Batteries

[Dave nichollsParticipant @davenicholls]

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.

[Dave nichollsParticipant @davenicholls]

[ashley needhamParticipant @ashleyneedham69188]

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 MilbournParticipant @davemilbourn48782]

"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 needhamParticipant @ashleyneedham69188]

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

[shipwrightParticipant @shipwright]

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):

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

Ian

[shipwrightParticipant @shipwright]

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 needhamParticipant @ashleyneedham69188]

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 nichollsParticipant @davenicholls]

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 MilbournParticipant @davemilbourn48782]

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 needhamParticipant @ashleyneedham69188]

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

[shipwrightParticipant @shipwright]

Here is a link to get information about NiMH batteries. The link that I provided in my 17/8/2012 posting (above) is broken :

**LINK**

Ian

[HowardParticipant @howard79726]

I've been watching Paul T and Bob Abell's 'Brutus' project in the Scratchbuilt forum and, amid the current (excuse pun) discussions on motors, Esc's, wiring etc. Dave M suggested that if all else fails a pair of Speed 700 BB's with 40mm props might be worth considering. Coincidentally, I have a couple of these motors earmarked for a fast patrol boat hull of around 1200mm as the next project, and I was wondering what batteries to go for, i.e. a couple of Nimh packs at 12v or Lipo's at 11.1v? The latter would be lighter but perhaps requiring more care regarding discharge limits etc. or would these motors which seem to have reasonable muscle cope OK with the weight of the Nimh's?

Hope nobody minds me adding my musings here, but I didn't want to gatecrash the 'Brutus' thread with a rather tangential question.

Howard

Edited By Howard on 23/03/2014 11:13:44

[Dave MilbournParticipant @davemilbourn48782]

Howard

There's not much to choose here. For example a 12v 5000mAH NiMH pack from Component Shop will deliver 35C maximum (far more current than you'll ever need), weigh about 750gm and cost £41.75. A comparable 3S (11.1v) LiPo 5000maH pack will also deliver 35C, weigh about 400gm and cost £45. You'll get about the same run-time from either type and you can fast-charge either at the lakeside with suitable equipment.

In a model that size the weight difference (about 350gm – or 12oz) is pretty much irrelevant, as is the size. Many folk are scared of LiPo packs as they do need more attention, particularly to the discharge voltage limit and charging. I would certainly recommend a speed controller which you can program for low voltage alarm or cut-out. Microgyros do a beauty. Failing that instal a low-voltage audible alarm. You will also need a balance charger, but these aren't expensive. Again, alarms and chargers are all available from CompShop.

In short, if out-and-out performance is what you want with these motors then go for the lighter pack (LiPo). If the maintenance and potential safety thing is worrying you then stick to NiMH. Go ahead – toss a coin!

Dave M

[HowardParticipant @howard79726]

Dave

Thanks very much for your reply – no substitute for knowledge and experience, and yours has helped me to make the choice.

I use the Microgyros F40 – no problems and a competitive price! I need to contact them about setting the low voltage indicator as I believe one needs a jumper to do this between 2S and 3S, and I don't know if I can get them from themselves or Maplins or simply make one. None supplied with the unit.

Thanks again

Howard

[Dave MilbournParticipant @davemilbourn48782]

Howard
I've put the relevant pages of the FR40 Instructions in My Album. Trying to contact Mike S is not easy!
Dave M

[HowardParticipant @howard79726]

Thanks again Dave, that answers all my queries! I see from the Microgyros site that they now feature a 'face lifted' FR40 which appears to come with a jumper.

Howard

[Dave MilbournParticipant @davemilbourn48782]

Mike included a couple of resistors and capacitors with my FR40 "in case I didn't have any"…………… I think he was being ironic.
DM

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