DC to DC Converter

What is your input voltage? What is the load current per line? Are the +ve and -ve outputs loaded equally? Are they isolating converters?

Despite all of the details you've given, there's not enough information to give you a definitive answer. It would be helpful to know which module you're using and how much power you're converting? While 60°C (aka 140°F) is not an impossible temperature to operate electronics. I would certainly want to know how much power the supply is trying to dissipate to prevent it from overheating.

As far as your fuse though, you might find that there's also a temperature coefficient problem there, too. Particularly if you're trying to use a thermo-chemical self resetting fuse. A quick glance at one of these data sheets show that the hold current of a PTC fuse halves as it goes from 20°C to 60°C.

If the problem is that only one of the outputs (+ve or -ve) is failing while the other is maintaining the correct output voltage (and presumably current - but the jury's still out on that), what could that possibly have to do with an input fuse?

EMF can only be measured relative to a reference point. If someone wanted to get +- with respect to a common current return path (usually bonded to a common point like earth ground) then the unregulated dc connection would consist of three wires: a wire positive [to the neutral], the neutral itself, and a negative [to the neutral]. Over current protection in the form of a fuse is then installed on "voltage carrying conductors".

A converter providing +/- 15V DC would have (at least) three terminals on the output side, typically designated "+15V", "Common" and "-15V". If the converter output is isolated from the input, the common could be connected to any potential you like (provided the input/output differential does not exceed the device limits for breakdown).

Who mentioned an unregulated connection? Where did you copy/paste this from? What are you trying to tell us?

ok i try to further elaborate:

the input voltage to the converter is 28V.

im using 12v converter for digital chip based two phase generating circuit(definitely incorporating some analog section like mosfets). the total current that the card intake is 50mA without load.

on the application of load, it first increases but then decreases and maintains to near about some 200mA.

Another converter with same input is being used in a circuit to produce +-15V. this supply is also driving some analog electronics dealing with ADC chips.

the fuse in use by now is nothing but a thin stranded wire.

the basic scheme of overall module is that i have a sensor to sense the position of motor and im transferring this data to pC. 12Vconverter provides two phase to motor. while +-15v converter drives the circuit converting analog signal into digital.

is that ok now.

kindly suggest some suitable fuse or preferrably any other converter that would not require any fuse and can operate properly without using any such fuse.

It would help anyone who may be trying to help you if you gave us the part numbers of the devices in question - or better still, links to the manufacturer's data sheets.

You seem to be asking two questions, one relating to output failure, and one to input fusing. Please clarify.

i dont find any option to attach the data sheet. the converters are DC to DC converters of dual polarity (+-12 and that of +-15) from C&D technology.

actually the output is dying out. while analyzing the problem, it was my doubt that the selection of a simple stranded wire instead of a suitable fuse might have caused the problem due to high current flow at 60C and asked whether it could be a cause or not?

Right now I would not rule out anything with the information you've given. While a suitable fuse at the input and output of all supplies may have limited failure to only the failing component, premature fuse failure from these elevated temperatures may also become a problem. You may be just on either end of the bathtub shaped lifetime to failure probability curve for the dead supply. Your wiring insulation or your assortment of loads maybe showing a temperature accelerated failure rate that is toasting this (these?) supply.

There are many other companies that make a wide assortment of DC/DC switching supplies; Vicor, Astec, Astrodyne, Lambda to just name a few. Before replacing your failing supply with another company's product, I'd determine if the supplies used were properly sized for the load and if the load or supply side of the dead supply was the cause of your failure.

Can you give us the dc-dc part numbers and the fuse rating and type you are currently using. It may be just a case of under-rated devices being used.

At the higher-than-normal temperatures you are experiencing, you may wish to consider upgrading your dc-dc's so that they effectively output a lower proportion of their maximum output capability.

yes te part no. is WP06R24D12 and WPO6R24D15 for 12 and 15v respectively.

Then: the data sheet is here:-

http://www.murata-ps.com/data/power/ncl/tdc_wp06r.pdf

and, it looks as though you are running everything within spec.

the units are rated up to 6 Watts "output" power (All Other Models 6.0 W):-

They will take up to 310 mA input current:-

and critically the thermal derating doesn't kick in until 71°C

How well balanced is the output load? The product selection chart shows a maximum of 3 Watts per rail.

Any chance of posting part of the circuit diagram. Get it somewhere on your PC as a .jpg; click on the little green camera:-

and, browse to the picture.

The data sheet does give you one other suggestion:-

http://www.mouser.com/catalog/630/1655.PDF

28V @ 200mA is 5.6 Watts .....so

I'd have thought he'd be really pushing his luck with the WP06R series (5 to 6 Watts).

So my bet is on WPN20R24D12C and WPN20R24D15C.

Like John I'm confused by the indictment of the fuse.

As JohnDG and others have cited: specifics such as the part number(s) from araees is needed in order to be of help.

I read his post as the peak current from each terminal, pos. and neg., is "some 200 mA". If so, then he is pushing the spec. of the part, which would explain why he is having failures.

araees are you having failure problems with both types?

I too find any mention about the fuse a mystery.

I've used these DC-DC dual OP converters with great success, but where I design-in a part where it is to operate under 50-60% of its rating.

DC to DC converters are normally rated at 20 deg. C. As the temperature rises, the ratings drop. By the time it gets to 60 deg. C it may not be capable of much current or voltage. Check the data sheet - it will show how much you can expect from it at the higher temperatures. Even though it will work at a high temperature, the output will be severely reduced.

The symptoms you are describing are consistent with the converter dropping it's output voltage to maintain a reduced current output.