Adjustable voltage Li-ion battery pack chargers - why uncommon?

I just built up my first ebike and want to find out how to maintain that massive AU$500 battery properly.

I read in various places, to extend battery life, I should aim to keep its charge between 20% and 80% at all times.

Now considering the length of the commute I built the ebike to do in this COVID19 world that 60% band is completely viable - all I need is a charger that will stop at 80% that is.

I've been looking around, and there seems very few of those. I found this one on Aliexpress:
https://www.aliexpress.com/item/4001152342980.html?spm=2114.12057483.0.0.4d6637fcAdRARY

My questions are, why aren't these more common, and, whether this charger I found above is good for my purpose - i.e. setting the cutoff voltage at 52.0V for my nominally 48V pack?

Cheers

https://cdn11.bigcommerce.com/s-9vkjq73s/images/stencil/2048x2048/products/258/11121/48v__68401.1552976523.jpg?c=2

There is also the Cycle Satiator from Grin tech. Been using one for years for various packs.

Charlie Whiskey said:

/item
My questions are, why aren't these more common

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Because used without understanding the ramifications, especially with cheap poorly built packs (whcih are the most common kind), they'll cause problems rather than solve them.

The cheap packs don't have well-matched cells, and may even be built of recycled garbage cells. So they dont' have the same capacity, internal resistance, or other properties. So in use they become unbalanced, moreso the longer they're used, so their states of charge are not equal, and since the lowest capacity/lowest state of charge cell determines the avialable capacity of the pack, the packs' usable capacity drops every time it's used.

This is why the BMS does the balancing it does, ot help fix that, but with the typical cheap BMS, the charger has to charge to 100% (for the worst packs, every time) to do this.


So if you use one of these adjustable chargers, and don't charge to 100%, then eventually the pack gets so out of balance it's unusable, and if you don't know to use it at 100% to rebalance it, you're stuck with getting a new pack.

So aside from the fact that it's more expensive to make an adjustable charger, the above is probably a big reason they're not more common.

Thanks for the reply @amberwolf.

The battery I've came from a local reputable supplier with warranty and explicitly specified the cells used so I feel assured to a certain extent.

I'm not sure whether the cells are matched when the pack was built.

I'm not sure whether the BMS does load balancing if the pack is not charged to full. The specification only lists the functions that the BMS performs but not the how.

Would you think it's a good strategy if I charge to 80% most of the time, but say every 10 charges I take it to 100%?

Most people are completely ignorant of those issues, or just don't care much about longevity, or as amber loints out fail to ensure flexibility in their balancing gear

therefore the market is small.

One solution is a PSU with adjustable V&A output, good ones bought new are pricey but sometimes great deals come up on eBay, Sorensen HP TDK etc.

But then you need to manually handle charge termination (w/ BMS for failsafe backup, not a great idea with cheap Chinese)

A safer cheaper simpler more flexible way is just have a charge source with a setpoint higher than you will ever want

controlled by an independent adjustable LVC that interrupts your charge source's input power.

To maximize range, a bit higher voltage can compensate for the CC-stage only profile delivered.

A balancer that works at any user selected voltage is best.

Charlie Whiskey said:

Would you think it's a good strategy if I charge to 80% most of the time, but say every 10 charges I take it to 100%?

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What you can do is keep track of the pack's usable capacity. If it changes, or begins dropping in voltage more than usual under load, it is probably becoming unbalanced, and then you can use the 100% charge, leaving it on until the charger stops turning on and off every so often.

Or use gear that lets you view cell level voltages directly

and balance in a way that fits in with your normal charging routines, and doesn't force you to guess at what's going on

john61ct said:

Or use gear that lets you view cell level voltages directly..

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That could be even more complex and expensive just to keep an ebike battery happy.

..and balance in a way that fits in with your normal charging routines, and doesn't force you to guess at what's going on

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Ahh ! Sounds like a job for a good BMS ? ...preferably one that allows adjustable HVC and LVC programming

Charlie Whiskey said:

This charger I found above is good for my purpose

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That'd work. I'd buy one if I needed another charger.

Just be careful that you don't accidentally change the voltage during charging. It'd be easy to bump the knob and overcharge your pack.

Buying something from a reputable seller in USA/Canada would be preferable, BUT what many people living there take for granted, is that they have access to a large marketplace with cheap/free shipping. In Australia, basically everything is shipped in from overseas, so we get smashed with freight costs (particularly from USA), and ridiculous shipping delays (particularly from China). Often the "quality" gear from USA is way out of reach.

I have a charger from em3ev with 3-position switch for 50%-80%-100% charge. There are pots inside for adjusting the specific voltages for the positions. Mine has worked flawlessly for several years.

I dont think they still sell this exact model, but instead one with a 2-position switch for 90%-100%. I do not know if it is adjustable like mine.

serious_sam said:

In Australia, basically everything is shipped in from overseas, so we get smashed with freight costs (particularly from USA), and ridiculous shipping delays (particularly from China). Often the "quality" gear from USA is way out of reach.

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I've already checked the US stuff, the ones I found don't even ship here at all.

serious_sam said:

In Australia, basically everything is shipped in from overseas, so we get smashed with freight costs (particularly from USA), and ridiculous shipping delays (particularly from China). Often the "quality" gear from USA is way out of reach.

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Believe me there are a myriad of advantages to being a citizen of "the lucky country" that more than compensate for paying more for stuff.

Adjustable voltage chargers for lithium packs are uncommon, because most consumers can reliably be considered retards, and setting the charger at the wrong voltage can easily kill a battery pack or worse, start a fire.

isdt chargers are good. they allow varying voltage charges.

https://www.ebay.co.uk/itm/1PC-ISDT-T6-Lite-600W-25A-Smart-Battery-Balance-Charger-for-2S-6S-Lipo-Battery-A/254328225280?epid=0&hash=item3b3724be00:g:MeMAAOSwJrpdUQsU

only problem is i think the max they do is a 6s or 8s....

i get around this on my 72v pack by having it split into 3x 6s batteries. i charge them in parrallel.

Charlie Whiskey said:

I've been looking around, and there seems very few of those. I found this one on Aliexpress:
https://www.aliexpress.com/item/4001152342980.html?spm=2114.12057483.0.0.4d6637fcAdRARY

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For anybody interested I did end up getting this charger. It seems to work as intended, or at least things hadn't caught fire... :wink:

I've 48V ebike batteries as well as 7.4V units for the lights / phone on my non-motorised bikes. No issue charging them to 80% approx as confirmed by the ebike's head unit.

Some down sides are, the unit looks like a DIY job (that's as described), and the 5.5x2.1 output cable I opted for looks rather flimsy and very short. There is also no spark suppression so plugging it into the battery often triggers a massive zap. I'll try probably replace that cable with something thicker / more sturdy and with an XT90S in the middle hoping that will help with the sparking issue.

Charlie Whiskey said:

There is also no spark suppression so plugging it into the battery often triggers a massive zap.

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Do you still get the spark if you turn on the charger before plugging in the battery? That solved the problem for me.

You can also just use a 12V server power supply with an adjustable digital boost converter like the MingHe BST900W.
The adjustable digital boost converter allows you to choose a charge voltage anywhere between 10V and 120V. Very versatile and cheap.
Search the forum for "MingHe BST900".
The poor man's cycle satiator.

Matador

A DC-DC converter is not a charger

Just like an AC-DC PSU, it lacks a Full-target detection algorithm to enable stop-charge termination.

NP if you have a good (adjustable) LVC mechanism.

Just saying, Satiator has that functionality, well implemented and built in.

The other key element with LI chemistries, is reliable current limiting.

That Ming He DC-DC converter unit unmodded apparently is dicey.

But there are firmware add-ons that help, e.g. https://github.com/delboy711/BST900

serious_sam said:

Charlie Whiskey said:

There is also no spark suppression so plugging it into the battery often triggers a massive zap.

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Do you still get the spark if you turn on the charger before plugging in the battery? That solved the problem for me.

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Yes that's what I do and I'm still getting spark.