Boost battery

[markcycle]

Does the circuit below, using a brush motor give a voltage boost hence a speed boost without damaging the BMS circuits in a LI-ION pack. My concern is that the FET controlled BMS current limit not be damaged by the higher voltage.

Thanks

Mark

 

[Beagle123]

Hi:

I don't beleive your diagram is correct. The Li battery should have two wiress going to the controller, then there should be two wires going from the controller to the motor.

I don't think you can just splice in a battery between the controller and the motor because the controller emits pulses of juice to the motor, not a typical flow of current.

 

[fechter]

A couple of things to keep in mind:

The FET switch in the controller is between the motor and battery (-).

Battery (+) goes straight to the motor inside a typical brushed controller. There's also a freewheel diode not shown on your drawing. In this case, it's not real important.

If you're running full throttle with the boost on, and your BMS decides to open, the full voltage of both packs will be on the BMS. It would be the same if the boost pack was ahead of the controller.

At partial throttle, especially during acceleration, the current in the motor wires might be MUCH higher than the current coming out of the battery, which might make the boost pack unhappy.

If possible, the boost pack should probably go next to the main battery.
If the controller voltage rating is not high enough for that, then the way you drew it should work.

 

[xyster]

Wired like this, there's a short across the boost battery when the DPST switch is closed, and no circuit when it's open.

 

[xyster]

Here's a boost-pack/controller bypass schematic I had posted in the schematic library. An SPDT switch can be used in lieu of the relay/push-button. When the button is pushed, a 12V battery is in series with the main 36V pack; power is routed around the controller. With the button unpushed, 36 volts routes to the controller normally.
http://endless-sphere.com/forums/viewtopic.php?t=278

 

[markcycle]

Who said that was a DPDT switch I don't show how the contacts are controlled Just a concept drawing. I.m looking for a way to isolate the BMS FETs from seeing the higher boost voltage and getting destroyed. Using SLA or NiHM its of course it's trivial to do a boost design, but with LI-ION the BMS fets need to be considered. Also everyone assumed the controller as I showed it is a standard controller. I would design the controller and have it turn off if the LI-ION should go to zero volts. The question is can I save the BMS fets and do it fast enough. Also if I put back to back zeners across the battery does that help protect the BMS fets. I'll draw it in tonight got to go to work now