# What could you convert yourself for the price of a Vectrix?

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andrew
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Last seen: 13 years 1 month ago
Joined: Tuesday, November 28, 2006 - 17:21
Points: 1361
Re: What could you convert yourself for the price of a Vectrix?

I don't really know, but I deduct from general experience etc. that doubling the number of motors will not double, but possibly quadruple the potential for trouble.

Not necessarily, but the mechanical system will be more complex. Twice the number of brushes (any of which can fail and cause motor failure), twice the number of motor bearings, and the mechanical complexity of a coupling system. The coupling system will waste a small amount of energy depending on the type. Also, two motors will probably be less efficient at low power output, such as when you need to cruise at less-than top speed. So, one motor is a more simple design, and preferable from an engineering perspective.

So sometimes they'll be hungover or half the crew is sick, and one motor in a duo-setup might therefore end up performing differently than the other.

Would this matter?

It might matter somewhat, but can be corrected for. If the motors are just dropped in, and unbalanced in terms of their torque/speed characteristics than one motor will draw more current than the other. This does present a risk of one motor taking most of the load and overheating. The way to deal with this is to adjust the motor timing. The timing of the motor that is underloaded can be advanced until the motor loading is balanced.

This was actually quite a PITA for me, until I used the proper method. I'm running one etek CW, and the other CCW, and for some reason they appear to have a completely different torque/speed characteristic when run CCW. When I tried and adjust the timing on the CCW motor so the current matched the CW motor with an amp meter at low speed, the CW motor would still get a lot hotter. And it would draw more current than the CCW motor at higher speed.

I eventually used motor temperature to balance the average load, for a typical high-speed ride on my motorcycle. Really what I balanced was the motor heating, and heating is the critical factor. Heating will cause one motor to overheat and fry while the other may remain cool. The current load may be approximately balanced for a particular speed, but on the average it is balanced in a manner that causes both motors to heat up the same.

I recommend using motor heat as feedback to balance the load on the motors. It is easily done with an infrared thermometer, but will take some time for trial and error as the motors will need to be allowed to cool each time and run for a typical ride on the motorcycle for each test.

Does all the power in a two-motor-bike come from all the batteries equally, then gets split up to the two motors?

All the batteries will always see the same current draw, as they are all in the same circuit (if all put in series). They don't care what you are using to load them, whether it be 1 motor or 10 motors and a string of light bulbs, or a water heater, and two TVs and a radio.

What if one motor draws more power than the other one (because it does not have exactly the same efficiency)? Does this introduce more risk for battery imbalance?

No.

For example, if the weaker motor only contributes 15hp whilst the stronger one contributes 19hp, the resultant power would be 34hp = 17hp x 2.

If the continuous power rating for the motors is 17hp, then the "stronger" motor would be running above specs at 19hp continuously for the duo to produce 34hp.

I guess the stronger motor would not last long under the circumstances.

True, but how fast can 34 hp get you on a bike? Here's a bicycle speed calculator: http://www.kreuzotter.de/english/espeed.htm At high speed most of the losses are aerodynamic, and I might guess that the drag profile might be somewhere similar to a mountain bike. Leaving the setup stock and adjusting the weight to 500 lbs for MTB, yields 96.5 mph.

First, if you have the motors mounted anywhere near the air stream they are going to get a load of cooling air at this speed. Secondly, I don't imagine you are planning to cruise this fast so most of the time the power requirements will be well below the continuous rating of the motor system. At ~63 mph (my top speed) my bike draws about 120 amps, that's 60 amps per motor; well below the 100 amp continuous rating, and the motors are out in the air stream and could probably handle more like 150 amps continuous. So, even if they were unbalanced, they both would be running well within safe limits.

But maybe the gnomes making motors are more reliable than the battery gnomes - anyone with insight into this?

Probably the same gnomes as the ones that made your lawnmower, or your TV. They didn't do too bad a job did they?

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
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frodus
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Last seen: 7 years 4 months ago
Joined: Monday, March 17, 2008 - 08:39
Points: 189
Re: What could you convert yourself for the price of a Vectrix?

well, If I could build a dream bike.... I'd do what I'm doing now...haha (except I'm starting with SLA and moving to lithium)

I've got a VFR700 (Any 600-800CC chassis would be ideal)
K91-4003 motor, 6.7" 73V, but can run at 96V, 50Ftlbs of torque and around 20HP max.
100V of liFePo batteries
Custom built balancing Charger/BMS
Custom built 600A 156V DC Series controller (Helping with this now)
PDA Interface to controller and BMS
Vicor 200W 100-200VDC in/15V out DC-DC Converter (might be ellimintated due to BMS/Charger system)
Allbright 2 pole contactor, SW190, with aux contacts

So far, I've got everything but the LiFePo (I've got 12 18Ah batteries to start with now)

But somewhere along those lines is what I'd do... maybe as some new AC motors come out, and some new AC controllers, I'd consider that route. It seems like the Highperformance Golf Cart motor (Electricmotorsport/thunderstruck) is nice, but is it the only choice for lower voltages? Don't mention the Mars, its too small for my requirements.

____________

Travis Gintz
1986 Honda VFR Conversion
www.evfr.net

Mik
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Last seen: 7 years 6 days ago
Joined: Tuesday, December 11, 2007 - 15:27
Points: 3739
Re: What could you convert yourself for the price of a Vectrix?

well, If I could build a dream bike.... I'd do what I'm doing now...haha (except I'm starting with SLA and moving to lithium)

I've got a VFR700 (Any 600-800CC chassis would be ideal)
K91-4003 motor, 6.7" 73V, but can run at 96V, 50Ftlbs of torque and around 20HP max.
100V of liFePo batteries
Custom built balancing Charger/BMS
Custom built 600A 156V DC Series controller (Helping with this now)
PDA Interface to controller and BMS
Vicor 200W 100-200VDC in/15V out DC-DC Converter (might be ellimintated due to BMS/Charger system)
Allbright 2 pole contactor, SW190, with aux contacts

Thanks, Travis!

I was thinking about the L91-4003 for more grunt, but it might cost too much range.

Mr. Mik

This information may be used entirely at your own risk.

There is always a way if there is no other way!

frodus
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Last seen: 7 years 4 months ago
Joined: Monday, March 17, 2008 - 08:39
Points: 189
Re: What could you convert yourself for the price of a Vectrix?

i meant 72V :)

But yeah, L91 is 15.34" long motor, thats kind of large for a bike. mine is like 11.5" long. Its also double shaft and 84lbs... a bit overkill for a motorcycle. You don't need double shaft do you? K91 is 56lbs.

The K91 can be had for under 700 if you look. Mine is actually a K99-4007, doesn't have the baseplate, and the shaft is longer, otherwise its the same. People use smaller motors than mine and get great results. Its got thermal mass, so its not going to melt down like one of the eteks or PM132's. Great torque and HP ratings, and you can run them WELL over their rated voltage. They'll handle the speed.

____________

Travis Gintz
1986 Honda VFR Conversion
www.evfr.net

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