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Dave nicholls17/08/2012 07:59:43
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16 forum posts
26 photos

Morning,

Can anyone suggest a battery set up to improve longer running times & more go!. At present i am using 2x 6volt 5.0 AH/20HR lead acid batteries to give me 12volts. Azimut Atlantic Challenger is the boat in question, it has two jet drives with 2 Graupner 700BB Neodym Turbo 9.6 volt motors, these motors are direct drive to prop shafts. Have changed all wiring connections to gold bullets & a fan to help with cooling, 2x 50 amp speed controllers with 30amp fuses are fitted.

Regards, Dave.

ashley needham17/08/2012 08:15:59
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6753 forum posts
198 photos

Dave. Ditch the gell cells and buy a 12v 5Ahr Nimh pack.

Much better performance from the weight saving alone, likely longer run time.

I have swapped for same in my Fantome and Seahawk, and there is a noticeable performance increase in both , previously they had 12v 7Ahr gel batteries in.

Small gel cells do not appear to give up the current as well as Nimh cells in my limited experience, so you may get more power as a by-product of fitting Nimh batts.

Oviously there will be a dimension change so check the new battery measurements etc. Suppliers such as the Component shop can make up pack to order and even supply split packs.

Ashley

Dave Milbourn17/08/2012 09:54:05
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4018 forum posts
282 photos

"Small gel cells do not appear to give up the current as well as Nimh cells in my limited experience, so you may get more power as a by-product of fitting Nimh batts".

 

Perhaps the understatement of the year, if not all time! Two of those motors are likely to want a total current in excess of 30A at full chat. No SLA battery we could buy can possibly supply that amount of current continuously, whereas modern NiMH and LiPo batteries are good for 30C+ (C being the 1 hour charge/discharge rate e.g. a 5000mAH battery would have C=5). They are also much lighter than SLA batteries for the same capacity - the clue is that L stands for Lead.

The only sensible application for SLA batteries is in conjunction with very low current motors and where multiple batteries can be used in parallel as useful ballast e.g. tugs, motor sailers. For planing models they make no sense at all.

Dave M

 

Edited By Dave Milbourn on 17/08/2012 09:54:34

ashley needham17/08/2012 10:19:16
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6753 forum posts
198 photos

Dave. Sorry, will overstate next time !

I dont have anything drawing this sort of current so put in the understatement, too many experts out there. Dont want to get shot down etc etc

Ashley

shipwright17/08/2012 11:56:13
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250 forum posts
54 photos

I thought that some munufacturer's data might help. The following was extracted from datasheet for PowerSonic 12 volt 7Ah battery (as an example this battery will give 8 minutes to a final voltage of 8 volts at a discharge rate of 14 Amps):

sla_ps1270_discharge_characteristic.jpg

I'll see if I can find data for a 12v 7ah NiMH battery for comparison.

Ian

shipwright17/08/2012 13:36:39
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250 forum posts
54 photos

Slight error in my previous post - should have said "..... will give 12 minutes to a final voltage of 8 volts at a discharge rate of 14 Amps".

The graphs illustrate that the Ah rating for batteries can be misleading unless you read the small print. The Ah capacity of a battery is often quoted for the C/10 rate. An example - say you have a battery quoted as 10 Ah then C = 10 Amps. Therefore C/10 = 1 Amp. So the battery will provide a current of 1 Amp for 10 hours. But if you require a discharge current of say 2 Amps then you will not get 5 hours discharge time - likely to get a lot less time say 2 hours giving an effective 4 Ah. Basically the higher the discharge current the smaller the effective capacity. Manufacturers' data sheets will provide the effectrive capacity at a given dischrge rate (as in the example graphs in my previous post).

As an example for NiMH, some data is available at this website :

**LINK**

Ian

ashley needham17/08/2012 20:20:43
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6753 forum posts
198 photos

ian. Most interesting. An answer to a lot of questions there I think! Still, its all a bit hit and miss, regarding run time due to a whole stack of variables.

The data is perhaps at its best when used in a fast boat situation, whereby the throttle is fully open for most of the time.

Ashley.

Dave nicholls18/08/2012 18:57:45
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16 forum posts
26 photos

Many thanks for all the info you guys, going out tomorrow with all the old stuff in the boat to give the swans & gease a run for there money!.

Dave.

ps Sunday being a day of rest, i will start Monday modifying things on the boat .

Dave Milbourn19/08/2012 09:26:46
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4018 forum posts
282 photos

Dave. Sorry, will overstate next time !

I dont have anything drawing this sort of current so put in the understatement, too many experts out there. Dont want to get shot down etc etc

Ashley

Foreven the diplomat, Ash! No offence intended, mate, but this is a particularly large bee in my own bonnet - having seen far too many Huntsmen fitted with enormous SLA batteries plodding round the pond like narrow boats.

Dave M

ashley needham19/08/2012 18:26:06
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6753 forum posts
198 photos

Dave, didnt take offence at all.

It is difficult making the ultimate "i am right statement" on this or any forum as there are always experts out there and some of them dont take kindly to misinformation.

I go down the route of suggesting that this (whatever it is) is my personal opinion and others are quite free to disagree or agree with it.

I know you to be an expert and somepne who does not overstate his case and so would certainly not disagree with anything you might suggest in your field of expertise.

Ashley

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