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climbon asked

Multiplus - Cooked

I have a Multiplus Compact 12/2000/80-50. It gave up the magic smoke. I've run it flawlessly for 18 months in my RV, including a 2 week trip we just completed. On our last night of the trip, we stopped at a rest area and I started my Honda EU2000 genny and plugged in so I could run my Air Conditioning for a bit. I've done this many times. The AC didn't respond and I heard a buzzing from the Multi, smelled the electrical ghost, and the Multiplus showed an overload condition. I switched it off. I wasn't prepared to dig into things 800 miles from home on our final night of the trip.

Now that I am home. I confirmed the Multiplus is burnt up. I confirmed the generator output is at 126 volts with no load (is that too high?). I intend to remove the Multiplus and reconnect AC power to try and troubleshoot if there is a short somewhere. I have suspicions my Air Conditioner may have something to do with it, it was acting up a bit the last time I used it, but I was thinking the thermostat was going out, but it worked. Maybe there was more to it...

Is there anything I should do before I completely disconnect the Multiplus? Any thoughts on where to look for a cause? I fear installing a new Multiplus only to burn it up again.

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MultiPlus Quattro Inverter Charger
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img-4092.jpg (209.1 KiB)
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7 Answers
ddickov avatar image
ddickov answered ·

Hi there just to ask have you matched your air conditioner unit start up load with the inverter, a single phase motor can draw 6 times it’s rated running value at start up and a three phase motor can draw up to three times it’s rated power at start up, I would maybe check the amperage the air conditioner draws at start up if it’s still running maybe could check on a grid connection if available, the multiplus compact will have a lower supply current at start up than the larger units I have a suspicion maybe the load is too great for a 2kva unit if you have a large air con unit I would seek advice from professionals as to which multi would power the air con with ease, air con units can draw large currents.

Hope it helps a bit thanks david

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ddickov avatar image
ddickov answered ·
No problem it maybe tho if you are say cooking and using power at 30a for a while then the air con kicks in it could be using up to well over the rating of the multi it will supply power at peak value I think for 30 seconds but any longer will go into overload, I would also double check all cabling sizes and connections are to spec as this can also cause issues, I would over size your next inverter to cope comfortably with the loads and ensuring this will greatly extend the inverter life.
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Kevin Windrem avatar image
Kevin Windrem answered ·

I have a Multi compact in my travel trailer with the same sized AC unit. I also have a 2000 VA generator. The generator and the Multi together would start the AC but it was a struggle so I added a MicroAir soft start. You hardly notice the compressor start now.

I highly recommend a soft start. It's $$$ well spent.

The damage I see in your first picture is not in the passthru path, rather in the inverter/charger core.

The flicker in the lights could be the shift between float and absorption voltage. It's likely the microwave presents a load which is not constant.

126 volts is typical of an unloaded generator and isn't high enough to harm the Multi.

Glad you got a replacement up and running. Hope it was covered under warranty.

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climbon avatar image
climbon answered ·

Thanks I will verify that. I thought since the passthrough is 50a and my whole camper is only 30a, that I would be fine. I'm not running the Air Conditioning from batteries of course, only run it when I am on shore power or a genny.

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climbon avatar image
climbon answered ·

I have now removed and bypassed the Multiplus and connected the camper to shore power. The air conditioner seems to be working fine on shore power.

I checked the spec on the air conditioner....It's on a 20a breaker. The whole camper is on a 30a main breaker. Air conditioner is 13,500 BTU. The air conditioner's compressor spec is 52 LRA. I'm not positive here, but if passthrough on the Multiplus is 50a and the air conditioner is rated at 52 LRA, I'm likely exceeding the passthrough spec, and is likely the cause why the MultiPlus failed.

Am I interpreting this correctly?

I don't understand why a 20a breaker wouldn't trip though...?

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pwfarnell avatar image pwfarnell commented ·

Have a read of the following

Understanding trip curves

Most trip devices do not instantaneously trip at their rated capacity, they have a curve where if they are just over the rated capacity they will take some time to trip and for 3 times rated capacity will trip in 5 seconds and for higher multiples of the rated current trip very quickly. This is to allow for start up surge currents of inductive loads or motors. There are various trip curves to allow for higher multiples of start up current to not cause a trip.

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ddickov avatar image ddickov commented ·

Locked rotor amps and it tells you how many amps are motor will draw when it's not allowed to spin. It can be useful to know for troubleshooting purposes or when choosing the overcurrent protection for the motor.

You can't really convert from LRA to running amps because it will be different for different motors and operating conditions. The LRA is usually five to ten times the running amp rating.


To match the amperage properly thanks david

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ddickov avatar image
ddickov answered ·

If you can download the victron app and the guides the videos online are also superb, it will help you determine the correct size of system required for your needs and if in doubt always get it check by an electrician to verify it before switch on, I got mine checked and all was good to go after a couple of adjustments. I would always say go for the highest inverter rating you can afford bearing in mind the standby current that’s drawn by the larger inverters has to also match your battery bank to ensure it can cope with the demand and supply loads no problem. I hope you get it sorted.

Thanks david

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climbon avatar image
climbon answered ·

I spoke with the dealer where I got the batteries and the rest of the system about sizing the new inverter. I was told the 12/2000 is within spec., but the 3000 might give me better reliability over the long run. I just couldn't justify the 3000 since it would require another battery and I don't really need the additional capacity. So I went with the 2000 again. It's installed now and we are out camping again for a few days. I haven't tried the air conditioner yet. But I noticed an odd behavior with the microwave on shore power. For about 2 or 3 seconds when the micro starts, the light flicker, more like strobe actually, then it runs fine. It does not do this when I run the microwave on battery power alone (off shore power). Micro didn't do that on the old Multi...

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ddickov avatar image ddickov commented ·
That’s good you got another one sorted hope it goes well :-)
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