Lipo short circuit problem

[mikejbb]

I was testing my new lipo with a vom when I slipped and shorted it out just for a moment. Too late, a poof of smoke and the lipo is shot. I put it back into the charger to see that 1 or 2 cells no longer work, probably 1, but not sure since the charger only has red and green led's for status. 1 green and 2 red, should mean 1 bad and 2 charging, but I'm not sure. My question is it appears there must be a fuse in the serial connection as 0 volts come out now (with no slipping). Can I open up the lipo and put in a new fuse or don't bother, just throw it out?
Thanks
Mike

[flydiver]

Chances are you cooked a wire or a solder joint. You can carefully cut back the covering and inspect it and check from the connection to the end for broken/cooked wire. Soldering a wire back on to a blob of existing solder isn't too hard. Soldering directly onto a cell needs special solder, flux and methods-never done that.
Actual lipo may or may not be shot. If you want to be really conservative you trash it. I'd check it out more extensively first, then make a decision. I don't think a momentary short would actually ruin the cell itself but certainly put out enough energy to burn a wire.

Another good reason for a wattmeter to check safely.

fly

[mikejbb]

Thanks fly, I took the lipo apart and found one connection broken. I tested pushing it together and the serial 11.1v was good and then tested the lipo on the charger and all was good. I then soldered the broken connection. That was hard, the side with solder was fine, but the leadin connection didn't want to melt the solder for a good connection. I guess my 15 watt solder gun was too small. I'll have to redo the joint with a hotter solder gun.

Anyway I then connected the 11.1v 2400mha lipo to my cub and all ran perfectly, except with a lot more rpm. As per this site I will test to see how hot the new battery and original esc get before flying. I also pulled the low voltage cutoff jumper so the lipo will not be run down too much.

And I will be ordering the wattsup wattmeter today.

Thanks
Mike

[flydiver]

Hopefully you have a balancing connector. If so, balance charge that sucka in a safe place and watch it. Then run it easy the first time out and check it after a minute of flying.

15W is too small for this sport most of the time. Think 40W iron. I have a fine point for work like you did and a large chisel point for Dean's. The long exposure of the battery to heat is not good for it. Same with the Dean's-do it quickly.

If you are going to 3S it would be a prudent idea to prop down to a GWS 10x6 HD or APCe 10x5 thin electric. The stock prop is a bit much for the increased RPM's-too much load. The electrics are borderline for 3S-the bigger prop is what often cooks them.

fly

[mikejbb]

Yes I have a balancing charger and it charged just fine. I went flying and the new 3s lipo worked great! Thanks fly and to everyone here for giving me the courage to try it. I landed after a minute or 2 to check on overheating and the lipo and esc were just a little warm, definitely not hot. so I took off again. It was very windy, 8mph-12 gusts and for the first time my sc acted like the wind wasn't that much of a problem at half throttle.

I wish I could say all went well, and all went very well until one of the servo's worked it's way loose during flight. My advice is to add some glue to them even if they seem snug.

Anyway, then I went into a nose down spin and broke the prop, the wing in half, all 4 strut connection hooks broke off, the fuse has a crack from the battary box half way up to the wing, the connectors to the tail broke the pin, and the propeller shaft is bent. All is fixed right now except the propeller shaft needs a little more unbending, but it's too noisy and my wife's asleep now. I'll finish that in the morning. Gorilla glue is amazing, good thing I just bought some yesterday. I'll be checking the other posts re strengthening the wing and replacing the struts, I remember I read about them in the past few weeks.

Only issue is the motor must have been VERY hot, I didn't check it when I landed the first time. But when I got home, about 10 minutes after the crash, it was still VERY hot. So my guess is that in my case the battery and esc will be fine, and my motor will burn out. I used a master screw 10-8 which did not pull the sc very well with the stock battery so I thought it'd be ok with the 3s lipo. Not sure now, doesn't matter, it broke and the next one I'll try is the gws 10-6 I have and fly said might be ok.

The new brushless and esc should arrive early this week so if the motor overheats, I'll live.

Thanks again
Mike

[flydiver]

MAS are generally not known for being good props. I pass this on a rumor-haven't tried them myself based on this info.
Told you 10x8 was too much on a 3S lipo. DO NOT get the SF (fat) prop. You need the straight sided 'skinny' one. You were pulling too many amps through the motor and it can't handle it. Turns it to heat.
Sorry about the crash. Never a fun thing.

fly

[snapperz]

Apr 20, 2008 16:54:53 GMT 1 flydiver said:

If you are going to 3S it would be a prudent idea to prop down to a GWS 10x6 HD or APCe 10x5 thin electric. The stock prop is a bit much for the increased RPM's-too much load. The electrics are borderline for 3S-the bigger prop is what often cooks them.

fly

So As I have read, the stock motor and esc will work fine with the 3S lipos as long as you prop down and pull the jumper.

Propping down (10x6) will prevent the frying of the ESC (Is that correct?). Meaning the motor will only pull so many amps? If the motor pulls too many amps, POOF goes the ESC?

OR

It looks like I need to get a Lipo which has a maximum discharge rate (in amps) less than what the ESC can handle (Is that correct). If so, what is the default maximum of the Cub?

I would like to go ahead and get the Lipos so when I move up to a different plane, I will have not wasted money on the 8 cell 9.6v batteries.

[flydiver]

May 30, 2008 17:51:10 GMT 1 snapperz said:

So As I have read, the stock motor and esc will work fine with the 3S lipos as long as you prop down and pull the jumper.

Propping down (10x6) will prevent the frying of the ESC (Is that correct?). Meaning the motor will only pull so many amps? If the motor pulls too many amps, POOF goes the ESC?

OR

It looks like I need to get a Lipo which has a maximum discharge rate (in amps) less than what the ESC can handle (Is that correct). If so, what is the default maximum of the Cub?

Yes, propping down lowers the load on the motor and ESC. The extra voltage increases RPM > increases work > increases heat.
The ONLY thing pulling the jumper does is re-set the LVC to 8.9v. Personally I wouldn't trust it and would fly by time and keep my resting voltage greater than 3.7v/cell > that's 10.1v for your math deficient folks.
Resting voltage will not be the same as working voltage and will read higher.

RE the Lipo: NO NO NO!!! You want to get a lipo that can do MORE than is required of it. If you put an inadequate Lipo in and the system tries to get MORE it over taxes the lipo and ruins it.

You CONTROL the work with the proper sized prop. Motors have a NARROW operating range. If you increase the RPM's you need to decrease the prop to keep the draw in the same vicinity.
YOU CANNOT GET EXTRA PERFORMANCE WITHOUT A COST SOMEWHERE!!! Basic physics.

Try it-slap a 12x8 on there with a 3S. Cub will go like stink for about 3" and then the motor or ESC will burn up.

The brushed Cub stock motor on 3S will pull ~12A depending on the battery and prop. If you are unfamiliar with these term and limitations that will not mean a thing to you.

Your BEST tool to start understanding this is a device called a wattmeter. Get one and learn to use it. When you start doing your own motor/prop/battery/ESC combos you are working in the dark without it.

ParkZone has done the work figuring this out FOR you. If you change ANYTHING you are messing with the balance and if you don't know what you are doing you have only your ignorance to blame. There are a LOT of burned up systems out there to verify this statement.

fly

[snapperz]

Alright. I am trying to understand it all (as I read post after post on Lipos).

If the 3S pulls only 12A, why are the ESC burning up? The people must be using to large of a prop. Otherwise, the stock ESC should be able to handle 12A, right? If I could match that with a 3S Lipo and smaller prop, then I wouldn't worry about frying anything. I guess I would only worry about wearing out the engine....

Is all of that correct?

[flydiver]

PROPERLY propped on 3S it pulls ~12A. On stock 7-cell it's considerably under that. That's WHY you get a performance increase when going to 3S and WHY you are pushing the electronics to the limit. They are borderline for the jump.

When you go to 3S the stock 10x8 slow fly is NOT properly propped anymore > it is OVER propped. If you keep the throttle down you can get by. But most people don't go 3S so they can fly conservatively, they hot rod and enjoy the fast Cub until it burns up and wonder what they did wrong.

Electric motors are constant speed devices. The speed (RPM) is a function of the way they are built (wound) and the voltage. Potential RPM is defined in RC as KV (1000 RPM/volt). So theoretically a 1200KV motor would turn 12,000 RPM if you put 10v into it. More volts > more RPM. The prop is the load. Bigger prop = bigger load. Ask a bigger load to go faster and at some point the motor simply cannot do it and starts turning the extra volts to heat.

You can't ask a VW Bug to pull a 50' trailer at 60mph-can't do it. Yet somehow people think they should be able to throw more volts and a bigger prop on a plane and it should just TAKE it.

ESC's are designed to deal with an AMP load-they are RATED. Unfortunatley Parkzone doesn't tell you the KV of their motor or the rating of their ESC. You learn the 'hard way'!

If you put too big a prop on the motor TRIES to get to that RPM, pulls more amps, turns it to heat > now it's a race to see which one fries first. If you have attached a battery that is not capable of the output it stresses the battery too. It gets hot and if a lipo potentially puffs (a bad thing).

Brushed motors are also designed for a voltage range. As the volts go up the arcing at the brushes increases as well as the load on the motor. Yes, it wears faster on higher voltage. Don't do it, baby it, or suck it up and buy another $10 motor when it burns up. Lots for sale in the [Sale section] since people convert to brushless a lot.

fly

[snapperz]

Thanks a lot Fly.

I have read information on the KV before, but it wasn't until now that it is starting to make more sense. In the end, I am trying to have it all make sense before I do something wrong. I guess however, I will end up making some mistakes anyway! (I just don't want them to be too costly).

On a separate thought, I ran my cub into a light poll tonight. resilient sucker! I went for another 15 minutes after I made sure there was no damage. What a great plane to learn with.