Extending the range of an electric bike...

No question. My point is that improving the efficiency of the rest of the system (motor controller/drive, gearing, rolling resistance) may have relatively minor effects when you push the battery that hard. The effiency of the rest of the system is probably a great deal higher than that simple calculation suggests, since it assumes a perfect battery.

A newer battery might help but this draw is in the range where I would expect to lose 1/2 to 2/3 of the capacity of the battery, partly depending on how low a terminal voltage the application can accept with reasonable performance.

Note, it's possible that the control system relies on the batteries internal resistance to be part of the current limit. That would make using a larger battery a bad idea. Although a larger battery is likely to give a non-linear increase in run-time.

Robert

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this

They give a fairly good number for "average in shape" people. Back when I was fit, this would have been about what I could do without much effort. In the middle term, breathing is the limiting factor. You can produce bursts of more power but the erobic when you are using the big leg muscles, is mostly from how much air you can pump.

he

But on the other foot: If you improve the rest of the stuff and stay at 17MPH, you won't be pushing the battery quite so hard.

Plead guilty to lumping all the losses together in one pile.

A different chemistry battery may also help. If there is a good PWM system in use, a "supoer cap" may also help.

Unless the lower resistance causes flames to come out of the motor.

Nope. Unsupported assumptions.

1) That all of the energy was extracted from the battery 2) That the rate of discharge when running the bike is the same as the rate of discharge at which the battery was rated. 3) That the range was limited to 12 miles. 4) That the battery was fully charged and in brand new condition.

_Serious_ flaws for a design group.

I made no statements about the hp developed by a cyclist. But let me throw some "phoney math", based on facts, at you. The Gossamer Albatross requires .3 hp to fly in still air. It was driven across the channel (22.2) miles in 2 hours and 49 minutes. To determine how much hp the cyclist could have generated for

42 minutes: 189/42*.3 = 1.35 : end phoney math :

We have no idea what speed 1/4 hp will produce. On a mountain bike in high gear on a level road, you go like a bat out of hell with very little hp input, as compared to climbing a steep hill in low gear where you are barely moving but providing maximum hp input.

And we are cluless about the course conditions for his bike, as you allude to.

Assumption, see above. The op stated "it does 12 miles at 17 mph quite comfortably with no input from the rider."

Only if you allow the assumptions. It's a huge leap from the "there is this much hp in a battery" math to the "therefore we used that much hp". As pointed out, we have no clue how much power was initially available nor how much was used.

And even if you accept some assumptions, the conclusion that "there are huge losses somewhere in the system" could just as easily be "your battery is very weak" or some such.

Ed

The user said that this was the "range". Any energy not going to make the range is a loss of some form or other.

If you are doing so, you are incurring a loss.

This is what the OP said. Are you suggesting he lied?

The OP said that it was the range and spoke of a charger.

No you just have taken too narrow of a view of what is called a loss.

Once again "paleface" comment pops to mind.

Define very little. Have you ever measured? or even estimated it?

These all come from the OP's post, which was, as you have shown above, vague and technically lacking.

Indeed. We should railroad that dave_mallon123 guy!

That assumes constant energy, which is not at all likely for a human (at least on the hourly scale). I know better than to make such a baseless assumption.

No, it was implied by the poster. 12 miles [range], 17MPH, 36V "12A" battery. If 12Ah is assumed to be meant, then a quantity of energy is well defined, as is the time it was spent over.

Speaking of whom, he hasn't come back. We can only assume some more that this is a useless argument anyway-- that is, we'll never get the information needed to complete the problem at hand.

Tim

-- "Librarians are hiding something." - Steven Colbert Website @

Thanks everyone for the replies.

Having 2 * 36v 10Ah batteries looks like the way to go.

.=2E.btw, I found a switch that lets the throttle take over & I averaged 9-10mph with little effort for 35 miles today (9-10mph because it's only got 1 gear and anything after 10mph..I can't cycle quick enough!)

Cheers for all the discussions Dave

Well at a 50% capacity drop the 432 Wh figure drops to 216Wh. At the

2/3 drop, which would not surprise me given the use it drops, to 144Wh.

You are quite possibly losing enough capacity from driving the battery this hard that other efficiency gains are irrelevant.

Yep, although a properly sized battery would be better. The weight advantage of a differnt chemistry night make it worth the extra cost. We're starting to get into the range where you are talking about replacing the drive and charger though.

A battery being discharged in under an hour is definitely undersized for the job. Of course it does keep it lighter and cheaper and increases the market for aftermerket replacement batteries ;)

yep, A lot will depend on who designed it and with what criteria. If the controller came from the EV industry it likely will be just fine. If it came from the consumer electronics industry though they may well have considered the battery a fixed component that wouldn't possibly be upgraded.

The conservative method is to use swappable batteries. Slightly riskier would be to use a larger battery pack.

Robert

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< 2 legs, on average.

Best regards, Spehro Pefhany

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"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Nope. They came from Moosefet.

Exactly. It's flawed, that's why I called it phoney. Just as assuming constant energy from the battery is flawed.

Design by implication? :-) Your second statement above is wrong. The rate of discharge is unknown. The 12 AH spec is at a specific rate. If you discharge it harder, the total AH you can get out of it is less than 12 AH; discharge it slower, and you get a higher total AH. On top of that, we have no idea of the condition of that battery. The quantity of energy is not defined at all, let alone well defined.

He did come back yesterday - you must have missed it.

Ed

No, he did not. He said he did 12 miles at 17 mph comfortably. He did not say 12 miles is the range. And why do you think that range = total energy in the battery? I've got a couple of 12V lead acid car batteries that won't crank over the car starter, but happily run a headlamp for over an hour at ~6.5 amps. We don't know th state of charge of his battery so it is impossible to know that all of the enery was extracted.

Completely ambiguous, and it is not a closed system. For example, energy expended to fight a headwind is energy going to make the range, so it doesn't fit into "energy not going to make the range". It is not energy expended in a non-productive way, but it is a drain on the total energy. So it is ambiguous as to whether you call that a loss or not, but the net effect is that more energy is required.

If you are doing what?

No. He said: "At the moment, it does 12 miles at 17 mph quite comfortably with no input from the rider."

He did not say "the range was *limited* to 12 miles." You assumed "limited".

He did *not* say it was the range. And what does the part about he "spoke of a charger" have to do with it? Go read the post. He said: "Just curious to what you think of this idea of extending the range.

A leisure battery from a scrap yard 12v 110 amp - £30 A fast charger 22amp from Argos - £40 A 12v to 36 dc to dc convertor - £70 A current limiting diode."

That may be true. But it does not change my objection to the assumptions that the battery was fully capable of meeting its 12AH rating; that the discharge rate matched the 12 AH spec; that the full 12 AH was extracted from the battery. Now if all of that is lumped under "loss", then the statement that there are huge losses in the system is true. But it is meaningless under that wide of a meaning of "loss". For example, suppose the 12AH battery is old and weak, and the best it can do is

6 AH. "Your battery may be weak" is a whole lot more helpful than "there are huge losses in the system".

Aside from that, the glaring error is performing the calculations against 12AH when you don't know the rate of discharge and the battery's capacity at that rate. You do know, don't you, that batteries discharged at a rate above their specified AH will provide lower total AH at the higher rate?

So provide figures. Your comment is just a smokescreen.

You must have never ridden a bike to take exception to the statement. I've ridden it, and measured speed. But measuring is just another smokescreen. The difference in speed and effort is so big that no metrology is required to know it.

But set that aside - look at world class cyclists in a race. When they are climbing mountains, they go at a snail's pace as compared to ridng on level roads and have to expend a lot more energy and develop a lot more power climbing. Watch the Tour du France - the commentators will mention speed and effort. In the Gossamer Albatross, hp was measured, and considerably more was required in turbulent air vs still air.

Ed

Et Cetera, et cetera, in the bruised integer range.

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 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
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vague

Hi,

In the last few days, I've bought a 22 inch electric bike 2nd hand for =A3120.

It's been pretty impressive so far imho.

Problem is, as people probably already know, is the battery...

At the moment, it does 12 miles at 17 mph quite comfortably with no input from the rider. (36v 12 amp lead acid battery)

Just curious to what you think of this idea of extending the range.

A leisure battery from a scrap yard 12v 110 amp - =A330 A fast charger 22amp from Argos - =A340 A 12v to 36 dc to dc convertor - =A370 A current limiting diode.

ie 12v at 110amps, probably equals 36 volt at 30amp =3D 2 times as far =3D 25 miles, (taking into account the extra weight and the loss of electric convertion)

but I reckon it should be good for an approx range of 30 miles of effortless riding.

Any comments? Ideas?

Thanks, Dave

****** end copy ******

Note that he said "does" and then says "Range". He is talking of its range.

[=2E...]

I never assumed "constant energy from the battery" I assumed constant energy in the battery. The lower amount you get from the battery isbecause of a loss as far as finding the range in concerned.

He said "does" and then followed it with the statement about range. He meant range.

I think nothing of the kind. Energy you don't get out of the battery is a loss as far as finding the range is concerned.

There is nothing ambiguos about it at all. The energy either gets used in making range or it does not. Everything that doesn't is a loss as far as range calculation is concerned,

[.....]

Read the next thing he said so you take the word "does" in context.