Regenerative Braking
Note: you need to have a hub motor which does not have a
freewheel mechanism if its a geared motor to do this. If its a gearless motor
then you can do it no problem.
Firstly I must say before anyone tries this, there are controllers available
that will automatically do regen. braking for you. There is really absolutely no
need to do it the way I have done it here, so why the hell did I do all this
...............well its a brushed motor.........and the controller I have for a
brushed motor that does regen. braking I haven't worked out how to use it yet,
have been waiting for the supplier to give me a wiring diagram for months
..................couldn't wait any longer and couldn't figure out
how the controller was supposed to be wired up to give regen. ................so
here it is.........oh it would be quite possible to use this circuit below for a
brushless motor (you would "just" need to rectify the output of the motor
when in regen. mode i.e. turn the ac current the motor produces into dc, that
just needs either some more diodes in a certain configuration or some
rectifiers).
(postscript: turns out the controller I thought had a regen function did not
have regen anyway!)
So this is my first attempt at a regenerative braking circuit. The circuit
works very well and I used to use the bike most days, the reason I made the regen
braking is that where I previously lived (near the base of Mt Wellington in
Hobart) there are long steep hills. With the weight of lead acid batteries my
brakes were not adequate for the hills, I put a drum brake on the motor (in rear
wheel) but it got extremely hot by the time I would get to the bottom of the
hill. I have wanted to make my own regen. circuit for a long time and necessity
made it happen.
Below is a picture of the final circuit with battery box and wiring, relays,
diodes but also in the picture wiring for battery charging, voltmeters, ammeter
are also shown.
But this is just to give you an idea if its worth reading any
further, this is quite a complex (well complex for me) circuit to make, there
may well be a much simpler way to do it, but this is just how it turned out for
me. So I would only recommend you try this circuit if you are the following:
1. well up on circuits
2. have alot of patience and
3.dont have a stressful life or a nervous disorder!!!. It will cause
stress!!!!!!!!!!!! I can almost guarentee that.
I'm actually quite amazed that I can get on the bike each day and
everything works, I'm usually expecting (when I switch everything on ) to see a
big smoke plume but thus far its seems very reliable and works amazingly well
(if I do say so myself)...............................
I'll start off with some basic drawings and gradually get to the final
circuit exactly how I have it on the bike.
What I've done is broken down the circuit into little bits (my brain can only
handle lots of little simple bits at one time but when it comes altogether it
works). I've had to redesign some bits as when testing as I went along I just
did some things wrong and had to adjust things or got lazy and said "oh
I'll just try this way" but to get it to work properly it was necessary to
understand exactly what was going on , most of it was
on paper in some form to start with. But when it was all finished I found I had
to go back over the wiring and draw it all from scratch, as my drawings didn't
always keep up with the adjustments I made when building/testing.
(I was intending to go straight into the batteries with the regen.energy but
that turns out to be a bit more complex than the circuit I'm describing here and
this circuit is complex enough!!! But I will soonish redirect the energy from
regen. into the batteries, as soon as my therapy sessions finish!!!!!)
At the moment I only have the regenerative energy going back into the motor not
into the batteries as yet.
This is the maximum regenerative force the motor can generate when the energy is
dissipated through the motor windings. I've been extremely surprised at the
amount of energy that is created. At 10km/hr I get about 10amps, at 20km/hr
about 20amps and at 30km/hr about 30amps. I haven't as yet measured what
voltages that are being produced but the motor is a 36volt brushed gearless
motor and it has never shown any signs of overheating (it does certainly get
warm though), it seems to cope quite well with these large currents that are
produced. I must admit I do try to keep the regen. current below about 20amps as
the relays, if I go too high ,the contacts weld themselves together inside the
relay from the heat of the current passing through them. This has only occurred
once when I let the regen. braking get up to 37amps when going rather quickly
down a hill and then hitting the regen. braking.
When I hook up the regen. energy to go back into the batteries (in the future
I hope , haven't tried it yet, still in need of some therapy after this project) the
amount of braking force you can get drops off alot as the batteries internal
resistance reduces the amount of current that can flow from the motor to the
batteries. This is one reason why people often say you cant get much energy back
from regen. There is actually a huge amount of energy created by the motor, its
finding someway to store it is the problem, as batteries can only take so much
current at one time ( hybrid cars like the toyota prius now use super-capacitors
which can store large currents and put back into the batteries slowly, like
a temporary storage).
So now I'm getting 20amps at 20km/hr this is likely to drop down to 5amps
(very rough guesstimate) when its connected to the batteries.(with the regen.
current just going through the motor, effectively I'm just shorting the motor,
its easy to see this effect on a hub motor, try spinning the wheel while the
motor wires are joined to each other).
Just a note, I'll start off simple and get to the final circuit. These first
diagrams cannot be used as shown to make a regen. circuit, they are
just the basics there are quite a few bits and pieces have to be added to get
the regen. to work properly (in fact it turned out to be quite a bit more
complex than I was anticipating). All together it took me 4 relays, and 7 car
alternator diodes and quite a bit of wiring to get it to work (it took about a
week or so to get some basic results and about another 3 weeks to iron out all
the bugs).
There are still lots of improvements could be made, at the moment I'm using the
relays at near their peak ratings or a bit over, so larger relays would be much
better but I just used what was readily available at Dick Smiths Electronics and
a local Auto-electrician. So its quite easy to get the parts and not very
expensive.
The Main Relay:
There is one main relay that I used to switch the motor wires from being
connected to the controller (power mode) to just shorting out the motor (regen.
mode). Unfortunately the largest relay I could get from Dick Smith was rated at
10amps which just isn't high enough, so I bought two of them and put them in
parallel (well to tell the truth I tried it with just one relay but one
contact welded to itself, but got it unstuck and bought another one and put it
in parallel with the original one. No need to throw out these relays if you put
too much current through them, just open it up and unstick the contact and clean
it up a bit where it go hot). But to understand how it works I'll just show
one of the relays to start with which makes it easier to understand how it
works. If I could get a 12v relay that could handle up to 40 or 50amps that
would be perfect. Oh the other thing is this relay has 8 pins on it, 2 pins to
power it from the battery (12v)(i.e. to turn it on /off) and the other 6 pins
are used to direct the current to where ever.
Below are a couple of pictures of the relay I used: its from dick smith
electronics and rated to 10A. I've soldered on some thin but high current wire
(same wire as comes out of the hub motors) to the relay and used some connectors
to make instal easier and also mounted it onto a yellow plastic base just with a
zip tie..
Below is a picture describing the
basics of how the relay works..
A brief description of the above: If you connect a 12v battery to pins 1 and 2
the relay turns on. This allows current to flow from x to y, and also from a to
b. If you dont have any power to the relay (no 12v power supply at pins 1 and 2)
the current can flow from point x to z, and from point a to c. So by having a
switch on the 12v power supply which turns the relay on and off, you can turn
the relay on/off. I use my left hand brake handle switch to operate the relay,
the power being supplied by one of the 12v batteries on my bike (its wise to put
a fuse on the 12v power supply, 2amp fuse should be ok as later there are some
more relays, the relay draws a very small amount of current).
Below are two circuit diagrams which show the two different states of the hub
motor setup: a: power on (normal riding motor being powered by batteries via
controller)
b: regen. on (braking due
to motor being shorted)
Below the Picture shows POWER ON, the hub motor is running via the relay
(which is in its off position), the green lines show the direction of current or
electron flow.The motor is being powered by the batteries via the controller.
(Note diode D1 must be installed as it protects the controller when you turn
on the regen. braking, there is a high voltage spike when the relay is switched
which can damage the mosfets in the controller if you dont have this diode in
place)
Below shows the simplified version of the regen. circuit when the relay is
turned on via the brake handle inbuilt switch.
( I say this is simplified because there are some diodes which need to
be added to the circuit which I have not shown at this stage but will be
included in later diagrams.)
Notice above the direction of electron flow is reversed from the POWER ON
circuit as the motor is now acting as a generator and making electrons flow in
the opposite direction. Also note that the batteries and controller are now
completely isolated from the regen,. circuit, the current is just going through
the motor windings and the energy is lost as heat and also as the current flow
is opposing the direction of magnet rotation or rotation of the wheel, which
also helps slow you down.
August 29th 2006: Have decided to just put up the circuit
pretty much as far as I got when living in tassie, dont have time to go into too
much detail at the moment but below is the circuit to get regen energy to be
dissipated through the motor windings for a brushed motor. This makes for a good
tool to measure the maximum current output of a motor , you can use the circuit
to measure the amps when braking at speed, a cheap way to test a motors output
when used as a generator, also it makes a damn good brake.
Next step is to put the regen current back into the batteries. It can either
go back into the batteries while they are in series or more difficult put it
back into them while they are in parallel (you would regain more regen. if they
are in parallel as resistance of the batteries is lower than if in series).
As of now the bike is being used by a student at Tassie Uni to use in
some project work on regen. braking, when I get the bike sent back to me in
Newcastle I'll redirect the current into the batteries and do some testing of
how effective it is in series and parallel. Diagram below shows two relays used
in parallel to handle the current one relay can be used as long as it has high
enough current rating, about 40amps would be enough.
Its pretty simple circuit really, the two small square shaped boxes inbetween
the batteries are relays that isolate the batteries, cant remember what I put
them their for but play some role for some reason!!! I do have some decent
relays now that I will be able to use simplifying things a bit.
Bon Apetit!
Postscript: just looking at this circuit it might be the one for puting regen.
back into the batteries, I'll have to check later when brain is a bit clearer!
anyway this circuit is from a sketch I did after the circuit was built, so its
not based on theory anyway is based on what I had working (well still working
but bike is in tassie and I'm not) , but I do need to check if this is correct
diagram, I have a bunch of scribbled diagrams I have to take my time and check,
bit of a rush now.
anyway you can imagine once you include the big power on/off switches, the
charging circuit (show on this page:
http://www.users.bigpond.com/solarbbq/batteries/batteries.htm), some switches
and fuses for the voltmeters, a circuit breaker, a switch so that regen. can be
used or not used when the brake applied, it all becomes pretty damn complex, and
putting the regen. back into the batteries will complicate things even more, but
will be interesting to see what type of currents can be put back into the batts
when I get up to that part.
One thing I never figured out was this: when regen is on you get most of
the current goes through one side of the relay, it should be possible to get the
regen. to go through both sides of the relay (not that its important would just
mean you could use lower amp rated relays but afraid my poor old head just
couldn't fathom that one).
Would also be interesting to compare a brushed controller with regen.
built into it and this type of basic regen. circuit to see if there is a
difference in amount of energy you can utilise.
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