# Ok weird question about "coasting"



## IamIan (Mar 29, 2009)

todayican said:


> Ok, something was posed to me today, and I have no idea, so here goes.
> 
> Say I have a mars 709 (etek like motor) chugging along at lets say 3000 rpm and the vehicle is going 50mph
> 
> ...


Depends on the specific characteristics of that motor ... which I do not happen to know.

If it is little load probably no significant net generator action if any at all.

If it is no load than no net generator action.

Net generator action happens when you start to see a load pulling away some of that 6 HP ICE... Then the amount of generator action will be related to the amount of the 6 HP ICE you are taking away and the generator specifications of the motor.... unless you are doing regenerative braking generator action then you might be generating even more than the 6HP of the ICE.

Depending on the specifics ... the MARS might still be adding power to the drive train allowing you to move faster than the 6HP ICE alone would allow.

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Technically there is always motor and generator action... at the same time at any speed ... but ... it is usually more useful to look at the net effect instead of isolated parts of the motor / generator system.


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## major (Apr 4, 2008)

todayican said:


> Ok, something was posed to me today, and I have no idea, so here goes.
> 
> Say I have a mars 709 (etek like motor) chugging along at lets say 3000 rpm and the vehicle is going 50mph
> 
> ...


Hi tod,

That is a PM machine. If it is rotating, it is generating. That is; the armature has a generated voltage present at the brushes. If a voltage is applied which is greater than the generated voltage, it is a motor. If an electrical load is connected which has a voltage lower than the generated voltage, it becomes a generator.

That generated voltage in the armature is proportional to RPM. So, let’s say at 3000 RPM the generated voltage (Eg) was 100 volts. To get it to motor at that speed, you need to apply 105 volts (for example). Now raise it 4500 RPM. Then Eg = 150 volts. To get it to motor at 4500, you need to apply more than 150 volts. 

At any RPM, if you want it to operate as a generator, you need to apply an electrical load. At any RPM, if you do not apply a voltage or load, it still generates voltage, but is open circuit producing no current, no torque and just free-wheels.

Regards,

major


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## Juiced (May 2, 2009)

Yes, what they said. 

The Mars motor will generate good chunk of volts. That is what these were original used for, (The B&S version) and some are still today, wind mill generators. 

They are great for Regen, but you have have weight in the vehicle to make Regen useful. 

Ed


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## todayican (Jul 31, 2008)

Ok, I am nearly following, let me shift it to a real world dillema then..

I want to drive a 500lb very aero trike with 2 motors, the mars and a 6hp i.c.e. the mars for up to say 50 and the 6hp running via the centrifigual clutch to the same shaft on the mars the main drive sprocket is on.

(also, I am using an alltrax 7245 controller) 

so here in the real world, once the 6hp is called upon to essencially take the rpms up on the motor by 50% the resulting "gen effect" would likely negate any hp the 6hp i.c.e. is trying to apply to the road?

if, as I kind of suspect the mars is being asked to go 75 (which I dont think it can btw) would the "tailwind" being created in this example by the ice just reduce the amp draw considerably?

another question I have is if I gear it so that it doesent have any danger of "generating" would I have a prayer of competent accelleration with 500 lb of vehicle, and 250 or rider?


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## Juiced (May 2, 2009)

I would use a electrical (like on a AC unit) clutch to disengagement the Mars motor when the ICE kicks in. 

A question Sir, Can the 6HP can move the trike at 75?

Note: A Mars motor has 18 HP at 300 amps. 

Ed


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