Limit the max charge voltage of cheap charger to expand battery lifetime

Hi there

Reading about in this forum, grintech and the web it became clear to me that it can really expand the lithium batteries lifetime, if I don't charge a lithium battery to the max.

However, how can I do that, if my charger is just one of those black bricks that come with a hailong battery?
I was wonderning if I could just put a diode in series while charging, using the voltage drop over the diode to prevent the full charge voltage to ever reach the battery.
Or would the charger compensate for that?

In my case I have a 13s 14.5ah 48v battery with LiCoxNiyMnzO2 18650 Panasonic cells. The BMS limits to 54,6V and turns off at 35,75V. I'd prefer to charge only to around 53Volts.


I am aware that I could use a better charger or switch to a smarter BMS. But I'm really trying to find out, if there is a low cost solution of reducing the max charge voltage by about 1.5V with the given components.

Thank you for your time and thoughts.

A diode would work. I sucessefully did this in the past. Sy some of my pics of the mod here:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=98771#p1446395

Matador.

Raphael, a single diode isn't going to get you where you want to be to be very effective in extending battery life. The trick is getting your pack big enough that giving up 10-15% of capacity for everyday use is no big deal, so you end up in the 4.05V or so top-of-charge range.

Another complication you have to consider is that the balancing function of your BMS requires you to take the cells to 4.2V to balance them, so what you really need is an additional charger, a must have AFAIC anyway since a dead charger leaves you without transportation if you only have one. Then you use the charger you have for occasional full charging to balance or in anticipation of longer than usual rides to make use of the full capacity of the pack. For the new charger, get yourself one of the quite affordable aluminum case chargers, which are quite easy to change the top of charge cutoff, and use that charger after adjusting it down to say 52.6V as your every day charger. Making that kind of change along with adopting other simple battery life extension approaches can give your battery many times the service life.

Thank you both for your valuable insights!

Both is very interesting, important and helpful. For one, diodes work, for the other the easily overlooked or neglected "Detail" of the BMS balancing at full voltage is very important!

@John in CR, what "affordable aluminum case chargers" are you refering to?

Raphael303 said:

@John in CR, what "affordable aluminum case chargers" are you refering to?

Click to expand...

Something like this https://www.aliexpress.com/item/935894254.html?spm=2114.12010612.8148356.11.25063b94LEOhC6, which is quite easy to adjust the cutoff voltage using a tiny flat head screwdriver. Just remove the 2 top screws on each of the end plates, and pop the cover off. Clip the pos and neg output wires to a multimeter set to the correct DC voltage range and turn the charger on. Carefully (since everything is live with electricity) turn the output trimpot, which is the one nearest the charger output wires, until you get to the voltage you want to set. Turn charger off and disconnect from the wall...put the cover back on and measure the output cutoff voltage again to make sure it is properly set, and verify the cutoff again the first time you charge the battery. Monitor the charge voltage during the first charge to make absolutely sure it doesn't overcharge your pack.

While buying the charge also get an ebike tester, a simple cheap tool for diagnosing problems. Another extra to keep on hand is an extra throttle, which is a common failure item...and a 3 speed switch too, since thosee cheap plastic switches are easy to break.

Thank you very much John! Those are very valuable tipps! Didn't know these "bricks" could be modified! Awesome!