36 volts vs. 42 volts

[cgtech]

First- switching to 42v, that's easy. As long as your "max voltage" slider in alltrax software was set high enough (as shipped from alltrax, it is). It's as simple as adding a battery, 42v charger, and one battery cable, given your current status with upgraded solenoid & such. I would still leave your "max amps" where they are now.

Second- making your old pack into the "house pack"- do this before you remove them from the cart, you need to rate your old 6v's, 1-6, 1 being the best one, 6 being the worst one. Do this by fully charging them, then driving a good distance. Wait for the batteries to recover. Then measure the voltage of each. Label the highest voltage battery #1, second highest #2, all the way down to lowest voltage #6. Pair #1 & 2 together to make them a 12v, do the same for #3 & 4, same for #5 & 6. Going "series/parallel" 12v is much more forgiving than a long string of series batteries for 36v. I also suggest putting your load/charge leads at opposite ends of this big pack. (example- main B- lead on a 12v battery & main B+ lead at the opposite end on one of your "2x 6v" pairs, all energy is fed/drawn evenly). I'll add a drawing in a few minutes. Here ya go, straight from the table in my yard at 65°f, on a custom beer box.

[coosa]

CGtech - thanks for the great info. If I leave the slider at 80%, will adding the extra battery still give me an increase in torque and give me a better chance to get across that creek? When I tried it Saturday, it absolutely stalled on the steep bank. Nobody has to tell me how bad that is on the cart; I set the brake and finished the climb with the winch. With just a little more power it could finish that climb.

I was planning to wire the house pack the way you drew it, but I never thought of pairing the batteries that way. Thanks for that too. So I guess you think I won't damage the newer 6 volt batteries if I tie in the older 12 volts? It would solve several problems if I can keep them usable.

A good day to all. I'm headed out to buy batteries.

[JohnnieB]

Sounds like you need a higher torque motor as well as higher battery pack voltage.

Heat kills motors and when a motor is stalled, all the amps going through it are converted to heat, so it doesn't take very long to burn out a motor when 400A amps are flowing through it while stalled and it takes a lot less time at 500A since the heat generated increases exponentially to the increase in amp flow.

When the motor is loaded down to the point where it can only turn at 200 RPM or less (about 1 MPH with your 22" tall tires), all the amps not converted to torque are converted to heat and sepex motors are very inefficient at low RPM, so a lot of heat is generated.

It will take roughly the same amount of torque to climb the creek bank at 42V as it does at 36V, but at 42V there will be 16.7% few amps needed to produce that torque, which in turn means about 280% less heat generated.

In a nutshell, your motor will run cooler at 42V than it does at 36V, but I'm not sure if the 16.7% increase in torque will be enough to climb the creek bank without stalling, or nearly stalling.

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When I shipped it, that DCX500 was set up to run a D&D ES-76-51 motor at 42V and Field Map#4 was loaded so it ought to be good to go with a stock PDS motor at 42V with the max amps turned down to 400A.

Keep an eye on the motor temperature.

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Setting pack voltage and controller amps aside, the 22" tires reduces the torque where rubber meets road by 18%, so you need a motor that produces at least 18% more than stock torque to break even. The hilly terrain and rough ground are going to limit the cart to slow speeds some of the time and the motor RPM will be low during the periods of slow speeds, so a lot of motor heat will be generated and a motor with better than stock heat dissipation is needed. If you ever go to a different motor, look for one that has a physically longer case than a stock PDS motor (8.5").

The motor I'm running is 1.25" longer than a stock PDS motor and has 30% more torque than a stock PDS motor, yet has roughly the same RPM for voltage applied.

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As for the house batteries. When charged in parallel, the difference in battery age and capacity isn't critical since all of the batteries will have the same voltage applied and will draw charging current based on their respective internal resistance. When charged in seriesm the same current passes through all the batteries and the voltage across each battery varies according the their internal resistance, so they have to be evenly matched to receive equal charging.

The 6V batteries will be two in series, so they should be evenly matched, as CG explained how to match them.

[coosa]

Thanks JohnnieB, I just picked up the batteries. The old fellow griped and complained about me wanting a 7th battery, but he did sell it to me. Told me I was making a big mistake going to 42 volts and was gonna ruin my cart.

So you and ScottyB have been telling me for years how much better my cart will be at 42 v, but now you will be telling me I gotta have a new motor too. :). I guess there is no end to the upgrades. I keep a laser thermometer on the cart and keep a close eye on motor temp. I forgot it Saturday, so I don't know how hot it got on the creek bank, but I stopped it instantly when I realized it wasn't gonna make it. All your warnings about stalling have at least made some difference.

Turkey season comes in tomorrow, so I have got to run it a while with the stock motor. I'm not too worried about it, but I know it will probably take the controller with it when it goes. I guess that will be a good time to upgrade it too.

I have room to put the 7th battery behind the driver's seat, but the metal there doesn't look strong. Are you guys putting down plywood or something to strengthen that area?

Thanks again for all the help!

[JohnnieB]

What make/Model batteries did you get?

42V is a sweet spot for 36V PDS carts. Not too mild, not too wild.

A stock PDS motor does okay turning tires up to about 20" tall on moderately steep hills or taller tires on more level ground, but 22" tall tires on steep hills is a bit much for it. Mentioning the cart stalled, or almost stalled, on the creek bank was what got me thinking you might want to look into putting a more robust motor into it.

The turf tread on my tires is a built in safety factor for me. When I try to climb something too steep, the tires spin instead of the motor stalling.

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I don't have the space in front of the driver side wheel well reinforced and my 245AH batteries weigh about 68 lbs each, but my cart came off a 3 year lease in Arizona and had no rust. Check the total battery height for top clearance. The drive side hip guard on the seat is the lowest point that has to be cleared.

My batteries are 11.625" tall and the bottom of the hip guard rested on the terminal when I first installed the seventh one. I got a longer cable and moved it forward when I discovered that conflict.

IIRC, that metal panel is flush with the frame on the bottom, so you can add something like 1" angle iron under it if it is rusty on your cart.

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Good luck with the gooblers.

[coosa]

JohnnieB - I got the Trojan T-105s; had to drive an hour one way to get to a place that stocks them. They were $106 each, which is a good price in this area.

I know that an aftermarket motor would be much better for the cart, but this was the first time ever that it stalled. I should have made a pic of the creek crossing to show how crazy it was to even try to cross it in an electric cart. Several guys in my club made it, but I found out after the day I crossed it that they were not able to get a 2wd ATV across it. Only the guys with 4x4 were able to use it. Its not quite straight up, but close to it. And the creek bottom is so rough that I couldn't get a running start at all. Even then, it almost made it; just needed a little more boost. I might have made it on a second try, but I remember how much you and others here have warned against stalling it. And it was a 2 minute job to use the winch, so I didn't push it.

Its gonna be real close to get the 7th battery to fit under the drivers seat. The limiting factor is gonna be height, just as you said. I was thinking of putting a piece of 3/4" plywood down for the battery to rest on, but that's gonna make the cables stick into the bottom of the seat. Looks like I gotta use something really thin, like a rubber mat, or just let it rest on the metal. I just ordered one of Scotty's high tech chargers so I gotta make it work somehow. The metal looks to be in good shape. Thanks!

[yurtle]

I have a series cart, and drove through water that covered my feet. I literally pulled dead guppies out from under the plastic foot cover the next day.

While most folks will say water and electricity don't mix well, I've recovered many cell phones that went into the washer, and one that went into salt water, and had to wait 'til low tide.

[coosa]

Yurtle, I made it through the water fine; it was those steep banks that stopped me. I looked at the crossing again, and there is about 3.5 feet of rise over a horizontal distance of about 6'. It's pretty steep.

I carried the battery pack from the cart to the camp and installed them as suggested here. Looks like we will have plenty of power now. I installed the 7 new batteries in the cart today and there is a very noticeable increase in power and in top speed as well. I think this upgrade is gonna really improve the cart.

ScottyB's high tech 42 volt charger hasn't arrived yet, so I put the cables back to 36 volts and am charging 6 of them with the old charger. I had planned to charge the 7th battery with a 6 volt charger, but I found out my charger was only 12/24. I guess I can put a light on one of the batteries in the pack and pull it down to the same charge level as #7 and then charge them together at 12 volts. Gotta have the cart for turkey hunting Monday.

Thanks to all for the help with this project.