M45 Quadmount 12v Motor Overheating

[greeneagleking]

Hi all,

I am currently restoring an M45 Quadmount anti-aircraft gun and having some issues with the motor.

The 12v 100amp motor has just been reconditioned and works really well with no load, no smoke or anything. (Annoyingly I didn't take a reading to compare)

When the motor is under load with the gearboxes and pulleys attached the motor begins to smoke after about 30 seconds pulling around 9.5v during operation. It has just been reconditioned so not expecting it to get so hot so quickly. I spoke to the motor shop and they said to make sure you are using a good 12v battery. I am using 2x 6v batteries freshly charged (12.6v) and still struggling underload and getting hot. Has anyone else has had experience with this issue or can help?

Here is a link to a video showing the mount in operation and subsequent smoking motor.

https://youtu.be/rPkFfrKya6I

I may end up taking the motor back to them for testing, but it is a task taking the motor out of the mount so want to make sure it is not a problem at my end.

Thanks,

Ben

[DDTrustee]

You should not experience a voltage drop to 9.5 volts if the current handling capacity of the wiring and the batteries are up to allowing the 12.6v at 90 amps....look for high resistance terminal; some wiring getting hot, or limited battery capacity....
You might try a 12v battery with jumpers to the two 6 v series batteries...with a meter across the motor terminal...the voltage at the motor terminals should tell the story.

[Steve Webb]

Put a DC amp probe on it also. I am an electrical contractor and just checking voltage drop only is helpful but finding out if weak battery or motor draw is covering both directions.

[greeneagleking]

Thanks both for the reply.

The wires on the motor do get very warm. Have not been able to pinpoint any particular bad connections. Both 6v batteries are pretty much brand new and charged. I will try adding the 12v battery into the circuit, but currently i have disassembled the gearboxes etc as I'm taking the motor to be looked at at the repair shop.Hopefully they can read the amps it's pulling there as I don't have the tools for checking 100amps or so.

I did test just the motor by itself and it ran at 11.6v and it did not get hot at all. This suggests to me the problem is to do with the load of the gearboxes and pulleys on the motor. Could this mean the motor is running without issue and it is simply not able to draw enough current from the batteries?

[GaryD.]

Mine also was smoking I had it rebuilt.The magic smoke does not try to leave it anymore but it pulls about 80 to 100 amps when running under load.It has 2- 6 volt batteries and I run the generator everytime it is ran just like the manual says.If memory serves it says 5 minutes on and so many minutes off with generator running.Make sure the gear boxes are free and belts are adjusted right.

[mfrance]

What size are those battery cables you made #2 or #4 cable From battery to motors. ?

[GPW43]

Hello
I was going to comment on the wires as they looked somewhat thin to me for 90A continuous pull.
I would eliminate the gearbox stuff first, then the battery stuff (wiring included) and then suspect the motor.

Like previous poster comments make sure the gearbox and belts are set as they need to be. Can you disconnect the motor and turn them to make sure they work freely without too much resistance.

As for the source, how large are those 6v batteries. Can you say hook up anther high amp 12v source to the 12v batteries? to make sure you have enough Juice. If you are dropping that much voltage that isn't good (12.8 to 9.5 is a large drop under load);

GP

[GPW43]

Hello
I was going to comment on the wires as they need to be 2 gauge minimum. Is the connection solid no corrosion etc and torqued well?
I would eliminate the gearbox stuff first, then the battery stuff (wiring included) and then suspect the motor.

Like previous poster commented make sure the gearbox and belts are set as they need to be. Can you disconnect the motor and turn them to make sure they work freely without too much resistance?

As for the source, how large are those 6v batteries? Can you hook up anther high amp 12v source to the batteries? to make sure you have enough Juice. If you are dropping that much voltage that isn't good (12.8 to 9.5 is a large drop under load);

BTW is the motor getting that HOT to smoke? or is it the bearing on the front under load?

GP

[greeneagleking]

Interesting to hear your motor also smoked. I haven't been topping up the batteries with the generator as they are being used which may explain the voltage drop, but surely still you wouldn't expect it to drop so much?

There is resistance from the gearboxes, but nothing I would class as too tight, the motor does not struggle to power up at all, it's instant. With the belts connected, you can hand turn them without much force. The belt tension is at its loosest and tightening them to the manual spec of 1/2inch finger pressed deformation just increases the load too much causing further voltage drop and heat.

In the video I used 170amp rated starter cable, I also thought the cables were not thick enough for the current draw, so I have since reduced their length to 1m from the battery and the new cable is rated at 300amp. This has not affected the voltage reading massively, it now reads 10v (up from 9.5v)and still gets very hot with smoke from the brushes end of the motor.

When I get the motor back assuming if they find nothing wrong I will try adding the 12v battery into the circuit to eliminate battery issues.

Thanks all for the input!

[greeneagleking]

Update:

So I have made some progress, but I believe the motor is still not running at its full potential.

Current status:

1. The original 12v 100amp motor has been repaired and refurbished professionally and bench tests at 11.5v and no longer smokes.
2. I'm using a 2x 6v setup and have a brand new 12v 130ah battery for testing as well.
3. The mount wiring, gears and pulleys are all connected as they should be (out of test rig now).

I have tested the motor with different load setups: (these readings were taken once motor warmed up, cold start is around 9v)

1. No belts - gearbox load only = 11v 80amps
2. Traverse belts only - 11v 130amps
3. All belts connected - 10v 180amps
4. All belts connected including a 12v 12amp boost from the mains to represent the power charger - 10.5v 150amps (connected directly from battery to motor)

As you can see as more load is added more current is drawn and as a result voltage drops. The cables get warm and the mount doesn't traverse at the 60degree per second benchmark. I am only looking for that extra 1v as I believe running at 11v would be optimum.

Do I need more battery cap? Are the new belts adding extra load? Am I worrying about a non-issue?

Any input would be appreciated

Thanks,
Ben

[Steve Webb]

What size are your cables. It doesn't seem like much but DC power always draws and AC it cycles on-off very rapidly but it still cycles.

[greeneagleking]

Test cables directly to motor i have used 25mm3 170amp cable first and then upped it to 40mm3 300amp and it made no noticeable improvement.

The original wiring used in the tests looks to be definitely 170amp capable and I suspect a little larger. I would note the wiring connection (solid copper connector) from the battery through to the switch gets noticeable warm, not sure if this is showing something?

I have also noticed there is a 0.5volt drop while using the original wiring and circuit compared with connecting directly to the motor from the battery. Does this seem a lot?

The new motor cables from the posts to the motor itself do seem to be on the smaller size, but the length must only be 20cm.

[Steve Webb]

I don't think you have problems with cable. Not sure what the transition of metric sizes to awg is but amps are amps and you are sized for the load. Hmmm.