Battery Life

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23 May 2012 at 18:33 #34564
Alan Tadd
Participant
@alantadd57458
I gave my new build boat, (Nautical Marine Models "Dark Biter" MTB), it's maiden voyage and was fairly pleased with the results….at least it didn't sink!.

The boat did get up to plane and looked balanced, but I felt it should be a little quicker….Turning radius was quiet large and I may need to look again at the twin rudder linkages to see if I can obtain more rudder movement

Battery life was very short, about 10 minutes max, and I wondered if I could upgrade my current batteries or look at fitting twin packs or something else. Your advice would be appreciated. Would fitting a 12volt Lead acid be any better or possibly these LIPo things (which completley mystify me!), in which case, which one?.

The boat has twin Graphner equivilent 600 motors, (Westborne models sourced these)
Battery – Nimh Battery Pack SubC 3800mah 9.6v Premium Sport (Tornado)
Single ESC with BEC, Not sure of the size but Westborne assurred me it was more than capable of running the motors and BEC.
Twin Props, 3 blade 30mm dia.
Hi Tech Servo
Planet 2.4 TX and RX.

Regards

Alan
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23 May 2012 at 18:33 #2132
Alan Tadd
Participant
@alantadd57458
Maiden Voyage of Nautical Marine Models MTB “Dark Biter”
24 May 2012 at 17:13 #34572
Paul Freshney
Participant
@paulfreshney24971
Alan

Graupner Speed 600 (or equivalent) are high revving and can be thirsty for amps – see specification on Cornwall Models website.

My NMM Dark Biter has two Caldercraft CEM550S motors (£7.99 each) from Cornwall Models, running on a single 8.4v 3700mAh Sub-C pack from Component Shop, direct driving 3 bladed warship style 35mm brass props from G. Sitek. Running time is approx 40 mins at a variety of speeds. One MTroniks 20 Amp Viper esc controls both motors. Model performs well in excess of scale maximum speed.

38mm props give a similar performance, but slightly shorter running time.

On load, both motors together draw approx 5 amps, so running time is therefore about right from an 8.4v battery pack.

Motor specs as follows.

Nominal Voltage: 8.4V
Operating Range: 2.4-12V
RPM at Nominal Voltage: 11500
No Load Current: 1A
Part No: CEM550S

Hope this helps

Paul Freshney

Editor of MB
24 May 2012 at 19:40 #34574
ashley needham
Participant
@ashleyneedham69188
Do you know that I have had, indirectly, the same experience recently, courtesy of a new poster, Mr T, who has discovered our very nice pond is nearby…

He has two speed 600`s fitted, and was running them off a 10Ahr gel battery and had an Mtronics 25A ESC.

Needless to say the ESC frazzled and when I looked up the motors, was horrified to see current draws of 12A or so each…so giving a massive 24A draw in total !! Not having much experience of heavy-draw motors I didnt twig at the time that running the boat at that time was BAD with a capital B. No doubt, as the performance was a bit lack-lustre, the battery was similarly unable to cope for very long?

I have loads of boats with twin or triple motors but all small units, two boats have single speed 600`s but of the ECO variety which only draw about 7a or so.

I didnt think at the time of Mr T`s motors being hungry animals but there we are.

He has a 50A controller now and some 4300 Nimh batteries, but even then he may experience your problem of short run times. Will be interesting (as it will be his boat and expense and not mine!!!) to see what happens, at the very least i think we will need to force cool the ESC. I have a pair of ECO 600`s and loads of "standard" 540`s so I think we will be swapping motors soon.

Makes you think …my next project has a powerful brushless and the recomended 60A ESC !! I may be a bit more careful when testing it out now..

Ashley
24 May 2012 at 21:25 #34586
shipwright
Participant
@shipwright
Alan,

I also have constructed a NMM Dark Biter. I followed Dave Abbott's review article and installed 2 x Graupner 7.2v 600 ECO motors and a pair of 3300 mAh 7.2v NiMH batteries connected in parallel. It is a "thirsty" rig and I have measured current consumption at about 9 amps per motor going flat out (I made a special deck and mounted a digital ammeter and voltmeter on the deck – I then videoed the boat and was able to read the voltage and current – boat looked a bit strange but it was an effective method !!). I couldn't achieve full scale speed (which is about 8 knots) – I got about 6 knots. I installed a 40 amp mtroniks ESC and also a 20 amp fuse for protection of motors and ESC. The brass props are naval style Raboesch 35mm diameter. Duration – obviously depends on how you sail it – but if you assume that you are not going flat out all the time I can achieve about 20 minutes or so. I would encourage all Dark Biter owners to send pics to NMM to put on their website – that way we can see the variations in the way they are fitted out and painted.

Ian
24 May 2012 at 22:02 #34589
Alan Tadd
Participant
@alantadd57458
Interesting information Gentlemen. Thank you.

It would appear thatI have a thirsy combination and the answer may be to add a parallel battery.

Image of my boat:-

Sorry it wasn't on the pond long enough to take vidio or photo's….

Alan
24 May 2012 at 22:11 #34590
Paul Freshney
Participant
@paulfreshney24971
Alan

If you look at Customer's Boats on the NMM site you can see the interior of my Dark Biter. The second battery at the stern is a spare 'old' 7.2v Sub-C pack – the model normally only uses the battery in front of the motors. Then if I wish to run the model some more later in the day, it is an easy matter to unplug and change the power supply without actually taking the battery pack(s) out of the model. Performance is more 'scale-like' on 7.2v, but rather more fun on 8.4v!

Paul Freshney

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