Problem with my Battery/ESC/motor combination

[Michel Paquette]

I have an electrical dilemma that I need clarified
I have just received my new ESC which is rates as follows:

480A ESC Product Parameters:
Forward: continuous current 80A / peak current 480A
Reverse: continuous current 60A / peak current 300A
Supported voltage range: 2-4 Lipo or 5-12 NiMH batteries
Support motor speed:
2 Li-ion or 6 Ni-MH 540, 550, 775 size motors: ≥12T or RPM below 20,000 rpm
3 Lithium batteries or 9 NiMH 540 550, 775 size motors: ≥18T or RPM less than 15000 rpm
4 Lithium batteries or 12 NiMH 540, 550, 775 size motors: ≥24T or less than 10,000 RPM

I have connected my system using a 12V gel cell from a U.P.S for computers and my motor is a 12V automotive motor.
Between my ESC and my motor I have installed a voltmeter and an amp meter.
I tested to see what kind of amperage, RPM and voltage I would get in different situation and I was puzzled at my results.
As expected, my amperage would increase and my RPM decrease as the loading on my propeller was increased. But what surprised me is the voltage drop.
Running motor alone I was running about 11 V. ( my amperage was about 1 Amp with 17000 RPM)
Running the motor installed on the boat and out of water, voltage dropped to 8.7 V
Running with prop submerged, it went down to 3.3V

Prop is 2 1/2" and running with motor direct drive (thru 2 U-joints in proper phasing)

I repeated the test with a 9V Ni-Cd and also tested with my original 2 in I ESC/RX on a 7.2V NiMh.

All three did the same voltage drop.

Is this normal or is there a compatibility problem between my motor and ESC's

Michel

[Michel Paquette]

Hi folks
I see nobody attempted to give me a reply on this
I posted the same question on another forum and they suggested I bypass the ESC and see what king of results I would get. I did and from the sound of the motor, I concluded that I was getting the same results when I connected directly to the battery. So the problem here is that my motor can't do the job without a gear box.

Michel

[T.S.Davis]

Michel, you'll have a hard time finding anyone that even recognizes what you're running. Nobody runs brushed motors anymore. The guys that were well versed have moved on. I myself haven't messed with that type of setup in 15 years.

[785boats]

Hi Michael.
A couple of questions first.
Can you give us some details on the 'automotive motor'. Is it a blower motor out of a heater unit?
What was the current draw when you had the prop in the water with each of those batteries?.
What is the capacity of the gel cell battery?
Does the driveline spin freely when turned by hand?

It sounds to me as if the batteries weren't fully charged. Both in voltage & capacity.
A fully charged gel cell should be around 13.0v, and it shouldn't drop to 11V with only 1 amp load.

A fully submerged 2-1/2" prop on a motor trying to spin up to 17,000 rpm will draw some decent amps.
If the battery doesn't have a high enough capacity or amp hour rating, it will suffer from excess voltage drop.

This also applies to the other batteries that you tried too.

What type of boat is this setup installed in?

[Michel Paquette]

785boats
The motor is out of an emergency air pack. It had a pump and a light.

All 3 batteries would go down to about 3volts with propeller fully submerged. As for amperage they were all around the 13 amps
My battery was not fully charged on that first set of results I listed
I did recharge later and it went up to 12.75V At this point I ran my test starting from no water to fully submerged and it ran from 8.6V, 3.6 Amp and 11000 RPM out of the water to 3.5V, 13 Amp and 1500 RPM fully submerged. After doing these tests, running the motor for maybe about 5 min, Voltage had gone down to 12.28V (battery capacity is a 7.2Ah)

As for the driveline, it does turn freely, but the U-joints that I am using might not be the best quality.

The boat is a 65” long, 45# semi displacement hull cabin cruiser.

Michel

[785boats]

I don't really know what to say.
That is a huge voltage drop.
It might be that the motor is just not up to the task & is being severely overloaded.
Even dropping to 8.6V with no load on it out of the water seems extremely excessive to me.
Did it get hot in that 5 minute run under full load?

Any chance you can show us what size & type of motor it is?
A 65" boat will need a pretty powerful motor or two.

[Michel Paquette]

785boats
I agree with you on the motor not being up to the task. At least not without a gear box.
As for motor temperature, the 5 min runtime was not continuous so I have no idea. But it does warrant more testing to check this out before I go do any testing on the water where I cant monitor my temperature.
I will get back to this forum after more testing.

Michel

[Fluid]

I suspect the problem is the battery. A ?gel cell? really tells us little, but typically batteries for a UPC do not supply much current. If the OP?s battery had high internal resistance - very likely - then even a relatively low amp draw (in FE terms anyway) would cause a large voltage drop. Since we know almost nothing about the battery or the motor, it is impossible to tell for certain.


.

[Michel Paquette]

Fluid
Mack Products sells a battery that seam identical to the one I have. Its product number 7020. the difference that I can see offhand is that the brand name on Mack's is a Torqmaster LG, while mine is a Panasonic. If the problem is my battery, then it;s because it has a bit of age on it. But it has not gone thru a whole lot of discharge/charge cycle.
you are right about the motor. I don't much about it.

Michel