Powabyke x6, brushed motor: Is the low voltage protection set too high?

[jackhandy]

Good evening all,

I've asked about this before but, now that I've got a Data Logger I can show you why I think the low voltage protection may be cutting the power too soon:

This video was taken on a steep ill, 8 miles out, with the standard (4.5 or 6 ah) battery on the bike:
Note that, as the power draw rises, power cuts off at <500 watts with battery voltage seemingly >33 volts: Unless there's a sudden dip that's not showing on the meter, this would seem to be about 3 volts higher than necessary to prevent battery stress?
[video=youtube_share;Q6oIzmg0gkE]

If it seems to you, who have far more experience of such matters, that I've got hold of the proper end of the stick this time, can anyone suggest a way of rectifying the problem? If necessary, would I be able to get a suitable replacement controller?

I'm fairly sure it's not the BMS, as I bought one of Cyclezee's 10ah flatpack batteries & that, while going further than the standard battery, cuts out if I try reascending the other side of the ridge, at about 12 miles.

You'll have to excuse the view of my backside.

I haven't tried the bigger battery on the "data logger" setup yet, as I can only manage that particular pair of hills once in any day!

 

[rog_london]

If you're running a fairly small battery at 416 watts, 33.5 volts you might be hitting a current limit built in to either the controller or the battery BMS rather than anything to do with battery voltage. If the controller is responsible it would cut out no matter what the size of the battery might be.

Also, where exactly is the data logger connected? If you're picking up the voltage reading at the battery rather than at the controller you might be getting a lower voltage at the controller due to voltage drop along the cable between the battery and the controller. With more than 12 amps flowing you'd only need around 0.25 ohms cable or connector resistance to shed around three volts.

Rog.

 

[Deleted member 4366]

On bikes with generic controllers that I've ridden, when the LVC trips, the power normally stays off, so you have to switch off and on to get going again, but when the BMS over-current trips, it allows power again as soon as the current reduces. Maybe you controller has a strange way of dealing with it's maximun current.

500w at 33v is over 15 amps. Do you know the current limit of your BMS?

 

[jackhandy]

@rog.
The meter is @ the battery, with 50cm cables in & out + the bike's cable, so could well be causing some voltage drop.
I was only taking the wattage into account when I sized the cable, so will try some heavier guage twin core and try again.

I got readings of over 17amps earlier on the route (it's a stinker of a route that I use to really put the bikes through their paces) but seem to have problems on that particular hill, when the battery's getting a bit tired.

 

[jackhandy]

Hi d8veh,

The only information I have is the controller label, which is in chinese but the numbers are:

36v : 18a : 31v : 1+1. I've no idea what the 1+1 refers to, but I assume the 31v is the low-volt cutoff?

There's nothing at all on the battery but it's the standard 6ah Powabyke bottle one which, I am told, may well be only 4.5ah.

I tried the 9ah bottle battery from my 8fun kit on this bike & it cut out at pretty well the same point on the same hill: It's ratede at 9ah : 15a continuous : 18a pulse (10 minutes). I've never had it cut out on the bike with the 8fun kit fitted.

I intend to try both the powabyke & ezee batteries on the 8fun bike with the meter, now that I have an adaptor lead for them.

It's just frustrating to have power cutting off when I've only used 3ah of grunt!

Thanks again for your interest.

 

[Deleted member 4366]

Strange that you've just reported this problem because I experienced the same thing today on a bike with a bottle battery.

Early in the journey I could use as much power as I wanted, but after 34 miles, and down to my last bar on the meter it was cutting and resetting at 350w. Then, after another couple of miles up a relatively steep hill, it was cutting at about 250w.

So maybe it is the LVC that's tripping, but according to the instructions, the last bar should flash before the battery's empty, and there was no sign of the battery sagging. I'd be more worried if it dis it when the battery was full

 

[jackhandy]

When my 8fun battery is down to 1 led, it will start flashing if I carry on making it work hard - On one very long slog it goes from 2 leds to 1 flashing & recovers to 2, may happen several times before I get home; but it has never cut out on me.

This powabyke of my missus' just cuts out, no warning, then goes on again if I go easy on the throttle. She doesn't intend to tackle any major hills on it, so perhaps it's just something to be lived with.

It would be interesting to know if other x6 owners have the same issue?

 

[seumas]

Hi, I have an X24 MK2, sounds like the same controller and battery. I have experienced some infrequent ( a couple of times in a few months worth of riding ) cutouts on that bike, what model of wattmeter are you using?

Do you notice significant increases in range with the 8fun or Ezee batteries?

I can get over 8 miles out of the Powabyke battery if I take it easy, although I am about 95kg. Did you just cut the battery cable coming from the standard controller and put a new socket on it for the other batteries?

 

[jackhandy]

Hi Seumas,

The meter is this one on ebay - took a couple of weeks to come from HK:
60V 100A Battery Analyzer Checker Balancer Voltage Power Watt Meter Servo Test | eBay

The camera is an act20 action camera, but anything will do, including a phone

It looks like 8-10 miles is about it for these batteries, but my wife's only shows as having used 3 ah when it starts cutting out

My 8fun 9ah bottle battery shows no significant improvement over the powabyke battery, but the 10ah flatpack battery from cyclezee definitely goes further: It'll surge up the hill that causes the problem, another couple of miles and halfway up the next major hill. I'm still not convinced that is all it's capable of but, until I checkit out on the bike, with the meter & camera, I won't know for sure.

In a previous incarnation I used to be an amateur sound engineer, for various local amdram, so I have a box of XLR plugs & sockets, which is what's used on the powabyke; so I made-up an adaptor cable for each of the other batteries.

 

[Old_Dave]

Rather than swapping meter connections about.. I'd just use 3 leds (with suitable resistors and one zenner), one on the battery with the zenner (33v ish), one on the bms output / controller input and the last one on the controller output.

Depending on what's lit and what's not lit at the time of the fault condition the exact answer will be known in a flash

 

[rog_london]

@rog.
The meter is @ the battery, with 50cm cables in & out + the bike's cable, so could well be causing some voltage drop.
I was only taking the wattage into account when I sized the cable, so will try some heavier guage twin core and try again.

I got readings of over 17amps earlier on the route (it's a stinker of a route that I use to really put the bikes through their paces) but seem to have problems on that particular hill, when the battery's getting a bit tired.

Measuring the current draw on an ebike can be problematic because of the large currents involved and the relatively low supply voltage - if you have cables running from the battery to the controller via your logger that can represent a significant resistance since it only needs a very small resistance to lose several volts and cause the controller to cut off. The logger itself is also likely to present a small resistance since current measurement usually works by measuring the voltage drop across a very low value but accurately calibrated shunt resistor.

There is a way of doing it without causing voltage drop. It's possible to use a Hall effect current sensing device clamped around the battery-to-controller cable which works by sensing the magnetic field around the cable. I doubt this option would be available to you though.

On your controller label, could it say '31v -1 +1'? In other words, cut off at 31v plus or minus one volt, being the calibration tolerance of the controller. That would be a classic case of 'report what you see, not what you THINK you see!'

Rog.

 

[NRG]

I agree with Rog, if you've not made the connections well (what have you used?) IE: not soldered them or are using low current cable then you can get quite a noticeable voltage drop. However, I doubt its the shunt in the Watt meter, typically the shunt will be 5 milliohms or so and drop 0.075v @ 15amps...

 

[jackhandy]

On your controller label, could it say '31v -1 +1'? In other words, cut off at 31v plus or minus one volt, being the calibration tolerance of the controller. That would be a classic case of 'report what you see, not what you THINK you see!'

Rog.

Nope... but there is a space before the 1, so it's possible. Anyone read Chinese?

 

[jackhandy]

Funny thing... I put the powabyke battery on my 8fun euipped bike today & covered about 17 miles of more sensible terrain - a couple of short slopes & a mile-long drag - before the 8fun controller Low led was flashing consistently: Checked the video &, just before I stopped, the meter was reading 30v (+ or - 0.5v) and 4ah used, which is pretty much what I would expect from a 2-year-old battery that could well only have 4.5ah capacity from new.

Couldn't read the rest of the meter readout for crud - Must improve the weather protection, or only use it in the drieth.