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post #4 of Old 03-27-2005
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Inverters and AC Transfer switch

Hi, Paul - hope the season''s changing quickly for and you get to leave work early every day.<g>

I think there are two kinds of issues raised by your question. Most of today''s larger inverters have a built-in AC sense circuit, which allows one to leave the inverter (or inverter side of the inverter/charger)energized for instant AC use, should shore power (or generator power) be interrupted. E.g. on our Freedom 10, I can unplug the shore power cord and there won''t be a nanosecond''s blip on anything pulling AC...not that this is a good practice.

However, there is a second issue which has to do with what you power from your AC panel; I think this is partly what you are concerned with. You can either feed your incoming AC line VIA the inverter and then on to the AC Panel, or you can feed it first to a transfer switch. The reason you would choose to do the latter is that you may have some AC systems on the AC but your inverter can''t handle...and so these systems have to be wired to accept shore power but not inverter power. This is the more idiot proof choice...sort of. The wiring becomes much more complicated and one can also argue that keeping wiring simple precludes problems, too.

FWIW we chose to keep it simple and power the panel VIA the inverter. Normally when on shore power, the inverter sense circuit is kept off; if we lose AC power then we just momentarily lose power until I troubleshoot why. Since our boat is relatively simple and we have no AC generator, we only have two systems that the inverter would choke on: hot water heater and HVAC. Our Freedom inverter, like all the rest, has circuit protection and, provided it works, the inverter pops a breaker if it''s called on to do too much. Since I depend on breakers for lots of other things, it seemed reasonable to me to count on one in this case, as well.

I found the Freedom installation manual to discuss both these options; I haven''t regretted the choice we made.

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