Hi all,

Last night my 24V Mecer/Axpert 3kVA (SOL-I-AX-3MPLUS24) popped while charging from mains.

I known my batteries desperately need to be replaced, and last night the voltage was dipping quite low, even with only a couple of amps being used. So I plugged it into the mains to charge the battery and as usual the fans spun up and about 20 amps was being pushed into the batteries. A minute or two into charging I started to hear a slight buzzing should along with the fan noise that I had never heard before. Then pop, a flash came out of the right-hand side on the inverter and the trip switch for the plug tripped.

However the unit didn't turn off and didn't show any error code on the screen. I wasn't going to try charge from mains again, so I disconnected it from the mains and also switched off the breaker to the solar panel since I didn't know what would happen in the morning when the panels would get sun.

Overnight the battery voltages went very low and eventually the unit turned itself off. When I got up this morning I swapped out the deep-cycle batteries to some charged ones that weren't being used and switched everything back on again.

The unit turned on and did its start up sequences, fans on, inverter on and then into standby like I usually have it operating (I don't use the AC output much, so leave it in "sense" mode most of the time). I switched on the breaker to the solar panels and the batteries (which were already mostly charged) went up to over 28v as normal with 1-2amps coming in. But a quiet somewhat high pitched buzzing noise started inside and gradually got louder until the loudness stabilised, but the pitch kept varying up and down randomly. The inverter was still on standby, so pulsing and not running fully and the noise continued even when I flipped the solar breaker to off. There were no error codes on the screen of the unit. I switched off the whole unit and the noise still continued for a few minutes and then abruptly stopped. After leaving for a few minutes after that and then turning on the unit again, the noise did not start again and the unit seemed to be working fine.

 

So has anyone else had something pop in these units when charging from mains with this unit and what could it be?

Any explanation for the initial buzzing (I thought initially it was an inductor with a loose winding but now I'm wondering if it's a faulty cap)?

Is it safe to keep using the unit to charge my batteries and maybe run the inverter if I'm not going to connect it into mains again?

 

Thanks in advance!

3 hours ago, Lindsay said:

what could it be?

Most of the 24 V models have a separate AC charger. Usually, it's a flyback type circuit, with a multi-winding inductor (like a transformer but it can store magnetic flux in an air gap). I'd guess that the MOSFET or IGBT in that circuit has failed, possibly due to (a) capacitor(s) drying out.

3 hours ago, Lindsay said:

Any explanation for the initial buzzing (I thought initially it was an inductor with a loose winding but now I'm wondering if it's a faulty cap)?

It's really hard to guess, but if I had to, I'd go with the inductor. Or possibly carbon tracking on the PCB causing arcing, and you are hearing a subharmonic of the oscillator frequency (usually of the order of 20-40 kHz).

3 hours ago, Lindsay said:

Is it safe to keep using the unit to charge my batteries and maybe run the inverter if I'm not going to connect it into mains again?

Since the AC charger is totally separate, I'd say yes, it would be safe. Keep a watchful eye on it anyway, of course.

Thanks for the replies Coulomb.

Just to let you know what I did after my original post. As I said, I removed the 6 deep cycle batteries that were now very low voltage and connected 2 charged batteries that I had removed a few months ago since I suspected they were no longer usable. After the sun went down their voltages also dropped off quick. So I had to quickly put 2 of the 6 batteries I had pulled out the night before, that seemed to have the highest voltages after resting for the day, onto a separate 12V charger and once charged swapped them in. They seemed ok overnight, so then I took the 2 with the next highest voltages of the 6 and charged them the next day and added them to the array that evening. 

After going from 6 to 4 batteries the voltage is higher overnight, so it seems the battery bringing the whole array down was one of the 2 I've removed. I've charged these as well and will see on the weekend if it's just one of them or both that are dead.

I'm glad to hear that I can still use my unit, and I haven't heard that high pitch buzzing again so the unit seems to be working ok. I do plan on carefully opening it at some point to take a look and I'll post pics here when I do that. I gather it's out of warranty since I've had it over 2 years now.

Thanks again.