GNG 48v 900w Speed Problems.. help?

[PARADOXICLES]

In the fall/winter i bought a GNG 48v 900w mid drive dual motor kit,directly from GNG. For various reasons, mostly saving up money, i wasnt able to order a battery till recently, i purchased a 48v 15Ah PING LiPO brand new directly from ping. i put every thing on a Shimano 21 speed bike, that is now 7 speeds due to the ebike kit. today was the first real test of it, i used a gps app on my phone as a speedometer, and disappointingly my top speed was exactly 20mph(32kmh)... on a slight downhill.... when i bought the kit it was advertised as reaching 65kmh(45mph), more then double the speeds im getting. Sure i didnt expect the full 45mph because nothing is ever advertised as it really is, but is should get atleast 30-35, or so i would think. and yes i understand weight is a factor, which me and the bike together are about 212 pounds ( 96 kilos)..reasonably light id say...and yes i weighed it and me. i dont know what the cause of the low speeds is, if any one has suggestions i could try to fix this, id appreciate it. i simply have no idea what i could do to boost the speed closer to what was advertised.

 

[Secret1511]

What kind of controller do you use?

 

[PARADOXICLES]

the one that came with the kit, 48v 900w is what the sticker on it says , i considered that as an issue, but i really dont know enough about them to accurately say if that would help or not. i also considered that there is a short or lose wire some where but i do not see anything that seams to be as such, all seams properly in place.

 

[bowlofsalad]

45mph at what voltage? I don't know how well you understand mid drives, but the speed you go is very dependent upon the gearing on your bike. You say you have only 7 speeds now. Maybe a lack of gear range has to do with your lack of speed? I sure hope you understand the dangers involved in going 45mph on something like a motorcycle.

 

[wesnewell]

What gear were you in?

 

[PARADOXICLES]

7th... the highest( fastest) gear i have, of course i tried all my gears and what not...its just maxing out early, like its not getting enough energy, like half power. there is no stalling,shuttering or anything of that nature, its simply not going faster then 20mph like it should.

 

[rp3]

You sure that battery you have is LiPO and not Li-ion? Some of those Li-ion packs are only 1-2C.

 

[wesnewell]

Says he has a 15ah 48V ping, which would be lifepo4. 35A controller is a little too much for it, but shouldn't be causing this much speed loss unless it's bad or sagging to under 24V. Check voltage under load. Should be 50V or more. What tooth count is your front chain ring? It should be at least 44T and preferably higher. The smaller the front chain ring the slower you'll go.

 

[PARADOXICLES]

where exactly are you recommending checking the voltage? there are lots of wires i could check ( i have to find my volt meter first). based on my understanding the ping batteries are at least 2c rated at minimum, so when giving it that max power i should be able to out put 30 amps, if not more ( at the cost of less range). so to my understanding it should be fine... and yes im sure is this exact battery, cuz this is the exact place i ordered it from... http://www.pingbattery.com/servlet/the-12/48V-15AH-V2.5-LiFePO4/Detail

.. i have some shitty plugs i may try replacing to see if they are impeding my power flow,( the gng ones were mismatched and did not connect so i had to replace them ) but i wanna try simpler things first, before i go out buying more stuff. as for the sprockets, my front is the sprocket GNG gives you with the kit, i dont know the tooth number, but its the same size as my original gear set, except the smaller gear is missing... because its not needed ( i didnt even use it when i had it)... the bigger, outer gear, is the one the motors attach to, the smaller inner gear is where the main peddle chain is, when the motors turn, the whole sprocket assembly turns, turning both sprockets at once to power the chain to the rear wheels.

i also got a brand new rear sprocket set for my rear wheel, which is this, http://www.amazon.com/Shimano-MF-TZ31-Tourney-Freewheel-14-34T/dp/B003RLNOKC/ref=pd_sim_sg_2 it has an extra low sprocket to help me peddle with all my new extra weight,especially up hills, but all the other sprockets are the standard on any 21 speed bike, and no i was not stuck on the big one, the motors are more then strong enough to skip it, i could start in 7th if i take it slow( if i dont chain slips, and crunches,) i have no problems what so ever with torque, i actually broke the kits brand new chain on my first test drive cuz of it... which is one of the reasons i chose the 2 motor kit, mote torque, the other was more speed.... getting the torque, not the speed

 

[M4SK13]

I'm new here but wanted to put in my 2 pence worth, but what has gears got to do with it? Sure if you want to pedal assist and then get up to those speeds then gears has something to do with it (very little). But the manufacturers of the motors advertise as you say

Volt/Motor = Top Speed = Range = Battery Rec.
24V/500W = 16mph (26KM/H) = 17M (28KM) = 24V20AH
36V/500W = 19mph (31KM/H) = 19M (31KM) = 36V15AH
48V/500W = 26mph (43KM/H) = 26M (43KM) = 48V15AH
48V/1000W = 32mph (52KM/H) = 26M (43KM) = 48V15AH
24V/350W(Geared Motor) = 14.29mph (23KM/H) = 12.42M (20KM) = 24V9AH
36V/350W(Geared Motor) = 16.77mph (27KM/H) 19.25M (31KM) = 36V9AH

I have the 48v 500w with a BMS Battery/KU123 controller on a lifePO4 10a and I get 20mph lifting the wheel off the ground and full throttle, but that said I get 20 with me on it too (yes, i weigh 16st too) which i found strange on the flats. During my research the said that you multiply the V by the Ah to get your recommended motor; and based on this theory you have 15ah by 48v = 720w. Meaning your way short on your motor capacity, good side is you'll not be stressing the motor should last you years :-0 not the answer i suspect you were after. Also on my research they say to get above 28mph requires huge power on motor and battery due to wind resistant etc. I think for you to get the results you need to a cycle analyst to get some proper stats so you know whats happening. You have the more impresive direct drive systems which only mean more torque for hills and getting to the top speed quicker. Remember I am new, please dont shoot me down if am wrong on anything.

 

[wesnewell]

VA=W, Not VAh. With a 35A controller, that's 35*48, not 15*48. Gears has everything to do with speed because the motors turn the chain ring which in turn drives the drive chain. If you have a 34T chain ring and a 34T rear sprocket, then it's 1*1, so 60rpm pedaling means 60rpm wheel rotation. I don't think you understand how these things work at all. Motors have reduction gearing that drives the chain ring at a certain rpm. The chain ring drives the chain to the rear freewheel which turns the wheel. All the different gears in between the motors and wheel will determine the speed.

 

[PARADOXICLES]

ok i have to ask.. where are you getting that my controller is 35a? the only sticker on it says 48v 900w ....and some shit in chinese that i have no idea what says...i think brand name.....

i was looking at other controllers to see how that might help,and i got the idea of... my bike has 2 motors, what if i got two 48v 450w controlers, and rigged them each up to their own motor, but still use the same battery and throttle for both? each controller would take less power, but my bike over all would have the same power, right?

 

[M4SK13]

OK I may sound thick here...

Regardless of gears he is not going to get 25mph from changing the gears from what he has? I take on board that 1:1 ratios and what you say about the use of gears, but my concern was about his power getting to the motor to drive those 7 exisiting gears he already has and we know about.

From your maths he has 1680w which means more than enough to drive the 900w motor (too much?), so he shouldn't have a problem, but he does. I hope someone can point out something for him to try. Yes I am new to the ebike era, yes i too had problems with power delivery but I got some very good constructive advice from these forums good luck paradoxicles let us know how you get on and what you did to resolve if you did manage to fix it.

 

[PARADOXICLES]

yeah, im new to electric bikes too, ive done lots of other electrical projects, lights, rc cars, boats, planes, hover craft, a useless machine,animatronic zombie head, and many other projects, but this is my first electric bike

 

[bowlofsalad]

I am having trouble following most of this.

The front chain rings seem not to exist on your bike? But you have a rear sprocket and you are swapping that out. I doubt you'll gain a ton in speed through that. If it's possible, you'd probably be better off adding those three extra speeds typically found on the front chain ring.

Do you have a voltmeter? If you don't, you should. Checking pack voltage is a wise idea. You can use the volt meter to check an entire pack using some of the wires you'd plug from the battery to the controller, if that makes sense.

 

[PARADOXICLES]

bowlofsalad... nothing is missing.... ive simply replaced the original 3 front sprockets, with a 2 sprocket set that came with my ebike kit, one for the motor chain, and the other for the chain to the back wheel, both are ratcheted so they can turn with or with out the peddles/motors... my rear sprocket set was as an upgrade for peddling with the extra weight, not as as an upgrade for the motors, and the gears that are for the motor are the normal standard sprockets

i dont know why my gears are such an issue for every one, i know for a fact that my gears are absolutely not the cause of my power problem... im 10000000% sure of that...

 

[bowlofsalad]

The idea that is likely being focused on is the gear ratio. Different gear ratios will yield you different maximum speeds and torque. If you can shift to a high enough gear while still maintaining the appropriate RPM, you will be capable of going very fast. So it sounds like either your motor isn't getting as much power as it should, or you aren't achieving the appropriate gear ratio. That extra speed on your front gearing likely will hinder you some how, either your low or high end, unless it's just skipping something typically found in the middle.

https://en.wikipedia.org/wiki/Gear_ratio

Do you have something like a cycleanalyst? That should tell you for sure what your controller has in terms of voltage and what is going on with your output when you are on the move.

 

[wesnewell]

Is it possible that the controller has a speed limiter wire. I know some controller have this to limit speed.. If not, then either the motors aren't turning a max speed or the reduction gearing of the motors are too high. This is a simple concept. High speed motors are used for efficiency. They have reduction gears on the end of the motor to reduce motor cog rotation which in turn drives the chain ring, which in turn drives the rear chain. These are brushed motors. If one is not getting power it drag down the other. I'd remove the motor chain and verify both motors are working properly in sinc with each other. Other than that I don't know what to tell you.

 

[PARADOXICLES]

yeah both motors turn fine and at what appears to be the same speed ( i have no way to measure rpms) ..... plus the sprockets are ratcheted so they dont add resistance when not in use ( although this dose make them catch the ratchet when pushing the bike in reverse, so reverse has alot of resistance when taking it off a bike rake or what not)

noone ever answered what they think of my 2 controller idea. use two 450w controlers instead of the one 900w i have now, wire each one to their own motor, but have them share the same battery and throttle. in theory, this should be similar to having 2 video cards in a comp or dual exhaust in a car. maybe...

 

[PARADOXICLES]

and assuming that idea works, it would give me the advantage of a back up system if one motor or controller dies... i dunno...

 

[PARADOXICLES]

UPDATE.... ok so its been a while sens i got on here... long story short, i fried my plugs ordered more, now i have them installed. it didnt fix my speed problem but sofar my max speed has been 25mph, and max range 17.7 miles...... but today when i went to ride ti the front motor is making a weird noise from the gears built into it.... i have no idea how to take it apart cuz of its design, but ill see what i can do... deceded to ride it any way and see what all was going on, but then my rear chain started slipping in the higher gears, i stoped to check it out and realized that the chain was just slipping and grinding down the gears ( which were brand new)..... so considering all my problems, and that i want disc brakes, at this point i think it might just be easier, and cheeper to just buy a new bike,and then transfer my ebike kit to it... i dont know, i dont have the money so it may be a while before my next post