Range and speed troubleshooting help

[checkoutmyjunk]

Originally Posted by JohnnieB

Deep-cycle batteries only have about 75% of their rated storage capacity when new and it take a couple dozen charge cycles for them to reach anywhere near their rated capacity and upwards of a hundred to reach it.

If they were fully charge before they sat idle for a month, then they make not have been damaged too much. Cart batteries self-discharge at about 1% SoC per day, so they only went down to 70% SoC and the aging (plate sulfation) is faster under 70% SoC.

The average SoC maintained throughout the battery's cradle to grave lifespan is a major factor determining the length of that lifespan, so recharge after each use, or at least overnight if the cart was used that day. And never let the batteries set for more than a month without being charged, less time sitting is better.

Also, it is winter. so the temperature is lower and the colder a battery is, the less storage capacity and performance are.

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A for motor and controller, your 955E has 14.78:1 gears and 17.75" tires, so the motor has to spin at about 2800 RPM for the cart to do 10MPH and about 4200RPM to do 15MPH. (279.9RPM per 1MPH)

How fast do you want the cart to go?

Personally, I put an Alltrax SR48500 or SR48600 in it and the longest motor I could fit between differential and rear shocks, or other obstruction.

In general terms, a series motors can be wound for high speed and low torque or for low speed and high torque - or someplace between those two extremes. In other words, speed is sacrificed to get more torque or torque is sacrificed to get more speed. However, with larger armature and stator coils, more torque can be obtained while maintaining the same speed to torque ratio.

The diameter of the motor is more or less dictated by the dimensions of the mounting surface on the differential, but the motor case can be lengthened a few inches to build a more powerful motor. For example a stock PDS motor is 8.5" long while my motor is 9.75" long and is stock speed with 30% more torque. D7D also has a sepex motor is 10.5" case the has 40% more than stock torque, but is a bit slower than stock speed. The same physics apply to series motor case lengths.

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The cart's top speed is also determined by the rolling resistance of the cart. Your cart is a heavy beast, so when pushing it by hand, it'll take a bit of effort to get it moving, but once it is moving, keeping it moving ought to be fairly easy. Any mechanical drag like bad bearings or dragging brakes will lower top speed.

I was showing 49.7 when I left for my voltage tests. That should have put them at about 75%, I suppose I avoided damaging them? This is stupid but, I did not charge them because I was not sure where the water levels were, I have yet to top them off. I have checked to ensure all the plate are submerged, just not sure where Trojan would like the water level to be. I also need to pick up some water for them, I don't think my well water would help.

If it matters the cart has been living in my garage and I keep that at 50°F or so, more typically. I just ordered a mini split for in there but that's anther subject.


As far as speed, I have low expectations. 5-6mph up hill and 8-10mph on the flats seemed wrong to me. Initially, in this shuttle journey I tried to draw knowledge from ScottyB as he has one of these cart. ScottyB made it clear that he didn't want to help me unless I lowered my expectations and I respect that he didn't want to lead me down the road to my false expectations. At the time I was hoping for a homemade lift, 22" tires, 6 adults and 15mph off road. ScottyB left me with the impression that was a pipe dream. I accepted that but still needed to find out if the there was a problem with the cart or was it preforming as it should. If the 955E was preforming as it should and I added a new motor and controller and it still preformed the same I would have been pretty bummed.


I talked to Plum Quick and D&D, I liked both but D&D appealed to my engineering side more and I felt more confrontable with how and why they selected a motor for my application. I attached an image of what they are suggesting. They were clear that their speed ratings were base on factors that did not apply to me like the final drive ratio that you calculated from my differential ratio and tire height.

I am lucky in that I have a lift that I can put the cart on and easily get all 4 tires in the air, mechanical resistance from dragging brakes and worn bearings are pretty easy to trouble shoot for me.

My next plan is to pull the motor off and inspect the bearings, brushes and commutator. I suppose I should check all the windings for shorts in the coating and make sure they have a similar resistance too. If I am so inspired by what I see in there I will throw the commutator on the manual lathe at work and turn a thou or two off. I few minutes of google searching says that at least I can get brushes for about $50 bucks.

I really appreciate you sticking with me on this, its all new to me and you have helped to flatten the learning curve!

[JohnnieB]

Here's a SoC chart for Trojan brand batteries and an electrolyte level drawing.

D&D listed 16 to 19 MPH with that motor in a cart with 18" tires and 12.44:1 gears which translated to 13.3 to 15.8 MPH with 17.75" tires and 14.78:1 gears. However, your shorter tire height and lower gear ratio gives you a 20.5% torque increase across the motor's RPM spectrum, so it might spin a little faster.

The motor D&D recommended has 50% more torque than stock, plus the 20% gain due to the final drive ratio adds up to about 70% more torque than you now have, so 15MPH on level pavement might be reachable.

An electric motor draws the maximum number of amps it is capable of drawing when it is stalled (0 RPM) and due to something called Back EMF, the number of amps it is capable of drawing decreases as RPM increases. The amount of torque produced by the motor is directly proportional to the amp flow through it, so the amount of torque produced by the motor (with the same voltage applied) also decreases as the RPM increases.

The motor's RPM will increase until the number of amps the motor can draw produces an amount of torque equal to the mechanical load place on the motor. At that point, the cart is at its top speed. Therefore, you want to reduce the mechanical load as much as possible. Make sure brakes aren't dragging, put synthetic 75W-90 gear oil in differential, replace wheel and other bearings as needed.

When the cart starts climbing a hill, the mechanical load on the motor increase and the motor slows (RPM decreases) until it can draw the number of amps needed to produce the torque enough to once again equal the new mechanical load. Carts with series motors slow the most going up hills.

[checkoutmyjunk]

Originally Posted by JohnnieB

Here's a SoC chart for Trojan brand batteries and an electrolyte level drawing.

D&D listed 16 to 19 MPH with that motor in a cart with 18" tires and 12.44:1 gears which translated to 13.3 to 15.8 MPH with 17.75" tires and 14.78:1 gears. However, your shorter tire height and lower gear ratio gives you a 20.5% torque increase across the motor's RPM spectrum, so it might spin a little faster.

The motor D&D recommended has 50% more torque than stock, plus the 20% gain due to the final drive ratio adds up to about 70% more torque than you now have, so 15MPH on level pavement might be reachable.

An electric motor draws the maximum number of amps it is capable of drawing when it is stalled (0 RPM) and due to something called Back EMF, the number of amps it is capable of drawing decreases as RPM increases. The amount of torque produced by the motor is directly proportional to the amp flow through it, so the amount of torque produced by the motor (with the same voltage applied) also decreases as the RPM increases.

The motor's RPM will increase until the number of amps the motor can draw produces an amount of torque equal to the mechanical load place on the motor. At that point, the cart is at its top speed. Therefore, you want to reduce the mechanical load as much as possible. Make sure brakes aren't dragging, put synthetic 75W-90 gear oil in differential, replace wheel and other bearings as needed.

When the cart starts climbing a hill, the mechanical load on the motor increase and the motor slows (RPM decreases) until it can draw the number of amps needed to produce the torque enough to once again equal the new mechanical load. Carts with series motors slow the most going up hills.

I was hoping that when I pulled the motor apart there was obvious wear and damage. This was not the case. The brushes looked pretty meaty and the bearing was smooth. The commutator looked a little scored and burnt but not shockingly so. I pressed the shaft out of the bearing at work and have it waiting for some manual lathe time. I think just a little emery cloth will clean it up. Can I just let the brushes bed themselves or do they need resurfaced or replaced? In my mind I liken them to brake pads, you should replace them if you change the rotors but if you don't it will likely bed in just fine.

[checkoutmyjunk]

Put the armature on the lathe!

[mikec557]

Originally Posted by checkoutmyjunk

Put the armature on the lathe!

Love the pictures. Let's see how it looks after you clean it up.

[checkoutmyjunk]

Originally Posted by mikec557

Love the pictures. Let's see how it looks after you clean it up.

I got so excited to get it back together that I did not snap any with it all cleaned up. In all, I removed 8 thousands or so.

I gained about 1mph but the brushes needed to seat yet, no testing on range either.