headway battery charging.

[robbo1972]

Hi Guys,
I have recently put together a fs mountain bike with a cellman 8t kit with a 12 fet controller (great fun). I use a headway 48v 10ah battery for getting to work (6 miles) and I am only using 4ah to get there. Am I better off top up charging the battery when I get to work or would I be better off going to work and back one a single charge? What I really want to know is which charging technique would make the battery last longer? My ride to and from work is mainly at 15 to 25 amp draw with an odd couple of seconds up to 35 amps. kind regards Rob

 

[dnmun]

charge at work if you can. less discharge is best, just don't overcharge. if you know how long it regularly takes to charge it, you could charge @home immediately before leaving if you have the time to reach full charge, so the pack spends less time at max charge. same at work.

 

[robbo1972]

Thanks for your promp reply. So being at 3.65ish per cell is bad for them then. . hmm that will change the way I charge them then as when I get to work I put them straight on charge so they sit there at max charge for say 8 hours then when I get home I put them on charge straight away and they sit there fully charged all night for 12ish hours. So for 18 hours a day they are at full charge. Is this the way all lifepo4 batteries are? cheers Rob

 

[Gregor]

I think headway range is 3.65v fully charged to 3.2v nominal to a safe lower limit of about 3 volts. I assume your pack is 12s, so I hope you have at least a voltage monitor on your handlebars to check how things are going during those high amp periods?

 

[Gregor]

Sorry about that--for a 48v pack it would be 16s lifepo4.

 

[dnmun]

if you have 16S lifepo4 then you need 16x3.65V=58.4V minimum from the charger. you can measure the voltage of each cell to see how it balances but that headway BMS usually balances each cell right at 3.65V so you should have some extra voltage above that so the slow cells can catch up while the other high ones bleed down.

which charger do you use?

it has to be more than the 58.4V, how much depends on how easily the pack goes outa balance, not so much for the headways i expect.

 

[robbo1972]

Hi Dnmum,
I just had a quick look at the charger and its a 4amp kp charger and it does say 58.4 on it. When hot off the charger it is 58.4 but that quickly drops down to 52 odd volts according to the cycle analyst. The bms that I am using is from eclipse bikes in the uk and all cells do seem to be perfectly balanced. This pack was until last week a 8s2p pack that I put together for a currie electrodrive that I had on my bike. But then when I had some money put to one side and after lots of looking around this site decided on a mac 8t motor kit from cellman. Then after buying a new 16s bms put it all together last weekend. I will today try going to work and back on one charge (8a ish) just to see if I am getting a decent capacity from my battery but will then look at top up charging just prior to using the bike. Thanks for your help Rob.

 

[dogman dan]

I wouldn't sweat the charge just before you ride thing with lifepo4. I know it matters more with lipo but lipo has a shorter lifespan to begin with, so maximizing it gets more important perhaps?

Yeah, yeah, I know it does make some difference and I know some people can't be happy unless they get max lifespan from everything.

But my opinion is that if you charge at work, you will do a much bigger beneficial effect. Every chemistry loves a 50% discharge depth. That will help a ton. I just thing charge timing is only going to help one pound. Insignificant compared to the ton.

I say definitely charge at work if it's quite convenient, but don't sweat getting up at 4 am so you can ride the bike at 6. Just charge it and go to bed. Life is short, don't sweat the little things.

 

[robbo1972]

Thanks dogman, my main concern really was whether top up charging the battery would count as a full charge in the 1000ish charges that these batteries are supposed to give hence giving me only 500 days charges instead of 1000.