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Converting a 24V alternator with an inverter in a 230V generator for a multiplus II 48/3000. To good to be true?


Still designing, came onto an approach which seems to me almost to good to be true (in my case), so I have the suspicion I make a mistake. Can you enlighten me?

The engine of my truck exists with 24V 35/55/80A alternators, so I assume that on the 80A model I could use about 50A (so roughly 1000W) without impacting the core of the truck.

I would prefer to run my "ESS" on 48V as it makes technically and financially most sense.

Now I could run 24-48 DCDC convertors, but to get to 25A on 48V takes 3.

But I could also run a 24V inverter and use it to convert my 50A spare of 80A 24V alternator in a 1000W 230V generator, which I connect to the ACin of the multiplus. In order not to stretch my alternator, and leave my truck stater batteries alone, I need a multiplus where I can set a very low limit on the ACin, only the 48/3000 model with limit minimum of 4.3 A stays in the 1000W ballpark (5000 is 6A). If I put a Cyrix 230A between alternator/starter battery & the inverter which I can program a bit, I should be able to make sure the invertor only kicks in when the engine is running. As the inverter can be rather simple, the 24 1000W (or let's say 1500W to be safe), can be a more plain (cheaper) brand as Victron. Or do you see a benefit of using a Phoenix

Fringe benefit, I can boost the AC out 2400W of the multiplus to 3400W (or about) by running the engine, and while I drive my base equipment runs on the alternator, only using the mutiplus/battery/solar for powerassist , and for charging my living batteries with whatever is spare of the 1000W.

When connecting to a landline (or other 230V source), I disconnect the inverter and replace it with the landline, the UPS function makes this transparent on the ACout side.

Eventually I can add a low power 230V 24V charger to AC out, and use that to maintain the truck starter batteries during longer stops (e.g. think parked 6 Months between holidays). I don't risk to make a loop as when the engine runs, the charger will detect high voltage on the starter side, and quit charging.

I would put a CerboGX to tie stuff together, and it seems to me I could use that to eventually add a temperature sensor on the alternator which the GX could use to kill the inverter, e.g. by opening the cyrix.

Looking forward to your views, spend many hours reading, but only experience makes a master, and that I lack.

Many thanks


UPDATE: A potential weak point (to be checked in real life) could be the alternator overheating when having to deliver the 1000W with the engine @ idle => low rpm => low cooling => it gets too hot and brakes. In the this setup it seems the throttling of the 1000W could only be done, by cutting ACin (4.3 A being the minimum limit) on the multiplus or switching the inverter on-off (limit it to e.g. 500W makes no sense it seems to me, as this gets below the multiplus threshold) . This would be beter manageable in a charger based system, where you could throttle.

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If you use a relay on the remote switch input on the inverter you could control the inverter from an oil pressure switch to ensure it only operates when the engine is running.

I can't see why your plan wouldn't work, you might have to allow for some inefficiency though.

Another way to charge 48v in this situation is to add a 48v alternator and keep both systems completely separate.

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Thank you for your input.

dedicated 48V alternator would indeed be an option, but I cannot assess cost & feasibility. And I would still need the inverter to boost AC out, to offload the ESS system. Good side would be to be able to move to +-1500W available @ alternator side (extra 80A 24V or 40A 48V alternator) so I can switch to 48/5000 multiplus model which more cost-effective as I could use the extra muscle over time.

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