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  #1  
Old 15th August 2019, 09:43 PM
Mike O'Pray Mike O'Pray is offline
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Default ac/dc adaptor for Jessops lightbox - help needed

My Jessops ac/dc adaptor that came with my Jessops lightbox has stopped working. There is no output light when plugged in. I have ascertained that the florescent tube is still OK as it works with batteries.

So first question: Is there any kind of a fuse inside that might have blown and if there is how do I undo the adaptor to get to it? In the top right as you look at the 3 prongs of the plug there is a hole with what may be a metal screw inside it but if it is a screw it doesn't look like any screw head that I have seen before. It may be a permanent thing that cannot be removed i.e. it seals the adaptor for life and if the adaptor fails it is for the waste bin anyway

On the lightbox where the female jack plug goes there is the label "dc 9v/ 800mA" so I think this means that the adaptor I need has to be 9v or have a 9v slot that can be selected if it is multi-voltage but I am unsure what 800 mA means vis a vis the decreasing voltage change as you move from 3v to 12v.

On the adaptor I have in mind to buy it says that 9v is 0.65A but I am ignorant of whether this will cope with 800mA

I did a bit of research today and I think that the Amazonbasics Universal DC Power Supply with 7 Detachable Tips 3v-12v Reversible Polarity meets the requirements for my lightbox

One of the tips has the same colour code as the Jessops current tip and as the polarity is reversible I can get the polarity to be as per the diagram on the lightbox which is: circle with a + then solid circle then circle with a -

So I think I just need to be sure that 800mA on the lightbox is compatible with the Amazon adaptor that says that 9v is 0.65a

If anyone who knows about these things and has the time can look at the Amazon adaptor in question and give me the OK I'd be grateful

Needless to say I don't want to run the lightbox on batteries for any longer than I have to as I have had to take batteries from other appliances as a temporary stopgap measure

Thanks all

Mike
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  #2  
Old 16th August 2019, 05:26 AM
Chrisvclick Chrisvclick is offline
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800ma is the current that the lightbox needs, so a 650ma power supply is not powerfull enough.

0.8 amp is 800 milliamp (ma)
0.65 amp is 650 milliamp (ma)
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Old 16th August 2019, 11:25 AM
Terry S Terry S is offline
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I agree with Chris but you are on the right route Mike.

I've had to buy various new transformers for things over the years.

Most of them today have multi-use ends, so that bit is good. You just have to find one now that has the right ma. Take a look on ebay, as that's where I've bought mine from cheaply, especially after my local Maplin's closed. Although, just checking, they still have an online presence, so worth checking out: https://www.maplin.co.uk/

Terry S

PS I've just checked Maplin and surprisingly their search didn't find anything...

BUT, on ebay, they all seem to have the same price in the UK, but there's only one that lists as having a multi-adapter:

https://www.ebay.co.uk/itm/9V-800mA-...EAAOSwv0tVVCwe

Last edited by Terry S; 16th August 2019 at 11:31 AM.
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Old 16th August 2019, 01:30 PM
Mike O'Pray Mike O'Pray is offline
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Thanks both for your responses. Terry, the adaptor your link gives me would appear to be OK but I have asked about polarity. The info you get on e-bay items is never enough.

Chris or anyone else with such knowledge: I assume that the fact that it needs to operate on 9v has some leeway. I say this because currently it has 6 rechargeable D batteries in it which work and yet each battery is only 1.2v so adds up to 7.2v and not 9v

Secondly how does one work out if 6 D batteries @1.2V each add up to 800mA or is there some leeway there as well?

Thanks

Mike
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Old 16th August 2019, 01:51 PM
alexmuir alexmuir is offline
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Mike, why donít you order the Amazon option, and send it back if it doesnít work? Iím not an electrical expert, but Iíve used different transformers over the years with equipment which had perhaps lost the original unit, with some success. If the voltage rating matches, you may find that it works. If you decide to do that, check that there is a return option available.
Alex


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Old 16th August 2019, 02:49 PM
Mike O'Pray Mike O'Pray is offline
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Thanks Alex but given the rigmarole and time to send back I'd rather be sure that I get it right first time. I never knew that replacing a simple transformer would be such hard work. What with mA, polarity, cheaper than average adaptors that look as if they fit the bill but come all the way from China and take about a month to arrive

If there was an electrical shop in my town I'd gladly pay a bit more to be sure what I was getting was right. I used to patronise the place but sadly not enough of my townspeople did as it closed about 5 months ago.

There might just be the right adaptor in what passes for Homebase or Screwfix, both of which we have but the "assistants " have about as much electrical knowledge as the Tesco checkout person has about Tesco products

Mike
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Old 16th August 2019, 09:01 PM
Mike O'Pray Mike O'Pray is offline
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An update. I got an adaptor from Argos which works fine. I hadn't thought of Argos initially although it has a store in my town. I literally ordered it and picked it up about 30 minutes later

I would still be interested in answers to my questions above on what leeway if any there is between 650mA and the stated 800mA required The question about 7 D batteries only adding up to 7.2v and not 9v but working OK and how one works out what mA these batteries give

Thanks

Mike
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Old 18th August 2019, 08:19 AM
JohnX JohnX is offline
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If you run a 650ma transformer at 800ma, it will work but that is not its design loading and thus there is no guarantee it will last.
You do state the loading for the light box but I'm not sure you mention the rating of your original adapter ?
Anyway, the batteries...I'm guessing this light box was manufactured at a time when rechargeable battery's weren't as ubiquitous, and ordinary non-rechargeable were the norm, they are 1.5v so that's your 9v, you choose to use 1.2v cells.
The current rating of whatever battery you choose doesn't matter, it only dictates how long the light box will operate before they are flat.
It does matter for the adapter though, it won't just go flat it will fail.
The adapter is rated in ma, it is continuous delivery.
Battery's are rated in mah, that is current delivery over period of time since their output is finite.
The lightbox rated 800ma at 9v will probably work at 7.2v but it will doubtlessly be pulling more than 800ma at that voltage, that is ohms law...
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Old 18th August 2019, 01:06 PM
Mike O'Pray Mike O'Pray is offline
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Thanks for the reply,John. Not being electrically knowledgeable I may have misunderstood or not followed properly what you have said but on the battery issue I think you are saying that 6 D alkaline(non-rechargeable) batteries @ at 1.5v each will last longer than rechargeable 1.2v batteries because of what is being used by the lightbox which was rated at 800mA

So the practical effect of using rechargable v alkaline is that the batteries don't last as long but provided the 7.2v operates the lightbox then no problem i.e. batteries will deliver whatever is required by the lightbox . However an adaptor delivering 0.65 mA and not the required 0.8 mA might work for a short period but will fail or will fail immediately

As far as most adaptors I have seen are concerned the majority are only rated at 0.65mA at 9v so the risk is that such an adaptor might work apparently OK but has a limited life

Unfortunately I threw away the defunct Jessops adaptor yesterday so cannot look now to see what other information was on its label

Mike
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Old 18th August 2019, 03:40 PM
Mike O'Pray Mike O'Pray is offline
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John, I have just been wandering about the house and spotted the old Jessops adaptor. I thought I had thrown it out yesterday but it's still awaiting "the chuck"

Anyway looking at the label it gives primary and secondary circuit info and the secondary says :3/4.5/6/7.5/9/12V =1.25A so I assume that for all those voltages it is rated at 12500 mA which these days would be unusual but maybe not when this adaptor was made

Have I got this right about a constant amperage at all these voltages?

On the front it has a label which says JESSOPS MA1200 which I think means 1200 mA so close to the 1.25A on the back label. It also had reverse polarity and could be used from 100v -240v ~ 50/60Hz so a pretty versatile and robust piece of kit.

Mike

Mike
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