LiPo - Electronics setup
 

Dear all,

i just ordered 2 x Novak Goat Kits with the 18.5 turn motor up front and for the rear a 21 turn.

Now i need 2 Li Po battery but prices are so different. I found the following and would like to know if they are good for crawling due to their Burst Rate : 15C

here is the item

http://cgi.ebay.com/2x-7-4v-4000mAh-...3A1%7C294%3A50

Thanks

15c seems to low to me, from what i have been reading for crawlers you want a minimum of 20c with 30c burts , check out maxamps.com they have a big selection and you should find exactly what you need

For crawling that 4000 pack will be fine at 15c discharge.

John knows his stuff... but I am just curious where you are going to mount a pack of that size??? It is huge.

If it was me in a comp rig, I would be using this pack:

http://www.hobbycity.com/hobbycity/s...0C_Lipoly_Pack

I run the 3 cell version of this pack in my Bully and it provides plenty of juice...never even gets warm (Dual 45T handwounds). It would be nice if the Goat could use a 3 cell, but alas...No. A pair of these would cost $50 after shipping.

Those batteries are advertised as being 4000mAh and 15C burst, that's a maximum burst amperage of 4 x 15C = 60 watts.

Novak rates the 18.5T motor at 119 watts while the 21.5T is rated at 85 watts. Those two motors combined will put out 119 + 85 = 204 watts and can theoretically demand that much power from the battery and ESC.

Even with the two batteries wired in serial, which would give you 8000mAh of capacity, they would only allow 8 x 15C = 120 watts of power output, which is just barely enough for the 18.5T motor, let along the two motors combined.

Having written all that, it is still possible to use these batteries with the two motors you propose. The motors will likely not reach their peak performance, but they'll work...the batteries might get a little warm, just keep an eye on them. I run dual Novak Goat ESCs on one of my supers, which demands a theoretical max of 119 + 119 = 238 watts from my Lipo while my battery is only rated at 4.5 x 25C = 112.5 watts; that combo has been running well without any problems, knock on wood. On my other super I run dual Novak Rooster with 55T motors with 3S 1500mAh 25C batteries which allow a max output of 1.5 x 25C = 37.5 watts and that system runs just fine as well, knock on wood.

It would be 60 amps, not 60 watts.

Assuming the formula of (AMPS = WATTS / VOLTS) and that the volts are constant at 7.4volts (2 cell lipo), then:

The GOAT 18.5 would be AMPS = 119 watts / 7.4volts or Amps = 16.1

The GOAT 21.5 would be AMPS = 85 watts / 7.4volts or Amps = 12.1

Running one of each of these would pull a total of 28.2 amps.

So if he was to purchase the 4000mah 15C batteies that could produce 60amps....the would have plenty of capacity. But that battery is HUGE.

Using the Zippy battery from my previous post, that battery can produce approx 43.5 amps (1.45 x 30c) continuous and burst at about 58amps (1.45 x 40c). This could easily support 2 Goat systems. The smaller size of this type of pack allows for flexible placement...that huge eBay pack would be a bear to place low....if even possible.

I figuring what battery I should run for my ax10. This is very helpfull info.
Thanks

My bad :oops::oops::oops: on the unit analysis...it's amps not watts. It's been too long since I've sat in a physics course. The guys above are absolutely correct, the battery can supply 60 amps (not watts) burst, which is more than what's needed by the 2 brushless Novak mtors.

Thanks for all your help, would i need two of these, one for each ESC?

Only ONE battery is needed. I run my one battery on my rear axle on a homemade tray....then built an adapter to split to each ESC. I only stated the 2 quantity because you were pointing to an ebay ad for 2 batteries.

But splitting a 7.4 batt between 2 ESC wouldn't that split the voltage aswell?

Nope. This is how I have been running my rig for the past bunch of months. No loss of power. No shortage of power. Think of it like this...in your 1:1 vehicle if you were to connect 2 devices to the cigarette lighter/accessory plug would either of those devices get 1/2 of the 12 volts supplied? Or do they get all of the 12 volts? They get all of the 12 volts....they just drain the battery faster than if only one device was in use. BOTH devices get the full 12 volts. IF the battery could not supply enough AMPS to feed the devices, then there would be problems. See the AMPS calculations above. The battery choices described have enough to supply the AMPS required.

I see,

i thought of going for the following

ProTek R/C Li-Poly Receiver Battery Pack (7.4V/2000mAh)

http://www.amainhobbies.com/product_...ducts_id/13508

Is its spec any good and if i stop crawling i can always use them on my truggy / buggy lipo setup :)

What about installing two batteries, is there some sort of issue with that? or its just weight and space?

Thanks everyone

as long as you connect them in PARALLEL not in SERIES you will be fine.

All the red wires go to positive
All the BLACK wires go to neg



Edit: the receiver pack you are looking at might not be the best idea. The wires running to the connector are not heavy enough to handle the amp draw and thus may melt/short/catch on fire.

This has a VERY low discharge rating ans WILL NOT support your usage - check out holmeshobbies.com for the correct batteries.

i use elite 2s 2200 35c 7.4 volts 96mmx34mmx16mm from cheapbattery packs and get good run times

Those elite 2200s are killer cells, I have some myself. Great price for the product too. Obviously a good enough deal for me to buy.

ckrc has 3s 1500 mah with a 25c/35c rating for $40 I belive. A friend of mine just ordered 2 for hs berg

Can anyone kindly explain to me whats the diference between 2s & 3s is it cell count and if i remeber reading correctly you can't run a 3 cell on a goat esc right?