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'DelTang' Reverse Polarity Protection
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 Posted: Mon Aug 27th, 2018 03:40 am
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Budd
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Do the DelTang Receivers have reverse polarity protection ??

Mine is a tale of woe and a warning.

My new fit RX62 was playing up, it kept losing the signal and power.
I found out the issue was a bad connection within one of the LiPo's I used in my home made 3 cell pack.
To test my theory I plugged another 1C LiPo into the RX, which was quickly followed by a puff of smoke !

I pulled the pack plug straight away so didn't really notice where the smoke came from, but it doesn't want to work now !
I can't see any burnt components on the board and was hoping it was just the feed wire melting, but alas, she is kaput.

The warning is that the D.C. feeds on the pack I used were reversed.
I have eight LiPo's that came fitted with plugs and half of them were reversed.

The other side of the story was trying to find the standard wiring, ie which plug pin is + & -
I couldn't find anything definitive and looking at pictures showed different arrangements.

I think I have it right, but I do have it to a standard now
(I use the same plug on a few H0 builds)
and will remember to pay attention before I plug in any packs in future.
 
Wayne from Oz.




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Modelling the 3'6" gauge railways of South Australia of course.
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 Posted: Mon Aug 27th, 2018 06:51 am
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davecttr
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Ouch!

I am considering rebuilding all my installations to make them neater,
and will consider adding a small standard connector between the board and the battery.

Luckily my batteries have a standard UM connector and have all been OK so far.
It might be a good idea to test the polarity of any new batteries I buy !

What does a reverse polarity protection circuit look like?
Is it similar to the one on the DelTang site suggested for using track power with a Receiver ?




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 Posted: Mon Aug 27th, 2018 07:42 am
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Si.
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Hi Guys  :wave:



A pair of 'Schottky Diodes', 1 in each D.C. power-line to the Receiver Board, would provide good reverse-polarity protection.

'Schottky Diodes' drop an absolute minimum of Volts, compared to regular silicon types.

You can check the Voltage drop of various Ampage types, in your favorite suppliers catalogue data.

'Typically' the average Schottky Diode only drops around 0.25 Volts, sometimes less.

For a few Pennies each, It could be worth considering, to protect those expensive receivers.



:!:



Si.




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 Posted: Tue Aug 28th, 2018 01:03 am
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W C Greene
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Actually, invest in a good VOLT/OHM meter and then you can tell which post is pos/neg. Don't always trust the "black & red" wires, sometimes those 12 year old Chinese girls get the wires backwards!
Besides, a nice meter is useful for many other things anyway.

Woodie



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 Posted: Tue Aug 28th, 2018 05:13 pm
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Si.
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" What does a reverse polarity protection circuit look like ? "



Hi Dave  :wave:



A reverse polarity protection circuit is a simple & cheap solution for receiver protection.

It looks like this ...





A 'Schottky Diode' is always the best option here ...

... due to it's very low 'forward Voltage drop'.



A 2nd 'Schottky Diode' could also be added to the negative power-line ...

... the other way around, with it's 'arrow' pointing towards the battery 'minus' terminal.



No matter how much testing of batteries one does, or how 'reliable' the supplier is ...

... MISTAKES HAPPEN ! ... & '20-20 hindsight is a wonderful thing' as they say.  :f:



The 'Schottky Diode' circuit costing a few Pennies & a few minutes to install ...

... could save you  FIFTY $$$ BUCKS !!  :shocked:



:!:



Si.




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' Mysterious Moose Mountain ' - 1:35n2 - pt.II
http://www.freerails.com/view_topic.php?id=7318&forum_id=17&page=1

' M:R:W Motor Speedway !!! ' - 1:32 Slotcar Racing Layout
http://www.slotforum.com/forums/index.php?showtopic=59295&st=0&a
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 Posted: Sun Sep 2nd, 2018 08:43 pm
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bobquincy
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I smoked one DelTang receiver through carelessness.  
The motor driver devices burned out, but the P outputs still work, so I used the receiver for a model without a motor.

I would add a diode but many of my models are powered by 2xAA, so I still need a step-up (3,3 V) to power the receiver.
Not much voltage available to throw away.   :(  

Same with the Pololu DRV8835/8 motor driver.
I use the VM input to conserve voltage, but it has no reverse protection that way.




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 Posted: Sat Sep 8th, 2018 10:42 pm
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Si.
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        Well ...  L:

... for anyone not wishing to waste a   SINGLE ELECTRON   of power !  :shocked:



I found this pretty  C :cool: :cool: L  and 'fairly simple' circuit.  :)





When a 'Reverse Polarity' power-source is connected ...  :shocked:

... the relay-coil operates switch-contacts 'S1' ...

... cuts power to the Vout load ...

... & lights up the 'D3' red L.E.D to indicate 'Reverse Polarity' has been applied.  :!:



Power is only consumed when a 'Reverse Polarity' source is applied !  :)

Normal 'Correct Polarity' operation consumes ZERO power...  :bg:

... & there is NO VOLTAGE DROP whatsoever from using the circuit !!  :thumb:



Simples !  :dope:



:java::brill: 



Si.




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' Mysterious Moose Mountain ' - 1:35n2 - pt.II
http://www.freerails.com/view_topic.php?id=7318&forum_id=17&page=1

' M:R:W Motor Speedway !!! ' - 1:32 Slotcar Racing Layout
http://www.slotforum.com/forums/index.php?showtopic=59295&st=0&a
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 Posted: Sun Sep 9th, 2018 07:09 am
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Helmut
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IMHO this circuit perfectly makes sense where you draw considerable amps under normal operating conditions. 
G-scale models of Aristo-Craft come to mind. 
Smaller operations fare better with a Schottky-Diode wired in series.




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 Posted: Sun Sep 9th, 2018 08:43 pm
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bobquincy
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The reverse-voltage protection as used on the Pololu DRV motor control boards (P-ch FET with charge pump) is good and is fast enough to protect solid state devices (relays may not always be fast enough). The voltage drop should be no more than about 50 mV at 1 A.



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 Posted: Sun Sep 9th, 2018 09:28 pm
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Si.
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I should have added ...  :)

... That a 'Solid State Relay' would be ideal, as opposed to the old 'clunky' mechanical types.  :shocked:



These are available for a $1 Buck a bag on eBay of course ...  :thumb:

... So no great expense for specialised & difficult to get parts.  :bg: 



It is a simple circuit & could be made in a VERY compact package if needed.  :dt:



The 'Schottky Diode' however, with it's absolutely MINIMAL 'Forward Voltage Drop' ...

... is still the simplest option, for trains powered on 7.4 or 11.1 or 12 Volts etc.  :)



Some of the 'Shottky Diodes' available today, if you look, drop only a TINY fraction of a Volt ...

... high current is 'the norm' in terms of what is available, using one rated at 3x your battery Voltage is sensible.  :cool:



:!:




Si.




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' Mysterious Moose Mountain ' - 1:35n2 - pt.II
http://www.freerails.com/view_topic.php?id=7318&forum_id=17&page=1

' M:R:W Motor Speedway !!! ' - 1:32 Slotcar Racing Layout
http://www.slotforum.com/forums/index.php?showtopic=59295&st=0&a
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