500W kits .....36V or 48V ?

[freddofrog]

As I intend to be building something that's not restricted to 15 mph, I thought that I'd ask the question in this section of the forum.

I already have a 250W Izip with a 36V battery, and although the battery is now 3 years old, I have always looked after it and it still seems to have a good % of its original A-h

I want to convert a standard mountain bike and I'm thinking of getting a 500W kit, but I don't know whether to get 36V or 48V. I am leaning towards the 36V, but mainly because of the 36V battery that I have.

What are the advantages of 48V on a 500W kit ?

 

[Deleted member 4366]

Your 36v battery wouldn't be able to supply enough power even when it was new. You will send it to an early grave if you connect it to a 500w controller -that's if the BMS doesn't trip.

My advice is to get one of those 48v 09 bottle batteries with the included 20A sinewave controllers. It goes nicely with the 260 rpm 48v 500w BPM or the 36v 201 rpm Q128H.

 

[freddofrog]

It goes nicely with the 260 rpm 48v 500w BPM or the 36v 201 rpm Q128H.

maybe I worded my post badly LOL

what is the difference between the two that you mention ?
i.e. on what criteria am I choosing between 36V and 48V on a 500W kit ?

 

[Deleted member 4366]

If you run a 36v motor at 48v, it goes 33% faster, so a 201 rpm one becomes 260 rpm. The Q128H is lighter than the BPM. It's smaller, but spins faster internally and has a greater reduction ratio, so it still makes high torque. I'm just waiting for one to come from BMSBattery. Then I'll be able to tell you exactly how it performs.

The 260 rpm 36v BPM at 30 amps with a 36v battery will perform the same as a 260 rpm 48v one at about 23 amps with a 48v battery. When you increase the voltage, the torque and speed both increase more or less in proportion, so you have to be aware of what exactly the speed of your motor isvat any given voltage. If you make your motor go too fast for its power, it will run inefficiently. A 250w motor is OK up to about 20 mph, 500w up to 25 mph and 1000w for 30mph. It's not an exact dcience though because there's do many other variables.

 

[freddofrog]

I'm a bit confused, possibly by what I mean as a "kit"

From what you're saying, for top speed, a 500W 36V motor with a 48V battery and appropriate controller will go faster (for obvious reasons), but some "kits" come with a battery, and some without.

If I buy a 500W kit that has a 48V motor and includes a 48V battery and appropriate controller, why would this be any better than a 500W kit that has a 36V motor and includes a 36V battery and appropriate controller ?

 

[freddofrog]

The 260 rpm 36v BPM at 30 amps with a 36v battery will perform the same as a 260 rpm 48v one at about 23 amps with a 48v battery. When you increase the voltage, the torque and speed both increase more or less in proportion, so you have to be aware of what exactly the speed of your motor isvat any given voltage. If you make your motor go too fast for its power, it will run inefficiently. A 250w motor is OK up to about 20 mph, 500w up to 25 mph and 1000w for 30mph. It's not an exact dcience though because there's do many other variables.

ahhh that answers my question quite nicely in the second paragraph above which you added in #4 while I was typing #5 LOL

 

[appyarry]

Does this mean I would be better buying a 36 V motor but running 48V with a good controller and ensuring I only run the motor at the peak efficiency (RPM) rather than buy a 48 volt motor and battery.
Sorry if it is a silly question, I'm not up to speed with all the permutations, yet
Ta,

 

[freddofrog]

^ not a silly question IMO

 

[Deleted member 4366]

You get more power with 48v, but you have to be mindful of the speed. A 36v motor will spin 33% faster at 48v, but you can lose torque and efficiency if you make a motor spin too fast for its power, which not only wastes battery, but it can overheat your motor.