Fixing a laboratory DSC

[eccerr0r]

Re: Fixing a laboratory DSC

That's probably a switching power supply in there but again I'm just guessing based on the large disparity of input and output power - and lack of heat sinking. And the reason why the 600VA step up transformer works fine.

As most BCN people know, switching PSUs have a lot of ways to short out the input causing fuse blows. And the fact that MIDEC appears to have been fly by night, it's highly suspicious of being at fault here...

[vrasp]

Re: Fixing a laboratory DSC

On the photo below is the back label of the device. I assume that's how much current is drawn.

Yes, like you said, it either heats or cools but not at the same time. I thought that regardless of the the ouput of that device (whether it s heating or cooling), it would always draw 6 amps. But if that's not the case it all makes sense.

I don't know about the fuse blowing. I found the blown fuse and haven't been able to test anything as I m waiting for new fuses to be shipped. As soon as I get them I can get on it and try to gather some info.

Thank you for your help!

[eccerr0r]

Re: Fixing a laboratory DSC

Well without a picture it wasn't clear whether that 6A @230V is that device's transformer limit or is it actually drawing that much power? The implication from your post seems to imply that it was another "6A 230V" transformer of sorts and without more clarification or a photo of that input I could only assume what was in the machine.

If it really is a 1400W load, that in itself will overload the step up transformer, hence there's a contradiction here... unless that load is just an underused transformer. If it truly was an undersized step up transformer, then quite possibly that's your problem right there though it should have failed a lot earlier... and you need a new transformer.

BTW if that 6A 230V unit was only to power the 10A@24V (240W) heating and 6.2A@17.8V (111W) cooling, and both of these can't happen at the same time, then unless that 6A@230V unit was really inefficient, it's not going to draw 1400W continuously and the first step up transformer should be just fine. In this case only inrush needs to be considered (which may just be 6A@230V for a short while) and the 600VA step up should be able to handle things after that brief pulse.

Also, since you seem to be blowing fuses, is it instant blowing or blowing after a while? Might reveal some evidence on where to look next.

[vrasp]

Re: Fixing a laboratory DSC

The DSC is connected to a heating element and a cooling one. The device that draws the 6 amps at 230v is connected to these elements. Its outputs are 10 amps at 24v for the heating and 6.2 amps at 17.8v for the cooling.

I m not sure I understood. I always thought appliances power should not exceed that of the transformer to avoid overload. How can a 600w transformer not be overloaded with over 1800w of devices?

Thank you!

[eccerr0r]

Re: Fixing a laboratory DSC

Transformers(themselves) won't draw that much power continuously unless its output is drawing that power (or if the transformer is misdesigned for the frequency of operation). So depending on what's drawing power on it will determine how much power is needed for that apparent first stage step up transformer, probably as a cheese around to allow this device to be used in 120V-land like North America.

You say it's a calorimeter of sorts, so I suspect the main use for it is to detect temperature increases and decreases over time to estimate thermal energy change in a chemical reaction. Whether additional heating or cooling is necessary I don't know - perhaps to bring the reaction chamber ambient temperature to a fixed value - would consume the most power. This would be the most stress on that initial step up transformer.

[petehall347]

Re: Fixing a laboratory DSC

unplug everything .it might be simply a power supply fault .

[vrasp]

Hi guys,

The lab I work in has an equipment called a Differential Scannning Calorimetry. It essentially measures the enthalpy change as a function of temperature.

Anyways, the equipment is made up of several devices and PCBs that have different cuntions. The main fuse connected to the transformer blew and I m trying to figure out why. These fuses go for $50 dollars each and we bought a few. I m going to unplug everything and connect each device until I find what device causes the fuse to blow and go from there.

Here is what I don't understand. The main transformer has an inputs 120v and outputs 230v. It is rated at 2.5 amps and 600VA. Here is a picture of the label.

Two devices (and some small PCBs) are connected to the transformer. One is labelled "input: 230v 6 amps", the other "input: 230v 2 amps". Thats a total of 1840W just for these 2 devices. How could the transformer supply that if it's rated at 600VA?

Thank you!