Power for a Graupner 600

[Chris PearceParticipant @chrispearce30862]

I have installed a Graupner 600 (7.2V) engine in my 36 inch sea commander, with a 35mm P brass prop and 12 volt ESC, I tried it out with a Nicd 7.2V 1700ma, which lasted about 15 minutes which showed some good results.

With the above info would it be fair to go for a 7.2V Nicd or Nimh with a high ampage, any thoughts?

 ChrisP

[60wattParticipant @60watt]

Yes.You’ve done the arithmetic already by another method.

According to Johnson the 600 cans are fully rated at 30 watt heat loss without forced cooling so your motor will manage that or better if the end is metal.

Look in the johnsonmotor website for the 35dia motors and you see that consuming about 60 watts and converting 30w to the shaft they are at max power.

If you up the prop until revs fall to 50% of the free running figure you have the prop size for maximum thrust.See http://www.modelboats.co.uk/forum/forummessages.asp?dt=4&UTN=1196 in case it helps.

Doing that will reduce running time but increase speed to maximum.

Tom

[ashley needhamParticipant @ashleyneedham69188]

Chris. If the motor was running mostly at speed for 15 mins ok and not getting very hot, I cant see why you shouldnt increase battery capacity for longer run time. I think they have stopped making NiCads now, in any event NiMh is the more common, Is it an ECO motor? As you have a big boat perhaps your SLA`s would do, the ECO is not a massivley power hungry animal. Ashley

[Chris PearceParticipant @chrispearce30862]

Hi,

 It has a idle current drain of 2.0A  Current drain at max effciency 12A  blocking current drain 85A and Max efficiency 69%, not an ECO..

I haven’t tried my 6v 4amp lead, yet, looking at a 7.2v 4300 Nimh, would a 5000 be the dogs biscuits?

I take from the sums! a 30mm prop may prove a little better?

[60wattParticipant @60watt]

Hi Chris.

Is this a Sea Commander speedboat from Graupner?

For arguments sake,suppose your 35mm P brass prop and Nicd 7.2V 1700ma actually gave exactly 7.2 volt @ 6.8 amp for 15 minutes………It’s a bold assumption but it makes things easier to digest.

Assume also that " idle current drain of 2.0A  Current drain at max effciency 12A  blocking current drain 85A and Max efficiency 69%" is at 7.2 volt and also 100% true.

If both were correct you’d be to the left of D on this dc motor graph  and on that basis I would increase the prop a touch until point D .Power output would be 60 watts and heat loss 27 watts. That is fine for a 600 run continuously so long as there is air ventilation.

Tom

[ashley needhamParticipant @ashleyneedham69188]

Chris. Its an old  wooden  boat , not a graupner. You really need to know how many amps you are pulling with the current (pun) prop, This will tell you if the prop you have is ok, too large or too small. This will only tell you if you have reached max efficiency mind you, if you are using a brass prop then possibly a 2 blade plastic race type prop may give you better speed for the current draw.  Unless you know what amps you are actually drawing, any fancy calculations based on guesswork are useless.  Ashley

[60wattParticipant @60watt]

36″……….I thought something was fishy. (sorry)

Put the correct prop on that Graupner 600 then it will do the job.I’m left wondering if you might break a speed record in the process.

If you want the duration of > 6Amphour batteries ,not discharging in 10 minutes not saving weight then sealed Pb batteries are the way to go.

You have a good motor for a speedboat but a trawler or tug could utilise one of the pictured motors.A 550 gives you an idea of size.They have nylon parts and would only output 20 watt but can run much larger props and on a lower spec ESC.The 12v motor stalls at 6 amp and 6 volt one stalls at 13 compared to 70 amps for your one at 6v.

Ashley.Sometimes there’s a call for 600 motors in old wooden boats.This one is 10 y.o. and uses two 600’s It’s 36″ long and its 24″ version leaves some fast electrics in its wake.

Tom

[Chris PearceParticipant @chrispearce30862]

Hi,

I will leave it as it at the mo,well put that plastic one back on and try that, Ashley, when I can get to the pond on a Sunday I will let you have a look, then you can advise as we go…

Tom, Ashley put in some non Nicds, (?) and for awhile it went V well in deed, but soon dead, looked great.!

Update you soon with the plastic prop 2Bladed.

Cheers ChrisP

[ashley needhamParticipant @ashleyneedham69188]

Chris. I am sure it would have flown when we tried my battery if the speed controller had been up to it. The Graupner you have is a fairly serious bit of kit, it might be wise to find ouit the current capability of your ESC or get a 25A one from Mick Charles models or Addlestone models. I will leave my ammeter in the car so we can check you out , whenever. Ashley

[Chris PearceParticipant @chrispearce30862]

Update,

I replaced the brass back to the plastic twin prop and used the 6v 4amp went very well indeed, good turn of speed, the hot motor, battery and ESC are back!  

[ashley needhamParticipant @ashleyneedham69188]

Chris. really sounds like your ESC is not up to the job, the motor may well get warm/hot anyway as its a feisty animal, the battery (your gel cell??) will get hot as they dont like big amps being taken out of them. Anyway, NiMh cells get hot too as a matter of fact.   I will also put one of my Graupner 600 ECO motors in the car, these are not as hot as your current motor. Ashley

[ashley needhamParticipant @ashleyneedham69188]

Update…Chris had an x40 prop, and the speed from  this and the existing motor combination was a bit poor. Th ammeter said 20 amps drawn!!!!…but I have a feeling this was all the ESC would dish out. We tried a Graupner 600 ECO motor and an x35 prop, better, 40mm plastic 3 blade, worse…. 40mm brass 3 blade best yet…no overheating on motor/ESC/battery (6v 10Ah SLA)    We tried an standard 540 and this was a bit underpowered.

A suggestion from the assembled throng was that the performance demonstrated (and it looked ok to me) may be about right for the year… bearing in mind its not a powerboat.

Chris..go on, get a 40A ESc and a 4300 MaHr NiCd and make the B#### fly!!!!

(but just getting a 600 ECO would be cheaper.    ashley

[Chris PearceParticipant @chrispearce30862]

Ashley,

Good of you to help out with the Tech stuff.. learn’t lots, bundles…. in fact, your recommendation or hint is an idea…. maybe for the Sea Queen Aerokit for next year or maybe not watch this space….

All I know is that, this model boating stuff is got me buzzing !!

 Cheers

ChrisP

[Chris PearceParticipant @chrispearce30862]

[Author]

Posts