The Poor Man's Battery Saver/Satiator: a $10 Outlet Timer?

[Mass Deduction]

Batteries should not warm on 2C discharge. They're likely rated for 25C or more.
Yes, if it's discharged, plug it in and charge it up.

For near daily riders there's no need for any special care. Just charge and go. The trickle chargers supplied are as safe as you can possibly get, and will condition/balance your cells on each full charge. It's better to charge them all the way up if you're going to use the bike.

L-ion cells don't have a 'memory' effect, think...cell phone. Charge and go.

If you're typically charging to about 70% (and draining to 30-40%), wouldn't it take a very long time before any of the cells became so imbalanced that it started to create a problem? And that's assuming that the BMS on board the battery can't balance the cells on a cell-by-cell basis, which some of the better ones can (and I'm guessing Bosch and Shimano probably use some pretty good BMSs, but I'm more than happy to be educated to the contrary if Bosch and Shimano don't use BMSs as good as I think they may be).

From what I understand, Li-Ion cells do very slowly develop a very minor memory effect, but that it's so slow that most people fully discharge/recharge before it ever becomes noticeable.

That said, I will be fully charging the cells from time to time right before using the bike, and even fully draining them on rare occasions. So I think if I stay in that 25-75% zone most of the time, with very occasional full charge/full discharge, I'll be in good shape. I will definitely recharge promptly after any full discharge, and will typically wait until as close to the ride-time as reasonably possible before a full charge.

 

[AHicks]

If a quality BMS works anything like the quality chargers used in radio control (where an LCD display monitors pretty much everything going on), the charge rates are fairly high until at about 90%. At that point they taper off and it's at this stage the cells are balanced, at much lower charge rates.

 

[Browneye]

Yes. And yes.

Rather an 'ex-pert' with lipo, but otherwise all of our favorite cordless devices are Li-Ion. They're the milder more stable version of Li-Po.
In the beginning I was afraid of them, the lipos, the fire danger, but as long as you understand what's going on there and get some time with them the fear goes away. We run radio-control competition 1/10th scale rock crawlers with them - I have a small fleet of them, several thousand worth, most are hand or kit built, custom, not something you buy out of a store. Run time or 'driving time' is 3 or 4 hours and beyond. Remember the old ni-cad powered toys? THE most frustrating thing was their 20-minute run time!!

Our lipo powered 'tiny trucks' generally have a 2s or 3s power cell with the crawlers, then 4s, 6s, even more for the faster stuff and RC race cars. The power cells or packs are from 2ah to 7ah capacity. A 3s battery is rated at about 11.1 volts depending on the battery chemistry. These are all flat-packs, not round cells. The latter tend to be a little more stable and are better protected. Some lipos are packed in a plastic box, all are shrink-wrapped. In any case, a fire-proof bag is recommended for charging and storage. You disable them for disposal in a bucket of brine. The biggest problem we have with them is puffing - if the cell gets damaged and shorts itself, it will puff up. It's a warning before they actually blow up. You don't want them to blow up - the resulting fire WILL NOT extinguish until all the fuel is consumed. Plenty of burnt down garages and houses with these, by kids and people that don't know what they're doing. Adult supervision required.

Frankly I was surprised that the industry had adopted the 18650 cell nearly universally. My bet is we'll see some new battery configurations as the industry matures. I do like the newest ebikes with fully frame-integrated battery packs.

Your chargers are electronically controlled and matched to the cell pack. I have one with a cooling fan and one without. Frankly I prefer without, but it is what it is. Our lipo chargers are all fan-cooled, I've had the fan motors stick and chatter - beyond annoying.

Just a sidebar for the charger timer thread. Thanks for reading.

 

[Browneye]

I don't want to charge right away as I want to at least wait for the battery to adjust to room temperature, especially this time of year when it's pretty cold out and the battery is significantly colder than the ambient temperature of where it's being charged. By using a timer I don't need to remember to do it, it'll happen when the timer goes off to start the charging. And I always own multiple batteries for any bike I'm using regularly, so I'll always have another battery charged up to 70% or so in case a mistake is ever made, so I definitely feel no pressure to charge immediately "just in case".

I imagine the BMSs are pretty good for Bosch/Shimano, so they might be balancing the cells each charge without the need for a full charge or full discharge anyway? Good BMSs can do that on a cell by cell basis within the pack, and I'd imagine they're using pretty good cells and pretty good BMSs in those brands. Unless anyone knows otherwise? That said, they will get semi-frequent full charges right before big rides, and even occasional full discharges (again, on big rides).

I know that some of this stuff is all about marginal gains. I will again reiterate that I enjoy this kind of strategizing, so this is actually fun for me (believe it or not).

There isn't a way that I know of for a charger controller to read each cell voltage unless there's a hardwire for them. A feedwire from each cell pack. That's how the lipos are - you have a matching number of sensor wires for your packs, be they 2, 3, 4, or 6s. And you set the charger for the ah capacity so they always charge at 1C.

Here's a lipo charging setup - notice the flat ribbon cable with all the cell sensor wires. For all we know there's an internal bms on the bike packs that do this - perhaps someone can come along that builds these packs and explain the technical bits.

 

[AHicks]

So back on topic, if you're cutting off the top of an e-bike charge with a timer, you're cutting into or eliminating balance time.

 

[Browneye]

That would be my take as well. OTOH with such a slow charge rate the bms may simply cut off at a preset voltage level.
I still think it's a good idea to charge them all the way up when you're going to ride the bike. That gives you full range as well.

 

[Mass Deduction]

That would be my take as well. OTOH with such a slow charge rate the bms may simply cut off at a preset voltage level.
I still think it's a good idea to charge them all the way up when you're going to ride the bike. That gives you full range as well.

I think your advice is great for most people, who probably don't want to get in the weeds when it comes to treating a battery optimally. I recommend most people read what you wrote, and ignore what I'm about to write!

Full range doesn't matter to me, it's a bike with really good range even when using only 25-45% of its total capacity (which is what most of my rides use up). I can (and do) carry a second battery when necessary for very long rides, too.

But I do want to treat the cells optimally, even to the degree that it's a minor benefit. If I'm normally charging up to only about 70%, and occasionally topping it off to 100% in advance of a big ride, I don't think that's going to be a problem for cell balancing. I'm occasionally charging with a 4A charger, but more frequently charging with a 1.8A charger.

I suppose I could charge to 70% after a ride, and then top-up to 100% right before the next ride so that I'm balancing the cells and then immediately draining the battery back down below 80%. It's my desire to keep the individual cells below 80% as much as possible that has me charging up to only 70%, to allow for the cells to be a little unbalanced yet individually all still below 80%.

With good cells, a good BMS, charging slowly, and charging only to about 70%, it seems to me you could easily do dozens (if not hundreds) of rides before you needed to charge to 100% for rebalancing. My expectation is that in such an ideal situation that the cells would become unbalanced only very slowly. In other words, if after dozens (hundreds?) of rides I recharge to 70% and some cells are actually as low as 60% and some are as high as 80%, that's still better for the battery than all the cells being charged to 100%, right?

But I'd be pleased to be re-educated if I'm incorrect!

 

[Mass Deduction]

So back on topic, if you're cutting off the top of an e-bike charge with a timer, you're cutting into or eliminating balance time.

Does that matter if:

- the pack has very good cells,
- you're using a brand-name charger,
- you're charging very slowly (a 14Ah battery and either a 4A or a 1.8A charger, so a very low "C" rating),
- only charging to 70% (so that even imbalanced cells are probably in the 65-75% range after dozens of rides, maybe 60-80% at the worst),
- and occasionally charging to 100% right before a big ride, which will do a full re-balance anyway?

It seems to me that it's not important to re-balance all the cells every single charge, especially if you're charging to 70%. I can see rebalancing being more important if you were, for example, charging to 90% after a ride. It's the fact that I'm aiming for only 70% after each ride that makes a full rebalance unimportant (and undesirable), IMO.

At the moment I've done several dozen short rides, and charged up to 70% after each one. Now I'm about to do a big ride, and I'm going to recharge up to 100% right beforehand. Then I'll probably do several dozen more short rides and charge up to 70% after each one for a while, before contemplating a big ride again.

My understanding of battery chemistry is that this scenario is better than charging to 100% every time, as unbalanced cells charged up to 65-75% each (or even 60-80% each in a worst-case), and being drained down to about 35% on the display (so, maybe 25-30% being the worst case for individual cells), is better than charging all the cells to 100% each time.

If you know otherwise, I'd love to learn more. I've "gamified" my charging, as I'm challenging myself to see how many charges/years I can get out of my packs, for the nerdy entertainment value!

 

[AHicks]

I would call what you are thinking of as "wishful strategizing", as you are not basing any of your thinking on the actual charge levels/voltages of the individual cells.

Go for it if you like. I doubt seriously that either of us can be proven right or wrong by actual cell longevity. I can tell you for certain that when a battery balance gets too far out of whack due to lack of balancing, there's a pretty good chance the charger will be charging noticably longer as it spends a lot of time carefully bringing low cells back up to optimal. At some point in the batteries life, the charger is not going to shut off, indicating you have a cell or cells that will not reach full voltage.

 

[Mass Deduction]

I would call what you are thinking of as "wishful strategizing", as you are not basing any of your thinking on the actual charge levels/voltages of the individual cells.

Go for it if you like. I doubt seriously that either of us can be proven right or wrong by actual cell longevity. I can tell you for certain that when a battery balance gets too far out of whack due to lack of balancing, there's a pretty good chance the charger will be charging noticably longer as it spends a lot of time carefully bringing low cells back up to optimal. At some point in the batteries life, the charger is not going to shut off, indicating you have a cell or cells that will not reach full voltage.

That's actually really good feedback. Since I put the bike on a timer for recharge, if I don't get as much of a recharge as I expect for the amount of time that it's on then that's a sign that it's time to do a full rebalance, so thank you for that. I suspect I'll never get there, though, as I will occasionally be charging up to 100% before big rides anyway, and I suspect that will happen often enough that the cells will never get out of whack to significantly slow charging, let alone allow a cell to get to the point that it won't reach full voltage!

 

[tomjasz]

MANY, VERY MANY, batteries do not have a BMS with a balance function. Got a UPP battery or early Luna battery? You do not have a balance function. What I suggest to periodically do a long charge, 8-10 hours. I'm finding that my old packs from 2014 still have some decent life. I charge them to 80 or 90% and then do monthly a long charge.

All charges are done in an Ammo can modified with rubber grommets for charger wires. I remove the watertight gasket and latch the top. I will be doing a demo burn soon.

!!!!NEVER LEAVE A LONG CHARGE UNATTENDED!!!

 

[tomjasz]

For all we know there's an internal bms on the bike packs that do this

We sure ought to know, but guaranteed those lower-priced batteries have budget BMS.

So back on topic, if you're cutting off the top of an e-bike charge with a timer, you're cutting into or eliminating balance time.

With a timer, we really should be doing those extended charges. I'm really liking the BT BMS and smartphone app. Easy to get real-time cell conditions