Conversion kit lessons learned after first month/250miles

Well it's been about a month now since I completed my first ebike conversion and I've covered 250miles back and forth to work and I thought I'd share my experiences for those considering doing something similar. Fortunately the weather has been kind and it's mostly been T-shirt temperatures, in fact, it's been a bit too warm on occasion (more on temperatures later!).

 

I converted my Giant Talon MTB with a 60V 1500W kit, it's old hat now what with 26" wheels but the bike was sat unused in near new condition so it was prime candidate. The conversion was relatively straight forward ,the only modification required being the spacing of the rear disc and caliper as the caliper was in firm contact with the hub motor casing.

 

Before this conversion I had no experience of ebikes whatsoever. I've owned motorbikes for 20 years, finally giving in and getting rid of my last bike last year with the arrival of our first child. I decided that traffic levels on the roads nowadays are just too heavy and a few near misses with unattentive drivers made me feel like I was on borrowed time. I have been knocked off twice before in my younger years, both times I was hit by another vehicle and the aching pins and plates are a reminder of what can go wrong.

 

Anyway, when trying to decide on what amount of power to go for, I think I was swayed by reports of 40-50mph, which, on a motorbike feel quite pedestrian to a seasoned rider. However, I was wrong to make this association. It turns out that on a bicycle, these speeds are downright scary and more to the point, uncomfortable! Maybe a more robust full suspension downhill or freeride MTB would feel a little more stable, but the shallow head angle and hard tail of my bike make it a little sketchy at high speed.

 

I invested in a new set of suspension forks and a Thudbuster suspension seat post which have really toned the harsh ride down. The seat post has pushed the seat back making the reach to the bars a little too far, so I had to get a shorter stem to accommodate. I also upgraded the front disc to a larger 180mm version and converted the drivetrain to a 1x7 with a wide narrow 38T chainring to encourage me to pedal more at higher cruising speeds.

 

I had to dial back the controller to deliver only 50% of the available amps. I was seeing peak power not far off 3000W and it was just too much for the canal and cycle paths I commute along. They're rough as a badgers behind in places and anything over 16mph gets really bumpy and it was too easy to get up to silly speeds with pedestrians and dogs around every corner.

 

Another reason for dialling back the power was the temperature the controller was generating. The kit came with a frame bag to house the controller and after my first outing where I was abusing the power somewhat, it was red hot and the wires had all gone soft!

 

Subsequently I have modified the bag to provide some airflow by a forced air inlet hole and a top exhaust hole, both on the FET side of the controller. I fitted large plastic curtain rings in the holes with some mesh stretched across them and they work really well. The controller barely gets warm now, even on a hot day if I decide to pull 1000W all the way home. I don't plan on riding in heavy rain so I foresee no issues with water ingress.

 

Mudguards became a necessity last week when despite being a sunny morning, an overnight downpour left the canal path a bit boggy in places, resulting in me having muddy splashes all over my work clothes.

 

Then I had what nobody wants on a rear hub ebike.....a rear puncture. I rimmed the rear tyre against an unseen kerb and pinch punctured the rear tube. It took about 30mins to change the tube on the canal side, a job that would normally take 5 minutes but having the right tools meant I got home without walking thankfully.

 

I have now modified my route to work. As lovely as the canal path is, the anti-motorbike styles, pedestrians & low bridges etc were making the journey hard work. Instead I am using the pavement which runs along side the main road to work which is completely devoid of people due to it leading out of town to an industrial region. I run the last mile or so on the canal where the routes join back up in order to avoid a dual carriageway. This route has proven to be 10mins quicker, whilst cruising at a much lower, more leisurely pace and using about 50% less battery due to less climbing and more pedal input from me.

 

So to summarise, if you are considering a conversion, especially for commuting, I'd keep the following points in mind.

 

1. Don't get carried away with power. If I was buying again I'd probably go for 1000W max as cruising on motor only at 16-18mph on the flat sees my motor puling 300-500W depending on headwind. Quite frankly, if you're already a decent cyclist who's prepared to keep on pedalling, 250W is probably enough.

 

2. Buying the conversion may lead to the compulsory purchase of other parts and/or modification to existing parts!

 

2. Consider the route you will take and the bike you wish to convert. I've been very surprised at how the quality (or lack thereof) of the surface you're riding on becomes an issue a higher than normal speeds.

 

3. Don't expect to cut your commuting time in half! It took me 57 minutes on a pedal only test run and it takes about 35mins with the conversion. The time saving is apparently in maintaining a decent speed up hills.

 

Anyway that's my 2p worth after my (very) short ebike experience so far. I continue to enjoy not pouring Diesel into the motor every week and look forward to racking up a good few more miles over the summer months!

 

Edited July 6, 20178 yr by superjonnyboy

If you get a kit with a KT controller, they use current control on the pedal assist, so you can turn the power right down by selecting level 1 or 2. That makes it just like a 250w bike. The KT controllers are the ones with the LCD3 display - if that makes any sense to you.

 

One of those motors at 60v would be totally unsuitable for canal paths because you'd be riding outside it's efficient zone all the time. That's why your phase wires over-heated. You were going too slow. The same happened on my friend's bike, he slowed down to stay with me while climbing a steep hill and his phase wires melted completely between the controller and the motor connector. The motor wires from that connector to the motor are normally PTFE coated, so don't melt.

 

We keep telling people, but they never listen (or read), that those motors are great for sustained high speed riding, where they can stay in their efficient zone, but for anything off-road, hills or stop-start, you have a nice electric heater. The higher the voltage, the faster the motor and the lower the efficiency at low speed. 40+ mph top speed means something like 50% efficiency at 15 mph.

Yup it's a KT, I have the pedal assist turned down between 1-3 most of the time. With C5 set to 10 it was still too quick though so it's set to 4 or 5 now.

 

Admittedly I got swamped by the amount of information when choosing a kit and just went with a complete kit that was a one-click purchase. In hind sight, the vendor didn't give me the best advice, or perhaps didn't ask me enough about the application. 60V is better than 48V right? Well that's what he said anyway!

 

The day I had high temps I had been giving it some welly and it was the controller casing that was super hot on the FET side, I assumed the wires softened as they were all in the same tight space. In hind sight it was mostly stop start acceleration so what you say rings true.

 

It's a 48V motor, I believe, over-volted. On the new route I cruise a bit faster, around 20-25mph and it barely gets above ambient temperature. Maybe that's why I see less battery consumption and I guess the 26" wheel helps, over a 29er, say (more RPM). Any faster and I'd have to ride on the road but I don't want to do that, too sketchy at rush hour.

 

Anyway, temperatures are all OK now. It's a shame I may not be running at peak efficiency but then my car never was when in the stop start traffic

 

Lesson learned point 4: Ride faster !

Edited July 6, 20178 yr by superjonnyboy

You've got me thinking now d8veh, can we calculate the most efficient speed for my bike? I know the motors used in my RC stuff are rated RPM/Volt, the same should apply to this hub motor, although I don't know what that value is.

 

Any ideas or is that a "how long's a piece of string question"? Perhaps you'd recognise the motor from a close up pic?

can we calculate the most efficient speed for my bike?

that would be staying legal, 15mph or less.

You go over 20mph, the battery consumption begins to rocket upward.

If you lift the wheel off the ground and spin it to maximum, we can get the rpm per volt (kV). For your use, 48v would be better than 60V.

 

When you go with a higher voltage, the torque increases nearly in proportion, but you can get the same torque by increasing the current and keeping the voltage the same.

 

Increasing the voltage increases the speed of the motor in proportion, but also shifts the efficiency curve up the speed range too.

 

Basically, you need to match the motor speed and controller current to your modal riding conditions. it's not like a car, where you can have an excess of power and still drive around normally. With an e-bike, there's a penalty in every direction when you go away from the ideal parameters.

With an e-bike, there's a penalty in every direction when you go away from the ideal parameters.

wise words indeed!

If you lift the wheel off the ground and spin it to maximum, we can get the rpm per volt (kV)

 

OK - 61mph @ 66V. By my maths that equals 788RPM, so about 12kV.

 

Does that sound about right?

Another of my crazy ideas...

 

Running a 36V oil cooled 260 rpm BPM at 72 V (2 x 36 V batteries in series) and 18-20 Amps. That is the flat road configuration, speed not torque. Hilly configuration back to 36 V (2 x 36 V batteries in parallel) and 20 Amps. I have the very convenient position of being on the dividing line between flat routes (to the north) and hilly routes (to the south).

Another of my crazy ideas...

 

Running a 36V oil cooled 260 rpm BPM at 72 V (2 x 36 V batteries in series) and 18-20 Amps. That is the flat road configuration, speed not torque. Hilly configuration back to 36 V (2 x 36 V batteries in parallel) and 20 Amps. I have the very convenient position of being on the dividing line between flat routes (to the north) and hilly routes (to the south).

 

That sounds like a neat solution I might have to try it!

OK - 61mph @ 66V. By my maths that equals 788RPM, so about 12kV.

 

Does that sound about right?

You need about 260 rpm for canal paths!

Good job I'm mostly off them now then

 

Based on that info, is it possible to calculate the most efficient speed?

 

EDIT: or are we saying 788rpm IS the most efficient speed?

 

Purely out of interest, to be honest I'm happy with the bike now and despite maybe not being the most efficient, it had loads of range for what I need.

Edited July 6, 20178 yr by superjonnyboy

Best efficiency comed at about 75% of max rpm, which would be 45 mph.

Best efficiency comed at about 75% of max rpm, which would be 45 mph.

 

Wow, yup I over did it a bit then. Maybe I should dig the helmet out and hit the road!

you'll need 60A to hold on to that speed.

As a little experiment this morning, I donned my helmet and a lightweight motorbike jacket and left for work early. It was lovely and quiet so I did the whole trip apart from the last mile or so on the road. Its a very wide single carriageway, probably wide enough for 3 lanes but is only marked as two lanes so there's plenty of room for cars to overtake, although only about 5 or 6 did in total. Incredibly smooth compared to the trail that runs along side

 

With C5 turned back up to 10, I saw cruise speeds of 38-44mph depending on gradient and a top speed of 47mph. I got to work in the same time it normally takes in the car!

 

Took a good amount out of the battery, obviously, but the controller, wires and motor were all barely warm to the touch when I stopped.

 

My guesstimate is that the happy medium on this bike, balancing battery drain against motor efficiency is somewhere between 25-30mph.

 

Anyway, another lesson learned. Bigger numbers don't always mean best, next time I'll research motors a bit more. I always have the option of dropping to 48V on this setup, as and when I replace the battery. Controllers aren't expensive so it's feasible.

Controllers can often work at different voltages. Some select the voltage automatically, some have a setting in the LCD and some have a jumper or bridge on the PCB. Even the crappy fixed voltage controllers can be adjusted downwards, by adding a resistor to the voltage divider on the pcb. that's not difficult to do. Volting downwards is never a problem. it's volting upwards that can be tricky.

Yes I've noted the minimum voltage setting on the LCD3 but it won't reduce it enough to compensate for a 48V battery. I seem to remember the minimum being -2V which would be 48V for my controller.

 

The same 18FET controller is used for 36/48V though, so it's probably a jumper as you say, something to investigate in time.

Barrelling along at 40+mph on what is obviously an ebike may attract official attention.

 

The laws are not widely understood, but increasingly people grasp the 15.5mph motor cut off, if not all the rest of it.

Barrelling along at 40+mph on what is obviously an ebike may attract official attention.

 

The laws are not widely understood, but increasingly people grasp the 15.5mph motor cut off, if not all the rest of it.

 

Yeah I'm aware of all that, I won't be making a habit of it, it was more of a test. Pedalling along at 25-30mph should hopefully look a little less conspicuous, but I need to fing a MUCH bigger chainring!

Yes I've noted the minimum voltage setting on the LCD3 but it won't reduce it enough to compensate for a 48V battery. I seem to remember the minimum being -2V which would be 48V for my controller.

 

The same 18FET controller is used for 36/48V though, so it's probably a jumper as you say, something to investigate in time.

C12 is to make minor adjustments to the LVC.

 

The LCD3 is normally fully automatic between 24, 36 and 48v. I'm sure I've seen some marked as 36v, 48v and 60V, but I've also some marked as just 60v. Whatever the situation, I think it's only the LCD that deals with voltage control, so in the worst case, that's probably all you need to change.