Lithium Trolling Motor Question

[Zwy]

"An assumption people often make is that since low voltage increases the amperage draw on motors, then high voltage must reduce the amperage draw and heating of the motor. This is not the case. High voltage on a motor tends to push the magnetic portion of the motor into saturation. This causes the motor to draw excessive current in an effort to magnetize the iron beyond the point where magnetizing is practical."

We are referring to a 0.6V increase in voltage for a 12V nominal system, 1.2V for a 24V nominal system, not running say a 12V nominal motor on 24V or a 24V nominal motor on 48V.

Attempts to "win" an argument by cherry picking out of context is not the answer.

"The current a motor will see, is directly related to the load. As the load of a motor increases the amount of current also increases. Current is what contributes to heat. As current increases the heat built up in the motor also increases."

This is correct and what I referred to, you finally admit you were wrong to begin with. Go back and read what I posted, the words "watts are what make horsepower. If you increase voltage, the motor uses less amps for a given load."

The trolling motor will use X number of watts to propel the boat for the given load whether it has a FLA, AGM or LFP battery.

 

[BobR]

Hello - For the past 20 years I have been using a 40lb thrust Minn Kota trolling motor as the main thrust for a small inflatable boat used for fishing. I always used a traditional wet acid battery however am finally upgrading to:

- Minn Kota Traxis 50 or 55lb thrust motor
- Renogy 12V 50 Ah & 100Ah LiFePO4 Lithium Iron Phosphate Battery Deep Cycle https://ca.renogy.com/100ah-12-volt-smart-lithium-iron-phosphate-battery/

The reason I bought two batteries is due to a 40% sale by Renogy so i bought the 100ah as the main trolling battery and the 50ah one solely as a backup. However I am trying to understand this statement by Minn Kota:

""Minn Kota trolling motors can run on Lithium Ion batteries. However, they are specifically designed to run on traditional lead acid batteries (flooded, AGM or GEL). Lithium Ion batteries maintain higher voltages for longer periods of time than lead acid. Therefore, running a Minn Kota trolling motor at speeds higher than 85% for a prolonged period could cause permanent damage to the motor. The LiFePO4 Lithium batteries can be used with our motor. LiFePO4 batteries that have a maximum continuous output current ratings need to be higher than the maximum current ratings of the trolling motor or the battery will turn off."

When I asked for clarification on this statement they replied:

What our statement is referring to is if the battery lists a maximum current rating, meaning the maximum load in amps they allow on the battery, that must be less than the maximum amp draw of our motor.

I am still confused, according the chart below by Minn Kota the 50/55lb thrust motor both have a maximum 50 amp draw. Are all they trying to say is the ah rating on the battery should be higher than the motor? So a 100 ah battery should be fine with the 50/55lb motor but how about the 50 ah battery which is the same rating as the battery?



View attachment 89410

This is from the Newport Vessels web site. "Similar to all other trolling motor brands, we also advise against using lithium batteries with our products. Lithium batteries tend to run at a higher voltage for longer durations (14-16V) than Lead-Acid batteries (13V). Trolling motors are designed to be used with batteries that output around 13V at most and then primarily 12V. Using a higher voltage can put wear and tear on the motor and potentially damage some of the internal components and ruin your motor"

 

[wholybee]

Question. If a higher voltage is applied to a motor, does the work the motor does increase? Will the motor turn faster?
I'm not sure a statement saying that as the voltage goes up, the amps goes down is entirely correct. Yes, it is correct if the same amount of *work* is done. Work is the important factor, as Watt-hour is a unit of work. But one would presume that increasing voltage increases the speed of the motor, and thus the work performed. (the boat will travel more distance in the same amount of time) So with increased work (more watts are used in the same amount of time), Amps would at least need to remain the same, if not increase. If the resistive load of the motor is the same, amps will increase if voltage is increased. (I do understand that a motor is not a purely resistive load).

I am disregarding how the PWM controller will react. If you increase voltage, but the PWM controller regulates the pulse width such that a specific RPM is maintained at the higher voltage, then the work performed will be the same, and current would decrease. But I don't think the controller in these motors is that sophisticated. I suspect the throttle simply varies the pulse width between min and max values without regard to power or RPM. So, an increase of voltage will not change the pulse width, the RPM of the motor will increase, and the work performed by the motor will increase. The increased work will result in higher motor temps.

Am I wrong?

Also, the manufactures statement to not run at max throttle supports this, to limit the power output of the motor to what it would be with a LA battery. Ultimately though, I suspect the manufacture just hasn't tested LFP batteries thoroughly enough to officially guarantee them. If this motor is the type where the motor is submerged, it should have more than adequate cooling to use LFP.

 

[Zwy]

If you take a 12V motor and run it on 24V, it will draw the same amperage as 12V, thus the wattage doubles. However, the speed of the motor will double as the amount of work being performed is at twice the speed.

Thus, if you ran a 12V motor on 24V with variable speed control (PWM), you would actually draw 1/2 the amps to perform the same amount of work at the same speed.

I know this for a fact as I've tested motors rated for 12/24V for both amperage and speed plus hp.

It takes X number of watts to do X amount of work.

 

[Zwy]

This is from the Newport Vessels web site. "Similar to all other trolling motor brands, we also advise against using lithium batteries with our products. Lithium batteries tend to run at a higher voltage for longer durations (14-16V) than Lead-Acid batteries (13V). Trolling motors are designed to be used with batteries that output around 13V at most and then primarily 12V. Using a higher voltage can put wear and tear on the motor and potentially damage some of the internal components and ruin your motor"

Truly laughable, right off their website: https://newportvessels.com/collecti...products/epropulsion-e-series-lithium-battery

"You can run LFP but only if you buy it from Newport Vessels. "

But wait there is more, https://newportvessels.com/products...m-battery-lifepo4?_pos=1&_sid=eea1db661&_ss=r

Charger is set for 14.6V, hmmmmmmmm......... 3.65V X 4 = 14.6V

Then, we look at the Owner's manual and the open circuit voltage, I wonder if it just happens to be 14.6V?

Sure enough page 1. https://cdn.shopify.com/s/files/1/0219/0154/files/BLF-1280AS_User_Manual_rev_04_23_2019.pdf?209

Bring on some more Bob.

 

[saskguy]

Drop in batteries have a BMS that will turn off the battery before it is damaged. So, in effect, you can run it to zero (the point at which it stops)
You will slightly reduce the life of the battery if you do this every time you go out, but it will still last longer than a Lead Acid Battery. The advise to not go below 20% is to get the most life out of the battery. It is also a bit conservative, 5%-10% is enough.

If you do run it until it stops, you won't likely get a warning. LFP batteries hold voltage very well until they are nearly depleted, so you may not notice the motor getting slower. It will just stop. Or, you might notice it getting slower, but it will be subtle, and it will stop very quickly after that. If this happens, you do want to get it on a charger as quickly as possible, because while taking it down that low shouldn't damage it, letting it sit at that low level can.

The bonus is that you will probably get 2x the run time from a 100Ah LFP than from a 100Ah Lead. So, if the Lead was large enough for a typical outing, then you won't likely ever run it down.

Sorry if I can just clarify this please. How do you know how much battery power you have left? I have never had a meter with my old lead acid battery and just went by feel, once I lost that "zip" from speed 1 to 5 I knew it was dropping and headed for shore. Since I am likely to use more power on higher speeds to get from point a to point b how do I know I am down 25 or 50%? I have not used the Traxis yet, do I rely on that to show the power remaining of buy some sort of a meter?

 

[Zwy]

Use a shunt like this: https://www.amazon.com/gp/product/B0824X5MKM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[wholybee]

Sorry if I can just clarify this please. How do you know how much battery power you have left? I have never had a meter with my old lead acid battery and just went by feel, once I lost that "zip" from speed 1 to 5 I knew it was dropping and headed for shore. Since I am likely to use more power on higher speeds to get from point a to point b how do I know I am down 25 or 50%? I have not used the Traxis yet, do I rely on that to show the power remaining of buy some sort of a meter?

Before you buy a battery, check that it is one that has Bluetooth. That is the easiest way, then you have an app on your phone that tells you the battery charge left, how many Amps you are using, etc.

If you already have a battery that doesn't have bluetooth, you will need to buy a meter with a shunt, like recommended above. I strongly prefer and recommend the victron meters/shunts, but they are quite expensive and the cheap one linked to should work fine.

 

[saskguy]

Sorry one more question on this thread if I may. I am told you have to be more careful with lithium batteries and keeping them level, not tipping them or shaking too much. I was planning on keeping my back up battery at the front of my boat which on my inflatable is on an angle. How much of a concern would this be?

 

[BobR]

Sorry one more question on this thread if I may. I am told you have to be more careful with lithium batteries and keeping them level, not tipping them or shaking too much. I was planning on keeping my back up battery at the front of my boat which on my inflatable is on an angle. How much of a concern would this be?

Tilting some will not be a problem a lot of people lay them on edge; it's not recommended but has been done. the shaking on your inflatable will not be a problem the problem is in rough seas and falling off of waves etc.