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[Sonparc]

I have a long standing problem with one of my boats that I have not been able to fix and would welcome any advice.

After running beautifully at speed for about five minutes the power dies but after a couple of minutes apply throttle again and it is away again.Further running makes the dead periods longer.I have changed the speed controller and rerouted the aerial but no change.

The spec is - Motor Robbe 710/12 Power Plus water cooled.

Speed controller - Jeti JES 600 water cooled

Power - 2 x 7.2 volt nicad packs

Receiver - Futaba 6 channel ( only using 3 )

Sonparc

[tobyker]

Sounds to me like something's getting hot and seizing. Prop shaft bearings, motor end bearings? Losing end float in motor/shaft? either that or the electric fluid can't get through the wires fast enough - no doubt FLJ will have a view on that.

[andyn]

Low voltage shutoff.

[boatmadman]

My money is on losing the end float on the shaft and/or overheating a bush. Have you lubricated the shaft at all?

Ian

[grasshopper]

After you've been through all the mechanical and wiring checks - and seeing as you tried another speed controller, I'd also check the connections to the motor internals as well as external - if you're drawing a lot of current it is possible that the electrical joints inside the motor are failing - the brushes are sometimes only a press fit into the copper strip - I've had these go 'iffy ' when running a bit over current.

Irrespective of the sticker, they're mostly made by Mabuchi, in their millions so getting a duff motor is always a possibility.

[Sonparc]

Thanks for some very quick replies!

I am sorry but I do not understand 'low voltage shutoff' and 'losing the end float in the shaft',would you gents kindly explain please?

Maybe I should have added that the boat is a water jet so has a very short drive shaft which had teflon grease put on it when I built the boat - maybe it has all worn away.

Perhaps a new motor is the answer,I don't mind the cost but it will be a very awkward big job as it is difficult to get at with a lot of other stuff to move as well.I have just tried the boat again after putting a bit of play on the coupling - however it always works on the bench.

[DickyD]

Low voltage shutoff.

Dont see how if he can start it up and run longer the next time without recharging the battery.

[Timo2]

Hi

   Can you tell us  Battery Size ?  .   2 Battery = 7.2 v    or 2 battery  =  14.4 v  plus size of the jet unit

    Timo2

[knoby]

Hi Sonparc, I had a similar problem with my swordsman. The problem was I was using the esc's built in bec circuit, as soon as the battery voltage dropped the esc would cut out. I solved the problem by using a receiver pack instead of the bec.

I'm not familiar with your esc, but I know its not uncommon to have bec problems with motors that draw higher currents.

Cheers Glenn

[Umi_Ryuzuki]

For that type of system, a jet drive, and those batteries, five to eight minutes of
running time isn't abnormal.. The boat should slow down and then stop, or the esc/bec
will detect low power, and shut off. After a few minutes, the batteries will gather a bit of
energy, and will run a bit longer...

Doing that to the batteries is hard on them. Nicads will often reverse a cell when over discharged.

[Sonparc]

Hi All

Timo2  -- The two batteries give 8 volts when fully charged

Glenn   --  I am not using BEC and have a receiver battery

Umi     --   When the boat stops it stops and does not slow down and when it goes again it has full power.The jet is about 20mm diameter

Sonparc  

[grasshopper]

The problem is unlikely to appear on the bench - no load on the motor!

Sod's law dictates that any problem will manifest itself at the worst possible time.....I still think your motor's iffy

[Sub driver]

Hi,
Check the blurb that came with the speedo ...

Sounds to me that it may have an automatic thermal cut out fitted.....as the speedo gets too hot it cuts power then cools down and the thermo cut out re sets and off you go again...until it gets too hot again then cuts...sounds like you are pulling too many amps for the speedo to cope.

If it is then it has saved you a few pounds as the speedo would have fried and burst into flames.

check the load amperage and also the capability of the speedo and if not already done so install an in line fuse  below the speedos limit.... if the fuse keeps blowing it is also an indication of too many amps for the speedo to cope.

That jet drive on 14.4 volts will probably be in the 30 amp range, I run a similar set up on a jet drive PBR and mine certainly is.

Hope its of use.

Sub.

[Sub driver]

Hi,

Is the controller the jeti JES 600 Navy ?

If so.............. you are on the maximum cell capability at 12 cels for that controller, and it HAS a current limiter fitted that will shut power off when it gets exceeded.


See below..............


Features include: BEC - Battery Eliminator Circuitry - provides the receiver and servos with a 5 volt supply direct from the drive battery - eliminating the need for a separate receiver battery.
PCO - Power Cut Off system - gives a safety margin during the flight. As the drive battery voltage falls, the PCO checks the value and cuts off the motor at a point which leaves sufficient power to operate the receiver and servos for a reasonable period of time. It also provides a small margin of power for emergency motor operation during landing difficulties, for example.
Current limiter - each controller (except Jes 050) will tolerate 200% of the specified Continuous Current Rating for a period of 0.5 seconds. If this is exceeded, the controller automatically shuts off the power to the motor. This is particularly useful if the propeller is accidentally stopped whilst still at full power, during landings, for example.


 
Specifications
Power (continuous) 50A
Number of cells  6-12
BEC 3-4 Servos
Dimensions 40x22x9
Weight (inc wires)  17g
 
Regards Sub.


 
     
 

 
 
 

[Timo2]

Hi

   Have a look at this may help,    https://shop.graupner.de/webuerp/servlet/AI?ARTN=2341      jets units look for Torque

 Timo2

[Sonparc]

Just to recap I am using 12 cells at a max output of 8 volts.The speed controller is the Jeti Jes 600 Navy which can handle up to 30 cells and is rated 60A.

I am a long way from being an expert on electrics but I use the same battery packs in my Robbe San Diego which has TWO similar sized motors with a 50A speed controller supposedly suitable for up to 10 cells and get up to 30 minutes sailing without a problem.

The speed controller I replaced by the Jeti was a Robbe navy 535R rated 35A and suitable for up to 14 cells.I am of the opinion that the hardware I am using is adequate but I stand to be corrected.It is possible that the water cooling feed to the Jeti is blocked but would it over heat and shut down in 5 minutes?

As per a previous post is the next thing to try a new motor? The present one is 10 years old but as it was bought new for this boat and because of the troubles  has not had a lot of running.
 
Sonparc

[DickyD]

I'm inclined to go with sub driver here after reading that spec he's posted, have you another speed controller you could try ?

[Timo2]

Hi 

  It is possible that the water cooling feed to the Jeti is blocked but would it over heat and shut down in 5 minutes?   quote]

    YES      Heat and more heat

     Unit design to water cooled has to have water to cool it  ?

   Timo2

    PS  Pipe cleaners ??

[Sub driver]

I had presumed that you had checked all the simple things prior to posting......a blocked intake would probably do it.