When the battery goes flat

[OldNick]

Or at least circuitry cuts out from low voltage.

I am looking a the Golden Magic pie III hub and kit. I like the regen braking and cruise control options and the price seems pretty good.

I have read a comment that when the battery is flat, there is significant "resistance" (I assume drag) from the motor, which is over and above the extra weight. Surely that can be overcome by opening the circuit in some way?

However, my question is. "Is there a significant drag from the motor after the power is removed?"

Any advice on this greatly appreciated.

Nick

 

[dnmun]

advice is to not ever run your battery down to LVC.

 

[Lebowski]

There will be drag even if you completely unconnect the (3) motor wires but it depends on your motor construction.

when the motor uses metal in the windings (typically in the form of laminations, the thinner the better) there will
be losses (drag) caused by eddy currents

when the motor is would in delta (which many are), due to inequalities in magnets etc the windings will supply power
to each other, powerflow which has losses and thus causes drag.

My motor has no iron in the windings and is wound in WYE so has practically no electrical drag, only mechanical drag from bearings..

 

[dogman dan]

Interesting reply.


Here's my experience with other motors, one a clone of the crystalyte 407, the others 9 continent or clones of 9c. Unpowered, pedaling is hard, after all, you have a motor that weighs more, and battery. 25 pounds added to the bike is not unusual.

Then there is the drag of the motor. It's not that bad at 5 mph, but as you pedal faster it increases. By 20 mph, not that you'll get there, it resists a lot more. You see this coasting down a big hill. With a dd motor, you will get a braking effect, and a hill that you used to coast to 40 mph down will not reach 40 mph anymore.

Dunmun hit the nail dead center. Don't ride till cutoff if you can help it.

Many reasons to try to avoid it unless you are doing a test of total capacity. The bms might not work, so you want to know your voltage just in case it doesn't shut off. A battery ridden till the bms trips will tend to be out of balance on the next charge, so if you can't let it have a day or so on the charger, your next ride may not have full capacity.

Here is what you should do. If you have a reason to believe your might not have enough battery capacity, slow down significantly long before it's too late. For example, say you normaly ride home from work or school, and use 80% of your battery. But today, you have to ride into a 25 mph headwind. You know you won't make it. But you will if you ride home slow enough to stretch your range.

That's great if you can anticipate it. But suppose you are 3 miles from home, and you see on your voltmeter that your battery is dropping fast, you know you have at most 1 mile left. What to do now? Again, SLOW DOWN. But in this case, you will need to slow down a LOT. You might have less than 50 watthours left in there. So stop trying to let the motor get you there, and start pedaling briskly. Once going about 8 mph, then apply just a tiny bit of throttle. Not enough to go 10 mph, but just enough to remove that motor resistance.

Now pedal home without the motor drag.

If you have gone and popped that bms, you can pedal for 10-15 min to let the battery rest, then reset the bms, and you might be able to get a mile more with the motor resistance gone before it pops again. The key is to not use the throttle one bit till you are moving 7-8 mph.

 

[BarkMau]

There will be drag even if you completely unconnect the (3) motor wires but it depends on your motor construction.

when the motor uses metal in the windings (typically in the form of laminations, the thinner the better) there will
be losses (drag) caused by eddy currents

when the motor is would in delta (which many are), due to inequalities in magnets etc the windings will supply power
to each other, powerflow which has losses and thus causes drag.

My motor has no iron in the windings and is wound in WYE so has practically no electrical drag, only mechanical drag from bearings..

What is that motor of yours? Sounds good!

 

[dogman dan]

Why? once you pack 30 pounds of motor and battery on a bike who wants to ride pedal only? Hell, if you pedal that strong, ride a bike that weighs 15 pounds, not a 60 pounder.

 

[John in CR]

If you anticipate running out of electricity often or just ride the ebike with no electric assist, then a geared hubmotor that freewheels or a motor driving a belt or chain is for you. All direct drive hubmotors have noticeable drag, some more than others.

 

[John in CR]

Why? once you pack 30 pounds of motor and battery on a bike who wants to ride pedal only? Hell, if you pedal that strong, ride a bike that weighs 15 pounds, not a 60 pounder.

It's better exercise. Maybe he wants to arrive at work fresh, but get a good workout going home.

 

[Punx0r]

IMO a regular bicycle more than hard enough work...

 

[dogman dan]

I guess what I mean is, if you are going to pedal that much, a very light road bike is a lot more fun to pedal than an ebike without power.

You can double your range by just slowing down and pedaling moderately hard, so that is the thing to do, rather than run out and pedal unpowered imo. You still get to ride reasonably fast, say 15 mph, but with the same effort it used to take when you were 18 and weighed 115 pounds.

If you are very fit though, you can ride faster and get great wh/mi numbers. I just think any riding a heavy ebike unpowered is sucky. Buy enough battery so you don't do that.

 

[Lessss]

If you WANT to pedal then get a low wattage lightweight motor running at 24V because you are obviously only going to want it for help with the hills, or assistance when you are tuckered out. Use high torque not high speed. Use 24V because it will be lighter.

 

[OldNick]

Firstly, sorry for not responding. I was assuming email notification.

I will respond to replies

Nick

 

[OldNick]

advice is to not ever run your battery down to LVC.

Thanks for the reply. I realise that and I am going to monitor every cell using an RC model monitor. But that still means that at some stage I have to stop using the battery and start pedalling.

Nick

 

[OldNick]

There will be drag even if you completely unconnect the (3) motor wires but it depends on your motor construction.

when the motor uses metal in the windings (typically in the form of laminations, the thinner the better) there will
be losses (drag) caused by eddy currents

when the motor is would in delta (which many are), due to inequalities in magnets etc the windings will supply power
to each other, powerflow which has losses and thus causes drag.

My motor has no iron in the windings and is wound in WYE so has practically no electrical drag, only mechanical drag from bearings..

I have bought the kit. Sorry guys. As I said I did not realise I had so many replies. Yes you are correct there is drag just trying to turn the axles in the hub even before it's all wired up. I have no idea if this is delta wound or not, but the drag is significant. I have seen a picture of the guts of the motor. I will check again to see if there is any iron there,

Nick

 

[OldNick]

If you anticipate running out of electricity often or just ride the ebike with no electric assist, then a geared hubmotor that freewheels or a motor driving a belt or chain is for you. All direct drive hubmotors have noticeable drag, some more than others.

Well I hope not _often_ . I was planning to ride "without assist" by simply feathering the throttle. But yes it seems I now have drag.

Nick

 

[OldNick]

Here is what you should do. If you have a reason to believe your might not have enough battery capacity, slow down significantly long before it's too late. For example, say you normaly ride home from work or school, and use 80% of your battery. But today, you have to ride into a 25 mph headwind. You know you won't make it. But you will if you ride home slow enough to stretch your range.

That's great if you can anticipate it. But suppose you are 3 miles from home, and you see on your voltmeter that your battery is dropping fast, you know you have at most 1 mile left. What to do now? Again, SLOW DOWN. But in this case, you will need to slow down a LOT. You might have less than 50 watthours left in there. So stop trying to let the motor get you there, and start pedaling briskly. Once going about 8 mph, then apply just a tiny bit of throttle. Not enough to go 10 mph, but just enough to remove that motor resistance.

Now pedal home without the motor drag.

If you have gone and popped that bms, you can pedal for 10-15 min to let the battery rest, then reset the bms, and you might be able to get a mile more with the motor resistance gone before it pops again. The key is to not use the throttle one bit till you are moving 7-8 mph.

OK. Thanks. That is good advice indeed. Makes a lot of sense. Use the motor basically just to overcome its own drag.

Interesting. I got the regen braking cables included in the kit. But if the motor drags all that much already, that is going to be a bit less effective than it might be. I am assuming that if the motor is generating, there will still be current irregularities that cause drag.

Nick

 

[OldNick]

I guess what I mean is, if you are going to pedal that much, a very light road bike is a lot more fun to pedal than an ebike without power.

You can double your range by just slowing down and pedaling moderately hard, so that is the thing to do, rather than run out and pedal unpowered imo. You still get to ride reasonably fast, say 15 mph, but with the same effort it used to take when you were 18 and weighed 115 pounds.

If you are very fit though, you can ride faster and get great wh/mi numbers. I just think any riding a heavy ebike unpowered is sucky. Buy enough battery so you don't do that.

HAH! When I was 18 I was fatter than I am now and a lot less fit and strong!....however....I certainly intend to pedal to conserve battery. I agree that riding a lighter bike is easier, but I will have a trailer (12Kg) and a dog (25Kg) in tow for many of the rides: we take the dog on the road in the trailer, then she's able to run on the shared paths. It just gets more pleasant to have a little help. I have to hope that the e-bike gives more help than it takes back!

I will _try_ to get enough battery...but how long is a piece of string? I just wanted to know what happens if I do get caught.

Nick

 

[OldNick]

If you anticipate running out of electricity often or just ride the ebike with no electric assist, then a geared hubmotor that freewheels or a motor driving a belt or chain is for you. All direct drive hubmotors have noticeable drag, some more than others.

Yes I start to see that. I was attracted by less gear noise etc on the gearless and perhaps a little more efficiency.

I am surprised that the gearless motors are not given some sort of freewheel, or have a way to allow the stator/armature to revolve with the magnets. It should be easy enough. AFAICS, it would prevent regen braking, but it could be lockable.

Nick

 

[OldNick]

It's better exercise. Maybe he wants to arrive at work fresh, but get a good workout going home.

Yeah the trouble is with the motor drag, it's a _really_ good workout. Like killing.

Nick

 

[OldNick]

If you WANT to pedal then get a low wattage lightweight motor running at 24V because you are obviously only going to want it for help with the hills, or assistance when you are tuckered out. Use high torque not high speed. Use 24V because it will be lighter.

Well the weight of the motor is moot, for me. I will be dragging 40Kg+ of trailer/dog/gear behind me. Also, given the drag of the motor, weight becomes less significant. However I can imagine that a little 250W motor would have a lot _less_ drag than this monster. However I wanted the bigger motor precisely because I can underdrive it at 24V and not risk its getting hot under heavy loads on hills. I also reckon it will have more torque at 24V than the smaller motor, and the 24V will just lower its top speed. I play with RFC toys and that's pretty much how it works with brushless motors and controllers in that world.

Nick

 

[neptronix]

The magic pie III and II have a good amount of drag. You can pedal along, but you will know it is there working against you.

If you want a motor with zero drag, the BMC and MAC motors are some of the best. The 9C/MXUS/golden motor 'pro' kit style DD hub has lower drag, if you need a DD.

 

[shock]

You could also check out geared hubs, as these are lighter and will freewheel without power.