Charging voltage cutoff device

Hello everyone,

I've been looking for a simple device to add in series to my existing charger and limit cutoff voltage from 4.2V/cell to 4.1 or less and also keep it on storage voltage level when not using it. Are there any such devices? I consider it fairly simple (if you just only regulate voltage) but just add some "smart" capabilities to the existing cheap charger - can be done with a microcontroller with a display to select voltage and linear regulator to drop the voltage a bit. The only downside is some power dissipation for the voltage drop but in my case I use only 3A charger so the maximum is about 15W for 3.7V/cell...

Power diodes and have published forward voltage drop figures, and can be placed in series to achieve the drop you need. Bridge rectifiers have the voltage drop of two diodes in series.

https://www.ebay.com/itm/293646454008

Because you are reducing the voltage you might find it easier to just modify your charger, there's quite a few threads here on that topic , try searching 'adjustable charger mod' 'or 'variable voltage charger' there's also good vids on youtube. Also have a search for your model of charger, many chargers have a variable resistor that can be turned up or down, so charger manufacturers can just churn out the same charger and adjust the voltage and current as needed depending on the customers demands. You can add a cheap led voltmeter and ammeter to the output. Although, double check the accuracy with a good multimeter as sometimes they're not so accurate.

NickF23 said:

Also have a search for your model of charger, many chargers have a variable resistor that can be turned up or down, so charger manufacturers can just churn out the same charger and adjust the voltage and current as needed depending on the customers demands.

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I just opened up a couple of my cheapo chargers to try to lower the voltage from a measured 54.7V to something a little healthier. I found that turning the trim pot all the way down to the limit took the charger's output to 54.1V, but no lower. I settled for that, though I was hoping for something under 53V.

you can use a buck converter in series before the battery. I use them to charge my 3s and 4s battery packs, but they can handle much higher voltages. And with a buck converter you can "dial in" the final voltage and also the max charge amps. On mine I use a cheap 5 dollar volt/amp led meter so I can see the voltage/amp going into the pack. A buck converter depending on the max amps output can cost as little as 5 dollars.

These are plug and play, once you set up the voltage/amps, just plug the input/output (I use xt60 connectors) and it starts charging.

Actually I have Meanwell 150W power supply which I can mod for lower voltage/current. However still I need some schematic to cut the charging at the end otherwise I have to monitor the current and turn it off at some point. That's why was thinking about a device which can do all this by monitoring current and voltage and regulate the voltage effectively making any charger or power supply a kind of "smart charger", even if you don't have power supply or charger which can drop down the voltage so much. Meanwell is good as it can control the voltage in pretty big range by default like 43-55V.

Also since I am new to these ebikes stuff I am not sure how the commodity chargers are working exactly, still waiting my battery with charger to arrive to test it. Is it really cutting off the charge when reaches low current at the end or just there is a green LED which indicates low current but the topping up voltage is still there.