Bafang DPC18 display - battery life - when to charge

[kiltedcelt]

When I bought my Bafang BBSHD for my cargo bike it came with the C965 display which I quickly learned does not register proper battery life for 52v batteries. I now have a Bafang DPC18 display which does in fact properly register the voltage. Since installing the new display with a fully 100 percent charged battery I've been riding around using the bike for work and generally keeping an eye on the battery level and mileage to try to get some sense of how much range I can get using this setup. Back when I used this battery on a different bike with a hub motor I was able to get over 90 miles of range with the battery starting out at a 100 percent charge (rather than an 80 percent charge). Now, with the BBSHD I'm having to readjust my assessment of what sort of range I can expect with this battery being used in a mid-drive setup. So far I have over 60 miles on the odometer and the battery is about 50-something percent right now. So a couple questions occurred to me -

1. Back when I had a Cycle Analyst you had to input the voltage of the battery, number of strings, and battery chemistry seemingly to get the most accurate information from the display on battery level, watt hours used, etc. On the Bafang display there doesn't seem to be any way to enter this info and the display basically sees "Oh, you have a 52v battery fully charged to 58v let's start there." Is it not necessary for the display to know anything more specific about the battery - simply the input voltage? I'm guessing that with a Bafang motor and display you don't need to know that extra stuff that the CA required, and you'll still get pretty accurate measurements of the battery's state of charge/discharge as long as the display is capable of recognizing a 52v battery, which the DPC18 can.

2. This goes back to that old - "How to get the most life from your battery" question. I've seen it hashed over many times in many different threads, and I think most of the time from here on out I'll be charging to 80 percent to make sure to get the most recharge cycles. However, I do need the bike occasionally for VERY long rides where I might have 60 or more miles, possibly even close to 100 miles round trip. In those instances where I anticipate a MUCH longer potential round trip distance I'll fully charge to 100 percent which I figure gets me maximum range and also ticks the box of occasionally fully charging the battery to make sure it gets properly balanced. My question though is should I just keep riding until I'm getting close to that 20 percent level before charging? I obviously don't want to run it right down to the low voltage cutoff where the system just cuts power to save the battery, but ideally I'd still like to run as low as possible before recharging just to make sure I'm getting the max amount of range before I actually NEED to recharge. Suggestions?

Anyway, so far I'm really liking this system. I think this huge EM3EV battery I bought a few years back is giving me the practical range I need, and the Bafang BBSHD seems to be a more efficient motor in terms of battery usage than the Mac geared hub motor I used to have. When I had the Mac motor on a Surly Troll I used as a commuter I think I was actually getting slightly less battery life than when I had the Mac motor installed on the Yuba Mundo I used to have. I'm sure there were some settings I could've played with in the CA to get a better economical power output, but for the most part it seemed like the Mac/CA was inherently less efficient somehow than the same battery but coupled with the BBSHD and the DPC18 display.

 

[amberwolf]

Back when I used this battery on a different bike with a hub motor I was able to get over 90 miles of range with the battery starting out at a 100 percent charge (rather than an 80 percent charge). Now, with the BBSHD I'm having to readjust my assessment of what sort of range I can expect with this battery being used in a mid-drive setup. So far I have over 60 miles on the odometer and the battery is about 50-something percent right now.

since the middrive uses the bikes gearing, if you are shifting properly for low gears at startups and hills and other high load situations, then it's much more efficient than the hubmotor, so you can expect potentially much higher range, depending on the usage scenario. if there's lots of starts and stops and lots of slower speeds on hills, etc.,

total mass will also make a difference in those usages, so if the middrive bike is a lot lighter it'll have less power usage.

aero / speeds also make a differenc,e so if both are usaed at same speeds it doesn't matter, if top and average speeds are higher on one than the toher thne power usage is higher on that one.

1. Back when I had a Cycle Analyst you had to input the voltage of the battery, number of strings, and battery chemistry seemingly to get the most accurate information from the display on battery level, watt hours used, etc. On the Bafang display there doesn't seem to be any way to enter this info and the display basically sees "Oh, you have a 52v battery fully charged to 58v let's start there." Is it not necessary for the display to know anything more specific about the battery - simply the input voltage? I'm guessing that with a Bafang motor and display you don't need to know that extra stuff that the CA required, and you'll still get pretty accurate measurements of the battery's state of charge/discharge as long as the display is capable of recognizing a 52v battery, which the DPC18 can.

the system that knows what chemistry it is and other info would be "more accurate" than the basic type that just reads the voltage and displays a voltage bar.

exactly how the dpc calcluates the bar i don't know, but if it is just voltage based, and it doesn't actually measure wh used, or involve battery internal resistance, etc., it's not as accurate as something that does.

you can test which kind it is if you have a variable power supply, by powering the system from it instead of the battery, and then just suddenly lower the voltage from the full voltage to the near-empty voltage. if the display follows taht sudden change then it's just a voltmeter. if it takes time to adjust down its' doing some more complex calculation (based on what, we won't know, though careful observation of many variations of this experiment might tell you).

the most likely thing is that it simply has a few preprogrammed profiles that it switches between based on the battery voltage it detects when it's turned on. this can be a pretty severe problem if it's not done right, and there have been problematic controllers that did this. so lets say you had a 48v battery that is almost empty when you turn it on. the voltage can actually be so low that it is about the same as a full 36v battery., the display now shows yo a full battery, even though it isn't. but you don't know that because you don't remember that you used the battery up last time, so you go riding, then a few hundred feet down the road it dies, even though the meter says it's still full.

similarly a completely full 36v pack is about the same as a tottally empty 48v...so you charge up your pack and turn it on, and the display flashes empty (and maybe even refuses to operate depending on it's safety features). but you know it's full...so you figure it's broken. :/ just very very slightly discharging the battery and then turning the system on suddenly makes it see the pack as a full 36v, and it works again.....

so a 52v vs 48v pack has even more overlap, so you can easily see the system thinking it's still completely full for much longer than it should with 52v if it thnks its a 48v pack, because of turning the system off after enough rides to drain the 52v pack down to where a 48v pack would be when it's full. only about a 4v difference. then the meter starts over from the full mark again, if it even ever got below that becaus some have big segments that are more than 4v worth of pack voltage anyway.

2. This goes back to that old - "How to get the most life from your battery" question. I've seen it hashed over many times in many different threads, and I think most of the time from here on out I'll be charging to 80 percent to make sure to get the most recharge cycles. However, I do need the bike occasionally for VERY long rides where I might have 60 or more miles, possibly even close to 100 miles round trip. In those instances where I anticipate a MUCH longer potential round trip distance I'll fully charge to 100 percent which I figure gets me maximum range and also ticks the box of occasionally fully charging the battery to make sure it gets properly balanced. My question though is should I just keep riding until I'm getting close to that 20 percent level before charging? I obviously don't want to run it right down to the low voltage cutoff where the system just cuts power to save the battery, but ideally I'd still like to run as low as possible before recharging just to make sure I'm getting the max amount of range before I actually NEED to recharge. Suggestions?

honestly that's all up to your own usage pattern and needs.

if you don't need much range on any particular ride, and can always just sit there and wait for it to recharge before you go ride if it isn't enough of a charge to go the distance you know you're going to need on that ride, it's nto a problem.

if you know there's times you won't be able to wait for that recharge, and you know those will be unpredictable, you're going to have to always keep it charged to at least enough to do those rides.

in my case, for instance, i almost always need only just enough to get from home to work and back again, which is only around 5ah or so. but i may unpredictably find i have to run an errand either for work (which could come up at any moment and have to be done right then, no waiting, and could require 20-30ah) or just after work like groceries (which takes another few ah but could potentially wait long enough to add that much to the pack charge since i can plug in to the wall in the breakroom and sit there till it's done).

so i pretty much always recharge every day or two, and i also have the charger mounted on the trike, and keep a long extension cord in it to recharge at work/etc if it's necessary, assuming i have the time to wait for that to happen.

i'd rather just keep it at about half charge all the time...but practically i can't do that.

 

[kiltedcelt]

I do know there was an issue with the C965 display that it would work with a 52v battery but didn't actually support it, so the battery meter would show it being full for ages, then when it finally started going down a few bars (I got 80-90 miles - can't remember how much it was), the battery was significantly depleted. The DPC18 has support for 52v batteries and it does give a live read-out of watt hours being used which of course varies depending on what gear you're in, what level of assist you have it set on and whether you're pedaling or not. I'm just going to keep riding the bike and racking the miles up until I've (hopefully), come close to 100 miles. If that happens and it's still not reached the low voltage cutoff, then I'll know that under reasonable condition I can probably expect upwards of 100 miles of range out of the pack which is good enough for me for most trips I'd take in one day. If I was going to take a longer trip, like using the bike to go on a camping trip then as long as I knew I had an option for recharging the battery somewhere along the route I'd be willing to use the bike for a much longer distance ride.

 

[dogman dan]

Charge to 80% for most rides will be fine, but do charge it to 80% at every convenient opportunity. Don't ride it several days because you can, the battery needs to be charged when it gets below 30% left at least. This will keep it from needing much balancing. Basically, it can be way the heck out of balance, but if you ride it between 30 and 80%, who cares? You will never get anywhere near over discharging or over charging. But in reality, it won't likely get even slightly out of balance if you treat the pack that nice. But the main thing I'm trying to say is charging it daily to 80% is not going to shorten its life enough to care about. So charge it when you can, so you have the juice when you need it, without discharging it deep.

But any time you do discharge it deep, then you will definitely need to balance the pack. Only 100% charge can do that, because of how bms's work. But then, to maximize lifespan, don't let it sit long at full charge. Ride it back to 80% voltage right away, or begin your longer trip ASAP.

So first off, your pack needs that 100% charge at least occasionally, to let the bms restore it to fully balanced anyway. So anytime you think you need more range than half the battery will give you, charge it full. Charging it full briefly will not harm it, but discharging it deeply enough often will. So better to charge full, get the balance, and then not have to drain it 100%. IMO, the damage, or at least the unbalancing effect, happens in that last 5% or so. If you are watching a regular voltmeter, you can see when this happens. Suddenly sag under load greatly increases, and it drops in volts much faster. This is over the cliff in the discharge graph. Stay on the top of the voltage cliff, to maximize lifespan of the cells.

Some day you will need to take it all, and don't hesitate when you have to. Just creep home on minimum power once you are in that last 5%.

What I do personally, is just watch a CA, for volts. My drop dead voltage is 42v. When it sags to 42v under load, I know I'm getting close to the end, and I stop then ideally. But if not back home, I just slow down trying to keep it from sagging below 42v under load. At 42v resting, then a bms kicks it off on my 52v luna pack, or if running lipo, the controller will lvc.

 

[Mutinyguy]

Where do you indicate you have a 52v battery in the DPC18 settings? I don’t see that setting anywhere. MY % has stayed at 100% after a 40 mile ride.

JIM