Voltage sag monitoring

[patpatbut]

Hi all,

I have finally finished my build using Bafang CST 36 250w (205 rpm on 26inch version) on my hybrid bike (700c) and it runs around 18mph with pedalling.

The problem I am having now is occasionally there is a voltage sag (lose power for like half sec)

I am not sure if it is the PAS (12 magnets one from BMSB) causing it or something else so does anyone know what is the best way to check if there is the voltage sag?

I have the watt meter (from hobby king) and I will link it up with my bike. Would I be able to see if there is a voltage sag?

Thanks
Pat

 

[Geebee]

My guess is that its the battery/BMS it is probably close to its limit, My Tonaro does something similar but when run off a high current battery no issues.
I don't worry about it as it is momentary and occasional.

The other thing you could check is the brake cutouts, if they are high off try unplugging one at a time and test riding

 

[Alan Quay]

Hi all,

I have finally finished my build using Bafang CST 36 250w (205 rpm on 26inch version) on my hybrid bike (700c) and it runs around 18mph with pedalling.

The problem I am having now is occasionally there is a voltage sag (lose power for like half sec)

I am not sure if it is the PAS (12 magnets one from BMSB) causing it or something else so does anyone know what is the best way to check if there is the voltage sag?

I have the watt meter (from hobby king) and I will link it up with my bike. Would I be able to see if there is a voltage sag?

Thanks
Pat

Yes, watt meter will record Vm, which will give you the lowest voltage. Just be aware that if the BMS is cutting the battery output, then the watt meter will have reset, so Vm will not be valid.

 

[Deleted member 4366]

Which CST do you have? Is it the new SWX size, or the original BPM size?
How many amps is your controller set to?
What controller do you have?
What battery do you have?

 

[patpatbut]

I am using BPM size one cst using s06s controller so 15 amps I think. The battery is 36v 12ah liftpo4 battery from BMSbattery it should be capable to draw 2C and 3C max.

The power does not cut off completely and I can't see anything change on the LCD. Also I am using the HWBS and I doubt it is the cause.

Pat

 

[Deleted member 4366]

Have you got a different controller to try?

 

[patpatbut]

Yes ku65 but I do not want swap it until this is the last resort. Will I be able to see on watt meter If there is a voltage sage?

Pat

 

[Deleted member 4366]

The only reason I ask is because a few people have mentioned cut-outs on S-series controllers, so it would be nice to eliminate the controller; however, the other ones stayed off until re-booted. I've only seen one go off and on. It was when I was testing a battery. The battery was knackered and sagged a lot so that it it kept sagging to LVC, the controller would cut, the battery would then recover, and the controller would then give power again. Once it had reached that point, the going on and off only got worse.

If you have a LED or LCD control panel, it'll switch off and stay off if there's any interruption of power from the battery like a bad connection or BMS tripping, so your problem must be either in the controller, it's sensors or the motor.

 

[patpatbut]

Thanks Dave

I migrated the s06s from my 26 swxh motor to this motor. I did no remember there is a voltage sage.

The main difference i feel that the bafang cst draws a lot more power than swxh ( the battery level bar drops in 5 miles instead of 10)

If I can monitor the watt carefully would I be able to see what the problem?

Pat

 

[Deleted member 4366]

You need to be able to see the volts in real time. You can use a voltmeter or wattmeter. The meter in the S06s has some sort of damping in it, so it won't show what's happening. You can go into the advanced settings, make a note of the P5 setting, then change it to zero. The battery display will then go up and down in real-time like a voltmeter.

 

[patpatbut]

Thanks Dave, Let me try the P5 setting to see what happen then.

Pat