Super reliable PSU? - Page 1
Forum section: electronics / projects

author: funkyant
author_rank: Unknown
timestamp: August 22, 2015, 10:00:03 pm
content: Hi guys.I need a few 220V to 9V 500mA power supplies which I need to go for 9 months before failure, outdoors in a desert. Expected ambient temperatures of up to 60 degrees Celsius (140F).So far every off the shelf unit I've tested has failed rather quickly, and these units are 8m in the air and a PITA to replace regularly.The application is powering Artnet > DMX lighting protocol decoders in a garden lighting installation, in an Oasis in the desert between Dubai and Abu Dhabi.Any suggestions (including DIY ones) would be appreciatedJames

author: fivefish
author_rank: Frequent Contributor
timestamp: August 22, 2015, 10:10:19 pm
content: How are you insulating the power supply from the 140F ambient temp?

author: nctnico
author_rank: Super Contributor
timestamp: August 22, 2015, 10:12:06 pm
content: Which brands did you test? And how is the shielding against direct sunlight? You may need to add a shield over the enclosure to get rid of the direct sunlight. Meanwell usually holds up pretty well but you have to derate for the ambient temperature. So you likely need 9V >3A models.

author: acbern
author_rank: Frequent Contributor
timestamp: August 23, 2015, 07:16:44 am
content: You need to use a PSU that is also suitable for MIL or severe industrial/car use. Thats where high temp PSUs had their origin.Probably the cheapest and very well suited one with respect to your environment is from Vicor, would recommend the DC/DC models with base plate cooling and 300V DC in. You need to have a rectifier/filter upfront, and you can cool them through an attached heatsink, no fans required. Are sealed, so no dust/sand issues either. There are also AC/DC modules but too high power. Have a wide operating temp range, up to 100C, and pretty high power density. They produce more output current than you need though. VI J6M may e.g. be a solution, goes up to 85C base plate.Other options may be power one or Martek/Eaton. Lower power output, but may be more expensive.Meanwell is NOT an option for this application imo.

author: singapol
author_rank: Frequent Contributor
timestamp: August 23, 2015, 07:27:15 am
content: Apart from shielding direct sunlight, another extra would be a solar powered fan for extra cooling and ventilation.

author: plesa
author_rank: Frequent Contributor
timestamp: August 23, 2015, 07:27:20 am
content: Quote from: nctnico on August 22, 2015, 10:12:06 pmI have opposite experience, Meanwell it is crap, but it can depends on exact model. You are right that they needs to be overrated.I will consider using Pulse ( Mike use them) but I did not use them yet. Also check the TDK Lambda their application guys can help with such an high temperatures.

author: mariush
author_rank: Super Contributor
timestamp: August 23, 2015, 07:45:45 am
content: I wonder if a dyi would make sense, if it would be more reliable.Transformer :http://uk.farnell.com/myrra/44266/transformer-10va-9v/dp/1689087Rectifier :http://uk.farnell.com/vishay-general-semiconductor/gbpc106-e4/bridge-rectifier-1-ph/dp/1702783(can do 1A even at up to around 120 C, more when heatsinked)Capacitor after rectifier :http://ro.farnell.com/panasonic-electronic-components/eeutp1e222s/capacitor-radial-25v-2200uf/dp/1890549(5000h @ 125c no worries)9v regulator :http://uk.farnell.com/texas-instruments/lm2940t-9-0/ic-v-reg-ldo-9-0v-2940-to-220/dp/9493514(up to 125c)(and a couple of smaller capacitors for the linear regulator and a dc jack)Put some thermal paste on the rectifier and regulator and screw them to a metal box with some holes in it and maybe add a 80-120mm fan at the bottom of the box to pull air through the holes and out the box for some air movement (though it's debatable if it's a good idea with the sand in Dubai).

author: Psi
author_rank: Super Contributor
timestamp: August 23, 2015, 07:58:29 am
content: Flick an email to the powerstream guys.They might have something available, or be able to give you the name of another company who does.http://www.powerstream.com/Also, the powersupples you've been using so far that have failed. What was their current rating?Personally, if i was running something in the desert i would derate the current a lot.I might use a 3-5A psu for 500mA

author: sleemanj
author_rank: Super Contributor
timestamp: August 23, 2015, 11:33:13 am
content: Quote from: funkyant on August 22, 2015, 10:00:03 pmDid you determine the failed component(s) in particular?For example, if your supplies always fail because of an electrolytic failing in the constant heat, fixing it could be as easy as swapping in some better quality high temperature electrolytics.

author: Kalvin
author_rank: Super Contributor
timestamp: August 23, 2015, 12:11:46 pm
content: 9V @ 500mA equals to 5W. To play safe, make the power supply for at least 20W so the power supply will not be pushed to its limit at any time. 220V / 12V / 20W toroidal transformer with full-wave rectifier and a linear regulator in TO-3 attached to the heat sink, plus few good quality elcos in parallel. The voltage across the linear regulator will max. 5V so it will dissipate 2.5W at 500mA which should be easy to dissipate. Alternatively, place few linear regulators in TO-220 package parallel with ballast resistors in order to reduce power dissipation of each individual regulator below 1W. Place the fuse, overvoltage protection and filtering to the mains side of transformer. Place a crowbar and a fuse to the output in order to protect the device connected to the power supply. Construct the design so that the sun will not shine directly to the enclosure. Use some sort of sun shade if necessary to keep the enclosure itself as cool as possible**. Add a good quality fan with a simple temperature control to increase the air-flow if the temperature is still too high**. Make the mechanical design, PCB and connectors etc. so that they will tolerate high temperature changes. Measure the output voltage ripple and the temperature in the enclosure and linear regulators at 1.5 times the full load (9V @ 750mA) in 80C baking oven. Then place the power supply into a fridge and a freezer. Repeat the measurements few times. Destroy few power supplies by increasing the oven temperature 5C at a time in 2h intervals up to the temperature the power supplies fail or you reach the 110C, observe what happens before the power supply fails. Analyze the results (did the output voltage increase beyond the nominal 9V? Add a crowbar if needed to protect the device connected to the power supply. Did the power supply experience any catastrophic failure like flames or smoke? What component gave up first? Did the output ripple change as the elcos were heated?). Be careful. Protect your eyes. Don't burn your house.Quote from: singapol on August 23, 2015, 07:27:15 am** Construct the sun shade from the solar panel feeding the fan.

author: acbern
author_rank: Frequent Contributor
timestamp: August 23, 2015, 03:11:20 pm
content: In an environment like this, and if reliability is an issue, one would never use a fan if it can be avoided, and it can easily be avoided here. (A high rel fan, for applications it cannot be avoided, costs a fortune.)

author: Siwastaja
author_rank: Super Contributor
timestamp: August 23, 2015, 03:34:38 pm
content: I'd DIY a linear supply (because the linear is easier to DIY, and the power rating is so low), but you really have to properly derate all the components, and this includes the transformer! I would never use the transformer mariush linked in a hot environment; those smallish plastic-cased PCB mount transformers have fairly high resistive losses, even when idle (no output current) because of very thin wire in primary. The thin primary wire also burns easily. Some have thermal fuses, but it'll cause down time as well.You need larger current rating for the transformer than the output current is because of the peeky nature of rectification. You can google for the exact ratio and math behind it, but in any case, I would pick a transformer that is:- rated for larger input voltage (240V or even 250V specified would be great)- rated for 2A, at very leastRectification and regulation are fairly easy to derate, think about a 10-15A diode bridge and a regulator in the TO-3 case, both mounted on the heatsink. I think 1.5A or even 1A rating for the regulator is enough, the TO-3 case being more important. Although, even a single 1A rated TO-220 regulator can work, it's just a bit marginal.Just add a huge heatsink and make sure that the sun never directly shines on it.

author: fivefish
author_rank: Frequent Contributor
timestamp: August 23, 2015, 05:50:27 pm
content: QuoteI'd consider burying the PSU inside a protective case in the ground instead. Should be cooler vs. exposed in desert sun.

author: PChi
author_rank: Frequent Contributor
timestamp: August 23, 2015, 05:54:20 pm
content: The 'professional' power supplies specify de-rating versus ambient temperature. I would expect them to achieve their specifications.Is it heat killing the power supplies, input transients or could it be lightning strikes?Another possibility is condensation. Power supply manufacturers used to offer tropicalisation which coated everything.I believe it gets cold in the desert at night, the power supply gets cold. During the day time any moisture in the air condenses on the pcb and with off line switch mode power supplies causes failures. Coating the PCBs fixed the failures in one application.

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: August 24, 2015, 03:58:45 am
content: i would probably go with a power supply that has a higher current output than what you need so you can add some cooling fans if that would help. also i would shield the power supply to give it some shade like everyone else recommends.i hope this helps.