A little last minute help with my BMS shopping list please

[KirstinS]

A little help with my BMS shopping list

I'm finally biting the bullet and spending the cash after months of attempting to avoid it. Mostly because my 36v battery packed up and I'm spending 8quid a day on my return train fare so suddenly became and easy sell to the wife !

Before I hit go on my BMS shopping list I'd like to run past the great and good on here in case I missed anything please. And actually I do have a question as well

I have an 8fun 36v 250 kit but am intending to upgrade - I want more speed but don’t really need more torque on my 15 mile flat commute. I also want to keep ability to use throttle only - very key for me as I currently don’t even have PAS fitted (I do pedal quite a bit but I just prefer the control the throttle gives and like to take the odd little rest). My shopping list is

1) One 10ah 48v Lifepo4. This one

48V10Ah LiFePO4 Shrink Tube EBike Battery Pack - BMSBATTERY

2) Either Ku93 controller (I think a Ku123 controller will kill 250w motor ?). May as well get two controlers in case

KU93 450W 9Mosfets High Speed Controller - BMSBATTERY

3) Some torques arms whilst I there in case of future motor upgrade (or more likely an off road build - this is my commuter bike)

4) Some connectors so I can use power leads I already have


My main question is

1) My On/off handlebar panel with three level PAS assist, toggle to throttle and battery meter - will this work with new controller ?. If not what should I/can I replace it with ? I asked BMS battery direct but I don’t think they understood my question.


thanks as ever

 

[Deleted member 4366]

The KU123 controller will smoke your motor instantly and the KU93 will smoke it within about 5 miles at 48v. You need a 15amp controller at 48v, but BMSBattery don't do one.

A KU93 won't work with your existing panel. If you have a look at the Conhismotor site, they have controllers with nice LCD displays and variable PAS levels. Also, the KU93 doesn't have variable PAS, which is bad because you''ll get full power whenever you pedal, which is worse with the extra torque.
http://www.conhismotor.com/ProductShow.asp?id=315

I wouldn't recommend the Conhismotor batteries.They may be OK, but I have one in my kitchen at the moment with problems, and I've heard of other similar problems.

You might want to get a pair of the BMSBattery torque arms if you place an order there. You can use one and sell the other one on to get your money back. Edit: sorry, I see you already planned that.

 

[KirstinS]

Oh, didn't realise the ku93 would kill it as well

Thanks, will the 48v conhismotor controller give me more than 15.5 assist ? Uktimely that's what I'm after

 

[Old_Dave]

the KU93

I believe (I've got one I can take apart and check) that the KU93 has 2 shunts in parallel, so its doable to adjust the current by taking one out and then soldering the other to get the amps right, but an amp meter would be required see whats happening.

Also, the KU93 doesn't have variable PAS

Which kinda puts a tin hat on it, lol (if you want PAS that is)

 

[KirstinS]

Thanks old Dave but that's a step too far for me right now!

I've emailed conhismotor to ask the question - cant see an amp rating for that controller

 

[Old_Dave]

Life would be sooooooooo much easier if you stuck to 36v lol

 

[KirstinS]

I would happily stick to 36v.........if I could get more speed !

 

[Old_Dave]

I would happily stick to 36v.........if I could get more speed !

Yes..

The dark side is great... but it brings problems

 

[KirstinS]

I originally thought I could stick with 36v and get a faster wound motor - I forget why I was advised against this

 

[KirstinS]

@ old dave - With great power comes great responsibility , as a man in spandex once said

 

[Deleted member 4366]

You have to think about watts. A 48v battery is about 60v fully charged, so the KU123 controller at 30 amps will be drawing 1800w from the battery. The KU93 at 22amps will draw 1320w. Most of that power will go into your motor, and when you're going up hill with only 30% efficiency, 70% of that power will be converted to heat, so the KU123 will give you the equivalent of a 1kw electric fire inside your motor.

Normally 250w controllers are 14 or15 amps at 36v, so a 48v 15 amp one would be 333w, which would be rounded upto 350w, so I'm pretty sure that the 48v 350w one is the one you want.

The Bafang 250w motors go a lot better at 800w (20 amps and 36v battery). Presently, you have 560w. You can push them to 900w, but then you have to think about not labouring up hills for too long. At that power they become quite noisy (growl) and the difference from 800w isn't so noticeable.
Watts = volts x amps, so 48v (actually about 55v) at 15 amps will give you 825w from the battery, which should be enough to sustain 20 to 22 mph on the flat without pedalling.

 

[KirstinS]

Thanks d8veh, so , if understand correctly then 48v battery is 60v off charger. As long as the conhismotor controller is rated at 15a then i have 60v x 15a = 900w . Which is doable on my 250w moor but noisy an I need to be very careful on hills as I'm running it on the very edge of what's possible (there are none on my commute so I am happy with this)

As the battery runs down it will go 40v before LVC kicks in. So lowest watts is 40v x 15a = 600w

So just need to be 100% sure on amp rating ?

I am I getting it ? Or getting hopelessly confused ?!

Thank you

 

[KirstinS]

Response from conhismotor is 15a but 20a max

So I think this will also fry motor ?

20a x 60v is 1200w

 

[Deleted member 4366]

This one then.
http://www.conhismotor.com/ProductShow.asp?id=311
You could confirm with them what the maximum current rating is.

Even if it's too low, you can easily get it up to 15A by soldering the shunt. It's also possible to reduce the current by soldering in a resistor, but that's a bit harder than soldering the shunt.