Y 36-24 not 12

unjonharley · Post by **unjonharley** » Wed Feb 28, 2007 7:20 am

explain to me why is a scooter 24v/36vdc instead of leaving it at 12v..I should know this..But it escapes at the time..

i don't like this gettng old shit..

Bob · Post by **Bob** » Wed Feb 28, 2007 7:48 am

P=IV, I believe.

Toolmaker · Post by **Toolmaker** » Wed Feb 28, 2007 8:27 am

unjonharley wrote:explain to me why is a scooter 24v/36vdc instead of leaving it at 12v..I should know this..But it escapes at the time..

i don't like this gettng old shit..

More Volts=More Power

Kinda like my cordless tools.. these 19V tools are much better than the crap I had 10 years ago.

dragonfly Jafe · Post by **dragonfly Jafe** » Wed Feb 28, 2007 9:28 am

You can only put so much current thru a wire. To transfer the greatest power, you need the highest voltage, since

(power) = (current) X (volts)

MikeVDS · Post by **MikeVDS** » Wed Feb 28, 2007 9:31 am

More Volts=More Power

Yes and no. That's not really complete and can be confusing. More volts with constant current = more power. Since there can be low voltage systems with less power than high voltage systems.

The best analogy of voltage to explain to someone who doesn't want to go into theoretical formula is the analogy of a hose and water. In this analogy voltage would be like pressure. So if you're hose is kinked(resistance from devices and wire) or you run a little turbine(electric motor) in your hose, you will get pressure(voltage) drops. The higher your pressure(voltage) the easier it is to overcome these drops. Also with higher pressure(voltage) you can use a smaller hose(wire) and transmit the same amount of energy.

That's how I think of things. Since electricity is not really tangible that makes it easier for me to think of things. Voltage is just like pressure and current is just like flow rate. Resistance is just like... resistance or head loss. The analogy works so well that if you know how to calculate one you can calculate the other

Rocket75377 · Post by **Rocket75377** » Wed Feb 28, 2007 9:45 am

This is how I think of things (and please, correct me if I'm wrong), but let's say you have a 12v, 24v, and 36v battery of the same size. Wouldn't the 24v last half as long as the 12v, and the 12v three times as long as the 36v? It would seem that with batteries it boils down to trading life for juice.

Post by **mdmf007** » Wed Feb 28, 2007 10:33 am

Watts / Volts = AMPS

If you run a DC motor at higher voltage, and the same wattage you lower the AMPS.

360 watts / 36 volts = 10 Amps

360 watts / 12 volts = 30 Amps

The lower the amperage the more efficiently energy is transmitted and the less heat (waste) it produces.

Bob · Post by **Bob** » Wed Feb 28, 2007 10:43 am

I already said all that.

MikeVDS · Post by **MikeVDS** » Wed Feb 28, 2007 4:51 pm

This is how I think of things (and please, correct me if I'm wrong), but let's say you have a 12v, 24v, and 36v battery of the same size. Wouldn't the 24v last half as long as the 12v, and the 12v three times as long as the 36v? It would seem that with batteries it boils down to trading life for juice.

That's generally incorrect. A 24 volt and 12 volt battery the same size should have the same potential chemical energy. A 1 HP motor running on 12 volts or on 24 volts should still draw about 750 watts and run out of charge at the same time. A 1hp motor will draw about 31 amps from a 24 volt battery and will draw about 62 amps from the 12 volt battery, but the 12 volt battery the same size will have twice the amp-hour rating.

It can get confusing the way people rate things. I design things so I hate when people use amp ratings because it's assumed a specific voltage for certain systems, but working with all sorts of systems I find watts or HP to be more useful a number to have on hand. In general higher voltage systems actually have less loss and so you'll squeeze a little more out of a higher voltage battery because our systems are not perfect and have losses.

*My numbers are rounded off and assuming lossless systems for simplicity.

P.S. I know that is what mdmf007 said and even Bob, but I did it more wordy as to possibly be understood a little more by those who aren't math geeks. I don't think saying just V=IR helps anyone much who asked the question in the first place. Sure they need to understand that formula to truly understand why certain voltages are used for certain applications, but real understanding would be hard to come by just reading some forums.

Token · Post by **Token** » Wed Feb 28, 2007 5:57 pm

P = V * I - Power is the product of voltage and current.
I = V / R - Current is the ratio of the voltage and resistance

then

P = V * V / R = V^2/R

Since R is a set function of the length of the wire in the motor and number of windings on the armature etc. and is relatively constant and constrained much more by the size/geometry of the device etc. the best bang for the performance buck in hot rod-ding a 12V motor is to boost the voltage given constant Resistance.

Increasing voltage on the same motor provides some nice power gain, quadratic to be precise provided the increased current doesn't fry the sucker.

gyre · Post by **gyre** » Wed Feb 28, 2007 7:24 pm

I think what counts here is that, if it is built for it, a higher voltage motor is more efficient for it's wattage than a low voltage one.
There is a penalty in needing more cells to generate the voltage, but it seems to be made up for.
The new pulse wave modulation controllers can run a great deal of power into a motor for a short time and then limit it to what is needed, saving your batteries.
The good ones I have looked at are a significant part of the price and very important. ( such as Heinzmann)

Rocket75377 · Post by **Rocket75377** » Wed Feb 28, 2007 8:36 pm

I'm supposed to know this for a class. I'm going to write this down.

Toolmaker · Post by **Toolmaker** » Wed Feb 28, 2007 8:52 pm

Good stuff to know for when you need it.. myself I am not too good with the electrical stuff since I'm a metalworker by trade. What Mike said holds true to my cordless tools.. my 19V tools have more usable life before charging than the old 12V ones. Back when I had 12V I had 4 extra batteries constantly on charge so I could use the tool throughout the whole workday. Now with 19V I only need 2 backups.. the batteries charge faster now. I am OK with math but not a math geek per se.. trig functions give me grief sometimes thats why I am so thankful for Texas Instruments calculators and my handy "pocketref" book from carrlane. For those that NEED to know stuff like this the bible in my toolbox is "the machinery handbook" and this book has all kinds of great things when you need to look something up.

PS I have heard about another "bible" for engineering relating more to electronics.. anyone know the title of this one?

unjonharley · Post by **unjonharley** » Wed Feb 28, 2007 8:59 pm

ThanX guys good read..

A while ago i asked about compost toilets..Got the best reads on the subject..

gyre · Post by **gyre** » Wed Feb 28, 2007 9:06 pm

Rocket75377 wrote:This is how I think of things (and please, correct me if I'm wrong), but let's say you have a 12v, 24v, and 36v battery of the same size. Wouldn't the 24v last half as long as the 12v, and the 12v three times as long as the 36v? It would seem that with batteries it boils down to trading life for juice.

If you run into a dead load like a big resistor, then this is true.
The power burned goes up with the voltage.
And batteries are more complex and less efficient for their size as the voltage goes up.
When you need the amount of power needed on a bike, for instance, the extra cost and complexity pays off, especially with a proper controller.
A motor is a much more complex question than a simple resistor or light bulb.
I think the pwm maintains voltage and varies amperage

By the way, I always found the pipeline comparison more confusing than useful for electricity.
Maybe that's just me.
I like to think of electric devices as powered by wishful thinking.

All hail Tesla!
Father of the electric grid!

And don't forget Philo T. Farnsworth.

gyre · Post by **gyre** » Wed Feb 28, 2007 9:27 pm

I'm not sure about which electronics handbook you are referring to,
but the bosch automotive handbook has tons of conversions and useful information.
It is mostly automotive, but there is a great deal of electronics information.
SAE-the Society of Automotive Engineers has a great book selection and good prices.
You can join as a student for $10.
There is access to aerospace information and lots of online material if you are inclined.

http://www.sae.org/servlets/index
http://store.sae.org/

If you are building or just interested in anything that moves,
you may find the material valuable.

Steven bradford · Post by **Steven bradford** » Wed Feb 28, 2007 9:30 pm

And don't forget Philo T. Farnsworth.

You got that right! See http://fusor.net/

MikeVDS · Post by **MikeVDS** » Thu Mar 01, 2007 5:51 am

By the way, I always found the pipeline comparison more confusing than useful for electricity.

I've heard the same thing before too. Some people do not like it. I personally build a visual model of everything in my mind. There I can play with it, change it and alter it. It was easier for me to picture pipes with water, pressure and flow, than invisible electrons, volts and amps. I have a decent understanding of it now so I don't need to go back to the pipe diagram in my mind.

For me it was like learning a foreign language. At first you always have to translate from your native to the foreign in your mind, then at some point you start just thinking in that language and it's faster. I needed that step of thinking in pipes and translating to electric because of the way I think about things. I've met others who it helped and some who it confused.

robotland · Post by **robotland** » Thu Mar 01, 2007 6:01 am

Fuggit. I'm just bringin' my bicycle.

Y 36-24 not 12

Y 36-24 not 12

Re: Y 36-24 not 12

!