Trolling motor current draw at rest

[jloo283]

I'm talking about the Minkotta Maxxum 80lb. Recently, it's been loosing thrust quicker than usual. I used to be able to run all day without a drop in thrust, but recently it'll start weakening after a few hours.

My group 27 led-acid batteries are only 22 months old. Load test at Kragen's came back good so I inspected all wirings and connectors. Nothing unusual to speak of but I cleaned them anyways. Then the trip on Sunday evening lasted about 2hrs in the wind, running at 65%.

Just out of curiosity, I checked current draw at rest, with the switch in OFF and MOM positions as well as unplugged. The results are as follow.

Unplugged: 0mA
Plugged in, in OFF position: approx 17mA
Plugged in, in MOM position: approx 68 mA

These newer digital motors use PWM control circuity so I suspect it requires some amount of current to operate in MOM. What bothers me is the 17mA draw when the rocker switch is completely OFF while the motor is plugged in. I don't get it. Despite the fact that it's very little, it bothers me.

I need some input from some of you guys who are mechanics or who may have done such measurements. Are these figures normal and acceptable? Do you suspect a short of some sort somewhere?

The fact that the motor starts out strong leads me to believe it's battery issue, despite the good load test. I'll be testing with new batteries soon.

The take away is, be aware that your trolling motor constantly draws current at all times so keep your on-board chargers plugged in. Battery load test didn't appear to be reliable. And get the best batteries you can afford. For me, that would be Costco Kirklands

James

[JLS (Jay Liu's Service)]

jloo, here's the best way to test deep cycle batteries. Jay Liu's Tip of the Month
Deep Cycle Battery Test

Batteries used with trolling motors are different than automobile batteries. They are deep cycle batteries. Many of my customers tell me that when they were having trolling motor battery trouble, they took their battery back to the store to have it tested. It was tested by attaching a cold cranking AMP Tester to it and then declared OK. This is not the way to test a deep cycle battery.
1. You must know the Ampere-hour rating of your battery (most group 27 batteries are rated at 105 Ampere-hour)
2. The battery must be fully charged and each cell tested with a Hydrometer, making sure all cells read 1275 or better (if one cell is low then your battery is bad).
3. You will have to get some head lamps and measure the Amp draw, then hook them up to the battery and take a gravity reading every hour and record the Hydrometer readings, (it should drop evenly between cells) for as many hours that it takes to add to 100 amps.
For instance;
A. Head lamps = 10 Amps (10 Amps X 10 hours = 100 Amps).
B. Head lamps = 5 Amps (5 Amps X 20 hours = 100 Amps).
The gravity reading should not vary more than 10 points from cell to cell while doing this test. If they vary, the low reading cell is weak and you should replace your battery unless you don’t mind rowing your boat.
99% of us will never test our batteries if we have to go through all the above so an easier way to do this test is to make sure your battery is fully charged; test the battery using the step #2; and then go fishing. When you get home, and BEFORE you charge the battery, check each cell with the Hydrometer. Your readings will be lower than your previous reading but each cell should not vary more than 10 points from each other. If they vary more than 10 point that cell is bad.
I do not recommend using “Maintenance Free” batteries since they do not allow you to access to test them. Also you spent $20,000 or more for you Bass boat so you don’t want to scrimp on the cost of your batteries since your trolling motor is used 90% of your fishing time.

[Oldschool]

You have 2 each group 27* wet cell type deep cycle marine batteries wired in series that are 2 years old. That would be 12 cells, 6 for each battery and as noted if 1 cell is bad than the 24 volt system will be degraded by the 1 bad cell.
Maintaining wet cell deep cylce marine batteries in the bass boat is a constant problem; looking at each cell for water levels so one cell doesn't go dry across the top of the plates and cleaning the corrosion caused by gases when charging never ceases. When 1 cell goes bad in one battery, you should change both batteries so they are the same strength.
I finally gave up on wet cell marine batteries and change over to AGM's and no more battery issues.
You shouldn't have any current draw with your trolling motor switched off; unless you have something else wired to the trolling motor batteries. If you don't have anything wired to the TM batteries, then unplug the power to the TM and check the plug and receptcle for corrosion.
Tom
* group 27's are marginal for TM batteries, better to go with group 31's and change the trays for the longer battery.

[jloo283]

Jay, thanks for the tips. At this time, I've decided to simply get new batteries. Thanks for confirming my suspicion on the load test, that it didn't reliably work.

Oldschool, I've inspected all wires and connectors for issues, they were fine. I still cleaned them anyways. As far as AGMs, I do use the Sears Platinum for cranking and they're great. Just don't don't feel like spending $600+ for a pair right now for the trolling motor. That leaves me with Everstart, Die hard, or Costco that I can immediately pick up locally. I went with Costco due to their 3 years replacement policy, at $84 each. Can't beat that. If I get 3 years out of these, I'll be more than happy.

I'll have to keep digging why there's a 17mA current draw in OFF position. I can't think of anything right now. I hope someone can check out their setup and confirm.

Thanks for your replies.
James

[Oldschool]

It is really hard to clean the receptacle mounted on the front panel where you plug in the TM motor, I use a contact spray. The plug contacts should show any corrosion that might be present.
Galvanic corrosion from electrolytic action does create current; that is how a battery works.
The top of the batteries can also creep some current if they are damp. Coating the battery post and connections with Vaseline helps to reduce those issues. I used Flow-Rite watering system fo years to keep wet cell (Trogan SC225) batteries full and it worked good. You should get about 5 years out of a good quality battery, 2 or 3 out of (Interstate type) batteries.
Cosco's return policy makes it easy to exchange batteries!
Good luck.
Tom

[scottsweet]

I'm talking about the Minkotta Maxxum 80lb. Recently, it's been loosing thrust quicker than usual. I used to be able to run all day without a drop in thrust, but recently it'll start weakening after a few hours.

My group 27 led-acid batteries are only 22 months old. Load test at Kragen's came back good so I inspected all wirings and connectors. Nothing unusual to speak of but I cleaned them anyways. Then the trip on Sunday evening lasted about 2hrs in the wind, running at 65%.

Just out of curiosity, I checked current draw at rest, with the switch in OFF and MOM positions as well as unplugged. The results are as follow.

Unplugged: 0mA
Plugged in, in OFF position: approx 17mA
Plugged in, in MOM position: approx 68 mA

These newer digital motors use PWM control circuity so I suspect it requires some amount of current to operate in MOM. What bothers me is the 17mA draw when the rocker switch is completely OFF while the motor is plugged in. I don't get it. Despite the fact that it's very little, it bothers me.

I need some input from some of you guys who are mechanics or who may have done such measurements. Are these figures normal and acceptable? Do you suspect a short of some sort somewhere?

The fact that the motor starts out strong leads me to believe it's battery issue, despite the good load test. I'll be testing with new batteries soon.

The take away is, be aware that your trolling motor constantly draws current at all times so keep your on-board chargers plugged in. Battery load test didn't appear to be reliable. And get the best batteries you can afford. For me, that would be Costco Kirklands

James

James,

Here are a few things about batteries. The hydrometer testing as mentioned is a good way. However, all batteries over time will become unbalanced and it will be necessary to fully charge each of them individually to ensure a full 24V or 36V charge. Whether they are traditional wet cell batteries or AGM or whatever, the best way to check this is as follows.

1. Fully charge your batteries overnight and then let stand for at least 8 hours, but preferably overnight again. It is important to let the batteries cool after a full charge.
2. Using a digital volt meter, check the voltage of each battery individually. First, they should be the same. Each battery technology has a different standing voltage after a full charge. Wet cells should be between 12.7 and 12.8. Some AGMs could be as high as 13.1V. The key is they should be the same. If the voltage is significantly higher (.3 - .5V higher) than mentioned here, than sulfation on the battery is significant and you are getting a false resting voltage reading. An out of balance battery is .2V or more compared to the other batteries.
3. Turn on your trolling motor on high and run for 30 seconds. Let stand for 30 seconds. Check the voltage again. The batteries should fully recover back to the standing voltage you measured in #2. If not, you likely have a weak battery.

If you find you have one battery out of balance, use a single battery charger and charge the battery individually again to a full charge and test again. If this battery is not fully recovered, you have a weak battery.

Another thing is the last trolling motor battery in the series with the negative battery line connected to the trolling motor will always get weak over time. It is the last in the series. One of the things I do is use my emergency perko switch to connect my last battery in to the cranking battery, that is in parallel, to bump the last battery every few months or so. To see how I did that wiring, check out http://www.dropbox.com/gallery/58977625 ... 1?h=2c03bf or my facebook page.

Out of balance batteries is a major cause for trolling motor battery issues on the water. If one is more than .2 V more or less than another, it means that the stronger batteries are working harder to make up for the weaker battery. It in turns gets hotter and weaker faster than the other batteries further causing an out of balance situation. So it is important to check the balance every 90 days if you use your boat a lot or perhaps every 6 months depending on how many times you recharge your batteries.

If you have sulfation, than your batteries are shot and will fade quickly over time. Sulfation is caused by not charging your batteries right away after being on the water running the batteries. What happens is when the batteries drop about .2V from full charge, they begin to develop a film of sulfate on the plates. If this film of sulfate gets too thick, it creates resistance and doesn't allow the batteries to fully charge properly when you apply the charger. It also causes your batteries to have an artificial high voltage when you measure it with a digital volt meter. If you put your charger on within a few hours after returning home from being on the water, the normal charge and heat cause the thin film to break apart naturally and dissolve back in to the water or media of the battery. If you don't do the charge, the film begins to grow thicker and over time it gets to a point that it can't be broken up at all. Some battery charges (Stealth 1 for example) use a pulse technology or a vibration in the charge wave that helps reduce sulfation during the charge and breaks up this sulfate film. If you have ever had an old battery that seems to get a full charge in a very short time, but seems to lose its juice in a short time as well, this is a symptom of sulfation. Since sulfation causes resistance, it results in a higher measured voltage (for you science guys Ohms Law, V=IR)...which in turn causes the battery charger to turn off too early...thereby not fully charging your batteries. This becomes the cycle and the batteries become useless.

There is this guy who is "magically restoring your batteries" online here. There is a company who created a substance that you can put in to batteries that are not maintenance free. Effectively this substance is removing the sulfate from the plates exposing the lead once again so the batteries can be charged and useful, albeit shorter than new batteries since there is actually less lead on the plates compared to when the batteries were new. I ran in to one of these suppliers a couple years back...the battery companies are very hush hush as you can imagine .

As for the trolling motor having a drain, even if it is turned off with the switch, is normal actually. I turn off my breaker when I store my boat to ensure no current is being drawn from the trolling motor batteries.

Hope this helps . Oh, if you have any more questions, let me know...happy to assist.

[jloo283]

Hey Scott, thanks for the detailed insights. The 3-step test seems pretty trivial and reasonable, I'll keep that in mind.

As far as having the need to charger batteries individually, I do have 3-bank on-board charger that charges and keeps track of individual banks. I do agree though, increasing R due to sulfates could cause the charger to detect that bank as fully charged falsely.

I don't have the old batteries anymore but I do recall over 0.2V differential between the two, even after a full charge (according to the charger's green light anyways), can't remember if it was the last one in series that the motor's negative was connected or not. It probably was. I've always kept the on-board charger connected the moment I get home every time though.

It's an interesting trick how you rig your cranking battery parallel to the last trolling motor battery in series. So you control the pos side with a perko switch and have the neg connected at all times I assume. Does that cause interference with the bow mounted sounder at all? Or do you use a separate battery for all electornics? This does seem like a convenient way to jump start the motor if needed to, although I carry a low tech jumper cable for that specific purpose

Oh and thanks for confirming the minuscule current draw at OFF position, I'll stop worrying about that.

James

[scottsweet]

Hey Scott, thanks for the detailed insights. The 3-step test seems pretty trivial and reasonable, I'll keep that in mind.

As far as having the need to charger batteries individually, I do have 3-bank on-board charger that charges and keeps track of individual banks. I do agree though, increasing R due to sulfates could cause the charger to detect that bank as fully charged falsely.

I don't have the old batteries anymore but I do recall over 0.2V differential between the two, even after a full charge (according to the charger's green light anyways), can't remember if it was the last one in series that the motor's negative was connected or not. It probably was. I've always kept the on-board charger connected the moment I get home every time though.

It's an interesting trick how you rig your cranking battery parallel to the last trolling motor battery in series. So you control the pos side with a perko switch and have the neg connected at all times I assume. Does that cause interference with the bow mounted sounder at all? Or do you use a separate battery for all electornics? This does seem like a convenient way to jump start the motor if needed to, although I carry a low tech jumper cable for that specific purpose

The perko is on the positive and has a 1, 2 and 1 & 2 option. I normally run the 1 which has the cranking battery only. If I want the trolling motor battery, I put it on 1 & 2. Actually the common ground usually eliminates or reduces trolling motor noise on the graphs. That is one of the tricks to reduce the noise.

Oh and thanks for confirming the minuscule current draw at OFF position, I'll stop worrying about that.

James

[Ceaser]

theres a couple ways to de-sulphate a battery. The "charge" has to be strong enough to cause the sulphate to release. A good high voltage shock, pulse, can do this. Sulphate is a normal process that happens in lead acid battery and can be removed with ample knowledge of how it is formed. Charging the batteries releases the sulphate, so with extensive sulphate build the normal small amperage chargers will take a long time to convert the lead sulphate back to acid and a soluble state. Sulphate is soluble and will turn back to acid when exposed to acid or water and charging. The bad hydrometer readings are due un converted sulphate retained on the plates. Hydometer is giving you a density that is a direct reflection of acid strength. High amperage shocking and prolonged charging can bring a battery back, without a "magic solution". I am employeed at a Sulfuric Acid Plant and this is a common maintenance issue. If sulphate could not be removed our equipment wouldnt last a year. Lead acid "wet" batteries are most damaged by vibration and weakening of the lead plates and connections internally. If you drop a plate or it moves or shifts, its pretty much game over, a common cause of a failed battery. The dead cell is because of physical damage. Shock and vibration dampening of the battery tray will extend the life a battery nicely. When a battery seems to be gone a 50 amp shock a few times and 3-7 days on a trickle charger will sometimes do the trick. Anytime the top of a battery is open remember that the solution inside is sulfuric acid and the lower the level of the cell, the stronger the acid is. Be careful, it can be nasty stuff