Electric motor temperature sensor

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Electric motor temperature sensor

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4 October 2011 at 10:56 #31936
Barzo
Participant
@barzo
Hi Folks,

The electric motor in my boat gets very hot, I have a water cooling circuit that operates via an underwater scoop, but it relies on the boat going reasonably fast, once I slow down the ram effect is not enough to force water through the system. It occurred to me that I might install a water pump that starts when the motor body temp. reaches a a certain value.

Has any one any references/projects that will switch on a small water pump when the temperature of my motor reaches a certain temperature?

Regards Barzo
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4 October 2011 at 10:56 #5140
Barzo
Participant
@barzo
A project to switch on a water pump
4 October 2011 at 18:45 #31940
Ian Gardner
Participant
@iangardner62867
One solutuon might be to use a pump which delivers water irrespective of motor speed-another would be to address the problem of the overheating motor. If it gets hot when the boat is running at slow speeds I imagine it’s drawing much too much current.

Just a thought!
4 October 2011 at 19:07 #31941
Barzo
Participant
@barzo
Ian,

Many thanks for the reply.

The motor is an mmb900 on 20 volts with a 50mm three bladed prop..

I have just measured the current drawn, running the motor in air. The reading is 1.15 amps.

On Sunday I had approximately 40 mins pootling around at two thirds to full speed and it was only at the end I thought I would try some low speed manoeuvring. I suspect that the heat in the motor was not being extracted because the water circuit was not being driven by the forward ram effect.

I will certainly give some thought to a continuously running pump. As it stands I don’t think I could try steering courses.

Regards Barzo

Edited By Barzo on 04/10/2011 19:10:55
4 October 2011 at 23:00 #31947
Telstar
Participant
@telstar
Hi Barzo

When we placed water scoops on I/C powered boats we placed them close behind the prop,slightly to one side of center,

This seemed to give a good supply of water even at lower speeds ( as long as the prop was turning)

Cheers Toms
5 October 2011 at 08:02 #31949
ashley needham
Participant
@ashleyneedham69188
Barzo. is it possible to get an “in the water” current reading, as the 1 amp or so would appear just to be the no load value.

As telstar says , the only way to get a good reliable flow of cooling water is to have the pickupp after the prop.

What is, or what style is your boat ?? do you have air circulation in the hull? from what I have read, a 900 even on 20v should be man enough for a 50mm prop and not get hot..

Ashley pictures plse
5 October 2011 at 19:39 #31951
The Long Build
Participant
@thelongbuild
An easy way would be to use a bimetallic strip, Not sure where you could get some from but would iliminate any electronics..

Another thought

As it is also an mmb900 on 20v I would imagine it is a reasonably sized boat, I am looking at a setup at the moment , not for the water cooling but on the plans, it showes a pump linked into the electronics.

See Link from ACtion Electronics

http://www.action-electronics.co.uk/pdfs/Flying%20Phantom%20-%20John%20Bradford.pdf

Edited By The Long Build on 05/10/2011 19:56:58
5 October 2011 at 20:39 #31952
ashley needham
Participant
@ashleyneedham69188
One little hole above and behind the prop, Araldite and a bit of bent tube…job done. 15 mins. Another chap on the pond is mucking about with water scoops with not much success. On my Seahawk you can see the water coming through the watercooling system at 1/4 throttle !!

This setup also will cool the motor after a fast run, pootling about afterwards.

Ashley
5 October 2011 at 22:51 #31955
Steve Gregory 1
Participant
@stevegregory1
its sounds like the motor is certanly having its work cutout with that size of prop and battery, no wonder its getting the motor hot to the touch [if you dare]

I would also suggest altering your sailing style too, try less “full ahead” for long periods, try more slower “steering course stuff” intermixed with the fast stuff,.

Dont try and do slow work immediately afetr full speed cruising it does not give chance for the motor to cool off anyway

the water cooling pickup should supplu cooling water at all times anyway, even at slower speeds if placed as suggested above. it works for a lot of other boaters. fitting electric pumps is ok, but thats another battery drain to consider, so your fast speed sailing times will be reduced accordingly, simply due to battery drain.
5 October 2011 at 23:03 #31958
Telstar
Participant
@telstar
hi If you feel you must have a controlled pump there is a temp operated switch that closes at 90 C and is small enough to strap to the motor direct

it resets at about 75 C (ie opens again)

this should do the job

Cheers Tom
5 October 2011 at 23:05 #31959
Telstar
Participant
@telstar
Sorry missed a bit Here.

Edited By Colin Bishop, Website Editor on 20/10/2011 10:11:35
5 October 2011 at 23:12 #31960
Steve Gregory 1
Participant
@stevegregory1
its a bit pricey though, especially when you have to buy a pack of 25 sensors. But if you can find buyers for the other 24, you’d be in business!
5 October 2011 at 23:32 #31961
Telstar
Participant
@telstar
Hi possible alternative

http://www.rapidonline.com/Electronic-Components/90DEG-C-NORM-OPEN-THERM-SWITCH-26-7430

cheers Tom
6 October 2011 at 00:04 #31962
Barzo
Participant
@barzo
Hi everybody,

Thanks for all the replies.

For Telstar and Ashley, I have added two more pics to my photos, showing the Stern gear arrangement.

When the boat was in its prime – 30 years ago she had a HP40 glow engine that turned at about 15000rpm, it certainly developed enough water pressure in the cooling system to produce an almost horizontal water jet. The water pipes are much the same now, as then, but the engine revs are only about 7000 rpm.

For Steve, I have gone back to my 45mm diam. three bladed prop to see if the reduced loading and sllghtly higher revs. will reduce the motor temperature.

To follow-up on the pump idea I will do some more research on miniature pumps

Thanks again

Barzo

Edited By Barzo on 06/10/2011 00:07:47
6 October 2011 at 00:06 #31963
Barzo
Participant
@barzo
SORRY FOLKS – FINGER TROUBLE-PLEASE IGNORE

Hi everybody,

Thanks for all the replies.

For Telstar and Ashley, I have added two more pics to my photos, showing the Stern gear arrangement.

When the boat was in its prime – 30 years ago she had a HP40 glow engine that turned at about 15000rpm, it certainly developed enough water pressure in the cooling system to produce an almost horizontal water jet. The water pipes are much the same now, as then, but the engine revs are only about 7000 rpm.

For Steve, I have gone back to my 45mm diam. three bladed prop to see if the reduced loading and sllghtly higher revs. will reduce the motor temperature.

To follow-up on the pump idea I will do some more research on miniature pumps

Thanks again

Barzo

Edited By Barzo on 06/10/2011 00:10:01
6 October 2011 at 10:07 #31968
Ian Gardner
Participant
@iangardner62867
Having looked at your photos- nice boat by the way- I recognise the location, and live not a million miles from there. Isn’t that pier a wondeful creation!?

Hope you get the overheating problem sorted out – I’m sure we’d all be interested in developments- all adds to the body of knowledge.

Ian
6 October 2011 at 11:44 #31969
Barzo
Participant
@barzo
Ian,

The original pier was built using track from Brunel’s defunct wide gauge railway.

Should you be interested the following web site details its colourful history: http://www.clevedonpier.com/

Having looked at the pictures on the various contributors accounts my one boat is quite small beer !

I do have a new project on the blocks and that is a surface piercing hydrofoil. It should be ready for next spring.

Thanks again Alan
6 October 2011 at 14:55 #31970
Ian Gardner
Participant
@iangardner62867
Alan,

Pardon my previous typo.

Do you know I’ve lived in Devon for thirty eight years but had never visited Clevedon until about two years ago. I found the pier absolutely magical- and the boating pond at Clevedon too, and have often meant to return. I have often seen photos of boats sailing there, especially on the Waverley Models website. What a fascinating backdrop with the Bristol Channel and the pier.

I also remember reading about the wide gauge track- thanks for the link.

Unless you’re very unusual you can only sail one at a time – and it looks as though your Huntsman is a treasured member of the family!

All the best,

Ian
7 October 2011 at 02:02 #31977
60watt
Participant
@60watt
Barzo you are now heading in the wrong direction by reducing the prop size.

It is all down to the large ratio of iron to copper.There is a big iron core,strong magnets and a narrow air gap which gives the motor its large torque in the small size.The trade off is high iron loss and low peak efficiency.

Removing the torque ring would only nudge it in the right direction.You want to reduce the voltage and use a much larger prop or choose a motor with a higher no load RPM.

A test on six volts you should see the best matched prop draw 6 to 7 amps flat out.
7 October 2011 at 11:07 #31981
Barzo
Participant
@barzo
Hi 60 watt,

If ever I had a need for a cold shower to wake me up, I think I will read your response.

I have found the content discombobulating on several levels. Perhaps you could help me interpret the content?!

1. How does the iron copper ratio affect the heat generated.

2. What is a torque ring?

3. Given that the particular model is supposed to go quick, how does reducing the motor voltage help it go fast?

4. My intuition tells me that by increasing the prop. size it throws more load on the motor and it will get hotter?

5. If I were to use 6volts at 7 amps – 42 watts, I don’t think the boat would get up onto the plane?

6. The amount of energy the boat needs to reach the speeds of which it is capable, is approx. 700 watts. Even using compensated, Froude’s scaling rules, it requires 400 watts to match the scale speeds.

Maybe I have an unrealistic hope that the present 400 watt input should not generate unwanted heat.

However since I desire the speed, my intuition tells me that I should expect a heat dissipation problem.

In the words of one of my past bosses – ” help me understand what you mean Barzo”

I look forward to your elucidation.

Kindest regards,

Barzo

PS I have tried to look at your ‘posts’, but I have as yet not been successful in locating them.

PPS If the response is likely to be too long for this Forum I will be please to follow-up any external references, papers/books etc..
7 October 2011 at 12:06 #31982
60watt
Participant
@60watt
1. How does the iron copper ratio affect the heat generated.

To get torque you need a strong magnetic field.
You need iron to make a strong magnetic field in a confined space

That makes that particular motor inefficient if you don’t use a substantial prop.

2. What is a torque ring?

Sheet metal sleeve around the outside which changes the torque/speed characteristic.

3. Given that the particular model is supposed to go quick, how does reducing the motor voltage help it go fast?

It does not.

4. My intuition tells me that by increasing the prop. size it throws more load on the motor and it will get hotter?

It will but you have to get the right prop first.

5. If I were to use 6volts at 7 amps – 42 watts, I don’t think the boat would get up onto the plane?

No but I am suggesting that you could do your prop experiments at 6 volts.

What current measurements do you get with your props at full throttle?

6. The amount of energy the boat needs to reach the speeds of which it is capable, is approx. 700 watts. Even using compensated, Froude’s scaling rules, it requires 400 watts to match the scale speeds.

You can only get Pin x Vin x Efficiency out of the motor.

External references:-

1. 12 volt Motor Data from a vendor (A stall current of 50 amp is missing).

2. What to do with four parameters to generate power out and efficiency curves

Your blue peak is around 6-7 amp @ 6 v,around 13 amp @ 12 v and 22 amp @ 20 v

Red peak is a tiny fraction over half the stall current at each voltage.

In reality that motor has strong core magnetics so its key data points are derived graphically.

P.S. Just try bigger and not smaller props.that’s all!

Edited By 60watt on 07/10/2011 12:08:27
7 October 2011 at 14:24 #31986
Gareth Jones
Participant
@garethjones79649
Hi Barzo,

I also struggled with 60watt’s explanation but after a bit of thought I think I understand the point he is trying to make.

You are probably correct that at 20 volts, the propeller you are using is too large a diameter for the motor and it is running well below the motors optimum speed and therefore quite inefficiently, generating lots of waste heat.

The following figures are not necessarily correct but I am just trying to illustrate a point. Assume your present set up takes 20 amps at 20 volts and has an efficiency of 40% the output power will be 160 watts and waste heating will be 240 watts.

If you run it a lower voltage with a bigger propeller your combination might be 40 amps at 10 volts. However if this combination is closer to the optimum speed of the motor the efficiency will be higher. Lets say its now 50 %, the output power will be 40 x 10 x 0.5 = 200 watts and waste heating 200 watts. However the bigger propeller will in itself be more efficent than the smaller one so the benefits will be even greater.

I think 60watts suggestion is not just try a bigger propeller, but try a bigger propeller at a lower voltage. I hope this makes sense to you (and 60watt)

Gareth
7 October 2011 at 14:35 #31987
ashley needham
Participant
@ashleyneedham69188
I dont have any experience of the 900, but certainly I have seen previous posts that indicate the 900 can turn up tp 65mm props… so overheating on a 50mm one indicated a problem, and reducing voltage and upping prop size makes sense.

The much maligned MFA 800 or 850 turns a 50mm prop easily and all day with out getting over hot, and this is , or at least by reputation, a less efficient and powerful beast….

Ashley
7 October 2011 at 15:04 #31990
60watt
Participant
@60watt
See the Mabuchi graph.

Whatever the voltage the ideal prop should cause a drain of between 1/4 and 1/2 the stall figure.That should be the peak efficiency and peak power points for this one.

At 12v the target area is 13 to 25 amp

At 6v it is 6.5 to 12 amp
7 October 2011 at 16:34 #31991
Telstar
Participant
@telstar
Hi Barzo Looking at your Pics the water scoop is just about where I would have it, so I’m no help there.

All this Iron loss, copper loss etc. is so much smoke. These parameters are built into the motor at manufacture. so if you can’t change them why bother.

Things you can change are supply voltage, and load (prop size)

The voltage determins the maximum speed (rpm) the motor can achieve (no load rpm), It does not DIRECTLY determin the current, this is mainly governed by the load.

IF the load is CONSTANT, increasing the voltage increases the speed, but not the current.

However a prop is not a constant load the prop loading IS speed dependant (ie the torque on a prop varies with the speed it’s turned)

No motor is perfect (100% Effy.) so tradeoffs have to be made when using them from MMB data the mmb900 is most efficient when on 20V running at 9600 rpm taking 10A giving output power to prop about 140 W. it delivers most power to the prop, when running at 5400 rpm taking nearly 40 A and delivering 400W to the prop.

However at Max power out the efficiency is about 50%, so you have to get rid of the 400W fo lost power as heat generated in the motor (at max effy. heat losses is about 60W).

So to get the MAX out of the motor fit a prop that will slow the motor to about half the no load speed, then find ways to deal with the heat generated

KISS is the only way

Cheers Tom
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