3500W hub motor, question about real power and breaker

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Orphee's picture
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Hi all

I have a (small) problem on my electrical motorcycle (you can see the project here :
Here I use a 100A breaker
I saw I often exceed this value except if, of course, I set the Kelly 72801 controller to 35%. If I did this acceleration power is much more low. If I let max power, breaker may sometime disconnect all system ... witch may be a problem when you are running in town: bike will ask for "key" and start alarme because bike is already running.
When I started this project, I don't remember I had a problem with such a consumption. Perhaps I had another breaker or, if not, is there a problem with motor (or controller) ?
So my question is simple: if you have a 3500W motor, what is your breaker value ? (is my breaker too low for the motor ?) what max consumption at acceleration ?
Anyway, it's VERY pleasant to run with such a funny/pretty bike !

Thanks for help and sorry for my bad english

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MEroller's picture
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Re: 3500W hub motor, question about real power and breaker

You seem to have the same controller as I, though my motor is a 5...8kW variant. My circuit braker is 80A (AC) and has never tripped despite regularly over 100A (DC) going uphill, and during acceleration a short burst of up to 160A. I have also limited the battery max current to 35%.
An AC circuit braker will usually take more DC current to trip it, so your 100A part should only trip at above 150A DC or so. It may be damaged and thus trip too early...

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My ride: E-Sprit Fury (basis is the ZAP/Erider Thunder 5000) since May 03, 2011. Mods: Battery temp. gauge and battery heating (off the grid and off the battery), Kelly KEB72801X, reverse activated, luggage rack with topcase, HC Cycle Analyst, Emsiso BMS2405, 35mm³ battery cables

Orphee's picture
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Re: 3500W hub motor, question about real power and breaker

Thanks MEroller

I forgot to mention I had a 48V battery with A123 cells (16*15 cells) so I can deliver very high current is needed.
My breaker is this one: http://www.ebay.ca/itm/100-AMP-12V-DC-CIRCUIT-BREAKER-REPLACE-FUSE-100A-12VDC-/250777413473?pt=Motors_Car_Truck_Parts_Accessorie...

Normally it's for 12V , perhaps this is the real problem...

Could you give me your consumption at 75km/h (0%) so I can compare ?

Some pictures:
9 esthetique finale 5.JPG
mini avant2.jpg
arr3.jpg

Orphee's picture
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Re: 3500W hub motor, question about real power and breaker

And, of course, if someone has a product reference for a GOOD breaker which can support 72V / 100-140A please send me links !!

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Re: 3500W hub motor, question about real power and breaker

I'm not sure about the breaker, but if you are running 48v (lithium I assume) then hot off the charger you should have 58.4v.
Under power you probably only have 50v so we will work on that. To get 3500w from 50v is 70Amps. But there are losses so 3500w to the motor may pull around 3800w which is 76 Amps

I have an 8000w hub motor scooter from erider and it usually takes about 3000w to hold 70km/h (flat) and about 5000w to hold 80km/h and 8500w to try and hold 92km/h. I'm currently building a 48v dirt bike with lithium using a Mars ME0708 but because I don't have it running, I can't tell you the power consumption for that.

Very nice looking bike. I would suggest a Cycle Analyst (google it if not sure) because then you will see exactly at what current the breaker trips. Then maybe try your hardware shop for other breakers and see what works. You really only want a breaker in case of a short which will be in hundreds and hundres of amps.

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------------------------------
eRider 8000w Scooter - PDT Version
72v 50AH CHL battery
350A Sevcon controller

24km: Delivered - 24 September 2011
2490km: Installed dual 35w HID lights Bi-Xenon Projectors - 27 November 2011
8313km: Installed BMS - 13 October 2012

"Scrappy" - Custom 48v Electric Dirtbike Conversion
20 Feb 2012: Bought 2005 Suzuki DRZ-400SM Motorcross Bike for $100
Motor: MARS ME0708
Controller: Alltrax AXE4844 400A controller
Battery: 16xCHL 50Ah LiFePo4 = 48v

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Re: 3500W hub motor, question about real power and breaker

Orphee,

You may be aware of this, but breakers have different trip ratings, for current, heat ...

It is a series circuit, & 100 A @ 12 V = 1200 W [1.2 KW].
100 A @ 48 V =4800 W [4.8 KW]. This representa *Lot* more heat.

A quick peak of ~5 KW is quite different than going up a hill with a much longer 5 KW load.

Be sure any breaker you buy is rated for your DC voltage, and read the specs re amount of overload current vs time required to trip. A few [very few] breakers have both AC & DC ratings, but they are always larger, and more expensive.

My wall light switch may be rated for 20 A, but I would not expect it to last a few minutes on an 80 A load. The contacts would probably weld when first turned on. An AC switch, with a DC overload, would be even worse.

Another problem with overloading a breaker may be voltage drop, added to drop in all wires and connections between batteries and motor. Welding cable is unusual on a bike, but I ran two #2 welding cables between my camper front and rear 12 V batteries.

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Orphee's picture
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Re: 3500W hub motor, question about real power and breaker

Thanks everybody

In fact, this night, I remember a "detail" ;-) in fact the history : at first test I was using a fuse, not a breaker. When I was doing so, I had no problem at all. But after, I thought it would not be usefull to replace fuse if needed so I put a 80A 12V breaker. Next I found this breaker cut sometime so I replaced by same with 100A value (but always 12V).
So I was wondering about problems on motor but I thinks there is only problem with breaker.
One thing I forgot to precise is that I like accelerating (and it very spectacular). When I put 35% kelly power setting, accelerating is very "poor" in comparison.

So what ? I will change the breaker (and the size of wiring for power too)

Thanks again

MEroller's picture
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Re: 3500W hub motor, question about real power and breaker

This is the circuit breaker in my ride, a Chinese part:

As you can see it is a 230V AC 80A breaker, not 12V, and not especially for DC either. Which is the reason why it will easily accept over 100A DC current without tripping. Something the originally installed 230V AC 60A part, also from Chint, did not. It tripped during 100A+ uphill stints.
My electrical power usage at 75km/h is around 4400W. As my battery is 24 cell "72V" and was sitting at around 74V my current draw was 60A. Yours will be a lot higher due to the lower voltage.

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My ride: E-Sprit Fury (basis is the ZAP/Erider Thunder 5000) since May 03, 2011. Mods: Battery temp. gauge and battery heating (off the grid and off the battery), Kelly KEB72801X, reverse activated, luggage rack with topcase, HC Cycle Analyst, Emsiso BMS2405, 35mm³ battery cables

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Re: 3500W hub motor, question about real power and breaker

Thanks for your informations so I will compare. At the beginning I was using a "cycle analyst" but I choose to integrate mine in my system (with no resistor but ACS754 200 amp current sensor)

Finally I ordered this breaker:

http://www.ebay.ca/itm/220666129340?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649#ht_1281wt_1064

( Bussman DC Circuit Breaker 150 Amp 48V )

One think I forgot to tell: I use a capacitive BMS witch is in serial with battery and normally protected (150A) so this breaker is in addition

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Re: 3500W hub motor, question about real power and breaker

Most AC breakers are not rated for _any_ DC current. Breakers rated for both AC & DC are clearly labeled, larger, and mort costly.

AC breakers, when used on AC, have arc suppression due to the AC going through Zero V twice each cycle [Hertz].

When the same breaker is used [Misused] on DC, the narrower gap arcs -- and keeps arcing -- unless it is designed for DC. A DC breaker has wider gap, and may also have magnetic arc suppression..

The high curent DC can weld the contacts together, and overload can melt insulation, start fires ...

You _may_ get away with DC on an AC only breaker, IF breaker is never manually switched, when high current is made, or broken. THEN, when there IS an overload, and breaker trips, resulting arc can start fire, weld contacts together, overheat wiring, ruin batteries, motor ...

If all it did was ruin breaker, melt wires, & burn a little paint, the damage would still be far more than than you could ever pay for one breaker. [And you would still need another breaker. If really lucky, you would still have bought two breakers.]

Breakers only look expensive, until you stop to think about the larger picture.

I suggest reading on Google about .

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Re: 3500W hub motor, question about real power and breaker

Thanks for your opinion Jack-son

You're right: breaker default may be dangerous... but one time I made a short circuit on my battery and have been surprised to see wiring immediatly destroyed ! no time for fire ... A123 cells can deliver too much current.

Also
I was waiting for my breaker, ordered in may. In fact I never received it and, above all, company ask me to pay for another one because they wait part return to them before refunding ! (if the breaker return one day)
So I'm riding my bike and, as we have very good weather, I run for many kilometers every day ... and without problem. In fact, I can run at 70-80 km/h, I just have to be cool during hills or low speed accelerations.
When I'm on a big hill I look to consumption so it doesn't exceed 80 to 100A, this gives me about 50km/h (hill is difficult with a 15 level speed bicycle) so I think I have no problem with motor.
But, one day, I would like to find a "low" cost good 48-72V breaker (72V because I don't need to run for many kilometers and it will be funny to go at 100km/h)

Orphee's picture
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Re: 3500W hub motor, question about real power and breaker

Also: I set kelly controler to 65%, this made the bike very reactive (best acceleration than a standard car). My pleasure is ton run at low speed, like a bicycle for example, and I "wait" for a car behind me. The car come and, in a few seconds, I'm at maximum speed ! (and car is far away) ;-)

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