Power supply issues

[Gina]

The box needs a top but I think it will do for testing.  I won't be running all night tonight - I have no doubt there will be things to fix.  I was hoping to set up in daylight on the far hill and trees but the night has beaten me to it   Oh well, a good use for the moon

If the tests prove successful I may be able to do some imaging of the Heart Nebula if the moon isn't in the way.

Very slowly getting there   Wonder where I put that fan heater - want it in the warm room!

[kev]

I wonder. Have you ever worked out your ratio of tinkering time to observing time? You certainly keep busy!

Impressed with the results.

Sent from my iPhone so excuse the typos!

[Gina]

Must be at least 100:1

Thank you

[Gina]

Done the focus remote control box so now off out to the obsy to try things

Here's a couple of pics.  Not the best effort on my part but not worried if it works.  It was a box I had available a year or two ago when I first set up remote focussing.  It's far too big for what it contains - I may print a smaller one sometime

[Gina]

Test failed!   Connected power and checked voltages - seemed OK.     PSU showing 2.4A  Bit high I thought but had dew heaters on.  13.4v at power box   Looked out USB cables and connected hub to its 5v supply - no blue light, so a problem.  Then I saw smoke coming from the power box   So I have some faultfinding to do  

Maybe I'm rushing things too much.  I think there's a fair bit of testing I ought to do in daylight before I try to check things in the relatively poor lighting in my scope room.  It's cold at night too.

I thought sorting out the power was a relatively simple job - HUH.  Hope I'm not getting past it

Now I need to think about how I shall proceed.  The power box was fine indoors on my bench PSU so I don't know why there was a problem out in the observatory.  Maybe I should have checked it on the fixed 13.8v supply though I don't really see why - I tested the box on up to 14v indoors.

[Gina]

It was the thyristor that was cooking.  I suspect that either it was oscillating or maybe there are spikes on the fixed 13.8v supply.  I think maybe I should look at it with the oscilloscope.  I don't think I feel happy at running several grands worth of cameras etc. off it even if several others have found this make totally satisfactory.  I'm thinking Ptarmigan may be right to regulate the 12v supply at the scope end.  I may order some LM1085IT-12/NOPB, Low Dropout Voltage Regulator, 3A as these only need 1.5v overhead ie. 13.5v supply, as was mentioned earlier in this thread.

[Ptarmigan]

Ouch !

I was about to return and say something to the effect of - if not power conditioning then at least consider a LPF, or even just some capacitance at the equipment end and rely on the resistance of the long bit of wire. *
But I wont say anything about that now !! I will return to my previous and agree, a reg. is better to blow up than your pride&joys !

Yes, I also have used the car battery method, a gert big lead acid job can absorb considerable indignities thrust upon it by a cheap  battery charger.
Even a car battery rejected as no longer suitable for use on your motor.
Just make sure that the junction between the battery and psu is as good or better than that between the psu and equipment

* I cannot tell a lie, I was going to return and make a joke,
I have been trying to resist it all day ! :-
Gina said "several decades ago when "
but Gina, valves are not as quick to blow as modern chips !!

Oooops, I have the feeling that now may not be the right time for jest !

[Gina]

Actually now IS the right time to jest - cheered me up   Thank you for your reply - good to have your input

[Ptarmigan]

Previously I kinda noted in passing your crowbar diagram as representative,

but in light of developments I looked again ! Is it actual ?

It is late at night so dont take this as verbatim, but for what it is worth, and in case you go to it before I am awake tomorrow !! :-

I dont think it is good to rely on the gate current to define the operating point of the zenner,

a resistor from thyristor gate / zenner to deck would better set the zenner current.

Some decoupling would be good as well, a few 10s of nF across that resistor.

A hundred(or 2) nF across the input.

EDIT Oh hang on , we have a couple of diags, I was looking at post #81 but now I see you have such a resistor in #95, good ! but still need some caps I think ?

[Gina]

Yes, you're right - I do normally scatter ceramic caps around to stop spikes/interference and improve stability.  Clearly I'm not thinking as clearly as I used to

But anyway, I'm going off the idea of an over-voltage crowbar in favour of voltage regulators in the power and focus control box to power the cameras and filter wheel.  The dew heaters can run straight off the 13.8v supply. 

Another point is that I think the Fusion/Tantronics PSUs are switch mode.

[Gina]

I have now lowered all the kit to the floor and brought most of it indoors ready for another go at the power arrangements and testing.

[Ptarmigan]

Fingers ( and allsorts) crossed, good luck,

Yep, in favour of doing the dew on their own supply.

As we have said I do like battery power when it comes to treasured toys at the end of long rural routes

getting immunity from lightning or other spikes etc. even a bit more obs time after everything else gets cut off !!

I'm just thinking aloud here, not suggesting or owt, wondering what I might do if I ever built an observatory.

maybe a hybrid system

the dew heaters off any ol'psu and the other special ( much lower power demand ? ) stuff on battery, then would not need such a big car battery.

I would probably be thinking, in my old fashioned way, of rechargable D cells or similar, or finding out what these LiPo things are that folk are talking about !

Sure you'll have it sorted soon.

oh I see it is nearly midday, I expect you have it sorted already where did that morning go !!

[Gina]

Haven't had a chance to get onto it this morning though I have ordered some of those low dropout 12v reg chips.

I originally bought a sealed lead acid battery to power a winch driven ROR on my observatory but that project has been shelved for now.  Then I used the winch as a hoist for raising and lowering heavy gear on and off my mount.  Later on when Tim needed a wheelchair and with steep ramps outside (live on the side of a hill), I bought another winch and battery to haul him and wheelchair up the ramps (made up a special remote control using car relays to control the winch).  Now I have two winches and two batteries that I can use so a powered roof might happen some time in the future

So I could certainly use a lead acid battery as power regulator and backup power.  In fact, backup power would be a very good idea - we do get power cuts every so often, often for no apparent reason, and to be able to park the scope(s) to clear the roof would definitely be a good thing.  These PSUs appear to be sold principally as battery chargers so I presume they are designed to be directly connected to lead acid batteries.  In fact the design I used for a tractor battery charger had current and voltage limiting much like a standard PSU.

Just had a thought - I could use the battery charger as my observatory supply   It's a linear mode supply and provides up to 10A.  It's portable so it could be dual purpose   I was thinking of making up another unit with similar parts to use as an obsy PSU but why do that when I could just use the charger?  Must check the circuit I used for the charger and confirm its suitability for obsy use. It could simply be connected to a car battery to provide power and keep it topped up anyway I would think.

[Ptarmigan]

 It could simply be connected to a car battery to provide power and keep it topped up anyway I would think.

Now you're rocking

Any old psu, even a dirty ol 1/2wave job will do if you give it manual attention and dont leave it connected all the time ie. unclip it when you hear lots of bubbles ! I jest, a bit

I did have a charger destroyed by a lightning surge once, but my radio gear was not connected at the time. (was always dissed when unattended)

So yes, with that spare battry capacity all your stuff could be isolated from the mains and alternately top them up as needed.

Now I will go make a coffee and think of Gina winching her whole observatory round the garden for different aspects lol !

[Gina]

LOL   Love it

[Tinker1947]

Thinking about getting the right volts/power to individual units i think i would go with a Master Power unit, say a 18 volt @ 10amps (or what ever is needed)   transformer, then rectified and smoothed, then individual units take the 18volts and reduce it to 13.8v, 12v or 5v these units have the own overvolt, short circuit protection, so if one goes down it doesn't affect the others, made as a project buying parts to help keep the price down....while i don't want one if i did this would be the way i would go...

[Gina]

This is certainly one of the options I was looking at   OTOH the idea of using a lead acid battery as backup and power regulation is also pretty convincing.  I like the ide of using my own home made PSU as I then know exactly what it will do

[Gina]

Brought my battery charger in from the shed - bit the worse for wear, but then it's quite "long in the tooth" now.  Still works though   Now to see what's wanted to use it for the observatory PSU or battery charger.  Of course, it should be fine as battery charger because that's what it is

[Gina]

Brought the oldest battery in from the observatory and have it charging from my charger.  It's drawing 3A on normal and 4A on Boost.  The voltage is now 13.6.  With the charger off the battery is showing 12.6v.  When I brought it in it had been pretty well discharged on the hoist.  Initially it drew 5A on normal and 6A on boost and showed 13.8v.  The charger gives 14.1v on no load. 

I haven't yet tried this system with a load.  Somewhere I have a variable and calibrated 0-10A load for 12v which I made and used when initially testing the charger.  I think it might be in one of the chests of drawers I took out to the shed.  I'll look for it tomorrow.

I think the charger will need some circuitry change for use as an obsy PSU.  It was designed for battery charging and it does that pretty well.

[Gina]

Now trying the Fusion/Tantronics 13.8v PSU.  It's showing 2.7A.  The battery is reading 13.3v on my DMM - so there is half a volt drop in the 4 metre charger cable.  I think I should get heavier cable for the charger

So far it seems that the Fusion 13.8v PSU would be best - the 10A battery charger doesn't seem to provide enough power.  I will need to check the circuit though to see if this could be improved.

As it stands it would seem that I will have to use either battery and no 12v regulators or PSU plus regulators.  There would not be enough voltage from the battery to use the 12v regulators without charging at the same time.

[Ptarmigan]

I think I should get heavier cable for the charger

I think the dia. of charger cable needed is inversly proportional to the average duration of cloud cover

Hmmmm,

I think I'll call that Ptarmigan's Law ?

[Gina]

Not sure if the two batteries are the same capacity as one isn't marked.  The marked one is 41AH and is the last one I bought.

EDIT - Just looked through my ebay purchase list and the batteries are the same.

[Gina]

Just been testing the power box and the thyristor still works in spite of running very hot yesterday.  Triggers at 14.3v as before.  Then tried the Fusion PSU both with a short cable and with the cable from the obsy.  Absolutely no problem and showing 0.0A.  Although the display says 13.8v my DMM shows 13.9v - near enough I guess   Even so I'm not really happy with the over-voltage crowbar - I think better protection is needed and with that the o-v crowbar would be redundant.

[Gina]

I have now removed the over-voltage crowbar - thyristor, two zener diodes and resistor plus the now unused part of the stripboard

I have also found where that 2.4A that the supply was showing yesterday was going.  I plugged in the dew heater on the ST80 and it drew 1.5A.  That plus the 0.9A for the MN190 adds up to 2.4A.  I will need to redo the ST80 dew heater.  It needs it anyway as it was just bare nichrome wire separated with insulating tape.  In fact as I watched and felt the dew heater the plastic insulating tape melted and the wire shorted out - powered off immediately   I bought a good supply of 32swg nichrome wire and heat shrink sleeving so that will not be a problem.

[Ptarmigan]

 In fact as I watched and felt the dew heater the plastic insulating tape melted and the wire shorted out - powered off immediately

That's what I call real hands-on science

Brill !!