How hot is too hot?

[tim slocum]

Hi guys/gals, Since I "hopped up" my Proboat Runabout the motor and batteries have been getting hot. Im going to install a water jacket for the motor,but I dont know how hot is too hot for the battery and what I could do about it if it is too hot?Surprisingly, the esc just gets warm :) Here is a pic of the water jacket Im installing on the motor.Says its more efficient than aluminum coil type.

[tim slocum]

P.S. Now my Proboat Runabout screams :eek: :D :D :cool:

[Deestingray]

Hey Tim,

Just a bit of a heads up but the reason that this water jacket is so good is that it has direct water contact with the can. I understand that you are running a brushed motor. Does yours have any cutouts to hold the magnets in place? If so, basic physics will tell you that water will leak straight out of your jacket into your motor.
I also use one of these jackets on a johnson 785 which I was lucky to have a torque ring on, it was just a simple case of being able to silicone around the ring and I haven't had a drama with it since. I hear that these jackets have a habit of leaking from the sealing point on the can, you might want to put an ever so thin smear of silicone around the can, where your jacket will sit wait for it to start to set and then slide the jacket in place.
Glad to hear that it is screaming, nothing impresses me more than seeing a stupidly fast woody!!!!

About your batteries, I found that mine get quite hot too, it came down to using a less aggressive prop. I had been using a Graupner CF 40mm which was pretty impressive to watch but ate one motor and destroyed a couple of packs. The idea is to let the motor wind out to max revs, you will find that it will stay cooler and your batteries will thank you for it too.

[tim slocum]

Deestingray, I've heard that these cooling jackets come with some shrink wrap that goes around the motor and covers the slits so no water can get in.I just hope the motor doesnt get so hot it melts the jacket! I do have a need for speed. I love the way she curls the water back.Its hard to describe, but the boat curls the water back making a "water pipe", its cool to see. Maybe I can flag down a passing police officer and use his speed gun ,so I can find out how fast my boat is.

[Deestingray]

Yes, you are correct, they do come with a piece of shrinkwrap and yes it could be used for sealing the can. I never even thought of that, I suppose that is my backwards way of thinking. I just wonder though if the shrinkwrap will dissipate the heat fast enough.
You shouldn't melt the jacket though, silicone has a pretty high tolerance to temperature and I can tell you that mine was getting super hot to the point that I had some very hot water coming out after a run.
These woodies seem to be able to really get some good water effects going at speed, I cannot wait to get mine back in the water, it is in dry dock at the moment, I had a similar problem to Kmot with the clear coat cracking up. It is now epoxied and hopefully a lot stronger.

[Shaun Hendricks]

Well, it's been awhile... been very busy. Topic for another thread tho... :D

A battery is too hot when you can't handle it with your bare hands for more than a standing 4 count. Be very careful with hot batteries, it means you are asking more current from the battery than it can easily provide. You might look at upgrading your batteries to higher C or higher mah ratings. Either will up the ability to dump power out.

[Rex R]

you don't want your temps to exceed 150F. the shrink that is used on batteries will start to melt around 180F. the 5 second rule works pretty well(if you cant keep a pinkie on it for 5 seconds, its too hot). one thing to watch out for with batt packs is whether they use welded tabs(tabs are thin and overheat at around 30+amps) or soldered bars(much better than thin tabs). hth
rex

[tim slocum]

Im using a Powerizer 7.2v 3300mah NiMh. I can still hold the battery after a run, so I guess its not too hot.I just didnt know how hot was too hot. Thanks for the info. The motor gets hot enough that if you pour a little water on the motor after a run, it will sizzle. I hope that if I cool the motor the batteries wont get hotter. Where would be a good place to put an inlet for the watercooling on a wooden runabout?Also, the jacket is only about half the size of the motor, is there a "best" place to put the jacket?All the way at one end , in the middle..?Thanks for any info.

[LtDoc]

I think I'd take that advice about the prop. Cooling the motor won't reduce it's current draw (in fact, it can increase the draw to some ridiculous point). The same amount of work will be asked of the battery so it's heating up won't change. If your motor gets 'sizzling' hot, you are asking too much of it.
- 'Doc

[mfr02]

Components getting uncomfortably hot is a sign that they are approaching, or are at, their operating limits.
If the motor is overheating, cooling or a bigger motor will be needed. A cooling coil around the can works, but with a brushed motor, cooling the brush mounts helps greatly.
Batteries getting uncomfortably warm indicates the need for a battery capable of giving more.
The fact that the ESC is barely warm is a GOOD SIGN. It can handle more. If this was not the case, the ESC would protest by either shutting down to cool off, or dying, possibly letting the magic smoke out.

As has been mentioned before, minimising friction in the driveline and having a prop that suits the motor best are vital to check as well.

[fleetmaster]

Tim, I find that my woody gets the same top speed on a 35mm prop as a 40mm.
The 40 gets out of the hole faster.
The 35 takes a little more to get going(gentler on the driveline too),but allows the motor to unwind and get closer to it's max efficiency(around 20 amps for a 700).
Everything runs cooler and i get better run times to boot!

[785boats]

Tim.
How's things. Just a thought on this.
A hard working brushed motor needs cooling on the brushes. Just solder a short length of 7/32 brass tube onto each terminal of the motor. Making sure they don't touch the can. Join them with a short piece of silicon tubing at one end. Attach the incoming water line to the +ve tube. From the -ve tube link to the cooling coil. The other side of the coil goes to the outlet. This makes one helluva difference to the motor temp.

PS glad you got the www.floataboat.com.au fittings catalogue. There must be someone over there that sells the same gear.

Have fun.

Paul.

[pompebled]

Im using a Powerizer 7.2v 3300mah NiMh. I can still hold the battery after a run, so I guess its not too hot.I just didnt know how hot was too hot. Thanks for the info. The motor gets hot enough that if you pour a little water on the motor after a run, it will sizzle. I hope that if I cool the motor the batteries wont get hotter. Where would be a good place to put an inlet for the watercooling on a wooden runabout?Also, the jacket is only about half the size of the motor, is there a "best" place to put the jacket?All the way at one end , in the middle..?Thanks for any info.

Hi Tim,

If things get this hot, you're in the process of killing things, you need to prop down.

If you want a more effective can cooling, look at the tips and info section at Offshore ( www.offshoreelectrics.com )
The brass sheet cooling jacket can be customized to fit every size motor and is the most effective around.
In stead of shrinking tube (too thick) I use a single layer of polyester tape, to shield the can from watercontact.
The aluminum foil, stickers are printed on (the thinnes sort) works very good too.
Together with brushtabs cooling it's the best way to keep your motor cool.

When you run in cold(ish) water, the cooling is so effective, the moisture inside the hull will condensate on the motorcan...

As mentioned above, this is not a mandate to 'abuse' your motor to destruction, even the best cooling can't prevent that.

Regards, Jan.

[tim slocum]

Thanks for all the info. This gives me more to think on. I have already downsized my prop from the stock,33mm,plastic one to a Octura,x430, 30mm.

[Gearhead99]

Let me get this right, you solder a piece of brass tubing to each electric lug for the motor. Without grounding them to the motor itself. Then run cooling water through these two pieces of brass tubing. This is in addition to a cooling wrap on the motor itself.

I'm new to electrics, encase you can't tell.

[Rex R]

gearhead: the brushcoolers are electrically isolated(more or less) by short bits of silicon tubing, but yes you are correct.
Tim:
as the others have pointed out...your motor just isn't spinning fast enough. there are some things you can try before changing motors though...;when trimmed to run straight is the rudder in fact straight or is it turned? shaft lube, unless you're using 3-in-one oil(or sewing machine oil :)) you prolly have 'room' to use a lighter grade lube. one could get one or more 'plastic' x431's from finedesignrc and try your hand at trimming them down... next bit would be to try a 27t motor(well that or go brushless a feigao 540 12s or 8L would be my choice,but was trying to keep the price down). then again your cg might be to far forward, try shifting it back till the boat is just starting to porpose. that might rpt MIGHT unload the motor just enough to cool things down. hth
rex

[tim slocum]

Ok, now Im probably going to sound like a real newbie, but, why doesnt this cause a short? Somebody set me straight please.

[Rex R]

might...if you were running in salt water :) in general the 'fresh' water just isn't conductive enough to cause problems.

[fleetmaster]

And the amperage isn't high-as opposed to mains power at home............

[mfr02]

If the cooled brushes were running salt water, the main problem would not be shorting, but corrosion. The current from brush to brush via the water will be small as against that oing via the motor. A regular check would need to be made to catch it before it went, as a coolant leak is one of the most common ways of sinking a boat in the full size world.

[quicksilver]

that was an interesting point, never thought of that. Guess the only way that COULD possibly be a problem, was if enough current passed through the tubing to heat the water a lot. Basically impossible, unless you had the boat standing still at WOT, with water in the lines, and still then the tubing would just melt expelling the water and ending the short.

Reminded me quickly of the "third rail episode" of mythbusters, where basically the water just couldnt carry the current.

[LtDoc]

The problem with any 'short' is that it causes a higher current draw than can be produced and handled by the 'rest' of the circuit. The short between brushes in salt water mean a higher current draw from the source (battery) through the ESC. At some point, that current draw will definitely make a difference to either the battery, the ESC, or the performance of the motor. It becomes most significant when the 'magic' smoke is released.
Sterile water is not a conductor of electricity. The 'dirtier' it gets, the more it conducts. Salt water is about as 'dirty' as it can get, normally. That state of conductance also depends on the voltage being applied. Higher is 'worser'. Almost 'clean' water would need a higher voltage to conduct than really 'dirty' water. All that is a matter of degree and the best idea is don't let it conduct at all.
- 'Doc

[Rex R]

there is yet another factor that reduces the 'shorting' problem, as most any model railroader will tell you, brass makes lousy rails. when the surface oxidizes it becomes a non-conducter(or at best a semi-conductor...) :)

[785boats]

Brush cooling is common practice here. Our lake can be pretty murky at times but has never caused a problem. Never tried it in salt water myself, so I don't know about that one. If you're worried about a short ,which I don't think is a problem with such low voltages, you could put a fuse in the line.

Can motors will actually run under water with no problems. In fact I've brought a flipped air boat back 50 odd meters several times with the Johnson 785 motor driving an 8"x 4" plane prop under water. No problems. that's with 14.4 volts running through her. The motor still runs like new. Just rev the water out, re-oil the bearings & throw her back in.

Regards

Paul.

[tim slocum]

I'll tell you what I've been doing until I install watercooling. Its very low tech.After about 10min of runnng, I bring the boat in,take a large turkey baster and put some water on the motor. Then I use the baster to take the water right back out of the hull.The procedure doesnt take long and your back in the water.This is just until I get the water cooling installed,but it does cool the motor some.I've even thought of putting a small sponge full of water on the motor.I'll get around to doing a more professional looking fix...sometime.With the way the motor is mounted, I will have to do some modifications to fit any of the cooling options discussed in this thread.For thoughs of you that have one of these boats you'll know what I mean.

[785boats]

Tim.
Another quick fix without water. R/C cars use a finned heat sink that just clips onto the can, you can even get them with a small fan on them. I have one on my crackerbox 540 motor (without the fan). Very effective. Cheap as chips too... Just a thought.

Paul.

[fleetmaster]

I always run my brushed motors in underwater,the extra friction caused by the water quickly matches the brush faces to the commutator.