Electronics > Repair
APC Smart-UPS 1500 (SMT1500)
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Bretterson:

--- Quote from: fmashockie on May 05, 2024, 09:54:05 am ---This MOV MV2 not being there isn't going to prevent your UPS from working.  As I said earlier, these things are very dangerous to work on.  You might want to invest in some additional equipment (DC benchtop supply, scope, etc) as well as gain a bit more experience in troubleshooting before proceeding.

--- End quote ---
I'd consider getting a DC power supply. It looks like they can be had for around $65, I'm just not sure whether I'd use it much in the future. I think an oscilloscope is more than I want to get into as I have zero familiarity with using them. It's probably a useful thing to have and know how to operate, but the learning curve seems high.

Also, you mentioned that the missing MOV wouldn't prevent it from working... could the leaky capacitor be to blame here? If not, then it sounds like there's definitely something else wrong I'd have to track down.


--- Quote from: asis on May 05, 2024, 01:37:50 pm ---It would be appropriate to check the condition of their contact groups, or better yet, dismantle them and check them individually.
You should also separately check the status of the MOSFET's of the inverter and the operation of the charger.
There are several threads on the forum that describe how to do this.
-
The rating of capacitor C53 for UPS in AC220V version is 2.2mF x 275V~.

--- End quote ---
Can those relays actually be put back together after opening them?
I can look up the info on testing that stuff.
This is a 120V unit and the capacitor at C53 is 20uF x 150V~.
I looked at the schematic you shared and the part number listed at MV2 matches the component found at MV4, but MV2 appears to be different.


--- Quote from: fmashockie on May 06, 2024, 02:57:09 pm ---The precautions one should take for checkin the mains portion or SMPS of the UPS are the same precautions one should take when working on any device powered by mains voltage. 

-Be careful when checking HV side or primary side
-It might be benefical to use a lamp series tester to protect from unknown shorts on the primary side
-If you plan to use a scope, make sure the unit is plugged into an isolation transformer.  If you plan to probe mains, you should only use methods that are safe - such as a HV differential active probe.

Those are just a few precautions one should take.  But the main thing that separates the UPS from other devices powered by mains is the UPS's battery which is usually two large 12VDC batteries in series that can deliver large amounts of current.  Keep in mind most of these devices are rated to deliver upwards of 1000W - that's a lot of power.  And a large battery that can deliver a lot of current is required.  If there is a short on the board in the charging or inverter circuit, this power can be delivered uncontrollably which could cause serious damage to life/property.  I've seen APC UPS units with shorts on the inverter MOSFETs that caused catastrophic damage and the battery protection fuses did not prevent this damage (I've done a few videos/threads on these topics).  So that is why I voiced my concern for troubleshooting these units without a DC power supply with current limiting.

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Is this the lamp series tester you're referring to?:

I really hate to give up on it, but I'm starting to question whether this thing is too much for me to take on :-\
fmashockie:
If this kind of work interests you or you would like to do more of it, a DC power supply is a good investment.  And they can be acquired for relatively cheap both used or new.  Good current limiting control is key.  Shop around and you can definitely find a good one for $100 or less.

The video you shared is unavailable, but this is an example of what I am referring to.
Most people build their own as they are very easy to make but I think they can be purchased assembled as well.

The MOV that got destroyed looks like it is for the mains input.  So typically these will get damaged like this from an external surge from your mains supply.  Based on Asis's schematic, I don't think that capacitor C53 is the cause of the MOV going up in smoke.  But I could be wrong!  Either way, it should be replaced.  They both should be replaced, but I was just saying the MOV is not critical to the unit running.  But it is important for protection.

You can test the relays in-circuit, but you would need a DC power supply to do so.  Look up the datasheet via the part # on each relay to get the pinout.  And place a voltage across the coil (enough to switch it on; for ex. if it is a 12V relay, apply 12V).  You need to make sure that you have the polarity right.  This would not matter if the relay was desoldered/removed from the board, but usually there is a protection diode across the coil in-circuit to prevent reverse polarity.  While you are applying voltage to the coil, use your multimeter to check for continuity to mak sure it is switching properly.  This is the easiest way to do it and to confirm your relays are working properly.

You don't have to give up on it! Just be careful and take precautions.  Use the advice from more experienced members in this forum.  And invest a bit in some additional tools.

Bretterson:

--- Quote from: fmashockie on May 07, 2024, 04:35:26 am ---You don't have to give up on it! Just be careful and take precautions.  Use the advice from more experienced members in this forum.  And invest a bit in some additional tools.

--- End quote ---
I've decided I probably shouldn't invest the time on this right now and will try to get a different one. Maybe I can revisit it later since I'll be able to open the other one up and compare how components should test out (I'll definitely report back if I do). I do appreciate all the advice though. If someone here is interested in the project I'd be willing to sell it for a good price.
Bretterson:
Ok, so, I did get another one. Same unit, but four years newer. I pulled up the datasheets, put the units side-by-side and checked the six relays, every MOV, and some of the capacitors in that area. I couldn't find any shorted MOVs and the relays seem to be in the correct position without power applied; I still have to test the relays with power. So far the only issues appear to be the cap at C53 that leaked substantially and the cap at C8 has the slightest bulge on top.

I think I will spring for a DC power supply. While I don't see myself using it much, there are times where I've wanted to test something I didn't have a power supply for and this way I could test it to know whether it's worth buying one.
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