I have a Bluegate 650VA that I Recently changed the MOSFETs in the UPS because the old ones got burnt out. Now, when I try to use it with battery all I hear is a beep and it turns off. I hanged the FQP50N06 To IRFZ44. Could that be why? or is it my battery?

 

Sooo many variables, so little info. Why did the originals burn out? Were any other parts bad? Have you measured the battery voltage while you test it? Is it showing any errors?

Your replacement fet is similar but an inferior replacement. Several specs are lesser than the original, not the least of which is that the original fets could dissipate 28% more heat than the replacements. I doubt that's the cause of it immediately turning off, but if the originals died then it's not likely that inferior replacements will work for long.

 

In most systems, when some part "burns out" there is a reason aside from that part just randomly failing. My guess is that is the case with this system. And since parts in a regular UPS are rather highly stressed, putting in a less adequate part is likely to lead to failure again.

 

I bought original MOSFETs and now its working, but they are getting soooooooooooo hottttt. any reasons? Battery voltage is 13.1v meaning battery is OK.

 

I bought original MOSFETs and now its working, but they are getting soooooooooooo hottttt. any reasons? Battery voltage is 13.1v meaning battery is OK.

OK, so the correct parts work. Yes, a UPS may only be designed to hold up long enough for an orderly save and shutdown. Many of them are made that way. Is there adequate grease to couple the transistors to the heatsink? Do the heatsinks get hot as well? How long does it take for the transistors to get too hot to touch? And what load are you driving? 50%, 75%, or 100% of the rating? And there may be an electrical defficiency, inadequate gate drive, or a high frequency parasitic oscillation. So I hope that we can have some answers.

 

i am only using my laptop charger that is 60 watts. the transistors have adequate heatsinks and they are connected properly according to manufacturers specification. do i need to add more mosfets as there are only two MOSFETs in the system? it takes instantly for the transistors to get hot.

 

Try loading the UPS by having it power some incandescent light bulbs, about 100 to 150 watts or so. it might possibly need a bit more load. Does the big transformer get hot also? I never heard of the Bluegate brand, perhaps they have a technical assistance place on their website. That may provide some help.

 

The transformer is not getting hot, Just the FET'S

 

Did you replace the fets with the same number of fets as it originally had, or did you leave some out? If it's original and getting hot, then you may have fixed the symptom (burned out fets) but not the actual problem. Start looking around at other parts near by, maybe diodes, capacitors, etc.. A diode might have failed which is leading to too much current through the fets. Check to see if any or either open or short.

 

it had 2 originally, and one open space to add another FET. all diodes and capacitors are fine.

 

Did you replace the fets with the same number of fets as it originally had, or did you leave some out? If it's original and getting hot, then you may have fixed the symptom (burned out fets) but not the actual problem. Start looking around at other parts near by, maybe diodes, capacitors, etc.. A diode might have failed which is leading to too much current through the fets. Check to see if any or either open or short.

I already suggested that it was not the FETs that caused their failure, back in post #3. Of course an adequate check requires additional test equipment. And there is also the possibility of a high frequency parasitic oscillation, possibly because of some open bypass capacitors.
And one more possibility is that the design is poor and it never worked any better than having the transistors get very hot very quickly. So a data sheet examination of the specifications is called for. Given the rated output power, 650 watts, and given the battery voltage, 13.5 volts, and that there are only the two power devices, meaning a push-pull circuit, calculating the transistor current can tell us how much loss there is in the transistors. that is, 650W/13.5V=48.15 amps. That presumes 100% efficiency. That is a whole lot of amps to be shared by 2 transistors even at a 50% duty cycle.

 

Suspiciously true. hmmm. It looks like I'll have to change all the FETs then.

 

650 watts? hell no! it's less than that for a small UPS. it should be around 300-400 watts.

 

650 watts? hell no! it's less than that for a small UPS. it should be around 300-400 watts.

The package was described as a 650 watt UPS in a very early post.

 

Hello,

It will not deliver 650 Watts. This statement will tell you more:

The Blue Gate 650V UPS, BG650, is an entry level unit, with output power rating of 390W. The BG650 can support low power consumption devices like laptop, printer decoder, TV, etc, up to the stated output capacity. Depending on the load, the backup time could be up to 15 minutes. This would be enough to save and secure your work if using a PC or to switch to a backup power generating unit. For more extended power backup (say for several hours, you should be looking at one of the inverter options).

https://www.swiftermall.com/blue-gate-ups/184-blugate-650va-ups-bg650.html

Bertus

 

That's the one. Thanks Mr Bertus. I bought new MOSFETs and I'm Gonna give it another try.

 

When you have fets in parallel, you should replace them all at the same time and all from the same batch. This will minimize differences between fets and make it less likely that only some of the fets share most of the load. Did you have mixed models of fets when it was turning off right away? If so, that could explain why it wasn't operating as expected.

 

Same FETs, All in parallel.

 

Hello,

It will not deliver 650 Watts. This statement will tell you more:

The Blue Gate 650V UPS, BG650, is an entry level unit, with output power rating of 390W. The BG650 can support low power consumption devices like laptop, printer decoder, TV, etc, up to the stated output capacity. Depending on the load, the backup time could be up to 15 minutes. This would be enough to save and secure your work if using a PC or to switch to a backup power generating unit. For more extended power backup (say for several hours, you should be looking at one of the inverter options).

https://www.swiftermall.com/blue-gate-ups/184-blugate-650va-ups-bg650.html

Bertus

The very first words of the very first post tend to give the impression that it is a 650VA UPS. Certainly that model number was carefully chosen to give that impression. So pardon my confusion.

So if we say that transistor power is less, 390 watts/13.5 volts=28.8 amps, divided among 2 transistors, iis still a lot of power, and so they will still get hot. If the saturation voltage is 0.1 volts then the effective power dissipated in each device is 14.4 watts. My soldering pencil is rated 25 watts and it melts solder fairly well. And it is a lot larger than the heat sink on those transistors, I would presume.

 

Here's a quick lesson ...

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