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Author Topic: Increasing Running Times  (Read 1748 times)

Tralee

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Increasing Running Times
« on: July 13, 2007, 09:11:23 PM »

 I have recently built a Robbe Kit Najade, I have to say that  I have followed their instruction with regard to electrics etc and have been very disappointed with the running time of about 15 to 20min duration. Performance is very good but of a short duration.
The current set up is a 700 12v motor (water cooled) 2nr 6v 4.5amp lead acid batteries. 40mm prop
Is anybody able to assist me in a set up with a longer running time without loss of performance
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johno 52-11

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Re: Increasing Running Times
« Reply #1 on: July 13, 2007, 09:38:17 PM »

Well looking at the spec on the 700 motor it draws 12.5amps at max Efficiency. So 20 mins out of 4.5 amp batteries seems about right. One way of increasing your amps to weight is to use NiMh batteries Model power do a 9000mAh cell for £5.99 so 10 of them together would give you 12V 9Ah twice the Amps twice the running time for less weight than your lead Acid Batteries.
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DickyD

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Re: Increasing Running Times
« Reply #2 on: July 13, 2007, 09:58:03 PM »

Check here for batteries. Excellent service and cheap prices. Lots on the forum use them.

http://www.component-shop.co.uk/html/nimh_flight_packs.html

Example: 12.0V 3700mAh NiMH SubC

Compact 12V SC pack. Ideal for larger planes, also the
compact shape makes this pack suitable where space is
limited, such as in some boat hulls. Light weight
replacement for traditional lead-acid batteries.

£23.25 each.
£21.10 discounted price for 3+
£19.25 discounted price for 10+

Using these you could use two instead of two lead acid.
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Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

PSSHIPS

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Re: Increasing Running Times
« Reply #3 on: July 13, 2007, 11:55:17 PM »

I've, been here before! It looks like your'e motor/ battery/ prop set up is well off sinc, try a low drain high peformance motor and take a look at prop size/ load and power consumption of your motor at peak under load. 12.5 Amps is not right!
 It should be about 3.5 Amps max!

 I am supprised you havn't fried you speed controller?
  :o
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johno 52-11

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Re: Increasing Running Times
« Reply #4 on: July 14, 2007, 12:37:08 PM »

I just took the info from the tecnical spec on the Westbourne models web site.

"Graupner 700 BB Turbo 12v
Ballraced motor with internal fan. Suitable for Power Gear 2:1 Or Direct drive.
Specification
Nominal voltage 12 V
Operating voltage range 7,2 ... 19,2 V
No-load rpm 11600 min–1
No-load current drain 2 A
Current drain at max. efficiency 12,5 A
Current drain when stalled 43 A
Max. efficiency without gearbox 75 %
Length of case, excl. shaft 67 mm
Diameter 44 mm
Free shaft length 14 mm
Shaft diameter 5 mm
Weight 350 g"

also found this http://www.modelboatmayhem.co.uk/Modellers/Steve%20Beasley/Najade.htm which gives figures of 30 mins of 2 6V 7amp Lead acids

The cheapest way of getting more running time is to get some more sets of lead acid battries and change them over. We only get 15 to 20 mins with the Severn running flat out and thats on 18V 12A


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FullLeatherJacket

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Re: Increasing Running Times
« Reply #5 on: July 14, 2007, 01:46:06 PM »

Ref Dickie D's suggestion - I purchased two 9Ah, 7.2V D-sized NiMH packs from Iain at Component Shop. Including Tamiya connectors & P+P the bill came to £63 -  that's for the two, not each. The Najade will perform better with lighter batteries, anyway. Why not ask Component Shop to quote you for a couple of 6v packs? This business is seriously good on price, quality and delivery.
"No connection, just a very happy customer" as they say.
FLJ  8)
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PSSHIPS

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Re: Increasing Running Times
« Reply #6 on: July 14, 2007, 02:43:47 PM »

Thats the reason I don't use Graupner motors, too heavy on juice.
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