Advice Needed V-Box blew up :(

[Vipersan]

Ok ...
for anyone planning to create something similar by utilising Gbox innards..
This is important..
Yes you still need a smooth isolated 5v supply for the micro etc...
but you also need a 12v supply ..
I've found out that the relays will not function at 5v ...
Simply not enough volts and the 12v supply for the relays is used _before_ the regulated reduction to 5v ...
So ..
I will still be using a seperate negative rail isolated supply to drive a 7805 ...but instead of fitting a seperate 5V supply ..I will have to fit a seperate isolated 12v supply ..and still employ a 5V regulator to further reduce the 12V to 5V
Alternatively I _could_ start replacing the relays ...but too much work fwiw..
rgds
VS

 

[Terryl]

Just use an old ATX PC power supply, it has the +5 volts and the +12 volts you need, and is well filtered.

 

[Vipersan]

Just use an old ATX PC power supply, it has the +5 volts and the +12 volts you need, and is well filtered.

..Wont physically fit buddy...
Far too large and serious overkill current wise.

 

[Llew]

I don't suppose that toroid I sent would fit in there? That has a separate 12V supply...

 

[Vipersan]

I don't suppose that toroid I sent would fit in there? That has a separate 12V supply...

No Llew ..
But this will
broke the plastic casing off a 12v switch mode 'power brick' from an old portable lcd TV
12v at 4Amp ..so more than enough..
Removed the Euro Socket (kettle lead type fitting) ...and mounted with a single screw through a heatsink on the secondary side ..
A sheet of plastic to seperate/protect from the Gbox pcbs ..and bobs yer aunties live in lover..
Fits the gap on the left nicely I think..

 

[Llew]

Which proves - don't chuck stuff away if anything's remotely useable. My shed and garage bear witness to this dictum

 

[Terryl]

..Wont physically fit buddy...
Far too large and serious overkill current wise.

I like serious over kill.....And didn't know you had a size limitation...I had some real nice DC to DC converters that were 2" by 6" and had some serious filtering in them, they took up to 48 VDC and gave me +12 and +5 at 5 amps each.....Hummmm now what did I do with those? Time to go dig in the barn.

 

[Vipersan]

Which proves - don't chuck stuff away if anything's remotely useable. My shed and garage bear witness to this dictum

Like you Llew ....
if I throw something away ...
It's garbage...
lol

 

[Terryl]

Which proves - don't chuck stuff away if anything's remotely useable. My shed and garage bear witness to this dictum

I agree, I have suff that goes back to the 50's and 60's, some stuff even has vacuum tubes in it, I'm saving that stuff for when the silicone stuff goes FUBAR during the next Apocalypse.....Or Zombi attack.

 

[Llew]

I agree, I have suff that goes back to the 50's and 60's, some stuff even has vacuum tubes in it, I'm saving that stuff for when the silicone stuff goes FUBAR during the next Apocalypse.....Or Zombi attack.

Yup. I've got a 50's Wayne Kerr video oscillator under the bench - weighs a ton, but often have it out just to check with the 'scope. Needs ten minutes though to warm up before the trace comes up to max
A modern equivalent would almost fit in a pocket I reckon.

Still have loads of books on electronics of a past era. Early in the 50's a Ham friend of my Dad gave me a 1947 ARRL Handbook, which really started off my interest. Laws and circuits and all that.

 

[Vipersan]

DAMMIT !!
The 24v 8amp 200W switch mode just died ..
No fireworks ...and only the AZ gbox active at the time ...
Nothing running hot to the touch ??
I simply reversed direction on the positioner...which had been running flawlessly for hours ...
The psu had been in use for at least a week...
But it died...and didn't even pop the 4amp fuse in the motor line...
Shyte components maybe ?

Maybe a brief moment when the relays weren't synced ...a delay in contacts opening/closing...
who knows ...
I guess I never will ..
But ..this psu is supposed to have short circuit protection..?
Very frustrating indeed ...and of course I cant return it cos I modified it to fit..
To say the least I'm gutted and now contemplating returning to a torroidal transformer generated 24v supply ...which _should_ cope better with loading and switching direction with relays..
If I do I'll still use a 12v switch mode for all but the motor power..
Grrrrr

 

[Riverblue]

Sorry to hear that VS after all your hard work!

 

[Captain Jack]

Wow... That sucks

 

[Vipersan]

So ...I hooked up the torroid kindly donated by Llew..
with a bridge rectifier and upgraded caps ..
All relevant ones now rated 63v
These are the ones which usually leak an fail in normal Gbox use..
Good job I did ...cos that torroid produces 51.1 v 0ff load..not 36v as expected..
Of course the motors now move very quickly ...and I'd got used to a slower and more accurate move at 24V
Ideally ..if I go down this route ...I would prefer the more leasurely 24v
Well ..at least it still works but the motor supply needs a re-think
rgds
VS

 

[Captain Jack]

Is the smps unsalvageable? How annoying considering what it cost....

 

[Vipersan]

Ok ..took a current reading of the actuator loading in amps whilst the dish was in transit..
Approx 1.5 amps ..which surprised me a little ..
I expected more..
So if both motors were active at the same time ...
approx 3 Amps ..
Now I always prefer to allow for loading (wind etc) and problems encountered ..
So allowing an extra 0.5amp for each motor ...we are back at my original approximation (2 amp per motor)
4 amp in total ..
So at 25v roughly this would hopefully equate to 24 x 4
my estimate is therefore 100W or 100VA
The psu that failed was 200W ..so no excuse for failure imo
but still ...if I went down the torroid route which I'm seriously considering ..
A dual secondary 12v (x2) seems a sensible option ..
Thus I would have 2 speeds
Slow and very slow
..the rating of which would I assume be 100VA
Do I have this right ?
rgds
VS

 

[Vipersan]

Is the smps unsalvageable? How annoying considering what it cost....

It could probably be salavaged ..but I'm not sure why it died ..
So am having a rethink re torroids..
They do run quiet and cool..
That I can confirm

 

[Vipersan]

I must be mad ...
Found a 120W 24v psu that has smaller dimensions 13 x 10 x 4 cm ...so would require no modding ..
It too claims the following ..but is a different design ..this time from the Philipines
£8 ish

So will give a smpsu one more chance ...but will have to wait a while for delivery.
It would cost about the same amount to repair the one that died ..so why bother..

DescriptionUniversal AC input / full range
It's good quality & high performance
Input: AC110-220V 50/60Hz
Out put: DC 24V 5A
100% full load burn-in test
Protections: overload/ over voltage/ short circuit
Cooling by free air convection
(Not suggest for use in bathroom)
This Power Supply Unit "DOES NOT" come with installation instruction, wiring cable, on/off switch, or screws. Professional installation of qualified electrician is highly recommended.



Type: 24V 5A 120W
Net Weight: 356g
Size: 13 x 10 x 4cm

..for anyone interested
ebay item 151417204228

 

[Waveguide]

Some types of relay switching of motors is safe if properly designed and the relays
are of the type "break before make". One type is the relay equivalent of a H-bridge.
Two two-pole relays with the contacts for one relay in the upper left and lower right
parts of the H. The other relay on the opposite diagonal. As long as both relays are
not ON the same time nothing can short the supply. The other variant is one relay
for On/Off in series with a relay to reverse the polarity to the motor. This has to
be "break before make" or the supply could be shorted when reversing with power
to the motor.

A brief shorting of the supply could explain why no transient suppression works,
the 24 V is gone and nothing fills the gap. Using another supply for 5 V will fix
the dropout.

 

[Vipersan]

Some types of relay switching of motors is safe if properly designed and the relays
are of the type "break before make". One type is the relay equivalent of a H-bridge.
Two two-pole relays with the contacts for one relay in the upper left and lower right
parts of the H. The other relay on the opposite diagonal. As long as both relays are
not ON the same time nothing can short the supply. The other variant is one relay
for On/Off in series with a relay to reverse the polarity to the motor. This has to
be "break before make" or the supply could be shorted when reversing with power
to the motor.

A brief shorting of the supply could explain why no transient suppression works,
the 24 V is gone and nothing fills the gap. Using another supply for 5 V will fix
the dropout.

Well I now have a seperate 12v / 5v supply so not relying on the 24v smpsu for this ..
but like you worry that the relays are the problem ..
is it possible that the cheap Gbox uses a non break before make ?
I wonder..
???