Homebuilt Rov Forum

Hi all, I am trying to make an informed decision on what to use for onboard batteries. I will not use lead acid for obvious reasons (explosive gasses and weight) and I am leaning towards Lithium packs for small size and weight reasons. I guess my question is how many 12v packs will be adequate to run 4 - 750kv brushless motors? And what amp hour rating would you recommend? On all the ebay listings the technical specifications are very poor.

funny you ask this question as i am in the very same position, I was lending towards lipos, I was thinking of 4 x 3000mAh 20c packs from hobbyking at about $13.09. But am undecided. I'll be interested to hear others input too.

Rob

What I am mainly concerned with is a limited run time. At most I will be running 2 motors at the same time plus 2 - 50W led lights. The camera draws so little current its not worth mentioning. Lighting load including a dc to dc converter to get my 30V forward voltage for the led's is Max 4 Amp.

lipos. light, small, cheap with high power density. just don't abuse them.

Hi derelicte, How many would you recommend for my design in a parallel battery bank? I am thinking about these from eBay using 4 packs paralleled. Should give me a decent run time. My hull is Schedule 80 PVC 6" diameter 16" long so I have tons of room for stuff in there.

http://www.ebay.ca/itm/300723424555?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

sizing a battery is pretty simple. you need to how much current your rov draws and how long you want to use it per charge. math will tell you how many of those 5000 mah batteries you will need to use in parallel.

just make sure you use a low voltage cutoff in you controller to prevent over discharge.

I would like to have an OSD board for my display. I want to be able to monitor internal temperatures, battery voltage, heading and depth. So much for a simple ROV like I planned when I started LOL.

The other great thing about lithium polymer batteries is they're pressure tolerant, i.e. they don't squish at depth, so no need for a pressure vessel. I intend using them in my hobby ROV design too.

http://martin-wareham.blogspot.co.uk/

Martin

Explosive gases with lead acid shouldn't be a problem should it? I thought they only emit hydrogen whilst charging, not discharging. Any one know different?

m_g, When the battery is being charged the higher voltages used will cause the water in the electrolyte to be broken down into its elemental components of hydrogen and oxygen and the mix of these two gases is as explosive as you would ever want to find. At high discharge rates or prolonged discharges the battery will also gas. Normally this is a non issue when open to the environment because it is in very small quanities but in an enclosure the slightest ignition source and.... BOOM!!! My rule would be 1. never run a vented lead acid cell in a sealed container for any reason. 2. Sealed lead acid batteries are much better but can still possibly be dangerous if for some reason you vent gases. IMHO I wouldnt trust anything that has the potential to become an explosive. I worked in an battery maintainance shop once where they charged batteries for aircraft equipment and let me tell you when something goes wrong its on heck of a bang. Just remember the Hindenberg!