re-post 24volt dc 100amp motor speed controller

[George Gosbee]

Hello all,

Required please a circuit for,

24volt dc 100amp reversing motor speed controller with dynamic breaking slow
speed high torque required for the 750W 24v motor.
This is for a miniature seven and a quarter inch gage railway engine of the
type used to pull sit upon carriages that will carry several adults or lots
of kids. Power source will be 2 12volt leisure batteries about 65ah.

TIA

George.

 

[Spehro Pefhany]

Hello all,

Required please a circuit for,

24volt dc 100amp reversing motor speed controller with dynamic breaking slow
speed high torque required for the 750W 24v motor.
This is for a miniature seven and a quarter inch gage railway engine of the
type used to pull sit upon carriages that will carry several adults or lots
of kids. Power source will be 2 12volt leisure batteries about 65ah.

TIA

George.

Suggest you buy one from these guys: http://www.4qd.co.uk/

They seem to know what they are doing.


Best regards,
Spehro Pefhany

 

[George Gosbee]

Suggest you buy one from these guys: http://www.4qd.co.uk/

They seem to know what they are doing.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
[email protected] Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com

£173 is why not.

George

 

[Luhan]

Hello all,

Required please a circuit for,

24volt dc 100amp reversing motor speed controller with dynamic breaking slow
speed high torque required for the 750W 24v motor.
This is for a miniature seven and a quarter inch gage railway engine of the
type used to pull sit upon carriages that will carry several adults or lots
of kids. Power source will be 2 12volt leisure batteries about 65ah.

Use PWM on a high power MOSFET to control the motor speed forward.

Do PWM to a resistive load for dynamic breaking.

Use a (big fat) DPDT toggle switch for reversing the motor.

Luhan

 

[George Gosbee]

Use PWM on a high power MOSFET to control the motor speed forward.

Do PWM to a resistive load for dynamic breaking.

Use a (big fat) DPDT toggle switch for reversing the motor.

Luhan

Anyway to get the braking to put some power back in to the batteries?

George.

 

[Paul E. Schoen]

Anyway to get the braking to put some power back in to the batteries?

George.

If the motor is a series wound type, it is difficult to do regeneration. If
it is a shunt wound or PM type, then it will become a generator when the
PWM drive is turned off. Some H-bridge type PWM drives turn on two
transistors to short the motor and provide dynamic braking. Otherwise, the
body diodes of the MOSFETs or IGBTs form a full wave bridge which dumps the
generated EMF back into the main supply. However, sometimes this is not of
ideal voltage and current for charging batteries. For this, a second full
wave bridge can be added and connected to a switching DC-DC converter and a
supercapacitor bank for quick storage, and then an idealized charger
circuit that can fully utilize the energy stored in the capacitor bank to
recharge the battery bank with ideal current and voltage.

Unless you have some long steep grades or need to make a lot of stops, you
may not get much useful regeneration.

You might find a suitable DC motor controller on eBay cheaply enough, and
possibly modify it for regen. However, motor type will be the first
consideration to determine what to buy.

Paul

 

[Phil Allison]

"George Gosbee"

24volt dc 100amp reversing motor speed controller with dynamic breaking
slow
speed high torque required for the 750W 24v motor.
This is for a miniature seven and a quarter inch gage railway engine of
the
type used to pull sit upon carriages that will carry several adults or
lots
of kids. Power source will be 2 12volt leisure batteries about 65ah.

** The torque output from a DC motor depends on the amount of current
flowing it its coils - however, the heat developed in the same motor
depends on the square of that current value. Hence - one soon runs out of
available torque if you do not want to burn out the motor.

The power ( which does the useful stuff ) developed depends on the torque
multiplied by the rpms while the rpms depend on the applied voltage.

So, the best way and most efficient to use a DC motor to do useful work is
to have it spinning fast with a moderate current flow. I suggest you best
forget using a costly and fragile PWM controller for your application.

Arrange the two batteries so that they can be switched in series or parallel
when in use, ie to give 12 or 24 volts.

PLUS use a variable gear system ( sun and planet ? ) to couple the motor to
the drive wheels.

Get so much torque it will skid the wheels.

Very scale.



....... Phil

 

[joseph2k]

Hello all,

Required please a circuit for,

24volt dc 100amp reversing motor speed controller with dynamic breaking slow
speed high torque required for the 750W 24v motor.
This is for a miniature seven and a quarter inch gage railway engine of the
type used to pull sit upon carriages that will carry several adults or lots
of kids. Power source will be 2 12volt leisure batteries about 65ah.

TIA

George.

I cannot begin to advise you without a LOT more information about the motor.
How is it built / what motor class is it? Series, shunt, compound,
universal, stepper, PM, induction, other?

 

[BobG]

Hi Paul. Lets say George is driving along at about 16V (66% PWM) and
takes his foot off the 'throttle'... the motor is generating about 15
or 16V, but he cant put that back in the 24V stack... a big contactor
could disconnect the motor from the main battery and main pwm speed
controller to a braking pwm controller that would pwm the motor onto
the cap bank to control the brake force... The Maxwell Boostcaps I've
seen are rated at 2.7V... I guess its obvious that we cant throw the
generated 16V onto a 2.7V cap right? So we need a series string of 9 or
10 of them? As the motor slows down, the generated voltage goes down,
and at some point reaches the cap voltage, at which point there is no
more braking force due to loading the motor with the cap bank. Guess we
need real brakes at this point? Then when we are back on the throttle
again, the cap bank would need to be dc to dc converted up to charge
the 24V stack and drain the cap bank. Any of this sound right or wrong?
Seems complicated, but doable.

 

[Paul E. Schoen]

Hi Paul. Lets say George is driving along at about 16V (66% PWM) and
takes his foot off the 'throttle'... the motor is generating about 15
or 16V, but he cant put that back in the 24V stack... a big contactor
could disconnect the motor from the main battery and main pwm speed
controller to a braking pwm controller that would pwm the motor onto
the cap bank to control the brake force... The Maxwell Boostcaps I've
seen are rated at 2.7V... I guess its obvious that we cant throw the
generated 16V onto a 2.7V cap right? So we need a series string of 9 or
10 of them? As the motor slows down, the generated voltage goes down,
and at some point reaches the cap voltage, at which point there is no
more braking force due to loading the motor with the cap bank. Guess we
need real brakes at this point? Then when we are back on the throttle
again, the cap bank would need to be dc to dc converted up to charge
the 24V stack and drain the cap bank. Any of this sound right or wrong?
Seems complicated, but doable.

I have not actually done it yet, but essentially you can have a second full
wave bridge across the motor, connected to a wide-input switching power
supply. No big contactor is needed. The output of this supply may be
optimized for charging a capacitor (constant current), or for charging a
battery (a little more complicated). The DC-DC converter adjusts its PWM to
produce the desired amount of braking at any motor speed, and hence any
voltage it may produce. This can be done up to the maximum parameters of
the capacitor or battery pack, without overvoltage or overcharging. Thus,
on a long downhill, with a near fully charged battery pack and capacitors,
you might lose braking or risk overheating and damage. At very low speeds,
motor generation becomes negligible, so you need at least some sort of
mechanical friction brake, and it should be present also in case of failure
of an electronic component.

Paul

 

[Tony Williams]

I have not actually done it yet, but essentially you can have a
second full wave bridge across the motor, connected to a
wide-input switching power supply. No big contactor is needed.

It might be worth speculating whether the components
of that wide-input switching power supply are already
there, in the main bridge. There just needs to be some
way of using the bridge to turn the motor's generated
voltage into a constant current output, back into the
battery.

Battery+ ---+---+---------------------+---+
| | | |
|-+ | | +-|
---||Q1 /_\D1 D3/_\ Q3||---
|-+ | | +-|
| | L - Vb + L | |
+---+--)))--[Motor]--)))--+---+
| | | |
|-+ | | +-|
---||Q2 /_\D2 D4/_\ Q4||---
|-+ | | +-|
| | | |
Battery- ---+---+---------------------+---+

I've added an explicit external dc inductor, in
series with the motor. It may or may not be needed
but is useful for explanation.

Suppose the motor has been motoring under PWM control,
Q1/Q4 Off, Q3 On, and Q2 doing the driving PWM. The
motor has acquired a back-emf of Vb, in the polarity
shown in the sketch.

So now we need to go into regenerative braking, from
that direction of motoring.

Set Q1+Q3 to Off, and Q2 to On. Chop Q4.

Every time Q4 goes On Vb supplies current into the
inductor, storing energy. When Q4 goes Off the inductor
discharges the stored enery into the supply.

Q4, L, (and D3) are now operating as a flyback dc-dc
converter, drawing current from Vb and feeding it back
to the battery. The flyback has the advantage that it
just delivers current, developing whatever voltage is
needed to do it. Note that the current is drawn from Vb
continuously because Vb is still in circuit during the
flyback.

Lots of details to work out, such as varying Q4's On/Off
timing as Vb decreases, but it might be a goer.

Umm.. I wonder if is possible during regen to chop both
Q2 and Q4 with the same waveform, let L charge up with
whatever polarity Vb is, then let D2 and D4 sort out the
discharge. That would be braking from either direction
automatically.

 

[joseph2k]

I have not actually done it yet, but essentially you can have a second full
wave bridge across the motor, connected to a wide-input switching power
supply. No big contactor is needed. The output of this supply may be
optimized for charging a capacitor (constant current), or for charging a
battery (a little more complicated). The DC-DC converter adjusts its PWM to
produce the desired amount of braking at any motor speed, and hence any
voltage it may produce. This can be done up to the maximum parameters of
the capacitor or battery pack, without overvoltage or overcharging. Thus,
on a long downhill, with a near fully charged battery pack and capacitors,
you might lose braking or risk overheating and damage. At very low speeds,
motor generation becomes negligible, so you need at least some sort of
mechanical friction brake, and it should be present also in case of failure
of an electronic component.

Paul

I just do not get all this assumption of DC motors, a dynamic breaking AFMC
(also called VFD) can do the job, and uses easier to work with voltages for
100 HP (75 kW) motors.

 

[BobG]

But dynamic braking doesnt recover any energy. We are trying to make
the batteries last longer!

 

[joseph2k]

But dynamic braking doesnt recover any energy. We are trying to make
the batteries last longer!

It sure does if done correctly.

 

[Roger Hamlett]

It sure does if done correctly.

The 'key', is that you need to be talking about a particular 'type' of
dynamic braking. Regenerative braking, is a form of 'dynamic braking', but
instead of dumping the energy, it is fed back into the storage device.

Best Wishes

 

[BobG]

Dynamic braking is shorting the armature so the armature tries to lock.
Regenerative braking tries to recover the generated volts. I have never
seen the two terms confused till this thread. Slot cars used dynamic
braking in '67 and no one was confused over how it worked. We are
talking about technical terms. Lets use accurate wording.

 

[Roger Hamlett]

Dynamic braking is shorting the armature so the armature tries to lock.
Regenerative braking tries to recover the generated volts. I have never
seen the two terms confused till this thread. Slot cars used dynamic
braking in '67 and no one was confused over how it worked. We are
talking about technical terms. Lets use accurate wording.

Dynamic braking, as a 'term', just implies adding load so that the
voltages being generated by the motor, provide braking force. The load can
be direct shorting, resistive, or feeding into a circuit to do work. If
the 'work' is recharging the batteries, then it becomes 'regenerative'.
You will find that some vehicles like fork lift trucks,have 'regenerative
dynamic braking' units fitted. There is no confusion, _except_ in thinking
that 'dynamic braking', automatically implies the power is wasted.
Regenerative braking, is the 'descendant' of traditional dynamic braking
solutions, in putting the power to constructive use.

Best Wishes

 

[prashanthkumarmachika]

Hello all,

Required please a circuit for,

24volt dc 100amp reversing motor speed controller with dynamic breaking slow
speed high torque required for the 750W 24v motor. for 1 hp motor