Lithium Trolling Motor Question

[saskguy]

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?

 

[CB-OTB]

you need a battery capable of supplying a 50A load. So it’s maximum discharge current needs to be 50A or more. Sometimes that is expressed in something like 1C or 2C. Which is 1 or 2 times the AH rating. If both of your batteries are rated 1C that should be fine, just don’t run the 50ah at wide open for extended periods.

 

[BobR]

Lead acid batteries do not hold there voltage as high as LifePo4 batteries do, through their useful state of charge, therefore your batteries will be delivering a higher voltage than lead acid batteries would be delivering. They are telling you to not run your trolling motor at 100% capacity because of heat buildup.

More voltage = more heat.

This statement (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.") is about amp draw.
If you try to pull more amps from a lifepo4 battery than the 'bms' will allow it will shut down to protect the battery.

Some batteries can supply higher amps than their AH rating expressed as their C rating.

If you run your trolling motor at less than 100% power you will be drawing less than its full rated 50 amps.

You can read here about batteries C ratings: https://www.power-sonic.com/blog/what-is-a-battery-c-rating/

 

[BobR]

From the Renogy site on your battery: "【High Discharging Performance】 The battery provides a maximum of 50Ah continuous discharge current to power most home appliances. The superior lithium-iron-phosphate technology ensures stable battery capacity and performance even under extreme temperatures from -4℉ (-20℃) to 140℉ (60℃)."

Your back up battery will work fine; lower motor speed means lower amp draw = longer run time.

 

[Zwy]

More voltage = more heat.

More amps = more heat

Not voltage........

 

[BobR]

More amps = more heat

Not voltage........

The higher voltage pushes more what; through the motor? Higher voltage pushes more current (amps) through the motor therefore running a higher voltage, to a motor designed for lead acid not lifepo4 which delivers a higher voltage than lead acid, raises the running temperature of the motor.

That is why MinnKota advises to only run their trolling motors at 85% power
for an extended period when using LifePo4 batteries.

 

[CB-OTB]

The higher voltage pushes more what; through the motor?

bunnies!

 

[saskguy]

Thank you so much for the replies! Good to know the 50ah back up battery will work as well. Just wondering, is there anyway to mitigate the risk of damaging the motor while running at 100% power for more than 10-15 minutes? I saw on another thread there was talk of using some sort of a regulator to reduce the voltage, may have been called a PWD?

 

[CB-OTB]

if this is anything like the motor on my dinghy, there‘s no reason to go full power. If you can‘t get on plane you are burning through exponentially more power to go marginally faster. you could incorporate some kind of limiter, but you could also just pull back the throttle a little.

 

[BobR]

if this is anything like the motor on my dinghy, there‘s no reason to go full power. If you can‘t get on plane you are burning through exponentially more power to go marginally faster. you could incorporate some kind of limiter, but you could also just pull back the throttle a little.

Thank you so much for the replies! Good to know the 50ah back up battery will work as well. Just wondering, is there anyway to mitigate the risk of damaging the motor while running at 100% power for more than 10-15 minutes? I saw on another thread there was talk of using some sort of a regulator to reduce the voltage, may have been called a PWD?

I believe your motor is an infinite variable speed motor. If I am correct then your motor is already controlled with a PWM. Adding another PWM would not help. I don't believe running your motor at 100% for short periods of time will hurt it; but I don't think you'll see much more speed increase from 85%-100%.

 

[BobR]

if this is anything like the motor on my dinghy, there‘s no reason to go full power. If you can‘t get on plane you are burning through exponentially more power to go marginally faster. you could incorporate some kind of limiter, but you could also just pull back the throttle a little.

What motor do you have? The trolling motors I have used will only push the boat 4-5 mph.

 

[CB-OTB]

What motor do you have? The trolling motors I have used will only push the boat 4-5 mph.

Mine is a 2.5hp Suzuki. 1/3 throttle will get you to 5-6mph. full throttle might get you to 7, maybe 8, but it’s a lot noisier and sucks down way more gas. I’m looking to switch this motor to an electric one sometime this year.

 

[Zwy]

The higher voltage pushes more what; through the motor? Higher voltage pushes more current (amps) through the motor therefore running a higher voltage, to a motor designed for lead acid not lifepo4 which delivers a higher voltage than lead acid, raises the running temperature of the motor.

That is why MinnKota advises to only run their trolling motors at 85% power
for an extended period when using LifePo4 batteries.

Simply not true, watts are what make horsepower. If you increase voltage, the motor uses less amps for a given load.

As voltage increases, the motor will not run at a higher temp.

Let's compare 12V battery voltages of FLA, AGM to LFP. FLA is charged at 13.8V to 14.4V, AGM is 14.6V to 14.8V. LFP is max of 14.6V. Resting, fully charged voltages are 12.6V for FLA, AGM 12.7V to 13.0V, LFP is 13.6V

0.6V will not harm that motor. For a 24V system, it would be 1.2V, 48V system would be 2.4V. None of these will hurt a DC rated motor.


Now companies like Minn Kota might be using inferior electronics (steering control, PWM for speed control, etc) that aren't truly designed for 48V systems, any electronics used on a 48V system should be rated for 60V. If this is the case, they most likely are using 36V rated components on 48V to maximize profit. PWM used for speed control requires switching, the higher the frequency, the more heat generated at the PWM controller as the "rest" period in between pulses will be shorter. However, if the unit is designed to run at full battery voltage for FLA or AGM, the controller should be able to handle it, although there is some voltage sag to FLA and AGM. Properly rated components however would handle the LFP that doesn't have inherent sag.

Many have been using LFP for years now. General consensus is that it is just a wives tale.

Minn Kota needs to step up their game if they want to compete as the trend will be more and more LFP usage for trolling motors if they are using components not properly rated.

 

[Zwy]

Mine is a 2.5hp Suzuki. 1/3 throttle will get you to 5-6mph. full throttle might get you to 7, maybe 8, but it’s a lot noisier and sucks down way more gas. I’m looking to switch this motor to an electric one sometime this year.

Change the prop if you want more speed at less rpm.

I run my kicker at idle most of the time. While I do use my electric trolling motor quite a bit, I wouldn't give up my kicker either.

 

[BobR]

Simply not true, watts are what make horsepower. If you increase voltage, the motor uses less amps for a given load.

As voltage increases, the motor will not run at a higher temp.

Let's compare 12V battery voltages of FLA, AGM to LFP. FLA is charged at 13.8V to 14.4V, AGM is 14.6V to 14.8V. LFP is max of 14.6V. Resting, fully charged voltages are 12.6V for FLA, AGM 12.7V to 13.0V, LFP is 13.6V

0.6V will not harm that motor. For a 24V system, it would be 1.2V, 48V system would be 2.4V. None of these will hurt a DC rated motor.


Now companies like Minn Kota might be using inferior electronics (steering control, PWM for speed control, etc) that aren't truly designed for 48V systems, any electronics used on a 48V system should be rated for 60V. If this is the case, they most likely are using 36V rated components on 48V to maximize profit. PWM used for speed control requires switching, the higher the frequency, the more heat generated at the PWM controller as the "rest" period in between pulses will be shorter. However, if the unit is designed to run at full battery voltage for FLA or AGM, the controller should be able to handle it, although there is some voltage sag to FLA and AGM. Properly rated components however would handle the LFP that doesn't have inherent sag.

Many have been using LFP for years now. General consensus is that it is just a wives tale.

Minn Kota needs to step up their game if they want to compete as the trend will be more and more LFP usage for trolling motors if they are using components not properly rated.

"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."

"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."

 

[BobR]

We can get all technical here; but the answer to the original post is that he will be fine with his batteries as long as he doesn't constantly run at 100% of the voltage available from his LifePo4 power supply.

 

[saskguy]

Very good education to read these posts. Another question please, on my old wet acid batteries I would sometimes run them down close to 0, by that I mean I could feel the thrust dropping at the end of the day and once or twice I ran them until the would not longer provide any noticeable thrust. I always presumed I had completely depleted the battery but now it seems I had used 50% of the battery since that is apparently how these wet cell batteries work. With a lithium can I use it until it stops or will that ruin the battery? I have seen conflicting information, some say that a lithium will provide full power until it is 100% depleted which is why it gives twice the longevity than a traditional one. Others say you should not go below 20% or it will be damaged?

 

[BobR]

Very good education to read these posts. Another question please, on my old wet acid batteries I would sometimes run them down close to 0, by that I mean I could feel the thrust dropping at the end of the day and once or twice I ran them until the would not longer provide any noticeable thrust. I always presumed I had completely depleted the battery but now it seems I had used 50% of the battery since that is apparently how these wet cell batteries work. With a lithium can I use it until it stops or will that ruin the battery? I have seen conflicting information, some say that a lithium will provide full power until it is 100% depleted which is why it gives twice the longevity than a traditional one. Others say you should not go below 20% or it will be damaged?

There may be other opinions here but running your battery down until the BMS cuts the battery off will not really damage the battery; that is why Lifepo4 batteries have a BMS. It may shorten the life of the battery some but unless you are doing it very often I personally wouldn't worry about it

 

[saskguy]

Thank you BobR.

 

[BobR]

Here is my 55lb MinnKota trolling motor it is now built into the keel of my solar dinghy.
Two 45 ah b12v batteries.

 

[CB-OTB]

You steer with the paddles, or do you have a rudder hanging off the back?

 

[BobR]

You steer with the paddles, or do you have a rudder hanging off the back?

Rudder

 

[saskguy]

Very interesting, is this a work in project still or have you had it out on the water? Also why go with two 45ah batteries instead of one 100ah?

 

[wholybee]

Very good education to read these posts. Another question please, on my old wet acid batteries I would sometimes run them down close to 0, by that I mean I could feel the thrust dropping at the end of the day and once or twice I ran them until the would not longer provide any noticeable thrust. I always presumed I had completely depleted the battery but now it seems I had used 50% of the battery since that is apparently how these wet cell batteries work. With a lithium can I use it until it stops or will that ruin the battery? I have seen conflicting information, some say that a lithium will provide full power until it is 100% depleted which is why it gives twice the longevity than a traditional one. Others say you should not go below 20% or it will be damaged?

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.

 

[BobR]

Very interesting, is this a work in project still or have you had it out on the water? Also why go with two 45ah batteries instead of one 100ah?

Still in progress. I am going to fiberglass the inside today; the outside is already glassed. Then it will get a small forward deck that will hold a 50 watt pv panel. Should be ready for sea trials (pond) as soon as it is warm enough.