how to figure amp draw

sonnysmith

I have been reading a lot about amps needs for controllers.Most of the post that I've read talks about over sized tires and big electric motors and etc,but I'm dealing Ez go series cart with a 3.5 H.p. standard motor in 36 volts that I'm going to run on 48 volts. Now I'm trying to figure out, do I need to put a large amp controller for this type installation? I have change the wiring to 4 gauge.I'm just trying to get more speed for the golf course.Now for some of my questions. with this set up,can you guess at the speed I can expect? can you tell me how figure amp draw or is there a formula for this?.The only thing I have found out is about 7 amps per horse power at 48 volts,but nothing on larger tires or lift kits, any comment on this?

Sorry for all the question from a newbie,but I know very little about dc voltage.
In the future I'll be trying to up grade some more carts, just taking baby steps at first.
Thanks
Sonny

BGW

__________________
This advertising will not be shown in this way to registered members.
Register your free account today and become a member on Buggies Gone Wild Golf Cart Forum

scottyb

For the golf course with stock tires on 48v I would use a 400a controller and 200amp solenoid. Expect about 18 mph on the fairways

sonnysmith

Thanks ScottyB

Would you tell me why,with a stock motor I should increase the amps on my controller.Has it got something to do with the voltage??
Sorry for all the questions,Just trying to get hand around this amp thing.
Sonny

rib33024

The more AMPs the more torque, and the more volts, is more speed, running a 36v motor on 48v is nice, it will put a smile on your face

sonnysmith

Thanks for the reply.
I know where I get more volts,going to 48 from 36,I just don't know where the extra amp come from.
Remember no question is a dumb one.HAHA

gornoman

Remember, controllers do not GENERATE amps, they MANAGE them. The MOTOR is what calls for amps, and if it calls for 350 amps during a stress event and the original controller can only allow 275 amps, the controller is going to be running at it's peak flow for longer periods of time than it was designed for. This leads to early failures. Install a 400 amp controller and this condition is improved. Same logic applies to the solenoid, F/R switch, and cables. The idea is to free up the amps so the motor can use them.

scottyb

Uncontrolled the motors draw amperage until they puke. The controller is a limiter. A 400 amp control is capable of about 50% delivery sustained.
Your cart draws about 50-70 rolling along under average conditions, but it takes much more than that to get moving or climb a grade.
Sorry I'm not an engineer, but one will swoop down on this thread like a hawk on a rabbit, if you wait.

yurtle

I think you described it perfectly.
Sometimes, "Engineer" is a four letter word around here.

Grossly simplifying here, but if you give a motor a certain amount of volts, it will demand a certain amount of amps, if not controlled by a controller.

The load on the motor determines how many amps it wants. The controller, under many conditions, gives it less than the motor wants, which is why climbing hills slows down so much, especially if you have a lot of passengers. The stock controller may say 275 amps (or whatever yours is), but that rating is good for only a certain amount of time. My AXE4855 is a 500 amp controller, but that's a 2 minute rating. It's rated for 350 amps at 5 minutes and 250 for 60 minutes, as ScottyB mentioned above. I keep mine limited to only 400 amps, but I've bought future capacity, if I upgrade my motor, and I also have a greater factor of safety for those nights when I get crazy.

If you're going from 36 volts to 48, you need a new controller anyway. And you're not going to be happy flying on the straightaways, then crawling uphill. And if you increase tire size, you get more top speed, but your motor needs additional amps to accelerate or climb hills. Have you ever driven a ten speed bike in a high gear from a dead stop? Hard to get started, but top end is improved. However, you may have to downshift if you climb a steep hill. You can't change gears on your buggy, but you can increase the power you send to the motor.

Going from 36 to 48 is what I recently did, and haven't had a single regret. Get a big controller, thicker wires, upgrade FNR, and solenoid, and you'll be happy you did.

yurtle

You make us sound like predatory stalkers.

JohnnieB

Warning: Technical content!!!.
May cause Brain Freeze if read before morning coffee kicks in.

1 horsepower = 745.699872 Watts (Commonly rounded to 746 for convenience)
1 Amp times 1 Volt = 1 Watt.
Therefore: 15.5A (not 7A) is required to develop 1 HP @ 48V. (Or 20.7A @ 36V)

Mechanically, HP = Torque times RPM divided by 5250

The stock rear end ratio for a TXT is 12.44:1 and the stock tire height is approximately 18", so with a little number crunching, you could figure out how many ft/lb of torque is needed to propel your cart at 14MPH and from that you could derive Watts needed per MPH and calculate the speed increase with a 33.3% increase in applied voltage, but there are many other factors involved, so it would only be approximate at best.

Basically, if it took about 70A @ 36V (2520W) to propel your cart at about 14 MPH, 70A @ 48V (3360W) will propel it at about 18 MPH. (28.5% increase rather that 33.3%)
Conversely, it would only take 52.5A @ 48V to propel it at 14MPH, hence the often mentioned statement that going to a 48V system reduces current and or increases run-time.

Hope this helps rather than confuses.

Back to circling on updrafts and looking for rabbits.