# Series Wound DC Brushed Motors



## Sunking (Aug 10, 2009)

Wanted to open a thread for my own education about Series Wound DC Brushed Motors, and their PWM Controllers. I am an Electrical Engineer, but my background is AC power generation/distribution, DC battery power plants, UPS, protective relaying, lightning protection, and protective grounding systems. In the last 10 years I have done quite a bit of work in Solar PV field for telephone companies and commercial clients, hence the username

I have never built an EV, only modified a few golf carts as a hobby, and want to learn more about the series wound brushed motor used in golf carts and their speed controllers. I understand of how a controller works, but I am missing something about the motors and how to match up a controller with a motor. A lot of it has to do with a lack of specifications on the motors used in the golf carts. For example I use a GE D398 motor and all that I can find published about it is:

36 Volt Spec
Non Peak HP = 6.1 @ 4600 RPM
Peak HP = 10 HP with 200 amp controller

48 Volt Spec:
Non Peak HP = 9 @ 5330 RPM
Peak HP = 15 with 350 Amp Controller

Other than tat the only other spec I can get from a different manufacture is FLA = 157 amps @ 36 volts which works out to around 7 HP

So how does one use these specs with such little information? Example what size controller to use. Most of the suppliers recommend a 450 amp controller, but there is no specs for that. I am confused and would expect there to be some power curves based on controller size. What am I missing?


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## major (Apr 4, 2008)

Sunking said:


> So how does one use these specs with such little information? Example what size controller to use. Most of the suppliers recommend a 450 amp controller, but there is no specs for that. I am confused and would expect there to be some power curves based on controller size. What am I missing?


Hey Sking,

These products (motors) are made by GE specifically for an OEM. GE does not want anyone but that OEM to know anything about the product. So there is no performance information available through GE. If you have a GE product, you can do whatever you want with it. I suspect they don't care, but they will not aid you. You want to know something about the product, find out yourself. I am surprised they put that much info on the nameplate . That's the way they do business.

Regards,

major


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## Tesseract (Sep 27, 2008)

Sunking said:


> ... I am missing something about the motors and how to match up a controller with a motor. A lot of it has to do with a lack of specifications on the motors used in the golf carts. For example I use a GE D398 motor and all that I can find published about it is:
> 
> 36 Volt Spec
> Non Peak HP = 6.1 @ 4600 RPM
> ...


Well, it would be helpful to have an efficiency spec for the motors, and how long the motor can deliver either the peak or non-peak power, but you can still derive quite a bit from just the meager information given.

For example, you can derive the mechanical torque of the motor using the equation: hp = (torque * rpm) / 5252

In the 36V case this gives you ~7 lb-ft of torque. If you assume that the motor is 85% efficient at its S2-60 current then you will need 148A to develop 6.1hp at 36V. If the field has already entered saturation at 148A then torque will increase linearly with current; e.g. - at 296A you could expect ~14 lb-ft of torque at the same 36V and 4600 RPM.

Motors obey the i²t rule just like everything else in electronics, so if you have (trustworthy!) S2-60 data you can make some reasonable estimates of overload performance, keeping in mind that commutation failure may put a stricter limit on overloading than i²t. 

So if the above figure of 6.1hp is the 60 minute rating then you should be able to extract 8.6hp for 30 minutes, or 12.2hp for 15 minutes. I would be hesitant to extrapolate farther than 4:1, though.

All that said, these runty little golf cart motors are basically one step up from those in vacuum cleaners when it comes to the believability of their specs...


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## Sunking (Aug 10, 2009)

Tesseract said:


> For example, you can derive the mechanical torque of the motor using the equation: hp = (torque * rpm) / 5252


Well on one site I did see a torque spec of 96 oz/ft but no mention of RPM or current. This is the problem. the recommended controllers range from 200 to 450 amps, and voltage as either 36 or 48. I converted my EZ-GO from 36 to 48 volts, and upgraded the wiring (6 to 4 AWG) F/R switch, Solenoid, 400 amp controller, and the GE D398. Just wondering if I could push the controller up to 500 amps and/or 60 volts.

Right now I get about 27 MPH on flat level hard surface. I live in a private golf community, and carts are allowed on the streets. I live about 1 mile from the course and use the streets to get there. The speed limit is 35, and I would like to get up to at least 30 MPH. Lifting the cart and large tires may get the job done at the expense of torque. Th ecourse is a bit hilly. Right now from a standing start the cart will bark the tires and raise the front tires off the ground for a moment and reaches top speed I guestimate in 20 to 30 feet.


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## major (Apr 4, 2008)

Sunking said:


> Just wondering if I could push the controller up to 500 amps and/or 60 volts.
> 
> Right now I get about 27 MPH on flat level hard surface. I live in a private golf community, and carts are allowed on the streets. I live about 1 mile from the course and use the streets to get there. The speed limit is 35, and I would like to get up to at least 30 MPH. Lifting the cart and large tires may get the job done at the expense of torque. Th ecourse is a bit hilly. Right now from a standing start the cart will bark the tires and raise the front tires off the ground for a moment and reaches top speed I guestimate in 20 to 30 feet.


Hi Sun,

Sounds like you'd still have the necessary torque going to 10-15 % larger tires to get your speed up. What you'd have to watch is motor heat. Are you using a totally enclosed motor? Same with going to a 500A controller. Likely the motor would commutate reasonably well. But for a lot of quick starts and/or hills, watch motor temp. 60 volts sounds like more trouble than it's worth. You don't see any controllers rated for 60V. And it is an odd charge voltage.

Regards,

major


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## jehan12413 (Feb 4, 2010)

If you're using a curtis 1204 or 1205 controller I wouldn't go over 36 volts. I have modified quite a few of those controllers and the control board can't handle much higher a voltage, the regulator gets pretty hot and also the filter capacitors have a 63 volt rating.


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## Sunking (Aug 10, 2009)

major said:


> Hi Sun,
> 
> 60 volts sounds like more trouble than it's worth.


You are probable right, and yes a charger would difficult to obtain unless I converter from a 48 volt battery plant rectifier, and not sure I could even do that. Probable a custom build.



major said:


> You don't see any controllers rated for 60V.


Well I do not know about that, Altax 7245 is rated 24 to 72 volts @ 450 amps


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## Sunking (Aug 10, 2009)

jehan12413 said:


> If you're using a curtis 1204 or 1205 controller I wouldn't go over 36 volts.


 I am currently using an Altrax 4845


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## Amberwolf (May 29, 2009)

jehan12413 said:


> If you're using a curtis 1204 or 1205 controller I wouldn't go over 36 volts. I have modified quite a few of those controllers and the control board can't handle much higher a voltage, the regulator gets pretty hot and also the filter capacitors have a 63 volt rating.


Depends on the 1204. Mine, a -410, is spec'd as a 36-48V unit. I haven't deeply investigated the control board, though.

Did you ever draw up schematics for the ones you've dealt with? 

I have considered using my 2QD controller minus the FETs, with larger driver transistors added, as a logic board for driving the Curtis power section. Then I can run up to probably at least 60V, maybe much more if I use parts capable of tolerating it in the 2QD. 

Or alternately, create a 36V regulated supply to run the Curtis logic board from, fed from whatever battery supply the power section gets.


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## TX_Dj (Jul 25, 2008)

60v is also more trouble than from a charge/controller perspective. yes, the 7245 should handle 60v fine, and a charger that can handle a range of voltages within the 60v nominal should handle 60v fine if configured correctly.

The real issue comes from the additional RPM at the motor. The more voltage, the more RPM capability. The more RPM, the more likely you are to tear the motor apart from the rotational forces imposed on the motor.

Some motors are really really beefy and can take a lot more RPM than they're rated for, but others will detonate at the slightest provocation.


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## Sunking (Aug 10, 2009)

OK let me ask a question a different way. Lets say the spec says:

36 Volt Spec
Non Peak HP = 6.1 @ 4600 RPM
Peak HP = 10 HP with 200 amp controller.

Can I conclude this is the mid point RPM, and that 9200 RPM is the maximum no load no torque RPM?


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## major (Apr 4, 2008)

Sunking said:


> OK let me ask a question a different way. Lets say the spec says:
> 
> 36 Volt Spec
> Non Peak HP = 6.1 @ 4600 RPM
> ...


Hi Sun,

No, don't conclude that. Where did the spec come from? I have never seen "Non Peak HP" used as a legitimate rating. And for all series wound motors, the no load (zero torque, or nothing attached to the shaft) RPM approaches infinity. Now the internal load on the motor will actually limit the no load (external speaking) to a finite RPM. But at rated voltage, this no load RPM will exceed the mechanical integrity of the rotor and damage the motor, if not exploding it. But at reduced voltage, like 6 or 12V, the series motor can be run at no load.

RPM becomes asymptotic when zero torque is approached for the series wound DC motor.

Regards,

major


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## Sunking (Aug 10, 2009)

major said:


> Where did the spec come from? I have never seen "Non Peak HP" used as a legitimate rating.


It came from a site like this, it is one of many of the golf cart motor suppliers.

Note they also say can be used for 48 volt applications.


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## Sunking (Aug 10, 2009)

Major or anyone else take a crack at these question, as they are the ones really burning in my mind.

Ok let's say we take the D398 motor. Instead of installing a speed controller, we just use a 48 volt battery and a relay to turn the motor off/on with. Nothing to limit the current with other than battery, cable, and connection resistance. 

If I were to monitor the current from what I think I know; max current and torque will be delivered the moment the relay energizes and the motor rpm is 0 or stalled. As RPM spools up current and torque decay. Ok I think I got that part right?

But the real question is the moment the relay energizes what limits the current to the motor? Is it the internal motor winding resistance? If so is that the max current I should be shooting for?

Here is what is really driving me. I am using the D398 motor in my own cart with a 450 amp controller. It gives me 27 MPH but I would like 30 because it is used on the streets where I live. In addition I have a couple of friends in the neighborhood who want to do the same with their carts. But my instinct tells me the motor cannot pull 450 amps at 48 volts, nor am I certain Trojan T-105 golf cart batteries can even deliver that much current without the voltage being cut in half. I suspect 450 amp controller is overkill, and a less expensive smaller controller can be used with no performance difference. 

I have talked to a few of the suppliers of this motor. They will not or do not have the true specs for the motor. All they tell me to get every bit out of this motor use a 48 volt battery with a 500 amp or more controller. My gut tells me that is a sales pitch, and a smaller controller will work just as good. Since I am already operating at 48 volts, I don't think adding a larger controller is going to add any speed what soever, only a little more torque on the low end which I have plenty of right now.


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## major (Apr 4, 2008)

Sunking said:


> But the real question is the moment the relay energizes what limits the current to the motor? Is it the internal motor winding resistance?


Hi Sun,

At stall (zero RPM), the current is the battery open circuit voltage divided by the total series circuit resistance. This includes the internal resistance in the battery, the resistance of the cables and the motor resistance. 

So for example:

Motor resistance = 0.010 Ohm
Battery internal resistance = 0.024 Ohm
Cable resistance = 0.005 Ohm

Total series circuit resistance = 0.039 Ohm

Stall current = 50V / 0.039 = 1282 Amperes



> If so is that the max current I should be shooting for?


I don't think so  You'd see too much torque so get mechanical stress or fractures. You'd see too much current for electrical circuit components and cause damage, like a nice big flash on the motor comm.

This is why motor controllers have a current limit. And the other reason is once you get going and current decreases to an acceptable level, if you run into an obstacle, there is nothing preventing the current from going back up to the stall level.

And the "Non Peak HP" figure is just one point on a non linear curve and is not even represented as a rating or anything. 

Going to an increased current limit controller will increase the maximum torque you can get from that motor. It may also increase the continuous current rating of the controller. But it will not increase the speed of the vehicle unless top speed is occurring in current limit with the present controller. Which I doubt for level roads, but maybe on steep hills.

Since you cannot change the gear ratio, use larger diameter tires and monitor motor temperature.

Regards,

major


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## Sunking (Aug 10, 2009)

major said:


> Motor resistance = 0.010 Ohm
> Battery internal resistance = 0.024 Ohm
> Cable resistance = 0.005 Ohm
> 
> ...


First, thank you Major and all others. Please feel free to express your opinions. I have thought all along larger tires are the way to go to get the extra speed. What was throwing me is all the garbage from suppliers, and my lack of knowledge of DC motors.

I was almost certain (75%) that the controller current rating had nothing to do with top end speed as that is a function of voltage. 

Now with all that said, I am still unclear on what the best amperage controller I should shoot for? If I could determine what 20 feet of #4 AWG (.008 ohms) all the compression crimp connectors, contacts, relay contacts, battery, motor, and controller resistance all added together I could guestimate the maximum current that can be delivered. My gut tells me it is above .1 ohms. If that is correct 450 amp controller is to much?

FWIW I want the extra speed of 3 to 5 MPH for 2 reasons: 



I live in a gated golf community and we can drive our carts on the streets with a speed limit of 30 to 35. My cart does 27 right now. So I would like to get at least 30 MPH as to not slow down traffic.
 On every 4th of July my community has golf cart drag races over an 1/8 mile stretch. I won last year electric competition with my current set up. If I set up a few neighbors with my set up I will not have an edge. I really want to squeeze that extra couple of MPH out of the cart on a flat level street. Two thoughts came to mind. One was to add another 8 volt battery to get 56 volts, no one can see that mod. Second is larger tires which will be noticed. I prefer stealth.


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## major (Apr 4, 2008)

Sunking said:


> If I could determine what 20 feet of #4 AWG (.008 ohms) all the compression crimp connectors, contacts, relay contacts, battery, motor, and controller resistance all added together I could guestimate the maximum current that can be delivered. My gut tells me it is above .1 ohms. If that is correct 450 amp controller is to much?


 
No. 

My numbers were just examples. But what I thought might be representative. If you have that much in cables, I'd shorten them up and go to larger gauge. And a good battery could be half that 0.024. Motor ???? I think I took a good guess. All in all, if you have a 450 amp stall current without the controller, your system sucks  And that will have a voltage drop which affects your running speed.

Your controller may not tolerate a 56 volt nominal system. For a drag race, think about power to weight ratio. And starting torque (launch). High current limit. And look at 4 12 volt AGMs. Like Genesis or Optimas. High current, low resistance. Or spring for some Lithium. How bad you want that trophy this year?


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## Sunking (Aug 10, 2009)

major said:


> My numbers were just examples. But what I thought might be representative.


I understood that, and I am guessing. 

Cable length cannot be shortened, they are as short as they can be now. In theory it would be possible I think, to make them larger say 2 AWG, problem would be finding compression connectors with the right size or small enough holes to fit the various components. One thing I really do not like about golf carts and the piece parts made for them is nothing is two stud or two hole mating interfaces. Everything is single hole or stud with 1/4 bolts, studs, or screws being the largest fastener. So electrical connection resistance cannot be guaranteed like we do in the telcom sector with 25 micro-ohms. Vibration is a killer in a cart with single hole electrical connections.

Batteries are as good as they get for the space, either Trojan t-105, 875, or 1275. Again I do not know if they are even capable of delivering 450 amps without the voltage falling off a cliff.

So i do not know with everything added up the resistance is lower than .106 ohms.


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## dougmcp (Jun 2, 2010)

Sunking said:


> Well on one site I did see a torque spec of 96 oz/ft but no mention of RPM or current. This is the problem. the recommended controllers range from 200 to 450 amps, and voltage as either 36 or 48. I converted my EZ-GO from 36 to 48 volts, and upgraded the wiring (6 to 4 AWG) F/R switch, Solenoid, 400 amp controller, and the GE D398. Just wondering if I could push the controller up to 500 amps and/or 60 volts.
> 
> Right now I get about 27 MPH on flat level hard surface. I live in a private golf community, and carts are allowed on the streets. I live about 1 mile from the course and use the streets to get there. The speed limit is 35, and I would like to get up to at least 30 MPH. Lifting the cart and large tires may get the job done at the expense of torque. Th ecourse is a bit hilly. Right now from a standing start the cart will bark the tires and raise the front tires off the ground for a moment and reaches top speed I guestimate in 20 to 30 feet.


I'm not sure if you have to change any of the electronics to pick up a little speed.
My guess is that you are running the stock 12.44:1 Dana rear axle in your Ezgo, if you are using an 18" diameter tire then your motor is spinning in the 6300 rpm area to get 27 mph. If you are looking for another 3 mph, you can change your tire size to a 20" diameter without adding a lift.
What is your wheel diameter and tire size now?


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## Sunking (Aug 10, 2009)

dougmcp said:


> I'm not sure if you have to change any of the electronics to pick up a little speed.
> My guess is that you are running the stock 12.44:1 Dana rear axle in your Ezgo, if you are using an 18" diameter tire then your motor is spinning in the 6300 rpm area to get 27 mph. If you are looking for another 3 mph, you can change your tire size to a 20" diameter without adding a lift.
> What is your wheel diameter and tire size now?


Hey Doug thanks. I think I have seen you over on BGW? Not real impressed with some of the regulars electrical knowledge over there and gave up. 

Anyway you are spot on, I had 18 inch wheels and went up to 20 inch and all is fine getting my 30 MPH now. Only thing I gave up is a little torque in climbing, but no big deal. It will still bark the tire, and a little wheel lift from a standing start. Just not as loud of a bark, or as high of a wheel lift.  However it will outrun anyone else electric buggie.

My next challenge is one of my neighbors wants his converted. The one change will be he has deeper pockets and will be using a 48 volt lithium pack rated at 100 AH. Well actually the pack voltage is around 52 volts which is not a problem for the controller. Should be a fun project, I just have to finnish after the 4th of July so he cannot beat me during the holiday races.


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## dougmcp (Jun 2, 2010)

Sunking said:


> Hey Doug thanks. I think I have seen you over on BGW? Not real impressed with some of the regulars electrical knowledge over there and gave up.
> 
> My next challenge is one of my neighbors wants his converted. The one change will be he has deeper pockets and will be using a 48 volt lithium pack rated at 100 AH. Well actually the pack voltage is around 52 volts which is not a problem for the controller.


Yes I am a member at various GC forums and BGW is one of them. Some people there have lots of mechanical knowledge and practical experience with carts but most are a little light in the electrical department, especially anything that goes beyond what they have tried.
The electrical answers that you are likely to get there is "I don't really know why but it works" or "that's the way we have always done it". Attaching any of that to theory or formulas is just not their forte.

Speaking of Li battery packs at 52v, a flooded 48v pack has 51v at 100% charge. For what I do with my cart, the bang for the buck is still with lead acid. If you want to smoke your neighbor on the sly, try a stand alone 12v battery and a relay to boost your power (short spurts) to 60v.


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## Sunking (Aug 10, 2009)

dougmcp said:


> Speaking of Li battery packs at 52v, a flooded 48v pack has 51v at 100% charge. For what I do with my cart, the bang for the buck is still with lead acid. If you want to smoke your neighbor on the sly, try a stand alone 12v battery and a relay to boost your power (short spurts) to 60v.


Yeah flooded lead acid works best for me too. I don't think the economics work for Lithium today, but it depends on the cycle life and capacity loss over time. The new Lithium Phosphate claims up to 3000+ cycles and 10 years but not proven to my knowledge so time will tell. But if they do get that kind life span just a little more price drop would justify the extra expense if you did not have to replace them for at least 10 years.

Lithium has a lot of advantages though like flatter discharge voltage curve, less space and weight, and you can discharge them down to 80 or 90% DOD. I can see them in carts in the next 5 years.


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## electrabishi (Mar 11, 2008)

Sunking said:


> ... I just have to finnish after the 4th of July so he cannot beat me during the holiday races.


You should talk to Rod Wilde over at www.evparts.com

He'll help you win that drag race 

http://www.youtube.com/watch?v=hSRAdt4LhFs

Mike


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## electrabishi (Mar 11, 2008)

Just for winning the race part consider spending the $400 and get you four of those Oddyssey PC680's. You can drop from your ~400 lb of battery to 56 lbs. And those things will give you 450 amps easy for an 1/8th mile run.

Alas range suffers greatly and I wouldn't use them to drive the course, but they will win you that race 

Mike


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## Sunking (Aug 10, 2009)

electrabishi said:


> Just for winning the race part consider spending the $400 and get you four of those Oddyssey PC680's. You can drop from your ~400 lb of battery to 56 lbs. And those things will give you 450 amps easy for an 1/8th mile run.


Mike thanks for the tip  The race I speak of is just a neighborhood 4th of July event. We live in a gated golf community and there is no prize money involved, just a worthless trophy and bragging rights for the year. The cart is used for its intended purpose: to carry my big butt and clubs around the golf course, and get around the community as an NEV on the local private owned streets. Someday in the future when prices come down I will look into using Lithium batteries, but for now my Trojan 875's do a very good job.

Thanks again


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## Sunking (Aug 10, 2009)

Well CRAP!! I thought I had the Bad Boy Buggie to win the race this 4th of July, but my dreams were shattered today. One of the community neighbors I played golf with today has one of these

He blew my doors off without even trying. I can get him off a standing start, but his 35 MPH top speed leaves me behind in an 1/8th mile drag

What really hacks me off it is an OBAMA golf cart he ordered December 31 of last year. We paid $4500 of it so it cost him only $4500 in the end which is less than I spent converting my EZ-GO. The real kick in the butt it is street legal, with all the bells and whistles. Darn thing even has a trunk, built in cooler, and an AC inverter and motor..


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## dougmcp (Jun 2, 2010)

Sunking said:


> He blew my doors off without even trying. I can get him off a standing start, but his 35 MPH top speed leaves me behind in an 1/8th mile drag


Should have used my Turbo wiring for that extra 12v of power, you would have smoked him. It would have given you 38mph.
Maybe next year.


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## Sunking (Aug 10, 2009)

dougmcp said:


> Should have used my Turbo wiring for that extra 12v of power, you would have smoked him. It would have given you 38mph.
> Maybe next year.


LOL, thanks for the support. When I rode with him in the cart on paved surface he was pusing 40. That was with my big butt, ice chest full, and a set of clubs


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