Modification - overvolt/turbo button question

[KirstinS]

Hi all,

First post here - I've spent a lot of time on here gleaning valuable info though. Still very much a newbie so hoping for your advice

I've been considering various options for my own build and then I came across Xipi bikes. They have a "turbo button" which increases speed (beyond legality for on road use). I've kind of assumed this is done by overvolting the hub (or more likely it is "undervolted" at normal usage, say 24v, and the turbo button connects the full voltage, of say 48v, to the hub). Does anyone know if my assumptions are correct ?

Essentially my idea is to hook up a couple of 7.2v RC packs into my overall build. At the push of a button this could provide an extra 14.4v to the motor. I understand that I need both a motor that can handle the voltage and a controller likewise. I also undetand that the batteries don't hold much juice. That's not a problem for me - a 250w motor and 24v type benchmark of assistance will be enough for me for 99% of the time.

I just really like the idea of a Moment of Madness button (or a Get away from Danger button depending on your viewpoint). I don't want it available all the time, I don’t want to run a high volt system as I just don't need it (the wieght or cost). I also like the idea that if you overuse it then your turbo button stops working but your main batteries keep on chugging away i.e. they are separate. You don't need any self control !

Is there a glaring reason why this concept cannot work ? Does having a hub and controller that can hack the brief extra voltage but runs for 99% of the time at a lower voltage cause any problems in itself ?

Finally any advice on hubs and controllers that could do the job ? Was wondering if an old school currie electro drive can be overvolted in this manner (as I've been offered a 3 year old unit and donor bike for £150 which seems very cheap - even with half decent SLAs)

I hope what I just wrote makes sense to someone……. I went and looked at endless sphere but this I didn’t understand any of it…..

Many thanks
Kirstin

PS I should prob post in technical but i dont seem to have the right priveledges to do so on my account, sorry

 

[Deleted member 4366]

Your idea in principle is good: However, if you have a nice (light) 250w motor, say 36v, then your extra 14.4 volts would give it a bit of a boost, but I wouln't describe it as a "turbo boost" - more like you've opened the throttle a bit more - as it'll give you about another 100 - 150 watts above the normal ca. 400 watts. As a percentage, it sounds a lot, but, having used a 350w motor of about that power, I can tell you that the difference is not easy to detect until you do a side by side comparison. You'd need a controller capable of handling 56 or more volts, which many of them can. The only way you can get real turbo boost is if you have a big motor and powerful battery, but then you'd have the weight as well.

 

[NRG]

And to add, it will depend on the Kv of the motor as to what speed you'll get ignoring drag etc. Taking 700c wheel, nominal 36v and 190RPM bafang motor (top legal speed of 25Km/h) the Kv is approx. 23 so switching from say 36v to 48v nominal would mean and increas in wheel RPM to 256 or thereabouts giving an unloaded wheel speed of approx 21mph.


You can switch voltage as you say but IMHO it would be easier to use a controller, like a 48v E-Crazyman and use the 3 speed switch capability these controllers have. The three speeds are programable and E-Crazyman can set the % per switch setting to give you 3 different speeds, say 100% = 21mph, 75% = 15.75mph and 62% = 13mph

 

[z0mb13e]

I'm not sure that connecting a couple of extra 7.2v RC packs in series with SLA or Lipo to increase the voltage is a good idea. The different battery chemistry's would offer different current discharge rates and internal resistances and you would likely dissipate current from one battery in the other. Best case is you waste power, worst case a cell goes pop. If you are determined to go down that route I would think matching the voltages so if your main battery is 24v then your boost battery should be 24v (or more providing some reverse current protection on each battery) which could then be switched in, in parallel. I'm no expert and my electronics knowledge is rusty, so by all means try it. You never know you might invent KERS for ebikes! As anyone on this forum who has worked with ebike batteries will tell you, be careful! These things hold a lot of power.

Also simply increasing the voltage won't necessarily increase the top speed if the controller is controlling a brush-less motor. This is controlled electronically by sending sequenced pulses of current into the separate motor windings or phases. You might get a bit of an extra kick from a higher voltage when accelerating if the controller can stand it. Brushed motors are more likely to give you a top speed boost for a higher voltage.

 

[KirstinS]

Thanks all - It did seem just a bit too easy ! I think the main point I've taken away is that, even if I can tip toe my way through the various pitfalls without blowing any of the parts or myself up, I'm unlikey to really get enough extra oomph to make the whole thing worthwhile

@ NRG, I notice you have the alien gs. I am also considering the alien gs matrix as an off the shelf option. This has a 3 speed power setting - does this work the same way as the e-crazyman contoller ?

 

[banbury frank]

Hi KirstinS


We have our standard controller that runs 33 amps top speed

Depending on the voltage off the battery and the motor windings

Hill climbing depends on the windings off the motor




Power 48 volt X 33 = 1500 watts to motor

36 volt 36 X 33 =1100 wats to motor

36 or 48 volt auto detect

our large controller is 60 Amps

48 volt and 60 volt selectable

So 48 X 60 a 2800 watts to motor

60 Volt X 60 A 3600 watts to motor


Our Motors are linear 9 RPM to 12.5 RPM per volt depending on the motor windings

we have a simple connection to the main micro processor and we can set the speed 15 MPH we now sell that connected If you disconnect a plug it for off road use or we can supply a twist throttle with a switch so if part off your journey is off rod you can switch easy

No Over volting Just real engineering done in the UK

It is like having A Taylor made suit made we need to no how tall you are how much you weigh journey length how many hills in the journey

Please come and try one in Banbury

Frank

 

[NRG]

Less of the semi soft sell please Frank.

...
Also simply increasing the voltage won't necessarily increase the top speed if the controller is controlling a brush-less motor. This is controlled electronically by sending sequenced pulses of current into the separate motor windings or phases. You might get a bit of an extra kick from a higher voltage when accelerating if the controller can stand it. Brushed motors are more likely to give you a top speed boost for a higher voltage.

Well yes it does. The controller can only PWM the voltage and the duty cycle is programmed in so upping the volts has a direct affect on the volts seen by the three phases, they are voltage controlled motors. Current control is a by-product as it where of the PWM control and unless there is a current shunt in each phase, phase current is essentially guessed at based on monitoring the battery current and a parameters programmed into the controller.

 

[NRG]

@ NRG, I notice you have the alien gs. I am also considering the alien gs matrix as an off the shelf option. This has a 3 speed power setting - does this work the same way as the e-crazyman contoller ?

I don't know KirstinS but at a guess I would say it works in the same way.

The E-Crazyman uses the 3 speed switch as throttle scaling IE the motor RPM is directly proportional to the throttle voltage, so if 4v gives 100% RPM, 2v would give 50% RPM....the physical throttle travel though remains the same...

 

[KirstinS]

@Frank - thanks for explaining that for me. I would love to come and look at your bikes but I'm afraid my budget just does not stretch that far It might one day if I had a longer commute but at present it is only 10 miles each way I really just want an alterntive to my normal road bike on those extra windy days (or lazy ones!) as I live on south coast near Brighton.

Until it is at least 20miles each way there is no way I'm gonna get Xipi bike expediture past the Minister for Home Affairs (aka the wife)

thanks again all

 

[banbury frank]

Hi KirstinS


Follow these links for a small kit + battery


Q128 500W Rear Driving E-Bike Kit - BMSBATTERY

36V 15Ah LiFePO4 Shrink Tube EBike Battery Pack - BMSBATTERY

Fit the battery pack and controller in one side off rear panier bags

They sell other wheel sizes + front or rear

I recommend Rear as you can Damage front suspension forks

others have bought from them

Please pay By paypal then you money is safe

Cost including delivery approx £350 normally takes 7 /10 working days

Hope I have helped with a unbiased posting


Frank