Controller Downgrade but same Performance...Why?

ClintBX

1 kW
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Mar 6, 2014
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Hi ESFMs,

I'm trying out different controllers lately and recently, I tested out what should be a downgrade from my previous controller.

My previous controller is a 12 fet, 30 amp max with a 17 amp continuous rating.

This new controller is a 9 fet, rated at 12 amps continuous with a max of 25 amps.

I was expecting a power cut but instead, its performing at about the same top speed (45 kph) and acceleration. In fact, I sometimes wonder if it doesn't have a little more.

The only real tangible difference is the take off. If I throttle from a dead stop (and I usually try not to) it struggles a little more.

I also noticed that the discharge rate is pretty much identical. I would have thought that being rated lower than my bigger controller, I would be saving energy too. I guess it doesn't work like that.

Can someone explain to me the impact of different amp draws and also shed some light on why I'm not experiencing a significant change in performance? Is a 5 amp drop too small a change for any noticeable difference?

Clinton
 
Easy, your top speed is likely drawing only 20- 22 amps, at 48v. This is typical for about 28 mph. So both controllers can do that. Both can supply what the motor draws at 45kph, about 950w.

Take off is slower on the 25 amps, as you said. That is your main difference.

Drop to a 15 amps controller, and you will see a speed limiting effect. Assuming 48v, then a 15 amps controller can only put out about 650w, and top speed will drop about 3-4 mph, because now your total wattage is not enough to push the air out of the way to go 28 mph.
 
You'd need to measure with a wattmeter to confirm the actual current. You can't aways go by what's written on the label
 
Also true. a "25 amps controller" might actually do 30, and a 30 amps controller might actually do 25.

But you did notice a slower acceleration, so one is more amps, but both can hit your max speed for the volts you run.
 
dogman dan said:
Easy, your top speed is likely drawing only 20- 22 amps, at 48v. This is typical for about 28 mph. So both controllers can do that. Both can supply what the motor draws at 45kph, about 950w.

Take off is slower on the 25 amps, as you said. That is your main difference.

Drop to a 15 amps controller, and you will see a speed limiting effect. Assuming 48v, then a 15 amps controller can only put out about 650w, and top speed will drop about 3-4 mph, because now your total wattage is not enough to push the air out of the way to go 28 mph.

I guess this makes sense. Yes, it's a 48v system. And this is with a 1200 watt motor. Yeah, I guess 5 all difference it's negligible. Though I'll have to properly measure their output with a watt meter. I know they under rate there controllers.
 
dogman dan said:
Also true. a "25 amps controller" might actually do 30, and a 30 amps controller might actually do 25.

But you did notice a slower acceleration, so one is more amps, but both can hit your max speed for the volts you run.

Actually, I said I noticed no difference in acceleration except for that 1 second when I throttle from a dead stop.

But, that said, I would need to count and compare my 0-40 kph time.
 
Another question;

In terms of energy, it seems that simply lowering the amp output doesn't necessarily mean less consumption . It just means that that controller has to work harder to reach the motor's full potential. Am I right?

I mean, unless you go all the way down to a 10-15 max amp controller but then you just go a hell of a lot slower and you end up using a similar amount of energy in the extra time it takes to complete the mileage.

What would reduce energy drain (per mile) in terms of picking a controller? I've read some things about back emf and reducing output to zero. Would this have an impact on energy consumption?
 
To pick something else that will change things, you first must know what you are using now, for watts, amps, etc.

What does your wattmeter show you are using now?

If you do not have one, you need to get one and measure these, in the various riding situations you encounter, before you can choose other things that will use less.

Otherwise all you are doing is guessing, which is a good way to use up money on things that won't do what you want.


Alternately, if the equipment you have is listed in the http://ebikes.ca/simulator, you can make better guesses by using it to simulate instants of your ride, then guesstimate those usages over segments of your ride similar to what you just simulated. Then repeat that for each different type of riding segment (acceleration, coasting, braking, hills, etc).



But it's still not as good as actual data from a wattmeter mounted on your bike that you look at while riding (or log the data from and look at later).


Even the cheap RC wattmeters are better than nothing, though ones like the Cycle Analyst will have more useful info (like wh/mile, which is a measure of efficiency) directly calculated on-the-go from measured data. You can calculate wh/mile from the RC wattmeter data, too, but you don't get to see it realtime.
 
Some controllers are programmable, and the previous 12-FET "might have been" de-tuned to a lower amp limit to reduce heating. Just a possibility...
 
dogman dan said:
Easy, your top speed is likely drawing only 20- 22 amps, at 48v. This is typical for about 28 mph. So both controllers can do that. Both can supply what the motor draws at 45kph, about 950w.

It sounds like my 1200 watt motor can only top out at that 22 amp max. Does that mean that I could put a much larger controller with a 40, 50+ amp max draw and it would still perform the same because this motor tops out at 22? And without consumming more energy?
 
ClintBX said:
dogman dan said:
Easy, your top speed is likely drawing only 20- 22 amps, at 48v. This is typical for about 28 mph. So both controllers can do that. Both can supply what the motor draws at 45kph, about 950w.

It sounds like my 1200 watt motor can only top out at that 22 amp max. Does that mean that I could put a much larger controller with a 40, 50+ amp max draw and it would still perform the same because this motor tops out at 22? And without consumming more energy?

As a geneneral rule, the more current you allow, the more torque you get and the more speed as well. Motors have a maximum speed that they can spin, to which depends on the battery voltage. If your motor already has enough current to reach its max rpm, increasing the current further won't make it go any faster.
 
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