... 52 volt battery usage ..

[diverdon]

   Hello , sorry if this is a dumb question ..How low do you let your 52 volt battery get before recharging ? I have been recharging at 49 volts but would like to go lower ..Thing is my ride uses 3-4 volts and I don't want to be caught short while I'm out on the "road" ...
         I'm wondering how the low voltage cutoff works in the battery ..what's the cutoff voltage (heard it is 44 volts) ... and does the battery need to just get to this voltage for only a second to shut off ? sometimes when I accelerate or going uphill there is some voltage lag for a moment ..is that going to shut off the battery if it goes below the cutoff voltage for a "short" ? time ..
 
     What I have been doing is recharging to a voltage that will still give me plenty for a ride ..not always to %100 but maybe 70-90 % ... I have read it's better for the battery to keep it in the mid voltage range ..
 
    The last battery lasted well over 3 years of almost daily use ... In the end it might have died because I didn't fully charge it ENOUGH to balance the cells Then to I have read it doesn't hurt to fully recharge the battery all the time as it doesn't have a "memory" like Ni-Cad's ... I'm totally happy with the use I got from this last battery..

      So I'm a little confused and could use some help ..say the battery was reading 49 volts and you knew the next ride would use 3-4 volts ... Recharge or not before the ride ? sorry for the dumb questions ..maybe someone else has had these "problems" ..ha .. Life is good ..Thanks for any help I can Get ... Don

[Bikemad]

Hi Don,

Keeping a lithium battery fully charged for long periods is not advised, but If you use the battery after it has been fully charged it should not be a problem.
If I'm going to do a long or very hilly ride, I will always charge the battery fully overnight before use.
I have regularly done this with my current battery which I purchased back in August 2020 and it still performs just as well as it did when it was new.
I like to ensure that the cells in the battery are regularly balanced, and with most batteries, cell balancing only occurs when they are fully charged.

My battery still takes around 20 hours to fully charge and completely balance the cells even if it is only 50% discharged.
I charge my battery through a Wattmeter to measure the amount of charge being put back into the battery, I record the data in a spreadsheet so that I can more accurately estimate how much capacity was used (and how much capacity was still available) from the resting voltage of the battery.

I also have a Balway battery meter which displays the estimated remaining capacity  as a percentage, based on the battery's resting voltage at the end of each ride, and it seems to be reasonably accurate when compared to the capacities indicated on the Wattmeter during the recharge.

Say the battery was reading 49 volts and you knew the next ride would use 3-4 volts ... Recharge or not before the ride ?

You need to realise that the relationship between the voltage drop and capacity consumption is not linear, therefore you cannot predict that the same trip will produce the same voltage drop when starting the trip from different voltages.
If a 10 mile trip with a fully charged battery uses 50% of its capacity, then you are unlikely to complete the same trip again with the remaining 50% capacity.
As the voltage reduces, you need to draw more current to maintain the same power output, therefore the battery will be discharged at a faster rate than it was on the first 10 mile trip, and should therefore run out before you can complete the same 10 mile trip for the second time.
 
Your 52V (14S) battery @ 49V is only 3.5V per cell, which typically equates to 0~18% of battery capacity remaining (dependant upon the cells used in your pack) so you should definitely recharge the battery before use.
Ideally, if you want your battery to last, then it's probably a good idea not to discharge it below 20% capacity, which for your battery could mean a minimum resting voltage of 49~52V (3.5~3.7V per cell).

Alan
 

[diverdon]

   I have learned a lot from you about battery's and bikes ..I did not know it took so long to fully charge/balance the battery .. I have the wattmeter you told me about on it and it is sure slow "topping off" .. didn't want to leave it totally full for long so I charged to 90% last night and am topping it off now just before my ride ..
   
       Thinking I will balance it 1 time a month ?? OK ?? The last 1 lasted over 3 years and perhaps that's just the life span of it ..
   I have looked up this Balway Meter and will look into it more .. I like "Gadgets" ..
 
   I have a chart with % of charge as related to the battery voltage I use to sorta determine the amount of capacity used ..at least I used to do that ..Then just started  charging to the voltage I need for the ride I'm taking .. I'm gonna track it some more now for a while ..

   2 questions .. What's the lowest you'd go on a 52 volt battery before recharging and/or what voltage/capacity do you think it's best to recharge at ? I want to let it go down but am afraid of going to low .. Which is my 2nd question .. Do you know what is the battery shut down voltage for a 52 volt battery ? I was thinking it is 44 volts ... Does the battery shut off if you hit this voltage for a second or a few seconds ? Like when going uphill and the voltage sag created by it ?
        Charging is down to 6 watts now and the green light has been on the charger for an hour or so ... So I'm off for 1-2 hours outside on the bike now ...

      Thanks so much for all of your help over the years ..You've really helped me ... Don

[diverdon]

        Just Read this so you had already answered 1 of my main questions and I was just to dumb to see it ..

           if you want your battery to last, then it's probably a good idea not to discharge it below 20% capacity, which for your battery could mean a minimum resting voltage of 49~52V (3.5~3.7V per cell).

     Your 52V (14S) battery @ 49V is only 3.5V per cell, which typically equates to 0~18% of battery capacity remaining (dependant upon the cells used in your pack) so you should definitely recharge the battery before use.
Ideally, if you want your battery to last, then it's probably a good idea not to discharge it below 20% capacity, which for your battery could mean a minimum resting voltage of 49~52V (3.5~3.7V per cell).

     The chart I have shows battery % at 49 volts as 31% not 0-18% ..am I missing something .. My chart shows %20 at 47.6 volts .. I'm thinking it's hard to pin the recharge voltage to 1 # so a range is better between 48.9 = %30 and at the lowest 48 volts = %23 ..... Perhaps I need to look up this specific battery for specs ??

    Thank You for your help ..sorry to bug you so much ...Don

[Bikemad]

Don, I don't know what chart you are using, but the remaining capacity based on the resting voltage can vary considerably between cell manufacturers (Panasonic, Samsung, Sony and LG etc.) and can also vary significantly between different cell types from the same manufacturer. LG alone have produced more than 60 different types of 18650 cells.

It is impossible to accurately determine the remaining capacity based on the cell voltage without knowing the exact cells used in your battery, and having a specific chart for that particular cell showing the capacity at different resting voltages. The temperature of the cells can also affect the remaining capacity at any given voltage.

The actual low voltage cut off will be dependant upon the battery's BMS. I don't know what the preset minimum cell voltage for your BMS is, but if it's programmed to cut off when any cell drops to 3.0V per cell, then your battery would cut out at 42V if all your cells are perfectly balanced. However, if your cells are not well balanced, or you have a weak cell group, the BMS will cut the power when the lowest/weakest cell group drops below the preset cut off voltage, but your battery voltage would still be higher than 42V due to the remaining stronger cells being at a higher voltage.

As an example, if you had a single weak cell group that dropped to 3.0V while all the other cell groups were still at 3.7V, your battery voltage immediately before cutting out would still have been 51.1V.
As this 51.1V would have been measured while the battery was under load, the actual battery voltage would be even higher as the cell voltages will typically rise after the load had been disconnected by the BMS.

Alan
 

[diverdon]

    Thank You for the help .. I wrote a long reply ..forum said it went thru but I don't see it .. Here's the setup I'm using now to fully charge the battery (balance it) ..You gave me the trick of the watt meter ..

     I have/had been using a charger that charges to 80-90 or 100% whatever you choose and then shuts off .. I wonder if it never really bananced the battery but rather shut off at the set voltage instead ..

[diverdon]

     if your cells are not well balanced, or you have a weak cell group, the BMS will cut the power when the lowest/weakest cell group drops below the preset cut off voltage, but your battery voltage would still be higher than 42V due to the remaining stronger cells being at a higher voltage.

As an example, if you had a single weak cell group that dropped to 3.0V while all the other cell groups were still at 3.7V, your battery voltage immediately before cutting out would still have been 51.1V.
As this 51.1V would have been measured while the battery was under load, the actual battery voltage would be even higher as the cell voltages will typically rise after the load had been disconnected by the BMS.
 
   I have learned some more here from you ..Thanks ... I have been doing some more "research" and stumbled on a forum post where you helped me with this a few years ago ..

     I understand it's not an exact science and there are a LOT of things to consider .. Think for now I will just stick with what has worked for a few years so far 48-49 volts and recharge to 80-90% then the change will be to Balance the battery 1 time a month ..we willsee ..thanks again for all the help ..

[diverdon]

     Just in case you're interested ..Here's the battery I bought ... First one they sent went bad in just over 1 month .. The picture of the voltmeter above is from when it happened .. It was the same as the first battery I bought for this bike ..except they advertise 2 more amp hours for a little bump in $$ so this is supposto be a 15 amp hour battery they say they do it with 3500 miliamp batterys instead of 3000 milliamp ones ..

              https://www.amazon.com/dp/B09MK949YZ?ref=ppx_yo2ov_dt_b_product_details&th=1

[diverdon]

    Here's the subject bicycle at the park I like to ride thru .. 2 1/2 hours of mostly Quiet ..

[diverdon]

     Here's what I like as an average ride ..nice and slow 7mph average ..2 1/2 hours with a few stretch breaks ..