DC motor voltages.

[bbriggs]

Originally Posted by 72volt_ezgo

He will be able to tow just as many boats as before and then some!

If he tows the boats at the same speed/motor RPM as before,he will be doing it for roughly half the amps and that would reflect nicely on the runtime by itself alone! Now if he had the room to simply double the amount of batteries he is using now, his total available energy would be twice the KW/h in the pack as well so under those conditions in theory he would quadruple the runtime. But he will probably have some fun with the extra torque and speed and possibly go with smaller A/h and higher voltage batteries so there it goes that quadruple theory

Runtime difference really comes down to the total KW/h available in the old pack vs new pack, (example: 36V X 220 A/h = 7920 W/h or 7.92KW/h) AND how much performance we are asking from the vehicle above what we got from it before! Because the performance will be there but can we behave with that right foot?

Barna

You lost me with the quadruple runtime theory with only double the batteries. Half the amps at twice the volts sounds like the same watts, but the batteries will go dead at just double the runtime I think - or am I missing something? Double still sounds pretty good.

[simple man]

This is sounding more doable as we go. I am now using ( 3 ) 12V marine deep cycle batteries. These are large commercial batteries. I may be able to get 3 more that are in about the same condition ( age and use ). I have room for them in a compartment under the deck. The controller would be my only real expense. The batteries I can probably get for a salvage price, so it's time to look at controllers. I can't outlay anything for awhile, but I sure can do some research! Thank you all for your inputs on this! I've Googled my butt off, but there is no substitute for talking with people that have done this stuff before and know electronics, which I don't! I'm getting there, though!

I'm also lucky in that I have 2 identical 36V chargers that I can charge the whole pack at once with.

[72volt_ezgo]

I believe you are right bbriggs! I can't count the advantage twice! I must have over theorized!

Let's see this scenario!

We have 1 cart with 6 - 12V golfcart batteries in it.(for the sake of testing)

Scenario#1:

We use all the batteries but configure it for 36V system (2p 3s).
Double the capacity by parallelling 2 batteries and connect the 3 pairs in series.
We run it wide open until say 60% SOC is reached. That is X amount of miles.

Scenario#2:

Now after recharging we configure it 72V by series connecting all 6 batteries on this same cart with the same batteries.

Now we have twice the voltage but half the capacity of the previous setup and we are running it on the same road at the same speed as the previous configuration ran on 36V, again until the pack reaches 60% SOC.

Which scenario will result in longer distance and why?

....Here I go with my theories again....I think the high voltage will win simply because the thermal losses are not there or in other words more of the batteries energy turns into motion instead of waste heat created in the cables,motor,f&r,solenoid contacts etc.

Barna

[72volt_ezgo]

Originally Posted by simple man

This is sounding more doable as we go. I am now using ( 3 ) 12V marine deep cycle batteries. These are large commercial batteries. I may be able to get 3 more that are in about the same condition ( age and use ). I have room for them in a compartment under the deck. The controller would be my only real expense. The batteries I can probably get for a salvage price, so it's time to look at controllers. I can't outlay anything for awhile, but I sure can do some research! Thank you all for your inputs on this! I've Googled my butt off, but there is no substitute for talking with people that have done this stuff before and know electronics, which I don't! I'm getting there, though!

I'm also lucky in that I have 2 identical 36V chargers that I can charge the whole pack at once with.

This is the cheapest 72V capable I can find: http://www.evdrives.com/alltrax_axe7234.html

And I have it's bigger brother:http://www.evdrives.com/alltrax_axe7245.html

Look at the used price! Says email for availability!

I paid $650 plus shipping back when I got mine from some other site.

Barna

[scottyb]

There are 72v 700 amp FSIP controllers for $575 but I'm not so sure that you can run them on a lamp cord and 12v charger clamp.

[72volt_ezgo]

Originally Posted by scottyb

There are 72v 700 amp FSIP controllers for $575 but I'm not so sure that you can run them on a lamp cord and 12v charger clamp.

Scotty I can't decide if your sarcasm is just funny or ridiculous but you are not letting off that's for sure!

I don't care if it is a 700 Giga amp controller if the cart only pulls so many amps it will run on a lamp cord and a 12V charger clamp possibly circles around 48V carts! Maybe because electrons don't give a crap what voltage rating is stamped on the components that they go through. But who am I to know this for sure when I've only been running mine for the past three years like that...

Barna

[scubabud]

Are you saying that the amount of amperage that can flow through 3, 14 gauge lamp cords in parallel is equal to the amount of amperage that can flow through 2 gauge wire?

Are you saying that all one needs is just a battery jumper cable clamp as opposed to a solid bolt down terminal?

Maybe for a quick test... but not for a permanent solution...

For anyone reading this thread... a quick analogy can be a water pipe with flowing water... the smaller the pipe the smaller the amount of water that can pass through. If you increase the pressure, (voltage,) you'll get a greater flow but with more resistance. The higher the resistance the greater the heat in electricity. To lower that heat and increase the flow, (current,) you increase the pipe size, (wire diameter.) That's why there is a CURRENT rating for all wire.

[bbriggs]

Originally Posted by 72volt_ezgo

I believe you are right bbriggs! I can't count the advantage twice! I must have over theorized!

Let's see this scenario!

We have 1 cart with 6 - 12V golfcart batteries in it.(for the sake of testing)

Scenario#1:

We use all the batteries but configure it for 36V system (2p 3s).
Double the capacity by parallelling 2 batteries and connect the 3 pairs in series.
We run it wide open until say 60% SOC is reached. That is X amount of miles.

Scenario#2:

Now after recharging we configure it 72V by series connecting all 6 batteries on this same cart with the same batteries.

Now we have twice the voltage but half the capacity of the previous setup and we are running it on the same road at the same speed as the previous configuration ran on 36V, again until the pack reaches 60% SOC.

Which scenario will result in longer distance and why?

....Here I go with my theories again....I think the high voltage will win simply because the thermal losses are not there or in other words more of the batteries energy turns into motion instead of waste heat created in the cables,motor,f&r,solenoid contacts etc.

Barna

For purely resistive loads, such as your 50 amp copper plated charger clamp hooked to several parallel premium lamp cords, the waste heat should be half at 72 volts than at 36 volts with the same wattage output. All else being equal, it would seem your argument is sound and more volts wins!

[scottyb]

You guys need to start manufacturing these 72 v carts with nothing more than stock low grade tin can motors on 2xs the original engineer's designed voltage run thru your premium lamp AC cords and your 50 amp premium clips so we can have more than one cart in this test group from which to draw all of this theory. Until you do.... it's one cart and one driver? Lots more golf cart aficianodos and high voltage testers have come before you all, this is not news to the golf cart world that the same motor on higher voltage uses lower amperage. What is news to us is that we no longer need to bolt battery cables securely and that we can use household lamp cord with cheap charger clips.... that's a little scary ~ anybody seen a battery melt or golf cart burn from a loose connection ? Do what you want with your own cart but, lets remain responsible to our readers.
Good night.

[arcitech]

Well, i woke up wondering why i'm still thinking about this, and I did some research. Something that has been overlooked is (1)counter-emf and (2)a what-if scenario.

(1)Counter-emf in a series wound motor is very high at slow speed and drops quickly as the motor increases speed. The formulas get deep, but simple is (Vsource -Vcemf)/ R of windings. So assuming that the winding resistance doesn't change, the higher the voltage (running to the same motor) the higher the overall resistance (at low speed from almost stop) So using a 66% emf value(somewhat arbitrary but .686 for power correction in a AC circuit was my rule of thumb back in the day and .66 is easier to calc with 36 and 72 volt systems) and .3ohms for motor resistance at rest, the wattage for the same starting speed is greater with 72v using 5500 watts and 36v using 1440watts. (77amps @72v vs 40amps @36v with both at the same low RPM)

(2) What if you run at less than top speed (i.e 5-6mph vs 20) for 75% of the time, with a full load, then the 72v system will draw more amperage for the same speed, but it will get to that speed faster, and by virtue of a larger battery bank, it will run longer. The only downside i can see is that if you are using a cart for slow, heavy(1000lb or greater boat) towing, there is a potential for the motor to get hotter on 72v vs 36 or 48 due to the higher wattage having to be dissipated by the motor. At high speeds with less load the 72v will go father, faster and longer with less heat buildup by nature of the series wound motor 72volts setup has proven this. Keep in mind that the controller will be the biggest factor in how fast the motor gets power and how it feels when driving the cart.

So, for slow speed heavy/constant workload and trying to save money at the same time, i would still get some input from the vendors on this site and get a recommendation for a setup that will do what you need it to do, as safely and consistently, as you require, for the least amount of work and money. If you have a source of free/low cost batteries then 72v might be a great way to get more bang for your buck, getting 3years of use out of reconditioned batteries is GREAT! Not everyone has the opportunity or desire, but where there is a will there is always a way.

My apologies to everyone for way overthinking this when all Simple-man wanted was a quick answer...I'm still interested in 72v conversions, just need some more funding.