Re: APC UPS units - troubleshooting

So sorry about the head ache. Take care of yourself. Absolutely will buy the beer when I get to Prague or you get to California. P

Re: APC UPS units - troubleshooting

At 24v in, I thought it was a little high but within range of the regulator's capability. I have been learning how inefficient these chips are especially when the input and output voltage is large. I pretty much decided that there was a small on-board transformer supplying 4 diodes to rectify the AC and that was it. If there was a mechanism to reduce or fine tune the input voltage to the regulator, I couldn't figure out where it was. You mentioned how crude these things were in a previous post and I'm inclined to agree. (Which in my case isn't...

Re: APC UPS units - troubleshooting

After recapping I started wondering if I wasn't getting charging because of a flakey 7815 as the old one looked as though it had gotten hot. I replaced it and it's charging now! It gets pretty hot when it starts charging so I added a heat sink. As battery voltage comes up, it gets less hot. Still not clear if there is something defective upstream causing the heat other than the inherent inefficiently of these linear supplies, but I buttoned it back up and we'll see. You may be able to see the heatsink in the attached photo. Paul...

Re: APC UPS units - troubleshooting

Definitely no inline diode from the transformer. I'm certainly learning as I go.

Re: APC UPS units - troubleshooting

I think I can answer my own question. It looks like it could be a center tap but I'm not clear why it would be on the positive lead.

Re: APC UPS units - troubleshooting

I'm still waiting to receive the filter cap for the 15v linear supply but I have a question related to UPS design theory. I have 15.1v at the output of the 15v voltage regulator which is all good.

The positive battery lead comes from the transformer. As far as I knew, you can't use a transformer for DC. How is this part of the charging circuit working? I understand the basic linear supply with bridge rectifier/voltage regulator chip/blocking diode, but the transformer has me stumped.

The negative lead comes from the...

Re: APC UPS units - troubleshooting

Thank you! Bhemot, I've replaced 8 of 10 electrolyics so far. I'll replace the last two in the next couple of days. It's good to know that some designs do charge from the SMPS. This unit was, in hind sight, probably a good starting point. At least I recognize the components in a full wave rectifier PS. SMT would seem to make repair considerably more challenging. I'm vaguely following so far. As long as I don't need to do anything with an SMT device, I'm happy.

Re: APC UPS units - troubleshooting



I think this may be the key to a problem I'm having with the charging circuit on an APC BE500R. I've taken this device on as a science experiment rather than to save it; it's a mostly worthless device but what better to learn on? I'm $25 into this.

I'd surmised that charging wasn't derived from the switching supply; the inverter is working fine with an externally charged battery. I'm very excited to learn that this positive regulator is likely a place to begin looking! Nothing on the board looks blown, but the LM78M15...

Re: New Members - please post your introductions here

Hi all. I'm Paul from Northern California. I've dabbled in electronics for many years but have much more time to play lately. I built kits as a kid and lately have been working with Arduinos and Raspberry Pis. I bought some cheap APC UPS lately to mess around with and one isn't charging. I'm going to try and figure out why.