Fried DC motors - under voltage

[rwaguilar]

Good day all,
I just recently fried 2 dc motors from what I believe to be from under volt use. I was working on windlass engine off and no charger applied. Started up and went to use thrusters and both failed.
Troubleshot thrusters with vendors (side shift and wesmar) and new motors on the way.
Question? Is there a low voltage protector I can install at the battery that will drop out and prevent juice to device but will stand up to high current draw these devices use?
Thanks
Rob
1994 36 foot Island Gypsy

 

[O C Diver]

Good day all,
I just recently fried 2 dc motors from what I believe to be from under volt use. I was working on windlass engine off and no charger applied. Started up and went to use thrusters and both failed.
Troubleshot thrusters with vendors (side shift and wesmar) and new motors on the way.
Question? Is there a low voltage protector I can install at the battery that will drop out and prevent juice to device but will stand up to high current draw these devices use?
Thanks
Rob
1994 36 foot Island Gypsy

I would imagine that doing such would be done in the control circuit (lever at the helm). I would imagine a voltage sensing circuit with a pair of relay contacts to disconnect power to the motor relays would work.

How long did you engage the motors for? I'm surprised the heat sensor didn't time out.

Ted

 

[KnotYet]

I agree with OCD that the thermal protection would intervene if present.
Before installing the new motors, I would look inside the dead ones to see if they might
be repairable. Depending on the cost of the new ones, fixing the oldies might be a savings.

 

[Nick F]

I'm sorry, but your suggestion (low voltage fries motors on thrusters) does not make sense to me (IMHO).

The thruster motor drives a propeller. The lower the voltage, the slower the motor will go. The slower the motor, the less torque it takes to turn the impeller. In general, torque is directly proportional to motor current. Therefore: your thruster motor would be running at lower current - and consequently generating less heat!

Also, often these motors have a thermal protection device which senses the motor temperature and cuts the power on high temperature.

I am interested to know if the motors are permanent magnet type. If not, it is possible that the lower voltage would mean a weaker field strength and hence higher current for the same torque (in contradiction to my statement above).

 

[rwaguilar]

The bow thruster will work to port. Not starboard. I Jumped out starboard solenoid and still no spin.

 

[KnotYet]

The bow thruster will work to port. Not starboard. I Jumped out starboard solenoid and still no spin.

Check for voltage at the motor to verify. Sounds like it could be a switching problem.

 

[rwaguilar]

I'm sorry, but your suggestion (low voltage fries motors on thrusters) does not make sense to me (IMHO).

The thruster motor drives a propeller. The lower the voltage, the slower the motor will go. The slower the motor, the less torque it takes to turn the impeller. In general, torque is directly proportional to motor current. Therefore: your thruster motor would be running at lower current - and consequently generating less heat!

Also, often these motors have a thermal protection device which senses the motor temperature and cuts the power on high temperature.

I am interested to know if the motors are permanent magnet type. If not, it is possible that the lower voltage would mean a weaker field strength and hence higher current for the same torque (in contradiction to my statement above).

A little out of my wheelhouse. Suspect low voltage hurt motor from feedback I received with vendor and online.
Open to all feedback and to learn so I do not repeat.

 

[rwaguilar]

Check for voltage at the motor to verify. Sounds like it could be a switching problem.

Thanks. I replaced solenoid and verified voltage to it. Also jumped over it directly (to be sure) to what I believe to be the winding post. X

 

[Nick F]

If it's a "3-wire" motor then you could have burnt out the winding for one of the directions, while the other direction continues to be functional.

A 3-wire motor will have 3 terminals and the other type will have 2 terminals.

 

[rwaguilar]

If it's a "3-wire" motor then you could have burnt out the winding for one of the directions, while the other direction continues to be functional.

A 3-wire motor will have 3 terminals and the other type will have 2 terminals.

Yes it is a 3 wire motor. Very important piece I left out.
Burnt out winding is where we landed after troubleshooting.

 

[Nick F]

Yes it is a 3 wire motor. Very important piece I left out.
Burnt out winding is where we landed after troubleshooting.

Or a problem with the brushes . . .

 

[Comodave]

Check that your battery cables are up to the job. Verify the round trip distance and current draw. Also go over all connections to make sure they are good. Make sure you are not feeding the new motors low voltage.

 

[l00smarble]

Just pull the motor and bring to a trusted local alternator/motor rebuilder shop and they can likely give if a full refurb for a fraction of the cost of new.

No need for some low voltage disconnect device that as the voltage drops during heavy use anyway. You would have to set it extrememly low to ensure it would not have nuisance "trips" during normal operation.

But if you are getting low volage to the motor you should check/test batteries, cabling, connections. Put a voltmeter directly on the battery terminals and run the load and watch the voltage drop. Then put hte voltmeter right on pos/neg stud on windlass or thruster motor and run it again and note the volage drop. If you have a large different (like more than a volt or so) then you have too much voltage drop due to undersized cabling, poor terminations, corrosion, loose connections, worn battery switch, etc.

 

[Nick F]

Re-reading the original post:
- OP ran windlass off battery with no charging of battery (engine off)
- OP started engine
- OP used thrusters and they failed

On my boat, soon after starting my engines the alternator regulator pushes the battery voltage quite high for a while. Is it possible that the OP's thruster motor failures were actually caused by HIGH voltage??

 

[luna]

What I got from the OP’s original post was a bit different.

-Battery bank was not being charged.

-Windlass was hoisting anchor.

-Thruster was energized at the same time.

POOF!

Does anyone know if there is a thermal overload shut off on their Windlass motor?

 

[O C Diver]

What I got from the OP’s original post was a bit different.

-Battery bank was not being charged.

-Windlass was hoisting anchor.

-Thruster was energized at the same time.

POOF!

Does anyone know if there is a thermal overload shut off on their Windlass motor?

As you overload a DC motor the amps go way up. This also occurs if the engine isn't running to maintain the voltage. For the same load (wattage) as volts decrease, amperage has to increase. So for a windlass, it's best to have the engine running and the alternator increase the battery voltage.

Ideally you want a circuit breaker to protect the electric motor from excess amperage.

At the risk of repeating myself, you want the engine running to move the boat forward and increase the voltage from the battery to the windlass. You move the boat forward so that the windlass is picking the chain up off the seabed. When the chain is near vertical, secure the chain so that breaking the anchor out of the bottom doesn't put tremendous force on the internals of the windlass. By doing the above, you don't damage the windlass or overload the electric motor.

Ted

 

[DDW]

I curious as to how long the motor was being run. Thruster motors are made for intermittent use, duty cycle is usually specified by the manufacturer and is quite low. This allows them to use a small motor to do a big job. I've seem people lean on the lever for seemly minutes at a time, that is not going to be good for it. Side Power doesn't say, but it is almost certainly a permanent magnet DC motor, so the lower the voltage the higher the current and power dissipation.

 

[JDCAVE]

Good day all,
I just recently fried 2 dc motors from what I believe to be from under volt use. I was working on windlass engine off and no charger applied. Started up and went to use thrusters and both failed.
Troubleshot thrusters with vendors (side shift and wesmar) and new motors on the way.
Question? Is there a low voltage protector I can install at the battery that will drop out and prevent juice to device but will stand up to high current draw these devices use?
Thanks
Rob
1994 36 foot Island Gypsy

Hmmm. New motors. I would have looked into seeing if an alternator shop would have been able to repair them. I think there is a misconception (ofttimes perpetrated by suppliers) that these need to be “rewound”. Often the fix is much simpler.

I had an outfit called “Brighouse Electric” who fixed my windlass motor when it failed. The do alternators and starter motors primarily. The fellow at Plath told me it would need to be rewound and that the manufacturer had gone out of business—I would need to send it to Los Angeles to be rewound. I took it to Brighouse and they cleaned it up. It was corroded inside. Still working 3 years later.

I agree with OCD above. My windlass is on the starter motor circuit. After starting the engine, I manually combine the house and start bank, and bring the engine revs up a bit. Pull the anchor. “Everybody” (start bank, house bank and alternator) pulls that anchor. I can definitely hear that windlass pull a little harder when the engine revs are increased. I then put the ACR back to auto.

Jim

 

[Nick F]

. . . a permanent magnet DC motor, so the lower the voltage the higher the current and power dissipation.

I am sorry, but this is simply not true (it is true for AC induction motors).

 

[DDW]

Depends on the load, doesn't it? To produce the same power at a lower voltage requires more current. More current = more I^2R loss. Also less cooling from the fan if running slower. On a free running motor, voltage and current are proportional. Back EMF limits current. On a weak thruster installation, motor is loaded, rpm drops, motor draws more current (less back EMF), voltage sags as a result of wiring and battery resistance, rpm drops further, current increases further.

 

[Nick F]

I won't try to go head to head with you, but the one irrefutable statement I can make is that at a lower voltage any DC motor attached to a thruster (a propeller) will not be called upon to produce the same power. This is because the torque to turn the propeller depends strongly on the propeller speed and at a lower voltage the motor will operate at a lower speed. Not only will the speed drop, but also (and much more dramatically) the torque will drop.

Once again, this is quite different from an AC induction motor which inherently tries to maintain a certain speed and, as you rightly describe, sucks more current to achieve this at lower voltages.

 

[JDCAVE]

I know that when my thruster batteries aged, they did not have the same “jump” as earlier in their life. When I replaced them, they had more life. Somewhere on this forum are some tests I did before and after replacement.

Jim

 

[JDCAVE]

Here is what I recorded by measuring voltages at the batteries and amperage with a clamp meter:

Old Northstar MS-210, Top battery: Volts: 9.0 Amps: 350
Old Northstar MS-210, Bottom battery: Volts: 9.9 Amps: 350

New Northstar 190FT Red, Top battery: Volts: 11.4 Amps: 425
New Northstar 190FT Red, Bottom battery: Volts: 11.14 Amps: 428

Jim

 

[O C Diver]

I won't try to go head to head with you, but the one irrefutable statement I can make is that at a lower voltage any DC motor attached to a thruster (a propeller) will not be called upon to produce the same power. This is because the torque to turn the propeller depends strongly on the propeller speed and at a lower voltage the motor will operate at a lower speed. Not only will the speed drop, but also (and much more dramatically) the torque will drop.

Once again, this is quite different from an AC induction motor which inherently tries to maintain a certain speed and, as you rightly describe, sucks more current to achieve this at lower voltages.

One of the things you will find with DC motors (windlasses and bow thrusters) is the efficiency drops as the voltage drops. As a result the windings generate more heat. You will find as your thruster batteries get old and the voltage drops, that the thermal overload kicks out sooner. This increased heat comes from increased amperage draw.

Without plugging in the battery charger (increasing voltage) my windlass would sometimes trip the breaker when loading the chain into the boat while in the boatyard. Plugging in the inverter / battery charger increased the voltage, no breaker trip.

Ted

 

[JDCAVE]

Except Ted, I found, experimentally, both voltage and amperage dropped with aging batteries.

 

[O C Diver]

Except Ted, I found, experimentally, both voltage and amperage dropped with aging batteries.

We're you measuring running amps or starting surge? My breaker never popped when the alternator was keeping the voltage above 13 VDC.

Ted

 

[Nick F]

Ted - I am guessing that you are talking about your windlass (and not thruster). The windlass load is quite different from a thruster. The load is there immediately. I can imagine that a lower voltage to a loaded windlass would take longer (than a higher voltage) to get a windlass turning. This extra time at high "startup" current could well make the difference in tripping a breaker.

Nick

 

[O C Diver]

Ted - I am guessing that you are talking about your windlass (and not thruster). The windlass load is quite different from a thruster. The load is there immediately. I can imagine that a lower voltage to a loaded windlass would take longer (than a higher voltage) to get a windlass turning. This extra time at high "startup" current could well make the difference in tripping a breaker.

Nick

Ok, explain the breaker popping on startup with a lower voltage.

Explain why it doesn't pop with higher voltage.

Ted

 

[Nick F]

Ok, explain the breaker popping on startup with a lower voltage.

Explain why it doesn't pop with higher voltage.

Ted

Ted - I thought I had proposed a possible explanation - repeating: the startup at lower voltage takes longer. The breaker has a delay in the trip and this "timeout" could be getting exceeded at lower voltages.

Just a theory, but something is happening and (as JDCave says) lower voltage pushes less current.

Nick

 

[JDCAVE]

We're you measuring running amps or starting surge? My breaker never popped when the alternator was keeping the voltage above 13 VDC.

Ted

No. It was a straight test of the health of the thruster batteries. Fully charged. Charger off for the test.

Jim