Motors & Overheating

[Dan WalkerParticipant @danwalker]

Hi Ken, Well my 60mm props i have purchased are very different to the ones supplied, Infact the ones supplied were useless and made the boat better in reverse then forward. I looked on cornwall model boats, and bought a pair of left and right hand 4 bladed brass 60mm props. one motor is getting red hot and doesnt seem to perform. i remember when i had the boat on the water for the first time, i hit a empty bread packet and it stalled the motor and it lifted the boat out of the water with the force of the stall. since its been pretty hit and miss with that motor, i think its shafted to be fair. i think upon reflection the props are infact to big, it just seems that the differnce between 75% and full power is questionable, this to me with sound advice from paul, ken and tom means the props. obviously motors get hot with general running and load but this thing is turning the shafts blue. Phil locke is indeed building a trent at the moment but updates on his website are painfully slow. ive seen pictures of his speedline trent with pretty much the same gear as i have, it looks mint but i bet a builder like him isnt getting the same issues as me!

i understand that the torpedo 850’s are better than the 800’s, mine barely run on 60mm props, i dare say you’ll blow fuses left right and centre with 80mm props! again, i think its all down to the shape and type of the hull, for example, my mates dad has a 33ft whitby coble with a big ford 4d engine in it, this creates a cruising speed of around 10 knots, theres no point putting a 800 hp man lifeboat engine in as doubt it would go faster than what the boat is designed for. i would maybe suggest you run torpedo 800s or 850s with a reduction gear which are available for about £25 a piece. i think this would solve any issues before even starting. tugs are meant to have torque and not speed.

anyway, i’ve babbled on a bit to much and will leave you to reflect on my comments.

P.S, when i get to spain, i’m boarding the second biggest lifting vessel in the world – have a look at this beauty – http://image05.webshots.com/5/3/2/32/61830232sAFzei_fs.jpg

Thats the S.S.C.V Saipem 7000. we’re laying a deepwater pipeline between spain and algeria….

Catch you all soon..

Dan

[60wattParticipant @60watt]

Dan,

Dan, I am electrical engineer with design experience of electrical power plant. What Ken is saying is B.S.

I was careful to stick to facts and not tell you what to do.

What I would recommend you do ,if you do not give 100% credence to what I say and anything to the contrary,is purchase or borrow two small fibreglass/nylon props at no more than £3 total (see smaller smc sizes)……Watch the difference……If you connected a voltmeter set to mVolt across a fuse and throttle up (pond side) you could see as well as feel the difference.Smaller prop would as much as triple your thrust and cut your consumption  to one third.

 An 850 is not a better motor than the 800. It has a no load revs x2 of an 800. The 800 motor is suitable for a prop of ~ 50% more torque than the 850.It is also suited to 50% more voltage Using an 800 motor would improve matters but the props would still be way too big.

Given what you have a cheap solution would be obtain two ex-equipment motors or get brass collet gears from shgmodels and 1 inch spacers,parallel plates and make a double gearbox for four pounds.

Tom

[Charles OatesParticipant @charlesoates31738]

Hi Dan, I’m not an electrical engineer, but I’ve had years of trying many motors and all the gubbins we use to make the boat go.

      I have to agree with Tom about the props. The relationship between prop size and the load on a motor is correct and very easy to see and measure. Do get some cheap props and give them a try, you will be amazed at what hapens. Do you have a simple ammeater? even a cheap one will be very usefull in the years to come. Measuring the current of a set-up can tell you 9/10 of what you need to know.

[60wattParticipant @60watt]

                        DC MOTORS ARE SIMPLE TO UNDERSTAND

Just look at the performance graph on the hyperlink to Johnson 540 type motor.

http://www.johnsonmotor.com/mediando/index.php?IdTreeGroup=49&IdProduct=457

It plots  SPEED  ,   CURRENT  , EFFICIENCY  are all plotted against TORQUE    ( prop size )

Put too big a prop on then your to the right of maximum power and just wasting power,limiting speed and duration of sail.

Put a very big prop such that you have nearly 60mNm with this motor load then the motor slows to a crawl, the current goes near to stall figure, efficiency is < 10% so  90% of your Volts x Amps is being converted to a thermal pile which will set fire to your boat.

Tom

[Dan WalkerParticipant @danwalker]

Hi guys, sorry for the long delay, internet access is sometimes tricky when your bobbing about in the middle of the med!

Yeah smaller props are the first things i´ll be looking at when i get home, i´ll try a ammeter over the current props and see what it shows. and then step down a size or 2 or until i get it right.

another thing which puzzled me slighty is the batteries themselves and their habbits, especially when charging.. i use 2 12v 7ah lead acid with a simple plug in charger for each battery that knocks the voltage to 12v and connects striaght to the terminals. i had them on charge for over 24 hours and they were still charging.. is this normal?

dan

[60wattParticipant @60watt]

Hi Dan,

 If your ammeter is a multimeter you can monitor if your chargers are actually charging or just floating as good chargers do.

The charge voltage when you put used batteries on is about 14 ++ volts (but may not reach that level for ages if your battery is really spent ). A two step charger will drop the voltage to a safe backup voltage of 13.5 volts at the end of the charge cycle.

Check for a regulated charging current of 400mA because that will take a full 24 hour day if a 12-7 is near flattened….If it’s a crude red/green one sometimes the charge light stays on regardless.It doesn’t mean the battery or charger is duff…..You need your meter to test that.

Your Torpedo-850 jaunts will have have used up a 12-7 battery in 10 -15 minutes.

That was the clue to the chap whose souped up speed controller kept going into thermal shutdown.

I measured his battery after a short sail and it was at 11 volts, ie flat.

Measured a fresh fully charged 12-7 battey before installing and that went flat in 15 minutes.

Third battery went in with an in-line resistor in the power line ( to read the amps by a voltmeter)  and it demonstrated the model was drawing 45 amp on a Mabuchi 750 motor….He had, previous week ,taken out the gearbox thinking it would make his model faster.

He wasn’t too sure I was taking him for a ride so he put a smaller prop on……the amps fell to 35 and the boat went noticeably faster.Repeated with a smaller prop and the amps went down to 20 but the boat was then so fast he borrowed a 6 volts 10 Ah with added ballast  where upon he still had his much improved speed and was now drawing 10 amps off the 6-10 battery when he started the day slower with 45 amps from a 12-7ah battery.

I kid you not !….He improved efficiency by 800 by matching his electric motor with the best loading.

In the end I tweaked the speed control’s trimpot so thathe got 50% at full stick and he got two hours out a 12-7…….You will get exactly the same effect.

When smaller props begin to reduce speed you have gone back to the point where the motor is at 50% efficiency and the revs will be up to 5,000+

If you did that with 2 60 mm 4-bladers yould empty a bathtub over a bathroom floor.

I don’t know what that does to the appearance of the boat but a previous mentioned diy gearbox  with the original props will do the same thing and keep the bearings happy.

—————————————————-

A typical multimeter will be destroyed if you meter your fuse busting currents.A DMM is not fused above 2 amps.Best follow my earlier recommendation of setting it to millivolts and measuring across the fuse or 10 cm of wire until you reckon your current is 10 amps.You can at least see how the second prop does in comparison to the first.

Tom

[Dan WalkerParticipant @danwalker]

Hi Tom,

 Wow, quite in-depth! I did notice the lagging speed after around the 15-20 minute mark. As for looks with a smaller prop, it will look silly but if the model is ever on display, then i guess they could be changed. so really after reading the above, i´m looking at something between the 20 and 30mm mark. i´ll buy both and run some tests with the multimeter.

As mentioned in previous posts, my motors got so hot the shafts turned blue… well would you say to maybe change the motors incase of damage or will they be fine?

 My chargers state they are the type that the battery is charged when the red light goes out., again, i´ll run some tests and see what happens.

Thanks again and look forward to hearing from you soon

Dan

[60wattParticipant @60watt]

Hi Dan,

 Your motors are fine! Your charger is fine,it is the correct type but optimised for a 2.6 battery!

Here’s the dogs bollocks. Yuasa 12V 7Ah 

My understanding from the charge cycling time graph is C(capacity) is 7 and you want a maximum charging current of 0.2 x C = 1.4 amps

Ideally a matching charger woud switch off  RED  at  3% of battery capacity i.e .03 x 7amp =210mA  .You may find by a roundabout route that your charger does that at  110 mA 

I f you added a 1.2 battery or resistance to the 12-7,the RED would go out.

Your charger RED may go off in 10 days or when temperature changes but that you can calculate it has charged in  C / (charger current) hours . Ignore the red light. Use arithmetic and add another 30% to see when it should be full.

You have a meter you can see. The box or charger instructions will tell you anyway.

My conclusion is the battery is charged,happy to lie on standby.

————————–

Thirty mil is fine. And eff me if your motors aren’t OK when you get the revs up to 4.5 K .     You could afford to blast a heat gun on them now.      On 60 mil props your motors were giving off a kilowatt of heat between the pair. That’s why I concluded all the previous advice about cooling and stripping down was BS (no offence intended to anyone)

I think you will eventually revert to gears in conjunction with your old props if the increased revs rattle the stern tubes and your eardrums.

Tom

[Dan WalkerParticipant @danwalker]

Hi Tom,

I was looking to buy some of the above batteries as the previous builds of my boat used them. Gearbox sounds tempting but ive sort of fibre glassed my prop shafts in and theres no way they are comming out without destroying the hull. i would need to change the angle of them to accomodate a reduction unit for the 850’s i run. i sort of balls’d these up when i put them in but they seem to work fine with direct drive (bar the heat issue). i fibreglassed the inside of the hull and used p45 on the outside. i guess i could maybe prise it all apart and start again with the reduction gear in mind. i will order some 30mm props on my return to the uk aswell as the batteries as stated above in your last message and go from there.

do you live far from the whitby/scarborough area? just thinking you could maybe have a look at my model so far electrically and maybe suggest a things for a few ideas i have.?

Your pretty good at this stuff so i salute you and i am really grateful for your sound advice.

thanks again

dan

[60wattParticipant @60watt]

Hi Dan ,

Before you buy any more stuff ,including 30 mm brass props,get along to http://www.bridmodelboats.co.uk/  You may find someone in a club is the source of ex standby burglar alarm batteries,car fan/windscreen motors.What you spent on motors,batteries and speed controls would have cost me £25 .

Check these three resources…

http://www.mpba.org.uk/    http://www.mpba.org.uk/mpba/mpba_finals_invitation.htm

http://www.sfmbc.net

If you’ve got a fast internet connection ,unlike me at home. , try http://www.[b]modelboatmayhem[/b%5D.co.uk/

It seems to me you see problems when others would see solutions.

I live in Fareham so Whitby is…er…. 

Tom

[Mike DavidsonParticipant @mikedavidson22772]

How long do your batteries retain a charge ? I can’t help thinking about unplanned routes for the electrons coming out of your power source. There might be some defective insulation on your motor windings short circuiting to the motor case. Get a multimeter on the amps DC range and put the meter in either or both the battery leads to see if any current is flowing when it should not be. Then flushed with success, switch to the ohms range, and check all motor terminals for continuity to the case which will tell you if you have an internal short circuit inside the motor. If you don’t have internal shorts,, give the motors a clean bill of health,and switch your attention to your speed controller. The manufacturer may well give you a procedure for a health check. Find them on the internet, and go by the customer service route. There may be internal components that fail causing a high leakage current through the motor. Final thought, pull the ESC control lead out of the receiver socket and see if the fault condition still exists :_) happy hunting Mike D

[Mike DavidsonParticipant @mikedavidson22772]

Dan you have just told me the story of a model boat of mine a good while ago. I used too high a voltage to drive her, and unknown to me, the insulation on the motor windings cooked, and niffed a bit every time I lifted her out of the water. this stripped the insulation off the motor windings eventually,so the motor resistance dropped far too low, demanding far too much current from the battery. eventually I had to scrap the poor old motor because it was a total mess and completely unrepairable, All this proves that model boats are just like women, If you want them to work, you’ve got to keep spending money on them

[60wattParticipant @60watt]

Guys, have you seen a man resembling this picture ? > 

[Dan WalkerParticipant @danwalker]

Motors & Overheating

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