Charging Battery - 4 AMP to Watts?

[Aushiker]

Hi

I am just trying to get an approximate idea of how long a Bosch 4 amp standard charger would take to provide a one-watt of charge. My understanding of amps and watts in this context is well non-existent. According to Bosch, a 50% charge of a PowerTube 625 will take 2.1 hours and a 100% charge would take 5.4 hours, so if I am working this out right, one watt would take ~ 1/2 minute. Yes or no?

As my bike has two 625 watt batteries a 50% charge is looking at ~ 4.2 hours. Is that right?

Thanks in advance

 

[leifg]

Yes, your calcs are quite close. I believe it's a 36V battery. So a 4A charger into a 36V pack is 36x4=144W (power)...and if that power is maintained for one hour then you added 144Whr (energy). Which means a 625Whr battery would take 625/144=4.3hrs to charge (or ~2hrs for 50% or ~4hrs for two batteries to 50%) . These numbers are all approx because charge profile varies in reality (ie voltage increases and current tapers throughout different charge regions, so Watts are not constant as I assumed above -- and the 5.4hrs you mentioned makes sense).

You asked how long to add 1W, (I believe you meant 1Whr) and you are correct, it's about half a minute -- I calculated 25s using above assumptions (1W/144Whr*3600s). Again, in reality this varies depending on what region of charge cycle you are in, with the end of charge cycle being much slower and taking more time to add 1Whr (>2min for example)

 

[Stefan Mikes]

Leif has explained that nicely!

Andrew, have a look at how your smartphone is being charged. First, the charger is in the Constant Current mode, and you can get to the 50% smartphone battery charge pretty quickly. Then, the charger goes into the Constant Voltage mode. The current and the power delivered to the battery become variable and diminishing over the time, as the ions inside battery are struggling to find some free space remaining on the battery electrode. You might have noticed the last 10% of the phone battery charging becomes painfully slow, right? It is exactly the same with the e-bike Li-ion batteries!

 

[Chargeride]

I upgraded from 2A charging to 4A, I checked the charge current and it was spot on 4A, I was expecting half the charge time, the reality was it was only 2/3rds for a complete charge.
The more you put in, its even harder for the ions to find a parking space

 

[Stefan Mikes]

I upgraded from 2A charging to 4A, I checked the charge current and it was spot on 4A, I was expecting half the charge time, the reality was it was only 2/3rds for a complete charge.
The more you put in, its even harder for the ions to find a parking space

Yes! You have certainly made the charging to 50% twice faster though.

 

[Chargeride]

50% doesnt get me to the end of my road

 

[Stefan Mikes]

50% doesnt get me to the end of my road

Unfortunately "You Can't Always Get What You Want"

 

[fooferdoggie]

from what I have heard is charging both batteries on the bike is going to take longer than normal because bosch switches back and forth between batteries and it just takes a lot longer.