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12V cigarette lighter style output 5A rated going cheap at Halfords

Beyond_Vision

By Beyond_Vision
in The Astro Lounge

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Reggie

Reggie

Posted
Posted

It was that model and it was me that got shocked, confirmed with a digital multimeter, 100v above earth, touching the mount leg made it feel like a light dimmer touchpad, brushing your wrist against it gave a low static type shock, I wouldn't recommend one at all.

I would however recommend something from this page, do not get anything that is switched mode, the models you are looking for are linear/regulated and obviously bear in mind the total Amps that you need:

http://www.maplin.co.uk/Search.aspx?menuno=11910

I settled on this one cos I'm tight and have plenty of batteries for everything else I own:

http://www.maplin.co.uk/Module.aspx?ModuleNo=231

don't worry about it not having a cigarette lighter socket, you can pick up a 4xsocket from somewhere like poundland for, errr, £1 :) simply snip the plug off the end and wire it up to the +/- posts(keeping in mind the polarity, mine has an LED on it so it will only work one way) or if you want to look pro solder/screw a couple of banana plugs to the end.

@Thing, yup, just put a cigarette light plug style Power lead into it.

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Greg

Greg

Posted
Posted

One thing to be aware of is that it's an unregulated supply..

Ok for dew heaters. For running a mount then a regulated supply would be better.

It was that model and it was me that got shocked, confirmed with a digital multimeter, 100v above earth, touching the mount leg made it feel like a light dimmer touchpad, brushing your wrist against it gave a low static type shock, I wouldn't recommend one at all.

The same thing happened to me the other night..My battery packs ran down and I plugged the mount into the unregulated supply ..I touched the mount legs with my arm and got an uncomfortable tingle.. :shock:

I didn't think to put my Volt meter on the legs to see what was travelling through the them.

I'd go for the 7amp one of these for the mount and the unrgulated one for the dew bands.

http://www.maplin.co.uk/Module.aspx?ModuleNo=231

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Psychobilly

Psychobilly

Posted
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If the mount is earthed then it wont be a problem - the -ve output will then be held at earth potential so no shock hazard...

My pier is earthed using a 4 foot long 1 inch wide 3/16thinch thick pure copper bar driven into the "ground" and bolted to the pier always better to be safe than sorry...

Billy...

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Mark at Beaufort

Mark at Beaufort

Posted
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I bought one of these a few weeks ago for use with my Nexstar 5. I used it for the first time outdoors this week and noted that the mount felt 'funny' - a minor tingle when you touched the legs. The power cable was attached to a RCD. Not being an electrician, of any sort, should I earth the tripod via a cooper cable into the ground? Advice please - I don't fancy been sent into orbit by this system!!

Mark

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Psychobilly

Psychobilly

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An RCD will protect you from "mains" shocks coming form the pimary side of the power supply.... as it works by detecting a differential in the current flowing in the live and netutral conductors - in a fault condition this current would normally be excpected to return to earth ...either through the case if the equipment is protectively earthed (3 core mains cable) or the attached equipment or you...

Billy...

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Psychobilly

Psychobilly

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Ah well thats a different issue aint it...:)

All the supplies I spec an use professionally cost a fortune as they have to comply with IEC60601-1 - medical equipment standards and have to be safe under fault conditions and in some cases multiple fault conditions.

Even some of the big boys get the designs wrong...

Billy...

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steppenwolf

steppenwolf

Posted
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In view of the three cases mentioned here I think it would be prudent for me to 'pull' the article from me website as despite my own lack of a problem with it, there is clearly something not right with the current (oops pun) model. Thanks for the heads up!

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Greg

Greg

Posted
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I'm tempted to buy one and have the lid off....and do some investigating...

Dont worry I do this all the time ... for a living... Put Medical device through electrical safety testing etc.. so I shouldnt kill myself...If I havent posted for a few days though.....

It would be interesting to see the result of a PAT test..

I generally use a 110ah leisure battery or my 60ah diesel battery for the mount and use the adapter for the dew heaters..Even at home!

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Psychobilly

Psychobilly

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Ok heres my findings...

The product carries two marks relevant to safety and is CE marked.

The S and GS marks have been applied under the Authority of Intertek... they are one of the "biggies" used by manufacturers to carry out safety testing and proabbly EMC testing of electrical and electronic equipment.

Products like this PSU would be subject to Batch testing and also the Technical Construction File would have been examined.

The PSU will have been CE marked for the Low Voltage Directive and the EMC Directive - on a nerdy point There should have been a declaration of confomity supplied with the unit stating what harmonised standards the device would have been tested to to prove copmpliance withthe "essential reqiuirements" of the EEC Directives...

The Unit is a switch mode PSU and is Double insulated (the two square one inside the other symbol) and is for indoor use only (the house symbol) probably due to the poor IP rating of the housing... dont get it damp or wet.,..

Right thats the boring regulatory carp out of the way...

Practically...

The Unit being double insulated does not have a mains earth connection... it doesn't need one as the protection against electical shock hazard is provided by the "double insulation".

The Output is "floating" with repsect to mains earth - measured 93V AC with respect to Earth.

The Earth leakage current from the output was measured at 93 uA or 93 millionth of an amp...

And as my safety guru used to say.. its the volts that jolt and the millis that killies...

The voltage is coming from a high impeadence source (it's leakage current) and as such is not hazardous...

Billy...

The test house is page is found here...

http://www.intertek-etlsemko.com/portal/page/cust_portal/ITK_PGR/

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Psychobilly

Psychobilly

Posted
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I have had the uniut apart... PLEASE DONT DO THIS AT HOME!!! - infact you cant get it apart by just removing the 4 screws inthe bottom of the case as theres a hidden security screw with a non standard head for this very reason...

Had the unit apart...

The PCB has all the right markings on it the circuits a typical low cost mass produce SMPS ... it's got the EMC bits in it - mains input filter , surge limiting devices on the mains input etc.

The PCB has all the neccessary safety features including the required seperation of the mains and output parts of the circuit...

Looks ok to me...

and I have seen a lot worse than this from some of the worlds biggest PSU manufactures

Billy..

REPEATS - PLEASE DO NOT TAKE YOUR UNIT APART !!!

Billy...

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Psychobilly

Psychobilly

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If you want to stop the tingles.. you can tie the negative output to mains earth...which can be achieved outdoors using an earth spike...chances are that the -ve terminal of the DC imput socket of the mount are connected to the "chassis" - if it wasn't then you wouldnt get a "tingle"

Basically when you touch the non earthed metal parts (the mount) your body is acting as a path for the Leakage current to get to earth.. the figures show that the output "impeadance" for the leakage is 1,000,000 ohms your body will act as a potential divider with this ouput impeadance so the 93V will collapse when you "earth" the floating ouput..result A "tingle"....

The leakage path is through the insulation (dielectric) in a pair of capacitors across the safety barrier... there are two in series to make sure that the unit remains safe in the event of a single short circuit failure of one of the caps...

Billy...

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