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Member postings for Rich too

Here is a list of all the postings Rich too has made in our forums. Click on a thread name to jump to the thread.

Thread: Glens Models 25% Sukhoi - manual anyone?
17/09/2019 20:59:34

It’s taken ages as usual!

Nearly there now. Ran the motor at the weekend and it ran a treat after a plug swap. Not bad considering it hadn’t run for over ten years surprise

John, do you remember if yours had the cowl baffled for cooling? This one hasn’t so I am wondering whether it needs it.

other than that, just balance set the throws and then the maiden beckons....

Edited By Rich too on 17/09/2019 21:00:23

Thread: SLEC Chipmunk build blog
17/09/2019 20:55:41

yes I do love the Chipmunk

Edited By Rich too on 17/09/2019 20:56:11

Thread: Repair of a Hanger 9 P-51 Mustang.
17/09/2019 06:38:53

Sub’d yes

i’m hoping to be inspired to sort out the u/c on my Thunderbolt.

Thread: Glenns models cap 232
15/09/2019 16:10:08

I would also add that twin batteries become a lot more popular as a way to isolate the ignition systems, but with 2.4 radio it is no longer an issue. We probably do not need to use twin batteries at all......

15/09/2019 08:11:23
Posted by Gary Manuel on 14/09/2019 14:05:43:

Good bit of info there Rich, but I have a query.

Imagine a model wired as you have shown in your sketch, and one of the cells in a 4 cell batteries fails short circuit. It then effectively becomes a 3 cell battery in parallel with a 4 cell battery. Surely the 4 cell battery would try to charge the 3 cell battery because there is now enough voltage per cell to generate the required charge current and cause the overall voltage to drop. An in-line diode would prevent this from happening - or does this not happen in practice for some reason I'm missing?

Note that I've never used batteries in parallel myself - I tend to use JR/Spectrum PowerSafe receivers (now obsolete?) when I want battery redundancy.

I believe the point of the article was that the chances of a short are very slim and other equipment failure is more likely. A short is more likely in the event of a crash. And LiFe batteries are very robust, that’s why I use them.

Each to their own yes

14/09/2019 10:56:03

These concerns show a lack in the understanding of the charge and discharge potentials involved in Ni-Cd cells. One pack cannot charge the another (equal number of cells) as the discharge voltage of a pack can never be as high as the voltage required to charge the other pack. For the doubters here is an experiment: completely discharged one pack to 4.0 volts and then connected to a fully charged pack having an equal number of cells. There will be less than a 10% transfer of charge in a 24 hour period. Since shorts rarely occur in fully charged packs the risk of one pack "dumping" into one with a shorted cell are insignificant. A simple ESE preflight test would detect a pack with a shorted cell.

While it is a fact that the typical failure mode of a battery is for a cell to fail shorted there are some subtleties here that escape many people. First,one of the major causes of "battery" failure has nothing to do with the batteries themselves but rather with a switch or connector in the battery circuit. The dual redundancy concept is to protect against the failure having the highest probability - that being the circuit path from the battery to the power buss in the receiver. Adding more components to this path, like regulators and/or diodes isn't going to help the matter but rather adds to the probability of failure.

Perhaps the following discussion on the nature of shorts will better help the modeler understand.

While it is agreed that shorts are the failure mode in Ni-Cds batteries one has to look further into the "when" of the failure.

A short develops in a Ni-Cd when conductive particulate bridge the separator or the separator itself deteriorates to the point where it allows the positive and negative plates to touch. Rarely does the short occur all at once but rather building up a very small conductance path termed "soft shorts". In a charged cell the energy in the cell will blow away any short as it tries to develop. You've heard about "zapping" cells. The cell actually zaps itself before the short can develop. Only in cases of severe overcharge at high rates can the separator melt down to the point where the plates contact each other (hard short). In this case the energy in the cell then dumps and we have what is referred to as a hot steamer, the electrolyte boils, nylon in the separator melts down and is forced by the steam through the vent. On some occasions the vent is clogged by the molten nylon separator and becomes inoperative causing the cell to rapidly disassemble. So under normal circumstances a cell maintained at some state of charge is much less likely to short than a cell that is completely discharged. It should be noted however that the self discharge increases rapidly in cells where there is a short building (high resistance -soft short) due to separator deterioration and/or cadmium migration. One other shorting mechanism is a manufacturing defect where the positive or negative collector tab bridges the opposite plate. These usually fall out before the cells are shipped or assembled into batteries.

Preflight procedure should involve checking each battery separately. First check each with ESV through charge jack. You should get nearly identical readings, then switch one on, check controls, switch off and then switch on the other battery, check controls again, then turn both systems on and fly with confidence.

Summary: Diodes are not required. Packs must be of the same number of cells. Packs may be of different capacities. Individual charge jacks must be provided for each pack (and not interconnected). Total capacity available will be the sum of the individual capacities. Specialized chargers are not required since standard packs (600-800 mAh AA packs)can be charged employing regular system wall chargers (1200 to 1600 mAh should cover most giant size projects).

14/09/2019 10:55:36

Parallel Operation = Reliability & More Flight Time

parallelbatt.jpg

The use of redundant parallel fight packs (packs may be of different capacity but MUST be of an equal number of cells) is an excellent way to increase the available flight time and significantly improve the reliability of the on power system. The simplest means is to run two complete wiring harness, switches and charge jacks from each pack and plug one into the normal battery port and the other into an extra channel on the receiver. No diodes or isolation is required (see below). This is simpler and more reliable than some of the complex battery backup systems being offered on the market. Whether you are using 4 or 5 cells is your option, remembering that a 5 cell pack will provide more power to the servos but at the same time discharge faster giving you less flight time.

Parallel charging of Ni-Cds is not recommended due to the tendency of the cells to have the voltage drop off after they reach full charge. Should one pack have a slightly different capacity than the other then it will reach full charge sooner and the voltage will start to drop off allowing more current to flow into this pack. The other pack may not then reach a full state of charge. Repeated charge/discharge cycles under this parallel arrangement causes additional charge unbalance. While you may experiment and find that you get what appears to be both packs charged you will eventually run into problems with this arrangement. As an extreme, take the case of two packs, one having 250 mAh capacity and one having 600. The smaller capacity pack will reach full charge much sooner assuming that there is at least an equal "sharing" of charge current. As it peaks and the voltage declines slightly due to the heating of the battery as the oxygen is recombined it will begin to take more and more current to maintain a voltage equal to the as yet uncharged pack and the voltage tries to drop further and demands even more current to keep it up. This pack will then be taking nearly all the charge current leaving the larger pack woefully short during what would be perceived as a normal charge time like 16 hours.

Many pseudo battery "experts" put forth the argument that plugging two battery packs into the same receiver with out blocking diodes is NOT a good thing, claiming that his creates a host of problems and the two packs will end up fighting each other or "cross charging".

14/09/2019 10:52:38

Each to their own, but I've done my research - I like to keep things simple and reliable.

http://www.hangtimes.com/parallel_packs.html

I've had switches fail so now I tend to use electronic ones that fail ON.

Happy flying yes

 

 

 

Edited By Rich too on 14/09/2019 10:53:44

Edited By Rich too on 14/09/2019 10:54:33

13/09/2019 12:34:16

As I understand it, that is highly unlikely. All my planes have twin battery set ups, and i've never had an issue. wink

13/09/2019 06:46:16

No need to remove it yes

13/09/2019 06:37:13

The batteries can always share any of the ports. I've put twin batteries/switches on a Y lead in the past. 

Edited By Rich too on 13/09/2019 06:38:08

Thread: Well this could get interesting
12/09/2019 13:51:21

This is unbelievable, and of course Steve, they have the right to protest - within the law.

Thread: Drones planned in Heathrow expansion protest
12/09/2019 13:50:16

Apologies, missed it. Can a mod please close this...thanks

12/09/2019 06:34:00

How irresponsible angry

**LINK**

Thread: Southern Model Show 2019
11/09/2019 04:54:34

They require no assembly and are a fit and forget item. Some petrol flyers strip down there tanks each season to check the fuel lines!

**LINK**

Thread: Finished
10/09/2019 13:27:26

Nice one Rob yes and a man after my own heart - you've given me some optimism!

Thread: Southern Model Show 2019
09/09/2019 18:11:02

Yes, i went on Sunday and had a great day. It was our third trip there but not been for a couple of years. I thought it was the best one. I think the good weather helped. I’ll be going again. yes

ps the oval car racing was brilliant. Those cars can take some abuse!

pps and I picked up two brand new  Rotoflow fuel tanks for £10 each! One was 40oz for my Sbach, and the other 14 oz. 

Edited By Rich too on 09/09/2019 18:16:59

Thread: Glenns models cap 232
08/09/2019 14:03:49

Nice looking model yes

Thread: Shortage of 35% (100cc) aerobatic kits in the U.K.
07/09/2019 22:46:24
Posted by cymaz on 07/09/2019 19:01:40:

Just purchased a used 50cc Glens Cap232. Does anyone know if the manual cg is correct?

Should be I would have thought.

Edited By Rich too on 07/09/2019 22:46:46

07/09/2019 22:44:43

Excellent Adrian, which is your preference? Look forward to the build....wink

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