SLA Batteries - Magic Pie II (Regen)

[dofbikes]

Hi everyone,

If I use 4 SLA batts each 12V 7Ah (48V 7Ah) do I need to create/use anything to disable regen (Magic Pie II) from recharge the batts? Or to make that regen safe?
My fear is that during my travels when I got steep hills (down) the high voltages damage the batts.
Note that until now I've not made any change to the internal controller of my Magic Pie II and I'm not sure if the regen is enabled by default.

Thanks,

Rui Santos

[Leslie]

An MP will over draw a 7ah SLA to almost 3c meaning you probally get 3C for 5 mins, depending on how you ride,  you will be lucky to get 200 meters down the road and no chance getting back up this hill before too long.. 

Regen is designed to shut off the controller at 60v and any regen too high will kill your 7ah SLA batteries in a few days just from current not volts.

[dofbikes]

Hi Les.
I've done a test with those 4 SLA batts (take a look into this post http://goldenmotor.com/SMF/index.php?topic=4141.msg24481#msg24481) and ride 8km almost flatland and with few pedal help... of course not too fast.
To be clear my point is not to get regen back to SLA's, my goal is to avoid any kind of explosion of the batts during downhill if they maintain connected to the motor (controller).
I've already thought about installing a switch off and during downhill turn it of in order to avoid regen. It can be tricky but is there any other simple solution?

Thanks,

Rui

[Leslie]

Youre heading toward controller failure if youre switching bike on or off during rides with regen or even just during rides.  Something about induction, motors and controllers not working well with intermittent power connects and disconnects while in use can cause the volts to spike. 

As I have said your SLA's can take 15v each 15* 4 is 60v.  The GM controller can not charge your batteries higher then 60v it will shut down automatically.

The only way I can think is buy another controller, this idea will only be easy with an external controller.  Hook another contoller up to the phase wires, connect the battery wires of this other controller to dump power into a big resistor, like 3 12v kettle ellements set in a wye config.   Parralell brake switches on both controllers and disable regen to your pack and enable regen to your resistors, ajust the controller software regen percentages to work correct with the resistors..  Haaa you maybe able to heat a cup of water with the kettle ellements or just heat sink glue some heat sink to the elements and allow plenty of air flow.

The massive current regen can give can indeed wreck your SLA's.

[e-lmer]

You may be able to switch in three shunt resistors to dump some power too.
 
I am just  tossing ideas off a napkin here...
 
Lets guess 1kW @ 60V x 15ishAmps.

That will take a honkin 4ohm resistor.

Be safe!  That will dump a LOT of heat! 

A dpdt knife switch could do it I think.

Maybe an old hair dryer heater?

[Leslie]

Shunts are to short to handle the voltage range required.  When you dump power the voltage must read from say minimum 24v to 60v max from each end point of the shunts.  This means the energy between the atoms will be too high and will cause them to fuse out.

They are only in the 1.5 to 3 ohm range.  24v/3 is 8 amps and 192 watts. 60v/3=20 amps 1200 watts  Compare this with a 5 watt resistor. 

This is why I suggest the controller as you can program the regen to suit your load.  And I suggest the 12v kettle elements in wye configuration, this will make them at least handle about 750 watts, and they too will get hot but they are larger and longer than anything I can think of and be easier to get the heat off.

You would have to pair the ground wires on the both dumping controller and motor controller, and I would use at least the logic wire, from the battery to the dump controller to keep it alive at all times and the means to switch it down..

[Leslie]

Three of these e-lmer, and you know WYE.

Ohh and I would also pair the dump controller hall sensors to the motor controller sensors. We need the motor operate the phases to the dump controller.. 

Interesting thought.  I think this will actually work and very well.

[e-lmer]

Nice, you can dump power AND brew tea  for the stop at the bottom of the hill at the same time.

[dofbikes]

I don't like the idea of having something like "heat sinks" in my back even if it's cold and I need a cup of hot tea like e-lmer said!
And what about the simple idea of turning of the regen feature? Is it possible to do in the controller (hardware)? Or using the software?

Thanks,
Rui Santos