UPS and inverter questions

[davmax]

Re: UPS and inverter questions

Have looked at this link: http://clivetec.superihost.com/SMD_CodesK.htm

Gives Q10 as 60V 0.11A MOSFET, D6 as 27V Zener and D7 KY3 as N FET ???

D7 needs check against another good one for FET or diode.

[andrew77]

Re: UPS and inverter questions

Have looked at this link: http://clivetec.superihost.com/SMD_CodesK.htm

Gives Q10 as 60V 0.11A MOSFET, D6 as 27V Zener and D7 KY3 as N FET ???

KY3 is wrong, search with google as KY3 diode. All the others are right, I think.



I'm going to sleep now, for sure this time.

[davmax]

Re: UPS and inverter questions

Have a good night . KY3 confirmed 13V Zener.

[davmax]

Re: UPS and inverter questions

The problem is now isolated to the low voltage control block. ie converter and inverter are operating from battery and failures are low voltage devices in charging and relay control. Concerns. 1. Several failures in this block. Is there a knock on from one failure? How are these devices related and have they damaged other components in the same circuit? 2. I am curious about how 115V line voltage gets to the low voltage control so that line failure can be monitored, there may be a problem there. 3. The centre tapped AVR transformer is a worry if RY1 switches in wrong conditions and doubles voltage (if circuit trace is right). The voltages you measured were correct and I presume measured under battery operation.

[andrew77]

Re: UPS and inverter questions

Here's what I did:

Replaced Q10. That didn't fix it, but I noticed when I unsoldered Q10, D7 was not bad.

So I made a diagram of how this part of the circuit works. I found out that D8 was two diodes, and both were blown open.

I replaced D8, and now all of it works.


Now all I have to do is order parts for the other one, and diagnose it.

Thanks for all the help that's been given. I'll order the parts and wait for their arrival. Probably be a couple weeks.

So what have we learned about overloading UPS's?

1. MOSFET's should be the first thing checked.
2. Check the fuses.
3. Check all the transistor drivers for the relays.
4. Check all the diodes.

Need to make a list of MOSFET's for substitution.

19NB2 - STP19NB20 200volt 19amp
94-2358 - IRF540 100volt 33amp
94-4311 - IRFZ44 55volt 49amp ??

Here's the pictures and some extra stuff.

[davmax]

Re: UPS and inverter questions

Well done. Your " all of it works" I assume means that line operation is now restored. I am still very curious about the tap on AVR transformer. Are the voltages the same on this transformer for both line and battery ops?

[andrew77]

Re: UPS and inverter questions

Well done. Your " all of it works" I assume means that line operation is now restored.

Correct.

I am still very curious about the tap on AVR transformer. Are the voltages the same on this transformer for both line and battery ops?

I think it might have to do with this straight from Conext:

Question:
What is AVR (Automatic Voltage Regulation)?

Answer:
Instead of going to battery during low or high input voltages, the unit will increase or reduce the voltage to a safe operating range without running on the battery. The main advantage of this is that it helps to prolong the battery life.

Oh yeah, that last file has some schematics and theory of operation for a typical APC UPS.

[davmax]

Re: UPS and inverter questions

Thanks for files.


I have looked at all four theory files and none bear any relation to th theory of your units. Very different and no real help as with previuos circuits we have looked at.

I suspect your tap changing explanation is not correct. The step 2:1 is too large. I am familair with normal tap changing for line compensation and this not normal.

The main thing is that you have achieved success.

[andrew77]

Re: UPS and inverter questions

I suspect your tap changing explanation is not correct. The step 2:1 is too large. I am familair with normal tap changing for line compensation and this not normal.

Would you tell me how this works? I'm interested in knowing.

The main thing is that you have achieved success.

Couldn't have done this without your help, I greatly appreciate it.

Thanks, again.

[davmax]

Re: UPS and inverter questions

Would you tell me how this works? I'm interested in knowing.

Not quite sure of your request. Do you mean principles of tap changing? I am pretty sure I cannot yet explain the 2:1 tap on your UPS, I do not have enough info to work with on that one.

[andrew77]

Re: UPS and inverter questions

Do you mean principles of tap changing? I am pretty sure I cannot yet explain the 2:1 tap on your UPS, I do not have enough info to work with on that one.

On the theory and how you came up with the 2:1.

[davmax]

Re: UPS and inverter questions

On the tap selection theory and how you came up with the 2:1.

Taking the last first. The 2:1 relates to the fact that the AVR transformer is centre tapped. With the neutral connection as reference take the tap as 1 and the end of the winding equals twice or 2. Hence 2:1 switch ratio if RY switches from tap to end or looking at it the other way switching from end to tap 1:0.5.

Tap switching comes in two forms
1: Primary switching. Usually there are at least three taps including the end. They can be arrange slightly differently but typically the mid connection respresents the nominal line voltage and the taps either side will be between 10 and 15%. A supply sensing circuit is then able to adjust taps that are plus and minus say 15%. So if the line rises by 10% the +15% tap is selected to bring the transformer voltages within a 5% tolerance. Similarly a lowering of line voltage will cause the lower tap selection.

2. Secondary tap switching. This is typically used for linear DC voltage regulating power supplies to reduce the heat loss in the regulator. eg an adjustable 0 - 30VDC supply will dissipate a large amount of heat if supplying a 0.5volt load from a 35V internal DC. To overcome this problem a transformer tap is selected to reduce the internal DC to about half. When the required output voltage is 15Volt or greater then the higher voltage tap is selected to provide 35 volts again. Here we have an example of a 2:1 tap ratio. Secondary tap changing uses larger steps.

[davmax]

Re: UPS and inverter questions

Further comment on primary tap switching. I picked a poor example.

Three tap method either uses 10% steps to compensate for +-15% to within 5% or 20% steps for +- 30% within 10%.

[starfury1]

Re: UPS and inverter questions

well good to hear its resolved Andrew77

Thanks too to davmax for really sticking with this and helping find a resolve to it.
I guess andrew77 was thankful of all input from everybody and every little bit does help

I myself like I said don't know much about them.

Guess as you say Davmax (think it was you)
it would be nice to know how the chain of events failure wise unfolded...what triggered the death of what that caused the demise of the other components

but very true one component can be the cause of the deaths of many more.

Keep us posted on the other one Andrew77...hope it isn't too much trouble now you got a better idea of how they work.

Cheers All

[andrew77]

Re: UPS and inverter questions

Would there be a problem replacing this mosfet:


Data Sheet

200volt 19amp RDS(on) 0.15 ohms 140watts max dissipation

with this one:


Data Sheet

200volt 28amp RDS(on) 0.082 ohms 156watts max dissipation

What I really need to know is, what to watch out for. Davmax mentioned earlier about stuff not being too critical when using these as switches, so I want to know what I can get away with. Without blowing myself up or frying myself.

Thank you.

[davmax]

Re: UPS and inverter questions

Would there be a problem replacing this mosfet:

http://www.fairchildsemi.com/ds/FQ/FQP19N20.pdf
Data Sheet

200volt 19amp RDS(on) 0.15 ohms 140watts max dissipation

with this one:

http://www.fairchildsemi.com/ds/FQ%2FFQP32N20C.pdf
Data Sheet

200volt 28amp RDS(on) 0.082 ohms 156watts max dissipation

What I really need to know is, what to watch out for. Davmax mentioned earlier about stuff not being too critical when using these as switches, so I want to know what I can get away with. Without blowing myself up or frying myself.

Andrew,
The main thing to watch out for is Total Charge Cg. Clearly the voltage and current ratings are fine. Cg max should be no more that 3 times greater. In this case this condition is met.

There are four in the circuit. Because switching times will be changed with the higher power MOSFET (slower with increased total charge) always replace in pairs. A pair is the two connected is series. Each MOSFET in each pair must be the same. Even better if all four are changed.

This is all about power sharing at the time of switching ON and OFF.

[davmax]

Re: UPS and inverter questions

Andrew,
A couple more points.
Before you replace the MOSFETs make sure that the drive transistors are not shorted and are fully functional or you will destroy the replacements.

I note the inverter circuit has L1 to limit the current drawn when the MOSFETs switch.ie consider a series pair, they are connected across 170VDC and as one switches ON fast the other switches OFF slower and very high current can flow for a short period causing high switching stress L1 limits this current. Good to see.

When one MOSFET in a pair goes short it will normally take the other out too.

When choosing MOSFET replacements always look for an L as the last part number character. This defines a logic level MOSFET ie the full ON gate voltage is 5 volts all other MOSFETS are 10 volts. The two data sheets reveal normal 10V jobs.

[andrew77]

Re: UPS and inverter questions

Andrew,
A couple more points.
Before you replace the MOSFETs make sure that the drive transistors are not shorted and are fully functional or you will destroy the replacements.

I note the inverter circuit has L1 to limit the current drawn when the MOSFETs switch.ie consider a series pair, they are connected across 170VDC and as one switches ON fast the other switches OFF slower and very high current can flow for a short period causing high switching stress L1 limits this current. Good to see.

When one MOSFET in a pair goes short it will normally take the other out too.

When choosing MOSFET replacements always look for an L as the last part number character. This defines a logic level MOSFET ie the full ON gate voltage is 5 volts all other MOSFETS are 10 volts. The two data sheets reveal normal 10V jobs.

Would logic level MOSFET's be damaged if they were overdriven? I mean if the MOSFET was meant to be turned on by 10volts and I replace it with a 5volt one.

I haven't spotted any shorted transistors yet.

I was thinking of replacing the whole set of MOSFET's so the circuit would be balanced. What would happen if the parts I used took too long to turn on and turn off? I'm assuming it would blow, since there would be switches switching when they're not supposed to be.

I found something disturbing about the working UPS. I pulled the batteries out and it looks like they're being overcharged. The cases are swelling and cracking. Guess I need to figure out how to check the output of the charger.

The charger is supposed to run all the time for the float charge, right? It seems like the charger puts out a little bit of heat. The core of the transformer is like 120F or maybe 130F, is this right? The side of the UPS gets to like 95F or so (not much warmer than my hand).

I need to figure out what spare parts I need before I order everything I need so that I don't have to pay more for shipping.

Anyway, this updates what is happening.

[davmax]

Re: UPS and inverter questions

Would logic level MOSFET's be damaged if they were overdriven? I mean if the MOSFET was meant to be turned on by 10volts and I replace it with a 5volt one.

No problem driving 5 volt gates with 10 volt

I haven't spotted any shorted transistors yet.

Great

I was thinking of replacing the whole set of MOSFET's so the circuit would be balanced. What would happen if the parts I used took too long to turn on and turn off? I'm assuming it would blow, since there would be switches switching when they're not supposed to be.

The alternate devices you posted are slowed to approx half the ON and OFF switching speeds with the same drive circuits. This is why they should be in pairs. It is not critical that the other pair is changed,they match, and the transformer winding will limit any current pulses across pairs. You will have no problem provided the drive circuits are OK

I found something disturbing about the working UPS. I pulled the batteries out and it looks like they're being overcharged. The cases are swelling and cracking. Guess I need to figure out how to check the output of the charger.

Yes those are disturbing signs of overcharge. There appears to be a charger fault. More circuit analysis and testing will be required. More detailed circuit trace of this block. A check of charging current at F1 is probably not too useful at this time, because of the overcharge signs, but may be a good reference reading to compare fault with fix. I suggest you compare with the charger circuit and currents of the other inverter using one set of batteries. As far as we know there has been no problem in that charging block.

The charger is supposed to run all the time for the float charge, right? It seems like the charger puts out a little bit of heat. The core of the transformer is like 120F or maybe 130F, is this right? The side of the UPS gets to like 95F or so (not much warmer than my hand).

This is hard to comment, some transformers do run hot even unloaded due to iron loss.

[andrew77]

Re: UPS and inverter questions

I'm almost thinking it's time for new batteries since the date on these is 2004 and sealed lead acid batteries usually only last 3 to 6 years. The cracking looks more like scratches, and it's not bulging as bad as I thought. These are the batteries that I didn't charge with that Black&Decker smart charger. Maybe they'll last a little while longer.

I'll monitor the amperage through F1 and go from there.

Thanks.