.2kWh pack.
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Re: Plausible to build custom variable voltage Lion charger?

Post by timmy66 » Oct 24 2017 1:29pm

These are available stocked in the US for about $19 shipped, too, eg.

https://www.ebay.com/itm/New-900W-DC-DC ... 1861952982?

This is a current detection board that could be used to force a cutoff when you get to C/10,

https://www.ebay.com/itm/0-10a-dc-curre ... 2400168287

The bst400 and the 3603 have also had their control boards hacked/reprogrammed to allow a little more clever control, so you could reprogram the daughterboard (as shown in the bst900) and do the control there instead of needing the other board.

Someone else that's done several cool homebrew charger setups wrote a lot about using this type of charging arrangement over the past 2 years with success.

It would nice to see a proper current/voltage profile for this.

For those that want to maximize charge lifes of their packs, I think this is the only way to do a proper saturation phase for an arbitrary voltage, where you're saturating down to C/10 after the target mass charge voltage.

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Re: Plausible to build custom variable voltage Lion charger?

Post by DrkAngel » Oct 24 2017 10:41pm

Current disconnect module with most complete info.
Sketchy description with no instructions
Can only hope instructions comes with it ?

Image

Only rated to 30VDC.
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Re: Plausible to build custom variable voltage Lion charger?

Post by timmy66 » Oct 25 2017 3:50am

I think you'd use the relay to turn off the charger completely (it breaks the NC connection to be open when the under current condition works, or you'd cheat the charger to be on while setting it, and let it operate as it would then be in the non-under-current mode, and it would remove power to charger after going under current.

It's a little "expensive" though for what it does, comparatively.


Some basic instructions on the ebay description for this:
===============================================


This module can detect DC current in the range of 0-10A, the accuracy is 0.01A.

Features:
Detecting range: DC 0~10A; accuracy: 0.01A(10mA).
Detect the current to control the relay then control the circuit on/off.
Set delay time to prevent output shock so as to protect the circuit.
With error calibration function.
Can turn off the LED display to reduce power consumption.

Functions Description:
P-1: Over-current Detection: when the detecting current<I1(low limit setting), the relay closes; >I2(high limit setting), the relay opens.
P-2: Under-current Detection: when the detecting current>I2, the relay closes; <I1, the relay opens.
P-3: Close in the Range: when the detecting current is between I1 and I2, the relay closes; relay opens in other situation.
P-4: Open in the Range: when the detecting current is between I1 and I2, the relay opens; relay closes in other situation.
P-5: Error Calibration and Delay Time Setting: the relay would not operate.

Buttons Description:
K1: Modes Selection;
K2: "+"
K3: "-"
Long press K1 for 2s into modes selection; short press K1 to select function and K2 to enter the mode.

Note:
After power on, the LED digits would pulse if the detecting current terminal is none.

Specifications:
Voltage: DC 12V
Detecting Range: DC 0~10A
Accuracy: 0.01A(10mA)
Standby Current: Approx. 20mA
Display: LED Digital Display
Item Size: 65 * 40 * 18mm
Package Weight: 29g / 1.04oz

Package List:
1 * DC Current Detection Module
E2034


DrkAngel wrote:Current disconnect module with most complete info.
Sketchy description with no instructions
Can only hope instructions comes with it ?

Image

Only rated to 30VDC.

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Re: Plausible to build custom variable voltage Lion charger?

Post by Punx0r » Oct 26 2017 6:04am

progrock wrote:
It seems like it should be easy enough to take your standard DC power supply (ie. a 12v or 24v Meanwell, or similar... so commonly used for powering LED lighting, 3D printers, etc.) and a Boost converter (a quick search came up with this variable voltage and variable current DC boost https://www.aliexpress.com/item/B900W-I ... 29270.html)... this should be capable of providing a variable charger that could charge a pack to your chosen voltage.

I clearly must be missing something, if it was this easy, I couldn't imagine it not being done more often... So what am I missing?
This is done. See here for a few examples: https://endless-sphere.com/forums/viewt ... 14&t=82731

The dc-dc converter provides adjustable voltage & current limits.

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Re: Plausible to build custom variable voltage Lion charger?

Post by progrock » Oct 26 2017 6:13pm

Very interesting. I ended up ordering a Cycle Satiator anyway, haha... but still thinking about building my own (or investigating these VV/VC meanwells as well.... been using Meanwells for both power 3D printers as well as LED lights, but all were constant 12v or 24v). Seems like the boost board I found could be work out... and those low current disconnects are a very interesting find. Seems like it really would not take much to get something that not only works... but works really well. I'm still confused at why these are not a common find in the ebike/ev world.... seems like we have proven it's a relatively easy thing to accomplish.

As for the potted Meanwell for attaching to a bike... very cool find... tho I currently have no interest in having one stay on the bike (at least until there's one that is extremely light and small... then it could be a practical addition... definitely would be nice to know I can charge the bike anywhere there is a power plug). At least for now, my current build's #1 goal is to be light (no elevator in my building, so need a bike that is not too impractical to carry up/down a flight of stairs.... bought a commercial ebike used for a good price not too long ago,, not a bad bike at all, but only used it twice because it's too much of a PITA to carry... will be selling it shortly to make space).

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