Crazy idea?

[Helirich]

Yea, I knew there was not any real speed to gain unless you were going slow due to weight. But there is no speed to gain from a higher amp controller either. (Unless you change the motor too.)

I was just thinking for someone who wanted more power, it would be a lot cheaper than a higher amp controller.

[DaveTM]

Yeah...I knew that.......I just couldn't put it into words.

[jackman08]

Im finding it hard to believe that a higher amp controller will not increase speed. After installing a 400 amp alltrax; I think my speed increased greatly. If I had to guess, and thats what it would be, a guess, I would say at least 5 mph, and I would really think more. Is this just my imagination?

[Sergio]

It would increase speed if it was a Sepex motor as the new controller probably has a lower Field voltage setting.

On a Series drive You either have to increase the overall voltage at the motor or reduce the Back EMF flux intensity by doing a "Field Weakening" shunt.

I think the other important aspect of the high current controller is that You have very granular control of that additional torque.

You can always add a 100HP NOS shot to your truck's engine, but it would not be very practical to pull Your boat out of the water (it could be entertaining though )

[Skydo]

Jonnie B. I appreciate the time you put into these forums. Your technical explanations are easy to understand and examples are spot on. And thank you to all of the "senior" members who provide guidance and tolerance to those of us who have seemingly silly questions.

[JohnnieB]

Originally Posted by jackman08

Im finding it hard to believe that a higher amp controller will not increase speed. After installing a 400 amp alltrax; I think my speed increased greatly. If I had to guess, and thats what it would be, a guess, I would say at least 5 mph, and I would really think more. Is this just my imagination?

If it was a SepEx Drive (DCS or PDS), there was a speed increase. This is probably due to different field mapping for the DCS. For the PDS, in addition to different field mapping, the 4200RPM limit imposed on the motor by the stock controller is eliminated and a stock PDS motor will spin at about 5600RPM at 36V.

Replacing a stock 300A PDS controller with an Alltrax DCX300, which is also a 300A controller, will up the top speed from 18MPG to 24MPH on 18" tires at 36V. However, replacing the stock PDS controller with a DCX400, or DCX500 or a DCX600 will also up the top speed to 24MPH on 18" tires at 36V.

If it was a Series Drive system, a top speed increase of 5MPH was probably due to other things replaced at the same time the controller was replaced. For example the voltage drop across the contacts of a used stock (85A) solenoid is greater than the voltage drop across the contacts of a new 200A solenoid. Same is true if with a new F/R switch and high current cables.


I'm not sure if it would produce a 5MPH speed gain, but higher ampacity controllers drop less voltage per 100A of current flow. For example an AXE4834 (300A series controller) drops about 0.30V per 100A while an AXE4855 (500A series controller) only drops about 0.09V per 100A. However at max RPM, the motor is most likely going to be drawing less than 100A, so the output voltage difference is very small. Unfortunately, I don't know what the voltage drop per 100A is for stock controllers, but it would have to be pretty high to get much of a speed gain by reducing it.

[Helirich]

Originally Posted by JohnnieB

The output of a controller is chopped DC. An array of a dozen or so MOSFETs (Metal Oxide Field Effect Transistor) connected in parallel is located between the battery pack and the motor and the MOSFETs are switched from completely OFF to completely ON about 18,000 times per second. The ratio of ON time vs Off time determines how much power is forwarded to the motor. The technical name for the process is called PWM (Pulse Width Modulation) and the duty cycle varies from 0% with throttle up to 100% with throttle wide open.

That makes sense. I've always wondered how a controller saves battery over a "risistor" cart. People have told me a resistor cart is running at full bore all the time. Just that the coil eats up the extra power making you go slow.

Originally Posted by JohnnieB

On the other hand, there are a few members of this loony bin that have used solenoids to bypass a stock controller and add an addition battery or two to the pack when the pedal is on the metal.

Did they do this with good results? I'm not sure I understand. Are you saying they somehow inserted the 6 or 12 volts in the line? I'm thinking they would have to have a selinoid cut the 36v and then add the new batteries in and reconnect. I would assume this would have to be done after the controller or maybe "around" the controller. This doesn't sound so good to me because of sepreate charging requirements.

Just to clarify for my feeble brain.

A given motor will spin at a set speed at a set voltage. (No load) it doesn't matter how many batteries you have as long as it's a set voltage.

It will draw very low amps unless it is artificly held to a lower speed. (Load) Then it will draw a certain amp amount based on the rpm its held to. Again, it doesn't matter how many batteries you have as long as it's at a set voltage.

[JohnnieB]

Originally Posted by Helirich

1. That makes sense. I've always wondered how a controller saves battery over a "risistor" cart. People have told me a resistor cart is running at full bore all the time. Just that the coil eats up the extra power making you go slow.


2. Did they do this with good results? I'm not sure I understand. Are you saying they somehow inserted the 6 or 12 volts in the line? I'm thinking they would have to have a selinoid cut the 36v and then add the new batteries in and reconnect. I would assume this would have to be done after the controller or maybe "around" the controller. This doesn't sound so good to me because of sepreate charging requirements.

Just to clarify for my feeble brain.

3. A given motor will spin at a set speed at a set voltage. (No load) it doesn't matter how many batteries you have as long as it's a set voltage.

4. It will draw very low amps unless it is artificly held to a lower speed. (Load) Then it will draw a certain amp amount based on the rpm its held to. Again, it doesn't matter how many batteries you have as long as it's at a set voltage.

1. Technically, it is more complex, but the end results are the same. The resistor coils convert some of the electrical energy supplied by the battery to heat rather than passing it on to the motor where it is mostly converted to torque.

FWIW: Bad high current cables in controller carts slow down the cart the same way as the resistor coils slow down resistor carts.

2. I have a SepEx drive and it only works with Series drives, so I haven't thoroughly dissected the theories. The have been some threads on it here and in Extreme DC, but I don't have a link to them saved. I'll take a quick look and if I find them, I'll post the link(s).

3. It takes twenty-four 2V Lead-Acid cells to make a 48V battery pack. The cells are typically packaged 3 to a box (6V battery), 4 to a box (8 battery) or 6 to a box (12V battery). The no-load RPM of a series wound DC motor with 48V applied will be the same whether the battery pack consists of four 12V batteries, six 8V batteries or eight 6V batteries.

Since the physical size of the 2V Lead-Acid cell determines its storage capacity (AH) and the boxes cells are packaged in tend to be pretty close to the same size for 6V, 8V and 12V batteries, 6V batteries tend to have more AH than 8V batteries and 8V batteries have more AH than 12V batteries.

Range (run-time) is determined by storage capacity, so a 8x6V 48V battery pack tends to have more range than a 6x8V 48V battery pack and a lot more range than a 4x12V battery pack .

4. That's it in a nutshell.

The motor specs I posted earlier illustrates the way it works.

Connected to a 48V battery pack, the unnamed motor can draw 526A and produce about 80ft/lb of torque at about 1,000RPM
Same motor connected to same battery pack can only draw 408A and produce 60ft/lb of torque at about 1,250RPM.
Same motor connected to same battery pack can only draw 291A and produce 40ft/lb of torque at about 1,575RPM.
Same motor connected to same battery pack can only draw 231A and produce 30ft/lb of torque at about 1,800RPM.


If the cart this motor was installed in imposed a 3 ft/lb load, the motor would be slowed to about 4300RPM so it could draw the 48A it needs to produce 3 ft/lb of torque. (Top speed of 18.5 MPH with 18" tall tires.)

However, if the cart this motor was installed in imposed a 5 ft/lb load, the motor would be slowed to about 3525RPM so it could draw the 66A it needs to produce 5 ft/lb of torque. (Top speed of 13.9 MPH with 18" tall tires.)

[UncleJerm76]

Way back when I first bought my 36V club car I also wanted 48v on a budget. Lots of searching lead me to a thread floating around here where a member was in the process of doing just that to his 36V resistor cart. For the most part he basically left his 36v resistor system alone and added two additional 6v batteries in the bagwell on a separate switch to give him the total of 48v he wanted. Now mind you it was more complex than it sounds. He had all kinds of problems at first, figuring out a way to charge the extra two batteries, burning up this and that but it was a blast to read the thread - everyone telling him it couldn't be done just added fuel to fire. He posted wiring diagrams and a parts list etc etc and eventually got it right after adding a lot of safety features, relays, microswitches. But at the end of the day he still had a resistor cart.

For the life of me I cannot find that post now. Now I'm not encouraging you to go that route (I went with the ScottyB solid state conversion and it has been phenomenal!) ...but if your absolutely gonna do it - you might as well learn from others mistakes and see what your getting into before you turn your cart into a fire chariot. You would need to use the same principles he did in order to bypass the controller on full throttle.

[Helirich]

Yea, right now I'm rebuilding/upgrading a TXT. It will be 48 V the right way. But when it's done and running good, I will have my old Marithon to play with. I'm not really on a budget, but I might take the challenge. I had not thought about adding batteries, but who knows?