Motor Direction Reversal And Brush Timing

Now for some technical stuff.

One of the things I had to do was reverse the direction of this motor because it spins the wrong way for my car. The most immediate question is: "Why don't you just reverse the polarity to the motor?" The answer is because a series wound motor will spin the same direction no matter what polarity you give it.

This is because when you reverse the polarity to the motor, it changes the direction of magnetism in the armature. But because it is series wound, it also reverses the direction of magnetism in the field at the same time. The result is a motor that still spins in the same direction. A series wound brushed motor runs fine on AC (alternating current) as well. Many small household appliances and power tools use them. (In case you care).

This means that to change the direction of this motor, we have to change the polarity of either the armature or field, and not the other. What I did to accomplish this was change the wiring inside the motor to reverse the polarity of the armature only.

I had to un-solder and re-solder the cable on one power post:

And bend one field power connector to hook it up to a different brush:

Now for brush timing. Brush timing is very important. As each commutator bar passes under a brush and current starts to flow into the armature at two points opposite each other, this must be timed perfectly so that maximum magnetic force against the nearby field shoes takes place. You would think that brush timing would be the same for every motor, but it is not. This motor has advanced timing, meaning that the brush is advanced when you compare it to the field pole, as you can see in this picture:

The long line is the field pole center line. It lines up with the field pole fasteners that are further down the motor body. You can see that the brush holder lines up with the "F" marks. I measured this timing to be 11-1/2 degrees advanced, which is about the max for brush timing. If I tried to run this motor without changing the timing, it would turn very slowly and the brushes and commutator would destroy themselves quickly. For the motor to have the same timing in the reversed direction, the brush holder will have to line up with the "R" marks:

I drilled new holes in the end plate where the brush holder fastens to and it now looks like this:

You can see the extra holes in the end cap where the brush holder used to bolt to:

Why have advanced brush timing at all? Many DC motors have neutral timing and work fine in either direction. However, for reasons that are far beyond me, as you increase the voltage and speed in a motor (typically beyond what it was designed for), you need to advance the timing. It is sort of like a gasoline engine that needs more ignition timing as RPM increases. If you do not advance the timing in a DC motor, harmful arcing will occur between the brushes and commutator as voltage and speed is increased and quickly destroy the brushes.

After I got it all back together, I hooked up 12 volts to it to test it out:

It spins the right way! And it seems to spin at a good speed when compared to before I modified it, so it looks like I got the brush timing right.

Motor Update

On Friday my new (to me) motor arrived. Right away I was able to start messing around with it. Here it is being powered up on the bench with 12 volts:

It spins much much faster than my sepex motor does unloaded, but series wound motors do that because of built in field weakening (something most DIY EVers take for granted!). And it spins backwards. Since it only has two power studs, this will require rewiring some of the internals to reverse the polarity between the armature and field.

Another concern is the tiny internal splines on the drive end. Check out how tiny they are:

The mating shaft is about 1/2" diameter at its smallest point. According to all my research, 50 ft/lbs of torque requires a shaft diameter of 0.55", so this would be iffy at best. One option here will be to bring the armature to my friend Matt (who is a machinist) so he can add a shaft on the end. This would be stronger and less difficult to adapt to my transmission input shaft.

Today I completely disassembled the motor:

After washing all the guk off the bits, this motor looks like it is in very good condition.

Here are the stator windings and armature:

Here are the stator windings and shoes installed in the case:

Here is the brush holder:

And here is what happened when I found some Cat yellow paint laying around:

I wish I would have done all this with my original motor instead of rushing to get the car on the road. It is making me appreciate what all goes on inside of these motors!

Finally...A Proper Video

Thank you iMovie for your help!

Growing TO DO List Excitement

The growing TO DO list on the Electric Booger is becoming quite long. My insurance will run out sometime in August, when I can hopefully tackle most of these things before the fall/winter commuting begins.

1. Vacuum accumulator - It does not have one right now, which means the vacuum pump runs for a second each time the brakes are applied. I would rather have it run for a few seconds after every 2 or 3 brake applications. This will be made of some 4" PVC pipe. Simple.

2. Vacuum pump indicator light - once the car is rolling, road noise is such that I cannot hear the vacuum pump. I will wire the [unused] engine oil light into the the vacuum pump circuit so I know exactly when it runs. I will then be able to react accordingly if I notice anything abnormal, indicating a vacuum pump failure.

3. Left door mirror - it is cracked. Has been this whole time. I am a procrastinator, what can I say....

4. Right axle - the right CV boot is torn and the CV joint is clicking like crazy on left hand turns. Maybe I can use my leftover [unused] radiator as trade in value at the auto wrecker.

5. Battery monitoring - eBay parts are on their way for the new and improved system that I have mentioned in a previous post.

6. Battery hold downs - something better than my current tie down straps would probably be a good idea.

7. TPS potentiometer - I am getting very erratic throttle signals after the car sits for a day. After a few cycles of the accelerator pedal (before or after turning the car on) and it is fine. I am going to try some good electric contact cleaner, and if that doesn't work I will have to buy a new pot.

8. Redundant throttle return spring - for safety in case the return spring in the pot box breaks.

9. Heater core - barely any air comes out of my heater vents because the [unused] heater core is plugged solid with crap - dust, dirt, leaves, etc. Removal takes days - a very nasty job - so I will try to cut into the heater box to dissect it out of there without disturbing much else. It's not like it needs to be in there anyway. There's no hole that duct tape cannot patch!

10. Tachometer - it would be cool to have it working. Maybe weld some pickup tabs on the  motor coupler, install a passive magnetic pickup and wire it into the ex-distributor position sensor wiring? Should work.

11. Lower grill block - this will keep the front two batteries from getting soaked in the pouring rain.

12. Controller cooling fans - I have two small 12V fans all ready to go.

And finally, the most exciting one......

13. NEW MOTOR. Well, new to me anyway. My friend Darin, co-creator of the infamous Forkenswift, has given me one of the two motors that he gleaned from a forklift to build his ultra-low-budget EV. All I have to pay for is shipping from Ontario. The Electric Booger will soon share DNA with a famous car!

It is a hydraulic pump drive motor from a 16,000 lb Baker electric forklift - 8" diameter and 15" long. It weighs in at 110 lbs, as opposed to my currently (PUN!) undersized 65 lb motor, so motor cooling should no longer be an issue. But the best thing is that it is a series wound motor (as opposed to my separately excited motor), so I will be able to ditch the field controller and the glitchyness that come with it.

My car will soon be smoother, quieter, faster and more efficient. Just when I thought I was all finished!

Hot Motor

Lately I have been concerned about the motor. It is, after all, quite small for a 3000 lb car. When I first started to drive this thing I felt the motor after each drive to see how hot it was getting. Lately I have been carrying an infrared temp gun in the glovebox to check the temperatures of the motor body and commutator after driving.

After the 6-1/2 km drive home from work, including a 1-1/2 km long uphill with a 4-way stop a quarter of the way up, the motor body is 120F and the commutator is 180F, so about normal internal combustion engine temps. No big deal.

After the 10 km drive home from church, including climbing the same hill, the motor body is 150F and the commutator is over 200F. Hmmm.....how long will this motor survive?

I posed the question on diyelectriccar.com, asking whether it may be time for an upgrade to a larger motor. The answer from a member named "major" (who has helped me a lot with this project) is that the limit for commutator temperature is 350F and not to worry even if the body reaches 212F.

Mine isn't even coming close to that. I guess I can stop worrying.

Plans For New Battery Monitoring System

It's time to upgrade my battery monitoring system for two reasons:

1) My current system is annoying to use. I have to reach over while I am driving to plug the voltmeter array in while I am driving. Not the safest thing ever.

2) One of the voltmeters on my current setup is dead, so it needs to be repaired anyway.

What I have planned is one voltmeter for system voltage (like I use already), and another switchable voltmeter for individual battery monitoring, both mounted in the dash panel. No reaching over - plugging in with one knee - holding the steering wheel straight anymore. A six position, two pole rotary switch will be used to toggle between each pair of batteries for monitoring.

Here is my current proposed wiring schematic:

All my bits are on order - eBay from China and Taiwan. Hopefully it will work!

60 MPH

After work at midnight I decided to finally find out the "performance" figures for the Electric Booger on the way home. Not exactly accurate as I was looking down at a stopwatch while I accelerated (really safe, I know!), but still, ball park figures to get an idea.

0-30 mph: 12 sec
0-40 mph: 22 sec
0-50 mph: 35 sec
0-60 mph: 55 sec

THAT'S RIGHT! 60 MPH IN A 72V EV!

It probably would have gone faster, but I didn't want my little motor to turn into molten lava, especially with the big hill I still had to climb on the way home.