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. 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

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

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

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

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

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