- Samles SSW2000 inverter early limit - 1 Update
| legg <legg@nospam.magma.ca>: Nov 06 11:16AM -0500 I've got an SSW2000 repair that seems to be turning into a science project. The customer bought it cheap off Kijiji. It didn't 'go'. I found all 10 of the 30A automotive fuses blown, suggestting that the last thing done to it was a reversed battery connection. None of the DC inverter fets were damaged - This section proved to run when a normal downsteam load was present. The two main HV bulk caps were dried out and had vented oton the wrapped heatsink. This over a long enough time period that the vented material had collected air fluff as it dried.A small spot of vented material had been deflected onto the LV driver control board, bridging board vias and requiring scrubbing w alcohol to remove. One side of the inverter bridge was shorted through the switching fets. When replaced, the recapped inverter ran normally under lighter loads (below 500W). I might mention that one of the unit's fans was dead, as well. There is a small visible nonlinearity in the negative-going sine output 'increasing' edge, which looks increasingly like undamped response as load increases. This (negative generating pwm) was the side of the bridge that had failed previously. At some point of increasing load, the negative going sine output flat-tops - coincident with the positive going side cutting out completely on its falling edge, then the unit latches off to an overload limit. I'm not sure if this performance is aggravated by the loading method - resistive through a variac, so any DC imbalance can result in largish mag current imbalance. Input to the low frequency AC limiting circuit seems normal, though it is designed with a ridiculously high impedance - a multimegohm RC filter from a 70milliohm sense resistor - possibly to cut down on C size. It floats on the swinging polarity of the negative bulk caps. Even some of my go-to diff probes leak enough to make this a 'hands-off' test point while in operation, but what I can see of larger signal stuff at 50:1 diff looks normal. There are no schematics available for the 3x control cct boards, which are basically 339s and 324s working with schmitt triggers and flip flops. Gate drive is optoisolated x4 with DC restored bootstrap power on each. LF AC reg (tl431)and fault signals are optoisolated A main board schematic is available on groups.io in Electronics101. This shows that any control cctry components on the main board are basically concerned with fan control or external comms. Red detail indicates modifications not present on production (this) units - again mainly fan control. http://ve3ute.ca/query/Samlex_SSW-2000_main_board_schema.pdf Any ideas or similar experience out there? RL Housekeeping supplies are reverse polarity protected, simple and solid. AC voltage output LF amplitude is well regulated. |
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