Regen Braking w/Series wound DC Motor???

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FrankG
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Regen Braking w/Series wound DC Motor???

I have a Marketeer Golf Cart (trike from the late 50's early 60's) that is very "Old School" in the motor control dept.

The Motor is a 4 1/2HP Gen Electric series wound motor that has 2 heater type resistive elements that limit the current to the field windings of the motor as the accelerator control is stepped on.

The Forward Reverse switch is a pair of 1/4" thick copper bars that have a 3rd bar that pivots such that the +ve and -ve lines are reversed.

When I descend a steep incline I have been engaging the reverse to slow the trike as it works far better than the brakes. If I depress the accelerator in reverse (while going down hill forward) the braking action is even more pronounced.

My initial question is, is this returning any energy back into the battery pack?

Along the same lines, I just recieved a "Pargo Bar-Car" that will be converted to a Utility hauler for our farm. It has a near identical motor but far more elabourate control system that employs 7 (seven) solenoids to accomplish the speed control as well as forward reverse.

The marketeer weighs just a couple of 100 lbs and has very robust simple components that are not likely to fail, but the Pargo will likely weigh over 1000lbs when fully loaded and I'm hesitant to risk it or myself if there is a chance that I could damage a solenoid by this practice.

Thanks for any info or ideas.

FrankG
www.theworkshop.ca

andrew
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Re: Regen Braking w/Series wound DC Motor???

It is difficult to determine.

A shunt is a great way to measure current from the batteries in combination with an amp meter. If there is any regeneration going on than the amp meter will go negative.

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FrankG
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Re: Regen Braking w/Series wound DC Motor???

Andrew,

I guess that would be the simplest idea... Thanks

I do have a couple of analog meters that I could play with, from what I recall I first have to determine the meter range and select an appropriate shunt per Ohms law to achieve a reasonable scale...

Also (unsure if I should start a seperate thread), given that the motor uses resistive elements to vary the field current, is this considered a SepEx (seperately Excited) motor, or would I just hard wire the series conection and try a PWM controller for greater efficiency (down the road)?

It just seems like such a waste to feel the heat coming off of the resistive elements that could be used for motive force instead.

FrankG
www.theworkshop.ca

andrew
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Re: Regen Braking w/Series wound DC Motor???

I think it depends on the top speed you want. Series motors are super great for starting torque but fall short somewhat at higher speed. I would double check how it is wired now and how it is controlling the speed. I suspect it is limiting the current to the armature windings. With a shunt motor (or separately excited motor) you can weaken the field current to increase the speed a bit.

Beware of using a PWM controller as it will limit the amps. My experience with a T/D Golf Cart using very large resistive elements to control the speed is that they did waste some power but a really nice advantage is that there was no current limit. You could always get more amps (that is until full on) by pushing the pedal down more. Depending on the PWM controller size it might limit the current in your application, limiting the maximum power. Only way to be sure is first measure the maximum current that you need before buying the controller. Otherwise, a PWM controller is really great for smooth speed control and saving power when you don't need maximum speed.

---
Avatar taken from http://www.electricmotorbike.org/
Anyone got one they want to sell?
My KZ750 Project: here

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

FrankG
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Last seen: 13 years 4 months ago
Joined: Friday, April 27, 2007 - 10:44
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Re: Regen Braking w/Series wound DC Motor???

Yes! Your right on about the PWM route, I've been sniffing around the "Vintage Golf Cart" forums and sites...

It seems like the Altraxx Axe type controller is a fairly common choice for the GE 4 1/2Hp motors. They typically are 36V with a 300Amp limit, which equates to a about 9Hp absoulte peak (14Hp before wiring and other inefficiencies), with 4 1/2Hp nominal output.

Unfortunately I'm upagainst a new set of battiers before any modding to the resistive network, as I went to move the unit under power 2 nights ago and one of the mis-matched cells that are currently in it started to hiss and melted a small hole out by the +ve terminal.

FrankG
www.theworkshop.ca

andrew
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Re: Regen Braking w/Series wound DC Motor???

Your calculation sounds right to me. From what I understand, the current limit is usually on the battery side so you may be able to get more than 300 motor amps out of a 300A controller. In a nutshell a controller is like a variable DC-DC converter and if you look at DC-DC power supplies some might have:

100v in at 1a, and 10v out at 9a being 90% efficient.

Your existing setup however operates like a DC circuit, that is current is the same on the motor and battery side of the resistive elements. What this should mean is that if you install an amp meter and it measures more than 300 amps, the 300A controller might provide just as many motor amps (more than 300).

I just thought of maybe a better way to explain it. The resistors cause a voltage drop in the circuit, so the 36v on the battery side might drop to 10v after the resistor resulting in 300 amps startup current to the motor. But the current is the same everywhere in the circuit, so the batteries have to deliver 300 amps, and the 26v drop at 300 amps or 7800 watts is being converted to heat.

A controller, however, is 95% efficient (or somewhere around there). Therefore if you have the same situation on startup and the controller is taking in 300 amps at 36v than the output would be 1026 amps at 10v.

I hope that better explains PMW controllers and their specified current limit. The numbers I used are arbitrary.

Good luck with the battery replacement.

---
Avatar taken from http://www.electricmotorbike.org/
Anyone got one they want to sell?
My KZ750 Project: here

[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri

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