Motors & Overheating

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Motors & Overheating

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5 August 2008 at 10:13 #15069
Dan Walker
Participant
@danwalker
Hi again,

well just been setting up my running gear and have noticed that even when the motors are not running, (just sat there on standby with batteries connected etc.) and have noticed that the motor casing is getting really hot. also the connected speed controller is getting quite hot. i have looked for short circuits but theres nothing obvious. i’m running a seperate circuit for each motor.

I’m using torpedo 850 motors, electronize fr30hx esc’s, 12v 7ah batteries all connected by 30 amp choc block connector and fuses. ive just disconnected everything and motor is still really hot, theres a lot of residual heat comming out.

any ideas?

Dan
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5 August 2008 at 11:11 #15070
Bob Abell 2
Participant
@bobabell2
Switch off ……….and wait for a reply!

Have you got fuses in the system?

Interesting?

Bob
5 August 2008 at 11:15 #15071
Bob Abell 2
Participant
@bobabell2
Sorry …I see you have mentioned the fuses

Bob
5 August 2008 at 11:18 #15072
Bob Abell 2
Participant
@bobabell2
The block connector sounds suspicious?

Why have you connected both batteries to it?

Bob
5 August 2008 at 11:30 #15073
Paul T
Participant
@pault84577
Hi Dan

It sounds very much like a short through the motor casing.

Are the batteries getting warm?

Try using a volt meter to check how much current is being drawn.

Could you post a circuit diagram showing how you have connected everything and list the parts giving all of the separate ratings and specs so that we will be able to help you better.

Paul
5 August 2008 at 11:34 #15074
Bob Abell 2
Participant
@bobabell2
Hello Paul……….How are you today?

Can you understand the block connector involvement?

All the best,,,……..Bob
5 August 2008 at 11:36 #15075
Dan Walker
Participant
@danwalker
Hi Bob

I havnt! From the esc, theres a red and black wire. The black goes to neg battery and the red goes to a 30 amp fuse and then to the pos battery. There is also a blue and yellow wire, these go into a choc block and then into the corresponding motor wire. i.e yellow for pos and blue for neg. This is what i class as a circuit of which both motors are seperated on their own battery, esc, fuse and choc block.

The choc block is a new one as the previous sort of melted on me, (must have only been a 15amp baby), so i bought this new one i am using whish is rated at 30amp as per ESC and fuses. All well so far as there is no melting plastic.

It might have been from when i was running the motor and then the heat slowly comming out but i swore it was getting hotter when it was still. How hot should these motors get? When i first put her on the pond i was ragging the arse of it as the props i had arnt very good and it didnt go anywhere… of which they have been changed today and are 100 times better. After it had been on the pond, I felt the motors and they were red hot, i couldnt touch them for more than a second.

Dan
5 August 2008 at 11:39 #15076
Dan Walker
Participant
@danwalker
Paul, wiring as per above….

batteries are fine, infact i did check them to see if they were warm but they are fine. another thing is aswell that i do have some motor suppression resister things but havnt yet soldered them on as i’m just really fitting out the hull etc..

Dan
5 August 2008 at 11:41 #15077
Bob Abell 2
Participant
@bobabell2
Hello Dan

Connectors shouldn`t melt?………….Suspicious still!

Have you overfilled the prop shafts with grease?

Bob
5 August 2008 at 11:43 #15078
Dan Walker
Participant
@danwalker
Oh and the original purpose of the block connector was basically for future connectability i.e sound unit or something like that as they are connected to the ESC but at the moment, theres nothing connected apart from motor.
5 August 2008 at 11:45 #15079
Dan Walker
Participant
@danwalker
well they shouldnt but the ones i was using were 15 amp ones i think and they just wernt up to the job, current ones are fine. Well, as for grease, i wouldnt say they are overfilled. Why would this matter anyway? resistance or something like that?

Dan
5 August 2008 at 12:02 #15080
Bob Abell 2
Participant
@bobabell2
Overfilled prop shafts overload the motor

Since the fuses haven`t blown……..the circuit seems ok

Try another switch on without running the motor……..and report back?

Bob
5 August 2008 at 12:40 #15082
Dan Walker
Participant
@danwalker
Ok Bob, will do.

I think i’m off to a mates later but the boat will be going as we will have a play with it, i will report back if theres any further issues.

Thanks again for you help – that includes you aswell Paul!

Dan
5 August 2008 at 14:00 #15084
Paul T
Participant
@pault84577
Hi Dan

As Bob says the motors will get very warm if they are working against more than the prop in the water i.e. an overfilled propshaft or a heavy grease in the shaft but after reading through your postings I think that your problem might just be the wrong props.

Now that the props have been changed I would suggest that you check the current draw on each motor in turn by putting the boat in the bath so that the props have somthing to push against and running each motor upto full power, this will give you a precise maximum amp loading for each motor.

Do the motors have built in cooling fans? if not you might have to fit cooling coils.

Paul
5 August 2008 at 14:08 #15085
Paul T
Participant
@pault84577
Hello Dr Bob

Had a bad day yesterday and had to call my GP out but I feel better today.

Like Dan I have also had problems with connector blocks melting due to current draw, sometimes I am amazed at just how many amps you can get out of a battery.

Paul
5 August 2008 at 14:19 #15086
Bob Abell 2
Participant
@bobabell2
Hello Paul

I`m very sorry to hear that you`re not too well these days and I`m beginning to fear that the Birchwood show will be too much for you……….better take it easy and have a good rest….eh?

There`s always the Blackpool show in October?

Back to the battery problem. Like you said….these 12v batteries certainly pack a punch…only in the last few days at Etherow, there were three ESC`s burnt out.!

And in Duckies Broom…………..both 540 motors lost their rear bearings!

Regards…….Bob
5 August 2008 at 15:04 #15089
Paul T
Participant
@pault84577
Hi Bob

I am also worrying about Birchwood as my Trent is not ready yet and I don’t want to let the lifeboat stand down…but I am determined to get both myself and the model there.

With regard to ESCs I am always burning them out so now I buy the 100amp units.

Paul
5 August 2008 at 18:53 #15092
60watt
Participant
@60watt
Hi Dan,

To give you peace of mind ……You can get a good full throttle current masurement by measuring d.c. voltage across a known low-ohmic in-circuit resistance (or 10 cm of 1mm cable at roughly 2 milliohm)….if the measurement drops to zero at zero throttle then the current is not due to a fault.

A few miscellaneous but pertinent observations……..

Small bushed d.c. motors,like 850’s, have a considerable heat capacity and small surface area so it is no surprise to me if they are very hot long after you throttle down.

A 200 degree Celcius motor winding temperature at full rated power is not unusual as these motors are normally operated around the 50% efficiency mark..

At that efficiency and power input you may get oven temperatures inside an unvented three foot model within minutes.

You say a change props improved matters…………there’s a clue!

An easy mistake to make when running scale boats with ungeared motors is the prop torque can be too high for the motor. In such a case, you find progressively smaller props create more propulsion for less power until the prop + friction torque is equal to half the stall torque of the motor.

Oh, I don’t mean to harp on about 30 amp fuses but in order to blow them the total (speedo,fuse,cable,motor winding,motor brushes,connectors and battery ) resistance would have to be less than ( 12 volts/ 60 amps) or 200 milliohm.

Tom
5 August 2008 at 20:19 #15093
60watt
Participant
@60watt
Hi Dan,

I’ve just noticed your thread "Props" in which you said ….

I have round some other 60mm 4 bladed brass from cornwall model boats, do you think i should just change them or does anybody have any suggestions on the supplied props?

Crikey,yes! ……. try something a bit smaller than the 60mm ones or put in a reduction gear. It’s no wonder the motors were cooking.

Tom
5 August 2008 at 22:20 #15099
Dan Walker
Participant
@danwalker
Hi Paul, Tom & Bob…

Yes i have had a similar conversation earlier today with a guy in the model shop i went to for some spares. He had a look at the wiring and said all is fine however he also said about the prop shafts possibly needing to bed in a bit more. He also commented on the props aswell. I understand fully the concept of the props and sizes and resistance etc… I only chose the 60mm ones as thats the size of the original ones i got with the model and didnt want it to look out out place. or be underpowered.

In reflection to todays test on the pond, the port side fuse is constantly blowing and just cant understand why. Both circuits are wired and set up the same – maybe down to the props again… In regards to what tom is saying about the size of the props versus smaller ones at half power… i noticed that at about 75% power, there wasnt much speed reduction from when it was on full power. Again half way through the testing, the portside fuse blew but i cranked it up to full power and had a blast around until i noticed the motor was smoking and smelt of burning. The torpedo 850s have a shaft comming ut of the front where the wiring connections are – i guess these are for the fan…? anyway, that little bit of shaft had turned blue with the heat…. as you can imagine, this is quite worrying… – help!

is there anybody who lives in the north east area or north yorkshire area who could possibly have a quick glance over my setup as i’ve never had to do this before on boats? Various alcoholic substances would be rewarded…. complete with full consumption demonstration by myself.

bob, in response to your advice earlier, i left the batteries connected and there was no heat build up so i assume the heat was the residual left from the thrashing and not a short circuit.

heres the link to the props i have bought – http://www.cornwallmodelboats.co.uk/acatalog/4bladem4.html – 60mm part numbers 544060 & 544061

so here are the key questions i really need answers to…
- what size prop (4 bladed), is recommended to go down to?
- what does it take to actualy fry an ESC? constantly high current over its rating running through it or just a quick belt of overated current?
- any further advice?
thanks again everyone, really appreciate the help!

Dan
6 August 2008 at 00:46 #15101
60watt
Participant
@60watt
Hi Dan,

You write ……………"I only chose the 60mm ones as thats the size of the original ones i got with the model and didnt want it to look out out place. or be underpowered.

It’s natural to think you get more speed or thrust the bigger the prop size……no…..Once you reach half the stall torque of the motor you you are working the motor at 50% efficiency and maximum power. Go beyond that prop size and you get less for more .

You need
1. a reduction gear OR
2. smaller sized prop to make the boat go faster ….that is….. more for less.
3. (or motors with larger torque constant)
Aim for a prop size no larger than (or gear ratio no smaller ) than that which results in half no load revs,or half stall current at 100% throttle.

Don’t use a meter on the amps range if you blow 30 amp fuses.Use a dc milli-voltmeter and low ohmic shunt resistance.

Tom
8 August 2008 at 14:15 #15161
Dan Walker
Participant
@danwalker
So if i went down say to a 50mm prop of the same type i have at the moment that might sort the issue out or certainly stop things blowing and over heating. can you recommend any better motors than mfa torpedo 850’s that are 12v and are the same size as the 850’s?

Dan
8 August 2008 at 20:19 #15169
60watt
Participant
@60watt
Hi Dan,

    I doubt a 50mm 4 bladed scale prop would do it because torque is proportional to current (almost) and you are probably x3 to x4 or more optimum current. I also know from experience that these props exert a much greater load torque than the two bladed types described/recommended by SMC below. The text is copied/pasted from google cache of SMC’s 800/850 description.

The minimal data supplied appears to indicate the 800 has x2 the torque constant (Nm/amp) of the 850 (electrically equivalent to a 2:1 reduction)..but that would also mean the 800 could drive bigger prop.     As ususual torque figure is missing.

               ——————————

Torpedo 800 Marine Motor
This motor is specifically for displacement (non-planing) medium size (i.e.76-122cm (30-40’’) model boats. It will give ‘cruising’ type performance with maximum battery duration. Suitable for Tugs, Cruisers, Warships etc. The motor comes complete with mounting bracket and connecting lead with 7.2v type socket fitted.

Torpedo 850 Marine Motor
This motor is designed for the high performance medium size (i.e.76-122cm(30-40’’) model boats. It gives ‘planing’ type performance and is ideal for fast cruisers, off-shore type powerboats etc. and where top performance is required.
The motor comes complete with mounting bracket and connecting lead with 7.2v type socket fitted.

Specifications of 800 and 850
Overall length 110mm (4.3/8’’) – Width (inc. fixing plate) 50mm (2’’) – Weight 585g (20.6OZ) – Voltage 12v DC (reversible by reversing polarity) – RPM for 800 (no load) 5100 & for 850 (no load) 9778 – Current consumption for 800 (no load) 1 amp- maximum efficiency 5.3amps-suggested maximum continuous 7 amps-current consumption stalled 28amps and for the 850 Current consumption 1.9amp (no load) – maximum efficiency 10.8 amps – suggested maximum continuous 13 amps – current consumption stalled 40 amps – Suggested prop size for both motors: 45,50,55 & 62mm in 2 blade nylon or equivalent 3 blade brass.
9 August 2008 at 00:01 #15171
Dan Walker
Participant
@danwalker
Hi Tom

Well you’ve burst my bubble , i guess its going to have to be a bit of trial and error in this as i didnt realise things get this complicated. I know the likes of phil locke who built his severn model started out with 4 mfa torpedo 850’s and hes moved on to 700 bb’s or something like that, either way if someone like him isnt impressed with them then they cant be that good surely?

I’m like anyone, i dont like throwing money into things to keep trying, i’d rather get it right the first time.

Sadly me and the trent are going to be ripped apart for 2 months as i have been called back to work in spain so the problem solving is going to have to wait!

Thanks again tom for you help and everybody else aswell…

Dan
10 August 2008 at 19:30 #15204
Manxman
Participant
@manxman
Hi Dan,

Been watching this thread with interest as I’ve recently purchased 2×800 Torpedo’s + 2x80mm props for fitting into an Imara tug next year (getting all the bits together) and at the £100 mark I will be well miffed if I have similar problems !.

There’s been a lot of good and technical advice given, perhaps too much, and like you I’m not a technical type. So may be its time to start again from the beginning and see whats causing the excessive heat.

Start by removing the running gear and mount the motor + battery + fuse to the bench – before connecting up – put 1 drop of light oil on both motor bearings and leave for a few minutes. Now run the motor for a few moments – does it get hot under a no load situation ?. Next add the ESC into the circuit, leave this switched on but without the motor running – any heat yet ? – then run the motor and check again.

To carry on the motor would have to be re-installed into the boat, then try it connected to the prop shaft (no prop) – then with prop

Some where along the line the cause of the heat is going to show up.

You mentioned you had a set of suppressors waiting to be fitted, if the 850s are similar to the 800s then they are already suppressed – inside !

Fitting a fan to the end shaft would be a NO – too easy to touch whilst moving, and to get a fan to fit between the terminals would be so small as to be usless.

Water cooling may be a way but you would need new motor mounts, there is not enough room to fit the coil between the motor and existing mount.

Phil Locke’s motor set up of 4x850s belted to 2 shafts looked real mean – using a sledge hammer to crack a nut – seemed totally over powered, I can’t remember him saying why he changed to just 2x700s they just appeared in one of the photos later on !

Good luck with your quest and have a safe journey and time back in Spain. Look forward to your return.

Cheers – Ken
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