Pick a Voltage, Any Voltage

[ShebeApples]

Hello

I have been loitering for a while and decided to ask; "What is the big thing about larger voltages". I understand enough to calculate power and ohms law, etc (school physics). I see that people say that higher voltage makes you go faster.

OK, but at what cost then? My mumma taught me "You do not get anything nothing girl".

So when people over volt there system, why and what is consequences?
When people talk of their next system being a higher voltage, why? What are the benefits?

I can see that it will mean less current and so maybe smaller wires and cheaper batteries. But power is still power!!

I am looking to buy something off the shelf to start with, but want to try and understand enough about it that I can change it as I want and as I come to understand more.

Shel
(Tomboy at heart)

 

[broloch]

Welcome to the boards, glad you removed that sexist comment in your post.

 

[ShebeApples]

Hmmmmmm

Sexist comments already. Now you see why I held off posting.

Some things may never change

Shel

 

[Icewrench]

Hi welcome to E S
More volts equals more speed.
A 9c kit will do @ 22 mph with a `36`volts. And will get @ 27mph on `48` volts.
More volts can blast some controllers to kingdom come, others can take moderate increases in juice.
Too many amps can melt phase wires, don`t ask how i know this.

 

[amberwolf]

I have been loitering for a while and decided to ask; "What is the big thing about larger voltages" (is it a man thing ). I understand enough to calculate power and ohms law, etc (school physics). I see that people say that higher voltage makes you go faster.

OK, but at what cost then? My mumma taught me "You do not get anything nothing girl".

So when people over volt there system, why and what is consequences?

The first cost is having more cells in your pack, which at the same Ah rating will make it physically larger and weigh more, but will give you more range.

The other cost is switching losses in the controller, since the MOSFETs will have a higher voltage across them during conduction and thus more wasted power as heat. Lower on-resistance (RDSon) will help, as will parallelling more MOSFETs, but it still uses more power in them than at lower voltages.

One must also use capacitors, transistors, and MOSFETs capable of handling that higher voltage, which may make them more expensive, depending on how far up you go.

There are other costs, such as having to be even more careful with your wiring and insulation so that there is less chance of accidental electrocution at *really* high voltages. The higher the voltage, the more likely it is to penetrate your skin resistance and pass thru, should you come in contact with a live wire for any reason, or should water get down into something it shouldn't, conduct power to the bike frame, and make the bike frame "live", relative to some other point you might touch.

Since the motor spins faster, you may end up needing a reduction gearing of some sort to generate the same torque for lower speeds that you did with high current and lower voltages, depending on what your goals are and what motor you use.

When people talk of their next system being a higher voltage, why? What are the benefits?

Generally the benefits seem to outweigh the disadvantages.

You can carry smaller Ah cells, which cost less and weigh less. However, if you stick to the same Ah cells while using more of them, you get more range.

You can have smaller power-routing wire, which costs less and weighs less.

You can use smaller motor winding wire, which also costs less, but since you want to pack the max copper in there, it won't really weigh any (or much) less.

You can use smaller-current-capacity MOSFETs in the controller, which will probably cost less.


I'm sure there are other things I did not think of or remember, too.

 

[dogman dan]

It's not so much a man thing,( high voltage) as a juvenile thing in my opinion. When younger I did lots of hauling ass on very powerfull motorcycles. I sometimes wonder why some of the guys here don't just get one. a 90 mph crotch rocket is really really fun if you can survive owning one.

But back to the facts about high voltage.

1 you will go faster

2 you will spend a lot more on the battery

3 you will blow through the kwh in the battery faster, since wind drag gets exponentially worse with increased speed.

I always like to say, about any activity, get the right tool for the job. So depending on the job you are going to do, the right thing might be 72v 10 ah at 50 amps. You'd want that to go about five miles, outrun traffic, cops, lycra pelotons, or scamper up a steep grade. Or if you want to ride stealthy, cops ignoring you, perhaps for 30 miles, then 36v 20 ah is the thing.

48v and 35 amps is a really good compromise between the two, and what a lot of people run. With the right motor, 30 mph is there, and 35 amps climbs most hills.

Personally, I kinda like the idea of being legal for commuting and cross country riding, but for dirt trails, I'd love a 72v 20 ah monster with a 50 amp controller. I just can't bring myself to buy that much battery. It would take about $2000 in battery and controller.

So it really just depends on what you want to do. And it's part of why I have three ebikes running, plus a motor or two laying around. Just experimenting with other voltages can be very fun.

 

[biohazardman]

Yup, it is a manly-man thing. ;^) Bigger badder, faster, stronger mentality that most of us have. I think it is usually built into the male genome. LOL! You seem to have a good grasp on things already. Yes, more voltage means you go faster and can use a little less amperage. The truth is that most that raise the voltage raise the amperage also. The end result is more speed more torque to accelerate and climb hills. Most stock e-bikes sold as a unit run on 24-36V and are OK for flat terrain. Try going up a hill and you will find them to be less than willing to do it alone. If you are healthy, you can make up the difference. If you are not healthy or near disabled, it becomes more difficult as the bikes will stall.

I found my first build http://goldenmotor.com/SMF/index.php?topic=279.0 a GM 500W 36V to be very helpful and it only bogged down on the steepest of hills in the area of which there are plenty in Portland, OR. Going to 48V was what I needed to get up the rest. I can now choose if I want to help it up the hills or let it do all the work most of the time. Did not take long for the bike to take it's toll on me physically. A new full suspension bike and a lighter more powerful motor was the solution. http://endless-sphere.com/forums/viewtopic.php?f=14&t=6586&start=15#p125502 It too was a great help and I now have the perfect city commuter. My desire to get out of the city will likely require more amperage draw than I can now produce and longer distances can be covered in less time at higher speeds so more voltage too. If the BMC600 is not up to it then another motor will be.

In the end the bike needs to do what you want it to be a dragster, off-road racer, city commuter or cross-country machine. It needs be designed and built for your specific application taking into account your weight, health intended mileage and type of usage. No one builds a bike that can do everything well nor can we.
I wish you luck in your search. Take the time to do the research and buy a bit more than you think you need so you have room to grow.

 

[voicecoils]

Hello

I have been loitering for a while and decided to ask; "What is the big thing about larger voltages". I understand enough to calculate power and ohms law, etc (school physics). I see that people say that higher voltage makes you go faster.

OK, but at what cost then? My mumma taught me "You do not get anything nothing girl".

So when people over volt there system, why and what is consequences?
When people talk of their next system being a higher voltage, why? What are the benefits?

I can see that it will mean less current and so maybe smaller wires and cheaper batteries. But power is still power!!

I am looking to buy something off the shelf to start with, but want to try and understand enough about it that I can change it as I want and as I come to understand more.

Shel
(Tomboy at heart)

* Voltage will determine your top speed at full throttle
* Current will determine the 'thrust' of the motor and therefore acceleration and hill climbing abilities

Power = voltage x current

The reason you often see people talking about voltage making you go faster is that increasing the voltage of an existing system with a higher voltage pack will make that existing system go faster. People like to upgrade and push the limits

Within limits, if your designing your motor, controller and battery pack from the ground up, you can select a system voltage from a wide range and still design the motor to reach a specific speed at that voltage whether it be 12V or 1200V

A few things to think about:

If you want to use your existing system with a higher voltage, is your controller rated for it? If you can't control the current limit of the controller, will the new higher voltage mean you draw more current (faster speeds, steeper hills) and then overheat and kill your motor?

If you want a 1kW (1,000W) system with a voltage of 10V, you'll need to supply 100A, that will require thick wires to handle the current with minimum voltage drop (Ohms law).

If you want to a 1kW system with a voltage of 100V, you'll need to supply 10A, that will require thinner wires but the higher voltage increases the risk of electrocution, shorts or arcs between the terminals relative to running a lower voltage.

I hope that gives some insight.

(Don't get hung up on any negative comments. My girlfriend sometimes rolls her eyes at my increasing pile of ebike parts :lol: but everyone has different interests!)

 

[biohazardman]

Hmmmmmm

Sexist comments already. Now you see why I held off posting.

Some things may never change

Shel

Some will poke fun even if they are not. For the most part things have changed so don't be easily offended and you can learn allot here.

 

[broloch]

Voltage increase the rate of rotation of the wheel. Its theoretical maximum without load is very high. To overcome load, you need amps.

 

[broloch]

200W may not be enough power for your purposes.

 

[broloch]

You ought to be concerned about the 200W limit.

 

[ShebeApples]

WOW

Thanks for all the great comments so quick. A lot to take in.

I am a Aussie (Melb), so limited to 200W, I want to 'try' and stay legal.

So if I have it right:

If the bike is designed to a certain power, then voltage makes little difference on performance. It is only if you increase beyond that is when you will see improved performance. So if that is the case, why wouldn't I just buy the a bike with that increased level. Oh, I am babbling

This is what I meant. Say I buy a 24V 200W bike, and then increased the voltage to 36V, so I have 36V 200W bike. Why should I just get a 36V bike. Wont it be the same.

I mean the above also allowing that a battery pack is provided with same output capacity. An example again; 24V 10A is same as 36V 7A (close enough).

Can someone point me to a posting or website that explains SIMPLY why higher volts means the motor turns faster, and any other advantages/disadvantages.

Thanks again for great answers. I have a lot of catch up to do.

Shel

 

[Russell]

Hello Shelby and welcome to the forum.

Motors are wound to spin at a certain RPM per Volt so applying more voltage makes the motor spin faster for greater speed. The law regarding E-bikes (here anyway) says 20mph unassisted is the maximum so manufacturers shoot for around there with their standard offerings at the nominal voltage which generally is 36V for kits or 24V for many pre-built E-bikes. So for folks looking for greater speed all that’s often needed is to raise the battery voltage to go faster. Most controllers and motors can handle higher voltages and power than what they are rated for so usually this is not a problem, at least if the average power is held somewhat close to the motor’s rating.

Hitting a certain speed also requires producing enough power so along with the voltage the battery and controller must supply enough current to produce the power level necessary to achieve a certain speed (power is Volts times Amps). For an average person on a flat road with no wind that power required is roughly 250W at 20mph, 400W at 25mph and 700W at 30mph at the wheel. I say at the wheel because to differentiate it from the power drawn from the battery with involves the efficiency of the controller and the motor which can vary greatly depending on the load. Riding against a strong headwind or climbing a hill requires substantially more power.

Now here are two real examples of what I’m talking about. I have a small geared motor wound for 6.4RPM/V which will move me along at close to 18mph with a 36V battery (actually 41V) when used with a 15A controller. The speed in this case is not limited by power but because the motor is designed to spin slower. When I use a 48V pack (~52V) and the same 15A controller the motor will now move me along at a bit over 23 mph, again this speed is limited by the motor’s design rather than by available power. I now use the motor with a 21A controller and the top speed is the same however there is now more power available on hills.

I also have another small motor wound for 9.1RPM/V which when powered by a 36V battery pack (actual 41V-peak) and a 15A controller will move me along at 23mph all by itself. If I up the voltage to 48V (52V actual) the speed barely increases to about 24mph when you would think it should go almost 30. In this instance the voltage under load multiplied by the current allowed by the controller multiplied by the efficiency of the motor and controller is simply not enough. When I upped the controller current limit to 22A the combination could get up to around 29mph and drew almost 1,000W from the battery.

Each of the motors above is rated for 250W so running them at full throttle at 23mph is pushing them past their design limit. Throw in a few hills or take the second motor up to maximum speed with a 48V battery and the power consumed by the motor can easily be 3X what it is designed for. Pushing either of them too hard for too long can (and has) damaged them due to the build up of heat. In the world of E-bikes size matters with big motors generally able to soak up far more power without self destructing.

-R

 

[ShebeApples]

Yes Broloch

I did delete my comment, as soon as I realised it would be misconstrued and expanded on. Yes I did comment on been female, my apologies for doing so. Have now learnt more than I expected from my first post here > Stick to facts, don't show who or what you are.

Thanks for lesson. I will stick to topic asked about Voltages, I hope you will also now.

Shelby

 

[biohazardman]

Hmmmmmm

Sexist comments already. Now you see why I held off posting.

Some things may never change

Shel

Some will poke fun even if they are not. For the most part things have changed so don't be easily offended and you can learn allot here.

You're missing the point. OP is likely a male, and trolling. Look at the join date and number of posts. The first post ShebeApples made had a sexist comment in it, which he/she deleted. Then OP felt it necessary, after making a sexist comment about males, to post that he/she is female, like it mattered.

ShebeApples=Troll.

Not missing the point. Really just does not matter to me one way or the other male, female, troll, not. My answers will be the same.

 

[ShebeApples]

Hi Russell

Thanks for welcome and answer.

I am quickly seeing that the question might be simple, but the answer is not. Oh well, I have time. I will do some looking around and see if I can find some simple explanation to how motors work. Probably a good place to start.

Thank you to all people who gave great info, and a starting point to do more research.

Shelby

 

[Lock]

Hi Shelby and welcome aboard ES... I like these two points:

...Bigger badder, faster, stronger mentality that most of us have.

...Pushing either of them too hard for too long can (and has) damaged them due to the build up of heat.

Much of the content here is all about buying the cheapest stuff imaginable then pushing it to the max.

And motors and controllers etc can mostly take all ya can give `em but this depends on how efficient each component is. The energy lost at each step along the way is lost mostly as heat, so then it matters how well this waste heat can be removed rather than it building up and melting stuff. Many components in ebike systems can handle "peak" power levels but only for short periods of time. Where a motor is rated as "200W" this is actually only a "nominal" rating meaning it can handle 200W of power all day long (continuous) without heat building up.

For example you'll see folks tapping here about "active" cooling where eg they're drilling holes in motor casings and blowing air through their motors just so they can "over-volt" a motor design that was never intended by the designer to do the work being asked of it...

A good approach for feedback from ES folk is to provide a mission statement including how heavy the vehicle is (including rider and cargo), what are typical distances and speeds, as well as maximums desirable, how hilly/windy your routes are... how much stop-and-go versus non-stop, how much time and distance between charging opportunities... if you already have a bike what sort (eg alum or steel)... there's more I guess... running out of steam... errr, I mean electrons...

Lock

 

[ShebeApples]

Hello Lock

Thanks for advising of other items I need to consider (I think ).

I started looking for an electric bike a while ago, but very quickly felt I was talking to 'inadequate' sales staff. Then I tried a couple of demos where I live and wondered why someone would buy one of these, they don't even go up a small hill.

Best said, that performance of bike did not match performance of sales talk.

So I started googling and ended up here a while ago. I see that most people on here are about speed and seeing what they can do. But I also see that it creates a lot of practical information.

Heat would be a big issue for me, as we get some doozies in summer. So I suppose as a start I have 3 considerations (with more thought also needed to come).

1. I want to stay legal at 200W
2. I want to go up moderate hills (not sure how best to explain moderate). Say 200m up an 'average' hill found in a city!!!
3. Able to run in high temperature in summer. From what has been said about motors getting hot, this may be more important than I first thought.

As I become happier with the bike I would like to ride further, so I have no clear distance in mind yet.

Shelby

 

[Russell]

A 200W motor at 24V and with say a 10A controller would be pretty lethargic however combine that same motor with a 36V lithium battery and a 15A controller and it would be more than adequate as an assist motor for riding up to 20 mph (32 kp/h). I use little 250W geared motors myself and at 190 lbs with a 60 lb bike (114Kg total) I can go up an 8% grade at 12 mph (19 kp/h) with little effort if I so choose or 14 mph if I pedal vigorously however the key is to provide some pedaling input (that's with a 48V/15A or 36V/22A combo, slightly slower on 36V/15A). If you ride most of the time on part throttle, again using the motor for a little assist, then overheating won't be a problem. The problems occur when you push the motor to it's limits for longer periods of time.

-R

 

[Lock]

I want to go up moderate hills (not sure how best to explain moderate). Say 200m up an 'average' hill found in a city!!!

From Wikipedia:
"...systems for expressing slope:
1.as an angle of inclination from the horizontal of a right triangle. (This is the angle α opposite the "rise" side of the triangle.)
2.as a percentage (also known as the grade), the formula for which is 100*(rise/run) which could also be expressed as the tangent of the angle of inclination times 100."

It's actually pretty important to know how long your hills are and for what height from bottom to top (top to bottom? ...not so much )
Just like yer muscles "burn" going up a steep hill, motors and batts etc can "burn" also... but they don't recover as well hehe

As I become happier with the bike I would like to ride further, so I have no clear distance in mind yet.

That's easy... how many hours d'you spend in the seat over a long day of biking, and at about what average speed?

3. Able to run in high temperature in summer. From what has been said about motors getting hot, this may be more important than I first thought.
Shelby

Like with a pedal bike, where you're limited to a very small amount of power, you know that the secret to hills is gearing. Same power, just slower speeds?

Same with electrics... Someone here has already mentioned gearing... chains and sprockets work too... It's important too to keep the *motor* RPMs up high as well, as motors tend to have a designed "sweet-spot" where they are most efficient, so generating the least amount of waste heat for the power actually getting to the pavement... Important for getting max. range from the charge in the batts too.

You'll see that the choice between using a hub motor built into a wheel (and these can have internal gearings too) versus using an external motor that drives the wheel via the pedal chain or a separate chain is an enduring debate on ES... There are pros and cons but I will suggest that a separate motor w/chain to drive the wheel will offer more opportunities for cooling the motor (as hot summer daze are a concern...) The larger electric motors designed for big RC (radio controller) models are generating a lot of interest in ES. Partly they are being mfgrd in volumes already that keep prices down, but their efficiencies and construction are very good too... Mostly they are designed to run an higher RPMs (than "stock" ebike motors) so again gearing or sprockets and chain called for...

As I said earlier here (and perhaps wasn't clear) much of the content here is about pushing things to the max. If you "overbuild" things enough to begin with, than you will never have to deal with many of the problems folks tap about here!

Lots of talk here about speed, but my priorities are more like safety, comfort and reliability :wink:

Other parts of mission statement include budget (there'll be some minimum you need to spend. Whatever folks here suggest, consider going higher...)

OH YAH... and, what will be the mix of propulsion! How much batteries, and how much human-assist!

Lock

 

[mrzed]

If you want to stay legal at 200w and get up hills, you have basically two options:

1. A chain drive system - there are many variants, some that use the bike's gears, some that use a separate drive chain.
2. A small geared hub motor that is set up for a low maximum speed and will be reasonably efficient at the slower speeds you would climb at.

In any case - a 'true' 200W will not be very impressive up the hills (though through the gears it could be at least half decent).

In some places (here in Canada for instance) the law does have a grey area - where the motor legality is based on the 'rated' or nominal wattage. Not sure if AUS is like that or not. In those cases you can usually get away with more as long as you don't destroy the top speed laws in the process.

 

[TylerDurden]

Don't sweat the small stuff kids... References to gender should be fine, as long as they are not derogatory.

As for higher voltages: they reduce resistive losses.
A low voltage motor can have the same power rating as a higher voltage motor, but the lower voltage motor will likely be less efficient.

There are links in the ES technical section regarding motor theory...
Here is a link to some basics (it is focused on RC airplanes, but the electrical elements apply):
http://adamone.rchomepage.com/guide5.htm

 

[amberwolf]

One thing that seems to be an assumption in a number of replies is that having higher voltage will make the bike go faster; this is not necessarily true, though it certainly can enable higher speeds more easily.

If the motor is wound for a certain voltage, then running it at a higher voltage will spin it faster for the same load on it.

If the motor is a hub motor, then running it at a higher voltage than originally wound for is going to spin the wheel faster, making the bike go faster.

If the motor is wound for a higher voltage (for the same RPM as the other motor wound for a lower voltage) to start with (or rewound to do so) then it will not run any faster, unless you increase it's voltage above design level.

If the motor is not a hub motor, but instead runs thru a reduction gearing setup (as mine does) then while the motor would indeed spin faster, it does not have to make the bike go faster, as it can simply be geared down by changing the ratio of the reduction gearing (as I did when i went from 24V to 36V to increase efficiency and range without doubling the weight of my battery pack).

You could say that the hub motors are "geared" for a certain speed at a certain voltage, and changing the voltage would require changing their "gearing" (windings) to make them stay the same speed at a higher voltage.


All that said, if you intend to use 36V eventually, you might as well start at that voltage. It'll mean everything you get is already designed to work at that voltage, and is less likely to require any kludges or workarounds to get it all to operate together.

Now here's where the math comes in again (I hate math):

Given that you are limited to 200W, @24V it will be drawing 8.4A battery current. That means the battery will only need to be able to supply 8.4A, assuming your controller has an absolute limit on it that prevents higher current draws.

If it is a battery that can output at "1C" meaning at the same level as it's rated Ah, then it only needs to be a 8.4Ah battery to give you enough power to run for an hour of full-throttle use....

...Except that there is an effect (Peukert) that essentially means that the faster you pull power out of a battery, the less power total you can pull out. (also, you can't totally pull all the power out of most batteries, which is called 100% DOD (depth of discharge), without destroying the battery).

It's worst in lead-acid (SLA (UPSs, bikes), AGM (wheelchairs, bikes), FLA (car battery)), but it also affects all the other chemistries to one degree or another, such as Li-Ion, NiCd, NiMH, LiFePO4, etc.

So if you used SLA batteries, you'd probably only get half an hour of runtime, maybe 45 minutes, even at 100% DOD. It's a lot better with other chemistries, but it still affects it.

Now, if you could draw less current, with the same battery, you'd get more runtime, even if you draw the same total amount of power (watt-hours, Wh).

So, @36V it will only be drawing 5.6A battery current. That means the battery will only need to supply 5.6A, and if it's an 8.4Ah battery, then it isn't working nearly as hard, and you'll get more power (Wh) out of it in total. Perhaps a full hour at 100% DOD.

Note that the actual Wh you get out of a battery and actual DOD levels before damage vary with brand and chemistry, but in general it is a good idea not to take more than 80% of the total Wh out of a battery, less if you can help it. It makes them last longer, generally.


All of the above is to show you one more reason why using a higher voltage may make sense. It is one reason i went to a higher voltage.

It's hard to explain in simpler terms (for me, anyway). I'm still a little shaky on some of it myself, mathwise, but I get the basic concepts.

 

[amberwolf]

1. I want to stay legal at 200W
2. I want to go up moderate hills (not sure how best to explain moderate). Say 200m up an 'average' hill found in a city!!!

For this, with only 200W, then as others have, I'd also highly recommend a chain-drive system that goes thru your regular bicycle drivetrain. That means you can shift gears just like you do for yourself, and make it easier for the motor to do it's job of helping you up.

Even though the bike will be much slower at those lower gears, you can shift up to higher gears to get to whatever max legal speed you have there (her in Phoenix it's 20MPH when using the motor, though when not using it the only limit is whatever the road is marked for).

I would recommend that if you are getting a new bike just for this purpose rather than converting an existing one, that you first pick a bike that you can ride easily up those hills yourself, and then make sure the motor can do it too.

I am not sure how the laws work there, but it seems likely that it is not whether your motor is marked as a 200W motor, but whether you are supplying more than 200W of total power to it. The controller may be programmable to limit this, and if it is not you can always get a Cycle Analyst which can be set to do so (and is very handy for other things, too).

If it is not the motor size itself that limits you, but rather the total power you can put thru it, I would also highly recommend getting a motor that's advertised as capable of higher than 200W sustained power (but does not *require* that much power to work) so that it can more easily handle the sustained load that hills present.

A motor has much more work to do when starting you up from a stop, or accelerating, or climbing a hill, than it does just keeping you at a particular speed. So it will run hotter during those times. Making sure the motor is capable of dissipating (getting rid of) more than 200W of heat for sustained periods would be a good idea.

3. Able to run in high temperature in summer. From what has been said about motors getting hot, this may be more important than I first thought.

Yes, it is; I am in Phoenix, AZ, so it gets pretty toasty here, too. It is not *as* important as other considerations, but it will make a difference if you leave the bike in the hot sun for the motor to preheat up to 35C-45C or more and *then* try to take it up a hill, as opposed to keeping it in shade or taking it inside an airconditioned building (not usually practical when out and about).

Getting a non-black motor would help, if it is going to have it's case exposed to sunlight, as far as that type of heating is concerned.

As I become happier with the bike I would like to ride further, so I have no clear distance in mind yet.

The good news is that you can always add more parallel battery packs for more range, or carry spare charged ones and swap them out, if they have quick disconnects. Or stop and charge along the way, if you have time for that.