Ebike battery charger

[ningaman151]

Hi all I want to build an ebike, and I've been thinking how I'll make the charger.

I stumbled across this video:
[youtube]ks2LefmuNZY[/youtube]

But in my case my battery would be a 14s3p battery. Same idea, but larger scale. Instead of the tp4056 modules I can use CC CV buck converters for faster charging of the 3 parallel batteries.

What do you guys think of this charger?

 

[john61ct]

Can't call it a charger unless it

terminates automatically according to some algorithm when the battery is full

is current limiting, not just protected from overcurrent conditions.

Using a PSU or converter you still need the latter, but you need to sit there watching with a good DMM and ammeter ready to stop manually when your setpoints are reached.

If you get distracted, stop watching for even a few minutes, very likely will start a bad fire one day.

 

[ningaman151]

Can't call it a charger unless it

terminates automatically according to some algorithm when the battery is full

is current limiting, not just protected from overcurrent conditions.

Using a PSU or converter you still need the latter, but you need to sit there watching with a good DMM and ammeter ready to stop manually when your setpoints are reached.

If you get distracted, stop watching for even a few minutes, very likely will start a bad fire one day.

Doesn't the tp4056 terminate automatically, because in that case I can use 3 of them in parallel (because there are 3 batteries in parallel) for each series stage.

Edit: the tp4056 terminated charge automatically when the charge current is 1/10th the programmed value.

 

[methods]

Can't call it a charger unless it

terminates automatically according to some algorithm when the battery is full

Quote your source on that please.
Is that an opinion or a regulation?
Algorithmic battery chargers are . . . pretty much a gimic in Lithium Charging, unless you consider the natural CC/CV to be algorithmic.

The only time an Algorithm is required is if you want to fast charge the last 10% or 20% by allowing dynamic voltages to exceed 4.2V, then periodically lowering current to 0A to check resting voltages. That is extremely dangerous and I never do it.

is current limiting, not just protected from overcurrent conditions.

Agreed
You can have CC, constant current, which is required
You can have hiccup mode, which does not work at all
You can have lockout mode, which does not work at all

Using a PSU or converter you still need the latter, but you need to sit there watching with a good DMM and ammeter ready to stop manually when your setpoints are reached.

If you get distracted, stop watching for even a few minutes, very likely will start a bad fire one day.

Not clear on what is being stated here.
If battery is being charged with no cells in series then the only thing required is a 4.2V (CV).

It is completely valid to charge a 3S battery with 3pcs of CC/CV

The trouble is that it does not scale well to larger packs, as you have to consider the Open Circuit voltage of the entire pack for every single cell charge module***

-methods

 

[ningaman151]

It is completely valid to charge a 3S battery with 3pcs of CC/CV

The trouble is that it does not scale well to larger packs, as you have to consider the Open Circuit voltage of the entire pack for every single cell charge module***

-methods

Sorry I don't understand why it wouldn't scale well to larger packs, can you please elaborate?

 

[methods]

Hey ningman

I do not have a lot of time, so let me share a rule of thumb which is valid:

RULE OF THUMB
"Any electronic component which is attached to a single cell of a multi-cell lithium battery must be populated with parts that are rated for the full pack voltage + margin"

This is easiest to understand if you perform the following test example

1) Wire up the battery, controller, and field load
2) Bring the system up to 500W
3) Open the battery pack in the middle, at the cell (or parallel group of cells) in question
4) Measure what happens here

At that moment in time, the full pack potential will be across that component that was in parallel with a single cell.

You can illustrate this with AC in your home

Black wire = Line
White wire = Neutral
Green wire = Ground

Ground ties to neutral in the box, so they are the same
Black wire is considered to be 120V potential to Neutral and ground

IF
You touch a White or Green wire. . . AT OR NEAR THE BOX... no electrical shock

IF
You touch a white wire which is returning from a bulb and is open circuit, 120V Shock

Because the current is flowing from Line, thru the bulb, and into your arm, into ground

....

So in both cases, you require an Open Circuit for this CONSTANT voltage to develop

BUT

In a battery that is connected to a controller you have Dynamic Voltages... noise spikes... pulses... wicked stuff like that. Going on constantly, and possibly an order or orders of magnitude higher than the pack voltage.

SO
If you run a 100V pack
and
You have a 4.2V component hooked up which is rated for 16V maxium
When
The gnarly 100V and 300V noise spikes happen, you will likely blow out the 16V rated parts

So -
If you look at a BMS design, they put Significant diode protection on the per-cell lines.

THEY CLAMP IT HARD

So basically, if you strap each of those 4.2V chargers with a heavy duty 1.5KW TVS diode that is rated for 4.2V, it will probably be fine.

I will go so far as to say that so long as your pack never opens in the middle, it will be fine

If your pack does open in the middle, primary current will attempt to run thru your small chargers... so dont leave them connected under load or if you do, fuse them in some way that is predictable.

-methods

 

[methods]

Example:

You would wire a leaded diode like this:
https://www.digikey.com/product-detail/en/vishay-semiconductor-diodes-division/1N6373-E3-54/1N6373-E3-54GITR-ND/2142609

Across each charger terminal.
band to the positive

This will "clamp" (send by) any voltage in excess of 7.5V, therefore never allowing it to hit your sensitive components in the small battery chargers.

I would back that up with local bypass capacitance on the board - so something to hold up its local rail and shoot any noise by. Generally speaking, think of the little charger as a sensitive little nugget. You want to shield it from outside noise... ideally it would be running on its own little reserve of capacitor energy and only connected to the outside world thru inductors and chokes... so fast moving things (the noise) cant get in.

-methods

 

[ningaman151]

Thank you for taking your time to reply to me. But sorry I'm confused about some things. I don't understand where the voltage spikes would come from (the chargers are isolated). I don't follow how the mains example relates to the battery charger ,(sorry I'm thick). I would have done your test example but I am unable to work on any hardware atm (I'm in hospital, but that's another story).

Sorry I'm not understanding your points, I've read them over like at least 10 times with no luck. (The problem is from me not you .

So to protect the charger and the battery I have to connect a diode (with the band towards +) and a capacitor across the + and - of the buck converter (what value/how do I choose a value?). What about a fuse?

Thank you for taking your time to reply to me I greatly appreciate it

 

[john61ct]

Can't call it a charger unless it

terminates automatically according to some algorithm when the battery is full

is current limiting, not just protected from overcurrent conditions.

Using a PSU or converter you still need the latter, but you need to sit there watching with a good DMM and ammeter ready to stop manually when your setpoints are reached.

If you get distracted, stop watching for even a few minutes, very likely will start a bad fire one day.

Doesn't the tp4056 terminate automatically, because in that case I can use 3 of them in parallel (because there are 3 batteries in parallel) for each series stage.

Edit: the tp4056 terminated charge automatically when the charge current is 1/10th the programmed value.

Yes, tp4056 is a charger.

I was drawing the distinction between that and the converter idea, which is not.

 

[john61ct]

Can't call it a charger unless it

terminates automatically according to some algorithm when the battery is full

Using a PSU or converter you still need the latter, but you need to sit there watching with a good DMM and ammeter ready to stop manually when your setpoints are reached.

If you get distracted, stop watching for even a few minutes, very likely will start a bad fire one day.

Not clear on what is being stated here.

CC-only stop-charging is a simpler algorithm than a CC/CV one, but it is still an algorithm.

My point is that a device that will charge forever until you remember to turn it off, should not be called a battery charger, and with these LI chemistries is inherently very dangerous.

Of course a LVC can be deployed to cut off the source input to a PSU or DCDC converter, in effect you've now built a charger, if it is also current limiting.

But most people don't want that level of DIY, and making such a rig failsafe is a bit of a challenge.

I am not addressing the issue of charging a series-wired battery here at all, just one pair of charging leads no matter the voltage involved.

 

[john61ct]

Coming back to your OP.

Best to not build your own charger, just choose an OTS unit suited to the pack you choose

Hi all I want to build an ebike, and I've been thinking how I'll make the charger.
…
But in my case my battery would be a 14s3p battery. Same idea, but larger scale. Instead of the tp4056 modules I can use CC CV buck converters for faster charging of the 3 parallel batteries.

You should not have 3 paralleled 14S batteries, the ideal is 3P groups in parallel, each group acts as a single cell, and they are then series'd to form a single 14S string.

If you want your pack to get balanced with every charge, build two 7S strings with JST XH balance leads as well as the power leads pair and charge each with a readily available hobby charger.

Put these modules in series to discharge as a 14S pack.

If you get two chargers that are fully isolated, you can keep that connection closed to charge using both at once.

Or you could use a 58V bulk charge source (no balancing) for normal usage cycling, and just have one hobby charger to do the balance charging one sub-pack module at a time, only when you see the cell-groups going out of balance.

 

[john61ct]

What do you guys think of this charger?

It's a mildly interesting hobbyist project. I guess he's doing this to run his power tools, in a location without mains power?

The fact that he is taking the DC output from a solar controller, inverting that

to create AC and then using those individual rectifiers

to produce 5Vdc output, and then using DCDC conversion

to bring the voltage down to what the batteries need

makes it too RubeGoldbergian to take seriously as a practical proposition in another context.

Taking those same cells putting into a 7S configuration and directly charging off the SC as a 24V battery would be 1000% more energy efficient, simpler cheaper safer...

but maybe not so "interesting".

 

[ningaman151]

What do you guys think of this charger?

It's a mildly interesting hobbyist project. I guess he's doing this to run his power tools, in a location without mains power?

The fact that he is taking the DC output from a solar controller, inverting that

to create AC and then using those individual rectifiers

to produce 5Vdc output, and then using DCDC conversion

to bring the voltage down to what the batteries need

makes it too RubeGoldbergian to take seriously as a practical proposition in another context.

Taking those same cells putting into a 7S configuration and directly charging off the SC as a 24V battery would be 1000% more energy efficient, simpler cheaper safer...

but maybe not so "interesting".

I linked the video to give an idea of how the charger is set up. I don't care about the other information in the video.

What's "SC"?

 

[ningaman151]

Coming back to your OP.

Best to not build your own charger, just choose an OTS unit suited to the pack you choose

Hi all I want to build an ebike, and I've been thinking how I'll make the charger.
…
But in my case my battery would be a 14s3p battery. Same idea, but larger scale. Instead of the tp4056 modules I can use CC CV buck converters for faster charging of the 3 parallel batteries.

You should not have 3 paralleled 14S batteries, the ideal is 3P groups in parallel, each group acts as a single cell, and they are then series'd to form a single 14S string.

What? What I meant was batteries in 3p configuration; in my case 14s3p. The charging works by charging each series set of batteries with an isolated buck converter.

Edit: I just re-read your post and yeah I have the 14s3p configuration; not 3 14s1p batteries. Cheers.

 

[john61ct]

I linked the video to give an idea of how the charger is set up. I don't care about the other information in the video.

What's "SC"?

Solar controller.

So I gave you my feedback.

There are plenty of OTS chargers that work this way, and in fact I'm looking for more examples

"This way" meaning, basically a collection of completely independent 1S chargers, each isolated from the others

no actual "balancing" going on using any of the three usual methods

just relying on each 1S unit using exactly the same algorithm so each cell/group ends up at the same exact resting voltage/SoC at the end of the cycle.

These are usually referred to as "node chargers" and are best limited to 4-5A each node, maybe 6-8A when pulsing algorithms are used,

because they are charging via each balance wire, which commonly use JST XH connectors and #18 wire, neither of which can go higher without danger of burning.

 

[john61ct]

I have the 14s3p configuration; not 3 14s1p batteries.

IMO then you have a 3P14S layout, which is much better than the 14S3P layout you implied above.

So each of the 1S chargers would be charging a single 1S group of 3P cells, each group in all ways acting as if a single cell with triple the Ah capacity.

A no-weld assembly method will allow you to periodically atomize those groups in order to monitor / test each cell independently.

Traditional spotwelding makes that a much more destructive process.

Another, very rarely implemented option, is to create say six modules, each 7S(1P), and while in use keep all six wired together in parallel at the cell level via balance leads.

Each half - three modules - could then be connected to each other at the power-lead 7S level in parallel

and then those two half-packs joined in series by those same leads to create your 3P14S pack.

Incredibly I know allowing all six of those modules to **at the same time** remain connected in parallel via the balance leads, managed "live" by a single 7S BMS and charged by a single 7-unit "node charger" at 1S voltages.

And this would allow both spot-welded modules, and getting easy periodic access to checking / testing / balancing each cell as an individual.

I find this all hard to grok myself, but smarter-electrickery fellas than me say it's true.

Unless I've misunderstood, or they misunderstood my questions, or we've been given wrong info. . .

 

[ningaman151]

Sorry I don't really follow you; what's wrong with the charger I'm proposing? By 3P14S do you mean 3 14SP1s in parallel? Why would I do that? Also, why would I break up the battery into 7S blocks?

Thank you for your time !

 

[obcd]

I assume you try to avoid a BMS with this method.
Let's not forget that a BMS also disconnects the battery if one of the cell group it's voltage becomes lower than the allowed treshold.
Discharging lithium cells 2 much will damage them and will increase the risk of catching fire when you recharge them.

Also have a look at the charge current that the usb charge pcb's can deliver. You don't want you battery to charge for 24 hours as you never should charge it unattended. 4P will charge 4 times slower compared to 1P which is what those charge circuits are usually designed 4. (Like a powerbank with one 18650 cell)
The DC/DC converters are isolated, but up to what voltage? Bad things can happen if the isolation of one of them decides to give up.
So you will need those circuits 14 times..? Will this really be so much cheaper compared to a good BMS?
The battery is the most expensive part of your E-bike, and also the most dangerous one. You better get it done right and spent a bit more on it imho.

 

[john61ct]

Sorry I don't really follow you; what's wrong with the charger I'm proposing?

Sorry maybe I missed it, what charger?

You want something off the shelf, not copying a DIY hobby experiment you found on YouTube.

The ideas I was floating are to allow for a reltively inexpensive charger to do proper balancing as well as get the whole pack charged quickly.

Also the ability to monitor / test at the per-cell level,

all these usually impossible with the normal pack construction methods.

Otherwise you should get say a Grin Satiator, and then you still need to figure out the balancing part.

 

[john61ct]

why would I break up the battery into 7S blocks?

https://www.rcgroups.com/forums/showthread.php?p=43745967

 

[ningaman151]

why would I break up the battery into 7S blocks?

https://www.rcgroups.com/forums/showthread.php?p=43745967

I'm sorry, after reading where the link leads in the forum, I still don't understand what's going on.

 

[john61ct]

Then it is even more clear you should just buy off the shelf, a good commercially produced charger that will take care of your battery without complications.

Do lots of reading in past threads and googling targeted terms and concepts, and over time things will get more clear.

Asking good specific questions once in a while, even starting new threads when justified, the community is here to help.

 

[john61ct]

There are two kinds of chargers.

For normal daily use one with just the two power leads that puts out your desired pack-level voltage at a fast enough current, no balancing.

So 58V at 5A for example, good for a 14S pack between say 5 and 50Ah, depending how fast a charge you need.

With a good BMS where you can monitor and adjust its balancing process, that may be all you need.

The second type is a hobby charger, includes an active balancing function

Very difficult to find for even 10S, forget 14S.

So breaking your 14S design into 2x 7S, or even 4S+5S+5S, these voltages are much more common in the RC world, very competitive pricing, so lots of choices means better chargers available at lower prices.

No longer need a BMS that does balancing well, just use one for protective functions instead.

Hope this helps.