Lifepo4 trolling motor help

[V8hunter99]

Someone please help-
I purchased 2 Power Sonic PSL-12450 Lifepo4
They are rated 45Ah 25a draw each
I have them ran in parallel to get 90ah and 50a draw
My trolling motor is Minn Kota 55 lb thrust
50a draw
It will run all day up to speed 3
On speed 4 and 5 the batteries cut off and then reset a minute later only to run at a lower speed.
What am I doing wrong?

 

[snoobler]

Welcome to the forum.

The motor: 50A is not the max. It's a maximum continuous rating. Motors have a surge, and as the boat is accelerating, the current is likely higher than 50A, but once you get to a steady-state top speed, it's probably pretty close to 50A.

It's likely that your load is not being shared equally between the two batteries, and one of them is experiencing a sustained current in excess of the battery's rating. When paralleling batteries, you can't count on a perfectly shared load.

Are you attaching the motor to the (+) of one battery and the (-) of the other, or are you attaching both to the same battery?

 

[Bob B]

You need to have a meter to be able to measure the actual current draw. Also, if you have a bad connection or undersized wire, the voltage to the motor will drop .... which will actually cause it to drop more current.
Your setup is right up against the spec for the batteries, which is never a good thing.

You may need to add a third battery in parallel. Also, wiring as Snoobler suggested will help balance the current in case on battery is seeing more draw than the other.

 

[V8hunter99]

Welcome to the forum.

The motor: 50A is not the max. It's a maximum continuous rating. Motors have a surge, and as the boat is accelerating, the current is likely higher than 50A, but once you get to a steady-state top speed, it's probably pretty close to 50A.

It's likely that your load is not being shared equally between the two batteries, and one of them is experiencing a sustained current in excess of the battery's rating. When paralleling batteries, you can't count on a perfectly shared load.

Are you attaching the motor to the (+) of one battery and the (-) of the other, or are you attaching both to the same battery?

Positive to one battery, negative to the second battery, also strange is it will run full speed out of the water but not under load in the water, so it’s tough to troubleshoot

 

[snoobler]

Positive to one battery, negative to the second battery, also strange is it will run full speed out of the water but not under load in the water, so it’s tough to troubleshoot

Not strange at all. There's no load on the prop when not in the water. Takes almost no current to spin it at max speed. Current is way less than 50A.

Since you've correctly placed your cables, it's like a matter of the batteries not sharing the load evenly as I mentioned above, and the one that's taking more of the load is cutting out, which causes the other battery to take all the load and then cut out.

Worth checking that all your connections are properly torqued.

Realistically, it's always a good idea to give yourself a margin - say 10%. Yes, you capacity is doubled, but your peak current isn't unless they're perfectly balanced, and that's almost impossible. 2X 25A capable batteries are capable of something closer to 45A.

 

[V8hunter99]

I’m going to check the amp draw while

Not strange at all. There's no load on the prop when not in the water. Takes almost no current to spin it at max speed. Current is way less than 50A.

Since you've correctly placed your cables, it's like a matter of the batteries not sharing the load evenly as I mentioned above, and the one that's taking more of the load is cutting out, which causes the other battery to take all the load and then cut out.

Worth checking that all your connections are properly torqued.

Realistically, it's always a good idea to give yourself a margin - say 10%. Yes, you capacity is doubled, but your peak current isn't unless they're perfectly balanced, and that's almost impossible. 2X 25A capable batteries are capable of something closer to 45A

 

[V8hunter99]

Not strange at all. There's no load on the prop when not in the water. Takes almost no current to spin it at max speed. Current is way less than 50A.

Since you've correctly placed your cables, it's like a matter of the batteries not sharing the load evenly as I mentioned above, and the one that's taking more of the load is cutting out, which causes the other battery to take all the load and then cut out.

Worth checking that all your connections are properly torqued.

Realistically, it's always a good idea to give yourself a margin - say 10%. Yes, you capacity is doubled, but your peak current isn't unless they're perfectly balanced, and that's almost impossible. 2X 25A capable batteries are capable of something closer to 45A.

I’m going to check the amp draw while in a water bucket. I really appreciate everyone’s help

 

[Bob B]

I’m going to check the amp draw while in a water bucket. I really appreciate everyone’s help

Sorry, but that won't be an accurate check. The water in a bucket will just create turbulence and not actual load.

 

[snoobler]

I’m going to check the amp draw while in a water bucket. I really appreciate everyone’s help

It would give you some indication, but it's likely not a faithful reproduction of the events causing failure. Being in open water, new water can advance to take it's place, and there's the inertial resistance of the boat. These act to counter the trolling motor and increase load.

The bucket is basically just a blender.

 

[V8hunter99]

Any ideas what I can do

Sorry, but that won't be an accurate check. The water in a bucket will just create turbulence and not actual load.

 

[Bob B]

Test the amps under normal operation on the water. Strongly consider adding another battery in parallel.

 

[snoobler]

3rd battery is likely the solve.

 

[V8hunter99]

3rd battery is likely the solve.

Ok I’m going to look into adding a third battery, that should give me 135ah and 75 amp draw

 

[snoobler]

Ok I’m going to look into adding a third battery, that should give me 135ah and 75 amp draw

I wouldn't count on 75, but 65-70 is very likely.

 

[V8hunter99]

I wouldn't count on 75, but 65-70 is very likely.

I feel like maybe I should just sell these batteries and buy a 100ah agm battery. I don’t really have the time to do any testing and don’t really need a huge power supply adding another battery for 150-200 bucks

 

[Deleted member 9967]

My scoote

I feel like maybe I should just sell these batteries and buy a 100ah agm battery. I don’t really have the time to do any testing and don’t really need a huge power supply adding another battery for 150-200 bucks

r is rated one way but if I am on a hill stopped and try to start from there. If it is steep it will shut off because the starting current is simply too high.
Motor need a LOT of current for some things. Like speeding up. Starting from a dead stop etc etc.
So like snoobler said, you have to kind of over compensate for this a bit. But yes, one more cell ought to be enough. But you really have to test it when under a load to see how much you really need.
Hope this helps.

 

[Bob B]

I feel like maybe I should just sell these batteries and buy a 100ah agm battery. I don’t really have the time to do any testing and don’t really need a huge power supply adding another battery for 150-200 bucks

It would be shame to scrap it when you are close to having it resolved .... Once you are done fiddling with it to get it to work, you will be done fiddling with it for a long time as long as you do a good job on your wiring.

If you go to the AGM .... you will be fiddling with it over and over again.

Chalk it up to a learning experience an get r done.

 

[Solgato]

Your batteries have a BMS in them with a 25A max discharge current limit.

Yes, wiring them in Parallel will double your ah capacity at the same voltage, but it won’t double the limitations built into the BMS’s.

Each BMS will see a max discharge dependent on how batteries are balanced, meaning one may be covering more of the load than the other.

Unless I’m missing something, your batteries are likely shutting down because you are exceeding the 25A max discharge rating when using the higher speeds.

 

[Bob B]

Your batteries have a BMS in them with a 25A max discharge current limit.

Yes, wiring them in Parallel will double your ah capacity at the same voltage, but it won’t double the limitations built into the BMS’s.

Each BMS will see whatever your max discharge is independently.

Unless I’m missing something, your batteries are likely shutting down because you are exceeding the 25A max discharge rating when using the higher speeds.

When two batteries are in parallel .... depending on wiring and each batteries internal resistance .... each battery will have about 1/2 the total current.
The BMS only knows how much current is passing thru it .... so, at 40 amps total as an example .... each BMS would see 20 amps

If the batteries were in series to make a 24V pack, each would see the same current.

 

[Solgato]

When two batteries are in parallel .... depending on wiring and each batteries internal resistance .... each battery will have about 1/2 the total current.
The BMS only knows how much current is passing thru it .... so, at 40 amps total as an example .... each BMS would see 20 amps

If the batteries were in series to make a 24V pack, each would see the same current.

Yes, I edited my post to better explain my point that one battery may be doing more work than the other.

In a properly balanced system, you would expect to see both doing their equal share, but it’s not a guarantee.

You can’t just assume you’ll be able to handle a 50A load between two 25A batteries.

Some people may look at it like you can double the limit of what each battery can handle since you can double the capacity, which is obviously not true and what I was trying to get at.

Since the OP hasn’t left much margin, it’s possible one BMS is reaching its limit, shutting it down, which is in turn causing the other batteries BMS to do the same as it tries to cover the entire load, as suggested in a previous post.

 

[Bob B]

Yes, I edited my post to better explain my point that one battery may be doing more work than the other.

In a properly balanced system, you would expect to see both doing their equal share, but it’s not a guarantee.

You can’t just assume you’ll be able to handle a 50A load between two 25A batteries.

Some people may look at it like you can double the limit of what each battery can handle since you can double the capacity, which is obviously not true and what I was trying to get at.

Since the OP hasn’t left much margin, it’s possible one BMS is reaching its limit, shutting it down, which is in turn causing the other batteries BMS to do the same as it tries to cover the entire load, as suggested in a previous post.

Hence the suggestion that adding a third battery in parallel and balancing the wiring will probably solve the issue.

 

[V8hunter99]

UPDATE
I purchased a Minn Kota c2 30 pound thrust motor yesterday with a max draw of 30 amps.
The motor was bow mounted and ran great all day at all speeds with no battery shutdown. The only new issue is one of the batteries was almost dead while the other one was still full?, still wired in parallel. I guess I could just use one until it’s drained and then switch over to the other.

 

[snoobler]

UPDATE
I purchased a Minn Kota c2 30 pound thrust motor yesterday with a max draw of 30 amps.
The motor was bow mounted and ran great all day at all speeds with no battery shutdown. The only new issue is one of the batteries was almost dead while the other one was still full?, still wired in parallel. I guess I could just use one until it’s drained and then switch over to the other.

Generally not possible when properly connected. If those are actually knurled nuts that you tighten with your fingers, I recommend you replace them with hex nuts and properly torque them. If they are just covers, I recommend you properly torque the hex nuts.

 

[Bob B]

What Snoobler said .... and also make sure you have them wired like this.

 

[BobR]

Someone please help-
I purchased 2 Power Sonic PSL-12450 Lifepo4
They are rated 45Ah 25a draw each
I have them ran in parallel to get 90ah and 50a draw
My trolling motor is Minn Kota 55 lb thrust
50a draw
It will run all day up to speed 3
On speed 4 and 5 the batteries cut off and then reset a minute later only to run at a lower speed.
What am I doing wrong?

I would change the control of the trolling motor to a pwm controller. Minn Kota suggests that that when running with a LifePo4 battery to only run the motor at 65% for extended periods. Lifepo4 batteries provide a higher voltage than the trolling motor is designed for.