Voltage from PSU decreasing as more load is added?

aplant92

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Hi all,

Was spending some time in the front yard today diagnosing why our mega tree looked like it was severely lacking power. We've got multiple injection points, so I didn't think it was a matter of needing more power, so decided to check what voltage I was getting from the PSU itself. When all lights are turned off, it's sitting at around 5V exactly. As soon as I start turning on some of the strands, the voltage being put out starts decreasing - to the point where if all lights are on, it's down to 4V.
Am I missing something here? I thought as long as the PSU was set to 5V and it had the capacity, it should push out 5v on each output, with each output just consuming more of it's load? Other PSUs seem OK, so not sure if this is just a PSU that's dying or what...
 

108CAM

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Well with any electrical circuit, both AC & DC, the voltage will slowly drop the further you get from the power source.
Could also be an early sign that the PSU is overloaded and can't provide enough power for all the lights.
 

aplant92

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So this is the voltage being put out directly from the power source though - not further along. E.g. I've got the multimeter connected to one output from the PSU as I turn on lights connected to the other outputs, and I see the voltage dropping further and further on the multimeter
 

aplant92

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I suspect maybe a PSU fault, just not sure if there's anything else I should look at before chalking it up to a fault!
 

AAH

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If you are getting a voltage drop pretty much at all before you reach the rated current of the power supply then I'd be very dubious about using it. If you have 4V at the output terminals the power supply is overloaded and it should actually be going into shutdown or the power supply is dodgy. This is assuming that there is a good reliable 240V going into the power supply and it's not drooping significantly.
 

scamper

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You also have 2 different types of power supply. A constant current supply, where you should set the voltage at max current, and a constant voltage supply where it will supply the voltage it is set at and as you load it up it will attempt to keep the voltage constant, but will start to lose current.
Either way, you must make sure you are not overloading your supplies. Check the max current you expect from your strings and don't go above that.
 

aplant92

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Yeah so overloading wise shouldn't be an issue - this behavior is observed with only a few strips connected. I am using one of those bunnings garden stake power things - maybe that's providing some dodgy power? Other power supplies don't seem to have the issue though...

Might try it out again tomorrow connected directly to the GPO in the garage!
 

aplant92

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Worth mentioning this is (AFAIK) a meanwell 5v 350w PSU purchased from trusted sources based on the auschristmaslighting PDF guide, as are all the other working PSUs
 

Skymaster

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The GPO/garden stake is unlikely to be the issue. If it is, you'd have a pretty unsafe setup overall.

I'd be more inclined to say the power supply is not great. What sort of PSU is it?
 

TerryK

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@aplant92 : Your thread posts #7 and #8 are rather contradictory. In post #8 you indicate you 'think' it's a Meanwell. If it is a Meanwell it will have a manufacturer's ID sticker on it. If there isn't any product identification then the supply is likely a low cost imitation.

Beyond that, as Alan mentioned (post #5), verify that the input voltage is correct for the supply. The supply should regulate at its set voltage up until it reaches its current limit and determines it needs to enter shutdown. However, some Meanwells shutdown is a 'hiccup' mode where the output turns off a bit and then attempts a restart. If still at current limit it enters another 'hiccup', and so on. Other Meanwells enter a current limit mode when the supply reaches maximum current with a corresponding drop in voltage. You may have the 2nd type of supply. To the point, can you provide an accurate description of the power supply manufacturer and model?
 

aplant92

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I'm not sure how they're contradictory, perhaps phrased poorly - all PSUs I have are the same, just the one powering the mega tree is exhibiting this behavior. Will confirm exactly what Meanwell PSU they are though just so that all the information is out there (and I suppose maybe some insight can be shed on this particular model!)
 

aplant92

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So confirming it's a Meanwell SE-600-5 PSU that we're seeing the problem with
 

Skymaster

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That power supply has a remote sense function, which is used to determine the voltage at the load and control the voltage regulation. I can't find the exact details of whether it can be switched to local sensing or not. This may be the cause of the misregulation of the power.
 

aplant92

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Ah that's good to know! Thanks for looking into it - I was trying a few more things this morning and now the PSU seems completely dead...wondering if that's perhaps not entirely expected given the way it was behaving beforehand.

Seems I'm in the market for a new PSU!
 
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