Good post!
Good post!
Reminds me of my first quarter of college. Nice post.
What? How can the drain rate be the same but battery capacity consumed be different?Originally Posted by Lou r Pitcher
Actually when the voltage goes down the current does increase. This fact. The load does not change and voltage and current are inversely proportional.
2 year old post?
Last edited by Lou r Pitcher; 07-01-2020 at 11:16 PM.
Not on most electric motors, if voltage goes down the current flow to do the same work will go up, This is why many motors die an early death when operated with lower voltage than design
As John mentioned at higher voltage it will require lower current flow to do the same amount of work. Pulsed motors always have a maximum field strength which is very efficient regardless of the amount of work being performed, reducing voltage thru resistors, reduces field strength thus much lower torque, increasing heat in the resistors and motor
I cant count the number of starter motors I have seen in my career that have been burnt up by heat from people just keep trying to start them with low or bad batteries esp. in 24 volts systems, as well as solenoid contacts welded closed. Permanent magnet motors are less sensitive to this but does still applies
I know most not comprehend this but it is a well proven fact in a motor circuits, Voltage goes down current flow goes up. This is very easy to test this fact with a inductive amp clamp on the starter cable and a carbon pile on the battery to lower voltage
The above post about blowing a fuse because or resistance is usually because the bad connection resistance is very near fuse and is heat transfer to the fuse
Last edited by lpugh; 07-01-2020 at 06:55 PM.
Thank You Leon Pugh
What you are not considering is that as voltage drops the power level is increased to maintain the amount of work done increasing the current flow and because of the lower voltage the motor is far less efficient increasing the watts consumed
Thank You Leon Pugh
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2016 Ranger 1850 LS Reata / Merc 150 4s / SmartCraft / Lowrance HDS Carbon SS3D
Y'all are forgetting CEMF. The slower a motor goes the less CEMF it develops and the higher the current when it is loaded. Sometimes when a motor is doing work, and the voltage goes down, the current increases as it goes slower.
Look. I am talking about 12 volt DC permanent magnet trolling motors. The 5 speed motors are controlled but reducing the voltage to armature. The less voltage applied to the armature the slower the motor turns and the less current it draws. This is fact. The less current it draws the longer the battery run time. This is fact. That is all I am saying.
People on here are saying that the 5 speed motors draw the same current no matter the speed setting. This is false.
People are also sating that PWM motors will provide longer run time then a 5 speed motor. This all depends on speed settings. etc...
I am saying that a 5 speed motor drawing 50 amps on high and a PWM motor drawing 50 amps on high will run the same length of time on the same battery.
Just like a 5 speed motor drawing 5 amps speed one and a PWM motor on Speed 10 drawing 5 amps will also run the same length of time on the same battery.
Both PWM and 5 speed motors will give different run times, on the same battery, at different speeds. That is fact. They just reduce voltage to the armature in different ways.
Not true. 12 volts to a 1 ohm load will produce 12 amps of current. 144 watts of power. 6 volts to a 1 ohm load will produce 6 amps of current. 36 watts of power. Lower voltage lower current and power. Ohms Law.
Everything you said here is true. With PWM, you don't lose efficiency at lower speeds, like you do with a pot or resistors. One thing I didn't see or missed in all the above is that on PWM, frequency has very little to do with it. It's a square wave, with the "on" time duration determining the total power available. As the PWM indicates, it's pulse width modulation, not pulse frequency modulation.
I never said a 5 speed motor was more efficient then PWM. I am just trying to point out that they are not a inefficient as others make them out to be. I like PWM because you get "full" voltage, and torque, to the armature all the time. You can keep a prop from turning on speed one on a 5 speed motor with your hand cause it is seeing about 3 volts and has little torque. At a slow speed on a PWM the armature is seeing 12 volts. Just not for a 100% on time. I would bet you cannot keep it from turning.
Totally incorrect.
Ohms is a measure of resistance, not "load." Ohms measure how much resistance a wire or component has to the flow of electricity.
Watts is a measure of how much energy it takes to make something do work, or "load."
12 volts to a 120 watt motor will draw 10 amps. 6 volts to that same 120 amps will draw 20 amps.
An Ohm measurement has no place in the calculation.
2015 Yellowfin 21 with 2014 Yamaha SHO 250
A motor is not a resistor. I will make a statement that you could pay attention to: "An electric motor draws maximum current at start". Just like a transformer, until the windings start to function, it is a direct short. Want to fry some wiring? Lock the rotor and turn it on, on High. UNDER LOAD, the slower it runs the more current it uses.
The faster it goes the more C E M F it develops and it draws less, with the voltage constant.
If you close off the hose on a vacuum cleaner what happens? It speeds up, and actually draws less current. I know, a trolling motor is not a vacuum cleaner, they are too heavy for the wife to lug around anyhow.
Some like Ohms Law, my daughter likes coleslaw.
With a 5 speed, ohms has everything to do with current draw. The resister chosen whether a switched one, or a pot, limits the current draw wired in series. And when you add the total impedance of the motor and electronics, total draw is even less. The impedance of the motor will vary with rpm and load, but it still adds resistance to current flow, meaning total amps will be less than a resistor only. ( a motor at low speeds has very little resistance in the wiring, but at it's rpm's increase, the reactance from the coils start limiting the current flow.)
And that's called C E M F, counter electromotive force.
Well I'm by far an expert on anything I'm just a user, but I know that I was told supposedly by design per an "Engineer" at Mercury for MotorGuide told me that trolling motors are not to be ran on constant speed. They are for intermittent use only. I called them to find out why my MotorGuide 36v 5 speed trolling motor current draw on high was right at 45 amps. The wiring on the trolling motor side was 10 gauge stranded including the wire going down the in the shaft good for 30 amps. I experienced a wire melt down from the plug and up into the head of the trolling motor one day when we decided to change locations and thought that we'd put some use on the batteries. The wiring started smoking after running for awhile which almost created a fire. The main purpose of my call was to find out why they used 10 gauge (too small of wire) for the actual current draw I was seeing on the trolling motor. Also then I questioned him if the trolling motor was designed for intermittent use only then why did they put a constant speed switch on these trolling motors. Well needless to say the conservation ended shortly after that with no answer except they're built for intermittent use only. But I believe they used too small of wire for that trolling motor per the amp draw I was seeing on high speed. The 4th speed was right at 30 amps. So never used high speed after that for any prolonged run time.
2019 Bass Cat Eyra
Mercury 250 Pro SX
4 Stroke 2B591496
You're right on AC power as voltage is increased the current load decreases. That's why all of the transmission voltages are increased so the wire size is decreased to carry the load a long distance. So if that wasn't the case can you visualize just how big of a cable that would be required to carry the load from the generator to your substation to your city or home. That's why we have substations and transformers to drop the voltage to a usable level for your home.
2019 Bass Cat Eyra
Mercury 250 Pro SX
4 Stroke 2B591496
True on almost all trolling motors. Running them at full speed for prolonged periods will find any weak links in the wiring AT the motor (not the boat usually) and that is usually the quick disconnect spade connections right at the top of the shaft. The main wiring is not able to carry the load according to the safe data sheet, but if it was any bigger it would be too cumbersome.
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