Battery recharge with dynamos?

[emirwati]

Hi all. I am Victor, now living in Malaysia. I built an electric bike during the COVID-19 times, using an old frame of mine plus a Chinese motor and battery. This motor is not prepared to recharge the battery during downhills and braking. I was wondering if it is possible to partially recharge the battery during long downhills by activating a pair of dynamos. My Li-Ca battery is 36-volts and I was thinking of a pair of dynamos, 12-volts each. Now, forgive my ignorance, but I suspect that the dynamo output needs to be modified and I am not sure if it will make a difference, given the voltage difference. Regards.

 

[Chargeride]

Technically possible, but most dynamos are much lower voltage, requring a converter, even top spec regen doesnt offer much reclaiming of energy.
If you are using a geared hub, you can weld up the clutch, but that introduces other problems and you need a regen controller.

 

[harryS]

Won't work at all. It costs power to spin those dyamos when they are not charging the battery. More power than they will return to the battery when activated.

Now you could do it anyway and pedal the bike harder to recharge the battery, Then you could say it works, without taking into account all the effort you put in. Do you know the extra effrtto pedal a bike with one light generating dynamo. Put three in series.

 

[Chargeride]

I was considering a mechanism to engage them downhill, probably nothing more than an interesting experiment.
Which is the backbone of discovery

 

[harryS]

The old fashioned bike dyamos already have the frame mount. As kids, we snapped them against the wheel and the tire sidewalls would spin them. Credit Ralf Roletshek for the picture. I remember they did drag.

You may want something bigger to put 2 amp hours into a battery.

 

[MartsEbike]

What's the opinion on the Grin Freegen... Seemed a pretty nifty concept.

 

[kevinmccune]

What's the opinion on the Grin Freegen... Seemed a pretty nifty concept.

more for saving the brakes than anything else,the main problem is most of us have a pretty low output,i figure my best pedaling around 80 watts. My heroic days are behind me,now i strive for comfort and a bit of exercise( had a pretty good hike one day when i spun the stator out on a bike i got from a friend,one side was clean loose i had actually checked the other side) so it goes check everything at least occasionly.

 

[Chargeride]

The problem is most batteries can at best charge 4 amps.
Coming down a mountain might take 10 minutes, but if you are limited to 4 amps, its no great reclaim.
If you could whack 20 amps in, then it would be a significant payback.

 

[Stefan Mikes]

What's the opinion on the Grin Freegen...

The opinion is you should pedal harder/faster uphill and then take the rest on the descents

\
Ask the man on the left (with the thumb up). He will tell you he got the 2nd place on a 50+ mi/+1000 ft elevation gain e-Sprint gravel race riding a standard Vado SL 4.0 EQ with one Range Extender (I asked him: he is 5 years your senior; I told him you've just bought a Vado SL, and he wishes you all the best on your rides!)

 

[MartsEbike]

The opinion is you should pedal harder/faster uphill and then take the rest on the descents

View attachment 185136\
Ask the man on the left (with the thumb up). He will tell you he got the 2nd place on a 50+ mi/+1000 ft elevation gain e-Sprint gravel race riding a standard Vado SL 4.0 EQ with one Range Extender (I asked him: he is 5 years your senior; I told him you've just bought a Vado SL, and he wishes you all the best on your rides!)

I am constantly amazed at what some riders can do! Yesterday I saw a guy riding a traditional bike and he was flying along at pace, easily 20mph+. I was struggling to keep him in my sights! I'd guess he was a good 15-20yrs older than me too! He wasn't riding anything flashy either just a simple drop bar touring bike. The stamina these guys have to produce that kind of power over long distances just blows me away!

My power is pretty good, but my stamina is severely lacking. I can make it up very steep but relatively short hills pretty easy, but if I hit a 1-2 mile climb on a much shallower gradient I'm soon wishing for it to end.

Thankfully I have a bike now to help work on that!

 

[Aushiker]

My experience with two bikes with dynamos is that over a day of riding (mostly touring or Audax), the dynamo will keep the lights on and maybe maintain the battery charge on the GPS or at least slow down the drain. Turning the lights off does help with the GPS charge, of course). I cannot see how it would make any notable difference to the charged state of a ebike battery.

 

[Stefan Mikes]

I am constantly amazed at what some riders can do!

The reason my mate bought a Vado SL was his bad back

 

[kevinmccune]

The reason my mate bought a Vado SL was his bad back

Vados can help( had my arse on a nice specialized one time the ease of operation was amazing)

 

[spinnanz]

To put the power needed to recharge a battery into perspective, to recharge a 36v battery at 2a, you would be required to produce 72w. A fairly decent non pro cyclist can maintain 175-210w for about an hour.

Can you imagine how hard it would be to pedal if cycling on its own (at a fair pace) requires 175-210w of energy, and you then add another 72w of load to the person? That will knock a fair bit off their speed and range.

Add to that, the energy used to recharge the battery has losses so it will reduce the cyclists range by more than it will give back.

 

[PCeBiker]

The old fashioned bike dyamos already have the frame mount. As kids, we snapped them against the wheel and the tire sidewalls would spin them.

View attachment 185105

I had the whole kit when I was a kid,..

I'd reach down and press the button and it would spring load onto the tire.
I had to grab the dynamo by hand to rotate it off the tire until it clicked to turn it off.
I only ever tried to shut it off once while I was riding.

It costs power to spin those dyamos when they are not charging the battery.

That generator Sucked !!
It was like pedaling uphill with the brakes on as soon as I turned the lights on.
I had a HUGE spring to push it into the tire so it would grab the tire hard enough to keep the armature spinning.

Do you know the extra effort to pedal a bike with one light generating dynamo. Put three in series.

Three of them would probably lock up the tire and you'd go over the handlebars.

,.. Credit Ralf Roletshek for the picture.

I stole my pictures off ebay,..
My generator had the splinned metal wheel on the armature.

Your picture shows a thinner rubber coated wheel against the tire.
I have never seen that before.
Looks like the Rolls-Royce version?
It probably works more efficiently?, but it's a bigger wheel so you'd have to pedal faster or your light would go dim.
I'd rather just pedal in the dark.

,..Do you know the extra effrtto pedal a bike with one light generating dynamo. Put three in series.

That Dynamo is rated 12V 6W, so three in series would be 36V 18W at ½ an amp to charge the battery.

You'd need Really soft sticky tires to grab the road without skidding, if you ever wanted to charge at 3 amps.