20A 48V controller/battery on a 36V 500W motor?

[alan0048]

I got myself a kt36/48svprd-hrd01, 36/48V 20A max controller and a 36V 500W rear motor hub (with shimano gears).

As I want to increase range I'm thinking about upgrading from 36V/15Ah to 48V/25Ah. Would it work, or is the controller too powerful for my 500W motor that is rated for 36V? I'm mostly worried about uphill and so on where the load increases. I don't want to accidentally burn the motor while riding my bike one day.

If so, would it be better to downgrade to a 17A 350W KT controller but running it at 48V? Or can my 500W/36V handle 20A/48V?
As long as I reach a minimum 20mph (~32km/h) I'm happy, I'm mostly interested in range rather than top speed.

48*17 = 816W (17A KT controller 350W)
36*20 = 720W (currently have)
48*20 = 960W (same but at 48V)

 

[E-HP]

I got myself a kt36/48svprd-hrd01, 36/48V 20A max controller and a 36V 500W geared motor hub (shimano).

As I want to increase range I'm thinking about upgrading from 36V/15Ah to 48V/25Ah. Would it work, or is the controller too powerful for my 500W motor that is rated for 36V? I'm mostly worried about uphill and so on where the load increases. I don't want to accidentally burn the motor while riding my bike one day.

If so, would it be better to downgrade to a 17A 350W KT controller but running it at 48V? Or can my 500W/36V handle 20A/48V?
As long as I reach a minimum 20mph (~32km/h) I'm happy, I'm mostly interested in range rather than top speed.

48*17 = 816W (17A KT controller 350W)
36*20 = 720W (currently have)
48*20 = 960W (same but at 48V)

If you are going to be riding at the same speed, then there won't be any issues, since you'll be using partial throttle, with effectively the same voltage and current flowing to the motor from the controller.

You can use the Grin simulator to see how the relationships work. In this case, using a Bafang G60 500W motor for the example, you can see how the two compare.

With both at full throttle, the 48V will go faster, have greater torque at higher speeds, and have some differences in other performance parameters:

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

With the same two setups, but running the 48V system at the same speed as the 36V (48V at partial throttle), you can see the other parameters become identical, except for more than double the range between 36V/15Ah and 48V/25Ah and greater torque at higher speeds.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

 

[AGS]

You don’t need to buy a new controller if you want to run it at less than 20 amps

The KT controller C5 parameter has 11 settings and you can reduce your controller output to limit the current to as low as 10 amps

C5 level 10 is maximum current, so that will be 20 amps and each level down reduces it a bit until 3 where it is reduced by half to 10 amps.

0, 1 and 2 are for soft start but maximum current.

 

[alan0048]

If you are going to be riding at the same speed

Thanks for the simulation! Limiting the speed 70% when going from 36V/15Ah to 48V/25Ah seemed to reach an equilibrium.

Range (100%, 70%)

44 km

107 km

Mtr Power (100%, 70%)

306W

281W

My kt36/48svprd-hrd01 controller has a speed limited wire (White wire) that will decrease the speed by 30%. So that would almost mean a perfect matchup.

The only worry for me has been, that speed limitation and current limitation are two different things? When it gets windy, or going uphill the motor will pull all the current that a controller can feed? Meaning all 20A despite going slow right? So even if I only do partial throttling, like pedal assitance I would end up with the first graph that showed the difference when both are at 100%

Load (both 100%)

317W

615W

Or am I wrong? Would the speed limited wire also control the current in some way? Or do I need another LCD display that has current limiter mode to always prevent pushing the limit?

 

[alan0048]

You don’t need to buy a new controller if you want to run it at less than 20 amps

The KT controller C5 parameter

I bought the cheapest one available on Aliexpress, KT-LED890 display that has no C5 parameter. But thanks for the info! I was unaware that the KT brand controllers/displays had the current limiter. I've only seen it mentioned on Bafang brand when I was ordering.

So, keeping the controller but changing the LCD display to another which has current limiter paramter is also an option. Good to know!

So as it stands.
Option 1. New LCD Display / Current limiter.
Option 2: Keep everything, If the in-built speed limiter wire (30% decrease) also works in similar way with limiting current?

 

[E-HP]

Thanks for the simulation! Limiting the speed 70% when going from 36V/15Ah to 48V/25Ah seemed to reach an equilibrium.

Range (100%, 70%)

44 km

107 km

Mtr Power (100%, 70%)

306W

281W

My kt36/48svprd-hrd01 controller has a speed limited wire (White wire) that will decrease the speed by 30%. So that would almost mean a perfect matchup.

The only worry for me has been, that speed limitation and current limitation are two different things? When it gets windy, or going uphill the motor will pull all the current that a controller can feed? Meaning all 20A despite going slow right? So even if I only do partial throttling, like pedal assitance I would end up with the first graph that showed the difference when both are at 100%

Load (both 100%)

317W

615W

Or am I wrong? Would the speed limited wire also control the current in some way? Or do I need another LCD controller that has current limiter mode?

Not sure what you mean by how they perform on a hill, but the principles are exactly the same if both motors are subject to the same load. Here's the simulation with a 6% hill for both systems, and the 48V system running at partial throttle to match the 36V system speed on the grade:

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

I'm still not sure why you need to limit current, unless you're doing for legal purposes.

 

[AGS]

The display that you purchased is no good. It won’t allow you to set up any of the parameters for the controller. The only way it will work is by making a link cable and copying the parameters from another KT display.

 

[fill]

Without a lcd display to configure the controller you not getting the best from your controller. Some(all?) the ktylcd displays also have a programming transfer capacity where a configuration can be transferred to a compatible display so you dont need to set everything 2x, or can use a less high profile display perhaps? Could be your simple led display is compatible, (i only browsed over that area of the manual as it wasnt relevant to my setup at the time. )

 

[AGS]

The led display is compatible with the controller, but the only way to get it to work is to configure it from another KT controller that has all of the correct settings.

 

[E-HP]

I don't want to accidentally burn the motor while riding my bike one day.

What do you mean by "burn the motor"? Overheat?

 

[alan0048]

What do you mean by "burn the motor"? Overheat?

Yeah exactly, pushing beyond the rating of the motor when going on hills or slopes at 48V (as its rated for 36V). Simulation shows 48V 70% throttle limit would be equal to 36V at 100% throttle in terms of motor power. But I'm was unsure about when it really pushes the motor if it would overheat or not.

 

[E-HP]

Yeah exactly, pushing beyond the rating of the motor when going on higher grades/hills at 48V (as its rated for 36V). Simulation shows 70% speed limit would be equal to 36V at 100% throttle in terms of motor power. But I'm was unsure about when it really pushes the motor if it would overheat or not.

That what the simulation is for. Your motor can overheat on 36V on the same hill, but probably faster if it nears stall speed, and not able to keep the speed in the higher efficiency range. Overheating a motor is totally in the rider's control, unless you install a temp sensor and a controller that will allow it to automatically reduce current when the temps rise, or if you monitor the temp to allow you to back down the throttle.
Absent monitoring the motor temp, the rider and the controller have no way of protecting the motor from overheating. Other than that, there's not much else that can protect to motor from the rider. Without temp data, the best thing you can do is keep the speed up above 15mph or so and cross your fingers, since it's not the power that overheats the motor, but the portion that gets converted to heat, and that portion is greater as the speed decreases. For climbing, slow speed kills.

 

[E-HP]

Yeah exactly, pushing beyond the rating of the motor when going on hills or slopes at 48V (as its rated for 36V).

Motors aren't rated for voltage, the are rated for power. You can run any voltage, as long as you keep the watts within the rating. They label voltage on motors since there's an assumption or speed "ratings" associated with running at a certain voltage (based on the motor kv). What matters for the motor is how many watts are being consumed and the efficiency at the speed it is turning. That in turn determines how much power is being converted to heat. If the efficiency is such that it can't shed the excess heat fast enough, the motor melts down. The best you can do, running at any voltage, is the keep the motor at a speed that's efficient, then let the motor stop to rest if you can't maintain a speed in that range.

 

[alan0048]

Motors aren't rated for voltage, the are rated for power. You can run any voltage, as long as you keep the watts within the rating. They label voltage on motors since there's an assumption or speed "ratings" associated with running at a certain voltage (based on the motor kv). What matters for the motor is how many watts are being consumed and the efficiency at the speed it is turning. That in turn determines how much power is being converted to heat. If the efficiency is such that it can't shed the excess heat fast enough, the motor melts down. The best you can do, running at any voltage, is the keep the motor at a speed that's efficient, then let the motor stop to rest if you can't maintain a speed in that range.

Seems I have no other choice than swapping the lcd display for one with a current limiter. As the graph showed by the first reply, the top speed for 36V and 48V are identical when the throttle limit is set to ~70%. However, from 9mph <-->16mph we're seeing power draw of upto 700W. Whereas the 36V only ever reaches 540W of motor power.

Motor simulation 70% throttle

If I want both motor power curves for 36V and 48V to be the same, through simulation the closest I would get is probably
36V/20A equals to 48V/15A. Both able to reach close to 20mph. So If I want to keep my controller when swapping to a 48V battery, I need to current limit everything to 15A.

36V/20A 100% compared to 48V/15A 70%

Thanks everyone for their input!

 

[E-HP]

Seems I have no other choice than swapping the lcd display for one with a current limiter. As the graph showed by the first user, the top speed for 36V and 48V are identical when the throttle limit is set to ~70%. However, from 9mph <-->16mph we're seeing power draw of upto 700W. Whereas the 36V only ever reaches 540W of motor power.

Motor simulation 70% throttle

Perhaps you need to read the info on the simulator page to understand how to model the parameters that you want to test. The numbers are exactly the same.

Here's the simulation with both systems running at 12mph:

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

 

[AGS]

I see you have done a simulation for a Bafang G060. Is that your motor?

I thought you said it was a Shimano reading your first post, although I wasn’t aware they built hub motors.

If you are running a G060 then it is capable of being run way above 500 watts. Bafang specifations are written to satisfy legal requirements for different markets and bear no resemblance to what the motor can actually be safely run at.

 

[E-HP]

I see you have done a simulation for a Bafang G060. Is that your motor?

I thought you said it was a Shimano reading your first post, although I wasn’t aware they built hub motors.

If you are running a G060 then it is capable of being run way above 500 watts. Bafang specifations are written to satisfy legal requirements for different markets and bear no resemblance to what the motor can actually be safely run at.

I did the initial simulation for illustrative purposes to show the relationships between motor speed, efficiency, load, etc. at both voltages, and the G060 to have a similar power level as the OP's motor.

 

[alan0048]

I see you have done a simulation for a Bafang G060. Is that your motor?

I thought you said it was a Shimano reading your first post, although I wasn’t aware they built hub motors.

If you are running a G060 then it is capable of being run way above 500 watts. Bafang specifations are written to satisfy legal requirements for different markets and bear no resemblance to what the motor can actually be safely run at.

The brand itself is unknown. Came with a Samebike foldable ebike 36V15Ah. But I changed the original controller for a KT brand. There is no info about the motor other than the Wattage rating and that it has Shimano gear shifter so that's why I mentioned it. I took E-HP simulation as a guideline, thought it probably would be the same.

Thanks anyways. If I need to limit the current in order to get the same power curve for the motor then I need to find another LCD display. Still unsure If i need that, or simply lower the throttle speed to 70% since I'm apparently not reading the simulations right haha.

 

[AGS]

Yep, if it is this motor then you have done the simulations for the wrong motor.

SAMEBIKE MOTOR

Original motor for Samebike Electric Bikes. Package included:1 xMotor Free Shipping:

www.samebikes.co.uk

 

[E-HP]

The brand itself is unknown. Came with a Samebike foldable ebike 36V15Ah. But I changed the original controller for a KT brand. There is no info about the motor other than the Wattage rating and that it has Shimano gear shifter so that's why I mentioned it. I took E-HP simulation as a guideline, thought it probably would be the same.

Thanks anyways. If I need to limit the current in order to get the same power curve for the motor then I need to find another LCD display. Still unsure If i need that, or simply lower the throttle speed to 70% since I'm apparently not reading the simulations right haha.

You can modify your throttle to set a max output to match 36V at full throttle. At that point, it will work like a 36V system, even with a 48V battery attached. The throttle determines what voltage (and therefore power) that the motor sees, and ~36V at full throttle for a 36V system. You can adjust the max throttle for the 48V system down so the max voltage to the motor is 36V.

Guide to Hall Sensor Throttle operation, testing, and modification. - Electricbike.com Ebike Forum

***** 8-16-2018 Welcome to the Hall Sensor Throttle Thread! If there is something you'd like to add, correct, needs better explanation, or have a question about... feel free to Private Message me. Better yet, open a new thread in the "Trouble Shooting...

electricbike.com

Only takes a couple of resistors/potentiometers and you're done. Plus you can adjust upwards when you want more speed or power.

 

[alan0048]

You can modify your throttle to set a max output to match 36V at full throttle. At that point, it will work like a 36V system, even with a 48V battery attached. The throttle determines what voltage (and therefore power) that the motor sees, and ~36V at full throttle for a 36V system. You can adjust the max throttle for the 48V system down so the max voltage to the motor is 36V.

Guide to Hall Sensor Throttle operation, testing, and modification. - Electricbike.com Ebike Forum

***** 8-16-2018 Welcome to the Hall Sensor Throttle Thread! If there is something you'd like to add, correct, needs better explanation, or have a question about... feel free to Private Message me. Better yet, open a new thread in the "Trouble Shooting...

electricbike.com

Only takes a couple of resistors/potentiometers and you're done. Plus you can adjust upwards when you want more speed or power.

The controller itself has a 30% decrease wire, so I was thinking of just connecting that along with a 48V battery. That way I get the 70% throttle limit.

Speed limiter, last picture.

Well. Let's just say my motor performs similar to a Bafang G60. Are you telling me I wouldn't have to bother with current limiting? Downhill, upphill. High slope, low slope, no slope no nothing. Business as regular, just 70% cap on the throttle to go from 36V to 48V on a 500W/36V motor with 20A controller?

 

[E-HP]

Well. Let's just say my motor performs similar to a Bafang G60. Are you telling me I wouldn't have to bother with current limiting? Downhill, upphill. High slope, low slope, no slope no nothing. Business as regular, just 70% cap on the throttle to go from 36V to 48V on a 500W/36V motor with 20A controller?

No, I'm saying a static current limit is not a solution for keeping motor from overheating. Only some sort of temp monitoring and ideally automatic rollback and shutdown, can help protect the motor from the rider. The 500W rating of your motor is based on a lot of assumptions, one being the motor is spinning. It can't take 500W when stalled or it will burn up. Whether 36V or 48V, you can fry the motor easily if you run it too slowly and efficiency goes to zero when stalled, when all 500W goes to heat.

You're trying to limit motor heat by controlling current without knowing how hot the motor is. Sort of like you're driving your car up a mountain pass during a heatwave, with a broken temperature gauge...and you should have turned off the AC two miles ago if you had known the engine temp, you or your system needs that information.

If I were in the same situation, and concerned about hills, I'd start by run at 48V, and invest $20 and an afternoon adding a temp sensor to your motor. That way you not only have peace of mind, but an ability to adjust or stop if needed. Or, just run 48V and stick with the cross your fingers approach that you're currently using (I'd probably go that route when weighing the hassle vs. increased risk, and I'd only ride a geared hub on moderate hills anyway).

If you want to give it a go, then maybe something like this for the gauge (needs a 5V source):

https://www.amazon.com/Thermometer-Temperature-Refrigerator-Humidifier-Accessories/dp/B0CVX4RG84/ref=sr_1_8?dib=eyJ2IjoiMSJ9.6C1bYIxvE12n90oNzVMIv0kRc-uuiUT2BIBktc8h9SxgnIWQzICPPoW7zeifBSTDdjOIH1el57_FVd7xDijjc8RRMJ2uQxFuChWiunustYULZBdBd8V9VEIjWIagbbly.sMiKNUT3W0V3HjQtv3DViYNdCaCZ-69dG8kAWG2H5VU&dib_tag=se&keywords=NTC%2B10K%2Btemperature%2Bmeter&qid=1712184235&s=home-garden&sr=1-8&th=1

But use a smaller sensor like this (since the meter accepts NTC 10k):

https://www.amazon.com/gp/product/B074JBZ63Z/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

One thing nice about having a temp sensor, is that you can optimize your climbing speed to maximize your climbing distance, and even control the motor temp by modulating the throttle, especially during times when you don't need to be applying power, like when cresting a hill, etc. If you have a lot of hills, you'll quickly learn how to optimize your throttle technique to minimize temps.

 

[E-HP]

Can you post a pic of your hub motor, plus one of any markings on it? I assume when you say Shimano gears, you mean the cassette or freewheel. I'm also assuming that it's a geared hub, since that's what more 500W motors seem to be. With more info, you may be able to get a better match on the simulator.

EDIT: never mind. I'm looking at the one linked above.

 

[alan0048]

Can you post a pic of your hub motor, plus one of any markings on it? I assume when you say Shimano gears, you mean the cassette or freewheel. I'm also assuming that it's a geared hub, since that's what more 500W motors seem to be. With more info, you may be able to get a better match on the simulator.

EDIT: never mind. I'm looking at the one linked above.

I previously read the simulation curve wrong. You're not suppose to just move the cursor left and right. To see how much power is drawn at each velocity just click (auto) and then select the speed. After that +/- grade and same thing check each velocity. I watched the youtube tutorials so now I understand better what the previous posts showed me.

Also updated the simulator.
26" Wheel, Fatbike Upright, 100kg (220)lb.
I still used Bafang G60 500W with the simulator, but I suspect it won't differ very much.

70% throttle limit (or 30% speed decline using limiter pin), and be wary of the speed in slopes should do the trick (mtr power ramps up kinda fast near 12mph above 6% slope). I would always use pedal assistance either way when I'm not on a flat road, so that's also gonna help. No need really for current limit although If I were to change LCD display I'll add that because it can always serve as another security feature.

The hub is all black, no markings just ''500W 36V'' 9-pin output. Hydraulic brakes back and front. 7-Speed shimano.