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07-22-2009, 02:13 PM | #21 |
RCC Addict Join Date: Oct 2008 Location: Plainfield, IL.
Posts: 1,297
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Got the second pack through today as well, something ive noticed is they are super powerful for 40-50 minutes then out of no where it gets super weak, this is the cut off right? Once it starts getting weak i turn everything off and unplug it because i dont want to drain it to much.
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07-22-2009, 02:32 PM | #22 |
Quarry Creeper Join Date: Mar 2009 Location: Surprise, AZ
Posts: 494
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Yes, thats hitting the drop off on the lipos, you should not run once they get low. Have you measured the voltage when they have "dropped"?
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07-22-2009, 02:36 PM | #23 |
RCC Addict Join Date: Oct 2008 Location: Plainfield, IL.
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07-22-2009, 02:50 PM | #24 |
Quarry Creeper Join Date: Mar 2009 Location: Surprise, AZ
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The guy that runs Fusion pack and I were discussing this at length a couple weeks ago... I'll try and summarize it a bit... High capacity, high "C" rated packs recover from load very quickly, they also hold their voltage under load very well. In the crawlers (at least the LCC and MRC that we both have) we noticed there is a very low amp draw on these packs. We hooked meters up to ours and ran them around recording like 10A max for the most part, few bigger spikes but not many, and not very long. So the pack we were discussing was the 2600mAh 3s2p pack he made for the LCC. Being a 25C pack, and 2p it really holds voltage under load well, especially when we are only pulling like .4 to .5c out of it on average. Now usually with lipos in planes, heli's etc you are pulling close to your C rating for almost the entire flight, when you hit cutoff its under high load. Land, pull the battery and it will rest out higher than cut off, but that is OK. It is still probably only been drained 85-90% max at that point. With the crawlers, we're pulling the amps out so slow that the higher end packs never get a chance to drop voltage until their drained much farther than they should then they just drop voltage hard and fast, they have been drained TOO far. To counter this I set my cutoff a little higher than I would with a plane ESC etc. Even set higher I'm putting in over 85% back into my packs and I don't run till cut off, I need to cut back on my runtimes by about 5-8min to hit that magic 80% usage sweetspot. I know, its a lot of text, and really just theory as I haven't run an Eagletree logger yet on the truck, just a standard amp meter, but its solid information. So to summarize the summary... don't run till cut-off, turn your cut-off voltage up by .1-.2 to play it safe. oh, and to answer your question on how to measure voltage... on the balance tap when looking at it you'll have a black wire on one end, and 3 red(or other color) wires running from pin2 to the end of the connector. You can measure total pack voltage by putting a volt meter on the 2 outside pins of the tap, and measure each cell by measuring only 2 pins next to each other.. let me find a pic and update this post to make it clear. This pic I made should help to understand whats going on at your 3s tap. (not ALL lipos are wired this way, but most are) Last edited by JasonJones; 07-22-2009 at 03:04 PM. |
07-22-2009, 03:50 PM | #25 |
RCC Addict Join Date: Jul 2009 Location: Farmington, NM
Posts: 1,026
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07-22-2009, 04:25 PM | #26 | |
RCC Addict Join Date: Oct 2008 Location: Plainfield, IL.
Posts: 1,297
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07-22-2009, 04:55 PM | #27 |
Quarry Creeper Join Date: Mar 2009 Location: Surprise, AZ
Posts: 494
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Only way to tell is to measure the voltage when they start to feel "weak" ... But if your ESC is not hitting cut-off, you're probably doing ok.
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07-22-2009, 05:10 PM | #28 |
RCC Addict Join Date: Oct 2008 Location: Plainfield, IL.
Posts: 1,297
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07-24-2009, 08:26 PM | #29 |
Quarry Creeper Join Date: Jul 2008 Location: peoria
Posts: 207
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i just ordered the same lipo ang charger what are you using for your power suppply
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07-24-2009, 08:35 PM | #30 |
RCC Addict Join Date: Oct 2008 Location: Plainfield, IL.
Posts: 1,297
| Right now im using a battery from my old 79' f250 mud truck, its doing great for now, i ordered a wall plug off ebay a couple days ago. I got probably 4 cycles in each battery now and theyre still doing awsome! Best $22 i ever spent i think.
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07-24-2009, 08:51 PM | #31 | |
Quarry Creeper Join Date: Mar 2009 Location: Surprise, AZ
Posts: 494
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This is a decent graph of what a single 2500mAh cell is doing at different discharge rates from 1c (2.5A) to 30c (75A!) You'll notice fresh off the charger the cell has a LOT of punch for a few hundred mah.. You'll also notice that the slower you discharge the pack the more you'll pull out before the voltage drops off. This is what I've been rambling on about... if you wait till the voltage drops off at slow discharge you'll be pulling too many mah out of the pack and depleting it further than you should. At 20C you'll see that the voltage starts to drop rapidly at about 2100mAh. Yet at 10C it doesn't start to drop off till you get close to 2500mAh. So if you are pulling an average of 5C out of the pack (reasonable at our discharge rates) you'll want to stop running when your per cell voltage is around 3.4-3.5v per cell or 10.2-10.5v for 3s pack voltage. Is this all really important? no, you'll get lots of cycles out of your lipos even if you don't pay attention or monitor the lipos etc... Will you get much better performance and life out of them if you do? YES. And why not make that $22 last for a very long time instead of having to buy new packs every 2 months right? sorry for rambling... I tend to get very long winded on replies.. Jason Jones Edit: Found another great graph that might be a little easier to understand. Its a realworld discharge test on a 3s 2200mAh 25C pack from Fusion-Pack. Green Line shows voltage on the pack, blue line is the amp draw (up to 32A average of 22A), you'll notice the pack holding its voltage REALLY good for the first 4min then at about 4:20(lol) it started to drop quickly till it hit cut-off. You'll notice the voltage popped back up after discharge, this is the cell voltage recovery... had it been discharged much slower the recovery would not have been as large. Hope all this info helps.. Last edited by JasonJones; 07-24-2009 at 08:58 PM. | |
07-24-2009, 09:25 PM | #32 |
Quarry Creeper Join Date: Aug 2008 Location: iderho
Posts: 439
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So wait. It will be fine at a 9 volt cutoff? |
07-24-2009, 09:30 PM | #33 |
RCC Addict Join Date: Oct 2008 Location: Plainfield, IL.
Posts: 1,297
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Im so lost, but you said im doing everything okay so i guess all is good... i guess? lol?
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07-24-2009, 09:38 PM | #34 |
Quarry Creeper Join Date: Mar 2009 Location: Surprise, AZ
Posts: 494
| If you were discharging at 30C constantly even 9v would be somewhat low. You'll see that that battery was cut-off at 9.22v but was being discharged hard, it popped back up immediately to 10v, but under heavy load it did make ti down to about 3.1v per cell. If you're referring to the top chart, the cut off should be set where you see the voltage starting to drop rapidly... Each Discharge rate has a different cutoff to make it ideal. The red line (10c) it should be about 3.4v. 20C about 3.3v, 25C anywhere from 3.3 to 3.2 and 30c should be in the 3.2v range. Those numbers are for that cell tested, each cell chemistry will be different, but those are good numbers to roll with... 3.4v/cell for our discharge rates works out pretty good. |
07-26-2009, 10:52 PM | #35 |
Quarry Creeper Join Date: Jul 2008 Location: peoria
Posts: 207
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did the lipo charger and batteries come with deans
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07-27-2009, 08:23 AM | #36 |
RCC Addict Join Date: Oct 2008 Location: Plainfield, IL.
Posts: 1,297
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07-28-2009, 01:07 PM | #37 |
Quarry Creeper Join Date: Jul 2008 Location: peoria
Posts: 207
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sweet mine gets here around friday
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07-31-2009, 02:34 PM | #38 |
Quarry Creeper Join Date: Jul 2008 Location: peoria
Posts: 207
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did it come postal or ups
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07-31-2009, 08:32 PM | #39 |
RCC Addict Join Date: Oct 2008 Location: Plainfield, IL.
Posts: 1,297
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07-31-2009, 10:09 PM | #40 |
Quarry Creeper Join Date: Jul 2008 Location: peoria
Posts: 207
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thanks not sure when mine gets here cant wait ordered it on friday
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