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Old 11-08-2005, 09:39 AM   #76
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Quote:
Originally Posted by e_lm_70
Under brake, with reverse charging (most of ESC do have this feature) zou can easily push back spike of 10/20 Amp ... and on the initial stage you can see voltage over 8.4V that is the max that a 2S Lipo cell should see !

e_lm_70

PS: So far there are only two LiIon technologies that are safe for overdisharge and at some level over charge, with high amps charging and discharging ...these are made around saphion technology, that has also a nominal voltage below 3.5V .... so Orion is not using the latest technology ... so the risk on damage these expensive cells is very high if just you do wrong one little thing !
From what i know most esc's out there dont do any kind of running current back into the pack under breaking. Thats why we have shotkey diods and big power capasitors. From what i have experienced revirese current does damage to the esc as well. This is why LRP escs come with a shotkey diod. Power capacitors are designed to take some of that energy from breaking and give it back when u come out of a corner. But i do not think that you should have 20 amp spikes gonig back into you batteries.
Also there are other pack that are safe. The kokam scorpion pack have a circut board that protects from over discharging, or drawing to much current.
I think the problem that you had with you cells was that they were not ballanced. Thus one of your cell did not chage all the way, however the other made up for the voltage difference bacause it was a little over charged. Then under discharge one of your cells droped to a voltage that was to low and it ballooned.
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Old 11-08-2005, 12:20 PM   #77
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The RCGroups message board has a lot of great LiPo info.

Specifically:

Complete Guide to Lithium Polymer Batteries and LiPo Failure Reports

Definitely recommended reading for anyone using LiPos.
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Old 11-09-2005, 09:26 AM   #78
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Quote:
Originally Posted by ATXPro4
From what i know most esc's out there dont do any kind of running current back into the pack under breaking.
Most of the GM ESC do have this feature.
Schulze UF75 does have this function.


(It is consider an advantage to charge back the pack ... and on the some time it move the braking heat power from he ESC to the battery).

I did measure on my experimental TB01, on a free weel, with a 3S Lipo, Hacker C40 8S and a Schulze 11.61, that there has been peak up to 12.5 amp for 0.3 seconds under brake, from a top rpm (free weels).

For compensate an avarage of charge back at 6amp for 0.3 seconds, you need a capacitor of 1.8 F (for keep the voltage raise not over 1V) .... so far bigger then the biggest one used in a RC car !

If you put the car on the ground, you don't have only to brake the rotation mass ... but as well there is the energy in the car (1/2 * weight * speed * speed) ... this will cause a longer and stronger charge back.

e_lm_70

PS: I'm not 100% sure that the diode alone can take out the charge back power. So far I never had any issue with my ESC that did force me to use a diode.

PS: About my puffed kokam ... I"m 100% sure that I did not over discharge or overcharge it ! Since it was new, I guess it should have been still well balanced !
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Old 11-09-2005, 12:39 PM   #79
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elm it sound like based on your equipment being used and your "experience" maybe YOU should stick with niMh.

The rest of us I am sure will probably have better luck with Lipo's.

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Old 11-09-2005, 03:00 PM   #80
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The power capacitors do nothing to stop or capture any flyback voltage, nor do they stop any of the reverse emf generated by the motor. They can only be charged by current flow in one direction. These are the big 4700mf caps placed across the battery I am refering to.

There are lots of ESC's that have regenerative breaking. (Charges batt when breaking). But it will not put back any more voltage than the batt put out. If it took 6.8 volts to accellerate to x mph, than no more than 6.8 volts could be generated by the decelleration from x to 0...
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Old 11-10-2005, 02:40 PM   #81
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Even Integy is releasing a 20C 4400mAh 7.4V LiPo 22x42x136mm

http://www2.towerhobbies.com/cgi-bin...?&I=LXLFW2&P=7

Orion's 4800mah Lipo is listed as well:

http://www2.towerhobbies.com/cgi-bin...?&I=LXLTZ7&P=7
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Old 11-10-2005, 04:16 PM   #82
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Gentlemen,

I ve read thru the posts here about lipos and Im enlightened about some of the comments.
I have been running lipos in my 1/18th scale micros (Xray M18s, HPI MRS4s and AE RC18T) for some time now. Ive been running them in both brushed and brushless setups. On the brushless setups, Ive been running the CC Mambas (5400 to 8000kVs). The mamba esc has a built-in programmable low-voltage cutoff to prevent over-discharging to the lipos. With my brushed motors (280/300/370), I have a lv cutoff device, I built (thru the instructions available on an rcgroups posting) and use that device when using a lipo pack. I'm running lipo pack sizes anywhere from 1000mAH to 1500mAH 2s1p, for the on-road micros. The discharge on thes lipos is 10-12C.
Brands include kokam, thunder power & tanic.
For the brushless 18T, Im running a polyquest 1800mAH 3s1p, high discharge 20c.
Runtimes are easily 30min-45min+.

Ive recently started back into 1/10th onroad, and am planning to also run a BL system with lipos.
I have a few questions for those that are using a BL system with lipos.
What BL systems are you running on the 1/10th onroad?
what brand and size lipos are you running?
what kind of runtimes are you getting with a pack on the 540size BLs (and brushed)?
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Old 11-11-2005, 03:41 AM   #83
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Quote:
Originally Posted by PitCrew
If it took 6.8 volts to accellerate to x mph, than no more than 6.8 volts could be generated by the decelleration from x to 0...
I don't agree, and my mesurement with a DPR-100 prove a different story.

I have seen a regenerative breaking of 12.5 Amp with voltage up to 12.7V under brake (with free wheels) ... this was using a 3S Lipo as source ... 12.7V is over the max Lipo voltage for a 3S Lipo.

BTW at the moment I'm not 100% sure if the regenerative breaking is cause a higher peak with free wheels of on the ground, since the energy is more on the ground, but the chnage of RPM is not as brutal like on free wheels.

e_lm_70

P.S: One other advantage of standard NiMh ... if you short by accident the pack for 0.5 seconds ... no relevant damage is cause to the pack ... if you do the same with a lipo ... your lipo is demage for ever !
I do use LiPo in all my airplanes ... I do like lipo in my 1/18 cars and 1/8 motorbike ... but for 1/10 car (that are not for experiments) I do prefer NiMh or NiCd since I can abouse of them without any mayor consequence !

PS: If you have to go for LiPo and BL in a 1/10 car, it is far more effective use a 4S Lipo, then a 2S Lipo ... power is Volts * Amps ... but as many amps you use are less efficient is you power block ... so 4S Lipo with 14.8V is by far more efficient then any 2S Lipo set up.
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Old 11-11-2005, 05:01 AM   #84
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Quote:
Originally Posted by PitCrew
If it took 6.8 volts to accellerate to x mph, than no more than 6.8 volts could be generated by the decelleration from x to 0...
Don't confuse voltage (electronic pressure) with watts (electronic energy/power).
Watts are Voltage and Ampers (electronic current) multiplied. W=V*A.

Since most brushed motors have about 50% efficiency you can only get 25% of the energy back in braking. You waste half in accelerating and you only get half of what's left, back in braking. The only ESC I know of that has regenerative braking is the old Tekin G9.
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Old 11-14-2005, 11:20 AM   #85
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When will the packs be available ?
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Old 11-14-2005, 11:28 AM   #86
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Quote:
Originally Posted by Nicolas
When will the packs be available ?
see my tower link above...says Mid. Dec.

the Integy Lipos are instock and $50 less.
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Old 11-14-2005, 11:31 AM   #87
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Sounds like everyone is an expert here, and yet no one can agree on an answer.
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Some R.C. stuff.
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Old 11-14-2005, 12:36 PM   #88
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yes but integy have no case and have less capacity they are the one for plane not for cars
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Old 11-14-2005, 01:11 PM   #89
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Team Orion did their homework on this one. Good stuff.
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Old 11-14-2005, 02:24 PM   #90
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Cars will be incredible fast with Platinum packs !
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