Converting CC (Ahem) to Lithium Power

[ronncat]

Originally Posted by sportcoupe

Alltrax AXE7245 has max input of 90v, so does the SPM72400. The SPM is easier to program and has a few better features. The AXE is a time proven performer.

So… Sportcoupe,

Do you think that 400 amps is enough, or should I bump it up to the 500 amp version??

I also decided to swap my 12 year old solenoid for a new one and get a reversing contractor in lieu of the F/R switch. Don't wanna weld anything shut

This conversion just got expensive A couple extra batteries, bms boards, contactor, solenoid, controller… and maybe even brakes…OUCH. The stupid thing is I already have that 84 Volt monster

Oh.. a tidbit more info. At 36 Volts the motor will turn 4150 RPM, so I'm thinking at 72 Volts, I can hope for around 8000. Hope I don't blow it up..That would mean even more $$$

[sportcoupe]

A 72v 400a controller will give more watts to the motor then a 48v 500a controller could. This is good if motor can take it. You mentioned 8000 rpm, that is boom territory. I'd limit rpm to 6500 before bad things happen.

[ronncat]

Originally Posted by sportcoupe

A 72v 400a controller will give more watts to the motor then a 48v 500a controller could. This is good if motor can take it. You mentioned 8000 rpm, that is boom territory. I'd limit rpm to 6500 before bad things happen.

That's what I was thinking Since all of my use is on my flat golf course and the flat road to it, I probably don't need the 500 amp controller. Let's see?

550 amps @ 48 Volts is 26400 watts
400 amps @72 Volts is 28800 watts
500 amps @ 72 Volts is 36000 watts

Doesn't seem to be a huge difference between 550/48 and 400/72. But as we know, the seat of our pants would probably tell us otherwise

[Volt_Ampere]

No way is a stock motor going to stay together at 8000 RPM.

[JohnnieB]

Voltage vs Torque vs RPM.

In a theoretically perfect DC series motor, if you double the voltage, you double the torque, which in turn doubles the RPM, if the load remains the same.

However, electric motors are not 100% efficient and the efficiency curve is not linear over the Torque vs RPM range, so about the best you can hope for is about 80% of a true doubling. (Only if the motor is 80% efficient, which it may not be at high RPM. The efficiency curve peaks about halfway between stall toque and no load RPM.)

4150 x 2 = 8300
8300 x 0.8 = 6640.

Also might be a little less because the cart will be moving faster, which ups the loading a little.

------------
As for 400A controller vs 500A controller. Once a motor is spinning above a certain RPM, it is incapable of drawing more than 400A, so the difference between the two only exists between Zero RPM and whatever the RPM is that above which the motor cannot draw more than the lesser ampacity controller's max amp throughput.

[sportcoupe]

Originally Posted by Volt_Ampere

No way is a stock motor going to stay together at 8000 RPM.

He has GE D380 48v motor but I still agree with you. 8000 rpm = boom

[ronncat]

JohnnieB and Sportcoupe,

Thanks as always for your advice and insight. I was only hoping/guessing for that ridiculous high rpm number. Pretty much knew it would be quite a bit lower. That said, I would think that that GE D380 could handle 6500 rpms. It is rated for 5700 @48 volts, so only asking for a few hundred more

Thinking of installing an Albright style SW202 style 72 Volt contactor. Will wire a switch in the existing F/R position and run it off the dedicated 12V system. Then I need to order a new solenoid…

Just one more decision to make, I'm leaning towards 400 amp controller…but burnouts are sooooo fun Definitely get off the line quicker with the 500 amp Alltrax Just need some more opinions from everyone.

[JohnnieB]

Originally Posted by ronncat

1. That said, I would think that that GE D380 could handle 6500 rpms. It is rated for 5700 @48 volts, so only asking for a few hundred more

2. Thinking of installing an Albright style SW202 style 72 Volt contactor. Will wire a switch in the existing F/R position and run it off the dedicated 12V system. Then I need to order a new solenoid…

3. Just one more decision to make, I'm leaning towards 400 amp controller…but burnouts are sooooo fun Definitely get off the line quicker with the 500 amp Alltrax Just need some more opinions from everyone.

1. When I exploded my stock PDS (Shunt wound aka SepEx) motor, it was spinning about 8200 RPM, but RPM alone didn't pull the armature apart. It was a combination of heat, RPM and the extreme magnetic forces generated by regenerative braking at that RPM. Had I not lifted my foot to make the turn at the bottom of the hill I was insanely going down at full throttle to see how fast the cart would go, I still might be running that same set-up.

The max RPM on the shaft bearings is likely to be upwards of 10k and a series motor doesn't do regen braking, so a series motor's max RPM is limited by armature construction and balance. Of course, what that number is, isn't something a motor manufacturer will let you know, if they do, in fact, know it. Instead you'll get a recommended Max RPM, which may vary depending on who you speak with at the manufacturer.

For example: The recommended Max on my motor is either 6,000 or 6,500, both from authoritative sources at D&D. Because my tires are only 17" tall, I can exceed 7,000 RPM on level ground at 42V, but I seldom go over 6,500 (26.5 MPH) since the speed limit is 25 MPH on nearly all the roads I travel on.

With taller tires or faster gears, I wouldn't be able to reach as high of an RPM at 42V due to the increased drag (loading) on the motor.

2. I not sure if I'm reading this right, but the voltage listed in a contactor's description is typically the coil voltage rather the the voltage rating of the contacts.

3. I don't know what your tire height or gear ratio is, but for a stock EZGO (18" tires and 12.44:1 gears) every 1 ft/lb of torque the motor generates applies 16.59 pounds of linear force where rubber meets road.

[ronncat]

Originally Posted by JohnnieB

1. When I exploded my stock PDS (Shunt wound aka SepEx) motor, it was spinning about 8200 RPM, but RPM alone didn't pull the armature apart. It was a combination of heat, RPM and the extreme magnetic forces generated by regenerative braking at that RPM. Had I not lifted my foot to make the turn at the bottom of the hill I was insanely going down at full throttle to see how fast the cart would go, I still might be running that same set-up.

The max RPM on the shaft bearings is likely to be upwards of 10k and a series motor doesn't do regen braking, so a series motor's max RPM is limited by armature construction and balance. Of course, what that number is, isn't something a motor manufacturer will let you know, if they do, in fact, know it. Instead you'll get a recommended Max RPM, which may vary depending on who you speak with at the manufacturer.

For example: The recommended Max on my motor is either 6,000 or 6,500, both from authoritative sources at D&D. Because my tires are only 17" tall, I can exceed 7,000 RPM on level ground at 42V, but I seldom go over 6,500 (26.5 MPH) since the speed limit is 25 MPH on nearly all the roads I travel on.

With taller tires or faster gears, I wouldn't be able to reach as high of an RPM at 42V due to the increased drag (loading) on the motor.

2. I not sure if I'm reading this right, but the voltage listed in a contactor's description is typically the coil voltage rather the the voltage rating of the contacts.

3. I don't know what your tire height or gear ratio is, but for a stock EZGO (18" tires and 12.44:1 gears) every 1 ft/lb of torque the motor generates applies 16.59 pounds of linear force where rubber meets road.

I did a little testing this morning. I was wondering why some of the guys that I used to blow by like they were stuck in the mud were now a lot harder to reel in. It's a short 1/2 mile blast up the private road to the club and now it might take me most of that distance to catch these guys if I gave them a few hundred yards head start.

Checked my resting charged voltage and it was 51.4V or so. Then I checked my tire pressure. OOPS… they were all 12 -15 lbs No wonder like it felt like I was the one stuck in the mud. Inflated them to 25 lbs (I know.. a bit overinflated) and did a few tests runs back and forth on the road. GPS showed anywhere from 25.8-26.4 mph.

I am running the stock CC gears (12.28:1, I think) and my tire diameter at 25 lbs is 17 inches. My batteries are getting old…I think they've been in there for 2 or three years. (They're Interstates, not Trojans:thumb down:) That means the motor must be turning around 6300 rpm according to the speed calculator. It does take it a bit of time to get to max speed though unlike my other cart.

Anyhow snapped a couple of pics to post before I get thecomment

This is the old reliable that getting the upgrade. Built is around 14 years or so ago. The stuff going in and the room I have to work with
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[ronncat]

I need to add…
After all the high speed runs, the motor was barely warm to the touch