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Author Topic: 2009 sepex GPR-S Owner's Review  (Read 3723 times)


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2009 sepex GPR-S Owner's Review
« on: September 07, 2010, 08:39:09 PM »

It looks like it was about time that the Electric Motorsport (EMS) forum had another thread. So here are my impressions of the 2009 D&D motor sepex GPR-S that I currently own and ride.

After my 2008 GPR-S suffered a BMS melt-down that put the vehicle out of commission for some time, I traded it back to EMS for a credit against a new 2009 GPR-S powered by a large D&D sepex motor and 24 50 Ah "Hi Power" batteries with a nominal voltage of 72 volts. I have been riding this motorcycle since it was built in January 2010.

The motorcycle that I purchased and have now ridden for 1200 miles, has a large electric motor, rated at 36/48 volts, which (I believe) is sometimes used in golf carts. The motor is a “sepex” type and weighs 58 pounds. It is rated as having a peak of 29 HP, but in practice the batteries can not supply sufficient electrical power to actually generate more than about 6 HP at the rear wheel. Sepex motors are described by EMS as being almost identical to traditional series motors except for the way their field is wired and controlled. Unlike a series-wound motor, whose armature and field windings are wired together in series, the sepex motor’s field and armature windings are excited separately by special sepex controllers that have wire leads to both the armature and the field. Separate control of the armature and field creates distinct advantages over a standard series wound motor, notably adjustable regenerative braking, higher rpm, longer power band, higher efficiency, and easy reversing. All of which sounded good (and new and different) and seemed to be worth a $1200 premium over their standard model, which uses an Etek-type motor and a 72 V/ 40 Ah system, consisting of 24 Thundersky batteries.

The primary interesting feature of the motorcycle is that when activating the brakes, which were relocated to the handlebars like a motor scooter, the electric motor turns into a generator and pushes electricity back into the batteries, extending the range slightly – to say nothing of reducing brake wear. Just a light touch on either brake lever activates the regenerative feature, which feels like closing the throttle on an internal combustion engine and slowing down under compression. The large size of the motor required cutting a hole in the right side of the fairing to allow the end of the motor to stick out in front of the right foot peg. It all seemed like it would provide an increase in performance and range. And it would have, except that the batteries that were installed in the motorcycle were not the latest “Thunder Sky” batteries, but a set of “Hi Power” batteries that had obviously been sitting around for some time, as the tops of the batteries were pretty dirty and EMS does not currently offer them for sale. These were the same type of 50 amp hour rated batteries that were used on my 2008 bike. (The new “Thunder Sky” batteries have a 50% greater discharge rate, according to their specifications.) As it turned out, the motorcycle, with its sepex motor and 24, 50 Ah “Hi Power” batteries, did not deliver as much of a performance upgrade as I had expected. However, since the batteries still have 3.6 kilowatt-hours (KWH) of storage capacity, it qualified for a 10% rebate from the Federal Government on my income tax return. Any DOT approved electric motorcycle that has a storage capacity of 2.5 KWH or greater qualifies for this rebate. Some states also provide additional rebates or credits toward the purchase price of a “plug-in” electric vehicle.

Top speed is only about 60 mph, with adequate acceleration from a stop, but not as much pulling power between 30 and 60 mph as had my previous bike. It appears that is because the power to the motor is limited to 7.5 KW (180 amps) peak, and only 6 KW during continuous riding. This is due to either the programming of the Sevcon motor controller, or the inability of the batteries to deliver any more power. When under a load, the voltage of the batteries sag from 76 volts down to 51 volts, at which time the controller cuts the power draw so that the voltage of the batteries will not drop below this value. If they were to do so, it could damage the battery pack. The net result is that it is sort of like having a big V8 engine in your car, fueled with a very small carburetor. Not a good performance combination, but one that is likely to be very under-stressed and reliable. Plus, the motorcycle can be easily upgraded with better batteries in the future (at a substantial cost, of course), with likely a noticeable improvement in performance. Right now the maximum range is 40 miles at a steady 30 mph and about 30 miles in stop-and-go, mostly full-throttle riding, including some up and down hills and riding at top speed on expressways. According to the Cycle Analyst, power usage varies between 70 and 90 watts per mile, depending upon how long full throttle was used.

Unfortunately, the bike has a drive-ability problem that would be familiar to some BMW fuel injected motorcycle riders. It surges under most riding conditions and feels like a 2000-era R1100 model riding around town. You feel constant power pulses at a steady speed and while going up hills. When the bike was new and you would ride over 50 mph for more than a couple of minutes, the power would be cut off without warning until the throttle could be closed and reopened again. This was apparently due to the batteries inability to provide high current for more than a few minutes. After several hundred miles of use, this problem disappeared.

Charging the batteries takes noticeably longer than it did on my 2008 GPR-S. This is due to the increased energy capacity of the batteries, 3600 KWH vs. the 3000 KWH of the previous vehicle and higher voltage and corresponding lower amperage output of the 6 amp charger, compared with the 8 amp charger that was used in the 2008 version. In any case, it now takes about 8 hours to bulk charge the batteries, at which point the “battery management system”, reduces the charging current and starts cycling the charger off and on for several more hours, until the batteries are fully topped-off. When fully charged, the system will indicate 84 volts (which drops quickly to 76 volts when riding, or after sitting around for a few hours) on the vehicle’s Cycle Analyst computer screen.

Upon fully charging the batteries from their 40 Ah depleted state, the charger consumes 4.4 KWH of power, according to a “Killawatt” meter. At my current electric power rate of 11.9 cents per kilowatt hour (KWH), the cost of charging the batteries is about 52 cents. I rode 30 miles at the time and this equates to about 1.7 cents per mile for “fuel”. Not too bad, as long as you can accept the restricted range and performance. The other advantage is the lack of motor maintenance and minimal chassis maintenance and its associated cost. Working around the chassis, even without a service manual for a home mechanic, is easy as it is a very basic design.

Is it worth the money? I would have to say no. But the Electric Motorsport Sepex GPR-S motorcycle is an interesting development that would appeal to hobbyists and electrical engineers, as it is easy to work on and to modify and upgrade (assuming that you know what you are doing). Anyone who wants to just own and ride an electric motorcycle in 2010 would be well advised to look into the Brammo Enertia, as sold by Best Buy or the more expensive Zero S. The cost of the Brammo is $8000, the vehicle is much more refined and if you have a problem, the Geek Squad will come to your house and take care of it for you. The Zero S has better performance than either the GPR-S or the Enertia, but costs over $10,000 and it does not yet have a “track record”.

I might add that I now have a more complete understanding of the phrase “early adopter” and a much greater appreciation of the value of the established internal combustion motorcycle manufacturers and the resources that they provide to an owner of their vehicles, such as providing a parts supply system, trained mechanics and good customer service – none of which you get with the Electric Motorsport (now Native) GPR-S, unless you have a nearby retail dealer.

Frankly, I can hardly wait for the Brammo Empulse to arrive next year. I have a 10.0 version on order and when it arrives; my daughter will get my current GPR-S. Her husband is an electrical engineer and programmer. Maybe he can get it to work better.
Richard's motorcycle collection:  2018 16.6 kWh Zero S, 2016 BMW R1200RS, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2005 Triumph T-100 Bonneville, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior.


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Re: 2009 sepex GPR-S Owner's Review
« Reply #1 on: September 23, 2010, 12:26:37 AM »

Minor notes.

1. Yeah, I am too cheap to be an early-adapter type, but I've been panting for an EV bike for some time. How, how, how????

2. I am pretty particular about using front versus rear versus both brakes. Bicycles have rear brake right hand but MC it is the front brake. Bad. Both brakes on bars sounds good for an EV bike but it will be inconsistent with one of those.

3. Is there some source that provides cheap batteries? How come there's no active after-market by now? Can't somebody buy up thousands of lithium cells and make good bike batteries? Can't owners do it? Where's the dirt on recycling, rebuilding, etc.?

4. As I've posted before, there should be enormous HP hidden in making very high speed motors, say dynamically balanced 12000 rpm... IC motors do it. But they will need further reducing gears which cut efficiency. Seems pretty wise for somebody to develop efficient speed reducers so faster motors can be spun.
biking 49 seasons, BMW boxer twins last 44
urban and touring
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