Bike that charge’s it’s self

[Footie]

The other day I took my bike for a short spin to test the new Speedo I fitted and I left the battery out. During the ride I noticed the power lights on the throttle were lighting up. At the time I thought it strange and forgot about it.

Recently I was looking at bikes on eBay and I found a dealer selling a bike very similar to mind. In fact it’s exactly the same except his is a steel frame and mine is aluminium.

EuroCycle - Electric Mountain Bike - Triple Mode on eBay, also, Bikes, Cycling, Sporting Goods (end time 18-Jan-08 17:45:00 GMT)

On his web site he claims his bike is fitted with a Triple Mode Motor.
Mode 1. Battery Switched on --- Pedal forwards and the hub mounted, brushless motor provides electrical assistance.
Mode 2. Battery Switched on --- Twist throttle grip to add extra power, or stop pedalling and coast along.
Mode 3. Battery switched OFF, -- Pedal forwards and the battery will recharge.

This Mode 3 would explain why the power lights were lighting up.
Is this peculiar to my bike or is this normal?
Should I be careful riding without a battery in case the generated charge fries something
Any thoughts on this?
.

 

[flecc]

No risk of frying anything, regeneration current is very small on bikes, more like solar power output than dedicated dynamo, so like a trickle charge maintaining the battery.

Very few bikes use regeneration. It's ok in direct drives like the BionX which has it, since those are very low drag motors, but in a geared hub motor, it means no freewheel so the motor is high drag all the time. That slows the downhill speed gain, and it's a pain if the battery ever runs out and you need to pedal home without power.

Giant have adopted it on their New Twist bike, and predictably that does have the high hub motor drag.
.

 

[Footie]

No risk of frying anything, regeneration current is very small on bikes, ....

Oh, that's good. Thanks flecc.

I had visions of my bike bursting into flames
.

 

[Bikerbob]

I think we can maybe get a false impression of regeneration. When I climb a long hill on my Giant Suede I can find that the charge level indicator goes down to one light (of three). At the top of the hill I switch the motor off and go down the other side at 20 - 25mph with the motor giving a shrill whine. When I next switch it on it can be up to three lights again. Looks like regeneration but Giant, through AtoB magazine, say not so. Perhaps during the period of sustained hard use the battery has given a false reading. Once it has had a rest it reverts to normal. That's my guess anyway! Does that happen on other bikes?

 

[coops]

Yes it does Bob, the battery meter usually indicates the voltage level of the battery, which drops measurably under heavy load such as on hills: for example, on ezee bikes with LED battery meter its similar, going from green to amber or even red under load, then back to amber or green when the voltage recovers after the load is reduced .

If you were to stop briefly at the top of the hill with the motor on, you should see the battery meter return to 2 or 3 lights (depending on the charge level remaining) before your downhill stretch, and that surely isn't regeneration while you are stationary!

A way to measure how fast regeneration occurs would be to find a good long downhill stretch & see if theres a measurable increase in voltage at the end: a 30 mile downhill would be good! .

Stuart.

 

[flecc]

There's also cell recovery on Li-ion batteries. Load one up and the charge meter can end up with a lowered reading even after shutting the throttle, but after a few seconds or minutes rest, the voltage and meter indication can rise again.

It's due to failings in the cathode and anode current carrying capabilities. The carbon anodes aren't so bad, but the manganese cathodes used on safety grounds struggle with high current delivery.

The previous cobalt cathodes were more capable, but they needed to be accompanied by a fire extinguisher.
.

 

[Jeremy]

As Flecc rightly says, the regeneration power is quite low on those systems that can make use of it, most probably around 5% to 10% of total Wh used (based on the regeneration readout in the Prius).

Peak regeneration current can be high though, especially when going down hill at a fair old lick. Usually this doesn't cause a problem, as very few controllers allow regeneration anyway, but for those that do you may well see charge current peaks in the tens of amps.

This is only for very short periods, so overall the regeneration average power is low, but it can cause battery balance problems for some types of pack. My guess is that SLA and NiMH are unlikely to be problematic, but I am not too sure about any lithium based chemistry battery, they tend to be more sensitive to maximum charge rates.

Although regeneration sounds as if it might be useful, in practice it doesn't seem worth the hassle of arranging the voltage multiplication needed to make it work. What is, apparently, worth doing is adding a load-dump brake. Essentially this just adds a low value resistor across the motor windings when the brake is applied lightly, before the friction brakes start to work. The result (for a non-freewheel hub motor) is a fairly powerful braking force that is dependent on speed - the faster you are going the more powerful the braking force. I might be useful if you have to descend steep hills regularly, as it saves wear on the friction brakes.

Jeremy

 

[Tiberius]

Although regeneration sounds as if it might be useful, in practice it doesn't seem worth the hassle of arranging the voltage multiplication needed to make it work.
Jeremy

Now I was thinking that, but I think it turns out that the voltage conversion is not difficult. In the forward direction the controller acts as a step down voltage converter; I suspect it takes very little extra circuitry to make it act in reverse when driven in reverse.

Nick

 

[Jeremy]

It's pretty simple to do, Nick, as you suggest. The easiest way is to use an extra simple brush motor controller and a three phase rectifier. The new controller "throttle" becomes the regeneration control. The PWM from the new controller works with the motor winding inductance to form a step-up converter. One of the chaps on the Endless Sphere forum came up with the idea.

It turns out that it isn't really worth the hassle though, unless, perhaps, you live in a hilly area.

Jeremy

 

[Ian]

I had a cheap bike that had a form of regeneration, the brushless controller implementation was very simple using six 75NF75 mosfets in the usual 3 phase bridge driver, but in addition these transistors have an integral 75A reverse biased diode across the drain and source which automatically forms a 3 phase bridge rectifier when uded in this arrangement. The diode is actually a zener which protects the FET against high forward voltage spikes as well.

The system did work surprisingly well, on a number of occasions I coasted downhill with a flat battery which acquired enough charge to give useful assistance on the way back up. Unfortunately the rest of the bike was so inefficient that a flat battery was a frequent occurrence, the inefficiencies more than negating any advantage and the bike was awful without power.

Another problem was that the Tonxgin motor by necessity had no freewheel which was a drag, literally. The most serious problem however was the bikes nasty habit of destroying controller mosfets when coasting downhill. I'm not sure why, the 75NF75 would seem to be a good choice being specifically intended for motor control applications and seemingly bombproof when used within it's perfectly adequate ratings.

 

[Bikerbob]

A way to measure how fast regeneration occurs would be to find a good long downhill stretch & see if theres a measurable increase in voltage at the end: a 30 mile downhill would be good! .

Stuart.

Thanks for the explanation Stuart. Living on a small island, I don't think I'll try the 30 mile downhill. I'd be swimming before I got that far!

 

[coops]

Don't do it!

I didn't realise you lived on the Isle of Man, Bob - my suggestion was rather tongue in cheek & I wouldn't have said it had I known...

A longish downhill should do the job and there are probably other, more convenient ways to test the regeneration - I wonder if its possible to cycle 'down' a treadmill?! (But those do use power themselves, as Ian said in the 'greener miles' thread, so maybe not best! ) Just finding a way to rotate the motor wheel would be enough - something like one of those 'rolling road' devices used by cars etc. might do it .

Stuart.

 

[Bikerbob]

I did realise that your comment was tongue-in-cheek Stuart and was replying in kind . I'll just accept that that the apparent regeneration is down to the way the battery/indicator works and not bother about it further. This sort of forum is a particular benefit for those of us who are geographically a bit isolated, and can't easily visit dealers or bike shows. I'm happy that I found it, and I'm certainly not going to take a bit of humour the wrong way!

 

[coops]

Thanks Bob, I thought so but posted in case I'd caused any problem, glad there wasn't . From what I've seen, your island is quite hilly in places, so if you do take a longer trip with ups & downs the regen may be useful to extend the range a bit, without you thinking about it too much, or getting wet either! Just watch out for the TT races . Take care!

Stuart.