Help needed: Step up converter / Buck converter for charging batteries

[Sajeel]

Dear Endless Spheres

TLDR: Can I limit CC charge to 1.6A from the output of a step up converter? If so, how? Can I control when the step up converter goes from CC to CV? If so, how? Is it possible to use a DC source 40V @ 5A (200 W) as input to the step up converter, having the step up converter output 57.4v @ 1.6A (~92 W) to the batterypack? Or do I need a DC source with lower current to match the wattage from the DC source? What happens with the excess power when the step up converter goes into CV mode and provides tampered current? Does it dissipate as heat in the step up converter, or is it simply not a possible solution?

Long story short:
I'm building my first eBike. Overvolting a 48v/1000W system running overvolted with 14S5P Samsung 50G cells @ 57.4v (charging each cell to 4.1v).

Finding a suitable charger able to do this, while also being able to regulate or limit the current looks very expensive - I've looked at "The Satiator" from Grin Technologies, but as I mentioned - it's too expensive. I want to preserve battery cycle life by limiting the charge current to ~1.6A (0.33C), but being able to fast charge when needed also seems like a very usable feature.

I want to build my own charger using a step up converter, but I'm in doubt about what I need to look for when I also want the current to tamper towards full charge of the battery.

I understand that it has to with CV (constant voltage) and CC (constant current). CC takes place while the battery is at low to medium-high battery capacity while charging, and then CV takes over towards full charge and the current is tampered. How does the circuit know when to swap to CV? Can I limit the CC to ~1.6A while CC is taking place? Can I control when CV takes over?

E.g. If I have a DC source suppling a step up converter with 40V @ 5A (200 W) and the step up converter supplies 57.4v @ 1.6A (~92 W), where does the rest of the power go? - Does it dissipate as heat through the step up converter? Or will it simply supply a higher current to match 200 W?
What happens when the step up converter goes into CV with tampering current? Even more heat that dissipates through the step up converter?

I like this solution if I can make it work, because it allows me to fully charge the batterypack every now and then for a full balance charge.

I will list the questions again, for the sake of anyone willing to help and provide valueable information:


1. Can I limit CC charge to 1.6A from the output of a step up converter? If so, how?
2. Can I control when the step up converter goes from CC to CV? If so, how?
3. Is it possible to use a DC source 40V @ 5A (200 W) as input to the step up converter, having the step up converter output 57.4v @ 1.6A (~92 W) to the batterypack, or do I need a DC source with lower current to match the wattage between converter and DC?
4. What happens with the excess power when the step up converter goes into CV mode and provides tampered current? Does it dissipate as heat in the step up converter, or is it simply not a possible solution?


Sorry for all the newbie questions. I'm doing my first build, which you can follow here.

Any input is much appreciated, thank you!

// Sajeel

 

[harrisonpatm]

You're not going to like this, but the short answer to most of your questions is, depends on your equipment.

1. Can I limit CC charge to 1.6A from the output of a step up converter? If so, how?

Yes, most step up converters will have some sort of current limiting feature. Usually adjusted via potentiometers, each model will be different in how you adjust it

2. Can I control when the step up converter goes from CC to CV? If so, how?

Again, depends on your chosen converter, but typically, yes. Especially with the higher power, more expensive ones

3. Is it possible to use a DC source 40V @ 5A (200 W) as input to the step up converter, having the step up converter output 57.4v @ 1.6A (~92 W) to the batterypack, or do I need a DC source with lower current to match the wattage between converter and DC?

Absolutely, this is possible, you don't need a lower amperage source, as long as the converter has current limiting feature, which most will, see above.

4. What happens with the excess power when the step up converter goes into CV mode and provides tampered current? Does it dissipate as heat in the step up converter, or is it simply not a possible solution?

This will depend on the DC source. Are you using a fixed supply like a wall wart, or an adjustable supply, or a bench power supply? A non technical explanation: once you set the current output of your boost converter to 1.6A, it will only "ask" the power supply for as much amperage as it needs to achieve that, minus efficiency losses. Excess is usually dissipated by resistors, as well as lost as heat during the conversion. For example, for your 57.4V at 1.6A, your output will indeed be close to 92W, but your power supply will likely be putting out anywhere from 100-120W, depending on its efficiency. This is all measurable, usually with a multimeter.

Have you picked out what kind of boost converter you need yet? I use two regularly:
https://www.aliexpress.us/item/3256801649870673.html?spm=a2g0o.productlist.0.0.3cb2165eaXpIt0&algo_pvid=6cfef8c3-75d5-4d09-aa48-731b0f2bf653&algo_exp_id=6cfef8c3-75d5-4d09-aa48-731b0f2bf653-1&pdp_ext_f=%7B%22sku_id%22%3A%2212000017798755626%22%7D&pdp_npi=2%40dis%21USD%2184.28%2142.14%21%21%21%21%21%402103143616658620594374881e24a5%2112000017798755626%21sea&curPageLogUid=JT41tQzyPDa2
This is adjustable to 2 decimal places on both voltage and amperage, lots of youtube videos about setting it. Horrible efficiency, like 60-80%. But okay for my uses. It is technically a solar charge controller, but as long as the PV input is over 12v, it doesn't care what the DC input comes from. Not all power supplies will work with it, some have protection functions that I don't fully understand, but it all depends.
https://www.aliexpress.us/item/3256803991635170.html?spm=a2g0o.productlist.0.0.267f626eAFdNtt&algo_pvid=2cc8052b-7337-41b1-994f-ac56b15c79c3&algo_exp_id=2cc8052b-7337-41b1-994f-ac56b15c79c3-0&pdp_ext_f=%7B%22sku_id%22%3A%2212000029019027117%22%7D&pdp_npi=2%40dis%21USD%2124.8%2115.38%21%21%21%21%21%402103255b16658620750223707e60e8%2112000029019027117%21sea&curPageLogUid=u2GNBwJiVuuh
This comes in power ratings less than 1800w, too. Can set output voltage, current, and low volt cutoff. Annoying to set (have to use a tiny screwdriver), but efficiency is better.

Just depends on what you're going to prefer. Just keep in mind, boost converters are never going to be that efficient. If that's what you need, so be it, but its usually better to start out with a voltage source higher than what you need and reduce it.

 

[Sajeel]

Just keep in mind, boost converters are never going to be that efficient. If that's what you need, so be it, but its usually better to start out with a voltage source higher than what you need and reduce it.

I was not aware that buck converters are more efficient!

This will depend on the DC source. Are you using a fixed supply like a wall wart, or an adjustable supply, or a bench power supply?

I was planning building two chargers: One or two using a wall wart, if I can get away with it. But I'm about to order an adjustable bench power supply tonight:

4 digit, 60V 5A 300W - click the picture for direct link to aliexpress.

It says CV and CC on the screen, but I'm not sure how I would apply it in practice when connected to a buck converter. Would it just lower the amps automatically when reaching full capacity, or do I need to do something actively, or is it just not possible using this power supply? - I would be fine using this for charging at home, but I'd invest in something other than this aswell like a wall wart.

For work I would very much like to use something cheaper like a wall wart.
I haven't bought anything yet - recommendations are very welcome!

Could you by chance recommend buck converters that would suit my case?
Recommendations to somewhat cheap bench units and wall warts would, as I said earlier, also be very welcome!


Thank you for your insight!

 

[harrisonpatm]

Just to be clear, is this purely to charge you ebike project? You want to charge your battery at 57.4V at 1.6A? If that's the case you'll be best off to find and purchase a dedicated battery charger suited for your battery. It'll be cheaper, perhaps more portable, you won't have to mess around with setting and double checking that it's set correctly every time... Lots of options on aliexpress if you want to go that route, just search "14s charger" or something like that. You'll find reviews for specific chargers using the search function for this forum. Anyway, that'd be my recommendation for a reliable, hassle free charging setup.

Perhaps thats not your goal though. Do you wish to play around with different components to learn more about the principles of charging and using batteries, and the different ways to do it? By all means knock yourself out. I firmly believe in learning by doing and trying and making mistakes. For example: you linked a variable bench power supply that goes up to 60V and 5A. Using that, you technically don't need anything else to charge your battery. You can set it to 57.4V and 1.6A, plug it into your battery, and you're good. No boost or buck needed; the variable supply is doing all the boosting and bucking for you. Note: this is very much not a charging situation that you should walk away from at all. Those sockets could slip out easily from your cat playing with them. A dial could slip or something and cause damage to your battery from overcharging, or at the very least turn off. But strictly speaking, that bench supply is technically capable of charging your battery on its own.

Yes, bucking is usually more efficient that boosting, but you'd need to start with a voltage higher than 60v, and sourcing a power supply that high is going to cost you as much, if not more, than just a 14s charger.

Does that make sense? No need to purchase 2-3 components if your goal is just to charge a battery. But if your goal is to experiment and learn and try new things, go for it. I've got dozens of cheap, dead, or no longer used Aliexpress components that I've played with for the last 2 years, worth every penny in how much I've learned in that time from using and abusing them.

 

[Sajeel]

Just to be clear, is this purely to charge you ebike project?

Everything you wrote makes sense!

This is my first eBike project - my first real electrical project actually. I would like to learn as I go and build things that are also _somewhat_ hassle free. I would like to avoid mistakes, as they are costly, but I also understand their value.

For instance in regard to using a buck converter with a wall wart as DC input I was planning to also wire up a display showing output of the buck converter. That way I won't have to double check every time. The charger would be somewhat portable (with a 3D printed housing) and I'd be more the wiser for building it.

Buying a 14S charger will not have a HVC at 4.1v per cell - 57.4v package - which was one of my first goals: Getting value for my cells by extending cycle life.
There's also a "cool factor" to consider, and the feeling of acomplishment when you have built something of your own. This is my main drive in my project right now, and I feel totally engulfed by it! - As a DIY'er I'm sure you can relate!

I'll be using the bench PSU to charge my battery pack for now, till I have built something that can replace it.

I'll look for a wall wart or fan'ed PSU (server PSU for instance) with +60v and +5 amps output. Do you have any experience with a buck converter that you'd recommend me?
I assume that I need to look for voltage/current range of the buck converter and CC/CV compliance. And the buck converter will automatically lower the current as near full capacity is being reached

//Sajeel

 

[harrisonpatm]

I'll look for a wall wart or fan'ed PSU (server PSU for instance) with +60v and +5 amps output. Do you have any experience with a buck converter that you'd recommend me?
I assume that I need to look for voltage/current range of the buck converter and CC/CV compliance. And the buck converter will automatically lower the current as near full capacity is being reached

Not sure about what specific buck converters will do with current as full capacity is reached, but you could always stick a measurement in line to see what happens the first time you try it. I haven't used buck converters in that range myself, I played around with wind turbines and used a dozen different models, all sub-30V range.

You could try this one, but it looks like you might be pushing it's rated amperage limits:
https://www.aliexpress.us/item/3256802885118464.html?spm=a2g0o.productlist.0.0.631b8b03Gf6Djd&algo_pvid=8a672874-53ed-4554-bc01-2688fe0cc5f4&algo_exp_id=8a672874-53ed-4554-bc01-2688fe0cc5f4-16&pdp_ext_f=%7B%22sku_id%22%3A%2212000023790445013%22%7D&pdp_npi=2%40dis%21USD%213.66%213.66%21%21%21%21%21%402101e9d316658761355904173ef878%2112000023790445013%21sea&curPageLogUid=UbHMuhTSCnnT

Buying a 14S charger will not have a HVC at 4.1v per cell - 57.4v package - which was one of my first goals: Getting value for my cells by extending cycle life.

See our recent thread: https://endless-sphere.com/forums/viewtopic.php?f=14&t=117975
In your case, one thing you could do is get a standard 14s charger, add a voltage display, and pull the plug when it gets to 57.5v. Not perfect, for sure, but just an option available.

 

[lnanek]

Most off the shelf chargers have potentiometers inside that control the max voltage and max amperage. Could take some apart and look. There's a a YouTube video on it. In one case there was even a third pot for controlling when it switches between CC and CV.