Tip Positive NEQ6.

[kirkster501]

Hi all,

Just sanity checking my findings here before making an expensive mistake!

Using my digital multimeter I have "buzzed out" the cigar lighter end to 2.5mm connector end of the cable and find the centre tip of the 2.5mm connects to the centre tip of the cigar lighter plug. When connecting the fag plug into my powertank I get +12v between the centre tip and the outer connector of the 2.5mm connector - this is when the red of my DMM is in the tip of the plug and the black lead of the DMM is on the outer connector  Hence the 12v is at the tip?  I am very aware that getting this wrong way round when making up a power box can blow the board of my mount....

The ATIK camera and EFW2 filter wheel power cables are identical cables in terms of connectors.

Does that fit with everyone else's experience please?

Thanks, Steve

 

[sloz1664]

Hi Steve, definitely tip positive mate.

 

Steve

[Tinker1947]

My NEQ6, Atik CCD and Filter wheel are all the same 2.1mm plug Positive tip...

[Gina]

Yes - confirmed

[perfrej]

Confirmed - but it is a 2.1mm, not 2.5, so a 2.5 plug may not connect properly...

[kirkster501]

Thanks everyone.  Yes indeed Per, 2.1mm.

As a follow up question, do you guys think it is wise to fuse them differently as I am thinking of doing so.  1A each for Camera and Filter wheel and 5A for the mount.  I also think 5A as a feed for my dew heater box supply.

Steve

[perfrej]

Fuse protection can be looked upon in two ways:

1 - Stop a device from getting too much secondary damage when something breaks in it

2 - Stop danger (smoke, fire etc)

In the case of 1, if a component in the device shorts, it will most likely damage other things in the device. In order to protect it from that it needs a fuse that is close to the max rating of the device and that comes off pretty fast. For an Atik camera, I find 1A to be totally impossibly too small - yet, that is what their spec says. The cooler should suck a few amps... Some devices draw a power spike when power is applied. This is usually a result of using low ESR capacitors on the power filtering for passing EC or FCC radiated emissions standards. These charge themselves very quickly! My SBIG ST-8300M consumes almost 20A for a few milliseconds when power is applied, then goes down to 0.6A, which is what it consumes with heater off. If you have a standard power supply, this is not an issue as the supply will dip under the load, but if you have a lead-acid battery, any fast acting 4A fuse will trip.

This tells us that case 1 - the minimizing of internal damage in a device - is not easy to achieve. In my power design I use a fuse implemented in software in order to manage this. It measures current a thousand times per second in order to do the job and it is still not perfect.

Case 2; making sure that your system loses power when something breaks is much easier. If an individual device goes haywire that device will have time to get damaged, but your power will eventually be cut. The idea is to fuse off the system as a whole with a fuse that can just take your maximum load.

I suggest a combination, especially when using batteries as a power source. Case 1 is tricky, but it is better to have some individual protection - even if it doesn't really save the device completely - than none. What would be good values for your fuses? Well...

If your Atik blows a FET internally, it is going to more or less short circuit completely until that FET burns off or a lead on the PCB does. That will draw much more than 1A. If you have a battery supply you could be looking at a short term draw of 50A (reduced by the cabling), which will burn off most of the stuff in there pretty quickly. As the draw is pretty high in that case, some margin on the fuse is acceptable. Go for 2A fast, and if that trips spontaneously try 1.5A or 2A slow blow.

NEQ6 draws very little power but needs some initial juice while ramping. 4A sounds about right. It has a circuit board with very small leads which will burn off very easily, essentially acting as smoking fuses. A filter wheel consumes next to nothing, 0.5A should do.

 

A note on fuses... One needs to actually check both the holding current and the tripping current in the data sheet. A "4A" fuse holds 4A but trips at a much higher current, and there is a time involved as well.

 

Morning rant, eh?

 

/per

 

[kirkster501]

Thanks Per.  So what fuses *do* we need to use then in order to build in in-line fuse protection for our gear?  If it varies so drastically it seems mad to use a 10A fuse just to cater for the milliseconnd on in-rush current?

I'm building a power box and I am fusing the outputs individually.  

[ChrisLX200]

I don't think something as simple as a fuse can 'protect' a complex digital electronic circuit - it takes very little current or over-voltage (or time) to do irreperable damage. So your gear is already toast long before a fuse can react. Preventing secondary damage (fire) is something else, that takes much more current so a fuse can be an effective limitation. The last time a cheap PSU failed in one of my computer builds it took out the MB, CPU, RAM, graphics card, Sound card, SSD hard disk. There was only a short 'pop' and the fuse went but still, the extent of the damage was extraordinary. Better NOT to use cheap components in the first place...

ChrisH

[Islander]

Fuses don't protect equipment, they protect the cabling and their primary purpose is to prevent overheating and fire in the event of a short circuit.  A fuse can pass a current much higher than its rating for a surprising amount of time as well.  If the load is largely resistive rather than reactive (i.e. inductive or capacitive then you can safely use a quick blow type.  If the load is reactive, then a slow blow or delay fuse is a better idea.  Delayed fuses are identified by a T after the rating - i.e 1AT whereas a qucik blow is only marked with the rating.  Delay fuses will have a tapered coil at one end or a blob in the middle of the wire to dissipate extra heat.

 

[StuartJPP]

1 hour ago, Islander said:

Fuses don't protect equipment, they protect the cabling and their primary purpose is to prevent overheating and fire in the event of a short circuit.  A fuse can pass a current much higher than its rating for a surprising amount of time as well.  If the load is largely resistive rather than reactive (i.e. inductive or capacitive then you can safely use a quick blow type.  If the load is reactive, then a slow blow or delay fuse is a better idea.  Delayed fuses are identified by a T after the rating - i.e 1AT whereas a qucik blow is only marked with the rating.  Delay fuses will have a tapered coil at one end or a blob in the middle of the wire to dissipate extra heat.

 

Fuses can protect equipment depending on how the circuit is designed. What you say is typical of domestic wiring or similar however fuses can protect the equipment as well.

These days there should be no excuse for a typical circuit board to toast because the voltage was too high (unless really excessive or not so excessive but for prolonged periods), reversed polarity, transients etc. It is all down to shoddy design and cost saving.

 

[Islander]

Yes, specialiised fuses on a circuit board or in components (thermal fuses are a good example), current limiter circuits and reverse and overvoltage protection circuits are all intended to limit damage in circuitry in the event of  component breakdown or a short/open circuit load being presented.  Where these are active rather than passive systems/devices, they are capable of acting quickly enough to prevent extensive damage from occurring.  However, a fuse in a power lead protects the wiring much the same as the fuses in a domestic mains system and fuses in themselves are generally intended to disconnect a load in a reasonably short time to prevent overheating and fire.  They operate far too slowly to prevent any other damage from occuring.

[kirkster501]

Interesting discussion guys.  I am going to fuse all the five 12v outputs(mount, EFW2 FW, ATIK, Dew Band Box Supply + one spare  - 5A,1A,1A,5A,BLANK respectively)

If an ATIK, for instance, says it is 0.8A then a 1.0A fuse should be sufficient?  I may have to just try it and see.  I have at last got all the bits for my power box - takes ages for third class post from Hong Kong where many of the bits came from! - so will start building it when I get some time.

[Tinker1947]

If your going with the fuses how about some Overvolt protection and short circuit there only small boards and easy to build or likely you can buy them ready made.

https://www.google.co.uk/search?q=12+volt+overvoltage+protection&espv=2&biw=1920&bih=1099&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwi_w4ij2MzLAhUIS5oKHVIPBqEQsAQIQA

[Gina]

Yes, I added overvoltage protection using zener plus thyristor - in conjunction with a fuse.  This is a well known addition to commercial high quality PSUs (or it used to be).  Well worth using to protect expensive equipment against errant power supplies.

[kirkster501]

Thanks guys.

So if I want to protect against overvoltage from the PSU I would do that to the common 12V output from the PSU, with the zenner across 12v-0V before feeding that common 12v to the individual fuses?

Surely such a simple measure would be built into the PSU?

 

[Islander]

51 minutes ago, Gina said:

Yes, I added overvoltage protection using zener plus thyristor - in conjunction with a fuse.  This is a well known addition to commercial high quality PSUs (or it used to be).  Well worth using to protect expensive equipment against errant power supplies.

Ah, a crowbar circuit.

Derived from the times when a train driver carried a crowbar to throw across the live tracks to blow a fuse down line in order to signal a problem (or so one of my lectiurers told me)

[kirkster501]

22 minutes ago, Islander said:

Ah, a crowbar circuit.

Derived from the times when a train driver carried a crowbar to throw across the live tracks to blow a fuse down line in order to signal a problem (or so one of my lectiurers told me)

https://en.wikibooks.org/wiki/Practical_Electronics/Crowbar_circuit

 

[Davey-T]

Knocked this up a while ago for Canon DSLR but not got much use out of it.

Uses MC3423 IC

http://www.onsemi.com/pub_link/Collateral/MC3423-D.PDF

 

[kirkster501]

http://www.mds975.co.uk/Content/amateur_radio_projects_07.html

I could build one of these and put it across the 12v output from the Power supply.

A niggling doubt I have hough is that I read many say the NEQ6 does not work well on 12V?  It needs 13v or so?

[Gina]

I run everything from 13.8v - the fully charged voltage of a lead acid car battery.  Astro gear is mostly rated at up to 15v.  And yes, I found the NEQ6 needed 12.5v.

[MarkyD]

2 hours ago, kirkster501 said:

http://www.mds975.co.uk/Content/amateur_radio_projects_07.html

I could build one of these and put it across the 12v output from the Power supply.

A niggling doubt I have hough is that I read many say the NEQ6 does not work well on 12V?  It needs 13v or so?

If I run mine on 12V the motors stall.  I'm running on 14V from a 240W power Supply and no problems

--

Mark