Home conversion on a budget

[lulubel]

I've finally decided that an ebike is the route I want to go down for my main transport. Currently, I just use my normal mountain bike, but I'm using taxis more often than I'd like when I have something heavy or bulky to transport.

So, here is what I need ...

Capable on hills - there are a few of 25% gradient around here

Able to tackle hills while carrying me (50kg), luggage (up to 30kg) and towing a trailer (up to 60kg)

It doesn't need a big range under those carrying/towing conditions because it's a 10km round trip to town and back, plus I've got legs and know how to use them. But I may want to use it to travel further without the load, and without arriving soaked with sweat (I live in Spain), and it's pretty much always hilly.

What I have ...

Very small framed ladies hardtail mountain bike with hydraulic disc brakes (not sure if this is suitable or even if I want to convert it, so may look to pick up a larger, rigid MTB).

Plenty of mechanical skill. I'd be very happy to buy the hub motor separately and build the wheel around it, with my choice of spokes and rim, for example.

Budget ...

There isn't one. It's seriously a case of finding the components that will do what I need at the best possible prices, and then scraping together the money to buy them.

Questions ...

Is it possible to convert the bike I have without losing the hydraulic brakes (which I'm not prepared to do)?

What should I look for in a bike if I need to buy one?

What components should I be looking at? (Motor power, battery size, brands, etc?)

Are the "good deals" on eBay really good deals?

And is it more or less expensive to buy the components than to buy a kit? (I've always built my own bikes because it's the only way to get exactly what I want, not because it works out cheaper.)

 

[103Alex1]

Are you trying to stay legal as per EU rules (no throttle & 250W rated) or are you looking for equipment really capable of taking that load up 25% with your maintaining at least 8-10kph pedalling speed ?

You'd need a hefty hub motor to capably take on 25%. Crank drive conversion might be needed otherwise.

 

[lulubel]

Are you trying to stay legal as per EU rules (no throttle & 250W rated) or are you looking for equipment really capable of taking that load up 25% with your maintaining at least 8-10kph pedalling speed ?

You'd need a hefty hub motor to capably take on 25%. Crank drive conversion might be needed otherwise.

I'm not concerned about being road legal. The local police know me (back from when I was involved in a nasty - and non fault - collision with a van on my road bike last year) and they're used to seeing me go flying by on the road bike, or at the top of a mountain on the MTB, so they know I'm very fit. As long as I wasn't riding at silly speeds while making it blatantly obvious the bike was doing all the work, I don't think they'd take any notice. I'd rather have a motor that can handle it rather than wasting my money on something underpowered .

Having said that, the load I mentioned is the absolute maximum I'd expect it to tackle (probably not on a regular basis), and I can get the bike and luggage up the hills myself without having to get off and walk (just haven't tried with a trailer as well), so I wouldn't mind putting in a bit of effort to help it out in those situations. The times when I'd like to put in minimum effort are when I want to put my nice clothes on to go out, and arrive clean and fresh, rather than turning up in sweaty cycling gear, and on those occasions, the only load would be me and my handbag!!

It would also be nice to have a powerful ebike with a throttle. Seeing as I'm going to use a mountain bike as the starting point, it could be a bit of a laugh on the extensive off road trails as well!

 

[103Alex1]

I'm not concerned about being road legal. The local police know me (back from when I was involved in a nasty - and non fault - collision with a van on my road bike last year) and they're used to seeing me go flying by on the road bike, or at the top of a mountain on the MTB, so they know I'm very fit. As long as I wasn't riding at silly speeds while making it blatantly obvious the bike was doing all the work, I don't think they'd take any notice. I'd rather have a motor that can handle it rather than wasting my money on something underpowered .

Having said that, the load I mentioned is the absolute maximum I'd expect it to tackle (probably not on a regular basis), and I can get the bike and luggage up the hills myself without having to get off and walk (just haven't tried with a trailer as well), so I wouldn't mind putting in a bit of effort to help it out in those situations. The times when I'd like to put in minimum effort are when I want to put my nice clothes on to go out, and arrive clean and fresh, rather than turning up in sweaty cycling gear, and on those occasions, the only load would be me and my handbag!!

It would also be nice to have a powerful ebike with a throttle. Seeing as I'm going to use a mountain bike as the starting point, it could be a bit of a laugh on the extensive off road trails as well!

Doesn't sound like range is such a big consideration and you can always use throttle sparingly to extend it. Since you're up for riding unpowered as well as powered, as far as hub motors are concerned I'd personally stick with a geared one (no significant motor drag issues). This will also help you maintain minimum motor speed when climbing steep hills to improve climbing efficiency. Due to towing I'd run it off 48V, minimum 10Ah (high-'C' rated Li-Ion battery) if you don't use LiPos. Otherwise you need a 15-20Ah battery to support the high current draw. This will give you a very capable bike. A bigger battery will extend high-powered range but at added weight and as importantly added bulk to accommodate somewhere on the bike.

Controller-wise you would likely want at least 23A (possibly up to 30A for towing up the steepest hills effectively). For this you likely need a 500W+ rated motor. A Bafang CST should be capable, is geared and cassette mounts direct to the motor with no freewheel required. So simple to install and better for riding unpowered. If you go much more powerful you likely need a direct drive motor which means you should bank on riding powered everywhere to overcome drag (and hence need more 'juice' although you can sacrifice speed of descent for slow descents with regen braking to put some power back ... often not much in practice though !). Remember hub motors are very greedy on power at low speeds and more efficient at higher ones. All motors consume large amounts of power up steep hills.

Crank-drive-wise, I wouldn't pick even a £3k retail 350W Bosch to make towing home a breeze up a 25% slope ! So a higher powered kit would likely work better if a little more roughly. You need high enough gearing to keep up with the motor on the flat. I've no experience of crank drive kits so can't really help you on that.

 

[jackhandy]

Sounds like another potential customer for Frank...

 

[103Alex1]

Sounds like another potential customer for Frank...

I thought that too ... except she's in Spain and is trying to do it as cheaply as she can.

 

[banbury frank]

Hi Sorry we dont supply out of the UK as we cant support it I found this though MAD MAD MAD


Fast Electric Bike Kit Double 3000 Watt 72 Volt, Top Speed upto 120km/h | eBay

Frank

 

[Deleted member 4366]

As the title says "on a budget", the kit I'd recommend is:

36v 201 rpm 500w Bafang BPM rear motor kit
20aH 36v shrink-tube battery

from BMSBattery. Order additionally their spoke key, and depending on your bike, you'll need 2 hidden wire brake sensors, a free-wheel gear-set and a torque arm.
Bafang BPM 36V500W Rear Driving Bike Conversion Kit - BMSBATTERY
36V 20Ah Li-Ion Shrink Tube EBike Battery Pack - BMSBATTERY


Total cost 500 to 550 Euros. Is that within your budget? Are you able to solder and do basic wiring?

This kit will give you a maximum speed of about 30km/h. If you wan't more speed, it'll cost more.

Forget about Ebay, there's not much new stuff suitable for what you want. There's a guy selling the GNG kits, which would also be suitable, but they require more maintenance; however, they go faster.

 

[lulubel]

Total cost 500 to 550 Euros. Is that within your budget? Are you able to solder and do basic wiring?

This kit will give you a maximum speed of about 30km/h. If you wan't more speed, it'll cost more.

Forget about Ebay, there's not much new stuff suitable for what you want. There's a guy selling the GNG kits, which would also be suitable, but they require more maintenance; however, they go faster.

I've helped rewire a house, if that counts, and have done lights and stuff on my own. I haven't done any soldering, but once you've built wheels, joining a few bits of metal together doesn't hold any fear.

The stretch for me is going to be finding the money for the battery all in one go, but that was always going to be an issue. (It's difficult to save up for something when you have so many things that need paying for.)

Anyway, I notice the kit you linked to includes brake levers. I assume these are the ones with the sensors that automatically kill the motor when the brakes are applied. They look like basic cable brakes - is that correct? If I'm not going to be able to use the hydraulic brakes on my existing bike, I'll also need to budget for a new bike because I still want to use the one I have for descending rocky trails, and once you've had hydraulic brakes, you don't really want to use anything less sensitive for that! Is it necessary to have the automatic cutout on the motor when the brakes are applied? I mean, I can drive a car without applying the throttle and the brake at the same time. I'm sure it isn't that difficult to do it on a bike.

 

[103Alex1]

If I'm not going to be able to use the hydraulic brakes on my existing bike, I'll also need to budget for a new bike because I still want to use the one I have for descending rocky trails, and once you've had hydraulic brakes, you don't really want to use anything less sensitive for that! Is it necessary to have the automatic cutout on the motor when the brakes are applied? I mean, I can drive a car without applying the throttle and the brake at the same time. I'm sure it isn't that difficult to do it on a bike.

The brake cutout is a safety feature for if the throttle sticks/breaks in the 'on' position. Some people don't use them but I wouldn't like having to overpower a 500W motor with my brakes until such time as I could kill the power to the bike without alternative quick-kill features. If you have throttle on/off switches and handlebar power kill features for example they all make having the cutouts less important in practice but a 500W motor is powerful and a runaway bike on a rocky trail might not be such a great outcome.

You can get fixes for fitting brake cutouts to hydraulic brakes if you want to keep them and their levers. I have combi-shifters (brake/gear) running hydraulic discs on my Trek and used an inline modified Magura switch instead. There are cheaper solutions for brakes without combi shifters. Which type of brakes do you have ?

 

[Deleted member 4366]

You chuck the levers that you get in the kit. With hydraulic brakes, you can't use the hidden wire sensors either, so that reduces the cost by $10. Hydraulic brakes is always a problem. Some levers are easier to adapt than others. You only need one switch - preferably in the rear, so the simplest solution is to replace the rear brake caliper and lever with a cable one. It's the front that does all the serious braking for which a hydraulic one is best. The rear doesn't matter so much. I think you'll find that a cable one will be more than adequate. Whatever hub-motor you fit, you need to increase the size of the disc rotor to at least 180mm. BMSB do a kit for only 6 euros, but you'll need the side-mount adapter for the caliper. Don't forget to select 180mm because 160mm is the default..
One Bicycle Disc Brake - BMSBATTERY
+20mm Disc Rotor Adaptor IS to IS 180mm 7In Hope Magura | eBay

The only way to reduce the battery cost is to get a smaller battery, which means a smaller less powerful motor that will struggle on the hills. You can save about 100 Euros by using a 10aH lipo pack. Lipos need to be managed properly, and if you get it wrong, you convert them to bricks, or make a rather smelly fire. The BMSBatteries are plug-and-play.

 

[banbury frank]

Hi Link for how to mod brake levers by adding hall sensor


Brake switch

also have a look around the site lots to read

Frank

 

[103Alex1]

The Magura switch has come down in price a bit and is now about £25 including shipping to Spain. Magura Druckschalter / Schlieer fr E-Bike

It saves fitting new brake levers but you also need to bleed and refill the hydraulic line with compatible fluid and change the connector so it can all start to add up. Plus if you need to change the rotor (I didn't) you have to build that extra cost in anyway. It's fairly easy to cost out the various options.