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Old Nov 17, 2012, 07:59 PM
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jeff reeves's Avatar
United States, WA, East Wenatchee
Joined Oct 2007
304 Posts
Help!
Twin electric setup the battery is getting hot and puffing

If anyone can help that would be great!
I have a twin setup on my OV-10 bronco.
I am using two ntm propdrive 35-48 1100kv
2 hobbyking ss series 90-100 amp escs (opto)
for rx power,
flite max voltage regulator with a venom 1200mah 7.4 volt lipo.
I have the escs hooked up to the motors with the stock leads (they are next to the motors in the nacelles

From the escs, I have the battery leads going into the middle fuse from both sides into a dean's connector. that way I can run either a single large mah battery or batteries in parallel (with of course a parallel adapter).

this system worked great on the first two flights. One using Two 3s 2600mah batteries in parallel and the other flight with two 4s 2200mah batteries in parallel.

On the third flight, I used a 4s 50000mah battery. It flew great for 5 minutes and I was doing the last turn to land, I lost power. The motors didn't stop but just lost power. I made it back to the runway but landed very hard doing a fair bit of damage to the underside of the plane including ripping out my retracts.

Upon inspection, the motors were not hot, the escs were not hot. But, the battery was very hot and puffed.
The battery still had 14.9 volts still in it. What the heck?
If someone might know what is wrong, that would be great if you would give me some advice.
Here is the second flight and everything went well.
OV 10 Bronco on 4s 2nd flight (9 min 34 sec)

Thanks in advance,
Jeff
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Last edited by jeff reeves; Nov 17, 2012 at 08:47 PM.
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Old Nov 17, 2012, 08:48 PM
We want... Information!
Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
5,185 Posts
14.9V is almost flat. Assuming it was fully charged before the flight, you drained ~80% of the battery's capacity in 5 minutes, so the average current draw was about 50A. Was the whole flight at full throttle? If not then the peak current draw must be been significantly higher.

Obviously your battery didn't like being pushed that hard. Insufficient cooling? Weak cell? Low 'C' rating?
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Old Nov 17, 2012, 09:00 PM
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jeff reeves's Avatar
United States, WA, East Wenatchee
Joined Oct 2007
304 Posts
Really? Almost flat? Wow. It was charged fully, but when I charged it again, there was a cell that was a bit lower than the rest of them. It is a 30-40c turnigy battery. I think there was ample cooling. It was 45 degrees outside and the hole for the retract is fairly large.
I ran it in my shop today and the same thing happened. Escs and motors cool but the battery lost its power at again 14.9 volts and was puffed and very warm.
I have been running electric stuff for a long time now and this has me a bit baffled.
Can the escs be too big? Are they taking too much too fast from the battery? Or can that even happen?
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Old Nov 17, 2012, 09:05 PM
I think I'm inverted. Maybe.
acetech09's Avatar
United States, CA, Pacifica
Joined Apr 2012
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Quote:
Originally Posted by jeff reeves View Post
I have been running electric stuff for a long time now and this has me a bit baffled.

Can the escs be too big? Are they taking too much too fast from the battery? Or can that even happen?
Those two statements are pretty contradictory. One who knows electrics would know that ESCs don't determine current draw, and can never be 'too big'.

That and you didn't know 14.9v was dead flat.


Hook your pack up to a reader that reads individual cell voltages, and do a full-throttle static test. See if you have a dead cell. And check your amp draw/C ratings and make sure everythings to spec.
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Old Nov 17, 2012, 09:28 PM
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scirocco's Avatar
Australia, ACT, Kambah
Joined Feb 2001
3,120 Posts
Anytime you talk about a power system problem and don't state the prop size, you're leaving out the vital information for any sort of analysis. Assuming you didn't change props between 3s and 4s, power will more than double. That could be enough to kill the pack, and you may have just got lucky not puffing the first 4s.
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Old Nov 17, 2012, 09:33 PM
I think I'm inverted. Maybe.
acetech09's Avatar
United States, CA, Pacifica
Joined Apr 2012
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Two more things now that I read the post again:

1) I missed that you stepped up a cell... that could double the current, and might be too much for the pack's max discharge.

2) Running battery leads from the wings into the fuse? Not using any capacitors? I'm thinking you might be having some issues with inductance - I don't know all the symptoms but it might be killing the battery somehow? Somebody who knows more about this, chime in?
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Old Nov 18, 2012, 02:56 AM
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Letchworth, Great Britain (UK)
Joined Jul 2004
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Generally speaking, it's not advisable to extend the battery-to-ESC leads beyond their supplied length, which is generally about 8 to 12" when you connect them together. If they're longer, electrical "spikes" can be induced in them, which can damage the ESC. Extra capacitors -- like the big ones near the battery leads on the ESC -- every 8" or so along long battery leads is a recommended solution if you're unable to shorten the leads.

Extending the motor leads from the ESC is not a problem, so the best solution usually is to mount the ESCs close to the battery, not close to the motors.
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Old Nov 18, 2012, 03:37 AM
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Staffs, UK
Joined Nov 2003
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Measure the current it's taking from that single 5000mAh pack using your wattmeter and let us know. Not got a wattmeter, get one.

There's no point trying to guess what's going on when it's so easy to actually find out.

Steve
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Old Nov 18, 2012, 02:29 PM
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Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
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Quote:
Originally Posted by jeff reeves View Post
when I charged it again, there was a cell that was a bit lower than the rest of them.
How much lower? If it is noticeable at full charge then it was probably much lower when 'flat'. The ESC's only look at the total voltage, so if one cell has less capacity then it can get over-discharged before the low voltage cutout activates.

You should charge the pack slowly (0.5A or less) in balance mode, until all the cell voltages equalize. This could take up to 10 hours, so make sure your charger is set to run for at least this long. If the charger cuts out before the pack is properly balanced, put it on again.

Quote:
I ran it in my shop today and the same thing happened. Escs and motors cool but the battery lost its power at again 14.9 volts and was puffed and very warm.
Running the battery out on the bench is not a good idea, as the normal cooling airflow is not present.

Quote:
I think there was ample cooling. It was 45 degrees outside and the hole for the retract is fairly large.
If the battery is getting hot then it has insufficient cooling. What size is the air exit hole?
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Old Nov 18, 2012, 05:35 PM
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tsymonds's Avatar
United States, TX, Killeen
Joined Jun 2011
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From the video Kv does not mean kilovolt. Those are big props for 1100kv motors on 4s specially being that they're 3 blade. No load rpm for those motors is 16,280rpm and with what looks like ~9" 3 bladers along with the comment about switching from 2 blade props and no use of a watt meter I'd bet the amp draw is way higher than you think it is.
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Old Nov 18, 2012, 06:43 PM
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jeff reeves's Avatar
United States, WA, East Wenatchee
Joined Oct 2007
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Thanks for all of your help guys!!
Very interesting. I don't have a watt meter but I am getting one soon that's for sure. What is weird is that on the second flight, I had no problems with a 6 minute flight. No battery puffing etc. But on the 3rd flight using everything the same is when I started having the probs. I did some experimentation today in my shop.
I ran both of my 4s 5000mah packs today without the props. No heat, very little discharge from the battery. I could run that forever. So, I know it isn't my escs or motors. It is about props. I stepped down from the 11x7 3 bladed props and went to a couple of 11x7 e props - thin. This didn't help with static. Only got about 4 minutes of varying throttles before the battery got hot. I changed out the props and put on 10x7 thin electric props and things started getting better. At half throttle (this is static so it should be cooler and better flying) I got about 5 1/2 min before the battery started to go. And when it went, it really fell fast. So, that tells me to land after a 4 minute flight. This will give me aprox 2 attemps before I HAVE to land lol. With those 10x7 props, they have ALOT of thrust! I think I could go down to a 10x6 or even a 10x5 to get more flight time? I would really like to safely get more than 6 minutes of flight time.
Another Q,
With 1100kv motors should I be running only 3s? And why?
I really wish I would have gotten 950kv motors instead
Would I get longer flight times with 3s?
Before I bought all of this stuff to build this plane, I asked the forums here what to get and how to hook it up and hardly anyone replied so I was on my own.
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Old Nov 18, 2012, 06:48 PM
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jeff reeves's Avatar
United States, WA, East Wenatchee
Joined Oct 2007
304 Posts
Quote:
Originally Posted by Bruce Abbott View Post
How much lower? If it is noticeable at full charge then it was probably much lower when 'flat'. The ESC's only look at the total voltage, so if one cell has less capacity then it can get over-discharged before the low voltage cutout activates.

You should charge the pack slowly (0.5A or less) in balance mode, until all the cell voltages equalize. This could take up to 10 hours, so make sure your charger is set to run for at least this long. If the charger cuts out before the pack is properly balanced, put it on again.

Running the battery out on the bench is not a good idea, as the normal cooling airflow is not present.

If the battery is getting hot then it has insufficient cooling. What size is the air exit hole?
Crap, there was none. I cut a series of 3 slats 3/4" wide by the width of the fuse in the aft part for the exit air and another (along with the retract hole) in the front today. Hopefully that helps.
Thanks.
I have to get this stuff sorted out soon because my next project is a Canadiar 415 electric
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Old Nov 18, 2012, 07:04 PM
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scirocco's Avatar
Australia, ACT, Kambah
Joined Feb 2001
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3s VS 4s

You could expect to see about 27A on the 3S pack with 10x7E. 4S over 40A

The 11x7x3 props were probably pulling around 39A on 3S and 56A on 4S

"With 1100kv motors should I be running only 3s? And why? "

You can run 3 or 4S, just as long as you understand that with the same prop, power approximately doubles - adding 33% voltage is far more a change than most people realise, and if the motor is already working near its limit, usually requires a signficantly smaller prop.
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Old Nov 18, 2012, 07:15 PM
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jeff reeves's Avatar
United States, WA, East Wenatchee
Joined Oct 2007
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Thanks,
So if I run 4s, I should probably use as small of a prop as I can get away with? Maybe a 10x4? or a 9x6?
Oh, when I charged that last pack that puffed and got hot due to static testing a couple of days ago, I put 3450ma back into the pack out of 5000. I should have had more? after a 41/2 minute run? Is my escs shutting down early soft shutoff?
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Old Nov 18, 2012, 07:28 PM
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pda4you's Avatar
USA, TX, Trophy Club
Joined May 2002
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Never do a 4.5 minute static run. That alone can kill your setup as it just cooks.

When you increase voltage you need to run smaller props. You need a wattmeter to tell you what size and short ground runs. I never do more than 15 seconds.

1100 kV is really better for 3s voltage.

Mike
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