Changing to brushless

[ashley needhamParticipant @ashleyneedham69188]

If you were using SLA batteries then you may not have been going as fast as poss due to the reluctance of lead batteries giving up the amps.

Nimh batteries would halve the weight and allow full current draw. Lipos are better from a weight point of view but not so good for any other reason, unless you already have boats/whatever that will use Lipos.

Ashley (usual disclaimer..personal view etc etc)

[harry smith 1Participant @harrysmith1]

Lipo batteries require you to use a good charger for a start.

A Lipo safety bag for charging and transporting.

DO NOT LEAVE THE BATTERY UNATTENDED WHILST CHARGED.

Use a voltage alarm when in use and set the ESC cut off voltage to 9.9Volts for 3S and 12.8Volts for 4S.

If you boat stops out in the middle(were else would it stop) wait a few minutes, the Lipo battery will come back up to a voltage that should let you get back to shore(steerage speed recommended).

New mickey mouse radio's have battery volt sensors and voice report to the user on volt levels.

Kicks for bucks a Lipo will out last a NiCad pack.

Weight e.g. Turnigy 2650mah 2S(7.4 volts) 30C is 139grams

NiCad 1800mah is 229grams

2400mah is 301grams

3300mah is 339grams

Size about the same.

C rating on Lipo's is the constant current draw, so if you motor/motors draw 20Amps the minimum you require is 20C.

Size, battery weight and placement, I have used two 1500mah batteries Y linked to get 3000mah in a small model(do not use different capacity batteries, you will kill to smaller one very easily).

[Dave MilbournParticipant @davemilbourn48782]

C rating on Lipo's is the constant current draw, so if you motor/motors draw 20Amps the minimum you require is 20C.

Not quite. The C rating of a LiPo pack indicates the maximum continuous current you can draw from it, but it depends on the capacity of the pack. For example, if a pack was actually 1000mAH and the C rating 20C then that would indeed be 20A (or 20,000mA). However most of the larger LiPo packs we use have a greater capacity than 1 Amp.Hour (=1000mAH) which means that you can draw a higher continuous current from them.

So take a typical 3300mAH (or 3.3AH) pack with a 35C rating. To obtain the maximum continuous discharge current you multiply the C value by the capacity; in this case that's 35 x 3.3 = 115.5A.

Dave M

[harry smith 1Participant @harrysmith1]

Yes you are right, but was trying to kept it simple!

What about temperature effect?

[Dave MilbournParticipant @davemilbourn48782]

I thought you were trying to keep it simple……………..

OK. Simply, batteries rely on a chemical reaction to provide power. Chemical reactions get slower the colder the ambient temperature, so batteries are less inclined to deliver maximum current or capacity, or charge up quickly when the weather is cold. You can now buy heated bags to keep your LiPo packs warm! **LINK**

DM

[harry smith 1Participant @harrysmith1]

I have seen on Hobbyking water cooler plates for Lipo's what do you think of the idea??

[Dave MilbournParticipant @davemilbourn48782]

Never thought about it. There must be folk reading this who have more experience of using the things than I have, and I do tend towards a conservative approach when matching batteries to motor to prop. I suppose if the LiPo pack gets that hot it would be sensible to provide some cooling, but I'd be more likely to try a different prop or even a different motor. Very hot batteries would suggest to me that they are being overloaded and I'd be wary of mistreating LiPo cells in any way. No doubt the fast-electric brigade have their own practices, but that's borderline abuse of the whole driveline!

DM

[harry smith 1Participant @harrysmith1]

I would be worried of the battery exploding and as you say tend towards conservative.

My mate runs a Spearfish with a 3639-1100kv on 3S with a 50mm x 1.4 pitch prop.

I think it's over prop but it all runs cool.

I ask him would he test a 37mm x 1.4 pitch 3 blade when it arrives and another motor.

Scared him a bit when I said it's a XK3674-B-1900kv 1155watt.

But he will give it a go!!!!

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