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36v 500w Ebike Hub using as Generator

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Musharaf Afridi

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Hi all,
i am using an ebike 36v 500w hub in my bike front wheel as a generator ....... when it spin, it produce 3 phase AC current which i convert to DC by 3 phase bridge rectifier .... i get 12v to 16v at a normal speed .... i want to charge 12v x 3, 5Ah batteries in series.
i try to charge them but taking too much time to charge it. i want to charge them fast as it can possible. Any suggestions?
 
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tcmtech

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Spin it faster.:rolleyes:
 

Musharaf Afridi

New Member
i actually need 36v from batteries, before these batteries were in parallel, for this purpose i connect these 3 batteries in series and made them 36v Dc output. so then i convert the ebike hub generating 12v output into 36v by dc dc boost converter and start charging batteries. so i spin it faster as 25 km/h but still no result which i m expected. is there any other device to boost up current instead of volts?
 

MikeMl

Well-Known Member
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You can boost voltage (and get a lower current). You can boost current (and get a lower voltage). Power = Voltage x Current. You cannot get more Power out than you put in... Trying to boost current and voltage at the same time violates the laws of thermodynamics.
 

Musharaf Afridi

New Member
Very useful comments tcmtech ....;)
It is i need to boost the current from ebike hub into batteries ... no matter volts ... but current ....
1. Is there any way other then spinning fast?
2. Is there any device for current like dc dc volts boost converter?

Hub is capable to produce more current.
 

Musharaf Afridi

New Member
How
You can boost voltage (and get a lower current). You can boost current (and get a lower voltage). Power = Voltage x Current. You cannot get more Power out than you put in... Trying to boost current and voltage at the same time violates the laws of thermodynamics.
Could i boost current? Only spinning fast is sulotion?
 

alec_t

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i convert the ebike hub generating 12v output into 36v by dc dc boost converter and start charging batteries.
The charger voltage needs to be somewhat higher than the battery voltage, otherwise the charging current is zero. Perhaps that is the effect you are seeing. Charging current also needs to be controlled, to prevent damage to the batteries. Have you checked out Battery University to see how batteries should be charged? Different cell chemistries require different charging profiles.
 

tcmtech

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Power output limits are dictated by power input limits minus losses.

Given it is rated at 500 watts 36 volts DC it more than likely had an average power consumption of around 15 amps DC ahead of its speed controller so given that you have at best around 15 amps continuous current (5 amps per phase) it can supply which means that to get more power out of it the only solution is to spin it faster to raise its output voltage.

Now to charge a 36-volt battery you need about 45 volts and being a motor is not as efficient when working as a generator to get that extra voltage yo will likely need to spin it at least 50% faster than whatever its top free wheeling speed was in motor mode and possibly more if you want that higher voltage at the motors maximum amp capacity as well.

So yes, your only realistic solution is to spin it faster.
 
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Musharaf Afridi

New Member
What could be your opionion guys if i made batteries in parallel (12v) for charging from hub then make it spinning fast .... and place a 20A dc dc 12v to 36v boost converter after batteries to load .. will it work?

I did one experiment, i placed 3 hollgen bulbs 90w each in series and i connected them to ebike hub to light them, with low resister they get bright on normal spinning ...

Its my first experience with ebike hub ..
 

tcmtech

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From what I can find online most 500-watt 36-volt e-bike hubs can spin up to around 300 RPM so given that to get 45 volts out of it at its rated amperage it would more than likely need to spin 550 - 600 RPM.

Any slower and you simply have the motors amperage limit times whatever voltage it will produce at that speed.

There is no magic circuit that will do anything for you other than let you exchange your availble amperage with voltage meaning if you only have 14.5 volts at 15 amps (218 watts) to work with while parallel charging the batteries boosting it up to 44.5 volts for series charging them will only give you ~5 amps to work with.

There is simply no other way around the problem of gaining more wattage to work with other than to spin it faster to add more working voltage to the available current limit it has.
 

Musharaf Afridi

New Member
From what I can find online most 500-watt 36-volt e-bike hubs can spin up to around 300 RPM so given that to get 45 volts out of it at its rated amperage it would more than likely need to spin 550 - 600 RPM.

Any slower and you simply have the motors amperage limit times whatever voltage it will produce at that speed.

There is no magic circuit that will do anything for you other than let you exchange your availble amperage with voltage meaning if you only have 14.5 volts at 15 amps (218 watts) to work with while parallel charging the batteries boosting it up to 44.5 volts for series charging them will only give you ~5 amps to work with.

There is simply no other way around the problem of gaining more wattage to work with other than to spin it faster to add more working voltage to the available current limit it has.
Thanks brother ... got you now ...
Really appreciable ......
 

dr pepper

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You might be able to reconfigure the motors windings to produce a higher voltage.
Beware that making more power will slow you down more, as all the power has to come from the rider.
 

audioguru

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What spins the wheel with the generator for charging the battery? The battery driving the motor? You can't Doo Dat!
The battery makes the ebike go. The generator makes the ebike stop. Then instead of charging the battery you are heating the motor and the generator, and are killing the battery.

Like the guy who tried a computer fan as a generator on his pedal bicycle to charge his phone. Not enough power. So he tried a huge fan that worked fine when the bicycle was stopped and the wind was blowing. But when the wind stopped it was a lot of work to pedal the bicycle and drive the fan generator, like pulling an opened umbrella behind him..
 

Musharaf Afridi

New Member
What spins the wheel with the generator for charging the battery? The battery driving the motor? You can't Doo Dat!
The battery makes the ebike go. The generator makes the ebike stop. Then instead of charging the battery you are heating the motor and the generator, and are killing the battery.

Like the guy who tried a computer fan as a generator on his pedal bicycle to charge his phone. Not enough power. So he tried a huge fan that worked fine when the bicycle was stopped and the wind was blowing. But when the wind stopped it was a lot of work to pedal the bicycle and drive the fan generator, like pulling an opened umbrella behind him..
I already tried the same senario and it extend my riding range, i am working further to extand my range more but i will switch from bike into trike or electric car. I cant say that i can drive freely without charging but i can extend my range with it.. which i tried and successed.
Later i will share my project on youtube and over on facebook .... will discuss there ...

I am very interesting to have more discussion in this matter ...
 

audioguru

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The generator will charge the battery with high current when the ebike is coasting fast downhill. Then the battery powers the motor with low current slowly uphill to go back. The range is increased because the charging speed is fast and the driving speed is slow. If the speeds are the same then the battery will go dead sooner with the generator. "Over-unity" is impossible.
 

tcmtech

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I already tried the same senario and it extend my riding range, i am working further to extand my range more but i will switch from bike into trike or electric car. I cant say that i can drive freely without charging but i can extend my range with it.. which i tried and successed.
Later i will share my project on youtube and over on facebook .... will discuss there ...

I am very interesting to have more discussion in this matter ...
So adding more mass to your bike plus more drag on the motor that drives by adding a second motor that drags along as a generator to charge the first motors battery it is making it go further?

Do explain being every known law of physics says otherwise. :facepalm:

If you really think its working then why not just add a third motor that spins a belt drive that spins the generator motor faster and use its output to charge the batteries and skip the ground drive stage altogether?

Or use the motor you have now to spin an automotive alternator that puts out way more amps than the hub motor can?o_O
 
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alec_t

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The generator will charge the battery with high current when the ebike is coasting fast downhill.
.... and while this charging is occurring there will be a (regenerative) braking effect on the bike. The energy for charging comes from the kinetic energy of the bike + rider. But that kinetic energy came from the battery initially!
 

audioguru

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.... and while this charging is occurring there will be a (regenerative) braking effect on the bike. The energy for charging comes from the kinetic energy of the bike + rider. But that kinetic energy came from the battery initially!
No. If the ebike goes downhill at a breakneck speed then it charges the battery with a high current. Then returning, the ebike goes uphill slowly using low current. Then the range is longer than without the generator.
Why can't the motor on the ebike be the charging generator when the ebike is doing downhill?
 
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