RC Car batteries for e bikes

[Richard1174]

That motor looks really sweet scott.

On your bike did you run your throttle control through a pot onto a servo tester and bec to the speed controller or is their another way to do it. whats the max voltage that the speed controller can handle

 

[scottclarke]

Richard - yes I wired in a linear 10K to the original pot solder spots. Its a very simple but also reliable way or doing things

 

[Richard1174]

I took some readings off my watts up meter on the run on the way home from work. Used total 60 watt hrs / 1.55amps from my 36v 10amp lion battery which came with the kit I purchased, thats with me pedalling along with motor pretty much constantly as I need the exercise, but that works out to 120watt hr round trip, 60v at 3700maH is 222 watt hrs so its possible that I might get to work and back on these batteries. Obviously a real world test will be the proof but its got potential. I'm doing around 18mph at the moment which isn't bad but twice if been stuck behind a tractor now and I just have not got enough beans to go round them effectively so I NEED MORE SPEED.

 

[Richard1174]

Hey you RC motor fans how about this little beauty.

http://www.e-flight.co.uk/shopexd.asp?id=713

 

[scottclarke]

Richard - my bike as it is is plenty fast enough - nearly got me in an accident twice today - almost every ride something happens........... It can pull away from lights faster than most car drivers *do* and goes faster than is safe (IMHO).I had free choice when looking at motors since I had not chosen a frame - I figured nearly 4HP would be plenty - and it is! Today I had an organised race against a 50cc scooter and he didn't stand a chance - he was 4M behind at 30mph and that was his max speed, but then, they do have only 1.7 or so HP and weigh 100KG more.....

The frame was chosen based on the motor diameter. I am having a wheel built using motorcycle spokes since I have all kinds of pinging sounds under accel............ I need this before I run it with the new controller since instead of cutting out it will simply pull harder..........

I think the 6kw motor (7HP) would be fine on a light motorcycle/scooter but massive overkill on a mtb!

Others will differ of course.

Scott

 

[Miles]

Here are the energy density figures given for the Vapextech 12V NiMH packs (@ 0.2Cdischarge):

3700 mAh - 66 Wh/kg

4300 mAh - 74 Wh/kg

[For comparison the LifeBatt cells are 80 Wh/kg]

 

[AussieJester]

I came across a seller on eBay selling 14.8volt 4000mah packs for 35 bucks More interesting he has some listed as bidding lists and there were several 14.8 volt packs sitting on 6 bucks with no bids and under an hour too go. Would 8 of these hooked up for ~56 volts be a good option?

 

[Richard1174]

My New packs should be here tomorow so I will rig it up and do some testing at the weekend. From the feedback I have had from scottclarke I would say that 8 14.4 v packs should do you a treat depending on how far you want to travel. If you have a relatively short commute but want to go quick I think these packs are the answer but I will know more after the weekend.

 

[Miles]

The ones that Aussie referenced were Li-Poly which, given his propensity to set things on fire......

 

[Richard1174]

Hi Miles

Just been looking at your bike in the photo section WHAT A CORKER you have got to be over the moon with how that turned out. (one day I will create a thing of beauty).

I assummed aussie was on about nimh not li poly I have not seen one them go up but I am told its not pretty.

Years ago a friend of mine put a 7.2 v 1200mah nicad race pack in his pocket fresh off the charger it shorted out on his keys ( insulation was damaged ) and it made a real mess of the top of his leg not good. Batteries can be very dangerous if there limitations are not respected.

How do you calculate the energy density of the 3700 mah packs.

 

[Miles]

Hi Richard,

Thanks!


3.7Ah X 12V = 44Wh

Pack weighs 0.668 kg

44 divided by 0.668 = 65.868........ Wh/kg

 

[Richard1174]

Thanks Miles

Now I can do some more maths

 

[AussieJester]

The ones that Aussie referenced were Li-Poly which, given his propensity to set things on fire......

Watched my Gaui 550 Hurricane electric chopper "self ignite" 50 foot off the ground upside down when one of the batteries went BANG hehe Seeing those batteries are rated at 20c and you wouldnt be pulling more than what 5c ? chances of them exploding are less than minimal i would think, that said i wouldnt use them as i have seen first hand how they go up hahaha guess you could always pop them in a lipo bag though?

 

[Miles]

Ok guys, here's my plan.

For a lightweight backpack, to last me until LiFePo4 situation stabilises a bit.

Get 4 of these:
http://cgi.ebay.co.uk/9-6v-NiMH-4600mAh-Rechargeable-Battery-Vapextech_W0QQitemZ220247020336QQihZ012QQcategoryZ34063QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262

9.6V NiMH
Capacity : 4600mAh (> 4300mAh at 30amps Discharge)
Weight : 560g
Max Discharge Current : 35,000mA (35 Amps)
Max Charge Current : 6000mA
Average Voltage under Load : 1.15V @ 30amps per cell

This will give me a pack weighing 2.24kg with a nominal voltage of 38.4V

Energy density works out at 79 Wh/kg, which is pretty much the same as the Lifebatt cells.

Using this charger I can charge them at 1.3C

So, nearly half the weight of my present NiCad pack with greater capacity and power.

I could also go with five 8.4V packs....

Any thoughts?

 

[Richard1174]

Hi Miles

I was looking at those aswell I only went for 12v packs so that I only needed 5 to get up to 60v to get some more speed out of my bafang motor. I ordered them tuesday evening and they came yesterday so delivery is pretty good. I bought a charger from another source but that has not turned up yet, don't think i'm going to see it today which is'nt good as I was hoping to get things up and running at the weekend. I think they are a practical solution as you can easily manipulate the required volts and amps for reasonable money. I am starting to look at some of the brushless rc motors aswell , I think as more people get success with them that they will become more popular mainly due to size, weight and cost.

 

[Miles]

Hi Richard,

For me, the 9.6V and 8.4V are better for combining to give a total initial voltage which isn't too close to my controllers maximum

 

[Richard1174]

Hey Miles

My new charger just arrived looks like we are in business for the weekend. I will let you know how these cells perform

 

[Richard1174]

Well the new batteries are installed and up and running and all I can say is wow it goes really well I can get up to nearly 30mph now where as I was on about 18mph before and it goes up hills like a rocket. Range appears to be around 10 miles but half of that was with quite a strong headwind so it looks like I will have to recharge at work but if I parrallel up another five packs to 7400maH it should have pretty good range enough for me anyway to do my 15 mile round trip. My 36v 18amp santoll speed controller held up perfectly at 60v and at one point I was up to 750watts. I checked out the voltage rating of the fets and capacitors last week and they are all rated at 100v so it should be pretty reliable.

If anyone is considering using these batteries all I can say is go for it give it a try I don't think you will be disapointed. All I need to do now is make a proper battery ox for them to side in the diamond of the frame and its sorted. At the moment they are just tie wraped on because I could'nt wait to try them.

 

[Miles]

Thanks for the feedback, Richard

 

[scottclarke]

If anyone is considering using these batteries all I can say is go for it give it a try I don't think you will be disapointed.

Well thank you!

I have been telling people they need to try these vapex cells for at least 2 years - you are the first - let there be many more!

I could get a job for them I am sure - but I'm simply a very happy customer

Scott

 

[Richard1174]

Thanks for your advice scott I am really pleased with how they perform. The real test will be tomorow when I go to work as it is a much more demanding route but its only 7.5 miles. I think I am going to go for a back pack battery pack to keep the bike as stealthy as possible that way it should'nt draw to much attention when I am on the road. If I have enough capacity to get to work ok then I will put another charging station at work so I don't have to carry the charger.

 

[Richard1174]

Well the new batteries made it to work no problem. Kept the speed down to just under 25mph so that I was'nt flat out all the time, it goes up the hills no problem at all. Hills that I was climbing in 4th or sometimes 3rd gear it went staight up in 6th so that was great. No detectable increase in heat from the motor or speed controller so everything looks good for a reliable but faster commute to work. I have decided to keep another charger at work so I don't have to carry the charger with me which makes my back pack a bit lighter as thats where the batteries are going to live for the time being.

 

[Miles]

Sounds good Richard.

I've ordered my charger from AstroFlight. I'll order my batteries tomorrow.

 

[Richard1174]

Well I have had 5 successful trouble free days of using the new batteries. I have been recharging at work so I have been carry the charger aswell as the batteries in my ruck sack ( not that comfortable I have to say ) but my other charger turned up today ( 2 days late but never mind) so I have a permenant charger at work and one at home now so thats much better. Just need to sort out fixing the battery to the bike so that its easily removable for charging.

Been doing full power runs for the last couple of days and its performed great. peak power so far has been 838 watts and its averaging around 130whrs for a 7.5 mile run with a few hills, there is around 1000maH left in the batteries at the end of the run so its not bad for 3700maH packs. Average speed is about 27 mph. So overall I'm very pleased. Still got a bit of work to do such as mounting the pack and shortening some cables but thats about it.

Miles

Have you got your new packs yet, let me know when you are up and running.

 

[Miles]

Richard,

Not yet, they're on the way. I won't get the charger from US till later next week, anyway.