Voltage Sag After Charging?

[geeeyejo1]

Well I believe that my pack has finally balanced - after two discharges of approx 4AH each the pack reached 59V on the charger last night. I disconnected the charger and when I woke early this AM noticed the pack was sitting at 53.7V (I have small voltmeter connected to positive terminal to monitor voltage while charging or sitting) I then connected it and it quickly (maybe 10 minutes rose to 59+V again) I left it connected to balance further and at 10AM it was at 59.5V. I disconnected and within 45 minutes pack is now at 56.5V. The voltmeter pulls only a few MA per hour so assume it is not contributing?
I am a noob to LIFEPO4 packs (its a Sunthing28 "Ping Clone") and do not know how they are supposed to "behave" - pack did work fine yesterday using less than 1AH per mile with mostly WOT. Vendor specs below indicate an "Open Voltage" "1 hour after fully charged" of 51V-57-V - not sure what this means but seems that my voltage is in that range - is this "normal" ?
Nominal Voltage 48V
Voltage Range 42 - 58.2V
Rated Capacity 15Ah
Over-discharge Voltage 2.100V( Any cell)
Over-charge Voltage 3.900V( Any cell)
Charge Voltage 60V
Open Voltage after fully charged 51V~57V (1 hour after being fully charged)
Maximum Charge Current 7.5A
Estimated Charge Time @3A About 5 hours
Discharge End Voltage 41.0-42.3v
Maximum sustained work current 20A
Maximum Discharge Current 35A
Over Protection Current 45A

 

[geeeyejo1]

Sitting at 55.5V after two hours off charger - cold and crappy out so not going to ride and pull any real AH out today - will let her sit for a few hours then charge again and let BMS do its thing...

 

[wesnewell]

I don't use likepo4, but it's my understanding that most new packs need to be left on the charger for 1 or more days to get then balanced good. When in good balance I think you should see it hold about 55-56V when it settles after charge.

 

[geeeyejo1]

Thanks - been reading old posts and some other on line info and that's what I'm figuring. Have to say that the voltage display I wired in line with fuse block has provided invaluable information on status of pack. Can only imagine how many people get pack with just provided charger and assume all is fine when green light comes on and possibly damage pack and/or do not get full range as cells never balance...

 

[dogman dan]

The drop is the surface charge dissipating. Depending on the quality of your cells, they will discharge to a resting voltage, and then tend to stay there for quite a while. 56v would be ideal, but it might be as low as 54. My old tired ping now rests at 53v.

The reason for the overcharge, is to help the balancing process. Up to 60v is ok. Keep leaving it on the charger all night for the first week or so.

 

[geeeyejo1]

Thanks - this has been a great learning process - just read about the surface charge earlier today - confident now that the battery is ok and behaving as it should. Glad that I took the time to do it right and not just give it a quick charge and then ride until DOD. Hopefully will get some nice use and life from this Sunthing unit....

 

[wesnewell]

If you want long life out of that 15ah pack, never give it wot from a stop. That's when the controller will draw max amps. Also don't bog it down on steep hills. Go into them as fast as you can and try and maintain speed to reduce amp draw. If it gets so slow you can pedal, do it. I hate the fact that most lifepo4 bms's have a 2.1V cutoff. IMO, that's way too low. If you can adjust it, take it to 2.5v. As an alternative, stop using the battery if voltage reaches 45V. With proper care, you might get 1000 cycles from it, or 3-5 years service from it. Make sure you disconnect or turn off the bms if you don't plan on riding for a few days. Leaving the charger hooked up might be an option too, but I really don't know since I don't use it. Check with others that do.

 

[dogman dan]

Good advice. Half throttle for just the first 6 feet or so really does make a difference. Keep the thing going 15 mph up hills for sure.

Charge every ride, even if it's just a mile or two, charge overnight at least every 10 cycles, if not every cycle.

Most don't get 1000 cycles. But what seems typical is closer to 700, and ought to mean 7-10,000 miles. Not a bad cost per mile. 7 cents per mile or less, plus less than a cent for the power itself.

Cycle life records get meaningless though, since they rarely are 100% cycles. My first battery went 7000 miles, and the average distance per cycle was 10-12 miles.

 

[geeeyejo1]

Thanks guys - I just swapped out my wireless speedo for a wired unit as interference was causing it to cut out - will be able to better monitor top speed and speed on hills now. Will keep an eye on wattmeter for riding conditions that cause high amp draw and look to limit those as well.

 

[Ykick]

Thanks guys - I just swapped out my wireless speedo for a wired unit as interference was causing it to cut out - will be able to better monitor top speed and speed on hills now. Will keep an eye on wattmeter for riding conditions that cause high amp draw and look to limit those as well.

Max moments are when to contribute more with the pedals for best range (and gentleness) of battery. It's good to pay attention to Ah/Wh, min/max V, range of course. After a while many things become 2nd nature and just part of the EV process.

 

[geeeyejo1]

Thanks guys - I just swapped out my wireless speedo for a wired unit as interference was causing it to cut out - will be able to better monitor top speed and speed on hills now. Will keep an eye on wattmeter for riding conditions that cause high amp draw and look to limit those as well.

Max moments are when to contribute more with the pedals for best range (and gentleness) of battery. It's good to pay attention to Ah/Wh, min/max V, range of course. After a while many things become 2nd nature and just part of the EV process.

Thanks - been pedaling consistently from start and when going up hills - easy to keep her at 17mph or so with minimal effort. Looks like top speed on flats this am with no pedaling (and 250 lbs or so of me) was 25 mph - not bad also assuming 20 deg F temps do no help battery performance either!