Motor, Controller, Battery matching

[camerart]

Hi,

Please make allowances for a hypothetical question:

I assume that if a 250W motor, and a 250W controller and a 250W battery are used to build a bike, this would be a matched kit. But if one of these three components is different, 'say' substitute a 500W motor or a 500W controller or 500W battery while keeping the other two components the same, this will be not matched, but what would be the consequences of each please?

Camerart.

 

[dogman dan]

Motors typically can take at least 3x their rated wattage. Sure, you can't climb pikes peak that way and expect the motor to stay cool, but typical riding is not so extreme.

So 250w motor can run on 750w with no big worries. The controller can be bigger, but not too much bigger. Run a 250w motor on 2000w, is asking for the motor to overheat, or break a gear, or something.

Controller matters less if the motor is too big. Why? Because a 250w controller with a 1000w motor will run at 250w. The big motor doesn't magically pull 1000w from a controller only able to run at 250w. However, a bad enough mis match can be hard on the controller. The big motor will pull the max amps for longer than a small motor. This can make it run hotter, and it may or may not take it. Likely it will take it for a while at least.

Best thing if you have a big motor, is to use a bigger controller. But then if you wish, limit the controller to 250w. Then it's a breeze for the controller to handle low wattage, when it's built for so much more.



The battery is mega important. You can very quickly kill a battery by running it at it's maximum possible amps all the time. I did some pretty significant damage to a ping battery in one afternoon. Ideally your battery is able to put out 500w, if your controller and motor will draw 250w. Better still if the battery can put out 3 or 4x your max watts or max amps.

Batteries are like a woman, You might treat her rough once in a while, but doing it all the time is trouble.

 

[camerart]

Hi Dan,

Thanks. So there's a fair bit of flexibility then, that's good.

I have 9X Turnigy 5.0 35-45 batteries. I'm going to series them up to 36V and parallel them X3. I'm waiting for connections etc, to make the pack, but I have enough stuff to try 3X singles. I didn't want to damage them for impatience sake. If I understand correctly this will allow me to have a little ride, till the first 3 run out then come back on a second 3

C.

 

[999zip999]

Can you just let us know what motor and controller we are talking about.

 

[camerart]

Can you just let us know what motor and controller we are talking about.

Hi 999,

We've already met on this thread: http://endless-sphere.com/forums/viewtopic.php?f=14&t=69778

So 15Amp controller.

C.

 

[Nobuo]

Usually you first think about the performance wanted as speed, acceleration, hill climbing capabilities, range... then what is the bike frame you are going to use and where do you want to install the motor.

So the common is first thinking about the motor: wattage, size, hub or middrive, front/rear. For the frame wanted.

Common motor ratings are 250W, 350W, 500W, 750W, 1000W, 1500W and 3000W.

Choosing the motor first and then the controller is the natural step.

Then the controller must fit in wattage (the rating is peak power). So a 1000W motor should be with a 1000W controller and that make sure you can climb anything and the motor won't overheat in any condition / ambience heat. As dogman dan said the controller peak power can be around 3x the motor rating, and will work usually smooth, just with some care considerations about the heat generated on long hills or on hot days.

Using a less rating controller than motor just must make you think if maybe a smaller, lighter and cheaper motor fit better on your build.

The battery power rating, usually measured just as amperage "max continuous amps" and "peak amps" must fit with the controller continuous and peak amps too. If the controller can push 20A continuously and your battery only 15A, You just are wasting capabilities on your build. If the battery ratting is higher than your controller, just perfect! than means more efficiency, healthy battery over the time, and more cycles to use.

A battery "overloaded" by the controller is not a problem if there is a BMS, because the battery rating is limited by (under safe ratings if the BMS is correctly configured or choosen). But if you are using a battery without a BMS and you take more than it should from the controller, you can destroy the battery cells in a very few uses.

 

[camerart]

Hi,

I'm glad I asked this question, early in my e-bike life, as these simple rules to work by will help me with the ideas I have.

It seems that the battery section is the area, that can be affected most. So in my case today, the batteries I'm using show 3s 5.0A 35-45C (X3=36V), and if I run my system to it's limit of 15A these batteries will be 3X over their 5.0Amp rating but from my understanding well below their C rating, so can I assume there should be no problem?

Thanks,

C.

 

[Nobuo]

I think you are confusing Ah (Amps-hour) with A (Amps)

Your batteries probably are 5.0Ah, that means they can push 5A during an hour (or 2.5A during 2 hours, or 10A during half an hour), it is a capacity rating

The C rating is the current rating. 1C = 1x cell Ah expressed in amps

If your cells are 5Ah and they are rated as 35C-45C that means they can push 35*5A to 45*5A continuously (just max capability not actually recommended)

so your battery are safe under your system power.

*the common rule is push your batteries below 1/3 of the max continuous C rating for efficient energy conversion

 

[camerart]

Hi Nobuo,

Yes, I do get A and AH mixed up sometimes.

Good! Sunny day, batteries charged, off for my first ride, TICK.

This is only temporary while I wait for connections to parallel X3 later.

Thanks, C.

 

[dogman dan]

Yep, you have your battery situation under control. Your 15 amps controller will be a breeze for your battery to handle.

I'm not sure what you have though. If you have 5 ah size packs, and will run them 3 in parallel, that will be 15 amp hours total.

Multiply that ah size by the C rate of the packs to get your max potential amps. For example, 15 amps x 20c = 300 amps!!!

However, the c rates of hobby batteries are wildly over stated. So a more practical number would be you can run 40 amps controllers on 10-15 ah of the 20c stuff, and get excellent results. If you have a higher c rate pack, then you can run even more amps on 10-15 ah of it.

 

[d8veh]

If you have lipo batteries, you don't have to worry about current. They can give more than whatever you'll need. Wattage ratings for motors and controllers are confusing. There's a lot of ifs and buts that come into whether they will be OK. The ratings (250w) are for continuously running at that power, so for a 250w controller that would be 250÷36 = 7 amps, but the controller will give a maximum of 14 or 1t amps. If you ran say a 328 rpm Q100 motor, it would be drawing that nearly all the time, so the controller would overheat, but if you had a 201 rpm, it would only draw that current when starting or going up a steep hill slowly. It could then cool down when you're up to speed and drawing less current. It's similar with a motor. With a hub-motor, the current drawn depends inversely on speed, so going fast is often better. What you can't do is have a setup where the motor can't reach its top speed because it's not got enough power.

In the ideal world, you have to consider the speed that you want to travel and select a motor that is rated at a power that's needed to reach that speed, bearing in mind how much power you want to add by pedalling, the hills that you need to climb and your weight. Next, choose a controller that's rated at that power and finally a battery that can give that amount of power.

 

[camerart]

Hi,

Plenty of useful information.

This was a hypothetical question, so that I have the basic information as a guide, to build on.

My first ride was great!

Thanks C.