How the PWM can save you more current when operated correctly. 

 

Thrust to Amps Ratio

This Blog deals with the actual current to thrust ratio for a 30lb electric trolling motor and will show why a PWM can save current and increase your time on the water. The following chart is based on a 30lb motor mounted on a KAYAK. The run time for each measurement was sufficient to establish the Amps-MPH average values. The Amps were tested with a meter, the MPH with a GPS and the battery used was a 12Vdc 75Ah lead acid.

Motor Amp vs MPH chart
Control Amps MPH Calculated MPH @ 30Amps full power

1 7.2 1.6 A/MPH = 7.2/1.6 =4.5Amp per MPH =30/4.5= 6.67MPH

2 9.3 2.0 A/MPH= 9.3/2.0 =4.65Amp per MPH 30/4.65= 6.45MPH

3 12.5 2.4 A/MPH=12.4/2.4=5.2Amp per MPH 30/5.2= 5.76 MPH

4 15.3 2.8 A/MPH=15.3/2.8=5.46Amp per MPH 30/5.46= 5.49 MPH

5 29.8 3.5 A/MPH=30/3.5=8.57Amp per MPH 30/8.57= 3.5 MPH

The chart shows a clear picture of what happens as the current is increased in your motor. In position (1) the motor draws 7.2 Amps and yields a speed of 1.6 MPH, the math shows that you get 1MPH for every 4.5 Amps you burn, or you should get a top speed of 30Amps/4.5Amps = 6.67 MPH when your motor draws 30 Amps.

So far so good.

The other positions (2), (3), and (4), show a very similar linear trend in Amps per MPH. The idea that you get a 1 to 1 relationship between Amps – Thrust is totally destroyed in the last 2 positions (4),(5) MPH.

Position (4) shows that you get 2.8 MPH drawing 15.3 Amps. If there is a 1 to 1 relationship, then if you double the Amps from 15 to 30Amps your speed should double also from 2.8 MPH to 5.6 MPH.

If the 1 to 1 relationship were to actually exist then when you add the Amps and MPH from position (4) you would get a higher MPH.

At 15.3 Amps you get 2.8 MPH and, adding 1 MPH to get 3.8 MPH requires only 5.46 Amps, that totals (15.3A+5.46A = 20.70 Amps), you have 30.00 Amps – 20.70 = 9.24 amps left.

Lets add 1 more MPH and that requires we add another 5.46 Amps.

The MPH goes from 3.8 to 4.8 MPH and the Amps used goes from 20.70 + 5.46 = 26.16Amps. You now have 30.00-26.16 = 3.84 Amps left. If we draw the full 30Amps we should be at (3.85/5.46 = .705 MPH ), add 4.8Mph to .705 MPH and you get 5.5MPH.

The tests show that in position (5) you are only doing 3.5MPH not 5.5MPH, like the 1 to 1 ratio indicated. So what happened to to all the extra Amps you had. The truth is they are wasted as heat in the armature of your motor.

They contribute to slow deterioration and fatigue of your motor, they are slowly wearing out your motor and you are going no-where fast. The power wasted in your motor will never translate to thrust output from your prop.

But wait! You say, I bought a 30lb thrust motor and it draws 30 Amps, why don’t I get my full 30lbs of thrust.

You do get your full 30lbs of thrust, it just happens before you draw 30Amps of current from your battery.

It all comes down to this: the characteristics of a Shunt Wound DC Motor has what I like to call the 80% / 80% factor. The motor is very efficient at the 50% current level, 15Amps yields about 80% of your thrust.

If you have a 30lb thrust motor then you get about 24lbs of thrust when you draw 15Amps of current.

• 30lbs thrust x .8 = 24lbs of thrust. Now you have 15Amps left and 6lbs of thrust left.
• Take ½ the current left (7.5Amps).
• Now add the 15Amps to the 7.5Amps for a total of 22.5Amps.
• Now take 80% of the remaining 6lbs of thrust (6 x.8)=and you get 4.8 lbs of thrust.
• Add 24lbs of thrust to the 4.8lbs of thrust you get 28.8lbs of thrust.
• You now have 7.5Amps remaining and 30lbs-28.8lbs = 1.2lbs thrust left.

Here you have a choice, waste 7.5 Amps of current to get 1.2lb of thrust, or back off the throttle and save the 7.5Amps for a longer stay on the water, you decide.

Now you know why you need a PWM for your motor. One you set your motor to position #5 and the PWM will give you 0-100% power in precise settings and two you will save about 25% of your current if you just back off the throttle a bit. The readout of you LCD controller or the read out of the voltage/current meter installed in your battery case will help you monitor your settings. We have given you two very important tools to operate your trolling motor. The PWM and the voltage/current readings. Kind of like having a speed odometer and a gas gauge all in one. So now you know “How the PWM can save you more current when operated correctly”.

Thanks and happy fishing, kayaking, or just casual boating, but do it with a WTP PWM.

http://www.wirelesstrollingpro.com/

My next blog will deal with the performance and cost of PWM's used in trolling motors vs the low cost high current units found on Ebay. If you are a DIY'er you will love this one.

Blog-PWM-1

8 June 2015

Wireless Trolling Pro

PWM For Your Electric Trolling Motors

Why would you own one?

Aside from the cool aspect of just having one, there is a very real, practical side for owning one. The number one reason is the ability to vary the speed of you boat. The second is the ability to save current from being wasted, when varying the speed of you motor.

Most motors come with 5 forward and 3 reverse speed settings. This method is very inefficient and results in wasted battery current. So much so, as to be as high as 5 times more current wasted at the low speed (1), then when compared to the current required at the same speed when using a PWM. That is a 5 to 1 ratio, you can fish for 1 hour or for 5 hours, pick one.

OK, so how does my PWM work?

It is easier to explain when

1. We pick a motor and battery combination. Lets say we purchased a 30lb thrust, trolling motor and 12Vdc 100 AH-Battery (100 amp hour battery). The electrical specifications are 12Vdc and the motor uses 30 amps, at the forward full speed position # (5).
   
   
2. The second thing is the PWM you purchased has a variable speed knob on/off, idle/run and a forward/reverse switch.

Here is the real beauty of the setup.

To operate the system after installing the PWM, Battery, and Motor you simply set the motor switch to full speed in the forward position #5, where you get 0-100% speed control , On/Off, Idle/Run, Fwd and Rev, all in a one hand held controller.

Speed Control

When you vary the speed control from 0 to 100% , you are just dividing the batteries 12Vdc into small portions of the total 12 volts. The PWM output goes from 0Vdc to 12Vdc, thus varying your motor speed from 0 to 100%.

So, just how do they divide up the 12Vdc and how small are the steps from 0 to 100% speed.

How does the speed control work?

The electronics in your PWM has the ability to convert the pot position setting by using a device called an ADC (Analog to Digital Converter) to divide the 12Vdc into 128, 256 or 1024 different values.

WTP uses the 256 value. It is simply the % ratio of pot setting to the 256 value. Lets say you turn the pot to 1/3 position. The PWM battery output is 85/256 = .333 x 12Vdc and that = 4Vdc applied to your motor. If you set the pot to ½ position then the output is 128/256 = .5 x 12Vdc and that is 6Vdc applied to your motor, if you set the pot to the full on position then the output is 256/256 = 1x12Vdc and that is 12Vdc applied to your motor.

Now you know why you should own one. It is this ability of the PWM to control your motor speed 0 to 100%, that gives you the increase in motor running time from 1 hour to 5 hours.

My next blog will deal with the Amps to thrust having a 1 to 1 ratio in performance.

How the PWM can save you more current when operated correctly.

Misconceptions:

The concept of 1-lb thrust = requires 1 amp of current or 1 amp current = 1 lb of thrust.

The power ratio of voltage to current (E x I) does not translate to a 1 to 1 ratio of prop rotation and current to thrust ratio.

Simply put the power consumed by the motor does not translate to the prop rotation on a 1 to 1 scale.

Thanks and happy fishing, kayaking, or just casual boating, but do it with a WTP PWM.

http://www.wirelesstrollingpro.com

Date Friday 5 2015

                              WTP Cable Controller's and PWM's for Electric Trolling Motors.

This is a new Controller (Cable) for all WTP PWM products. The controller is an automatic Fwd/Rev with a center off position. Turn the pot to the right and the motor goes into Idle, then into the Forward position with speed control from 0-100%. To go into Reverse simple turn the pot to the left and the controller goes from Off to Idle into the Rev mode automatically. Models start at 30lb, for as low as $69.95

This is a new Controller (Cable) for all WTP PWM products. The controller is a fisherman's dream. The controller has On/Off switch located in the pot. The 2 switches provide ideal control for all fishing requirements or just a casual outing. The unit has soft start in all modes. The soft start allows the angle to move at a fixed speed then go from Run to Idle, then glide for a bit then switch  from  Idle to Run, and the computer returns you to the exact same speed you left. You can go from Fwd to Rev or Rev to Fwd with a very smooth transition with the soft start system.  Models start at 30lb for as low as $79.95

This is a new LCD Controller (Cable) for all WTP PWM products. The controller has all the operating modes for one hand  operation at the push of a button. The display shows throttle setting 0-100% power, Motor current draw under load, Operating mode (Idle Fwd Rev) and Battery voltage under all operational settings, i.e. no load to full load. Now you have full control of you motor. Every operating mode has soft start motor control. This means no motor kick or bucking from large current surges when going from Run to Idle, Idle to Run, Fwd to Rev, Rev to Fwd, at any throttle speed.
Models start at 30lb's for as low as $109.95


For full product listing and specifications please visit WTP
http://www.wirelesstrollingpro.com/