Derbi senda 50cc electric conversion

Just thought I would share my first E bike build.
alloy frame derbi senda 50cc main frame,forks wheels and swingarm, wheels were re spoked onto 19" x 1.6 rims
motenergy me0909 motor running 48v 4kw constant with 15kw peak
4QD 300a 48v dc motor controller
4x 12v 17ah sla batteries
12T front sprocket 66T rear sprocket
Quite fast at around 40-45mph top speed, and acceleration is good but the sla batteries are the limiting factor.

Very nice. That would make a great suburban back yard machine. Are the SLA good enough for your purpose? Do you plan to register for street use?

It looks really nice, it's really a shame that sla's are in there. I can't imagine 15kw being pulled from them. And very interesting analog controller

that's BRILLIANT! congrats'

I dont post on here very much any more but wowser! thats lovely, I was thinking of using an old sinnis apache for the very same thing, pack some model lipo in there and it will make it even more awesome.

More pics please and any build before and after photos?

Thanks for the reply's guys.
The 4QD controller works really well with the domino twist grip throttle, I was very surprised by the control at slow speeds and the responsiveness.
been out tonight for a proper test off-road, it has enough power to start with then batteries voltage drops like a brick and controller drops into limp(safe) mode after about thirty minutes of playing.
I didn't think the sla batteries were pushing the motor at 15kw, when fully charged it is really fast for about five minutes then you can feel its not as fast.
I don't know enough about lipo batteries to do a upgrade as I would have to build the packs myself to fit the frame, but I would think it would be mind blowing with some proper batteries fitted.

Kevprojex said:

Thanks for the reply's guys.
The 4QD controller works really well with the domino twist grip throttle, I was very surprised by the control at slow speeds and the responsiveness.
been out tonight for a proper test off-road, it has enough power to start with then batteries voltage drops like a brick and controller drops into limp(safe) mode after about thirty minutes of playing.
I didn't think the sla batteries were pushing the motor at 15kw, when fully charged it is really fast for about five minutes then you can feel its not as fast.
I don't know enough about lipo batteries to do a upgrade as I would have to build the packs myself to fit the frame, but I would think it would be mind blowing with some proper batteries fitted.

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There are high performance batteries that are not lipo, that are safe.

http://endless-sphere.com/forums/viewtopic.php?f=14&t=57291

Some more pictures.

Nice work!

Why didn't you leave original rear shock position? And why bicycle seat instead of original?

Hi riba, to try and avoid unwanted attention I was trying to make it look as close to a mountain bike as possible.

Ok I get it! Really nice craftsmanship, it looks like it's from the factory!

Absolutely gorgeous build. Looks like a commercial ebike. Really nice job.

Its really very nice indeed, the SLA batteries will sag like an old tit and will get worse quickly I know this from experience.

There are loads of threads on here about building packs, at 15KW you are going to need a pretty decent pack to feed this, you could do it with model Lipo in parallel banks, or 18650 cells which is a bit more work, looking at your frame design you could easily fit in 8 x 25C 5ah batteries in there with ease that would give you 48V at 20Ah a real 20Ah as you wont be getting that from those lead acid batteries.

25c packs can be had for 30 quid a piece you could make a pack up for 300 quid or so that could in theory give you 250A at 48V - 20AH you can up it to 35C packs if you needed to although I would be tempted to dial the power back a little in the controller.

The cost and weight of those SLA bricks not to mention the chemistry will hold you back, I have been using lipo for well over 10 years and havent touched Lead since, I went from using Lead to Nimh batteries and then on to Lipo.

Have a dig around on the forum, if you dont want to make your own pack up contact steve at Jozzbikes http://www.jozztek.com/shop/ tell him that knoxie sent you he is only in brighton, he may still be making the packs up? not sure? I am sure that he would like a look at what you have done, he is a top top bloke.

Good Luck

I just saw this on Ebay, claims to be 48V 10AH 350A with a battery management system and a years warranty, its a little pricey maybe but it does have a BMS, they are used for those Osset electric trials bikes.

http://www.ebay.co.uk/itm/High-Powe...059?pt=LH_DefaultDomain_3&hash=item1e9d2c7bc3

Ok..i couldnt resist and registered, such a nice build! I think your ebike look succeded, it looks like one of those custom made ebike frames, but a tad more luxurious.
I always wondered (iam new to the scene), what is the downside of using rear hub motor?

Thanks for the info knoxie, I did look at that lipo oset battery pack after I had made the battery boxes so just decided to run with the spa batteries to see what it was like.
After my test last night I found the top speed to be useless as it was way too fast for the trails by my house and I was only using small amounts of throttle most of the time.
The 4QD comtroller says 24v to 48v so today i decided to drop the voltage down to 24v to slow the motor down to just over 2000rpm, I linked two pairs of the batteries in parallel then series wired them to the controller to give me 24v, am I right in thinking this has doubled my AH to 34ah instead of 17ah ?, I tested the bike after and the top speed is more than enough at just over 20mph and the bike seems to pull a lot better as well.
If I fitted lipo battery packs would they make a big difference to the performance or just the range.
Also after about half hour testing the 16mm cables to the battery were warm to the touch so would adding more power cause other problems or limit the use due to heat build up in the motor etc.

I couldn't tell you the answer to that one xtruder sorry, this is my first electric build, and coming from building motorcycles I just went with a design that looked ok to me, the customers that comes into my unit think it is a little strange looking though.

Hi Kev

halving the voltage will double the ah rating at 24V but you will still have the same watt hour rating and effective capacity, it will also have the effect of increasing the current through the cables hence the warming of the cables that you found, doubling up the batteries though will help reduce the overall sag and will reduce the Peukert effect, see wiki for an explanation of this.

The motor that you have will have an optimal efficiency rating at a certain speed, check with 4QD on that to find what it is, if you have current limiting on the controller I would use that feature and keep it at 48V but reduce the gearing to reduce the top end speed, this will give you more low down torque and make it more rideable on the throttle.

Throttle mapping may also help, again I dont know what the 4QD offers but other perm magnet motor controllers like the alltrax do let you adjust this so that you have a more even spread of power over the mechanical throw of the throttle, check with 4QD they are super helpful.

I dont blame you for trying out the lead acid option first, ideally and please dont think you have to change the bike a better motor would have been a brushless DC motor and a brushless controller such as the kelly controller, but you can make that an upgrade if you love riding the bike and think you will use it a lot, was going to ask if you have fitted a main contactor on the bike? its very important with a perm motor that you do, because if the motor controller fails there is a very real chance that the motor will run flat out until it hits something and stops, semi conductor fets almost always fail short circuit, this is less of an issue with a brushless controller motor combo but it very important with a perm mag motor combo that you have.

Lipo batteries would not sag any where near as much and would definitely improve the performance, they would give you more range as well partly due to the Peukert effect and their lower internal resistance.

The other thing that I was going to mention is the airflow over the motor and the controller, keep an eye on the temperature of both, mounting the motor and the controller inboard with no external airflow is hard on both, keep an eye on them and utilise motor and controller thermal overload protection if possible.

Speak to Steve at Jozztek about the batteries, in theory you could run a lipo pack in parallel with the lead batteries at the same voltage although you must not charge them that way, it would be best to just run lipo, however for now have some fun on the bike with the lead and think about lipo in the meantime.

You could buy 4 high capacity lipo pack from hobbyking and just try your own 10AH pack and see the difference, I think you would be amazed.

Newbie way of doing it it buy a 4 channel charger, you can charge all 4 packs in 1 go, each cell is monitored whilst charging and balanced, check the hobbyking site for the details.

4 of these

http://www.hobbyking.co.uk/hobbyking/store/uh_viewItem.asp?idProduct=19156

and one of these to charge them

http://www.hobbyking.co.uk/hobbykin...attro_4x6S_Lithium_Polymer_Multi_Charger.html

You would also need a good DC power supply to run the charger like this

http://www.moonraker.eu/alinco-dm-330mw-30-amp-power-supply

I have been running this combo on my ebikes for 5 years now with no problems, your bike is a bit more demanding on the power front so you would have to use more expensive batteries, you would also need to watch the power used as well, I would suggest using a high current cycle analyst as you dont want to run the lipos down low below 3.2V per cell.

right its late im to bed, would love to see some video of the bike running

knoxie said:

I just saw this on Ebay, claims to be 48V 10AH 350A with a battery management system and a years warranty, its a little pricey maybe but it does have a BMS, they are used for those Osset electric trials bikes.

http://www.ebay.co.uk/itm/High-Powe...059?pt=LH_DefaultDomain_3&hash=item1e9d2c7bc3

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its miss described .. it is a 60A constant bms .. and it is very pricey

edit..
the lifepo4 8.4ah 30c batterys that hobbyking sell are up to spec ( tested ) and being lifepo4 is a much more forgiving chemistry.. you can get 16s 80A bms for £25 delivered ( if you know where to look ) also a 5A charger for £30 .. 2x lifepo4 4s2p batterys approx £200 and £50 for charger and bms ( £250 total + a bit of work ).

Thanks guys this is all a learning curve for me as electrics are not my strongest subject, when I built the bike I used a basic motor and minimal wiring to get the bike working as it was simple enough for me to understand, The 4QD controller was simple to set up as it didn't need a computer to program the settings and has adjustments for the Ramp UP, Ramp DOWN, Current Min/Max, Low voltage cut-out and a trim pot to set the throttle potentiometer to the controller, I have set this up and the response and throttle sensitivity are way better than I thought it would be coming from petrol engines.
I do not have a main contactor fitted but it is a very good point about the controller fail to max output.
I have been out for another ride tonight for a hour on light trails and small hills after converting to 24v and the bike was still pulling and useable but lost some top speed.
After riding at 48v and then 24v one is too fast the other a little slow so would 36v be the best way to go ?
After reading some comments about adding lipos to the sla batteries, if I wired it for 36v removed one battery and fitted 3x 11.1v lipos in series up to the controller for added power ?.
if I went down the lipo battery route what would the best way to do this as they are all different voltages, would two battery banks of 8 x11.1v lipos be enough ?, or would it be better to use 4 x 22.2v batteries , if I fitted all the batteries in the bottom two boxes that would leave the large top battery box under the controller to fit a bms board and wiring or vice versa.
How many batteries will I need compared to the the lead acid I am using at the moment.
I think the bike is great to ride and I will probably upgrade to lipo batteries, so what would be the best voltage 24,36 or 48v, what AH rating on the lipo packs and best voltage on the lipos to add up to the voltage i want to run on the motor/controller. Its all confusing :?

if you look at lifepo4 then 4s is basically the same as 1 sla ( 14.4v hot off the charger )(as regards voltage ( lipo 4s if a slightly higher voltage ( 16.8v hot off the charger )) as you have a controller that can handle a fair bit of power then yes go for 36v... but may make it all a bit easier on the wiring and batterys if you went to 48v and reduced the gearing a little .

When choosing a RC Lipo batterys to make my pack is it better to choose ones with a higher C rating or a higher mah.

the C rating is the max discharge current that the battery can safely discharge at and is worked out by C rating X Ah's
e.g a lipo that is 5000mAh with a C rating of 20c can safely deliver 20x5 =100A

the mAh size is like the size of the fuel tank and the bigger the mAh's then the bigger the tank ( the more distance you can travel ).

if you parallel 2x 5000mAh batterys then this becomes a 10000mAh battery..

so basically you need to decide how big is your fuel tank going to be and also what is you maximum continuous current will be.

and if you work on a average of 1000mAh = 1mile round trip this will give you some idea of how many mAh's you need.

Ok I've got it bigger is better , I am guessing I need to fit a volt meter to keep an eye on the batteries so not do drain them down too far being lipo cells.

Kevprojex said:

Ok I've got it bigger is better , I am guessing I need to fit a volt meter to keep an eye on the batteries so not do drain them down too far being lipo cells.

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a volt meter is always a good thing..