# Electric Bike COntroller

Discussion in 'General Electronics Discussion' started by rajat, Aug 27, 2012.

1. ### rajat

16
0
Jun 3, 2012
Dear All,

Subject : Selection of Controller

I have 24 v 500 watt battery. I am looking for a controller that can suit it.

Will 24 v 350 watt controller be good ?

How do I decide what controller I need for 24 v 500 watt battery. Is there any good website that can give me guidance on selection of controller

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,852
Jan 21, 2010
Is your battery 500Wh? A rating in watts for a battery makes little sense.

To answer this properly the rating of the motor (which will be in watts) is almost essential.

3. ### rajat

16
0
Jun 3, 2012
Apologies !

Battery is 24 volt 8000 mAh
Motor is 24 volt 500 watt
Controller is 24 volt 350 watt.

The question is if my motor is 24 volt 500 watt and controller is 350 watt... can I use this controller ?

4. ### Harald KappModeratorModerator

12,454
2,984
Nov 17, 2011
You shouldn't. It lacks 150W and will probably burn out from the motor's load.

A 500W motor will draw ~21 A at 24 V. An 8 Ah battery will be drained in 0.4 h, that's 24 minutes of driving. And assuming the battery is in very good condition. With time the capacity of the battery will diminish and you'll have to recharge even sooner.

In my opinion either the battery is too weak or the motor too powerful.

5. ### rajat

16
0
Jun 3, 2012
Thanks Harald. I really appreciate your time and effort.

Understanding the way you derive the values:

To caluclate Volts:
I = P/V = 500/24 = 20.8333 = 21 amp (is this 21 amp-sec or 21 amp-hour) ?

How do calculate Time (i.e. drain time in 0.4 hours) ?

Please can someone explain me how is time derived ?

I am naive in electronics and any suggestion will help.

Many thanks

6. ### BobK

7,682
1,689
Jan 5, 2010
If a battery is rated at 8 AH that means the the product of the current and time to drain the battery will be 8. So if you draw 21A what time will you have to multiply by to get 8?

t * I = 8
t * 21 = 8
t = 8 / 21 = 0.38

Bob

7. ### rajat

16
0
Jun 3, 2012
Thanks Bob really appreciated.