Hub motor 250W 12V DC for electrical bicycle? 2

[gerhardl]

Is it possible to find a hub motor for an electrical bicycle utilizing (existing construction of) a 12VDC battery?

The discussion came up as a side issue of possible utilization from a producer/developer/inventor of alternative power sources.

Having looked at existing solutions most electrical hub motors and control systems all seems to be based on 30-36V or 24V and 10-16Ah (or somewhat higher), and most limited to a max effect of 250-300W, corresponding to a distance of 20-50km and 20-30km/h. This to confirm to limitations of official rules around the world of 'bicycles' to avoid registration as 'motor vehicle.'

It might also be obvious on the voltage side why the higer types voltage is selected (volt x ampere = watt).

I would anyway appreciate free comments from the electrical engineering side.

 

[rbulsara]

Did you try to find one? or you are asking others to find one for you?





Rafiq Bulsara

http://www.srengineersct.com

 

[LionelHutz]

Nothing in life is free. Or was that not the kind of comment you were looking for?

Is there really any difference between one big 12V battery or 2 smaller 12 volt batteries in series?

 

[gerhardl]

.. I did try to search without success, and yes, I have seen the possibillity of series connection.

... and regarding comments you have to excuse the inferior mind of a simple mechanical engineer in the outskirts of the civilized world (compared to the electrical engineers superiority...) but I was sort of hoping hoping for some positive technical based ideas and input ;-)

 

[rbulsara]

gerhardl:

I see that you have expertize in mechanical and valve engineering and been a positive contributor on this forum. We are not saying we are superior to anyone, but your question has no technical aspect. (Disregarding the fact that assisting DIY personal projects are not encouraged on this forum).

How does a 12V battery count as alternative energy source vs. a 24V DC battery? Is there an issue with using 24V DC motors that you have seen being used?

And yes, it may be possible to find a 12VDC motor if someone makes it. But what is technical about it?

It is also true higher voltage = lesser current for a given load. Less current= less copper=smaller size=less cost, etc.

So what is your technical question that you need the positive ideas on?




Rafiq Bulsara

http://www.srengineersct.com

 

[LionelHutz]

My point was that you need a certain battery capacity for a certain range. That will dictate the physical battery size. One big battery or a number of smaller batteries in series will be about the same size.

Using a higher voltage will likely reduce the cost of the controller.

I really don't see what benefits you expect from using 12V instead of 24V or 36V.

 

[Clyde38]

gerhardl,
When you find a source for a hub motor that you like, just ask them if they are willing to provide the same motor wound for the voltage you are interested in. It should be about the same amount of copper, the only difference will be the number of turns and the wire diameter of the magnet wire. Unless the manufacturer has some restriction on the diameter of wire they can wind due to the equipment they use, this will be no problem.


[link

http://www.linkedin.com/in/clydehancock

]

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[gerhardl]

Thank you all for the response. So far you confirm my thoughts, and again yes: I am aware that this at the moment is too general and unprecise as a technical question.

My problem at the moment is that I am sitting in the middle of some 'fuzzy logic' from a technical discussion partner, trying to sort it down to a technical description of what is needed as the next step (in a mecanical technical and commercial solution - electrical motor and power source only to be discussed here)

Is following a possible correct answer:

If you start with with available 12V batteries, it would be a better soulution to connect two or three batteries in series to obtain 24V or 36V to be suited to existing motors, than using 12V. If necssary more strings in parallell to increase capacity. In practice to 'build' from existing available units a battery of higher voltage by connecting the single 12V batteries?

Apart from the physical limitations (measures, weights, connections etc ) do you see any disadvantages doing this?

Would the batteries be controllable and drain and load in the same way as a single 24V or 36V battery?

Would a 36V battery and motor be a better choice than 24V?

 

[rbulsara]

Without pretending to be the technical expert on this particular application, my business mind would say: Those existing manufacturers you mentioned would have done this research. Why not benefit from them and start with the base they have laid and then experiment?

Identical batteries in parallel should work OK. They are used that way most of the time.

Rafiq Bulsara

http://www.srengineersct.com

 

[dpc]

All batteries are made up of cells with relative low potential. So putting two identical 12 V batteries in series, if wired appropriately, is the same as using a 24 V battery.

Usually, a higher voltage is going to be better in this voltage range due to reduced current draw and reduced voltage drop in the wiring. A look at available cordless tool will confirm this.

Car manufacturers are trying to move away from 12 V systems to 24 V or 48 V systems at some point in the future, I believe.

 

[abudabit]

24 - 48 v are the normal voltages for commercially available low power hub motors, 72 v are available for some higher powered ones.

Current^2 generates the heat so higher voltage lower current is better than lower voltage higher current. And voltage isn't a safety issue at 48 v.

Most bikes run 2 - 4 12v in series.

Most bike hub motors are brushed - some will be designed for high torque and some will be designed for high max speeds. 250 W with a brushed with no tranny won't perform well in a lot of situations. Human legs produce less than 200 W at max... but they are attached to pedals which are attached to a tranny.

I owned a 750 W electric bike motor... but because I stupidly chose the high max rpm wired one I often nearly killed it and never managed to hit max speed (35 mph) unless I had a long flat or downhill.

What's the app? If you're gonna need both torque and speed for different situations then hub motors will stink with out a tranny. Because of that many electric bike people use either non-hub motors and a mechanical drive or they use geared hub motors (expensive).

 

[itsmoked]

abudabit; Has it. 24, 36, 48 but definitely not 12.

A 12V speed controller has to be less efficient and built with larger traces, and semiconductors - more expensive.

Generally one of the more expensive aspects of e-bikes are the batteries. If you do a little research, you will find the price of LA batteries to be all over the map. Certain sizes are absurdly priced others are a huge bang for the buck.

The typical method of selection is to figure out the desired range and the resulting Whrs needed. Next, find the sweet-spot battery size needed $ wise. Finally do the math to see how many you need to stack in series to archive the Whrs. That will come to 2 for a couple-of-blocks bike, three for around-town-short-trips, and four for across-town and-around-town-too.

Of course LA batteries, ESPECIALLY gel cells, should not be drained below 50%, so you have to keep that in mind. Of course if you are making a crap bike and replacing the batteries every year is something you can foist off on your customers than go below 50%.

Always use the batteries in series. Do NOT use them in parallel. A shorted cell in parallel results in burst batteries, acid on the legs, screaming people, and ambulance chasing Vermin. A shorted cell in a series stack is not a big deal. It's quickly sorted out as the e-bike loses a lot of 'Go' as soon as a cell shorts alerting the user to a developing problem.

If you must tempt fate and your future solvency with parallel get-ups you must now include the added cost of fuses between each battery and the parallel bus to limit Vermin.

With all battery setups that exceed 24V you will promptly run into charger issues since 36 and 48 are generally custom chargers. You may need to hire someone to build one.

Zero e-bikes used to sell their e-motorcycles, which have a 42hp electric motor made by Briggs and Stratton, (I believe), with an included four 12V chargers tie-wrapped together to charge the four packs. It was extremely tacky and I couldn't convince them to let me design 'one' charger to replace the mess. I believe they finally did. But I digress.

Keith Cress
kcress -

http://www.flaminsystems.com