Amp output confusion - newbie.

[gerlewis]

I have a very newbie Amp question:

in these 2 ping batteries, one is 24v 10Ah, the other 24v 20Ah. - Would my bike (with 500watt motor) be the same speed and torque with both, but last longer with the latter? or would my bike be quicker/stronger with the latter?
Links:
http://www.pingbattery.com/servlet/the-4/24V-10AH-V2.5-LiFePO4/Detail
http://www.pingbattery.com/servlet/the-6/24V-20AH-V2.5-LiFePO4/Detail

The reason I ask is the 10Ah one says suitable for 200watt motor, but the other says 400watt motor. Why would this be so, unless the second one delivers a larger current - ie more power?

I see at the bottom in the detailed specs information about discharging current - is this a clue? or is this false information, would the all not discharge at same rate?

Ideally the information would be false, and the cheaper smaller battery will deliver the same BANG but for a shorter amount of time...


Please help!

Thanks - Great forum by the way.

 

[Anonymous]

.

 

[biohazardman]

The 10 AH battery pack will not discharge at the same amperage as the 20AH. Each cell has a maximum discharge rate. Going above the ratings will damage the batts. If you want to discharge at higher rates with Pings batteries you will need to get a pack with more batteries thus more AH. Unless you are using the Dewalt a123s or a couple of others that have a premium price tag, you will be somewhat limited on your discharge rates. Charge rates for most of these duct tape battery packs will usually be low also. Ping does have a good reputation around here for taking care of his customers from what I have read. Lots of info in the battery tech section.

 

[gerlewis]

so, if ive understood you both, the 20Ah battery will infact make the bike quicker as it will be discharging faster?

is it likely to discharge at the stated 20Amps or more like 40Amps? heres the spec:

"Rated Discharging Amperage: 20 Amps
Max Continuous Discharging Amperage: 40 Amps
Maximum Discharging Current: 60 Amps"

if 20 is the answer, then 20v x 20a = 400, so should I get a 400 watt motor instead of a 500 w motor?

Thanks again for the help so far!
Ger

 

[memy]

It will make very little diffrence to speed or torque as this is dependent on motor and controller.
Though you run the chance of the BMS tripping with a 30amp BMS limit IMO
If your motor is 500W nominal (about 20amps)then would expect to see peeks to at least 30amps, depending on controller. (on the edge of the capabilty of the 10amp pack and the BMS setting)

The cells in the 10amp batt will see 3C discharge as the BMS is set at 30AMPS. (This is MAX recomended cell rate for ping cells)
The 20amp hour Battery has the BMS set at 40amps so only 2c. The 20amp is a better deal, as you wont be abuseing the cells to the same extent.
The 10amp deal will allow a peak of 24V * 30AMP = 720watts though pulling 3c you should see some voltage sag.
The 20amp deal will allow 960W peak.

 

[gerlewis]

Thanks for that, they sell an in between 15Ah, which I might go for. best of both worlds, and not too BIG.

Thanks memy, a bit of that was over my head, but I will try and re-read it. (what is the 'C' in '3C'?)

Ger

 

[Velocipede]

24V 10Ah --- 1C = 10 amps, 2C = 20 amps

24V 20Ah --- 1C = 20 amps, 2C = 40 amps

If you pull more than 1C through a Ping regularly, you will diminish a lot it's life.
Yes, both battery will give you the same speed, but the 10Ah for less time. Also, since you will likely pull 20 amps out of a 10Ah battery, you will kill it fast.
Ping recommends 24V X 10A = 240Watts or 24V X 20A = 440Watts.

For your motor and controller (500W), the 24V 20Ah is the minimum.
Do you know that your speed will be quite slow with 24V? Top speed around 27kph.

If you have a way to limit amperage draw with your setup, I advise setting it to 1C, depending of the Ah of battery you get. You will limit your speed according to the capacity of your battery.

My suggestion is to get a 36V 20Ah. You will get about 37kph. No matter what voltage you choose, do not go under 15Ah if you want your battery to last and not die on you after a couple of months.

 

[memy]

C3 is regarding dischage rate of the cell.
The BMS on the 10Ah allows 3 times the cell capacity of the battery (pings MAX rateing on the current cells he is selling i belive).
The BMS on the 20Ah allows 2 times the cell capacity of the battery
The A123 cells are 60C (120C for below 10 sec peaks) For ebike use I'd tend to go capacity to get your discharge rate rather than a fantastic c rate.

So the 10amp pack will discharge at 30amps (for 20min in theory) without damage. You could probably do 40amps on the cells (if the BMS was not stoping the fun) but you would shorten the potential cycle life of the battery.
Hitting ping cells at C3 or C2 rates regularly will shorten its cycle life, maybe by even half but by then your sure to be on the upgrade path. :wink:

 

[gerlewis]

thanks again for the useful replies


"Do you know that your speed will be quite slow with 24V? Top speed around 27kph."

Well im going for a cyclone kit which this guy manages to reach 42kph on the flat without pedaling:
http://www.youtube.com/watch?v=KRDjbXTKSp4&feature=related


this is the kit im thinking of, but am not sure of the controller specs, it is internal:
http://www.eclipsebikes.com/chainwheel-watt-p-971.html
any advice on this setup?

"So the 10amp pack will discharge at 30amps (for 20min in theory) without damage. You could probably do 40amps on the cells (if the BMS was not stoping the fun) but you would shorten the potential cycle life of the battery.
Hitting ping cells at C3 or C2 rates regularly will shorten its cycle life, maybe by even half but by then your sure to be on the upgrade path."

so which battery would you recommend memy? - I have a 3-4mile commute.

Thanks again guys
Ger

 

[Anonymous]

.

 

[gerlewis]

I want to be able to go on a 7mile round trip on rare occasions, but mostly a 6mile round trip.
I want to go about 20mph, without pedaling on the flat. (so as not to get sweaty for work), and I want to be able to climb one big hill on the way home.

Ger

 

[Anonymous]

.

 

[dogman dan]

One thing about a cyclone or other system that pulls the chain is that you can put a tremendous strain on the battery if you are in too tall a gear and hit the throttle. Just like too tall a gear hurts your legs, it can hurt the battery. For this reason only, you should buy the bigger battery, that can deliver when you inevitably get in the wrong gear and start off. The huge amp spike you pull then will do more harm on the smaller batttery.

a 24v 20 ah ping is still a pretty small battery and very light.

A gearmotor like the fusin kit or a bafang would run good on a 48v 10 ah battery, which is the same number of cells.

 

[gerlewis]

Thanks for the info, I feel you have all educated me greatly!

Th only technical issue I have now with the cyclone, is moving the gear selector to the left hand of the handle bars will mean its upside down (I think).

Ger