what am i doing wrong ?

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what am i doing wrong ?

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17 January 2011 at 20:39 #29475
phill d
Participant
@philld
How hot is too hot with electric motors /

i have a decaperm and realy cannot tell if its 6 v or 12 volt.

anyway running on 12 volt in the bath for testing purposes with x70 nylon prop.

after about 4 to 5 mins the motor is too hot to touch, the amp meter shows it drawing around 4 to 5 amps.

Is this too hot ? do they normally run hot ? or is the prop too big ?

would it be that testing it in bath could be causing the prop to be loading up too much ?

both the 6 volt and 12 volt decaperm say max efficency current draw 3.5 amp

what am i doing wrong
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17 January 2011 at 20:39 #3688
phill d
Participant
@philld
motor too hot
18 January 2011 at 09:01 #29485
Dave Milbourn
Participant
@davemilbourn48782
Testing in the bath will produce a slightly ‘over-current’ situation c/w running in open water as the prop will normally unload with the forward speed of the model.

The motor is certainly overloaded, irrespective of what voltage it’s rated at. If it’s too hot to touch then it’s too hot and it shouldn’t be pulling that sort of current in any event. I’ve no personal experience of using Marx-Luder motors but 70mm does seem a bit big for a Decaperm from what I’ve seen and read about them.

Maybe the prop is too big; the shaft is binding on the tube/bearings; the prop nut at the back has tightened onto the rear bearing; the coupling is misaligned. Once you’ve checked all of those possibilites then try it at 6v and see if there’s any improvement.

If not then I’d suggest either a smaller prop or a motor transplant – a 900 on 12v wouldn’t break sweat with a 70mm prop.

Hope this helps.

Dave M
18 January 2011 at 11:50 #29487
Haig
Participant
@haig
I think the first thing to try is 6V, as you have a 50/50 chance of the motor being 6V or 12V.

The other considerations would be the number of blades and the pitch of the propeller.

From what can be Decaperm specs available on the web, the 6V model max efficiency is 7 amp, whereas the 12V model max efficiency is 3.5 amp. I am assuming that your motor has an inbuilt gearbox.

I would try 6V, check the amps. (and motor temperature). If still running hot I would try a smaller propeller.

I think that this is what the motor & prop survey and forthcoming article will be all about .

Haig
18 January 2011 at 13:28 #29488
Telstar
Participant
@telstar
Hi Phil

A x70 is too big for a Decaperm I do have these motors in use, on direct drive I have a 45mm 4 blade prop. the motor gets bearly warm.

Current is the cause of motor overheating the heating of the motor increases with the square of the current; (doubleing the current increases the heating by four times) .

If you halve the voltage you will halve the speed (rpm) but NOT halve the current. So I would :

            a   check the propshaft, for tightness ,alignment etc no load current should be less than 1A

            b    fit a less demanding prop, (smaller dia or less pitch)

If you get the current down to about 3.5A and the motor still gets hot, you have a faulty motor

Tom

Edited By Telstar on 18/01/2011 13:29:15
18 January 2011 at 16:07 #29490
phill d
Participant
@philld
The shaft is definitely not binding, and the motor and shaft are in perfect alingment.

when i check it no load at all its 1/2 amp, and the same with shaft connected.

I can that running in the bath would cause a power loss etc as the boat is not moving through free water and being more under load.

I have since tried it with a 50mm prop that is 70mm pitch and it stays coller than before.

With this prop it runs flat out at 3 to 3.5 amps.

The motor is a lot cooler with the smaller prop, but i think it will be far too slow with this prop.

I will try and test it down the canal today and see what results i get from that.

something tells me im going to be getting a different motor for the boat.

I do have a mfa barracuda, but the problem is weight of those, as they are a big lump,and this boat is not realy big enough or designed for this sort of weight.

If it turns out to be 6 volt, then it wont be any good at all for me as on 6 volts it definitely would be far too slow.

thanks for all the info guys, im not up on the leccy stuff by a long way, im normally on the ic side of things.

phill
18 January 2011 at 23:10 #29494
Dave Milbourn
Participant
@davemilbourn48782
If you tell us what the model is then maybe someone can offer the suggestion of a better motor based on experience. It rather sounds like a Decaperm just won’t cut the mustard.

DM
18 January 2011 at 23:33 #29495
neil hp
Participant
@neilhp
decaperms ARE NOT high performance motors………..they are sloggers for tugs, trawlers and old classic lifeboats etc………….if you want high performance you are going to need a motor to do the job.

neil.
19 January 2011 at 01:09 #29496
phill d
Participant
@philld
I do not know exactly what the boat is.

when i got it years ago it had 2 tiny little motors in it just for display purposes.

The model was a prototype from what i was told, it was scale model of something going into production in full size.

That was back in the 1980’s.

The boat is made from fibreglass.

Its like a patrol boat of some kind, 38 inches long,12 inch wide 10 inches high from chine to top of superstructure.

The hull is a planning hull with spray rails as well.

If i was to put an ic in ti i would imagine it could easy take a 40 size engine.

What i want from it is a quick ish rescue boat, sort of on the lines of pilot boats.

Nothing super fast, but faster than a tug boat.

Idealy i would like to get about 8 to 10mph out of it, and last about an hour if possible.

I would love to know exactly what it is and what a full size one looks like.

phill
19 January 2011 at 07:57 #29497
Dave Milbourn
Participant
@davemilbourn48782
Something along the lines of a 12v Speed 700BB Turbo with a 3-blade 35mm prop? Also avoid a lead-acid battery – far too heavy for a planing hull like this. I’d use a high-capacity NiMH pack e.g. 10 x Sub-C size 5200mAH.

DM
20 January 2011 at 00:38 #29505
phill d
Participant
@philld
3 bladed 35mm prop

what sort of pitch would this need to be ?

and would i get a decent amount of time with this type of set up ?

what sort of price could i expect to pay for such a motor and such battery pack ?

sorry to be asking so many questions, but like ive said before, i aint no good on the electric boats

phill
20 January 2011 at 08:28 #29506
Dave Milbourn
Participant
@davemilbourn48782
If you buy a ‘Prop Shop’ or ‘Raboesch Type A’ brass prop then there’s no choice of pitch required. Running time depends largely on how long you run at high-speed and the capacity of the pack you fit.

Speed 700BB Turbo 12v is about £30 while a 5.2AH pack as described would be around £40. The prop would be aprox £15 in brass; much less if you buy a plastic one (e.g. to test the best diameter for the boat).

DM
20 January 2011 at 11:50 #29509
phill d
Participant
@philld
No choice of pitch ???????

wouldnt this set up need a racing type blade, and wouldnt a 2 blade be even better ?

is a 700bb turbo similar to a mfa 800/850 ? or is it a different type of motor altogether ?

sounds like im gonna have to start from scratch.

I think ill have to sell the decaperm or just swap it for something that suits the boat.

phill

Edited By phill d on 20/01/2011 11:51:30
20 January 2011 at 16:12 #29511
Telstar
Participant
@telstar
Phil no need to get rid of the motor, if you fit water cooling, it is capable of more power. Unfortunately most model motors are poor efficiency, and to get the max output power you need to get rid of a lot of heat. typically 30 to 40 watts of heat, and 40 watts of output power which takesabout 7.5 amps froma 12vbattery. Most of the members of the club I visit need to water cool electric “fast patrol” type boats to get performance.

My decaperms are in scale ships (liner and cargo ) so do not need the max power out, although a “rooster tail” may look good on a cruise liner lol

Tom

Edited By Telstar on 20/01/2011 16:13:46
20 January 2011 at 17:42 #29516
ashley needham
Participant
@ashleyneedham69188
A 700bb turbo is a fast sort of motor , and the 850 is an agricultural sort, powerful of course but a bit bigger and heavier. The reccomended prop size on 12V for an 850 is 50mm, (works ok on my MFA Seahawk) I believe the 700 is better on a lesser diameter as stated.

As you are not looking for ultimate speed, a standard 3 blade brass prop will be fine. They are also better across a range of speeds unlike an “s” or “x” pitch “racing” 2 blade one (the normal sort).

Plastic props are alright, but have a finer pitch generally than brass ones, cheaper of course and may well work ok on your boat. There is no set formulae here, its suck it and see time!

Cornwall model boats has all the hardware on view on their website with the relavent specs and would no doubt offer advice over the phone.

Ashley

Edited By ashley needham on 20/01/2011 17:44:29
21 January 2011 at 00:03 #29522
phill d
Participant
@philld
ahhhh telstar has given me a bit of hope

if i water cool the motor it could be ok !!!!!!

well i can definitely water cool the motor easy, and even put a small pc fan near it if that would help.

if i can get anywhere near what i need, ill then change the battery for nimh ones to lose a bit of weight.

is it better to be as cold as possible with electric motors ?

phill
21 January 2011 at 08:59 #29523
neil hp
Participant
@neilhp
having had experience with decaperms in my long years of model boating, [ 50 plus years] they are a] not meant for running at high speads under load…..that’s why they fit gear boxes, and b] because of their build,change very little in performance and heatingdifference when being watercooled….from experience i fitted twoold but perfectly sounddeca’s without gear boxes and with watercooling copper piping as an experimentto a friends 44″ Waveney class lifeboat.. becausae he couldn’t afford two 850’s at the time……and two 3 blade 50mm brass props………..within three sails both motors burnt out their armatures and were completely knackered. i was also running two 6v designated motors on 12v…..decaperms are good for what they are built for……slow speed scale……but NOT for high speed planing boats……….and no amount of tweeking and time spending will ever change that.

the amount of time you will spend mucking about trying to get none available performance from a slow running motor could have been spent heeding the advice from a master like dave milbourn, and got your boat running on what he recommended……plenty for sale on ebay……..

there is a lot of experience on this forum…….try to take the advice from them.

neil
21 January 2011 at 10:48 #29524
phill d
Participant
@philld
mmmmmmmmmm

now im back to having a slow boat again then.

looks like i will sell the decaperm and try to get something like a 700bb turbo.

anyone have any idea what a almost zero use decaperm is worth ?

And not 100% sure if its 6 or 12 volt, but definitely not been run for long.

infact its only been in the bath for about 15 mins total testing.

phill
21 January 2011 at 12:55 #29526
neil hp
Participant
@neilhp
sometimes they go quite well on ebay……other times they flop, big time……..it’s the luck of the draw unless you protect with a reserve……but anywhere between 10 and 50 quid is normal.
21 January 2011 at 13:04 #29527
Telstar
Participant
@telstar
Niel I note you extoll your virtues in your post, and I do know you have an opinion on Everything, But because I don’t post every day does not mean I have no experiance in modelling I have probably worked with decaperm motors longer than you (70years old. modelling since my teens) and a qualified electrical engineer (with a degree in electronics) i dont advise people to MUCK ABOUT, any advise I offer is just that advice, and not dogmatic diatribe you tend to churn out.

Try thinking before you post, age old use may be usefull, but technical knowhow is better. that you BURN OUT motors is a good advert for your advice, and to burn out with water cooling WOW that takes some abuse.

By the way Dave (aka action electronics) does a very good job supplying ready made parts for modellers that don’t know electrics but these are his answers, not the holy grail (Sorry Dave, )

Slightly annoyed Tom
21 January 2011 at 19:18 #29536
ashley needham
Participant
@ashleyneedham69188
I am with Neil on this one. I have never seen a fast model with a decaperm. It would be a bit of a waste as nowadays there are loads of proper speed motors to choose from, at very reasonable prices. Or even brushless…

Dave has quoted a fairly tried and tested combination of bits guaranteed to deliver a reasonable performance on this size of boat, as a good starting point…and I know if there were a hundred posts on this item, they would all say something different. Yes, I know, how can they all be so wrong???

everyone has an opinion and a forum is the place to air it. If you dont think its right, well, thats also an opinion.

Ashley.
21 January 2011 at 20:22 #29541
phill d
Participant
@philld
I will settle all this tommorow

i shall get the boat down the canal and see if i can get any decent speed from it.

i dont care if the motor gets hot or not, it should go quick straight away if its gonna work.

if it does then i will get it out the water and water cool the motor, if it dont im liable to jump up and down on it ha ha

I will try to get video as well to see just how good or bad this will be.

phill
21 January 2011 at 21:01 #29542
neil hp
Participant
@neilhp
wowee, telstar that’s a great attitude to bring to a forum…….not only do you attack me, someone that you have never met, but attackl the guru of electronics as well…..you’ll go far, lol
21 January 2011 at 22:28 #29544
phill d
Participant
@philld
maybe he is a bit like me.

I am what is known as a equal opportunities argumentative offender

in other words i will have a go at anybody, it dont matter who they are.

colour ,religeon,race,sex,age,experiance etc etc etc. i take no prisoners.

especially when i know im right

phill
21 January 2011 at 23:20 #29545
Colin Bishop
Moderator
@colinbishop34627
Don’t fry the Decaperm – give it a good home, there’s always somebody who wants one and you can put the loot towards a proper performance motor.

Colin
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