Extending the range of an electric bike...

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

Reply to
dave_mallon123
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To me, it sounds like a complete non-starter. Don't EVER get a scrap battery and expect to do anything but pay somebody to haul it away.

You'd be better off to just get another 36V battery just like the one you have, slap it in parallel with the existing one, and either beef up the charger or charge it twice as long.

Or, get THREE of the big 12V honkers, and wire them for 36V, and just be done with it.

Although, you still have the weight issue. Other people might have other ideas about battery technology/power density, etc, but I'm at my limit here. :-)

Good Luck! Rich

Reply to
Rich Grise

Do you mean 12 Amp-hours?

Are you planning on replacing the existing battery with the above? Or paralleling the converter output with it?

What exactly do you mean by 'current limiting diode'? A blocking diode for parallel operation?

You could replace the 110 Ah, 12V battery with 3 40 Ah batteries in series (giving you 36V) and do away with the dc-dc converter, its losses and weight.

One thing you might want to consider before investing $$ (or ££) in a lot of range enhancing hardware: Test the existing battery capacity first. You said you bought this thing second hand and its possible that its battery capacity has diminished.

Hook up a voltmeter, ammeter and a suitable load (a couple of 12V headlights) and plot the battery current and voltage over time. No sense in re-engineering the whole contraption until you have established a good baseline for performance.

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Reply to
Paul Hovnanian P.E.

If you want extra watt hours, get a bigger 36 volt battery or just add another 36 volt battery in parallel with the one you already have.

Reply to
kell

On a sunny day (Sat, 07 Apr 2007 01:27:02 GMT) it happened Rich Grise wrote in :

Is not putting Lead Acid in parallel creating the possibility for giga-amps egalization currents?

Reply to
Jan Panteltje

Yeah, they say you should only parallel identical batteries of the same amp hours/brand/batch/age (new, in other words).

I owned a diesel Suburban with two batteries hard-wired in parallel. Must have been many thousands of those vehicles on the road, and I imagine a lot people ended up putting dissimilar batteries together, so I guess it's not a huge danger.

I know I would want to make sure at least that both batteries are in good condition, similar amp hour ratings and well charged before making the connection.

Reply to
kell

12 miles at 17mph takes: 0.7 hours

36V * 12AH =3D 432WH

432WA / 746 =3D 0.579 HpHr

0=2E579/0.7 =3D 0.8Hp

You have huge losses somewhere in the system. Making a bike go at

17MPH takes less than 1/4HP.
Reply to
MooseFET

Does it use regeneratice braking ? If not, employ it, if it does, it may not be very effective. Either way, MooseFET has a good point. Does it use resistive speed control, or PWM ?

Reply to
skenn_ie

Pump up the tyres

martin

Reply to
martin griffith

It may not have any control at all other than on/off.

A system for running on 12V, 24V or 36V is better than simple PWM but requires more smarts from the driver.

Reply to
MooseFET

You must know some things no one else knows. :-) Like: the weight of the rider & the bike, rolling resistance, the slopes encountered in the 17 miles, headwinds and tail winds, the state of charge at the end of 17 miles, how much energy was extracted from the battery etc.

In other words, we have no idea of the work done nor the energy expended.

Ed

Reply to
ehsjr

Yes I know lots and lots of things.

It just about doesn't matter within the normal range for adult humans. The width across the shoulders matters more. I am on the large end of the scale and assumed that since the person had not said anything about the subject they were not abnormally wide.

All bikes weight 50 pounds. A 10 pound bike needs a 40 pound lock and chain A 20 pound bike needs a 30 pound lock and chain A 30 pound bike needs a 20 pound lock and chain A 40 pound bike needs a 10 pound lock and chain A 50 pound bike doesn't need a lock and chain.

I assumed that the bike was a normal bike and that the tires were pumped up and that the various bits hadn't rusted together.

There may be light poles and phonepoles but there were no math poles enclosed during the ride.

I assumed the wind did not change and that it was low enough not to be remarked on.

The OP told us the "range" was 17 miles. The battery was discharged at the end.

Almost all the energy that could be.

What's this "we" paleface. I made a fairly good estimate based on what I know from experience.

Reply to
MooseFET

Well, that rating is for a longer discharge time. Maybe 5Hr but proabably 10Hr or 20Hr. The useable capacity with a 3/4 Hr discharge will be lower, probably substantially lower.

Robert

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Reply to
Robert Adsett

In the last few days, I've bought a 22 inch electric bike 2nd hand for £120.

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 - £30 A fast charger 22amp from Argos - £40 A 12v to 36 dc to dc convertor - £70 A current limiting diode.

ie 12v at 110amps, probably equals 36 volt at 30amp = 2 times as far = 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

Check the capacity of your batteries, they may be aging - other similar bikes running on 36V get a lot more range, see the link below (12V, 12Ah batteries weigh a little over 4 kg, this one has 14 kg of battery, so about a 36V 12 Ah battery). Do a google search for many more hits

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New batteries are fairly cheap (likely around £50 - 60) - don't waste your time with used batteries (especially don't waste your time with car / truck starting batteries for storage), mixing batteries, or voltage converters. Doing so will not give the expected results and could be dangerous. Ever see what happens when a car battery shorts out? They are capable of sustaining several thousand amps of current into a direct short. This is enough power to turn a section of the frame of your bike into a red hot chunk of steel, or vaporize a wire shorting it out. High power DC to DC converters are not likely a good answer. There are several very good reasons why a 36V system was initially used, and there is no reason to change it to a lower voltage.

Reply to
Jeff L

Nope, it all factors out. It's just a comparison.

Do you honestly know of any bicyclist who can put out 0.8HP for 42 minutes? The typical human can do about 1/4HP as I recall, making that figure a good basis for the power consumed at 17MPH. Depending on bearing quality/tire pressure, wind resistance, "uphill both ways", etc., of course.

Presumably, the energy expended was 432Wh, since the OP implied that 12 miles is the maximum range on the given batteries.

It's all just math and makes sense when looked at. Of course, facts don't produce such comments as:

which reflects badly on his attitude...

Tim

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

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Reply to
Tim Williams

FWIW the average human can produce about 3w/Kg body weight, so about

200W for about an hour.

martin

Reply to
martin griffith

A bike racer can put out more, but they go a lot faster than 17MPH.

[....]

That was an attempt at humor.

Reply to
MooseFET

I think that is a bit optimistic. The problem is with "average". You have to include a lot of the very unfit, the sick and the elderly if you say "average".

Reply to
MooseFET

This would be part of the losses of the total system, as would the losses in the motor. All together it is a rather poor efficiency.

Reply to
MooseFET

Thanks everyone for the replies.

Having 2 batteries looks like the way to go.

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!)

Dave

Reply to
dave_mallon123

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