24 volts from 2*36 v. batteries?

[Desertprep]

I am shopping next weekend for a folder...will then add a motor to the front fork. Yes, I am going to upgrade my insurance first

Most of the lithium batteries available in China are 36 volt - yes, I know, many are not safe..will have to do my homework. It seems to me that the Dewalt 36v. are by far the safest and most durable of all I have seen yet...but pricey.

On the low end, and for starters on this experiment, I am looking at some 24 volt motors. I do not think they will give a high top end speed but I think I will start there. Is there some way to use voltage reduction with these batteries without having a firehazard and still have efficient use of the batteries? If I have 2 36 volt Li batteries? Or do I need so many? I was thinking that 2x36=72 and 72 is an even multiple of 24

Also, what is the difference between a 500 watt 24v motor and a 500 watt 36 v. motor? OK, OK, I know...12 volts But for the sake of design and performance, batteries, etc what will be the difference? I have seen some high wattage motors that are only 24 volt. Keep in mind that rider and bike will be around 200 pounds, not including batteries.

 

[lazarus2405]

You're asking a lot of very vague questions.

What kind of motors? Brushed or brushless, hub motor or something else? Any information you can provide on the motors would help.

You should be fine running a 24v motor at 36v, without any trouble, as long as the controller can take it. It'll be more powerful and have a higher top speed than running the same motor at 24v. 24v is pretty low for EVs, and I've never heard of a bike motor that ran at 24v but not 36v. Still, without knowing anything about the motor...

Still, wattage ratings on motors don't usually mean a whole lot. In most cases, you can most likely get twice the rated power out of a motor before it overheats, or with better cooling. It depends on a lot of things.

The only efficient "voltage reduction" you could do would be to rewire the battery into a lower voltage, higher amp-hour configuration. And DC-DC converter system would at best be 80% efficient, meaning that it would get very, very hot having to dissipate that other 20%. And a setup able to deliver enough current would be more expensive than simply using a higher voltage motor.

If both a 24v and 36v 500w motor equally well deliver 500w, then the 24v motor is drawing more current to do so. It'll have a higher winding resistance, and likely run faster at the same voltage. They could be the exact same motor, wound differently. Without knowing any specifics, this is all complete guesswork.

 

[TylerDurden]

Better to simply run the 24V motor @ 36V.

 

[Drunkskunk]

And another thing, Dewalt 36v batteries are realy 33v batteries.

 

[cerewa]

The dewalts are made out of individual 3.3V cells, which means if you use them in a 7 series setup they're about 23V and if you use them in a 8 series setup they're about 26V.

(the 24V motors are designed to handle SLA batteries that give voltages in actual use between 20V and 26V or so, and any battery that is about the same voltage)