Help in choosing power transistors for 1000W Desi UPS

Aoa friends, please suggest me some good power transistors for my 1000W UPS, Presently I'm using 16 transistors with following descriptions 80NF 70 , GKOR5 V6, CHN247 ( all that written on transistor) but the problem is that 2-3 transistors always blow out after every 1-2 months and I'm really fed up to replace them again and again, so friends please suggest me some good transistors or could you please tell me specifically whats the problem is that cause them to blow, Thank you, Jazak Allah

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Waqar,

Heat is the biggest enemy of transistors.

Please post pictures of the mounting arrangement and cooling air fan in your UPS.

Aurangzeb

Aurangzeb bhai, Here are some pictures of heat sink plate and fan. Regards, Waqar Ahmad

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Waqar,

Do you normally use it with the cover closed or open?

It seems that it has been used quite extensivly. Please ensure that the next time an intervention is required, the heat sink plates are thoroughly cleansed particularly where the transistors are mounted. The mica insulation should be changed and fresh siiicon grease applied to improve heat transfer.

Without the aforementioned steps I am afraid that the problem will not go away. Changing transistors may or maynot solve the problems.

Aurangzeb

^Exactly all that

if this is the fan that came built with your ups, change It immediately.. those are 20rs very low speed sensor fans which do nothing but exhaust out a little air when running in inverter mode only.. buy a good fan,. preferably delta, since they are high quality, powerful flow and silent too..should be around 80-110 per fan for delta.. simple fans are 30rs for large ones and 25rs for this size..

and also if you are upto it, and know how to do cutting and fitting., a small high speed fan mounted in the front of ups with cutting with air blow towards the back fan will improve your cooling 100 folds and increase life of ALL the components of your ups..

Waqar,

The fan issue raised by Farhan is very valid. Note that the fan is pointed at one panel of transistors while the other panel has no airflow. If the transistors of any one particular panel keep blowing then it is another indication of the problem.

Aurangzeb

Aurangzeb and Farhan, I kept it covered, well never used any insulation greese between heat sink plate and transistors, and exactly the adjacent palte's transistor mostly blow off. So Now the solutions are to change that fan with a good quality big fan, and preferably if I get delta, and secondly cleansing of plates to be done followed by some proper insulation material, Yesterday I've changed the blown out transistors, and UPS will start working fine, but now its not tripping even after completing the charging process and Keeps on charging, the voltage on terminals with charger connected is around 14v with 5amp charging, but not tripping, I tried to trip it with adjusting battery full variable but it's still not tripping (Intial volts and amp at start of charging 12v,16Amp). So, exactly whats the problem is? I replaced same transistors, or I think the kit become faulty.

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^ UPS is not trippin` ? Stop using cheap cocaine.. :P

you also need to place another fan a much smaller one in front of the ups casing, either cut a square in the front or use drill holes for air flow.. preferable put the fan in front of the opposite transistor plate so that air flows on the un-cooled plate as well and exhausts as a whole from the end..

Farhan whats cheap in it??

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[quote=“waqar789, post:9, topic:21088”]

Farhan whats cheap in it?? Sent from my LT22i using Tapatalk

[/quote]

You missed the joke.

Anyway, besides the above steps, another thing you must do is to make a layer of solder, as thick as possible over the copper PCB material that connects all the emitters. This will help to break the concentration of current in some of the transistors which may be the cause of overload and burn out.

Aurangzeb

[quote=", post:, topic:"]

You missed the joke.

[/quote]

our community these days.. :(

[quote=“waqar789, post:, topic:”]

Aoa friends, please suggest me some good power transistors for my 1000W UPS, Presently I'm using 16 transistors with following descriptions 80NF 70 , GKOR5 V6, CHN247 ( all that written on transistor) but the problem is that 2-3 transistors always blow out after every 1-2 months and I'm really fed up to replace them again and again, so friends please suggest me some good transistors or could you please tell me specifically whats the problem is that cause them to blow, Thank you, Jazak Allah Sent from my LT22i using Tapatalk

[/quote]

Is this a 24V or 12V UPS ?

Do the same MOSFETs blow up every time ? Or at least on the same side or is it random ?

Do the MOSFETs blow only when UPS is operating at near full load conditions ? Have you observed ?

80NF70 is a MOSFET. This is a type of transistor which has some obvious advantages over the Bipolar Junction Transistors. But there is difference between driving both types i.e. MOSFET Vs BJT. The kit installed in the UPS seems to be designed for BJT types. MOSFETs require some different arrangement. You need to have a series resistor (10-47 Ohm typically) between "gate" terminal of each MOSFET when they are in parallel.

Without going into further details of driving MOSFETs, I will suggest to:

1) Change all the MOSFETs in a parallel bank when few of them blow up. If your UPS is 24V, then I would suggest to use a MOSFET with higher voltage rating. This is required because of the back EMF due to transformer winding. Chose something near or above 100V rating. This 80NF70 is merely 68V.

2) Add a suitable snubber/clamping circuit to protect the MOSFETs.

3) Insulate each MOSFET individually using a mica insulator from heatsink plate and mount the plate directly to the casing rather than using a wooden strip as insulator. This will dramatically reduce the junction temperature of MOSFETs when they are operating as compared to the present arrangement.

4) Use thermal grease under each MOSFET. This increases the contact area by filling in the micro sized uneven areas which are not visible to naked eye.

Farhan Sorry to say But I'm not here for jokes, secondly desi UPS are real hardcores according to our conditions of electricity, no doubt APCs are the best, but aren't for these purpose as nowadays our so called community are using them, secondly the fan installed in this UPS is already of delta electronics which you called a cheap fan, well leave it.

Aurangzeb bhai I’ve already made a thick layer of solder on the emitter side of transistor. Thank you for your kind suggestions may Allah Bless you

Ijaz bhai exactly these are MOSFETs, and its a 12 v system, No there is no obvious pattern, one month ago 2 of them blown off on one plate and now 3 were blown from the other plate, these transistors blow soon after the UPS starts working in Inverter mode and I think there’s no obvious load on the UPS, also the fuses installed on the back blown up with it although these are 15A,250V fuses,
Moreover please suggest me some good UPS Kit that is suitable with these MOSFETs.
Jazak Allah

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[quote=“waqar789, post:13, topic:21088”]

Ijaz bhai exactly these are MOSFETs, and its a 12 v system, No there is no obvious pattern, one month ago 2 of them blown off on one plate and now 3 were blown from the other plate, these transistors blow soon after the UPS starts working in Inverter mode and I think there's no obvious load on the UPS, also the fuses installed on the back blown up with it although these are 15A,250V fuses, Moreover please suggest me some good UPS Kit that is suitable with these MOSFETs. Jazak Allah Sent from my LT22i using Tapatalk

[/quote]

From the symptoms:

1) MOSFETs blow up randomly

2) The fuses also blow up (I assume fuses are on 220V output)

I tend to conclude that your UPS is overloaded and has no overload protection (or if it has, it is out of calibration). Carefully check your load. Most likely your UPS is overloaded and less likely you have a defective (or shorted ) transformer.

Regarding which kit is suitable for MOSFETs, I am sorry but I have no knowledge about currently available kits. May be this kit has been modified for MSOFETs (difficult to tell from the picture alone).

@ijaz ahmed @farhan_ds @aurangzebhaque After a hectic week with my desi UPS, today I moved to APC 1500VA with 2 AGS 135Ah, APC costs me 13000, and 2 batteries cost me 22,000, installed it in the afternoon and from now its still charging at a rate of 6.55 to 7.80 ( I've a Multiammeter which measures AC amps) So is this 6-7 Amps a normal charging? As I'm not much satisfied with these statistics because loadshedding situation may get worse in the coming weeks or shall it give me a better backup for 30% load on it for consecutive 3 hours loadshedding(2fans(80-90w), 3 energy savers(23w each), 2 WiFi routers, also I'm sharing some pictures of my setup, so sincere advice are welcome and highly appreciated.

Waqar Ahmad

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ISn't this the same model as what @farhan_ds is selling for Rs19K in used condition ?

^ No.

Waqar

You are trying to measure DC charging current going to the batteries with an AC measuring instrument. Thus the 6.71 figure does not represent the true value of the charging current. If you want to know the exact value the I am afraid you will have to either use a clamp meter capable of measuring DC or install a meter which is capable of measuring current in both directions.

Aurangzeb

[quote=“yousaf465, post:16, topic:21088”]

ISn’t this the same model as what @farhan_ds is selling for Rs19K in used condition ?
[/quote]Yousaf,
The model of my APC is SUA1500I

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[quote=“farhan_ds, post:17, topic:21088”]

^ No.
[/quote]So Farhan, what is the difference between these two?

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