Battery charging “rule of thumb”?

[Wallykl]

To newbs like me that are dabbling—researching how safe or sound it may be to increase the amp rate I charge my 52V, 20 amp-hr Valstrom battery. Came with a 3 amp charger accepting 120-240V input. As I read various threads on pros/cons of sending the battery higher amperage, my head starts to spin. Then I came across a statement that seemed to be implied as a safe rule of thumb. Went something like—sending your battery “up to, but no more than 30% of its amp-hr rating” usually is safe. So in my words—my 20 amp-hr battery should be safe to apply a 6amp charge (30% of amp-hr capacity) without harming me, others, or the battery?

Why do I ask? Seems like a rule of thumb is easier for my failing mind to remember. Or, is this “rule” just hogwash. I’m interested because this would be quite valuable by cutting my charging time in half, at literally no increased expense (of same physical size and relative cost of a 3 vs 6 amp charger).

Or should I quit before I hurt somebody? Never imagined that diving into e-bikes would require me to become adept at deciphering new tecnical nomenclature! But—it has been a blast!

 

[Jeremy McCreary]

To newbs like me that are dabbling—researching how safe or sound it may be to increase the amp rate I charge my 52V, 20 amp-hr Valstrom battery. Came with a 3 amp charger accepting 120-240V input. As I read various threads on pros/cons of sending the battery higher amperage, my head starts to spin. Then I came across a statement that seemed to be implied as a safe rule of thumb. Went something like—sending your battery “up to, but no more than 30% of its amp-hr rating” usually is safe. So in my words—my 20 amp-hr battery should be safe to apply a 6amp charge (30% of amp-hr capacity) without harming me, others, or the battery?

Why do I ask? Seems like a rule of thumb is easier for my failing mind to remember. Or, is this “rule” just hogwash. I’m interested because this would be quite valuable by cutting my charging time in half, at literally no increased expense (of same physical size and relative cost of a 3 vs 6 amp charger).

Or should I quit before I hurt somebody? Never imagined that diving into e-bikes would require me to become adept at deciphering new tecnical nomenclature! But—it has been a blast!

Sorry, can't speak to the rule of thumb in question, but always safest to stick with a charger designed specifically for your battery. If Valstrom offers a fast and slow charger specifically for your bike, it's reasonable to assume that both are safe fire-wise if used as directed. Others can advise you on how faster charging might affect battery service life.

Personally, I'd never use a 3rd party charger on any ebike — even it has the right connector. Might be different for a true battery expert, but I know just enough to be dangerous.

 

[Chazmo]

Hi Wally,

My advice is to live with the slow(er) charge rate. I can’t comment on that “rule,” and I would say that “safe” is not the only factor. The faster you charge, the more you impact battery life.

I have a similar 1000Wh size battery (52Vx19.2Ah) At one point, I considered getting a programmable charger that would have been capable of upping from 2A to 6A, but customer service at Juiced bikes said pretty much the same thing I just said to you. Since Juiced disappeared, I have been trying to make sure my battery lasts as long as possible.

So, no “fast” charging, and try to keep the battery above 20% when you drain it and below 80% when you charge it.

 

[Chazmo]

(sorry, it was 8A, Wally)...

This is what Juiced sent to me when I asked about the Grin Cycle Satiator power charger...

We are convinced that charging your battery with an 8amp cycle satiator is safe, if you fast charge your batteries they will discharge faster as well - keep that in mind if you are planning long trips the range will be a bit shorter. That third pin is unassigned, it does not currently have a use. The charger is good and durable, I do not have a profile list that is something you will need to make yourself.

Greg
Juiced Bikes Support

 

[harryS]

A 20AH battery is probably OK with a 6A charger, If it's made with 18650 cells, there will be at least six cells in parallel and 6A separates down to 1A per cell, which is OK for charging.

However, if you want the cells to stay cool and last longer, charge them at the lowest current that your patience will allow, This is my thought process anyway, I bought a 1A charger for my tiniest battery, a 13 cell 48V5AH after I noticed it getting kind of warm with a 3A charger.

 

[6zfshdb]

To newbs like me that are dabbling—researching how safe or sound it may be to increase the amp rate I charge my 52V, 20 amp-hr Valstrom battery. Came with a 3 amp charger accepting 120-240V input. As I read various threads on pros/cons of sending the battery higher amperage, my head starts to spin. Then I came across a statement that seemed to be implied as a safe rule of thumb. Went something like—sending your battery “up to, but no more than 30% of its amp-hr rating” usually is safe. So in my words—my 20 amp-hr battery should be safe to apply a 6amp charge (30% of amp-hr capacity) without harming me, others, or the battery?

Why do I ask? Seems like a rule of thumb is easier for my failing mind to remember. Or, is this “rule” just hogwash. I’m interested because this would be quite valuable by cutting my charging time in half, at literally no increased expense (of same physical size and relative cost of a 3 vs 6 amp charger).

Or should I quit before I hurt somebody? Never imagined that diving into e-bikes would require me to become adept at deciphering new tecnical nomenclature! But—it has been a blast!

Volumes have been written here on the proper care and feeding of Lithium batteries. I have yet to see a "rule of thumb" that applies to every e-bike battery. There are too many variables involved to make such a pat statement. Battery chemistry & capacity, case & BMS design, cell type, the connectors used and most of all, how well the battery is constructed all are contributing factors. Heat buildup is one of the biggest concerns. The higher the current, the more heat is generated and every battery case dissipates heat differently. As has already been mentioned, higher charge rates can shorten battery life. It becomes a question of whether to charge faster to save time, or charge slower and extend the life of the battery.

I have seven e-bike batteries ranging in age from 1 to 7 years. The charger that came with the bike is rated at 3 amps. To shorten charge times, I invested in a programmable Grin Satiator which can charge at up to 8 amps. I compromise by using a program that varies the rate from .3 A to 6A during the charge cycle. I charge the batteries on a wire rack with plenty of air flow to minimize heat buildup. This shortens the charge time from 6 hours to 4.5. My oldest batteries have lost close to 10% of their original capacity but it's difficult to tell if this is due to charge rate or age.

Welcome to the forum, and I'm sure others will offer additional information.

 

[Gionnirocket]

I concur... Too many variables, and most important being the cells used and BMS in question.
Some entry level battery BMS's can only handle a 3a charge even though the cells could probably handle more.
I'm on the other end of this as charging time for me is more than ample. My 21Ah battery can easily handle the 5a charger that it came with but I use my 2a charger because slow and steady wins this imho.

edit: the one base rule I have heard is 0.5C
This is confirmed by Google :
The standard charging rate for most 18650 lithium-ion batteries is 0.5C, which means half of the battery's capacity in amps. For example, a 2500mAh (2.5Ah) 18650 battery should be charged at 1.25A, according to IMREN Battery. Some batteries can safely handle higher charging rates, such as 1C or even 1.5C, but it's crucial to check the specific battery's datasheet for the manufacturer's recommendations.

And Samsung data sheet.


But again this does not takes into account the capabilities of the BMS.

 

[Wallykl]

Thx all. I did see the 0.5C rule as well.
I dare say there is no "rule" I see here!

 

[Chazmo]

I compromise by using a program that varies the rate from .3 A to 6A during the charge cycle.

This is really smart, I think, 6… Does it end up charging faster than the stock 2A/3A charger that you got with the bikes?

 

[Slaphappygamer]

The common 5.5MM x 2.1MM plugs are rated for 5A max. No matter if the cells can handle higher charging current. The plug can not safely handle higher current. One "rule of thumb" that I know about battery charging is, never leave your charging battery unattended. Specifically, don't charge while you are sleeping.

 

[6zfshdb]

This is really smart, I think, 6… Does it end up charging faster than the stock 2A/3A charger that you got with the bikes?

Yes, it shortens the total charge time from 6 hours to 4.5. It isn't clear whether it shortens battery life or not.

It should be noted however that the Satiator charger is expensive, and costs about half that of a new battery.