Increasing my top speed

[John Galvin]

Greed is a terrible thing and only a few days after my initial build I'm craving more speed.
I had the bike out on a 10k run the other night and I found that even on a decent downhill
stretch, it wouldn't go over around 28 km/h without huge effort.
With a 20" wheel and a 286 rpm motor, it runs out of puff around then and I reckon that's what's happening.
My controller is unlimited but once I hit max revs, it seems the resistance builds up.

Switching to a 328 rpm motor would give me an extra few km/h and I know that there are a few narrow (80mm) hubs that are as light as 1.4 kgs. Something like that would also bring down the weight of the bike.

I'd love to take the original wheel that came with my Tern Link and use that to build a wheel around such a motor.
It appears to be a double wall design with 20 spokes. The wheel supplied with my kit has 36 spokes that are much thicker.
Would a 20 spoke wheel be strong enough and are motors available drilled for 20 spokes? I have a guy in Dublin who reckons he could do the build.

If this is a good idea, who is the best supplier and what is the best motor? I don't want to spend a fortune on shipping either.
Finally, if I do something like this, would I need to upgrade from 36v?

TIA

 

[Deleted member 4366]

This will increase your speed and torque by 20%. You can swap from one battery to the next. Nothing else changes:



Fitted to my Dahon:

 

[John Galvin]

Seriously? I'm interested. What battery needs to go in it. I take it I'd have to get the soldering iron out again, but that's not a problem.

Thanks

This will increase your speed and torque by 20%. You can swap from one battery to the next. Nothing else changes:


Fitted to my Dahon:

 

[amigafan2003]

What battery needs to go in it.

Two of these.

No need for a soldering iron - get one of these as well and cut one end off and fit a matching connector to whatever is on your controller.

 

[John Galvin]

That's mighty. I'll give that a go.

After I move to 42v is there any point pursuing the 328 rpm motor or am I wasting my time?
I see that battery is 8Ah, compared to my own which is 10, but that's not a huge issue.
I'll see if they have anything equivalent with higher capacity on that site but if it comes to it, 8Ah will do me.

Thanks

Two of these.

No need for a soldering iron - get one of these as well and cut one end off and fit a matching connector to whatever is on your controller.

 

[Deleted member 4366]

You can make a lipo pack as big as you want, but you have to think about where to put it. A 328 rpm Q100 will also sort you out, then you can go for the 12S lipos for even more power and speed.

The 8ah lipos have 20% more volts than a 36v one. You have 360wh in your battert. An 8ah 12s lipo one has 352wh, so not a lot of difference except you'll want to use them quicker.

 

[Deleted member 4366]

The two lipos have to be connected in series and then to the connector inside the case. You have to charge each 6S pack individually. so you need to double-up the power wires from each one and run a connector externally. The lipos have a 6S balance lead (7 wires) that also has to run externally. I drilled two holes at the back to hang the connectors out. you can just see them hanging down in the picture of my Dahon.

For connectors, I use Deans which are small and easy to connect. Use 14g silicone wire that you can find on Ebay along with the Deans connectors. Here's the wiring. I draw ypu a schematic if you need it.

 

[Deleted member 4366]

 

[John Galvin]

So does that mean I have to either have two chargers or charge them one after the other?
My current setup has a number of cells wired in series to produce 36V. I thought that moving to 42 would just be a case of replacing the cells in series and working away. Am I completely wrong?

The two lipos have to be connected in series and then to the connector inside the case. You have to charge each 6S pack individually. so you need to double-up the power wires from each one and run a connector externally. The lipos have a 6S balance lead (7 wires) that also has to run externally. I drilled two holes at the back to hang the connectors out. you can just see them hanging down in the picture of my Dahon.

For connectors, I use Deans which are small and easy to connect. Use 14g silicone wire that you can find on Ebay along with the Deans connectors. Here's the wiring. I draw ypu a schematic if you need it.

 

[Deleted member 4366]

Lipo balance chargers are normally 6S, so you do one pack at a time. Most people start with a cheap charger.

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=29047

You need a 12v power supply for it. You can make a good one from an old PC power supply. You just have to join a few wires.

 

[John Galvin]

Just looking around at my options and I see that for $300 shipped I could get one of those 'shark' type batteries in 48v form (pic attched). It's a little bit more expensive than making a frog but it can be charged much more simply.
I'm experiencing the dreaded frog battery droop already so this might be a good solution.
Those batteries attach to the bottle cage holes don't they?

Is this a good approach?

TIA

Lipo balance chargers are normally 6S, so you do one pack at a time. Most people start with a cheap charger.

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=29047

You need a 12v power supply for it. You can make a good one from an old PC power supply. You just have to join a few wires.

 

[eHomer]

.....Those batteries attach to the bottle cage holes don't they?......

I bought one of those 48v batteries a few months ago, with exactly the same case design.

Yes, they are designed to be fixed via bottle mount tappings, though my suspension frame had insufficient clearance to be able to fit and remove the battery to it's holder, so I installed it to a board in a pannier bag instead.

I bought mine from a UK based Ebay seller, for just under £300.

Although the dollar exchange rate makes your $300 about £180, don't forget you may get hit for VAT and customs duty, they always get me, together with a swingeing "admin" fee, so it could end up with far less saving over the direct Chinese import.

My biggest worry about a battery though, would be if it was faulty, and the awkwardness of returning to China. I admit BMS have always given me very good service, with no faults, but I bought an expensive controller from another well known Chinese supplier, it never worked at all, and I never got any of my money back.

When spending hundreds on a battery, I'd rather spend an extra £40 or so to get the item much quicker, and be able to get an Ebay backed refund if the seller turned awkward.

http://www.ebay.co.uk/itm/2014-Model-48V-10-4ah-bottle-holdermount-lithium-Li-ion-electric-bike-battery-/171396735865?pt=UK_Bikes_GL&hash=item27e80aa379

http://www.ebay.co.uk/itm/48V-10-4ah-bottle-holder-mount-lithium-Li-ion-electric-bike-battery-White-/251604813020?pt=UK_Bikes_GL&hash=item3a94d0c4dc

 

[John Galvin]

Good point of course. I've been lucky so far with stuff coming from China but you never know. I came across some ebay sellers but £180 versus £300 is a fair difference, even given the chance of being caught by customs.

I'm in no great hurry as I want to enjoy my bike while the weather is reasonably good. This will be a winter project.

I bought one of those 48v batteries a few months ago, with exactly the same case design.


Although the dollar exchange rate makes your $300 about £180, don't forget you may get hit for VAT and customs duty, they always get me, together with a swingeing "admin" fee, so it could end up with far less saving over the direct Chinese import.

 

[eHomer]

Yes, point taken John.

I seem to remember the difference was less when I bought it a few months ago, so the decision was easier.

It's a great little battery though, no problems with it so far after about 6 months, quite neatly connected together inside.

 

[JohnCade]

Good point of course. I've been lucky so far with stuff coming from China but you never know. I came across some ebay sellers but £180 versus £300 is a fair difference, even given the chance of being caught by customs.

I'm in no great hurry as I want to enjoy my bike while the weather is reasonably good. This will be a winter project.

I may be wrong but I should have thought you will be hit for the VAT and admin charge for sure. A few years ago it was rare to have to pay but since customs have become the UK Border Agency they've got their act together and they aim to charge on everything coming from outside the EU. I've paid on everything I've imported for a couple of years now.

 

[Deleted member 4366]

286 rpm at 36v = 381 rpm at 48v (add 10% if 286 is nominal rpm)
381 rpm in a 20" wheel = 22 mph (+ 10%?)

A couple more things to make you decision even harder: Theres lots of batteries around with those pod-shaped cases. The quality varies a lot because it's what's inside that counts, not what the case looks like. If the vendor doesn't say what cells they are, assume that they're cheap saggy ones. Personally, I'd rather take my chance with BMSB than a UK supplier, who's selling an unknown brand. You'll definitely get caught for duty - something around £40.

When you get the urge for more power, there's a lot of different ways to do it. Whatever you do, you always end up trying to get a satisfactory balance between weight, range, convenience, cost and motor characteristics.

Increasing to 48v will give 33% more speed potential plus a lot more torque if the motor can handle it. The efficiency curve will change too. The motor will have significant efficiency loss when run at full throttle at less than half of its maximum rpm, which for a small motor can mean that it'll burn out struggling up a steep hill. The chance of burning depends on your weight and the motor's winding speed. You should be OK at 22mph, provided that you're sensible in the way that you use it.

You'll need a new controller if you go to 48v, but not for 12S lipos.

 

[trex]

if you want speed, get an 18A crank drive, 11T rear cog or Nexus hub gear

 

[John Galvin]

Ok, confused again!

When we were talking about upgrading the frog battery, I was under the impression that I would just change the battery and drive on.
Going with the shark battery, it's the same voltage (or is it slightly higher?) and I'll also need a new controller.
That's not a huge issue as it's not a huge amount of money but will I need to change anything else - throttle, pas etc?
I get that I'll need to be careful if I'm overclocking the motor but I'm 80kg and getting lighter and I won't be climbing the Alps anytime soon so I should be OK.
There's a version of that battery with a built in controller but that would mean bringing all the wires back to the battery, which I was planning to mount on the crossbar so I think I'd stick with a separate controller. From memory there's not much between them in price.

It may be different in the UK, but in Ireland, we can often get away with duty and VAT although it depends very much on who delivers the package.

From what you're saying though, the BMS supplied battery should be a good choice. If I get caught for the duty I'm no worse off than if I used a UK supplier so even though it will take longer to arrive, that's probably the way to go.

I'm put off modifying the frog battery because of the split charging. I have no problem modifying an old PC PSU to provide the volts but it would mean that I couldn't bring the charger with me in a rucksack if I ever needed to.

286 rpm at 36v = 381 rpm at 48v (add 10% if 286 is nominal rpm)
381 rpm in a 20" wheel = 22 mph (+ 10%?)

A couple more things to make you decision even harder: Theres lots of batteries around with those pod-shaped cases. The quality varies a lot because it's what's inside that counts, not what the case looks like. If the vendor doesn't say what cells they are, assume that they're cheap saggy ones. Personally, I'd rather take my chance with BMSB than a UK supplier, who's selling an unknown brand. You'll definitely get caught for duty - something around £40.

When you get the urge for more power, there's a lot of different ways to do it. Whatever you do, you always end up trying to get a satisfactory balance between weight, range, convenience, cost and motor characteristics.

Increasing to 48v will give 33% more speed potential plus a lot more torque if the motor can handle it. The efficiency curve will change too. The motor will have significant efficiency loss when run at full throttle at less than half of its maximum rpm, which for a small motor can mean that it'll burn out struggling up a steep hill. The chance of burning depends on your weight and the motor's winding speed. You should be OK at 22mph, provided that you're sensible in the way that you use it.

You'll need a new controller if you go to 48v, but not for 12S lipos.

 

[Deleted member 4366]

Yes, it does get a bit confusing. 12S lipos are 50.4v max. Most 36v controllers can manage that. 48v Li-ion batteries are 54.6v max. Most can't handle that.

You can buy 6S chargers with internal power supplies. They're proportionally more expensive; however, you still have to charge one at a time. I just had another think. Even with two chargers, you couldn't charge two at a time because the grounds would be common on the chargers but not on the battery, so one charger would smoke.

Lipo charging can be twice as fast as Li-ion batteries, so it wouldn't take longer to charge. This one can charge at 5A, so about 2hrs per pack (from empty to full).

http://www.hobbyking.co.uk/hobbyking/store/__6478__IMAX_B6_AC_Charger_Discharger_1_6_Cells_GENUINE_.html

 

[Tirano]

Thank you for a fascinating thread, I have a couple questions hope it's no too old


1.if I disconnect the batteries from each other I am able to charge both at the same time?
2. For a 5A charger I need a 5A 12v power supply?

Thanks