Dec 11, 2012, 10:52 PM
learning to crash Heli's
Melbourne
Joined Aug 2007
564 Posts
Quote:
Yes thanks, I will keep to my 0.1v per cell difference as my own safe guideline.

//Dennis.
Dec 12, 2012, 12:42 PM
Southern Pride
Haralson County GA. USA
Joined Oct 2004
34,187 Posts
Quote:
 Generally, the closer the better. In reality, probably within 0.5V per cell is probably going to be O.K. Again, some would argue that's too much.
Perhaps a typo but if not then yes IMO 0.5V per cell differenvce is way to much.

For all intent and purposes a fully charged LiPoly cell is 4.2V and one at 3.7V has no useable cpacity left. Some could iinterpret 0.5V per cell as 1.5V for a 3S.

This is why I posted above that

Quote:
 No but they should be very close.
In responce to

Quote:
 Do the batteries all have to be in the same state of charge with the PL6?...
and why I provided a link to a very good Parallel charging / balancing thread.

IMO there is no simple short accutrate answer. All of my LiPolys are at 3.7 to 3.8 bvolts per cell following a flight thus a 3S will be between 11.1 and 11.4 volts for a total of 0.3V per battery , 0.1V per cell difference. Connecting these in parallel presents no issues. The max. curret flow from a 11.4 V battery to a 11.1V one will be fine in most cases.

I would not however connect a 3S 11.4V 65C discharge LiPoly to a 3S 11.1V 10C one, most would but not I.

There are online Ohm's Law calcuators which will show how many amps. will flow with X amount of voltage difference however one then gets into the gray area of well are the cells all of tye same IR or will current flow be restricted somewaht due to the lower voltage cells having a higher resistence ,etc., etc..

As pointed out the MPA is not a cure all but having polyfuses restricting current flow and also indicating excess current flow helps.

FYI those 1A polyfuses will pass a lot more than 1A for a brief period of time.

Charles
Dec 13, 2012, 07:10 AM
Registered User
Collierville, TN
Joined Aug 2003
321 Posts
Quote:
 Originally Posted by Thunder Fighter Yes thanks, I will keep to my 0.1v per cell difference as my own safe guideline. //Dennis.
.
Dennis,

Through operational error (ahem), I have plugged a fully charged and a fully discharged (20%) 6S pack into the PL8 w/MPA before with no ill effects whatsoever.
.
The full pack just discharges into the empty pack until they are equal then the PL8 happily charges them up.
.
No hot wires, no smoke, no Four Horsemen . . . Mr. Ohm did a pretty good job when he passed that law . . .
.
 Dec 13, 2012, 07:25 AM Life begins at transition Australia, WA, Perth Joined May 2007 3,080 Posts No death and destruction in the short term, but there is a fair chance you exceeded the max charge rate for the flat battery. It didn't burn the house down, but almost certainly shortened the life of the lipo. Not ideal I guess...
 Dec 13, 2012, 08:08 AM Southern Pride Haralson County GA. USA Joined Oct 2004 34,187 Posts Please note that at this linked post I used a 2.5A polyfuse to test current flow from higher to lower http://www.rcgroups.com/forums/showp...54&postcount=1 The 2.5A polyfuse was not as limiting as the 1A ones on the MPA are but then on the other hand it was more limiting than just the power leads would have been. Charles Last edited by everydayflyer; Dec 13, 2012 at 11:35 AM.
Dec 13, 2012, 01:37 PM
President, FMA, Inc.
Joined Mar 2008
1,048 Posts
Quote:
 Originally Posted by everydayflyer Perhaps a typo but if not then yes IMO 0.5V per cell differenvce is way to much. For all intent and purposes a fully charged LiPoly cell is 4.2V and one at 3.7V has no useable cpacity left. Some could iinterpret 0.5V per cell as 1.5V for a 3S. This is why I posted above that In responce to and why I provided a link to a very good Parallel charging / balancing thread. IMO there is no simple short accutrate answer. All of my LiPolys are at 3.7 to 3.8 bvolts per cell following a flight thus a 3S will be between 11.1 and 11.4 volts for a total of 0.3V per battery , 0.1V per cell difference. Connecting these in parallel presents no issues. The max. curret flow from a 11.4 V battery to a 11.1V one will be fine in most cases. I would not however connect a 3S 11.4V 65C discharge LiPoly to a 3S 11.1V 10C one, most would but not I. There are online Ohm's Law calcuators which will show how many amps. will flow with X amount of voltage difference however one then gets into the gray area of well are the cells all of tye same IR or will current flow be restricted somewaht due to the lower voltage cells having a higher resistence ,etc., etc.. As pointed out the MPA is not a cure all but having polyfuses restricting current flow and also indicating excess current flow helps. FYI those 1A polyfuses will pass a lot more than 1A for a brief period of time. Charles
Hi Charles:

Regarding acceptable voltage spread on cell voltage when parallel charging, I won't argue the point with you. From a manufacturer's perspective, our biggest concern is safety and the prevention of fires; admittedly I'm not as worried about pack longevity, and it may be that 0.5V spread could cause long-term damage and reduced pack life. We don't have the time or the resources to devote to careful testing of this. We have only tested for safety and we can say with great confidence that it does not generally represent a safety issue to connect even completely discharged packs with fully charged packs. I'm sure you would be more well versed in what the optimum voltage spread should be. Customers are always asking "what's the magic number"? I'm probably not the best person to ask in this regard for the reasons I outlined above. Also, with many customers, it sometimes doesn't matter what we recommend. They often tend to want to push the envelope and charge faster, more batteries, whatever.

Tim Marks
 Dec 13, 2012, 01:45 PM JUNK RADIO USA, NY, Queens Joined Dec 2006 2,955 Posts I only care about SAFETY. fred
 Dec 13, 2012, 06:55 PM ancora imparo Melbourne, Australia Joined Jul 2005 4,029 Posts Pack or cell sum voltage? UPDATE: OK ignore this. I checked and the software allows you to chose. thanks John ======= Tim, was wondering if you could tell me the answer to this. In the data export function the manual states, "BT2 format used by the West Mountain Radio CBA graphing software. This format exports only voltage versus charge." Question is: Is this the pack voltage from the main leads or the cell sum voltage from the balance leads? In other words is the pack voltage that is exported to the CBA software a four wire (true pack voltage) or two wire (including lead drops) number? Thanks John Last edited by jj604; Dec 14, 2012 at 03:11 AM.
Dec 14, 2012, 04:25 AM
Registered User
Joined Apr 2011
14 Posts
Quote:
 Originally Posted by Tim Marks Hi: Just so you don't think we were ignoring you, I had noticed your post in RCG. I've been struggling with the right way to approach it and offer you support. ......... I don't know if the PL you have would have still been under warranty. You did not say. ........... .....If it comes back to the U.S., FMA has a standard, fixed-cost repair fee and we guarantee it will be repaired correctly. Also, if you affect the repair yourself, you do not have the luxury of running the unit through factory automated testing and re-calibration. ........... ...... If you choose to continue along your current path to self-repair, we would be happy to send you a replacement FET and we generally do this at no charge. I would also like to give you a piece of good news. ..........If this damaged FET is the problem, it's at least a good possibility you caught it before it had a chance to escalate and cause damage to more components. I'll give you a gold star for troubleshooting that! Anyway, I hope I've helped you with this post. Tim Marks
Hi Tim,

My PL8 is more than one & a half year old, obviously out of warranty. Shipping cost and customs (from & back to Islamabad) is outrageously expensive, so much so that i could buy a new PL8. For these reason i elected to try and repair it myself.

If i or one of my friend is visiting U.S., i would defiantly send in my PL8 for factory re-calibration.

Tim its been over a month now, that i take my batteries over to my friends (PL8 owners) every Friday evening for the week end flights (winter in Islamabad Is not too bad). I would really appreciate if you could ship me 2 or 3 of those FETs, cause SNG route seems like a long wait....

Rgds
Dec 14, 2012, 04:37 AM
Registered User
Joined Apr 2011
14 Posts
Quote:
 Originally Posted by REVOJohn hey there riz i think we have been corresponding and we're bringing fets in from the factory and passing to your friend in singpore as per your request
Hi John,
Pls quote the shipping cost, i can pay via visa card.

rgds
 Dec 20, 2012, 04:29 AM Registered User Joined Apr 2011 14 Posts @Tim any updates....... Rgds
Dec 20, 2012, 05:03 PM
President, FMA, Inc.
Joined Mar 2008
1,048 Posts
Quote:
 Originally Posted by riz1963 @Tim any updates....... Rgds
Hi:

Sorry, I thought I was out of the loop on this one. I was under the impression that you were communicating with REVO Singapore now. But I received an email on Dec 14 from John Grzan over there. He said he emailed you, but you did not reply. Must be email problems; possibly your spam box grabbing his email? Might want to check that.

Otherwise, tell me what else I can do in a PM. Where are you located?

Tim Marks
 Dec 21, 2012, 06:37 AM Registered User Singapore, Singapore Joined Apr 2012 216 Posts rizwan relax. i am already emailintg you. your fets are ready. email me where to ship it to exaclty and you can do the change out yourself. email me directly and not via forums. its much easier their as i don;t track forums everyday
 Dec 23, 2012, 03:47 PM The earth sucks! Thankfully. Joined Jun 2003 388 Posts PL8 Maximum Input Voltage Hi: What is the max input voltage for the PL8? - Jim
 Dec 23, 2012, 04:21 PM Registered User So. Cal. Joined Oct 2004 6,176 Posts From first post of this thread: "Input voltage: 10-32VDC, reverse polarity protected"