question

bruce32466 avatar image

what is the correct fuse size for a 24/5000/120 multiplus

Good morning all. I have a multiplus 24/5000/120 going into a battery protect 220 then into a 300 amp fuse and then into a Tesla 5 KW battery module. Maybe I'm doing the math wrong but as I understand 300 amps x 24 volts should be good for a 7200 watts?

If I over load the AC side of this unit, will that cause the issue?

Next question... Is the 220 battery protect adequate for this setup?

Thanks

MultiPlus Quattro Inverter ChargerBattery Protectinstallationfuse
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3 Answers
Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

Hello @bruce32466, a few things:

First, you must not connect a MultiPlus inverter/charger (or an inverter alone, for that matter) to a BatteryProtect. This is a strictly forbidden connection and will damage your system. Please review the BatteryProtect user manual for allowed connections.

Second, be aware that the Tesla battery you are using is not Victron-supported, and any damage to it or any components connected to it will not be covered by Victron's warranty. Also be aware that you must have a BMS on the system to help protect that battery from thermal runaway. Tesla batteries are not stable like LFP batteries. I strongly encourage you to reconsider using that battery; if you do proceed, just be aware that you are doing so at your own risk and that usage of a used, unstable, unsupported battery is not recommended.

Third, for fuse sizing please see your user manual, specifically the table in chapter 4.2 "connection of battery cables", in which both the minimum cable gauge is specified as well as the DC fuse size.

Finally, per your last question see above: the BatteryProtect MUST NOT be used here. This is very very important. I strongly encourage you to consult an experienced, reputable DC systems installer who is familiar with the Victron environment to help you reconfigure your system in a permitted manner.

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bruce32466 avatar image
bruce32466 answered ·

Just to be clear the 24/5000/120 is the DC load on the battery protect. EDITED Ithink I get it! For the charging of the battery, current is flowing the wrong direction as the battery protect has an in and an out which I didn't give a thought to.

As for the Tesla battery, I have low and temp sensors along with low and high voltage sensors with 24v relays that disconnect the battery via battery protect should any one get out of range (well tested and works=). The Multiplus is programmable and allows for proper charging. I understand that the BP is under rated for the 400A continuous load but couldn't find anything else and didn't really plan on putting that much load on the inverter. do you or anyone else have a better option to automatically disconnect the battery?

Thanks.

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Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@bruce32466, yes, you've got it as to why the BatteryProtect cannot be used on an inverter-charger, because of the reverse current... Likewise, however, you should not use one on a regular inverter because the inverter will trigger an E3 short-circuit error that will, whether quickly or over time, damage the BP's logic.

As for low-voltage shutdown, why not just program the Multi to shut down at your desired v? That's what the setting is there for... and also why the BP wasn't designed for this use, because all Victron inverters and inverter/chargers already have a user-configurable LV shutdown built in.

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