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Old Dec 04, 2010, 04:01 AM
I do this for fun!
Sunshine Coast, Australia
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PLD-ESJ-3A-LMA-LVA question

Hi Paul,

I need a power supply solution for my new Needle 100 slope glider. It's called a Needle because the fuse is really slim. I have a 2S LiFe Hyperion pack which I'm standardising on for my moulded gliders. Unlike others though, this fuselage is so small I can't fit my usual double wiring from pack to Rx and additional LED voltmeter.

Your PLD-ESJ-3A-LMA-LVA looks perfect, except for a couple of questions. Firstly, would it detect the 2S LiFe as a 5 cell pack and if so is the alarm voltage too high at 5.9V? Secondly, what are the risks of the plug failing and either not making reliable contact as the 'pin' is withdrawn or simply failing in flight - i.e. what happens in those scenarios?

Ken
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Old Dec 04, 2010, 09:30 PM
PLD
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Hello Ken,

Regarding the voltage cutoff - I can actually build you a version with a LiFe cutoff, if you give me the preferred voltage you'd like it to 'alarm' at (other than that it'll still blink out the actual voltage of the pack as normal too).

As for the failure modes of the connector; The ESJs are designed to be fail-safe by defaulting to 'power on' mode; the 3.5mm plug has to forcibly shutdown the system by pulling it to ground. The power when "on" doesn't flow through the plug itself, so mechanical wear, pitting, corrosion etc won't come into play.

Hope that helps.

Paul.
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Old Dec 04, 2010, 09:49 PM
I do this for fun!
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Thanks for your reply Paul,

I've done a little more research and the 95% cutoff voltage is apparently 3.0V per cell so 6.0V would be perfect, although 5.9V should do nicely.

The plug fail mode sounds perfect!

I don't suppose you're planning anything like the french system which steps up the voltage of 2 single cell LiFe independently and manages them as separate power sources, to provide a fully redundant power system which fits in small fuses?

Ken.
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Old Dec 04, 2010, 10:00 PM
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Ken,

Do you have a URL for the French system?

I have been doing dual-input/failover systems recently but for larger 50~100cc aircraft, rather than the smaller ones.

The 3V/cell cutoff~alarm sounds fine. Of course, LiFe's do have such a flat discharge that it gets difficult at times to know how far down the discharge path it is. None the less, at least if it gets to 3V/cell you know it's really time to recharge

Paul
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Old Dec 05, 2010, 02:55 AM
I do this for fun!
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here 'tis Paul:

http://www.greentronic.eu/en/index.p..._id=2&Itemid=1
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Old Dec 05, 2010, 03:24 AM
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Skyboyken,

Interesting device, certainly looks like they've got two active switchmode converters on the board there, feeding into the usual diode-pair. It's not how I'd personally have designed it but I suppose it comes down to where you consider your failure points.

I'd have gone with the dual-inputs being merged immediately into a single switchmode converter, it'd cut down on weight, cost and size considerably, as well as dropping the overall effective failure rate due to half the part count.

In my experience, the biggest causes of failures are;

1) connectors/cabling
2) batteries
3) solder failure / thermal fatigue
4) component failure

There is certainly some level of advantage to what they've done - but it does come with a lot of complexity (they have to synchronise their converters so that they don't do catastrophic things. To be fair, I do not have much experience with the way they've done things, mostly because of the synchronising issues - I'd be immensely curious to find out what their points were for doing it (and I'm sure they do have some good points - which is why I'm curious).

If I did a dual-input option, it'd be as mentioned above, dual packs in, merged, then switch-mode and dual physical connector outputs (again, dealing with the high connector failure probability).

Paul.
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Old Dec 05, 2010, 05:37 AM
I do this for fun!
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I guess the best thing to be said for their approach is that they do have full redundancy from the battery all the way to the Rx in a very small package. Their device is well proven in Europe, it is delivering reliable results in F3X gliders and it is the only redundant solution available which fits in the fuselages. It's pretty expensive though, but not compared to the cost of a plane.

I've been flying F3X gliders for a long time, and by far the biggest reason for total loss crashes is power failure. This is as true today as ever. A year ago I lost a new $2,600 glider within 2 months due to power failure while winch launching.

With regard to failure rates, as long as one half keeps functioning when the other half fails, their system would deliver higher operational reliability even though the component fail rate would be higher simply due to the doubling up of components. That really is the attraction of the system.

If you could deliver as high a reliability in a similar form factor at a lower cost There would definitely be a market. Talk to Bob at Soaring USA, I'm sure he would say the same.
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Old Dec 05, 2010, 06:52 AM
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The way I would design it, if I had to, would be that one has a primary and secondary booster.

For as long as the primary works, that's what is used - if the primary ever fails, it falls to the secondary.

Obviously on start-up it would be prudent for the control system to validate that both systems are functioning (would be rather unfortunate that if after 3 years your primary finally fails only to find that your secondary failed 3 months before hand).
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Old Dec 05, 2010, 06:57 AM
PLD
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Quote:
Originally Posted by skyboyken View Post
This is as true today as ever. A year ago I lost a new $2,600 glider within 2 months due to power failure while winch launching.
Absolutely agreed, power systems are the biggest failure rate, do you know what in the system failed (cable/connector, battery, electronics, PCB ?).

Given the design criterion, I'd say that their ~60 Euro pricing isn't too far from the mark, especially with most of our suppliers dropping bombs on us like going from $1.50 to $5.50 on many crucial parts.
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Old Dec 05, 2010, 05:28 PM
I do this for fun!
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"do you know what in the system failed (cable/connector, battery, electronics, PCB ?)."

No I don't. The plane had a previous crash and I had tested everything but my assumption is I missed something and had a wire or connector failure under the stress of launch. There wasn't much left intact to do post-mortem with.
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Old Dec 05, 2010, 06:02 PM
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Rather unfortunate when one cannot get a conclusive answer on the crash cause.

On to more products, one item I have been working on and probably will release soon is a simple dual-input, electronic switchjack. It's not a regulator and it's not exotic, however it does provide a rudimentary level of redundancy for those not quite after redundancy all the way up to the receiver.

An 'optional' version will also include a voltage readout (blinking readout, like the BAC units).
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Old Dec 09, 2010, 05:25 PM
I do this for fun!
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That would be a really handy unit,

particularly if it had dual inputs and dual outputs to the rx, or options for them to be soldered on.

What I mean is that when using high relibility batteries like LiFe cells the most important thing is to have a redundant current path to the Rx. I solder a set of leads onto the balance connector leads and use those plus the normal leads, for example. This way, my only single exposure is a battery failure.

So an electronic failsafe switchjack with dual inputs and outputs would be a really cool device

Ken.
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Old Dec 09, 2010, 05:30 PM
PLD
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Ken,

I've been going wild in the last week and have created a whole swathe of devices in this area.

Most of the discussion is in the NQRC thread in the Australian area; http://www.rcgroups.com/forums/showthread.php?t=622895

Attached is a picture of the top-end beast I've created which does dual-inputs, electronic-switch, regulated (3A) and alarm (visual and audio).
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