New to RC Boats: Electric Heat Question

[direwolf]

I bought this (http://www.cenracing.com/boats/grey.html) boat the other weekend for me and my sons to get out and have some fun together.

I have the one with the 550 electric motor which runs off a single 7.2 battery

I currently have four 1500 nicd batteries and I get about 5 minutes run time out of each. I plan on getting three 3700 batteries in the next couple of weeks which should get a bit longer on the water.

One thing I have found is that after 5 minutes running the motor and the battery are too hot to touch. Well the motor is, but I can only hold the battery for about 5 seconds before the heat is too much.

I'm thinking that this can't be too good for the long term life of the motor and batteries. Do I need some sort of cooling?

[Rex R]

cooling the motor would help, unless my math is wrong it looks like it is pulling around 18 amps, which is a bit high. a bit less prop would likely help too...unless it is a driveline problem. have you checked/lubed the propshaft? if not, try that 1st before you try plumbing for water cooling. considering that the pic shows sanyo 2400's I'd guess that either a) you have binding in the drive or b) more prop than was intended.
as for the batts, some of the low cost packs have higher internal resistance than the more expensive ones(turns them into heaters at high output), cooling them in boat may be futile...try to get the amp draw down 1st.

[direwolf]

I assume the pic on the site is of the 775 motor version which uses two 7.2v batteries. I run the 550 and a single (currently 1500) battery.

The batteries I have are cheap ones so I guess that would explain them getting hot?

The drive shaft is greased and moving ok.

I don't understand what you mean by more prop? The one I have is the one supplied in the kit. I can post some photos if need be?

[Rex R]

I'm not quite sure of the naming system for that prop(as listed on the web-site) but it would appear that they are using one size for both versions...and that is sized for the bigger motor. if I'm right your prop measures 42mm in dia., you prolly want one around 35mm dia., they do list a cooling kit...tho if you're handy you can make one for less (about $5 usd).

[direwolf]

Ahh ok.

I just measured the prop and it is 42mm.

I'll head down to my hobby shop tomorrow and pick up a 35mm one to see how it goes. Will this decrease the speed of my boat?

I think I saw tubing and stuff at the hobby shop so I might see if I can throw together a coil cooling system while I'm at it.

[n.h.schmidt]

Hi I have this boat. Mine uses the bigger motor with 12 cells. Your boat is way underpowered with the 550 motor and six or seven cells. You really need to cool the motor in every way you can think of. It should be easy as the outdrive already has a water pickup. You should already have the hull drilled for the tubeing to go in and out. If you want to go a lot faster ,it will be easy with your boat. Offshore Electrics has everything you need to change it to a fast 700 motor ,speed control and better props. You will go form about 15 mph or less to 25mph with 12 cells. I don't think a smaller prop will get your boat moveing as the boat is very large . I have had mine up to 28mph (GPS checked) useing a Graupner 8.4 700 motor ,12 cells and a Prather P 220 prop. n.h.schmidt

[direwolf]

hmmm ok

This is a new spin on things.

I have considered upgrading the motor to a 700 and will at some stage. For now the speed is ok for my boys and the size pond near home.

So I guess this boat has problems with motor heat normally? This is my main concern for now as I don't want to do any damage or shorten the life of anything. Once I get the 3700 batteries the run time on water is going to at least double so I am very concerned about how hot things are going to get.

Should I try a smaller prop anyway?

I live in Australia so I will need to find an Australian store like Offshore Electrics I guess.

[n.h.schmidt]

In Austraila you are in luck, Give Andrew at fastelecrtics.com a try. He has done a lot of work in this area. He could be of great help. For cooling if you put a aluminium coil on the motor ,you will cure most of the heat problems .Some guys have had good success using a little computer fan in the boat and have it blowing directly on the motor. As to a prop a Graupner CF K42 prop would give more speed and probably less heat at the same time. They are usually low cost at about $5-6 U.S. Much better than your typical plastic boat prop. n.h.schmidt

[direwolf]

Thanks for the info on fastelectrics.com, would never have found them otherwise :)

[direwolf]

Well I installed a cooling coil on the motor and took it down to the pond today.

End result = heat problem solved :)

Now after a 5 minute run the motor is cool enough to keep my fingers on it without getting burnt.

Even the batteries are cooler so there must have been a fair bit of heat transfer from the motor to the batteries.

I've got a 36mm prop on order, so I'll give it a test out when it arrives anyways.