Electric Motor Overheating

[Kevin Flack 2Participant @kevinflack2]

I have noticed that the electric motors on my scale motors get very hot with pond use.

Is this normal?

I have 540/545 types running off 6v 4Ahr sealed cells and get around 1-2 hrs use but both the speed controls and motors are too hot to touch and in some cases the speed control has its protection cut in and runs in slow mode.

 

I have thought of water cooloing but think at the rather low scale typical speeds the water would need to be pumped rather than pressure fed?

Do cooling fans and heatsinks help?

 

Our pond side ambients may easily be at 30 deg cent!

 

Please help!!!!!!!!!!!

[Kevin Flack 2Participant @kevinflack2]

[PierreParticipant @pierre]

Hi Kevin

I’ve used both cooling fans and heatsinks and they do help to a limited degree.

The real question is WHY are the motors overheating?  Usually it’s because there’s friction somewhere in the drivetrain, motors and shafts misaligned possibly?

Another possibility – the props you’re  using are too large for the motors-experiment with smaller props and see if that helps.

Hope this helps a bit.

Regards

Pierre

[ashley needhamParticipant @ashleyneedham69188]

Kevin. What sort of boat is it and how big??? I think it may well be too big a prop. I have a standard 500 motor on my 39″ Fishery protection vessel (trawler hull) and that uses a 35mm 3-blade plastic prop on 6v, no probs….and the lad drives it flat out everwhere. Ashley

 

[David MeierParticipant @davidmeier28154]

Hi Kevin.

If you are going to resize your prop, which sounds like it would be a good idea. I will pass on some info that was explained to me and I have found very useful.

If you alter the pitch the change in power is linear. ie. an increase in pitch from 1 to 1.2 will require 20% more power to drive the propeller at the same speed.

 

If you alter the diameter the power increase required  is = to the increase in diameter squared. ie. an increase in diameter from 1 to 1.2 will will require 1.2 x 1.2 = 1.44 times the power of the original prop to drive it at the same speed.

So changing to a smaller diameter prop of the same pitch is probably a good idea.

 
Finally if you are wanting to drive a propeller that is in your boat faster, to hopefully increase your boat’s speed, the power required is proportional to the RPM cubed.

 
I hope that this is of some use and I am not teaching my grandmother how to suck
eggs.

cheers.

David.

[Paul TParticipant @pault84577]

Good morning Kevin

 

This is a common problem and as you can see from all of the excellent advice that has already been posted there is a number of different things to check.

 

All that I can add is have you over packed the shaft with grease or tightened the retaining nuts to tight.

Try disconecting the motors from the shafts and turning the props by hand to see how easy they are to turn, if there is anything catching you should feel it.

 

Paul

[ashley needhamParticipant @ashleyneedham69188]

Chaps. we should have a guide set up somewhere on these common things, as the same sorts of issues crop up time and time again (for newcomers etc)  ??? such as things to check for problems like…overheating, slow performance, vibration…..Ashley

[Paul TParticipant @pault84577]

Good Idea Ashley

 

Perhaps it should be written as an article that we could ask Vinne to post, that way it would be easier for people to find.

 

Paul

 

 

[SeasprayParticipant @seaspray]

Sorry i don’t like grease in the propshaft it becomes a drag on the engine. I would strip it and clean it out throughly. Put in an oiler in the shaft so you can oil it pre running. Check you have a little backlash on your shaft by catching the prop and moving it back and forward. on the outer shaft coupled up to the engine You’ll see it move or make a small clicking as it hits it’s end movements. Also have washers that the nuts run up to on tighten Find you correct backlash and run the prop up to the nut then tighten the prop up to the nut trying not to move the nut upsetting the back lash you have got.

 

Seaspray

 

I’ve seen grease in a prop knock down a O.S. 20 Marine to constant stalling when put in the water.

[Kevin Flack 2Participant @kevinflack2]

Wow thanks for the great response!

 

Some more details to see if any of the above applies:

The model is the Badger from Deans Marine and is around 36inch/1 meter long with the prop a 45mm brass 4 blade, make unknown.

The shaft looks like those from Deans with an oiler pipe fitted.

The shaft spins very freely with a small amount of play for and aft and has no indicated snag points.

I use extreme low oil volumes so as to limit the build up in the shaft.

The model has probably done around 10hrs of sailing with no other hitches. I know that the pool and lake are different in the water types, the lake having a large algae build up at this time. The model just goes right through the weed as if it was not even there.

Deans did show a 2:1 gear used on their build but as this was not available locally I did not use one. They also used a mechanical speed controller and I installed a Timaya type locally available.

 

The other project on the workbench presently is Branaren with a similar setup but the prop is a cast type with a lower pitch. It is certainly not as smooth running as the Badger on the water, but this is more to do with the hull types probably?

Trials showed this not wanting to turn at low revs and ended up with a new brass shaft as the steel one was found very rusted! seems to be going fine now, Why do suppliers give steels that rust as this will cause problems if laid up for a while?

Kevin

 

 

 

[Kevin Flack 2Participant @kevinflack2]

 

Just thought of an issue,

The scale speeds are of courses very slow, the model runs with the trim control at max most of the time, does the high frequencies of the modern speed controls have an influence on the heating?

Speed controls for industrial mains motors are known to have similar concerns with special motors sometimes required?

 

Kevin

[David MeierParticipant @davidmeier28154]

Fitting a 2 : 1 gearbox has got to make a big improvement on your motor temperature I would think. the motor will run a lot faster therefor cooler.

David.

[TelstarParticipant @telstar]

Hi The only thing that makes electric motors get hot is current.

Motors generally available for modellers are not very efficient, a good quality 540 (Mabuchi)  can give output power of about 26W (about 0.03 Hp)  but at this rate it is only 45% efficient  that means that it is wasting just over 30W as heat in your boat.

At its most efficient according to Mabuchi the motor is 60%  and gives an output power of 14.5W.

I have played with some motors on a Dynamometer, and the results do agree with the data I got of the internet.  I am trying to make a test rig that can be used to measure the loading (torque), speed and output power of  propellers, from this I hope to be able to tabulate  for a (say) 2 blade 45mm prop at 2000rpm you would need Xwatts or at 3000rpm it would need Ywatts,

But this has to fit in with many other jobs

cheers Tom

[Dave MilbournParticipant @davemilbourn48782]

Neither motors nor speed controllers should get much more than warm in normal operation. Your motors are almost certainly over-propped if the original design called for 2:1 gearing; a 45mm x 4bl prop on straight drive is really past the limit of a 540/545.

Either reduce the prop diameter or the number of blades, or fit a gearbox.

Works for me; suit yourself.

DM

 

[ashley needhamParticipant @ashleyneedham69188]

A 45mm brass 4-blader is way way too big for an ungeared 540. Possibly 40mm 3 blade brass a maximum.  I have a 555 motor running on 12v that turns a 40mm 5-blade brass prop on a warship ok. Fit some gears or if you really must have that size prop, get G.Sitec or someone to make a really shallow pitched one. Ashley

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