# A question about voltage fall

Discussion in 'Electric Bicycles' started by Borromeo, May 4, 2009.

1. ### BorromeoNew Member

Dear people: I noticed that when I twist the throttle rapidly the 4-leds digital voltmeter indicates the voltage lows, even with full batteries. Before disassembly the batteries case I like to ask you about this.

I weld all the main connections from the battery to the controller and replaced that original weak fuse holder with a round one and a 15A tubular fuse.

I built a resistive load of 1.2 ohms with some Ralco resistances and I connect it at the output of the batteries case. The voltage is 38.4 V without load and 35.5 V with it. The intensity is 11.5 A.

Could be the internal resistance of batteries or any parasitic resistance of the key switch or fuse holder?

PD: They're CSB gel lead-acid, 3 x 12 V 12 AH
http://www.csb-battery.com/english/0...p?fid=4&pid=45

2. ### duivendykGuest

I can't make much sense from your measurements,what exactly did you do with this 1.2 Ohm load?,put it across the battery?.That implies a current draw of 38/1.2=32 Amps,not 11.5.Assuming that the current was really what I computed it implies a battery internal resistance of 2.9/32=0.090 Ohm which is reasonable.Advancing the throttle quickly can result in very high currents being drawn with most controllers.The controller is basically a speed control not a torque control like the throttle of a IC engine..So it commands the motor to get up to speed as quickly as possible,resulting in high currents.Rapid accelleration is quite wasteful (low motor efficiency).I'm surprised your fuse does not blow,but not that the voltage drops.

Last edited by a moderator: May 4, 2009
3. ### BorromeoNew Member

38.4 V / 11.5 A = 3.39 ohms and the load has 1.2, so there are (3.39 - 1.2) = 2.19 ohms in the circuit somewhere ...