Model Slipway Tamar

[Tim CooperParticipant @timcooper90034]

[Tim CooperParticipant @timcooper90034]

I took my Model Slipway Tamar for a sail the other day, no problems, good turn of speed, batteries lasted about 45 minutes.

Yesterday I was tidying some wiring in the hull when I noticed that the main fuse in the Action P92 Power Distribution Board had melted, well the green , plastic had! Surprisingly fuse and the board were still working. The green plastic was now a solid globule on the circuit board. It took a bit of careful prising and poking to remove the plastic and remains of the fuse but on replacing the fuse, the board was still working . Then I realised that the green fuse was a 30 amp, I don't remember when I put that in, it should be 25 amp.

Putting the board back in the boat and connecting up, all seems,to be working.

Has anyone an idea how the fuse could be so hot but not blow.

The boat is using 9.6 v batteries, Graupner 600 ECO motors and 35mm plastic 3 bladed props, with a separate 6v pack for lights, radar, and bow thruster (Speed 400) .

I am wondering if the 9.6 v batts are too much for the ECO 600 , so should I change to 8.4v packs or perhaps to 12 v motors.

Tim Cooper

[Dodgy Geezer 1Participant @dodgygeezer1]

I'd be surprised if the difference between 25A and 30A was sufficient to melt the plastic of a fuseholder, which ought to have quite a wide safety margin.

You may have had dirty contacts or some extra resistance in there somewhere to get the extra heat – this could result in melting even if the fuse was the correct one as specified. Though exceeding the specification didn't help…

[Dave MilbournParticipant @davemilbourn48782]

Some cheaper blade fuses are given a coat of lacquer to make them look pretty. A layer of this can act as an insulator except where the curled-over edges of the fuse holder bear down onto the fuse blade and scrapes it bare. This is naturally a very small area – more of a straight line – and resistance there increases drastically. The cure is to scuff the blades of the fuse before you fit it to increase the area of effective contact – or pay more for your fuses! BTW the screw terminals on P92 are rated to 28A.

You really ought to get a wattmeter and connect that between the battery and the P92. That will show you how much current the motors are drawing. They are small and inexpensive – at the risk of boring folk this is the one I use **LINK**

I always reckoned the 600ECO motors were borderline on power for this big lifeboat and suggested an upgrade to 12v Speed 700 motors. Fortunately these motors survived the demise of Graupner and are still available. They will happily turn 40mm 4-blade brass props without going near the melting point of Chinese plastic…………….. **LINK**

Dave M

[Tim CooperParticipant @timcooper90034]

Thanks

I will send an order off for a Wattmeter. I will have to think about the motor change, the 600's are low in the boat so a wider motor may be tricky to fit.

Tim

[ashley needhamParticipant @ashleyneedham69188]

Dave. It seems to me that not enough people have these cheap wattmeters. Since purchasing one, I am a convert and I think you cant say it enough.

The Graupner eco motor is not a very hot unit, but I would have thought that 35mm plastic 3 bladers would not overload it.

I have a 600eco on the Toyboata driving a brass 35mm prop AND the rear wheels, and it never gets hot even on 8.4V. I cant imagine 9.6V would cause it to fry fuses as described.

As Dave suggests, a larger motor would be more comfortable at this boat size.

Ashley

[Dave MilbournParticipant @davemilbourn48782]

Ashley

There's no problem with the combination of the motor, prop and battery. It's the fact that the Tamar is as big as a baby-bath and really needs more oomph than two of them. Fuses and holders with minimal contact area don't help matters. I would fit brushless motors to this model these days.

Tim

You could always use a 1:1 belt drive system like those Admiral Sir Colin Bishop espouses. That would allow you to fit the bigger motors off-line from the prop shafts. I think they call it lateral thinking…………………

DM

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