Q75 / Q85 Query

[Joneser]

Hello everyone.

I am attempting my first electric bike build. I have no expertise so have learned as much as possible from this forum, so thanks!

I have bought and received Q75 and Q85 front hub motor kits and I have ordered a 5Ah lifepo4 battery separately, which I'll hopefully receive in 2 weeks.

Maybe a stupid question, but the hub motors seem very stiff forwards (turning the axle by hand) and don't go backwards.

Is this normal?

I asked bmsbattery for installation instructions but they replied 'we don't think its necessary'

Cheers

 

[Deleted member 4366]

Put the motor in a frame or forks to test how free it is. There's always a bit of initial stiffness, which feels bad if you hold a bare motor and try and twist the axle because the diameter is so small.

Which 5aH battery have you ordered? Can it supply the current needed?

 

[Joneser]

battery current

Put the motor in a frame or forks to test how free it is. There's always a bit of initial stiffness, which feels bad if you hold a bare motor and try and twist the axle because the diameter is so small.

Which 5aH battery have you ordered? Can it supply the current needed?

Hi Dave

max cont. discharge current 7A
max pulse discharge current 20A

Please tell me this is ok! I should have checked here before buying it.

Cheers
Joneser

 

[Deleted member 4366]

It's a bit on the light side current-wise, but it depends how much assistance you want and what bike you fit those motors to. Normally, LiFePO4 is 1C, which means 5A continuous and 10A max. You'll have to try it to see.

Can you give us some more details: Why two motors? What bike? What speed are the motors, 201 or 328 rpm? What controller/s

 

[Joneser]

It's a bit on the light side current-wise, but it depends how much assistance you want and what bike you fit those motors to. Normally, LiFePO4 is 1C, which means 5A continuous and 10A max. You'll have to try it to see.

Can you give us some more details: Why two motors? What bike? What speed are the motors, 201 or 328 rpm? What controller/s

Hi Dave

I have a 20 mile round trip commute with some decent hills. See this cool website which shows the elevation profile (feet above sea level) of the route.

I can manage this unassisted and often enjoy it but would like some assist up those hills on the way home, especially in a head wind and when I'm not 100%. I have been borrowing a hybrid bike and need to buy my own, so I've actually bought a motor before the bike

So the plan is to end up with a 15kg hybrid bike including motor conversion kit - the Q75 is for the full size hybrid. I'm actually thinking of a Montague X50 for maximum flexibility but this would be a bit heavier and I haven't tried one yet. I had a nasty crash last week going over the handlebars when I hit a speed bump that I didn't see (it had no markings and it was night time), so I quite like the idea of front suspension forks for unexpected speed bumps and pot holes.

The Q85 is for the local (very hilly) runaround, mainly for my wife. We have a Dahon and a Brompton.

I was thinking of practicing the first conversion on the Dahon as its the oldest bike.

I also bought 2 of these batteries on jerrysimons brompton conversion advice but I don't have the expertise to join them together. Also I wouldn't know who to go to to try and pay for someone else to do it either?

The 5Ah battery I've ordered has a PCM and a charger so is hopefully more plug and play.

Any advice would be appreciated.

Cheers
Joneser

 

[jerrysimon]

Joneser,

Those cells are great for about 8 miles on flat terrain 5 or less on very hilly terrain.

My threads/post show you how to connect them together.

Do you have a link for the 5Ah battery you have purchased ?

Regards

Jerry

 

[Joneser]

Joneser,

Those cells are great for about 8 miles on flat terrain 5 or less on very hilly terrain.

My threads/post show you how to connect them together.

Do you have a link for the 5Ah battery you have purchased ?

Regards

Jerry

Hi Jerry
Thanks for replying - I'll check your posts again - maybe I was too quick to feel defeated with those A123's.
When you say 8 / 5 miles do you mean constant use? I suspect its fine as on my long commute I want to strictly limit motor use to when I most need it, and for the local runaround, its for less than 2 miles round trip, just hilly.
The other battery is 'bespoke' from forzatec. I might have led them to believe that I am an ebike conversion company asking for a sample But its still quite a lot of money so fingers crossed it arrives and works.
Joneser

 

[Deleted member 4366]

I just had a look at Forzatec and found the datasheet for the cells. I think they'll be OK, but at your discharge rate, you'll get a slightly reduced capacity.

You didn't say how many rpm the motors are. It makes a massive difference to their suitability for different bikes and batteries.

 

[Joneser]

I just had a look at Forzatec and found the datasheet for the cells. I think they'll be OK, but at your discharge rate, you'll get a slightly reduced capacity.

You didn't say how many rpm the motors are. It makes a massive difference to their suitability for different bikes and batteries.

Dave, yes sorry the Q75 is 201 (S06P controller) and Q85 328 (KU63 controller).
I've just noticed the KU63 is not listed as compatible with the Q85 but that is what BMS sent me as part of the kit.

 

[Deleted member 4366]

That means that the Q75 is only suitable for 26" wheels or bigger. It'll be much too slow in the Dahon or Brompton, and the Q85 can't be used in anything bigger than 20" wheels with those batteries because it'll draw too much current. I guess that you've got that figured out already from what you've said, but I just wanted to check.

 

[Joneser]

That means that the Q75 is only suitable for 26" wheels or bigger. It'll be much too slow in the Dahon or Brompton, and the Q85 can't be used in anything bigger than 20" wheels with those batteries because it'll draw too much current. I guess that you've got that figured out already from what you've said, but I just wanted to check.

Dave, yes thats it.

So if I managed to rig together the 2 x a123 batteries would they be best for my full size / long commute or the fold up local hilly runaround? The A123's are lighter so I'd prefer them on the long commute. I guess I can switch them around to see what works best.

I'm thinking I need to try to compile info that sets out the relationship between all the attributes involved, eg motor Watts, Volts, RPM, battery Ah, Amps and how they relate to usage. Do you know if this has been done somewhere?

ps re my original query are the motors supposed to freewheel backwards?

 

[Deleted member 4366]

The main problem with the A123s is the lack of BMS. You mustn't run any cell below 2v, so you need to leave a bit in reserve. In practice, they go down quite slowly for most of their capacity, and then accelerate downwards towards the end with power tailing right off, so it's not quite so bad. I wouldn't run any BMS-less batteries without a wattmeter that'll show actual voltage and amp-hours or watt-hours used.
New Digital 60V/100A Battery Balance LCD Voltage Power Analyzer Watt Meter | eBay

 

[Joneser]

Ok thanks for the link Dave. Will let you know how I get on.

 

[jerrysimon]

When you say 8 / 5 miles do you mean constant use?

Yep pretty much constant throttle use.

I have never used a BMS on any of my A123 packs. I agree though you should first test your regular commute with a watt meter to see how much capacity it takes and then ensure you don't discharge it more than 3/4.

Even though initially I ran my first pack flat every day on my regular commute it still lasted a year before I lost a couple of cells. Now I tend to charge my A123 packs at work after a 5 mile flat commute and I still have the original pack working after 4 years!

My new Konion 3Ah packs last me to work and back without charging. Note though I am using Tongxin and Keyde motors which probably draw less current than your two motors.

Jerry

 

[Deleted member 4366]

Electric bikes are somewhat different to the way they use power compared with motor vehicles.

If the motor had direct access to a current-limited battery (no PWM from the controller- like max throttle) ,from a stand-still it would draw the maximum current, but as the motor starts to rotate, it becomes a generator that generates a voltage that opposes the supplied voltage. This reduces the incoming current. The faster it goes the higher the voltage generated and the lower the current to the motor until the current is zero at the maximum RPM of the motor. This means that the maximum current drawn depends on speed. It goes down from max to zero as the speed goes from zero to max. It doesn't take much pedalling to exceed the maximum rpm of a motor in 16" wheels, so a lot of the time you're travelling you may be drawing no current. The end result is that the amount of battery you use depends a lot on the motor max rpm and the wheel size, so you have to be very careful about making comparison. A 328 rpm motor in a 20" wheel, will use about twice the amount of battery a 280 rpm Tongxin will in a 16" wheel, when travelling in the 12 to 15mph range.

 

[Joneser]

Dave
Thank you for trying to explain. It is clearly going to take a long time for me to get a thorough understanding.

In the mean time I think I just need to get the thing up and running. For someone that knows what they are doing I'm guessing I'm nearly there. Please see photo - I've had this kit for a few weeks now but have not progressed. Can you please help advise what I need to do to finish off?

Is it as simple as cables and connectors?

So the battery has Dean connectors. The controller has connectors I don't know the names of. The Turnigy charger has spring clamp on things.

So I need:

1) connectors and wire to link the batteries in series. Dean connectors. Wiring? Is it 2.5mm?
2) connections and wire to connect the batter and controller
3) how to connect the charger and batteries?
4) is there anything else I need to do, ie fuses?

Would really appreciate help finishing this.
Thanks
Joneser

 

[Joneser]

Ok thanks for the link Dave. Will let you know how I get on.

Thanks Jerry
If you could see my other recent post / photo and offer advice that would be most appreciated too!
Joneser

 

[Deleted member 4366]

This is the cable to connect your batteries. Don't forget to disconnect it when you charge them.
Deans T-Plug Connector Series Cable Serial Lead Connectors for Lipo NiMH battery | eBay

Cut off the connectors on the controller and solder on Deans - always a female on the battery side.

Deans Connectors T Plugs 5 Pairs With Heat Shrink | eBay

To charge the packs, you need a Deans on the charger. You plug the charger power lead to the battery power lead (Deans to Deans). You then connect the balance connector to the slot in the end of the charger. You're now ready for charging, but you have to set the parameters in the charger first: however many cells in the pack (6); 3.65v max per cell, unless it's automatic when you select "LiFePO4" (might be "Life"); the charge current, which should be about 60% of your power supply current. There's other default parameters for charge time and charge amount. You can leave them as they are for now. When charging finishes, check that you have 3,65v per cell or 21.9v total, but be aware that it will drop down a bit after charging finishes in case you don't check straight away.

You can make a fuse out of two Deans (male and female and a car fuse. You can get a pack of car fuses from the Pound Shop. Take one about 20 or 25 amps and solder each of the spades to the negative side of the Deans, so that it sits flat, then solder a short piece of wire between the two positive terminals. The wire needs to be thick enough to carry 20 amps (14g). Insulate it, and then fit it between the controller and battery pack. If the fuse blows, you can temporarily leave it out as long as the reason for it blowing has been sorted.

 

[Joneser]

Awesome thanks so much Dave.
My colleague has some soldering kit to lend me. Will let you know how I get on.

 

[Joneser]

Hi Dave,
Could I check with you the batteries to controller deans connection please.
You said "Cut off the connectors on the controller and solder on Deans - always a female on the battery side."
As photo this means I end up with a female to female connection so I put a male male in between?
Why should I do this?

I assume its important as you wrote it in bold, or I have misunderstood something.
Many thanks in advance.
Joneser