freewheel/regen mode switch

[mustangman]

 I am in no rush to get a 48 volt regen controller, so I will wait for the results of beta tests.

[Mordaz]

myelectricbike,

My idea was to use a diode instead of a switch so that the batteries would be always 'on', except when the back emf from the controller exceeds the battery pack voltage.  The diode would block the reverse current and the regenerative breaking would be disabled.  A switch (or relay contact) could be used in parallel with the 'zero-drop diode', as a regen/freewheel switch.

Any flaws in this theory? 

[cadstarsucks]

myelectricbike,

My idea was to use a diode instead of a switch so that the batteries would be always 'on', except when the back emf from the controller exceeds the battery pack voltage.  The diode would block the reverse current and the regenerative breaking would be disabled.  A switch (or relay contact) could be used in parallel with the 'zero-drop diode', as a regen/freewheel switch.

Any flaws in this theory? 

CEMF will never exceed the battery voltage.  At full speed and no load it is still less than the motor voltage since it has to be overcome at any given speed to drive current through the motor.  You need to boost the motor voltage past the battery voltage to allow regen braking.

Dan

[myelectricbike]

Mordaz

In concept a diode should prevent current from traveling in the reverse direction. You would need a diode that had a breakdown well above anything you might expect coming from the controller. The diodes in the regen controller are rated at 62 reverse breakdown volts and I think 62 amps.

cadstarsucks

In the setup Mordaz is describing (correct me if I am wrong) he would be inserting his device between the regen controller and the battery rather than between the motor and the battery so that his diode arrangement would be switching the "boosted" voltage from the controller. Can you explain to us how the voltage is boosted in the controller? Is it done with a voltage multiplier, or otherwise how is it done?

[cadstarsucks]

In the setup Mordaz is describing (correct me if I am wrong) he would be inserting his device between the regen controller and the battery rather than between the motor and the battery so that his diode arrangement would be switching the "boosted" voltage from the controller. Can you explain to us how the voltage is boosted in the controller? Is it done with a voltage multiplier, or otherwise how is it done?

I am not sure what he is thinking off hand...I was thinking of adding regen to an existing system... I is conceivable that a regen controller could use the motor inductance as the boost inductor since the inductor want to keep current flowing in the driven direction while the CEMF wants to drive it in the opposite direction. 

You would have to drive the motor to 20A and then let the motor inductance dump to the battery. Complicated on a BLDC to say the least.  On the other hand a bridge into a boost circuit, while clumsy, is a doable add on.

Da

[Mordaz]

myelectricbike, you got it right.  This 'zero-drop diode' would be inserted between the batteries and the controller.

cadstarsucks, the idea is not to add regen to a regular controller, but to disable the regen function in a regen controller.  Yes, of course cefm would never exceed the battery voltage.  I meant the reverse current the controller feeds back to the batteries when breaking / reducing speed.

Am I right to assume the regenerative breaking would be disabled by such series diode? 

Also, do you guys foresee any potential problem, like an overvoltage buildup due to the lack of a load (that is, the batteries to be charged)?

[myelectricbike]

A diode or a switch in the off position will disconnect the battery and hence the load, and the regen controller has no problem with disconnecting the battery and hence the load. Depending on the side of the battery to which you connect a switch there could be a spike problem for the controller, whereas a diode would eliminate the possibility of a spike problem for the controller altogether.

[Mordaz]

It's actually a diode AND a switch.  Here goes a pic of the idea.

When the switch is closed, the circuit is shorted and the regen controller behaves normally (regen mode).

When the switch is open, the circuit acts like a near zero drop diode, blocking any current from the controller to the batteries (freewheel mode, like the non-regen controller). 

Do you guys think this would work?

[mustangman]

 Thanks guys for all the information.

[myelectricbike]

Actually the controller may already be immune to spikes since power is normally connected by simply plugging and unplugging rather than using a switch.

The circuit you have drawn seems plausible for what you want to do but the issue for me with switching from a regen mode to a standard controller mode is on the opposite end. I need a circuit (actually a user selectable software routine) that will keep the regen controller from limiting top speed to the RPM of maximum efficiency while keeping regen fully operational for braking and downhill.

[Mordaz]

I see.  My aim is just to be able to pedal along with the motor without fighting the regenerative breaking.

I'll try the circuit and let you know the results.

[myelectricbike]

One of the new regen controllers I have, oddly enough still has the power cutoff break leads coming from the controller so that if you order a regen controller you might be able to specify that it is the one the also has the power cutoff break leads. Normally the power cutoff break levers come with the controller so just be sure they acknowledge your request and confirm this to be the case.

[Mordaz]

Today I have tried the regen controller for the first time.  I did not like it very much.  Don't take me wrong, it works just fine, but it doesn't feel like a bicycle anymore.  Changing the gears is also a problem, because you have to release the throttle in order to shift, and the regenerative braking kicks in.  A freewheel/regen mode switch is really a must.  I'll definitely try this idea.  Or go back to the regular controller.

Speaking of a freewheel/regen mode switch, I was wondering, would it be possible to modify the controller instead of using an external circuit?  Does anybody have an schematic of the regen controller?

[Mordaz]

Another question that just came to mind:  If I successfully disable the regen function (either using an external switching circuit or modifying the controller), is it right to assume the top speed limit be overriden?

[myelectricbike]

What did sales say, when you asked them?