Few questions - does this new motor sound normal? (video)

Hi,

 

Ive just received my Brompton 16 inch topbikekit akm74 motor. Just have a few questions:

1. Does this motor sound normal in the beginning and end. It sounds like internet dial up back in the day -

 

2. There's barely any freewheel with the motor connected or not. As soon as I stop throttle it pretty much just stops?

 

3. Currently using 2x power tool batteries for 36v 4ah the motor maxes out about 15mph (KT LCD4 already max speed set 72kph). How do you achieve 20mph to keep up with traffic? Is it possible to achieve a higher Peak power because there's a lot of steep hills here and it just drops to about 10mph even with pedalling. Controller is KT T06s 24/36. Will it be okay to use 48v battery as long as i check the controller capacitor is 63v and stop before it drops below 42v? Or will it be better to get a new controller altogether? Or is there something else I can do?

 

Many thanks!

Sound perfectly normal for no load speed running.

15mph is as fast as the motor will run in 16" wheel for a 328rpm hub, if wanting more speed one will need to try 48v but even then one won't see 20mph.

For a 16" wheel, every 1 mph needs approx. 21 rpm.

15mph is as fast as the motor will run in 16" wheel for a 328rpm hub, if wanting more speed one will need to try 48v but even then one won't see 20mph.

For a 16" wheel, every 1 mph needs 21 rpm.

 

Thanks. So ultimately this motor isn't as capable as the brompton kits from grin tech and sparticle kit? I thought I could get a higher amp controller and 48v to at least increase torque by about 30%?

 

And is the lack of freewheel normal because it's 16 inches?

The 24/36v controllers will have 50v caps, one would have to use a 36/48v s06s.

At 48v you might see 19mph.

It's a lightweight hub so don't go throwing 20a at it at 48v as likely the nylon gears will melt. 12 -15a should be plenty for 48v, one can get the 17/20a controller and dial down C5 and then see how it goes before giving full current.

 

The wheel should freewheel ok, it is new so might wants a few miles on it first. Other wise is it pinched at all on the d/o's.

It's a lightweight hub so don't go throwing 20a at it at 48v as likely the nylon gears will melt. 12 -15a should be plenty for 48v, one can get the 17/20a controller and dial down C5 and then see how it goes before giving full current.

 

The wheel should freewheel ok, it is new so might wants a few miles on it first. Other wise is it pinched at all on the d/o's.

 

Thanks, is it worth getting s09s controller? Also, would it drastically reduce the life of the akm74sx motor? My normal use is level 2 with pedal for flats but when i reach the hills i use full throttle with pedal. Starting to get into cycling again and trying to lose weight.

 

From the video as soon as i stop throttle the wheel doesnt freewheel. I dont think it's pinched at the dropouts, i think i used 30nm torque wrench with standard brompton fitting as torque arm

Try releasing the nuts, I don't torque mine up I simple do them spanner pinch tight and then give max 1/8 - 1/4 turn. If you have steel forks a T/A isn't needed.

 

S09s is 22a so defo dial down the power, one shouldn't need max power.

Although I don't use 16", but 700c with the front G370 mini hub and even towing a 120kg load on a trailer PAS 2 or 3 is the most I use for small inclines.

I dialled my s09s down to 19a, to get the power I want in pas 1-3 & not yet gone above PAS 3.

Try releasing the nuts, I don't torque mine up I simple do them spanner pinch tight and then give max 1/8 - 1/4 turn. If you have steel forks a T/A isn't needed.

 

S09s is 22a so defo dial down the power, one shouldn't need max power.

Although I don't use 16", but 700c with the front G370 mini hub and even towing a 120kg load on a trailer PAS 2 or 3 is the most I use for small inclines.

I dialled my s09s down to 19a, to get the power I want in pas 1-3 & not yet gone above PAS 3.

 

Even when nuts are released there's still no freewheel. Anyone know whether this is normal for 16inch motor?

 

Wow! 120kg load still PAS 2 or 3 only? That's really good!

 

Just have another question. I'm using 36v 4ah power tool atm and at 36v lcd reading it's already showing only a 1/4 battery left on the display? Is this normal? And sometimes it would fluctuate down to 33v on hills then go back up to 36v once flat again. For battery preservation, shall i set Low voltage cut off at 32v?

Yes 1/4 left on display sounds about right. Don't forget a proper 10s battery is 42v fully charged, are the tools batts only max 18v fully charged.

 

32v is a good idea, that's a downside to tool batteries one doesn't have much leeway.

Yes 1/4 left on display sounds about right. Don't forget a proper 10s battery is 42v fully charged, are the tools batts only max 18v fully charged.

 

32v is a good idea, that's a downside to tool batteries one doesn't have much leeway.

 

It's about 40 - 41v fully charged. Looks like everything is normal then. Thanks!

The battery bars are only a guide and not very accurate regarding remaining charge, the only time they are really accurate can be with a full battery and when the they go out and the bike cuts out.

With lcd4 one doesn't need to bother about battery bars as the display gives out real world voltage readings under load, I see about 0.3 - 0.5v sag under load in low PAS which is normal.

2. There's barely any freewheel with the motor connected or not. As soon as I stop throttle it pretty much just stops?

I think we had a discussion somewhere before about this. I think your hub has a two stage nylon helical gear reduction and some reported a freewheel time of about 10 seconds. May be less in your case with smaller wheel (less inertia). Some of the other larger wheeled straight cut nylon gears (no sideways thrust) single stage front wheel (e.g xf07) can freewheel for 90 seconds or more, but we are not comparing like with like. The power loss due to this normal extra friction in your case is normally insignificant and is outweighed by the extra efficiency of the greater gear reduction ratio .

My g370 is two stage gearing, in a 700c wheel it only freewheels five complete rotations given a good spin by hand. One is worrying over nothing.

It is the ability of how the motor rides with no power that is more useful, the smaller geared hubs being lighter and with far better gearing ratio's tend to ride so much better with no power and are ideal for longer range riding with a lighter battery.

All on had to be careful with is how much abuse they give the motor with current.

 

The g370 hasn't the grunt of my bpm, cst or amk128 but it certainly is a nicer ride then all of them with no power.

Edited April 29, 20223 yr by Nealh

The battery bars are only a guide and not very accurate regarding remaining charge, the only time they are really accurate can be with a full battery and when the they go out and the bike cuts out.

 

I see. So I'll get a new t09s 22a controller and limit max current to 17 or 19amps.

 

In the meantime, is it okay for me to use 3x power tool in series= 15s2p.

So 4.2v x 15 = 63volts 4ah

 

Or is that too much for the controller and akm74 motor to handle? If so I'll just use the 36v for now till i have time to build my own battery. Whats a reliable place to buy 18650 cells? Liitokala on AliExpress?

The voltage won't be too much but the current might be , at 15s limit the current to 10 - 12a which is 560w - 672w and see how it goes. The caps ae 63v rated on 48v controllers so one will be at the max, how much safety limit they have above the rating I don't know.

The voltage won't be too much but the current might be , at 15s limit the current to 10 - 12a which is 560w - 672w and see how it goes. The caps ae 63v rated on 48v controllers so one will be at the max, how much safety limit they have above the rating I don't know.

 

Thanks. Would it be better to get a 12 mosfet 48v controller to be on the safe side or is that overkill?

 

Is that 672w peak power safe for a 250w motor?

So if I were using normal 48v 13s; a safe limit is 15amp controller will equal to 13s x 3.7v x 15a limit = 722w peak power?

The guy on pedelec .de put over 2000w thru the 250w swxk hub.

The guy on pedelec .de put over 2000w thru the 250w swxk hub.

 

Thats absolutely mental. The swxk is a strong hub.

 

Can i ask when you say "limit the current to 12a-15a and see how it goes"; what do i do to see how it goes? Go up a hill then touch the hub and controller to see how hot it gets? In the lcd4 it says there's a temperature function but im not sure if my akm hub has a temperature sensor?

The displays only show ambient air temp and there isn't any controller wiring for temp, though one might be able to use the throttle wiring if one could fit a temp sensor. One can do so on the tsdz2 if the throttle isn't needed as the motor outer is static in the main housing with controller.

Reducing the current will reduce heat, the controller and hub can be felt for heat issues.

Without cooling the hub will have a limit of how much heat will melt the nylon gears.

As mentioned 12a x 52v is 624w & 15a is 780w. We know from experience the larger akm100 max was 20a @48v before the nylon gears melted and many had issues pushing it more.

The displays only show ambient air temp and there isn't any controller wiring for temp, though one might be able to use the throttle wiring if one could fit a temp sensor. One can do so on the tsdz2 if the throttle isn't needed as the motor outer is static in the main housing with controller.

Reducing the current will reduce heat, the controller and hub can be felt for heat issues.

Without cooling the hub will have a limit of how much heat will melt the nylon gears.

As mentioned 12a x 52v is 624w & 15a is 780w. We know from experience the larger akm100 max was 20a @48v before the nylon gears melted and many had issues pushing it more.

 

20a is insane! So if it's too hot to leave my hand on i should reduce the amps? Or use a thermometer and if it's above x celcius? Any idea at what Celcius does the nylon gears start to melt?

If a controller is too hot to leave your hand on, it will have likely thermally cut out before then if the mosfets don't fry.

Too hot then one needs to reduce the current.

Nylon temps not really but we know the Blue gear on the tsdz2 fails and we know some see 75 - 104c temps recorded internally with about 30/40c less recorded on the exterior.

The displays only show ambient air temp and there isn't any controller wiring for temp, though one might be able to use the throttle wiring if one could fit a temp sensor. One can do so on the tsdz2 if the throttle isn't needed as the motor outer is static in the main housing with controller.

Reducing the current will reduce heat, the controller and hub can be felt for heat issues.

Without cooling the hub will have a limit of how much heat will melt the nylon gears.

As mentioned 12a x 52v is 624w & 15a is 780w. We know from experience the larger akm100 max was 20a @48v before the nylon gears melted and many had issues pushing it more.

 

Hi Nealh,

 

I'm assuming the above you're talking about max current (peak current). However, if i were to get a kt 09s - 9mosfet 48v 22a controller and limit the max current to 10a, the Rated current (which i assume means continuous current) will still be delivered at 11a (instead of the 7a on the kt36v 15a controller). Hence, 52v x 11a = 572w continuous on a 250w motor. Will that be okay?