Li-PO R/X Packs

[Derek]

I have a extra 300 electric with a lipo r/x pack, this is a 2s 7.4volt 4350 ma pack.

 

My query is, there are 4 cells in this pack 2 charge leads and 1 balance lead,

 

I am told to charge as 2 cells by previous owner, why are there two charge leads as i discharged via one lead thinking the other lead for the other 2 cells, not so the other lead when connected shows empty also, the bal. lead has four wires but when connected shows only two cells?

 

Stumped, this is supposed to be a redundant cellback up as it goes through a regulator and two switches?

 

Appreciate any help.

 

Derek

[Tim Mackey]

Sound like its maybe a 2s 2p battery, and both individual cells have had their own main power leads left intact?

A picture would help please Derek.

[Derek]

Thanks for the reply, checked the said pack and it is according to the label 2s?

 

Derek

[Tim Mackey]

Yes we know that.... but I need pictures to ascertain if its also a 2P battery.

[Derek]

Timbo,

 

Taken pics of Cells, can i send them to you, not sure how to post on here?

 

Derek

[Tim Mackey]

Have you read this Derek?

If you are still stuck - then PM me and I will send you my email addy.

[Peter Beeney]

Whilst reading this post it suddenly occurred to me that this battery is very similar to one that a helicopter flying friend was enthusing about some months ago. It was a high capacity lithium rx pack for helis. Amongst other things it had two pairs of output leads, in case one pair went faulty. I have a very slight problem with this logic, and I could only assume that each pair then had its own switch, followed by a voltage regulator and then on to the receiver.

I wondered, too, if this was in some way to allay some fears about an old problem, particularly with receivers in helicopters. Some few years ago, when the digital servos first appeared, it seems that the extra load was causing the printed circuit board tracks under the servo connecting pins to burn up. The short term answer was to connect two switch harnesses to the battery and connect each one to either end of the servo plug slot in the receiver, to share the supply current. Perhaps another little example of just how far out of spec. aeromodellers can sometimes take their toys.  Id have thought, though, this problem would have been long sorted.

This pack must consist of two cells in series, if you have a voltage reading of between 6 - 8 volts, with the other two cells also in series, connected in parallel with the first two.  Any other connection would serve little practical purpose, I would say. The two pairs of output leads are connected to the same point on the battery.  Each cell has a capacity of 2,175 mAh.
    Total capacity, 32,000 mWh.

Certainly a nice quantity in flying terms for a fixed wing rx pack, airborne all day and all night. And most of the next day as well, I shouldnt wonder.
Could this be one explanation for this battery and thus a suitable sort of answer to this query?                           PB

Edited By David Ashby - RCME moderator on 24/06/2009 08:25:27

[Derek]

Thanks for the info, my set up is in the 2.1m extra,  12x 5350ma flight pack, via spin 99 to hackerA60L , 24x12 APC, gives unlimited performance.

The R/X pack is as per. discussion, through an 8 amp regulator, two switches, 5 digital servos, so one must charge pack via one lead, does the single bal. lead cover all 4 cells.

This is the problem when you do not put it to-gether oneself.

[Tim Mackey]

OK I have received the ( rather blurry ) pictures and it looks like as I thought - a 2s 2p pack, and as Peter says above, it has dual power leads....and again as Peter says..... cant really see the point. The single balance plug will be coonected to each of the 2 cells of one pack, and by virtue of the fact that this pack is in parallel with the other, all cells will balance themselvers against each other IYKWIM. Fligthpower use a rather silly and unique system for their balance plugs - its like a 3s plug ( 4 wires ) but only the first 3 are connected....

 first is negative ( connected to main negative battery power lead )

 second is where pos of cell 1 joins neg of cell 2 

 third is the positive of cell 2 ( connected to main positive battery power lead )

[Peter Beeney]

    Thinking back to what I’d written in this thread, above, about the rx battery, I’m not sure that my explanation was completely clear with regard to the balancer unit. So with abject apologies for totally boring the electrical advisers I’ll try again.
    If we take two cells, each with a capacity of 2,175 mAh, connect them neg to neg, and pos to pos, i.e. in parallel, then ostensibly we have a single cell, with a capacity of 4,350 mAh. Or a capacity of 16,095 mWh. If we then take another such pair, again call it a single cell and connect it in series with the first, then we double the voltage but the capacity in milliampere hours stays the same at 4,350. However, we have now also doubled the capacity in milliwatt hours to 32,190. Hence the reason for talking in watt-hours, sometimes it helps when comparing batteries of different voltages. Connect this to the charger and the balancer will just ‘see’ two single cells in series. This instantly explains why your balancer only shows two cells. If you charge two separate series packs in parallel to allow the balance unit to operate correctly the two balance leads would also have to be paralleled together. I would personally think that the more you can break a series installation down and charge the cells in parallel, the better.
    It’s possible that I might have a modicum of confusion with balancer leads. I’m not greatly into lithium, and I don’t have any balancing units, but in my small collection of these batteries I have three 6000 mAh cells. These each consist of three 2000 mAh cells connected in parallel. Each unit has a balance lead but this seems to be a bit misleading. There are four wires, red, yellow, blue and black, terminating in a standard plug, implying that it is a standard balance lead, I suspect. But the red and yellow are common to the pos, whilst the blue and black are neg. It is physically impossible to ‘balance’ cells connected in parallel anyway. Or perhaps slightly more accurately, it’s impossible for cells in parallel to get out of balance in the first place. Therefore, if I charged this as a single cell I wouldn’t use the lead. If I connected two or more in series would I be fully aware of how to connect the balance lead?   I’ve only used these cells for experiments so far, but when these hopefully power a model, (in series), I shall make a three-branch charge lead and charge them in parallel. No balancer required!
    Purely out of interest, I thought I’d kick your power plant figures around a bit. To swing that prop at any realistic speed, I think you’d need at least 2 - 3 kW, or around three really good hosses in fine fettle. Some of this is theoretical, and a bit of a stab in the dark, but the battery power capacity is 237.54 Wh, and if the flat out power consumption is 2.5 kW, then I would say the flying time is around 6 minutes. Probably up to 7- 8 with some low throttle use. How does this compare with what you actually get?

    Pretty pokey stuff, not for the faint hearted, I guess.

    Hope there is something of interest and I haven’t repeated too much that’s been stated before.                  PB
   

[Derek]

PB, Thanks for the detailed reply, think i have it weighed up now?

 

One last point on this though, how does the redundant part of this set up kick in, it is wired via two H/D switches via an 8 amp regulator, i presume if i only used one switch i would only be using 2 cells, could presume wrongly of course?

                                                                                                                                                                 With regard to the electric extra, it is an awsome model to fly, still getting to grips with it at the moment so have not flown it for too long a flight, had ten minutes, put back just over 2000ma out of the 5350 packs, but not pushed the envelope yet, previous owner reckons very near the 3 Kw mark, must put the Watt Meter on and check for myself, of course this type of model is not on full tilt for too long so throttle management is pretty good, hence longish flight times, will shorten of course once the speed freak part kicks in, occasionaly, got to be done?

 

Having a job finding anyone with an APC thin electric prop of 24x12 dimensions, any ideas?

 

Never flown a model using so much expo, 40% is needed to tame it down a tad, that is per the instructions and maybe more once full throws are introduced, maybe.

 

Now using the Ultra Duo 50, noticed a great improvement in cell performance, even with some of my older packs, like the facility of built in balancer, and with the purpose made li-po adaptors from Gliders it is easy to set up any of my packs, charge balance all at the same time,so much more effeciant,well  worth the money.

 

Regards,

Derek

[Peter Beeney]

    Derek,        I will try and answer your post, but at the moment the ads are appearing on top of the text in this tread, and so I can’t read what you’ve written. It happens in Safari 3, Firefox and Opera browsers so I guess it’s a problem for the system administrators. I could attempt a stab at an answer, but I’d prefer to wait. I’d be guessing.

    Hope you can read this reply ok!        PB

[Peter Beeney]

      Derek,    I might have semi-cracked this problem.    I’ve pulled the text outside the thread, so I’m now able to read your post. I hope you will be able to read this reply.
   
    The term redundant simply means ‘surplus to requirements.’ However, in engineering circles it’s sometimes just slightly different. If I had a battery say, supplying some equipment that could not be switched off under any circumstances, then I might arrange for a second battery that I could connect in parallel, without interruption, seamlessly in today’s jargon, a no-break change over in my old fashioned speak, so that I can take the first one out of service for maintenance purposes etc. This second pile of amps would be my redundant battery. In your case the two parallel supplies are there only in case one fails. They are always connected. It’s just a duplication.  One is redundant. ‘Belt and braces,’ so to speak The first you would know about a failure is if it happened when you’d forgotten to switch one on!
    Going back to what I said about the series/parallel combo and the balancer ‘seeing’ only two cells, consider it this way. You are actually ‘looking at’ four cells but you are only ‘seeing’ two cells. If the pack were sealed in a black plastic bag you would ‘know’ there were only two cells, simply because it’s a 7.4v output.
    So now you’re ahead of me and you can tell me that whether you switch one or both switches you are only ever connecting ‘two’ cells, that’s a max of 8.4v fully charged, to the regulator.
    Is your power supply system in the order - battery - regulator - switches - receiver? Or battery - switches - regulator - receiver? It might be worth just considering this.
    I can well believe the awesome model, a lot of practise to get up to top whack! Still, if you ever get to a full throttle flight at 3 kW, then it’s only going to fly for about four and a half minutes, something of a relief, perhaps?
    The propeller, I can only say try someone like West London Models. There must be a demand, so there’s surely a supplier.
    Re the exponential, I’ve got a sort of ‘less is best’ mentality. I would tend to start with none and then put in small amounts if necessary until I felt comfortable with it.
    And the Ultra Duo 50. I don’t know this baby, I’ve used a Schulze for many years. However, I certainly agree with the maxim of a serious charger for serious charging. Plus they don’t get much better than Graupner. The improvement is just a measure of the quality, (or lack of it), of your previous battery basher perhaps. Over time, I’m sure it will prove to be a good investment, for too many reasons to go into here.

    Good Luck with your model.                       PB
   

[Derek]

PB,

Well done and a very good overview of the problem , now i have it, thank you very much.

 

I doubt wether this model would need to be flown full chat for any length of time it is so graceful being flown slow and easy, just the odd fast hat on is good fun though.

 

The expo i use is from the manufacturers sheet, if there were none at all i think this model would have been in the bin in minutes, believe me it needs it, but with most models as you say less is best, i do not like using dual rates so expo is good for me, each to there own as they say.

 

Regards,

 

Derek

[Doug Ireland]

I can't read it either. Shame as I would like to use a LiPo as an Rx battery too.

[Derek]

PB,

 

Just to add, the R/X pack to switch to regulator to R/X.

 

Changing tack slightly, what do you reckon to the extended aerials on the ner AR 9300, or can we just extend the aerials on our other R/X, we would have four  whiskas instead of three to put outside the fuz?

 

Derek

[David Ashby - Moderator]

Peter, you're pasting text across from a word processor which distrorts the page, hides text under adverts and brings across unreadable/unconvertable characters. Please can you kindly write directly in the forum saving often, perhaps several shorter posts rather than a long one?

 

Thanks

David.

Edited By David Ashby - RCME moderator on 24/06/2009 08:29:17

[Doug Ireland]

Quick question David. How long does the "Post a reply" box stay open for text entry?

[David Ashby - Moderator]

About 20 mins Doug but if you click on the 'remember me' button when you log on then it should keep you logged in indefinately subject to using the same browser and computer.

 

Edited By David Ashby - RCME moderator on 24/06/2009 09:38:45

[Tim Mackey]

Doug. To use a LiPo for your rx, simply obtain a decent capacity ( 1500mahr  or so ) 2S battery, and a separat e BEC ( sometimes called a UBEC ). This drops the voltage down to either 5 or 6V ( you choose ) and simply plugs into the Rx in the normal battery socket.

Heres a link to a typical "stand alone" BEC or regulator.

Alternatively, why not consider 2 x A123 cells in series - at a tad over 6V these are fine used directly into the radio with no need for a regulator. Available form Puffin amongst others, and come in two flavours 2300mahr or 1200 mahr.

Most of the benefits of LiPo with MUCH longer life and almost bulletproof.

Edited By Timbo - Moderator on 24/06/2009 13:27:37

[Peter Beeney]

     Derek  -  Pleased that I was able to be of assistance!  -  Your power supply chain is in the right order, I thought it must be!  -  The expo. You're right, always use the instructions. I accept full responsibility for what I do, it's just that I throw everthing in to start with, after that it only gets easier. I'm with you on the rates, in the 30 odd years they've been around I think they've probably caused more problems than they've cured.  -  The AR3900. Sorry, I'm Multiplex, and I'm waiting for their 2.4 GHz. There must be plenty of people with the info. you want though.

                          Very Best Wishes.              PB

 

 

      David  -    Very sorry for all the hassle caused.   It says here, Powerful Word Processor, I just didn't realise how powerful. Won't it be nice when eventually one computer program will actually be compatable with another one.

      Anyway, I've finished for now, must get some flying in while this fine weather is on.

                     Cheers.                                  Pete.

 

[Doug Ireland]

Hi Timbo,

I've got a spare 3s 1500 LiPo going spare and I've just bought a 5-6v, 5A regulator. The regulator is (apparently) good for up to 30vdc input so I may just use the 3s.

[Tim Mackey]

Good idea Doug....nice long duration from that then !

Please do remember to not let the pack get too low....forget the normal 2.8V inimum per cell rule for such low current drain situations, and ideally  re-charge when the pack reaches around 10.5 -11V under load.....which should still see looong times between charges. Most of the regulators I use have inbuilt alarms to warn of impending low voltage, alternatively, buy a separate alarm such as THIS.

Edited By Timbo - Moderator on 24/06/2009 23:24:17