Question about batteries

[iain85]

If I was to change from a 36v 20ah Bms battery to a 36v 10.8ah bottle battery would I be right in expecting just the loss to be decreased milage or are there torque/ speed implications?

Many thanks,

 

[103Alex1]

Unless it's a high discharge battery it likely won't be up to powering that motor.

 

[iain85]

bottle ebike battery

This was the one that I had in mind. So a high discharge allows compensates for lower ah?

 

[Deleted member 4366]

If you look at the data, it says, "Continuous discharge current 10A", "Maximum discharge current 20A". These are the two two things to look for, although the latter is normally twice the other, so if you have one, you know the other.

The highest discharge ones that are readily available at the moment are the 11.6AH ones with Panasonic NCR18650B cells. They can do 18 amps continuous and 40 amps max.

 

[iain85]

Thanks,
so to check the suitability am I right in thinking for any given motor the calculation would be.

continuous amps x voltage = suitable wattage motor?

Eg 18 amps x 36 v = 684w

So this would be suitable for a 500 watt motor? Where does the max amps feature? Is this where the torque calculation comes in ?

 

[Deleted member 4366]

All motors will take whatever current you give them. It's the controller that controls the current, so you need to know ts rating. Sometimes, it's written on it, but you might see 15A. which could mean its continuous rating or its maximum.

If there's no current marking on the controller, but instead it says 500W. That will be its continuous rating, so you'd need to double it to get the max, so a typical 500w one would be 1000/36 = 30 amps

 

[iain85]

Thanks il have a look in the garage at mine later.

1, So given your example, the minimum battery it should run on would be a 30 amp max discharge and 15 amp continuous?

2, If the battery is oversized, does the controller reduce the current to what ever is specified (ie 15amps)? So to up the speed/torque a larger controller is needed?

3, Also at what point does each motor reach its max current power input and how does one calculate this?

4, Is the Ah the duration of the supplied continuous charge and not linked the the max amp rating?

Thanks D8veh, il understand the logic behind electrics one day!

 

[Deleted member 4366]

1. Correct

2. The controller measures the current and uses software to limit it based on the measurements. It doesn't know or care what battery you have. If the battery can't supply the current that the controller demands, you get voltage sag and shortened life of the battery.

3.You can't calculate the maximum current of the motor. If you use a larger controller to get more current, you get more torque, but, if you go too far, the motor burns. How much current you want to give it is a judgement. Some people fill their motors with oil for better cooling so they can go a long way higher on the current, but then there's a danger of stripping the gears unless you have a gearless one.

4. The aH rating is a measure of how much energy is in the battery. To know how much current it can give, you need to know the "C" rating. You multiply the "C" rating times the aH to get the max continuous current. A 1C 10aH Li-ion battery can give 1 x 10 amps. A 5aH 25C Lipo cang give 125 amps. The latest cells from Sony, Panasonic ans Samsung are now up to 3C, while as the cheaper ones are 1C. Normal LiFePo4 cells are 1C, but you can get special ones like A123 and Headway that can go very high.

 

[iain85]

I'm getting there ( I think!)

1, The higher the voltage the lower required current to power the same controller/motor?

3, I have the 500w bafang rear drive motor. Do you have experiance of a faster controller on this motor? I believe it is gear less.

4, So my battery is this one 36V 20Ah LiFePO4 Electric Bicycle Battery Pack - BMSBATTERY
As far as I can see there is no 'c' rating so I'd assume it's a 1 C? So there lies the advantage of lipo batteries ( the c rating) ?

Every day is a school day, thanks for the help

 

[banbury frank]

Hi You dont have a 500 watt motor you have a 350 watt motor if you use a 36 volt battery you only have a 500 watt motor if you use a 48 volt battery and controller

Frank

 

[Deleted member 4366]

1. The controller is designed for a certain voltage. You're not supposed to run them with more or less. The motor doesn't care about voltage., but increasing the voltage pushes its efficient operation to a higher speed, so, if you go too slow, you can overheat a motor that was OK at that speed with a lower voltage. It's getting complicated isn't it?

3 Controllers don't affect maximum speed. To get a higher speed , you have to go to a higher voltage. The later KU123 controller had some jumper wires to change from 36v to 48v. Most 36v controllers can go to 12S lipos (44v), but will probably eventually die with a 48v battery. Your motor is geared, but it can take a lot more than what you're presently giving it.

4. Your battery is 1C, so 20 amps continuous and 40 amps max.

If you want more speed, you'll have to change the battery. A 48v one with your present controller(KU123?) will give 33% more torque and speed. You need a 15aH normal one or you could get one with Headway cells of a lower capacity if you don't need the range:
48V 9Ah 38120S LiFePO4 Battery 16 Cells EBike Battery Pack - BMSBATTERY
48V 10Ah 38120 LiFePO4 Battery 16 Cells EBike Battery Pack - BMSBATTERY
48V 12Ah 38140 LiFePO4 Battery 16 Cells EBike Battery Pack - BMSBATTERY

Don't forget to tick the 30 - 60A BMS.

Another advantage of lipos is that they go in steps of 4v instead of 12v.

 

[iain85]

1, Yes, Just when I thought I was getting there aswell.

3, Ok so I should be ok with my controller if I change the jumper wire to 48v

4, Ok, is there any inherit value in my 36v 20 ah battery? Only been charged about 10 times and bought in January this year? Should I bite the bullet and consider LiPos or will my head explode with the extra information required to install and charge them?

5, Frank why is my motor only 350 watts? My battery is 36v and 20 ah so 36 x 20 = 720 watts?

6, My head hurts

 

[103Alex1]

5, Frank why is my motor only 350 watts? My battery is 36v and 20 ah so 36 x 20 = 720 watts?

Iain, 36V x 20Ah = 720 Watt-hours (a battery capacity measure). This is different to the power (Watts) actually supplied to the motor at any given time, which is driven by the amps regulated by the controller and volts of the battery used to supply it as d8veh says.

Forget the notional motor rating thing - it's pretty meaningless. If you're using a KU123 controller with 36V battery (approx 30A max) then your existing battery will actually supply 1.2KW of power to the motor off a fresh charge no problem. I've seen that 36V battery/controller combo supply a continuous measured 1.1+kW for over a mile uphill off Cycle Analyst. So if you're looking at 48V setups running at 40A the idea is to get 1.5 - 2.5kW of power to the motor. Which you only need to haul very heavy riders uphill effortlessly without doing any exercise as per sitting on a scooter that looks like a bicycle.

Re :- 6) ... don't worry I thought mine would explode when all this started - and sometimes I still do !

 

[Deleted member 4366]

There's two power versions of the BPM: 350w and 500w (if you don't count the 350w one with a 250w stamping). The Power rating is stamped on them, and that's the nominal continuous power at which they can run day and night in all conditions without over-heating, provided that you run them in their efficient zone. It's output power too, which is much less than what comes out of the battery that we normally talk about.

 

[iain85]

Ok Thanks guys. I'm going to re-read this thread over a few days and see if it sinks in. My brain is not operating in its efficient zone and probably will soon need oil (beer) cooling to ensure it doesn't overheat due to running at max discharge rate : )

 

[banbury frank]

Hi Forget WH that is Battery Capacity ( Range ) nothing to do with watts ( motor power ) power is the volts off the battery a 36 volt battery runs at 40 volts a 48 volt battery runs at 50 volts it is then the power in AMPS that your controller will output less 20% in losses through the wiring and motor

so your controller at 40 volts is aprox 20 amps if that so 40X 20 = 800 watts less 20% = 640 watts PEAK

50 Volts with the same controller aprox 25 amps all the wiring and motor less loss in cables 50X 25 = 1250 less 20% 1,000 watts Peak

Then CUT those figures in half to give you normal running if you run at above figures you would BURN out things

SO 36 volts 320 watts nominal 48 volt 500 watts nominal




Thanks Frank

 

[103Alex1]

Frank, if he has KU123 controller it is 30A at 40V off 36V battery and not 20A. So on the basis of your calc methodology at 40 volts it is 40 x 30 = 1200 less 20% = 960W peak not 680W. I know these are the approximate input figures as I'm measuring straight off the CA shunt using that same controller and battery.

Which is near-as what your 48V will do at 25A.



The 'losses' mentioned are surely theoretical as I thought I read somewhere that you can't measure power output on these hub motors ?

 

[banbury frank]

Hi Alex your KU123 controller would burst into flames at 30 Amps The Track on the PCB would melt Under any continuos load

Been there done IT
As for the CA you can input The wrong Shunt value and the reading will be nonsense

Frank

 

[103Alex1]

Hi Alex your KU123 controller would burst into flames at 30 Amps The Track on the PCB would melt Under any continuos load

Been there done IT
As for the CA you can input The wrong Shunt value and the reading will be nonsense

Frank

Somehow I can't go with what you're saying Frank. Are you saying that the shunt value off a £120 Standalone Cycle Analyst is complete nonsense ? Why are they used on high end eBikes in US if their readings are nonsense ? I seem to recall you installing them on your own kits ?

I've watched my Cycle Analyst on that setup for 850 miles and observed over 1kW measured draws completely problem-free off the battery continuously up a mile-long 18% hill with no overheating and no problem with the controller or motor. These correlate to what you would expect doing the maths rather than speculation.

So I think you have your wires crossed somewhere.

 

[Deleted member 4366]

I've measured the current from lots of KU123s with lots of different ammeters/wattmeters. They all show a maximum battery current in the range 30 to 32 amps. I've seen one KU123 with melted tracks. There's lots of different versions. Some have the power tracks thickened with wire soldered on. Some have just a thick layer of solder. If they look a bit thin (solder thickness), I usually drizzle a bit more on to thicken them up for better current carrying capacity.

In use, you rarely see that sort of current. You have to be going fairly slowly at maximum throttle.