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[BlueWotsit]

At the moment a 32 inch lifeboat,  which we use is powered by

2 x7.2v 3000mah batteries wired in parallel and connected to a 550 mtroniks motor, on each shaft, so there are a total of 4 batteries to charge up

As these only last about 20 minutes, Im wondering what other options we could consider.

The motors are rated for up to 12v and have built in fans, but I was thinking about connecting a 6v 12amp lead acid to each shaft and respective speed controller in place of them.

Obviously power would be down, but weight would be similar and longevity should increase.

Is this the route to go, and should I be looking to change the prop size as well - if so what should I be looking for

Any guidance would be great
 
cheers 

[Shipmate60]

BlueWotsit .
According to your figures your motors are pulling in excess of 18 amps.
6 Amp hour for 20 mins equates to 18 ampHr.
That is a bit excessive to say the least,
Do you have room to increase prop size and how is the performance?
What have you other lads used in your Lifeboats?

Bob

[BlueWotsit]

Bob

The boat gets up on the plane - personally I think it could go slower and still look good - but you know what teenagers are like !

Yes there is room to put a larger prop, Im not sure of the exact size of the current one at the moment, must check that tonight - how much bigger should I aim for, a little more or as much as could fit and still look ok when out of the water

[cbr900]

If you can fit it ten mil will make a big difference, I would suggest taking several props to the lake and try till it works...


Roy

[Shipmate60]

Sureley something like MFA 850's on direct drive would push her along quite well, they rev free at just over 9000 and pull about 10 ish amps.

Bob

[zetec]

Putting the batteries in parallel is not always a good idea as they will not be exactly the same so one will always be trying to discharge through the other, hence they will be discharging each other.  Changing to lead acid might be no better due to the extra weight, how about trying with just one battery pack and seeing the run time to get a true idea of the motor consumption...maybe bite the bullet and splash out on some 9ah "D" cells...

[justboatonic]

At the moment a 32 inch lifeboat,  which we use is powered by

2 x7.2v 3000mah batteries wired in parallel and connected to a 550 mtroniks motor, on each shaft, so there are a total of 4 batteries to charge up

As these only last about 20 minutes, Im wondering what other options we could consider.

The motors are rated for up to 12v and have built in fans, but I was thinking about connecting a 6v 12amp lead acid to each shaft and respective speed controller in place of them.

Obviously power would be down, but weight would be similar and longevity should increase.

Is this the route to go, and should I be looking to change the prop size as well - if so what should I be looking for

Any guidance would be great
 
cheers 

Hmmm. Depends what speed controllers you have (Mtroniks?) and what voltage they are rated for. Assuming you have Mtronik speedos, are these marine speedos or ones for cars? This is important as the marine versions can take 12v whereas the car ones acn only take a max 9.6v.

Therefore, if car speedos, why not up the battery voltage to 9.6 and go easy on the throttle which would give longer run times. Alternatively, if marine speedos, you could use either a 12v SLA or Nicad \ Nimh at 12v.

Another alternative is to buy some of the new 4200 Nimh cells (for 7.2, 9.6 or 12v configuration) to give longer duration?

[BlueWotsit]

yes they are the marine controllers - hence thinking about the 12v - hadnt realised batteries were up to 4.2 on nimh

[Shipmate60]

Are the motors in the boat Jonsons, with internal fans?
If they are junk them on higher voltages, re-engine possibly with Graupner Speed 600's or even 700's.

Bob

[BlueWotsit]

no theyre mtroniks power 500's