Please take me back to school battery electrics

[AlwaysUpHill]

OK, I can just about remember the relationship between watts, amps and volts (the very basics), but am getting confused when thinking about ebike batteries as there is also the small matter of a controller.

I get the fact that getting the voltage correct and matched to that of the bike motor is essential. But ebike batteries when advertised are normally specified just as voltage and amp hours (AH) and even I get the AH is the next calculation along from amps.

So if I am wanting a battery with the highest reasonable Amp hours (and leave the other practical problems of connections, dimensions to one side), if I get a match on the voltage, what do I need to check in terms of either watts or amps to make sure I'm not going to damage the controller or the motor in terms of the battery spec.

Sorry, I know this is basic and a little knowledge (very little in my case) is a dangerous thing. But I may have finally found a battery that fits the bike and I like the sound of the amp hours, the voltage is correct but I'm being told by the warehouse dealer, the electric specification is not a match for the bike, electrics wise (so would at least like to understand why and what to check for when buying a new battery.

Any help in on this battery specification electrics would be sooooooooooo appreciated.

 

[sjpt]

The capacity of the battery is AH (as you have realized). Also important are the amount of amps the battery can deliver, both long term and in bursts. If the battery can't deliver the current asked of it it will very quickly deteriorate. This is often an issue for people who buy cheap high power direct drive motors and then try to buy cheap low power batteries to go with them.

If the battery is capable of higher current delivery than needed that should not be an issue. The controller will limit the amount it is asked to deliver.

The overall capacity and current delivery capability are not inherently linked; it depends on the cells used. However, higher capacity batteries often achieve that by more cells groups in parallel, which will also increase the current delivery capability.

Most motors can accept more volts; it is fairly common to run a 36v (nominal) motor at 48v.
This will increase torque at low speeds and power delivery at higher speeds.
Most controllers cannot accept higher voltage, so controller would probably need to be changed.
There are people here more expert who can advise on particular controller/motor combinations.

 

[vfr400]

That's a good question, and the answer is quite complicated.

The first thing to understand is that motors don't care about voltage. The voltage affects their maximum speed in direct proportion, so the same motor will spin 30% faster at 48v (12S) compared with 36v (10S).

When running at full power, the motor has an efficiency curve that varies with speed. Once the speed drops below 50%, the efficiency accelerates downwards and the motor makes more and more heat. When choosing a motor, you should choose one that has a maximum RPM, considering the voltage, at about 120% to 130% of your planned modal speed.

It takes about 250W of output power to cruise at 15 mph and 1000w to cruise at 30 mph without pedalling. That would translate to about 360w and 1400w of input power for a well-chosen motor. some of the output power can come from your pedalling. Most reasonably fit people can manage 100w continuous during a ride ans regular cyclists can manage 200w. You can do the maths to calculate how much input power that requires.

The problem is hills, where you have to figure out how much power you need to get up them. Obviously, you'll be going much slower, so the efficiency will be low and the motor will heat up.

The controller provides the power to the motor. Each controller has it's own maximum current that it allows, though it can't provide that continuously. They're normally rated at half their maximum, so a 15A controller will run all day at 7.5A and will be OK for 5 minutes climbing a steep hill at 15A, though it will become quite hot. How long you can run at maximum depends on how much heat it can shed to its surroundings. In the open air, it might be able to go for avery long time, but in a tight sealed compartment, not so long.

The battery and controller need to work at compatible voltages. Some controllers can run at a range of different voltages by automatic detection. Some can through settings. Some only work at fixed voltages.

The battery only needs to be able to supply at least the current that the controller allows. That is the continuous current rating that you see in the battery's listing. Also, it needs to be able to provide enough charge to complete your worst case journey. That's the amp-hours in the listing.

A newb has no way of figuring out all these pqarameters, but you can get a good idea of what's going on by using the simulator at www.ebikes.ca/simulator.

If you tell us about your bike, yourself and what you want the bike to do, we can probably give you a good idea of what you need to acheieve it based on practical experience,

 

[Nealh]

A battery will have a continuous current (amp) supply rating, this rating needs to be more then the max draw of the controller. So for instance a battery with able to supply 20a continuous would be no good for a controller that can draw more then 20a, ideally the battery continuous current supply needs to be more then the controllers rating.

 

[AlwaysUpHill]

That's a good question, and the answer is quite complicated.

The first thing to understand is that motors don't care about voltage. The voltage affects their maximum speed in direct proportion, so the same motor will spin 30% faster at 48v (12S) compared with 36v (10S).

When running at full power, the motor has an efficiency curve that varies with speed. Once the speed drops below 50%, the efficiency accelerates downwards and the motor makes more and more heat. When choosing a motor, you should choose one that has a maximum RPM, considering the voltage, at about 120% to 130% of your planned modal speed.

It takes about 250W of output power to cruise at 15 mph and 1000w to cruise at 30 mph without pedalling. That would translate to about 360w and 1400w of input power for a well-chosen motor. some of the output power can come from your pedalling. Most reasonably fit people can manage 100w continuous during a ride ans regular cyclists can manage 200w. You can do the maths to calculate how much input power that requires.

The problem is hills, where you have to figure out how much power you need to get up them. Obviously, you'll be going much slower, so the efficiency will be low and the motor will heat up.

The controller provides the power to the motor. Each controller has it's own maximum current that it allows, though it can't provide that continuously. They're normally rated at half their maximum, so a 15A controller will run all day at 7.5A and will be OK for 5 minutes climbing a steep hill at 15A, though it will become quite hot. How long you can run at maximum depends on how much heat it can shed to its surroundings. In the open air, it might be able to go for avery long time, but in a tight sealed compartment, not so long.

The battery and controller need to work at compatible voltages. Some controllers can run at a range of different voltages by automatic detection. Some can through settings. Some only work at fixed voltages.

The battery only needs to be able to supply at least the current that the controller allows. That is the continuous current rating that you see in the battery's listing. Also, it needs to be able to provide enough charge to complete your worst case journey. That's the amp-hours in the listing.

A newb has no way of figuring out all these pqarameters, but you can get a good idea of what's going on by using the simulator at www.ebikes.ca/simulator.

If you tell us about your bike, yourself and what you want the bike to do, we can probably give you a good idea of what you need to acheieve it based on practical experience,

That's a good question, and the answer is quite complicated.

The first thing to understand is that motors don't care about voltage. The voltage affects their maximum speed in direct proportion, so the same motor will spin 30% faster at 48v (12S) compared with 36v (10S).

When running at full power, the motor has an efficiency curve that varies with speed. Once the speed drops below 50%, the efficiency accelerates downwards and the motor makes more and more heat. When choosing a motor, you should choose one that has a maximum RPM, considering the voltage, at about 120% to 130% of your planned modal speed.

It takes about 250W of output power to cruise at 15 mph and 1000w to cruise at 30 mph without pedalling. That would translate to about 360w and 1400w of input power for a well-chosen motor. some of the output power can come from your pedalling. Most reasonably fit people can manage 100w continuous during a ride ans regular cyclists can manage 200w. You can do the maths to calculate how much input power that requires.

The problem is hills, where you have to figure out how much power you need to get up them. Obviously, you'll be going much slower, so the efficiency will be low and the motor will heat up.

The controller provides the power to the motor. Each controller has it's own maximum current that it allows, though it can't provide that continuously. They're normally rated at half their maximum, so a 15A controller will run all day at 7.5A and will be OK for 5 minutes climbing a steep hill at 15A, though it will become quite hot. How long you can run at maximum depends on how much heat it can shed to its surroundings. In the open air, it might be able to go for avery long time, but in a tight sealed compartment, not so long.

The battery and controller need to work at compatible voltages. Some controllers can run at a range of different voltages by automatic detection. Some can through settings. Some only work at fixed voltages.

The battery only needs to be able to supply at least the current that the controller allows. That is the continuous current rating that you see in the battery's listing. Also, it needs to be able to provide enough charge to complete your worst case journey. That's the amp-hours in the listing.

A newb has no way of figuring out all these pqarameters, but you can get a good idea of what's going on by using the simulator at www.ebikes.ca/simulator.

If you tell us about your bike, yourself and what you want the bike to do, we can probably give you a good idea of what you need to acheieve it based on practical experience,

Thanks for this, as you suggest an approach of theory combined with others practical experience is probably the best combination. I did also want to understand this better and your reply has really helped me with this.

Over to the practical side, this is my first ebike and I have gone for a Biocycle Boxer

The application is lots of steep (road & country lane) hills immediately on leaving house (as I live on a hilly part of the Welsh Boarder). I could only buy the option with a 10 AH battery and am experiencing that lovely feeling of range anxiety.

In terms of me and using some of your numbers above. I am reasonably fit and I would hope to be able to contribute close to the higher of your watt numbers (but who knows). My 5'11" and 95kg is also a factor to allow for.

I realise someone may well come up with a better match of 'man to machine' but that's where I am and was on a budget for a first ebike experiment (but am now converted as really enjoying it).

I have looked at a Green cell 23.8 AH battery which might physically fit, but would have to find out more on the specification as it may well not be suitable. I can't see what amps it is rated at and I am fairly sure it is matched to a much larger motor wattage (but as you explain above that just converts to speed).

I think the controller is fairly bog standard and I can't see any ratings listed on it.

Hope some of the above may be useful to tap into some of the practical experience on the forum to combine with me struggling with the theory.

And all advice very welcome, - don't want to make anything 'go bang'!

 

[AlwaysUpHill]

A battery will have a continuous current (amp) supply rating, this rating needs to be more then the max draw of the controller. So for instance a battery with able to supply 20a continuous would be no good for a controller that can draw more then 20a, ideally the battery continuous current supply needs to be more then the controllers rating.

Thanks for this, I can see I may need to get some more info somehow on my controller.

 

[vfr400]

The application is lots of steep (road & country lane) hills immediately on leaving house (as I live on a hilly part of the Welsh Boarder). I could only buy the option with a 10 AH battery and am experiencing that lovely feeling of range anxiety.

Your battery is a standard silver fish. There are some minor differences in the connection plate, but tyhe batteris normally come with the plate and the lockstrip, so you cam replace the whole lot. Iccasionally, there might be some minor work to fit the replacement plate. Obviously, if the plate is different, you won't be able to use both batteries without some modification.

Your bike is not particularly powerful, so any silver fish battery would be OK. A battery with more capacity will most likely be able to supply more current yhan your present one, so there's nothing to worry about there unless you plan to get a more powerful controller.

I'm the same weight as you and have similar hills. I can manage with low power, but occasionally i might want more power on the hills. I have 48v, which gives 30% more torque and power..

If you're happy with the power, just get a bigger battery, but if you want more power and/or speed, it might be worth upgrading the controller and battery to 48v. The cost of the controller is fairly low compared with the battery.

 

[AlwaysUpHill]

Your battery is a standard silver fish. There are some minor differences in the connection plate, but tyhe batteris normally come with the plate and the lockstrip, so you cam replace the whole lot. Iccasionally, there might be some minor work to fit the replacement plate. Obviously, if the plate is different, you won't be able to use both batteries without some modification.

Your bike is not particularly powerful, so any silver fish battery would be OK. A battery with more capacity will most likely be able to supply more current yhan your present one, so there's nothing to worry about there unless you plan to get a more powerful controller.

I'm the same weight as you and have similar hills. I can manage with low power, but occasionally i might want more power on the hills. I have 48v, which gives 30% more torque and power..

If you're happy with the power, just get a bigger battery, but if you want more power and/or speed, it might be worth upgrading the controller and battery to 48v. The cost of the controller is fairly low compared with the battery.

Now that's given me some more to think about. I will do some research to see what's involved with your suggestion of changing both battery and controller to 48v. All this started with me naively thinking I just needed more AH, (but I'm learning thanks to you and other forum members, really appreciate all this help).
I know exactly what you mean by the silver fish coming with plate and base plate with the idea of changing the lot. I did go down this route with an ebay 15amp but was in the process of swapping the lot over when I hit a snag that the rectangular plug hole in the metal mounting plate was too small which stopped me from fitting the new base plate. I know many would have overcome this and ground it out but I wasn't looking to do this on a brand new bike.

I guess there will be other existing threads on the forum about controller change so I will take a look at those and also online. Yes 30% extra torque does sound attractive on some of our hills (speed is not an issue on the other side - just brakes!)

Thanks again

 

[Deleted member 33385]

Now that's given me some more to think about. I will do some research to see what's involved with your suggestion of changing both battery and controller to 48v. All this started with me naively thinking I just needed more AH, (but I'm learning thanks to you and other forum members, really appreciate all this help).
I know exactly what you mean by the silver fish coming with plate and base plate with the idea of changing the lot. I did go down this route with an ebay 15amp but was in the process of swapping the lot over when I hit a snag that the rectangular plug hole in the metal mounting plate was too small which stopped me from fitting the new base plate. I know many would have overcome this and ground it out but I wasn't looking to do this on a brand new bike.

I guess there will be other existing threads on the forum about controller change so I will take a look at those and also online. Yes 30% extra torque does sound attractive on some of our hills (speed is not an issue on the other side - just brakes!)

Thanks again

If you're returning the 15A battery for a refund, don't open it: If you've already got the 15A battery, perhaps you could rehouse the battery pack it contains inside a new compatible empty Silverfish case? Unless it really is too large. You'd have to measure the battery pack inside the 15A Silverfish to make sure it fits inside the new Silverfish case.

 

[AlwaysUpHill]

If you're returning the 15A battery for a refund, don't open it: If you've already got the 15A battery, perhaps you could rehouse the battery pack it contains inside a new compatible empty Silverfish case? Unless it really is too large. You'd have to measure the battery pack inside the 15A Silverfish to make sure it fits inside the new Silverfish case.

Fortunately it fits my wife's bike with no adaptation necessary, so we have done a deal

 

[kangooroo]

Fortunately it fits my wife's bike with no adaptation necessary, so we have done a deal.

- and wife is very happy with the deal!

 

[Deleted member 33385]

- and wife is very happy with the deal!

One wouldn't even begin to commence speculating about thinking about the nature, sound, or indeed colour, shape nor flavour or modality of a deal

 

[WheezyRider]

Now that's given me some more to think about. I will do some research to see what's involved with your suggestion of changing both battery and controller to 48v. All this started with me naively thinking I just needed more AH, (but I'm learning thanks to you and other forum members, really appreciate all this help).
I know exactly what you mean by the silver fish coming with plate and base plate with the idea of changing the lot. I did go down this route with an ebay 15amp but was in the process of swapping the lot over when I hit a snag that the rectangular plug hole in the metal mounting plate was too small which stopped me from fitting the new base plate. I know many would have overcome this and ground it out but I wasn't looking to do this on a brand new bike.

I guess there will be other existing threads on the forum about controller change so I will take a look at those and also online. Yes 30% extra torque does sound attractive on some of our hills (speed is not an issue on the other side - just brakes!)

Thanks again

If you are going to 48V and you have a 36V controller, in many cases the "36V" controller will work fine with 48V, except that the low voltage cut off will not work. Can you open up the controller and check the big capacitors inside? If they are rated for 63V, you should be ok to run at 48V.

 

[Deleted member 33385]

If you are going to 48V and you have a 36V controller, in many cases the "36V" controller will work fine with 48V, except that the low voltage cut off will not work. Can you open up the controller and check the big capacitors inside? If they are rated for 63V, you should be ok to run at 48V.

That's very interesting! How can one determine how much current the motor can handle? A BBS01b 250W for example?

 

[WheezyRider]

That's very interesting! How can one determine how much current the motor can handle? A BBS01b 250W for example?

I haven't got any experience with mid drives. However, the current limit will basically come down to how quickly you can get rid of heat, which should be better with a mid drive as I believe the coils are on the outside, so can cool better than a hub drive. People like VFR should be able to confirm that. The heating you get is proportional to the square of the current. Current is limited by your controller. A typical "250W" controller will be 15 A, so for 36V systems, peak power output from the controller will be about 600W. By soldering the shunt this can usually be increased to 20A without problems, increasing power to about 800W.

But, if you go to a "48V battery" (13 or 14 cell? both are often called 48V), you get more torque without increasing the current from the controller, which means you don't have to splash out on a more beefy controller. Of course, by transformer action, armature amps in the motor will increase. It's a complicated subject and probably best thought about using some of the online simulations.

I use a 50.4 V battery (58.8V max) with a basic 15A controller (normally 36V) and I just monitor the battery voltage myself to make sure that it doesn't get near the lower voltage limit before recharging.

Also, by replacing the main capacitors in one controller to 100V versions, I have had a 15A 36V controller running at over 70V with an experimental battery setup. I only didn't go higher, as I was already exceeding the rating of the mosfets at 70V. But I can tell you, the bike really shifted at that voltage!

I've found that up to about 1kW can be handled by most hub motors without issue. A mid drive may be even be able to handle much more.

Of course, this will impact your battery life and you have to ask, do I really need it? The acceleration is great, but the limit is 25kph, so you go like a rocket to 25kph, then bang, nothing.

It is great for hill climbing though. Increasing voltage allows you to maintain top speed up an incline better than just increasing the current limit, which is important if you are heavy, or carrying a heavy load.

 

[vfr400]

That's very interesting! How can one determine how much current the motor can handle? A BBS01b 250W for example?

Forums are the best source of info. People try different things and figure out what works,

The main factor is how you use it. It's high power at low speed (especially stopped) that kills controllers and motors.

Burnt motors are very rare these days. It happens a lot with RC models because their controllers don't normally have current control. They rely on the speed of the motor to limit the current, while as ebikes have controllers that limit the current.

It's normally the controller that blows first on an ebike or the wires melt on cheaper ones.

Once the controller has blown, it's possible to burn out the motor if you keep trying to give it power. You can't see electricity, so some people keep trying the throttle or the PAS hoping that the motor will kick back in, but all they're doing is dumping maximum battery current through a winding until it burns out, so the few burnt out motors are normally as a result of a controller or wiring fault.

In geared motors, it's often the gears that go first when running at high currents. The gears are not as strong at high temperatures and then the high torque from the high current strips them. That's especially true for crank-drive motors that can't shed heat so easily as a hub-motor.

Also, hall sensors don't like high temperatures, so that's another common failure when running with high currents.

You need to understand about efficiency when running with high currents. The efficiency is the proportion of energy converted into motive power. The rest mostly makes heat. Efficiency is disproportionally low at low speed, abut it's steady and high at high speed, which is why you can run at high currents as long as you keep the speed up. In the case of a crank motor, speed is your cadence. for a hub-motor, it's bike speed.

In summary, for a BBS01 motor, a fit cyclist with a cadence of 100 could probably run with double the current of an unfit rider with an average cadence of 60, who can't be bothered to change gear when a hill comes, and instead lets his cadence go down to 40 or less while the motor does all the work.

 

[cyclebuddy]

In summary, for a BBS01 motor, a fit cyclist with a cadence of 100 could probably run with double the current of an unfit rider with an average cadence of 60, who can't be bothered to change gear when a hill comes, and instead lets his cadence go down to 40 or less while the motor does all the work.

I do wonder why it is that e-bikes don't add cadence to the display - especially as the bike already knows what it actually is! It's useful to know at a personal health level, and at a motor efficiency and protection level too. Even my cheapish smart home cycle trainer can display it.

 

[Nealh]

One reason why I gave up on mid drive, although I use low gearing I just don't have a high cadence. I have the stamina but not the power to continually shift high rpm.
Hubs are so more forgiving though I gearing still needs to be used.

 

[WheezyRider]

...That's especially true for crank-drive motors that can't shed heat so easily as a hub-motor...

I've never had a crank drive, but from what I've read, the windings are on the outside rather than caged within the magnets and the wheel hub, as with a hub drive. Is this not the case or are there other reasons why the crank drive can't dissipate heat as easily as a hub?

 

[vfr400]

The hub-motor is spinning relative to the air, so it's like fan-assisted cooling, and it has a much bigger surface area to lose the heat from.

The surface area of an exposed on one side crank motor is 2piRL + piRR. For a hub motor it's 2piRL + 2piRR.
A BBS01 is about 4" dia and 4" long, and a typical 350w hub motor is 7" dia and 4" wide
That gives 62.8 sq ins compared with 241.9 sq ins. That's a massive difference, and when that hub-motor's surface is moving through the air much faster, it can probably shed about 8 times as much heat.