Bit confused about the Bosch Drive Unit Performance CX

[PH001]

As a manufacturer, just think about how you 'prove' what a motor is rated for. There is no practical technical documentation that can disclose that.

All you can prove is what the motor produces either in mechanical power (torque x rpm at its output) or in terms of the volts and amps (electrical power) it consumes from the battery.

 

[KTM Bike Industries UK]

Just think about how you 'prove' what a motor is rated for. There is no practical technical documentation that can tell you that.

All you can prove is what the motor produces either in mechanical power (torque x rpm at its output) or in terms of the volts and amps (hence power) it consumes from the battery.

Why would you ever need to prove it? Thats like saying I have to be able to prove my 60w lightbulb is 60w! Its not a problem for the consumer, its up to the testing bodies.

 

[PH001]

You have to prove it as to self declare you are required by law to keep a technical file in case you are ever investigated.

The technical file has to contain sufficient evidence to support your declaration.

Sorry - I am talking from the perspective of the manufacturer here just in case you misunderstood.

 

[flecc]

You have to prove it as to self declare you are required by law to keep a technical file in case you are ever investigated.

The technical file has to contain sufficient evidence to support your declaration.

That doesn't appear to be a problem. The Wisper brand models at least have been put through an approved testing lab EN15194 certification. Those models have used both Dapu and Suzhou Bafang motors at controller amperages producing power wattages which we know are far in excess of the legal 250 watt rating.

So they have the approval certificates to meet the full EU testing requirement for legal compliance.
.

 

[PH001]

I guess we would need to be able to read EN15194 in full to see how they managed that. It could be to do with input vs output power, i.e. the electrical input power may well be way over 250W but the mechanical output power (torque x rpm) may be within 250W. The ratio between the two is simply the electrical efficiency of the motor.

 

[flecc]

I guess we would need to be able to read EN15194 in full to see how they managed that. It could be to do with input vs output power, i.e. the electrical input power may well be way over 250W but the mechanical output power (torque x rpm) may be within 250W. The ratio between the two is simply the electrical efficiency of the motor.

That's not the case in a testable way, these motors don't have anything like as great an inefficiency factor. In the case of the Bosch CX, it would have to have only 42% efficiency! It's probably nearer twice that.

There's a circa €70 charge to buy the EN15194 PDF, but I can make a copy available for you to read if you wish.
.

 

[craiggor]

Why would you ever need to prove it? Thats like saying I have to be able to prove my 60w lightbulb is 60w! Its not a problem for the consumer, its up to the testing bodies.

Will the homebuilder have to prove it when taking a bike for the new type approval coming in 2018 ?

Sent from my D101 using Tapatalk

 

[PH001]

Absolutely right Flecc, I'm not pertaining that the Bosch CX is only 42% efficient as of course all the wasted power (input watts - output watts) would be dissipated as heat and the thing would glow red hot!

If you could mail me a copy of EN15194 then I would be most interested to read. Have sent you PM.

 

[Wisper Bikes]

We have just had our latest batch of ebikes certificated to EN15194. The motors are nominally 250W but peak at 612W. They were tested by TUV, so we as a manufacturer can rely on their findings. I should also say the bikes had throttles, restricted to 6kph unless the pedals were turning forward.

 

[nemesis]

Is it possible to be legal with a 350w motor or over that has the controller limiting the top speed to 15.5 mph with no access to tampering.

 

[KTM Bike Industries UK]

Is it possible to be legal with a 350w motor or over that has the controller limiting the top speed to 15.5 mph with no access to tampering.

no.

 

[PH001]

OK, so I have been thorough EN15194 in some detail but for the actual power calculation it refers to another standard EN 60034-1 which is very generic and less than helpful.

It does state however the that power measurement is defined as:

"continuous (or constant) output power specified by manufacturer, at which the motor reaches its thermal equilibrium at given ambient conditions"

Note it does say OUTPUT power so this clears that one up, as the electrical input power will certainly be higher than 250W.

Interestingly it perhaps assumes that nobody can get their head around EN60034-1 so describes an alternative method of measuring the power at the rear wheel in terms of work (power = force x speed).

Now, get this! It says the test is to be performed with the mass of the test bicycle equal to 150Kg!!! Holy cow, 130Kg is hardly an average rider weight!!

What does this mean? Well, basically as long as the motor propels a 150Kg mass from 0 to 25km/h in no less than 14.5 seconds you will pass the test. The electrical power into the motor is incidental, and I'd like to place a good bet it's far more than 250W!

 

[soundwave]

Is it possible to be legal with a 350w motor or over that has the controller limiting the top speed to 15.5 mph with no access to tampering.

all the bosch motors are 350w software limited to 15.5mph for non s class bikes.

the only difference is the speed limit.

 

[flecc]

Now, get this! It says the test is to be preformed with the mass of the test bicycle equal to 150Kg!!! Holy cow, 130Kg is hardly an average rider weight!!

What does this mean? Well, basically as long as the motor propels a 150Kg mass from 0 to 25km/h in no less than 14.5 seconds you will pass the test. The electrical power into the motor is incidental, and I'd like to place a good bet it's far more than 250W!

This is what I meant when mentioning the alternative test in Appendix D, basically an acceleration measure. As you say, the weight alone makes that easier, but there's another often used dodge which helps to pass that test. That dodge is incorporated into the following model.

One of my legal hub-motor pedelecs has been measured by two of us owning that model at a peak current drain of 1000 watts! Its peak net power must be about three times its legal rating.
.
.

 

[flecc]

Is it possible to be legal with a 350w motor or over that has the controller limiting the top speed to 15.5 mph with no access to tampering.

all the bosch motors are 350w software limited to 15.5mph for non s class bikes.

the only difference is the speed limit.

Yes, but to appear legal they are not rated as 350 watt for the EU and UK market. I think member Nemesis was probably asking about one rated as 350 watts.
.

 

[PH001]

One of my legal hub-motor pedelecs has been measured by two of us owning that model at a peak current drain of 1000 watts! Its peak net power must be about three times its legal rating.

This doesn't surprise me at all. As long as they pass the acceleration test they can whop a 250w badge on it and it will pass approval. Bear in mind also that you are measuring input power which is also irrelevant to the spec.

Incidentally, if you want to know how much mechanical power your ebike is really putting out, all you need to do is put your stats into this little formula....



Alternatively, PM me and I will email you the excel file.

 

[nemesis]

Yes, but to appear legal they are not rated as 350 watt for the EU and UK market. I think member Nemesis was probably asking about one rated as 350 watts.
.

Are the 250w and 350w bosch motors exactly the same except for a different cut out speed in the software ?

 

[soundwave]

Are the 250w and 350w bosch motors exactly the same except for a different cut out speed in the software ?

yes all the motors are the same just different settings for s class and hub gears,less power.

inside there all the same.

 

[KTM Bike Industries UK]

Soundwave, could you learn to use the "quote" key so that it makes your posts make a bit more sense.

Your obsession with the 350w/250w Bosch motor thing is fun to watch.

The key difference between the 2 is that the 250w is rated at 250w and says so on it... therefore is legal, the other isn't.

By removing the speed limit on motor, it has the result of the nominal power increasing even though the motor is the same. So the motor without the 25kph restriction is rated as 350w.

So the crucial difference is that the nominal power w rating is 250w on one and 350w on the other, so whilst the motors are identical, one is legal and the other not.

 

[PH001]

What has come to light here is the the 250W rating on these motors most likely refers to mechanical output power at the wheel. There is absolutely no way the authorities could measure voltage and current draw from the battery and determine the bike was legal or not as EN15194 takes into account all the drivetrain and tyre losses.

In conclusion - as long as you are limited to 25km/h.....