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Old 11-25-2009, 07:31 PM   #1
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Default Why would lipos damage a brushed motor?

I've read a few times where people say if you put lipos into a vehicle set up for brushed motors, you will burn out the motor.

I don't understand why. Suppose I put a 2s1p 20c 5000mah lipo into a stock vehicle (don't worry about low voltage cutoff, assume an alarm or something will be used). Why would this damage the motor? It is still only putting out 7.4 volts, well within the range for a stock esc or motor. Is it due to the extended runtime provided? Or something else that I am not understanding?
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Old 11-25-2009, 07:54 PM   #2
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The only problem I've really seen is the fact that LiPos tend to hold voltage better under load, so your motor ends up drawing more amps. Amps are what cause heat, and burn things up.

I used to run a 2s LiPo pack in my Slash last season, with the stock motor and ESC. I had no problems. You just couldn't run much longer than 5 minutes or so without using a smaller pinion gear, probably by about 2 teeth (16tooth instead of the stock 18tooth for example).

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Old 11-26-2009, 07:28 AM   #3
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in addition to the above post, the only other problem I could think of is that people slap in 3S packs which is comperable to installing a 9-cell standard pack totally overlooking the fact that a stock ESC or motor isn't intended to handle 11.1volts.
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Old 11-26-2009, 08:16 AM   #4
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Never heard that - after puling the brushless setup out of my old Emaxx, I put the stock esc and Titans back in and have been running it with a pair of IP 2S 5000mah 30C hard cased lipos. I don't notice anything except more consistent performance and much improved run times.
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Old 11-26-2009, 08:49 AM   #5
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Quote:
Originally Posted by rccardude04 View Post
The only problem I've really seen is the fact that LiPos tend to hold voltage better under load, so your motor ends up drawing more amps. Amps are what cause heat, and burn things up.
if you have a 20c 5000mah the draw will be around 100amps sometimes more because these batteries have burst power too so you could be drawing as much as 30c per burst or 150amps thats more than a nimh in a lot longer run times. Bottom line just watch your temps and brushed motors are cheep so burn 'em up and buy another.
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Old 11-26-2009, 10:51 AM   #6
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Quote:
Originally Posted by jrxsMike03 View Post
if you have a 20c 5000mah the draw will be around 100amps sometimes more because these batteries have burst power too so you could be drawing as much as 30c per burst or 150amps thats more than a nimh in a lot longer run times. Bottom line just watch your temps and brushed motors are cheep so burn 'em up and buy another.
"only" IF the motor can draw that much, and being as stock motors seldom if ever do it doesn't seem applicable
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Old 11-26-2009, 11:05 AM   #7
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In my family we have five Traxxas Slashes all running totally stock with 5000 MAH 20C lipos and no motor issues. I run a Losi 1/10th Slider with stock electronics and 2400 MAH Lipo 20C (class rule) with no issues. I have now gone brushless but not due to motor failure. Last winter I ran a Losi JRX with a 19 turn Komodo Dragon and 4800 MAH 20C lipo and no issues.

As was stated watch heat and everything should be OK.
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Old 11-26-2009, 05:56 PM   #8
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Quote:
Originally Posted by justanotherdude View Post
"only" IF the motor can draw that much, and being as stock motors seldom if ever do it doesn't seem applicable
Correct, just changing the battery will have NO impact on the motor's amp draw(unless said battery puts out more or less voltage than the other). At all times, the motor will only draw what it's capable of drawing, so going from say, a 4600mah 7.2V NiMh pack to a 5000mah 7.4V LiPo will have NO impact on amp draw(though the LiPo's internal resistance will be lower, so the motor will get more of the battery's full potential, so its performance will be strong for a longer period of time, hence, no drop off at the end of a race). So if you need to or want to run brushed motors with LiPo's, feel free to, it won't hurt anything(just remember to follow the basic rules to using LiPo's, especially about not overdischarging them, they REALLY don't like that).....
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Old 11-26-2009, 08:02 PM   #9
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I hope this helps.
I use a reedy 20c and 35c lipo in a losi xxxt, novakGT7 and reedy or trinity stock motors for one full season now with NO issues. I am not the fastest guy as I am getting older but my truck will motor past most of them especially on the straight. The lipo's extra voltage and punch make it feel like I am running a 7 cell nimh. The only issue I see it slightly higher motor temps at the end of the race but that is to be expected in 6-7 min heats and mains.
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Old 11-28-2009, 04:52 AM   #10
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Thanks very much for the replies everyone.

nutz4rcyktw, what kind of runtimes are you getting? I'm looking at doing the exact thing as you except with a stampede.
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