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Old Dec 19, 2010, 03:12 AM
PLD
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Dual input/output 5A electronic switchjack failsafe system

With modern receivers being more sensitive to power disturbances, coupled with digital servos imparting more demand onto batteries, it's now becoming essential to run power systems that are more than just a single set of 4 or 5 Ni cells.

Many people are now switching over to directly running with LiFe or A123 packs and we're providing the ESJ-5ADV as the ideal companion to keeping your gear running.

The ESJ-5ADV accepts dual battery pack inputs (they can even be difference chemistries and sizes, provides remote switching ability with even tiny switches and provides dual power outputs in the event that one of the cables fail to the receiver. Additionally, the ESJ-5ADV provides a voltage readout of the highest pack and includes strong capacitor decoupling to help smooth out those spikes and dips.

At 1.1x1.0" in size, complete with mounting points, the ESJ5-ADV is a very compact unit. The voltage drop across the ESJ5-ADV will very often be less than that experienced if you used a normal mechanical on/off switch system due to the superior low resistance switching of the MOSFET used.

The ESJ5-ADV is ideal for gliders, large electrics and glow planes.

Two initial levels of build will be available;

ESJ5-AD (dual in, dual out, decoupling, power good indicators) - $23.00
ESJ5-ADV ( +voltage readout ) - $33.00

Units will commence shipping in about 2 weeks.


ESJ-5AD - http://nqrc.com/?vp=PLD-ESJ-5AD
ESJ-5ADV - http://nqrc.com/?vp=PLD-ESJ-5ADV


Paul.
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Old Dec 19, 2010, 04:24 AM
PLD
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A few technical points to share about the design;

1. The balancing input stage can handle 3~5A constant under normal conditions.
2. The switchjack stage will cope with with 5A and only dissipate 75mW of heat and drop 15mV of voltage.
3. The LEDs will only draw 3~5mA each and will only be active when the switch is activated.
4. The dual-output headers are bonded to the same power rails
5. The choice of the switch used to turn on/off the ESJ doesn't really matter as there's only a tiny amount of power passed through it.
6. The whole ESJ has an off-state current draw of only 1.5uA, to put that into perspective, each 1mAh capacity of the battery will last 4 weeks. The battery itself will self-discharge faster.
7. The ESJ5AD[V] will have a 470uF low ESR decoupling capacitor.
8. Total forward voltage drop will range from 0.3~0.5V (this is mostly from the drop across the schoktty balancing diodes).
9. Reverse polarity protection.

Higher average currents can be achieved by placing small heatsinks on the balancing diodes.

Paul.
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Old Dec 22, 2010, 07:42 AM
PLD
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Seems like the PCB factory has gone on holiday - as I've not heard anything back yet since the submission of the boards. Normally by now I've got a FedEx notice.
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Old Dec 29, 2010, 07:28 AM
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Hi Paul,

nice one!

So if I understand it right, the unit doesn't include a switch. That is probably what the 2 wire header is for. Correct?

What state will the board be in if the switch goes open circuit when the switch is in closed circuit state? I.e. the switch fails

What will the board do if the switch contacts suffer from increasing resistance?

Do you have a switch you recommend?

Should the batteries be wired directly to the 'switchjack'?

How do you recommend charging the batteries? For the record I don't remove LiFe to charge them as they do not have an overtemp failure mode.

Please confirm the unit protects from a dead battery discharging the other (good) battery?

I'm asking these detailed questions because I'm keen on giving one a try for my lovely new slope rocket (Skorpion Needle).

TIA!

Ken.
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Old Dec 29, 2010, 07:38 AM
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Hi there skyboyken,

Quote:
Originally Posted by skyboyken View Post
Hi Paul,
So if I understand it right, the unit doesn't include a switch. That is probably what the 2 wire header is for. Correct?
That's right - the big problem is that everyone will have a different choice on what sort of switch they want and how long they want the wire.

Quote:
What state will the board be in if the switch goes open circuit when the switch is in closed circuit state? I.e. the switch fails
If the switch goes open circuit, or the cable disconnects, the power is ON.

Quote:
What will the board do if the switch contacts suffer from increasing resistance?
This will make it progressively slower to turn off, once the contacts exceed about 100K resistance the board will be effectively impossible to turn off.

Quote:
Do you have a switch you recommend?
I'd recommend any high quality action compact toggle switch. For double assurance you can put two in series, so that if one fails in a short circuit manner it won't deactivate the ESJ.

Quote:
Should the batteries be wired directly to the 'switchjack'?
I suppose that's subjective - personally I'd consider it the most reliable option but of course you will need to ensure the packs have their own charge headers.

Quote:
How do you recommend charging the batteries? For the record I don't remove LiFe to charge them as they do not have an overtemp failure mode.
I recommend each pack has a separate header/port for charging.

Quote:
Please confirm the unit protects from a dead battery discharging the other (good) battery?
That is correct. The system will only draw power from the highest voltage pack, as a consequence, if one pack collapses or goes internally high resistance, the other pack will supply the power but it will not be 'drawn down' by the failed pack.

Hope that gives you sufficient information

Paul.
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Old Dec 29, 2010, 07:36 PM
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Well, good news everyone.... the boards arrived about 10 minutes ago.

Now I have to actually build them!
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Old Dec 29, 2010, 09:53 PM
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Built and working

I've finished the first of the non-voltage-readout versions (ESJ-5AD).

One thing I did have to do is change to a 470uF 10V cap, which isn't a major problem. If additional decoupling is needed it will be better to be plugged directly into the RX with a VP470 or VP1000 unit.

Attached are some piccies

I've got two 2S lipos attached here but it'll work with 5 cell Ni, A123 or LiFe no problems.
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Old Dec 30, 2010, 04:15 AM
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I should make a note - you don't have to use two input packs. There's no reason you cannot just use this as a single battery switch system.

Paul.
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Old Dec 30, 2010, 08:07 PM
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Here's another diagram showing the intended configuration
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Last edited by PLD; Dec 30, 2010 at 10:42 PM. Reason: Uploaded newer picture detailing voltage drop
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Old Jan 01, 2011, 01:17 AM
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Simplified view

Attached is a simplified electrical model of the ESJ system, just to provide some clarification.

Note that the two batteries have their grounds tied together, which is okay because the two diodes in the balancing section prevent any substantial power flowing between the batteries (there is a small current flow on all back-biased diodes but it's insignificant in this situation).
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Old Jan 09, 2011, 02:01 AM
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I've changed the pricing on the new dual-input/output ESJ units; had a miscalculation there on the parts.

ESJ-5AD is now $23 (was $29) [ http://nqrc.com/?vp=PLD-ESJ-5AD ]
ESJ-5ADV is now $33 (was $45) [ http://nqrc.com/?vp=PLD-ESJ-5ADV ]

Paul.
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Old Jan 17, 2011, 02:14 AM
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Finally got the 5ADV firmware sorted out, it was a real nightmare to work on because I threw everything possible against myself.

The chip has to be programmed at 5V but I put it into a 2.48V circuit, the programming pins don't like any sort of load on them (during programming) but I put my buzzer and LED on those two pins [ remember, there's only 3 usable pins on this thing ]. The circuit board itself has no provision for programming pads so I had to jig it all together with fine 30AWG single-strand wire and try not move it too much (else they break of course). Finally, it had to be coded in Assembly... because the chip is so tiny it cannot handle the sort of firmware that would be generated from C (yet).

Good to have it working now... my wife is duly irritated at the "Damned beeping"
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