Hi guys,

I have attached a 20 Ohm resistor to my Dell PSU on the 5V rail since its a 2004 PSU and most of the current are in the +3.3V & +5V rail. I have seen on most youtube videos where they mention using such dummy loads but they are usually those ceramic resistors. I dont have one in my posession now. Just attched this resistor I had previously salvaged from an old Nokia charger. I have attached a picture below for better idea.Thanks in advance everyone.

 

It will work ok giving you 250mA drain current, it will be fine for a dummy load, if your psu won't keep running put another 20 ohms in parallel or change it for a 10 ohms @5W.

 

Hi guys,

I have attached a 20 Ohm resistor to my Dell PSU on the 5V rail since its a 2004 PSU and most of the current are in the +3.3V & +5V rail. I have seen on most youtube videos where they mention using such dummy loads but they are usually those ceramic resistors. I dont have one in my posession now. Just attched this resistor I had previously salvaged from an old Nokia charger. I have attached a picture below for better idea.Thanks in advance everyone.

Sometimes I use car bulbs - but you have to be a bit careful with the higher ratings, bulbs radiate more IR than resistors so its not impossible to set fire to things.

 

Sometimes I use car bulbs - but you have to be a bit careful with the higher ratings, bulbs radiate more IR than resistors so its not impossible to set fire to things.

I have two bulbs with me a 21W signal flasher bulb and a 60/55W headlamp. Thought of adding the 21W but like you mentioned heat will be an issue also this supply since its 250W there is limited space inside just enough for my binding posts.

 

It will work ok giving you 250mA drain current, it will be fine for a dummy load, if your psu won't keep running put another 20 ohms in parallel or change it for a 10 ohms @5W.

After attaching this load resistor, I tried running it with my Mini peltier cooler as its current draw was initially 3.1A and then it dropped and settled at 2.78A. The resistor was hot but not hot that it will burn or didn't produce that burning smell.

 

I just went through my entire collection and was able to find only one ceramic resistor 1 Ohm 5Watts which I guess wont do the job.

 

I have two bulbs with me a 21W signal flasher bulb and a 60/55W headlamp. Thought of adding the 21W but like you mentioned heat will be an issue also this supply since its 250W there is limited space inside just enough for my binding posts.

The headlamp bulb is certainly a fire risk - but you don't need to apply that much load to make it work.

Usually only the 3.3 & 5V rails are sensed for regulation, when they get up to speed the PWM throttles back until you draw some load. Meanwhile - the other rails aren't monitored (except by the OVP) so they might well collapse if you draw current from them.

 

The headlamp bulb is certainly a fire risk - but you don't need to apply that much load to make it work.

Usually only the 3.3 & 5V rails are sensed for regulation, when they get up to speed the PWM throttles back until you draw some load. Meanwhile - the other rails aren't monitored (except by the OVP) so they might well collapse if you draw current from them.

Update: Yes thats the reason why current I've added two 20 Ohms resistors in parallel. I hope thats sufficient to maintain the load. I do have one ceramic rectangular resistor but its only 1 Ohm 5W.

 

Also I have one question. Should I add an automotive 12V 15A fuse in line with the main +12V yellow line where all the wires are bunched together to the binding post or the inbuit short-circuit protection will take care of overload /short and shut it down?

 

Also I have one question. Should I add an automotive 12V 15A fuse in line with the main +12V yellow line where all the wires are bunched together to the binding post or the inbuit short-circuit protection will take care of overload /short and shut it down?

Even the 12V rail can shift a fair bit of current and is a lower priority on overload protection - a fuse is a good idea.

 

Even the 12V rail can shift a fair bit of current and is a lower priority on overload protection - a fuse is a good idea.

My +12V rails are capable of 16A. I just tried deliberately shorting the 12V and GND and the there was a tiny spark and the PSU shutdown. After resetting the Green and Black wire the PSU turned back on. But to see how it performed when connected to large current pulling devices, I had a 12V car cigarette lighter with me. Connected it to my 12V rail bunch and GND. In 12 Sec the plug was out and glowing bright orange. So, I think adding an inline 12V fuse is a must. The only thing is that I'm confused about the value.Should I go for a 15A or 20A fuse(PSU max +12V@16A)? I'm concerned if I add a 15A fuse will it blow sooner since the 12V line is 16A or if I go for 20A its too far from rating and it wont blow

 

My +12V rails are capable of 16A. I just tried deliberately shorting the 12V and GND and the there was a tiny spark and the PSU shutdown. After resetting the Green and Black wire the PSU turned back on. But to see how it performed when connected to large current pulling devices, I had a 12V car cigarette lighter with me. Connected it to my 12V rail bunch and GND. In 12 Sec the plug was out and glowing bright orange. So, I think adding an inline 12V fuse is a must. The only thing is that I'm confused about the value.Should I go for a 15A or 20A fuse(PSU max +12V@16A)? I'm concerned if I add a 15A fuse will it blow sooner since the 12V line is 16A or if I go for 20A its too far from rating and it wont blow

You could try a bit of experimentation - what's the biggest fuse that blows before the PSU trips.

If it trips safely without self destructing - you could dimension the fuse specifically to protect the load rather than the PSU.

 

You could try a bit of experimentation - what's the biggest fuse that blows before the PSU trips.

If it trips safely without self destructing - you could dimension the fuse specifically to protect the load rather than the PSU.

Hi,

I've currently added a 15A auto fuse. I decided to go with it since the biggest 12V load I've ever connected was I think a 130/100W halogen bulb at 10.8 A briefly connected and it did fine. But the heat blowing from the PSU increased very much. I'll try connecting the cigarette lighter also to see how much current it will be able to handle max. Ian I've a question related to another Dell 210W PSU which I use as a bench supply too. The output at +12V rail is only 11.68V on that PSU. I tried opening the cover and therer is a POT at output. The max value I can vary it to is +12.68V. What is the safe value I could increase too without compromising the PSU?

 

Hi,

I've currently added a 15A auto fuse. I decided to go with it since the biggest 12V load I've ever connected was I think a 130/100W halogen bulb at 10.8 A briefly connected and it did fine. But the heat blowing from the PSU increased very much. I'll try connecting the cigarette lighter also to see how much current it will be able to handle max. Ian I've a question related to another Dell 210W PSU which I use as a bench supply too. The output at +12V rail is only 11.68V on that PSU. I tried opening the cover and therer is a POT at output. The max value I can vary it to is +12.68V. What is the safe value I could increase too without compromising the PSU?

The limiting factor is usually the voltage ratings of electrolytics on the other rails.

Some PSUs have 6.3V electrolytics on the 5V rail, so you may need to keep an eye on that. 12V rails usually have 16V caps, so shouldn't be any problem there. Sometimes the 5V rail has 10V caps, which are unlikely to be a problem.

Shottky barrier rectifiers are usual, which tend to have pretty close headroom - probably not a problem for what you intend, but you can always search out the data sheets and see how much room to manouver.

You can add snubbers to SB rectifiers in flyback converters, but I doubt it does any good in push-pull types.

 

The limiting factor is usually the voltage ratings of electrolytics on the other rails.

Some PSUs have 6.3V electrolytics on the 5V rail, so you may need to keep an eye on that. 12V rails usually have 16V caps, so shouldn't be any problem there. Sometimes the 5V rail has 10V caps, which are unlikely to be a problem.

Shottky barrier rectifiers are usual, which tend to have pretty close headroom - probably not a problem for what you intend, but you can always search out the data sheets and see how much room to manouver.

You can add snubbers to SB rectifiers in flyback converters, but I doubt it does any good in push-pull types.

Thanks Ian. Currently I've set it at 12.05V and the 5V rail has 5.4V so I guess its within the safe limit and +3.3V rail seems to be pretty stable, around 3.34V.

 

Thanks Ian. Currently I've set it at 12.05V and the 5V rail has 5.4V so I guess its within the safe limit and +3.3V rail seems to be pretty stable, around 3.34V.

That might even still be within published spec.