Too much power for 250w motor?

Kiblams

Finding my (electric) wheels
Jul 18, 2019
7
0
Hi guys,

I'm new to electric bikes and after doing a moderate amount of research (only the tip of the ice berg it seems) I bought myself a Dillenger 250w road legal front wheel kit.

To say I am happy with it is an understatement! The kit went on the bike without any issues and I was test riding within 30 minutes (no wire management etc)

I am really surprised at how powerful the motor is and it can drag my 250lbs weight up some pretty harsh hills with minimal input at 10mph and on flats it outpaces my pedalling and levels out at 18mph mid battery level and 22mph at full charge. (It also happens to be unlimited out of the box)

My query is this; because I was so surprised by the performance I did a little research and checked out the stats. As I see it, the battery is putting out 36V and the controller is 15A, so is it actually putting 540w through the motor when set to full assist/full throttle?

I have checked the motor and controller temps after some big hill climbs and everything feels cool to the touch so I'm not massively concerned, but just wondered if I was wildly mistaken.

Cheers!

P.S. not sure why but my posts on here seem to be going missing so please excuse if I've posted this more than once.
 

pn_day

Pedelecer
Jul 26, 2013
185
40
St Andrews, Fife
I'm sure you'll get a fuller answer from somebody more knowledgeable, but here's my tuppence worth...

The EU spec of 250W is a bit confusing - it is a 'nominal' value. In practice you are perfectly correct - the combination of battery and controller often mean that a '250W' system might actually be peaking well above this.

In your case, you might well find that the 36V battery is closer to 42V fresh of the charger, so you max power may be closer to ~630W.

Don't worry about it - most other '250W' systems will be doing something similar.

About the only thing you can do to damage it is run the motor too slowly (i.e. go up a steep hill without pedalling at all). Apart from that, if you are using the stock controller and not increasing the current beyond the defaults you should be fine.

Enjoy the new freedom that having e-assist brings!
Phil
 
  • Like
Reactions: Kiblams

Danidl

Esteemed Pedelecer
Sep 29, 2016
8,608
12,253
73
Ireland
This is a hardy annual question and if you go back over numbers of postings it will reappear.
The definitions of power are not the electrical power going into the motor..the product of voltage by current consumed, but the mechanical power delivered to the wheel which is torque x revs per second x 2π . The power going into a stalled electric motor could be multiple kilowatts!!.,and yet priducing zero mechanical power.
Secondly the EU standard does not measure power of an electric motor over an instant,but the sustained power over a period.for which it is capable .... the actual specifications relate to the temperature rise over an hours continual operation experienced by the windings .
The nett effect of these two is very confusing, so leaving one in the very comfortable position that if the manufacturer or importer into the EU has stated that the product is type approved and has CE markings then it is legal.
 
  • Informative
  • Like
Reactions: dwvl and Kiblams

Kiblams

Finding my (electric) wheels
Jul 18, 2019
7
0
Thanks guys, I think that answers my question. I had no idea about the motor potentially drawing killowatts if rotating too slowly. Will certainly have to keep that in mind up hills.

Good to know the motor isn't at risk. Cheers!
 

sjpt

Esteemed Pedelecer
Jun 8, 2018
3,642
2,652
Winchester
If you are interested to see a lot of the tradoffs of power, speed, etc etc on many different motors, the ebikes simulator shows lots of information. https://www.ebikes.ca/tools/simulator.html
(It doesn't show risk of burnout though)
 
D

Deleted member 25121

Guest
Your 36V battery with a 15A controller can produce 540W maximum, even under stall conditions. There's no need to be concerned about your motor drawing kilowatts, it can't happen unless there's a fault. If it did wires and connectors would burn out with 2,000W/36V = 56A flowing instead of 15A!!!.
The 250W motor rating is an nominal value and perfectly legal 250W motors can produce far more than this peak.
So you can rest easy, or should I say ecycle easy, and make the most of your ebike. Enjoy.
 
Last edited:
  • Like
Reactions: Kiblams

vfr400

Esteemed Pedelecer
Jun 12, 2011
9,822
3,985
Basildon
36v x 15 amps is input power, not output power.

At the speeds where you can get that much current into the controller, the motor has an efficiency of 60% or less, which is a max of 324w output power. That will only happen at something like 10 mph. Below that, the efficiency drops off rapidly and above it, the motor restricts the current.

You only get maximum current at low speed. Above that, the motor's back emf regulates the current. It decreases it from 15 amps at some lowish speed to zero at maximum speed, so at 15 mph, you won't get anywhere near 15 amps.
 
  • Informative
Reactions: dwvl
D

Deleted member 25121

Guest
Yes, I was talking about input power and how it doesn't get into the kilowatts. I was encouraging the OP to enjoy his ebike and not worry about it exploding because of the power being drawn.

I made no mention of efficiency, that's a totally different issue....