36 volts vs. 42 volts

[harleychief]

It's come time to change the 6 6v batts. I've upgraded the controller to an Alltrex, and a new solenoid. The rub is we're getting ready to move into a town where GC's are legal on the street, so I'm thinking we'll be using the cart a lot more. I know if I go to 42 volt system I'll have to buy a new DPI charger, and of course and extra 6v battery. My dilemma is the cost difference worth having the extra voltage? I don't really need more speed (Scottyb's setup with the Alltrex gives the cart enough). I'm just not sure how much more run time I'd get and again if the gain is worth the $$.

[scottyb]

My 08 PDS has been on 42v for years. It is hands down the best voltage for this drive system. Power and speed are improved as well. Run time is a mater of battery capacity. The cart draws from all of the batteries equally so 225 amp reserve is the same for 6 batteries as it is for 7 BUT, the higher the operating voltage the lower the amperage draw for a given task. That is where the longer run time comes from.
Do it - you will not regret it.

[Golferdave]

:More speed, torque & run time
If you have easy to find room for the extra batt

[yurtle]

Pounds of lead equals performance and/or longevity.

[JohnnieB]

Scotty is on the right track about the higher voltage having a lower amp draw to do the same amount of work, which does extend range, but the bulk of the increased range (distance that can be traveled on a single charge) comes from carrying more stored energy in seven 225AH batteries than six 225AH batteries.

Range is determined by how many Watt-hours (Wh) are stored in the battery pack as well as how many Watt-hours the cart consumes per mile. Pack voltage plays a role in the cart's efficiency (Wh/Mi), but not how many Watt-hours are stored in the battery pack. That is simply Volts times AH.

Using nominal battery voltage (6V) times battery AH at 20-hour rate (225AH) a T-105 stores 1,350Wh of electrical energy. Six of them (36V pack) store 8,100Wh while seven of them (42V pack) store 9450WH, which is 16.67% more stored energy.

So you start with carrying 1/6th more stored energy, than factor in better cart efficiency at the higher voltage to get an increased range of over 16.67% better.

I ran a stock PDS motor with a DCX400 at 36V (6 x 6V T-105 - 225AH) and the same motor and controller at 42V (7 X 6V Exide GC-145 - 245AH), so I went from 8,100Wh stored to 10,290Wh, which is a 27% increase in storage.

My cart has tiny tires, only 17" tall vs 18" stock height (which gives me a 6% gain in torque) and 2Ga cables throughout, so it is very efficient and by measuring SoC decrease over a measured distances (>10 miles) and extrapolating to 50% SoC, I averaged 23.9 miles at 36V and 35.1 Miles at 42V. All range testing was done over approximately the same route and terrain, a combination of cross-country (mild off-road except for climbing a flood wall), paved and gravel roads and city streets with stop signs, very little level ground.

That is a 46.7% increase in range with only a 27% increase on stored energy. Of course, some of that additional gain was due to switching from, old batteries that had not been well maintained during the first 18 months of the life (Cart came off a golf course lease), but were in reasonably good health when retired, to new batteries. The rest is due to my efficient cart being more efficient at 42V.

My goal in going to 42V and higher AH batteries was for a greater than 30 mile range, the gains in torque and speed were incidental, but enjoyable.

My guess is that you ought to realize somewhere in the neighborhood of a 20% increase in range with a 16.7% increase in storage capacity. (IE: Using seven 225AH 6V batteries)

As for a speed increase not being desired, with a XCT-PDS controller you can limit the max motor RPM down to whatever speed you want.

Go for it!!!!!!!!!!

[JohnnieB]

Originally Posted by Golferdave

:More speed, torque & run time
If you have easy to find room for the extra batt

With a PDS cart, the seventh battery fits in front of the driver side wheel well and there is room on the passenger side (where the controller is) for a voltage reducer, or a smallish 12V battery for accessories.

If there are a lot of accessories and a 12V fuseblock/distribution panel is needed, it fits nicely on the driver side wheel well.

Going from 36V to 42V in a PDS cart is a very simple upgrade.

[JohnnieB]

Originally Posted by JohnnieB

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That is a 46.7% increase in range with only a 27% increase on stored energy. Of course, some of that additional gain was due to switching from, old batteries that had not been well maintained during the first 18 months of the life (Cart came off a golf course lease), but were in reasonably good health when retired, to new batteries. The rest is due to my efficient cart being more efficient at 42V.
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I was curious about how much of the gain was due to new batteries and how much was due to 42V being more efficient than 36V, so I went back to my range estimate data and crunched some more numbers.

Using the "Gas Mileage" yardstick used for EV comparisons (kWh/100Mi), I got 16.6kWh/100Mi at 36V and 14.4kWh/100Mi at 42V.

That makes it a 13.3% increase for the change in voltage and 6.4% increase for newer batteries.

In summary, increased range from:
27.0% = Storage capacity
13.3% = Higher Voltage
6.4% = Newer Batteries

[yurtle]

Is that additive? 46.7% increase?

EDIT: ignore old vs. new batteries, but is that increase in range over 40%?

[JohnnieB]

Originally Posted by yurtle

Is that additive? 46.7% increase?

EDIT: ignore old vs. new batteries, but is that increase in range over 40%?

Yes, it is additive, but just 0.3% over.
27% is a double whammy increase in stored energy. More batteries and Bigger batteries.
Went from 6 x 6V to 7 X 6V for a 16.7% increase and from 225AH to 245AH for another 8.9%. That adds up to only 25.6%, but when you calculate the percent increase based on Watt-Hours (8,100 to 10,290), you get 27.04%

The 13.3% increase speculation on the increased voltage increasing efficiency is based on using fewer Watt-hours per mile at 42V. At 36V I used 165.8 Watts-hours/Mile and at 42V I used 144.1 Watts-hours/Mile. Which works out to 13.088% less.

I used kWh/100Mi to calculate the percentage in my earlier post, so there is some rounding errors. 16.6 vs 14.4 = 13.25% less which rounds to 13.3%

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I hadn't given much thought to the range increase due to higher pack voltage before today and I'm surprised at how much it appears to be.

I still have a 36V DPI charger and my cart will still run at 36V, so for grins, when it warms up around here I'm thinking about doing a comparison of 36V vs 42V with a cart that weighs exactly the same over an identical route. I'll just bolt the cables to one battery together to keep the high current loop resistance as close to the same as I can get it. Since I'll be using the same batteries, or at least 6 of the 7, in both sets of tests, the variables induced by battery AH and age ought to be pretty well eliminated also.


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My guesstimate at this point is that going from a 36V-225AH pack to a 42V-225AH pack will up the range by 25% (or more) rather than just the 16.7% gain by the increased Watt-hours stored.

[scottyb]

This is definitely a tin foil hat thread