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Author Topic: short run time  (Read 4903 times)

surabaya

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short run time
« on: June 07, 2008, 01:49:28 PM »

hi all,
I have just been to my local river/canal to try out my just finished motor cruiser and I was pleased  :)apart from the time it lasted. :(
It is 50" long and I have 2 x 585 mabuchi motors  from one  50 amp Esc with a 12v 12ah sla battery and one servo for the twin rudders. It has twin props about 45 or 50 mm.
It cruises at a reasonable rate for what it is, Ie. cruiser, but the battery only lasts about 10 t o15 min.
I have two and they both do the same.
Any ideas on how to increase running time
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Shipmate60

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Re: short run time
« Reply #1 on: June 07, 2008, 02:15:42 PM »

surabaya,
There is something not right there. Those figures give you a current consumption of 24 Amps.
Do the motors or ESC get hot after the run?
I would certainly suggest changing at least the props to smaller ones as these would put a lot of load on direct drive.
In my opinion the motors are too small to power this size of model at a scale speed.
I would go for 550's or even 777's on 12 volts and a smaller prop.

Bob
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Stavros

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Re: short run time
« Reply #2 on: June 07, 2008, 05:01:11 PM »

As you sau Bob there os something really wrong here as I get at least 10hrs out of a TID Tug with a 700 and a 3ins prop,but I must admit and you should remember I had Exactly the same probs with the fireboat, mfa motors pulling horrendous amps as bob says change the motors asap


Stavros
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HS93 (RIP)

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Re: short run time
« Reply #3 on: June 07, 2008, 05:05:46 PM »

How hot do things get?

Hs93
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surabaya

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Re: short run time
« Reply #4 on: June 07, 2008, 05:39:30 PM »

Hi,
After running, I checked the Esc and the motors and they were not even warm. I could reduce the prop size , but at the moment they look right. Much smaller and they would look too small.
Are the motors drawing 2x 12 v, they are running in parallel. or do they still take 12v and more amps.
I never get these motor numbers, is a 550 stronger than a 585 then.
What if I use a bigger motor with a gearbox. Maybe the batteries are naff?
I don`t want to lose any speed, in fact maybe she could do with a little more.
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HS93 (RIP)

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Re: short run time
« Reply #5 on: June 07, 2008, 05:46:52 PM »

Borrow a battery of someone the same size or even less amps to try ,I think yours may be not as good as it should be.

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Martin [Admin]

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Re: short run time
« Reply #6 on: June 07, 2008, 05:58:28 PM »

Can you show us a picture of the internals?
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Shipmate60

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Re: short run time
« Reply #7 on: June 07, 2008, 06:26:33 PM »

surabaya,
What I didn't make clear is that the 24 Amps is for EACH motor.
If that was the case the motors would burn out after a few minutes!! They are just not designed to take that sort of current for long.
If you want to keep the props I would suggest something like 550 motors on a 2 or even 3:1 reduction gearbox.
The speed pictured isn't fast so these should allow that type of speed with much reduced current therefore longer battery life.
If there is any doubt about the reliability of the batteries replace them, or borrow a known good one.
If on a good battery she handles as you want with nothing getting hot, problem solved.
As Martin has said pics of the internal and external layout would make it much easier to tell.

Bob
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surabaya

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Re: short run time
« Reply #8 on: June 08, 2008, 12:24:35 AM »

Hi, These are a couple of pictures of the inside, pretty basic stuff.
2 motors, 1 Esc, 1 battery, acoms receiver, and a servo for the rudders plus some lead weights.
I have put the battery on charge over night to try again and I have a smaller 12v 4ah that I will try too.
If not I`ll nick the battery of of the Mrs car ;D. Only joking  ::)
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banjo

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Re: short run time
« Reply #9 on: June 08, 2008, 04:47:17 AM »

I have put the battery on charge over night to try again and

What sort of charger are you using, what charge and for how long?
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surabaya

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Re: short run time
« Reply #10 on: June 08, 2008, 07:56:30 AM »

It`s a multi voltage charger. It can be switched to  2, 6, or 12v at 600Ma and when charging is complete, it switches to trickle charge.
And you have just given me an idea, maybe it was not on long enough or I may have set it to 6v by mistake. ::)
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FullLeatherJacket

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Re: short run time
« Reply #11 on: June 08, 2008, 09:24:11 AM »

Mabuchi don't list a "585" so I think you must have 385 motors. These are best on 12v but those props do look a bit large for such motors. You might consider some "soft" 540-sized ones or, as has been suggested, geared motors. This would enable you to fit some decent-sized props e.g. 45mm 3 or 4 bladers without overloading the motors.
Having said all that I reckon it's a duff battery or faulty charging that's the real problem.
Keep us posted.
FLJ
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surabaya

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Re: short run time
« Reply #12 on: June 08, 2008, 09:40:57 AM »

Hi,
Sorry, I made an error regarding motor`s ::)

They are 540`s, RS540Sh to be precise.

FLJ : What is a "soft" 540?
And what motor would you reccomend?  ( keeping cost down)
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surabaya

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Re: short run time
« Reply #13 on: June 08, 2008, 09:43:51 AM »

Also, does anyone know how to work out charging time for a 12v 12ah battery with a 600MA charger?
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wombat

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Re: short run time
« Reply #14 on: June 08, 2008, 09:52:16 AM »

Assuming the battery is totally flat charge time will be greater than 12/0.6 = 20 hours - so a good 24 hours to get the thing up to full power.

If it is 385 motors in there, I can't see them taking 25A each for 15 minutes without combusting - I would guess that if you didn't burn out the windings, you would burn out the brushes.

I would suspect either a duff battery or a discharged battery

Wom
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surabaya

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Re: short run time
« Reply #15 on: June 08, 2008, 10:02:03 AM »

They are definitely 540`s and I am beginning to suspect the batteries more.
As for charging, am I right that you just Divide the V by the output = hours of charge.
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John W E

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Re: short run time
« Reply #16 on: June 08, 2008, 10:19:50 AM »

surabaya hi there

First comments; the batteries you are using - they are the same as I have in my model of HMS Leeds Castle - they are huge things.   Those batteries are a heavy sort in fact very heavy.      Your comment about the boat not performing fast enough for you, well with these weight of battery in you will find it extremely difficult to make your model perform at any reasonable speed.

As for, your charging time; I use a PowerTech multi charger  which is 600ma charge.   It takes anything between 24 hours to about 36 hours to put a full charge in these batters REMEMBER THOUGH WHILST CHARGING THEM KEEP A CLOSE EYE ON THEM - JUST IN CASE THEY OVERHEAT.

I have one battery which is a bit naff - one half of it stays cold and the rest of it becomes warm whilst charging - this is indicating naff plates on the inside.   This battery I just keep as balast for models or when I freshly instal new electronic systems in a model I will sometimes check it out using this battery.   

Your motors, can you attach an amp meter directly between the battery and the motor? just to give some indication of what amperage they are pulling whilst the model is out of the water.  540s / 585s should pull in the region of between 1.5 amp and just a little over 2 amps.  Whilst, as I say, free running.   Anymore amperage than this whilst the model is out of the water and we have some problem with alignment or friction in the drive between the motor and the propeller.  This may be the cause - very doubtful though, if you are saying there is no heat generated in the motor.

aye
john e
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Shipmate60

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Re: short run time
« Reply #17 on: June 08, 2008, 11:04:59 AM »

surabaya
If the motors are genuine 540's there is a problem.
Genuine 540's are basically car motors and as such designed to run on 7.2 volts.
Some however will run higher voltages but id is usually printed on the can.
These motors rely on rpm to give power so they would struggle on the props you are using.
As an example the smaller Fast Electric boats use 540's.
As Bluebird has rightly said the weight of the battery will always slow her right down as they are very heavy.
For out and out speed 2 x 700 BB turbos will have her planing easily, but your run times will be very short.
This can get expensive so can you tell us what you want to change?
The size of props will not allow you to use most of the faster motors as they are designed to give power by rpm, which the props wont allow.
You can however keep your set up and just change the motors but the compromise will always be speed.
2 x MFA 850's will power her along quite well but these motors are about 25 each.
For speed you will need lighter batteries, faster motors and racing props.
The decision is yours!!

Bob
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surabaya

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Re: short run time
« Reply #18 on: June 08, 2008, 11:26:56 AM »

Hi, Firstly, even if I reduce the size of battery, I then have to increase the ballast, so that is not really an option for me.
It does sound like I need to replace the motors with something a little stronger, but not faster.
Like you say, the motor I have are trying to turn the prop  too fast and if I use something with more torque but less rpm I maybe getting there.
Any other reccomended motors, other than the 850s?
I have heard someone mention a 777 somewhere?
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Shipmate60

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Re: short run time
« Reply #19 on: June 08, 2008, 11:30:31 AM »

I did,
I run 777's in a gunboat on 12 volts with about 45mm prop shop props.
On full power she is too fast but the motors do get hot.
I am reducing to 9.6 volts, but haven't run her on that yet.
Duration doesn't seem bad though as I run her on a 12 volt 5 Ah battery.

Bob
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malcolmfrary

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Re: short run time
« Reply #20 on: June 08, 2008, 11:56:45 AM »

As neither motors nor ESC are getting hot, the first suspect has to be the battery, either not getting fully charged, or not holding a charge.  I would check the voltage at the battery terminals.  Fully charged, you should see over 13.5 volts.  Swich on and spin the motors, the reading should not change by more than a very small percentage.  Or apply a test load such as a car headlamp bulb.
For motors, a couple of 15 volt 545s are a fairly cheap drop-in replacement, and should have a more suitable power delivery.  Looking at a web search for rs540sh, it seems a popular stock motor for cars - it is intended to rev freely, whereas you are needing torque.
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John W E

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Re: short run time
« Reply #21 on: June 08, 2008, 12:05:03 PM »

hi there Surabaya

Please can you confirm how you have your motors wired up?    Looking at your photograph it looks as though you have them wired up in series?  If they are, they may be contributing to your performance of the vessel.

I have included a little scribble to show what I mean about the wiring up.

If the motors are maximum voltage 6 volt;  to run them off 12 volt, you would have to wire them in series.   However, if the motors are 12 volt - 18 volt, you would be better off having them wired in parallel.

Having said that, if the motors are only 6 volt, you could get 2 x 6 volt x 10 amp batteries which would give you the equivalent of your 12 volt - 12 amp batter and then all you would have to do is wire your batteries in parallel to give you 6 volt 20 amps.

aye
john e
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surabaya

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Re: short run time
« Reply #22 on: June 08, 2008, 01:40:58 PM »

Hi, Bluebird,
Your "scribble" is exactly how I have the motors set up. Is this the best way . If I did it the other way, would they draw 12v each, therefore try to take 24v from the battery? andwould the Esc take it?
 Shipmate, the 777`s sound a little quick, what are your thoughts if I used the 555`s?
Ray
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Shipmate60

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Re: short run time
« Reply #23 on: June 08, 2008, 01:58:48 PM »

My thoughts are to go with the 777's and wire them in Parallel, so each motor gets 12 volts, if she is a little fast you could always not use full throttle, water cool them or go for smaller props.
What is happening with your boat now (well spotted John) is that basically you are running 2 racing motors on 6 volts which is a run down racing pack.
There are always alternatives to get the required result, just depends on how much you want to spend.
If it was me I would try the 777's on the present props, check the performance and bring her in after a full power trial and check the temp of the motors.
I would also fit the fuse in the red lead FROM the BATTERY, not where it is now.

Bob
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John W E

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Re: short run time
« Reply #24 on: June 08, 2008, 02:07:59 PM »

hi there all

well Bob, you can type faster than I can do a scribble  :D  as Shipmate 60 has said, in your set up now each motor is receiving 6 volts.  Now, if they are 12 volt motors, they will only be revving at approximately half the revs.  The thought is then if they are a 6 volt motor; they will be at their max rpm obviously.

Try setting them up in parallel as Shipmate Bob has described; be careful though of the amperage drawn from your motors wired in parallel, ensure that your speed controller can handle it.  In parallel say - if one motor is drawing 15 amps the other motor will be drawing 15 amps as well, so it will be a total of 30 amps.

aye
john e

I have included a scribble  O0
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