# [EVDL] What is plug braking vs. dynamic braking?



## EVDL List (Jul 27, 2007)

I see plug braking referred to in DC controllers, but very little is 
said about it. What is it? 

At first blush it sounds like dynamic braking, but wait -- I'm a 
railroad guy, so I'm familiar with dynamic braking as per locomotives: 
Reconfigure the traction motors as generators, then waste the regen into 
big racks of resistor grids. It's so effective that in hill country, 
they add locomotives to trains just to provide dynamic brakes.

But in the schematics I see for plug braking, I don't see any resistor 
grids. Where does the heat go?

Robert

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## EVDL List (Jul 27, 2007)

The heat goes into the motor and controller.


> Date: Mon, 8 Oct 2007 14:06:16 -0700
> From: [email protected]
> To: [email protected]
> Subject: [EVDL] What is plug braking vs. dynamic braking?
>
> I see plug braking referred to in DC controllers, but very little is
> said about it. What is it?
>
> At first blush it sounds like dynamic braking, but wait -- I'm a
> railroad guy, so I'm familiar with dynamic braking as per locomotives:
> Reconfigure the traction motors as generators, then waste the regen into
> big racks of resistor grids. It's so effective that in hill country,
> they add locomotives to trains just to provide dynamic brakes.
>
> But in the schematics I see for plug braking, I don't see any resistor
> grids. Where does the heat go?
>
> Robert
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev

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## EVDL List (Jul 27, 2007)

Hello Robert,

Dynamic braking is switching the motor from using a power source to a 
generator that retards the machine by generating current into a load bank. 
The motor continues to turn the same direction as it is slowed.

Plug braking a motor, is throwing it from full speed in one direction to 
full speed in the other. This requires a reversed forward magnetic motor 
contactor that has a time delay circuit, so that the forward contactor coil 
will drop out before the reversed contactor comes on.

It is like a reversing motor contactor that may have a mechanical interlock, 
so both contactors cannot come on at the same time, but delays the switch 
over until the motor inductances is reduce some.

Do not use plug braking in a EV unless you want to destroy something.

Regenerative braking is something like dynamic braking, except instead of 
burning up the energy in a load bank, but putting into a battery pack, or 
use the rotation energy to keep running mechanical driven accessories of the 
motor it self which also helps it brake.

Roland


----- Original Message ----- 
From: "Robert MacDowell" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Monday, October 08, 2007 3:06 PM
Subject: [EVDL] What is plug braking vs. dynamic braking?


> I see plug braking referred to in DC controllers, but very little is
> said about it. What is it?
>
> At first blush it sounds like dynamic braking, but wait -- I'm a
> railroad guy, so I'm familiar with dynamic braking as per locomotives:
> Reconfigure the traction motors as generators, then waste the regen into
> big racks of resistor grids. It's so effective that in hill country,
> they add locomotives to trains just to provide dynamic brakes.
>
> But in the schematics I see for plug braking, I don't see any resistor
> grids. Where does the heat go?
>
> Robert
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
> 

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev


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## EVDL List (Jul 27, 2007)

From: Robert MacDowell
> I see plug braking referred to in DC controllers, but very little is 
> said about it. What is it? 

Plug braking burns up the braking energy as heat in the motor and/or controller itself. The motor and controller get hotter as a result.

Dynamic braking burns up the braking energy in a resistor. Most of the heat is generated in the resistor instead of the motor or controller.

Regenerative braking uses the braking energy to recharge the batteries. It recaptures some of the braking energy (though a significant amount is still lost in heat).

--
"Those who say it cannot be done should not interrupt the one who is
doing it." -- Chinese proverb
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377

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## EVDL List (Jul 27, 2007)

Hi Robert,

The classic meaning of plugging is to reverse the
field of the motor while the motor is at speed. With
a series wound motor, this results in about twice the
stall current and twice the stall torque. Which is
likely enough to tear apart the drive line or lock up
the wheels. So, when solid state controllers are
used, a normally reversed biased diode is placed
across the armature, called the plugging diode. Then,
when the field is reversed, the plugging diode
conducts and you only get stall torque instead of
twice. The controller further controls the plug
braking by pulsing the field, to weaken the braking
torque and lessen the current. The current comes from
the battery. The braking energy is dissipated in the
motor armature and plugging diode.

Plug braking is a legitimate method of electric
braking. Forklifts use this method with series
motors. Forklift operators seldom use the brakes. 
They just go from forward to reverse. It is very hard
on the motor, but forklift motors do survive. With
modern separately excited systems, plug braking is
also available. I use this on vehicles powered by
generators, where regeneration is not possible. On
the battery powered versions, I use regen systems. 
>From the driver's feel, he cannot tell the difference.

Obviously, regeneration is the preferred method.

Hope this helps.

Jeff M





> --- Robert MacDowell <[email protected]> wrote:
> 
> > I see plug braking referred to in DC controllers,
> > but very little is
> ...


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## EVDL List (Jul 27, 2007)

In the mountain districts in Colorado, school busses are required to
have a electric retarder on the driveshaft...(since about 1978 when a
full school bus went over a cliff after losing the engine, which also
means losing the air brakes). This looks like a giant generator
(about 12" diam and 18" long or so) that the driveshaft goes through.
Doesn't seem to connect to anywhere else... so maybe it's just
dissipating heat in this generator thing? I've never researched how
it actually works, but it does work very effectively for slowing a
23,000lb vehicle down when going down hills or coming to a stop (works
down to about 10 or 15mph on the highest setting usually).

Z



> Jeff Major <[email protected]> wrote:
> >
> > Hi Robert,
> >
> ...


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