UPS and inverter questions

[davmax]

Re: UPS and inverter questions

Sorry, I must not have been using my head. U2 is L7812CV, a voltage regulator. T2 is the current sensing part of the circuit, the transformer is like 300 to 1 or something like it.

Probably should take a picture so you can see what the boards look like.

Well that solves the U2 part, apparently a 12Volt source derived from the converter.
Pictures are good and clearly identify T2 & T1(this looks like a high frequency ferrite cored transformer). Yes I included T2 in my evaluation of signal paths it would not represent much voltage drop in the load circuit.

Now remains working out your current APC UPS and why is has a block of three MOSFETs.

[starfury1]

Re: UPS and inverter questions

Seems my post must have got lost or I didnt hit the post button
...anyway just made mention it uses a SG 3525 A
(IC16 or 18) old chip

Thread has moved on a lot since then and Don't know if its already been discussed

[davmax]

Re: UPS and inverter questions

Thanks Starfury. Yes you did draw attention to that PWM chip. This seems to indicate a sinewave UPS.

[andrew77]

Re: UPS and inverter questions

OK, here's a rough schematic without any control circuits, and I wasn't sure what else not to include. It should give an idea of what's going on.

[andrew77]

Success

I've got one working now! There was a shorted SMD transistor(2F) Q35 that was causing it to not stay running. I robbed the transistor off the other one. Now it stays on.

I guess I have to fix the other one now. Thanks everybody for helping me solve this problem.

[davmax]

Re: UPS and inverter questions

Well done. You found the faulty transistor.

Also that diagram is sufficient. So the Three 94-2358 transistors are for charging the battery. It looks like the inverter only supports the load when input AC goes. Switched in by RY4. Certainly a similar design to the previous 150W job.

The burned 94-2358 points to a problem in the charger circuit/control. It would seem that F1 blew witha back flow of current from the battery. Presumably the MOSFET short.
Now you have to establish if the charger is working. You can now start to isolate circuit sections. ie a charged battery will run the inverter without F1, establish which of the two next stages is not working. Is there the right voltage at the input to the output inverter stage? ie across C50A.
and so on.

Making real progress now.

[andrew77]

Re: UPS and inverter questions

I guess it was a little too soon. It doesn't want to run from line power, but it to seems let you run the inverter as long as you want without line power. When you try to power it from the line, it shuts off and flashes the "Battery Outlet Overload" and the "Replace Battery" lights simultaneously. When you start it with the battery, then plug it into the line, it sparks a bit at the plug and runs about a second and shuts down.

Must still have a fault somewhere. Guess I need to plug it in while it's all apart. Might be the only way to really trouble shoot it.

I did notice after I took it back apart, the heatsinks for the low voltage side were warm, but the high voltage side was still cool.

[davmax]

Re: UPS and inverter questions

I guess it was a little too soon. It doesn't want to run from line power, but it to seems let you run the inverter as long as you want without line power. When you try to power it from the line, it shuts off and flashes the "Battery Outlet Overload" and the "Replace Battery" lights simultaneously. When you start it with the battery, then plug it into the line, it sparks a bit at the plug and runs about a second and shuts down.

Must still have a fault somewhere. Guess I need to plug it in while it's all apart. Might be the only way to really trouble shoot it.

I did notice after I took it back apart, the heatsinks for the low voltage side were warm, but the high voltage side was still cool.

Did you have a load on the inverter? If not the output heatsinks will be cool.

No running on input power . Check relays, charger circuit. Do batteries test as good?

[starfury1]

Re: UPS and inverter questions

OK I haven't read throughly through this post and like I said dont know much about them


just re reading post
Seems the charger isn't working if you cant get it to function with mains

But I'll leave the rest below anyway might twig you to something

Really just stating the obvious; and probably useless but here goes anyway

It sounds to me as if whatever circuit determines "switch over" from mains to battery
is still not functioning correctly.

Since you have found on fried trannie possibly more exist.

A faulty open circuit one for example my be masked by the diode action of another transistor semiconductor if you are checking them in circuit.
(unfortunately removing SMC trannies is a bugger)

So I would try (if you haven't already) to workout how this circuit functions...how doest it know to "switch over" "whats it using to sense mains input"
I assume its using a relay as switch over.

I think there was mention of an issue with the "charging circuit" for the batteries so "how does this tie in with the switchover circuit"

it can't charge them if there is no mains , so I an guessing this "charger circuit" must come it to play only when mains is connected (sensed)
So there must be some kind of signal to trigger this.

perhaps try fully charging the batteries and putting them back it. and see what happens.

I am guessing the battery charger circuit has to have some kind of sense to determine battery state.

Its as davmax said you need to isolate the building blocks and look at the interaction between them and check as best you can if each block is functioning as it should

Trouble is once you have feedback of any kind it can be a chicken and egg thing.
So you need to look at the control signals and try and work out who's the boss and who's the worker

But no guru and if you already been through this...then DOH!

HTH anyway

Cheers

[andrew77]

Re: UPS and inverter questions

I had a 60 watt lamp as a load for about 30 seconds. I know it's not fully charged, but it's at 25.2 volts. The other battery pack is at 23.0 volts. The batteries seem to be good. How would I go about testing them?

I need to plug it in while it's in pieces, so I can check the charging circuit, right?

Something strange about when it's plugged in to the line, the outlet for UPS power puts out 26 volts. The other outlets on it run straight to the line, they're surge only.

Thanks for all the suggestions, it gives me a place to start looking.

[davmax]

Re: UPS and inverter questions

I had a 60 watt lamp as a load for about 30 seconds. I know it's not fully charged, but it's at 25.2 volts. The other battery pack is at 23.0 volts. The batteries seem to be good. How would I go about testing them?

I need to plug it in while it's in pieces, so I can check the charging circuit, right?

Something strange about when it's plugged in to the line, the outlet for UPS power puts out 26 volts. The other outlets on it run straight to the line, they're surge only.

Thanks for all the suggestions, it gives me a place to start looking.

The batteries should be at least 24 volts, one seems OK. 23 volts either means lack of charge or even one dead cell. If the batteries are old there could be a problem. Best test is to charge them up independently if you can and are without the inverter charger operating correctly. When charged see how well the inverter runs without power.

With those lights coming ON it looks like you may not be charging the batteries. Charging can be checked by insert the multimeter set to 10-20 Amps in place of F1.

Must check what the relays are doing. Look for non operation, no contact/circuit even though the realy operates or even a stuck/ welded contact.

[PCBONEZ]

Re: UPS and inverter questions

23v sounds too high for a dead cell on a 24v battery.
Probably just needs charged.

[davmax]

Re: UPS and inverter questions

PCbonez it is very hard to tell. We do not know the state of charge. It is a possibility that one cell is down only if the other cells are well charged. At this stage all options are open. It most probably is low charge yes.

Charging and testing the batteries under load as suggested will clarify.

[PCBONEZ]

Re: UPS and inverter questions

Cells on lead-acid batteries are 2v per each.

But I agree it's hard to know.
(And I'm assuming they are lead-acid type.)

[starfury1]

Re: UPS and inverter questions

just on batteries

There has been posts of screwed batteries and thinking on it I am guessing this thing has been used somewhat
(batteries do have a finite life)

I think if you can then do so

At lest then you will know they are presenting the correct situation to the charger circuit

So yeah good point, clear then as a possible cause of issues.

both the warning lights are saying batt OL and Replace Batt when the mains is on
so maybe they are telling the truth.

[andrew77]

Re: UPS and inverter questions

Here is the exact batteries being used: link

On the low battery, one is 11.44 volts and the other is 11.80 volts.

Would it be alright if I use this charger on them? link

So far as I can tell the relays are not welded and seem to be working. I need to do more looking. I swapped transformers just to be sure that the charger transformer wasn't shorted. No difference.

I'll keep looking.

[davmax]

Re: UPS and inverter questions

Here is the exact batteries being used: link

Note the values of this Gel cell battery. eg voltage of two batteries should fall to 24 volts after a short load. Before that the float voltage is 27 to 27.6V and full charging should pull up to 28.8 -30V.

On the low battery, one is 11.44 volts and the other is 11.80 volts.

a little uneven , but as said charging and using is best test.

Would it be alright if I use this charger on them? link

The link comes up with a black background, no charger? Note that max recommended charge current is 2.16A this prevents damaging gas pressure in the sealed battery.

So far as I can tell the relays are not welded and seem to be working. I need to do more looking. I swapped transformers just to be sure that the charger transformer wasn't shorted. No difference.

I'll keep looking

The best method of finding the problem is electrical measurement when operating. Great care with voltages involved. From what you say the inverter works with battery so that part is hopefully solved. When input power is connected low output occurs. You need to measure the voltage starting from the output terminals and moving to the switch over relays to work out how this voltage occurs. It does seem to be switching because it is assumed that the battery under these conditions has not changed and the inverter can still operate. Somehow the switch to input power is not correct.

[andrew77]

Re: UPS and inverter questions

I get 180 volts at C50A while it's on. As I expected, I get battery power at C80.

RY4 is definitely not switching.

How do I check these relays in circuit while it is on?

[PCBONEZ]

Re: UPS and inverter questions

I have used that kind of charger with those kinds of batteries.
It works fine but mine has an ammeter so I can see what's happening.
Like Davmax said watch the charge rate.
If you go with that charger then set it at 2 amps.

[andrew77]

Re: UPS and inverter questions

If you go with that charger then set it at 2 amps.

I checked with my meter and it was charging at 2.25 amps for about 20 seconds and gradually went down. One of the batteries got to about 100 degrees when it was charging, and I didn't let it finish, since I didn't know whether or not it would kill it. The other battery went through the automatic charge and finished. Didn't even get warm. The one that finished is at 13.10 volts now, and the other one, after cooling off, is at 13.13 now. How long are they supposed to take to charge? 3 to 4 hours?


I found a mistake in my diagram after unsoldering the relay RY4. I had the high voltage output of the inverter going to only one side of RY4. RY4 doesn't have welded contacts and seems to be just fine. The logic part of the circuit must be telling it not to accept line power.

Here's the fixed schematic.