October 5, 20223 yr Good day, I have replaced the batteries on my Axpert. Everything turned on. Then I added loads systematically, lastly my pool pump which has always ran fine. The inverter then turned off and want start up. I have checked the battery voltage and when the inverter is not connected it reads 53V. When I connect them to the Inverter, the voltage drops to around 5V and then slowly climbs to 8V, but the inverter doesn't switch on. Has anyone come across this before?
October 6, 20223 yr 14 hours ago, doodsangel said: I have replaced the batteries on my Axpert. From what old battery to what new battery? What model Axpert? 14 hours ago, doodsangel said: When I connect them to the Inverter, the voltage drops to around 5V and then slowly climbs to 8V, but the inverter doesn't switch on. Presuming that this is a measurement from a trusted multimeter, it means that there is something drastic wrong with the new battery (modules?), or the wiring or protection (fuses, pre-charge circuit if any, breaker, etc). Certainly, no nominally 48 V battery should ever drop below about 44 V even briefly. If these are 4 nominally 12 V lead acid battery modules in series, check each module, it seems likely that one is dead on arrival. It might even be reversed. It is possible that the modules are just nearly flat and need charging, but 8 V total is really bad, and they almost certainly won't recover from that. If the new battery is a lithium battery module, it could be that the BMS is disconnecting the battery to save a cell going low voltage or similar. If so, it might just need a few hours of charging before you connect any challenging loads. If it's a single small lithium battery, it may be too small on its own for a load like a pool pump. Lots more details, please.
October 6, 20223 yr Author Thank you Coulomb, I was wondering if it could be some of the mosfets that maybe have gotten damaged, referring to this post: The multimeter is definitely trusted. I have it on the terminals and reads 53V and as soon as I switch the batteries in, the voltage drops. The Axpert does have a bit of mileage as we had it for 8+ years. and it worked perfectly two times. Both times as soon as we switch the pump in, it dropped. Last time was a permanent drop. The batteries as are 4x Blue Nova 22ah Lithium in series. Previously we mostly used it to carry us through loadshedding during the day, so (don't laugh), we were running it with 14x 3.7V 3000mah 18650 batteries, but with loadshedding increasing as well as fuel price, it was no longer sustainable not to be able to run it at night. Something is definitively amiss. An therefore, before making the post, I removed and rewired everything and checked every fuse (not inside the inverter) but all others externally, protection etc. And when swithcing batteries in, the load is also currently not placed on the inverter. I see you mention pre-charge circuit? What is and what does? Thanks in advance.
October 6, 20223 yr Author Hi Coulomb, So I charged all the 3.7. Get a good 55V reading. Put it on inverter and it is still dead dead. Sorry, the inverter is an old RCT Axpert Model: RCT-AXPERT-5k Rater Power 5000VA/4000W Edited October 6, 20223 yr by doodsangel
October 6, 20223 yr 8 hours ago, doodsangel said: I was wondering if it could be some of the mosfets that maybe have gotten damaged, It's possible. Your model probably has the reverse battery protection, making it impossible to check without opening it up. 8 hours ago, doodsangel said: The batteries as are 4x Blue Nova 22ah Lithium in series. They sound very small for running a pool pump, let alone starting it. Are they allowed to be operated in series, and if so, is 4S allowed? Many lithium battery modules have in the fine print that you can't operate them in series. If the battery modules can withstand 2C for short term loads like starting motors, that would be 44 A x 50 V = 2.2 kW. Call it 2 kW at the inverter output. If the start-up surge is 5x the run power, that limits the pool pump to around 400 W. What is its rated power? My guess is that the BMS on the battery modules has disconnected under load, and this has resulted in damage to the inverter and/or the battery modules (e.g. the first one to disconnect may have become reverse biased, and that might be damaging, and is possibly the reason that some modules aren't allowed to be connected in series). With the 18650 battery, which I assume has no BMS to disconnect it from the inverter, is there a high current when it switches on? Does the display show anything at all, even briefly? I think you'll have to do a complete repair, either yourself or in a workshop. 8 hours ago, doodsangel said: I see you mention pre-charge circuit? What is and what does? That's to limit the current surge charging the inverter capacitors when you first connect a battery to the inverter. With a lithium battery, usually the battery BMS will limit the maximum current, obviating the need for pre-charge. But with say a lead-acid battery, it's a good idea. I suspect that most people don't use one, and I shudder to think how that affects longevity. In my system, I have a lithium battery but the BMS doesn't disconnect the battery from the inverter via MOSFETs. A 3.3Ω (from memory) high pulse power resistor is used to limit the initial current, then after a second or two, a contactor shorts it out. That limits the surge current to a manageable 15 A or so. Without the pre-charge, the surge current would be well over 1000 A, depending on the battery. That surge current is very hard on the capacitors and whatever makes the final contact with the battery (breaker, fuse holder, whatever).
October 6, 20223 yr @Coulomb Could you perhaps COMMENT on why some distributors insist you cannot run their 12V lithium drops ins in parallel. The series side one can understand if any one would disconnect via BMS.
October 6, 20223 yr Author 1 hour ago, Coulomb said: I think you'll have to do a complete repair, either yourself or in a workshop. With my limited electronics knowledge, I took the plunge in the meantime to check the Transistors. IN the picture I have numbered them 1-9. These are the readings: #1-4: GP40660 GE: 49.5k GC: 700k CE: 650k However, that is initial reading. The longer you hold the meter there, the more the number climbs. SO this feels a little off. #5: IRGP47500 GE: 46.6k GC: 1095K CE: 1175K This one appears a little off #6-9: IRGP47500 GE: 22 GC: 185K CE: 185K These were the only ones measuring apparently what is expected. D13 +-: 860k -+: OL
October 7, 20223 yr 14 hours ago, Scorp007 said: COMMENT on why some distributors insist you cannot run their 12V lithium drops ins in parallel. No, makes no sense to me either.
October 7, 20223 yr 13 hours ago, doodsangel said: #1-4: GP40660 I assume that the last character is actually a "D" letter rather than a "0" digit: GP4066D. CE: 650k For collector to emitter, you should use the diode range on your multimeter, rather than the resistance range (despite what the service manual might say). You should get a high reading in one direction, and about 0.4 V with the negative multimeter lead on the collector. This applies to all 9 IGBTs, and all the MOSFETs as well (using drain and source in place of collector and emitter, respectively). Quote However, that is initial reading. The longer you hold the meter there, the more the number climbs. SO this feels a little off. That's due to large electrolytic capacitors gradually charging. Totally normal. Quote #5: IRGP47500 Similarly I expect IRGP4750D. Quote GE: 46.6k Yes, this is the buck transistor; it seems to have a 47k gate to emitter resistor, when the others have a 49.9k resistor. Quote GE: 22 This one is so low because the source is a transformer winding. Quote D13 +-: 860k -+: OL Similarly, you should use the diode range. You should get about 0.4 V with the negative (black) multimeter lead on the cathode (bar). A high value in the other direction.
October 7, 20223 yr 3 hours ago, Coulomb said: No, makes no sense to me either. Thanks for the input. So far I have not come across any technical guy that can give an answer why Mecer have a sticker on the 200Ah to this affect as well as quoting it on their Web.
October 7, 20223 yr Author 3 hours ago, Coulomb said: Similarly, you should use the diode range. You should get about 0.4 V with the negative (black) multimeter lead on the cathode (bar). A high value in the other direction. D13 Red Cathode, black Anode: 344 Black Cathode, red anode: OL Quote #1-4: GP4066D CE: 344 (black on collector) CE: OL reversed Quote #5: IRGP4750D CE: 346 (black on collector) CE: OL reversed Quote #6-9 IRGP4750D CE: 326(black on collector) CE: OL reversed Mosfets numbered from 1-16 with 1 closest to battery connection terminals. Quote #1,2,7,10,12 - 54W17WI DS: 406 (black on drain) DS: OL reversed Quote #3,4,5,6,9,11,14,15 - 54W17SI DS: 406 (black on drain) DS: OL reversed Quote #8,13,15 - 54W17DI DS: 406(black on drain) DS: OL reversed I have checked and the FUSE on the Anode of the battery connecter inside the unit hasn't burnt. Somewhere a powerup circuit must've gotten damaged. Edited October 7, 20223 yr by doodsangel
October 7, 20223 yr Author 20 hours ago, Coulomb said: My guess is that the BMS on the battery modules has disconnected under load, and this has resulted in damage to the inverter and/or the battery modules (e.g. the first one to disconnect may have become reverse biased, and that might be damaging, and is possibly the reason that some modules aren't allowed to be connected in series). Thanks for all your help. Your guess was 100% spot on. After all the checking and confirming that transistors and Mosfets are good, the wife sai, its been disconnected from power very long. She thinks with all the draining of caps, this would constitute a Cold Start, so close it and hook it up. As soon as I plugged it in, it fired up, but then I remembered I disconnected ALL cables, solar, loads everything, just battery connected. Which means I have to shut it down and get everything connected again. When I switched it on, it dead again. Waited a while, switched it on again and TADA. There was lights!
October 7, 20223 yr 5 hours ago, doodsangel said: D13 Red Cathode, black Anode: 344 Black Cathode, red anode: OL I'm presuming that the 344 represents millivolts, i.e. 344 mV = 0.344 V. That makes sense, except that you must have gotten anode and cathode swapped. All the rest look OK. But you know that now, since you've seen it working. 2 hours ago, doodsangel said: Waited a while, switched it on again and TADA. There was lights! That's great! Beware of high start-up loads. The BMSs may be a bit uneasy about having modules in series. You should be OK if the BMS never (or at least very rarely) has to disconnect due to overload.
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