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dion-patelis avatar image

Minimum specification for Phoenix 24/5000 inverter.

Is the minimum 400Ah 24v pack recommended in the manual for the Phoenix 24/5000 inverter based on lead acid battery chemistry?

Would I be correct in assuming that as LiFePo4 chemistry has more than double the usable energy of lead, that a 200Ah 24v LiFePo4 would suffice (with a BMS of 1C continuous / 3C for 1s burst) ?

Phoenix Inverterbatterybattery capacity
2 |3000

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2 Answers
Alexandra avatar image
Alexandra answered ·

@dion patelis

Yes the manuals usually refer to the lead acid based systems. And lithium can do much more than lead acid.

If your bms can give the full fault current to allow the inverter to shutdown without catching on fire then it is ok for use.

So in your case 5000÷ 24v = 208A bms ability for continuous running. Usually a bms will allow the overload fault current if you match the nominal continuous. Then make sure the cells you have chosen will also be ok with the current as well.

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dion-patelis answered ·

Hi @Alexandra,
Thank you for the reply. Yes it appears I've made a mistake in my calculations as I was looking at W instead of VA. It appears I need to add some batteries in parallel.
Just wondering if you know how long the 10Kw peak power on the Phoenix lasts for as the BMS on these batteries does 3C for 1s?
For this 10Kw burst I think I'll also need breakers rather than 100A Mega fuses on the batteries as the fault curve says the fuses blow at about 0.8s at 3C.

20211224_1241_wiring.pdf


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@dion patelis

Understanding overloads there is a video here. Its a long one. But is dependent on a number of factors like battery bank voltage sag and heat derating. The video explains best.

But really if you have sized your loads under the peak draw at the max 5000VA of the inverter you dont need to stress.

The fuses blowing Victrons ones are a bit special I have found. There is a guy who demos them here vs others.

We usually size them for the nominal max load. Not had one blow yet. I am not a fan of breakers on batteries, basically too much protection can also cause issues. But that is up to regulations or your preference. Maybe take a look at wiring unlimited linked at the end of the article so you can analyse your design idea.

Thank you for the info @Alexandra.

The video of the fuse tests rather concerns me as a few hours later I received 15 of the Victron Mega fuses in the post. I hope that was just a bad batch. Victron does not have any fuse blow graphs for these fuses on their product page like BlueSeas does. It seems a bit odd as everything else Victron is nothing but the highest standard from what I've seen so far.
The video by Johannes is also excellent.

As the first comment under the "Fuse test" video says, a 100A fuse is not supposed to blow at exactly 100A it should be able to carry 100A forever (if the environment is not to hot) and blow at some point above 100A depending on how much more and for how long.

In my opinion it is more concerning that the others blow at exactly 100A and I bet they will blow below 100A if you pull 80 or 90A for a while.
Those will also blow at the inrush current of inductive or capacitive loads.

A fuse is a cable protection, it protects the cable from over-current and short circuit.
The same is for your AC breakers at home. A 16A breaker is not opening at 16A and also not immediately at 17A or 20A. A 16A B (standard in Germany for normal home circuits) breaker can carry 1,13–1,45 times the current (18-23A) for 1h before breaking the circuit.
The short circuit cut-off will happen in less then 0,4s if the current is 3-5 times higher (48-80A).

For the 24/5000 Phoenix I would recommend a 200A fuse.
4000W continuously output power at 25ºC are 166A + conversion losses at the battery.
Then you have to use a wire that can handle 200A continuously depending on the length of the wire.

dion-patelis avatar image dion-patelis Matthias Lange - DE ♦ ·

Thank you @Matthias Lange - DE and @Alexandra

I am using the Victron 200A fuses to protect the cable.

The cable as per the manuals recommendation for closer than 5m.
2 * 50mm^2 cable for the negative and for the positive (i.e. 100mm^2 total wire cross section). It is also tinned as this is a marine environment with 400+ strands. A 200A fuse per cable.

Good to hear you're both satisfied with the Victron fuses.

It is still interesting that I can not find fuse curve spec sheets available. It would be nice to know exactly how long they can handle high inrush currents for. Might you have a link to one please?

@dion patelis

In rush current means just that. The initial current drawn by the inverter powerpack during initial connect of an inverter system with its battery. So more than a few seconds but less than a minute.

I have not looked for a datasheet. I dont think there is one publicly available.

Most of the time fuses blow from wire short circuit. Curve not needed to be known then ;).

Thank you.
gonzalor avatar image gonzalor Matthias Lange - DE ♦ ·

Hi , I think that the 400amp fuse is recomended because Peak power (W) (10000 )/V (24)= 416 amps

@dion patelis

Not sure what concerns you with the Victron. Their ratings are what they handle continuous running. They are my go to even on non victron systems.

Their manuals cover the correct sizing. Use the recommended size of their product and it is sorted. They also don't nuisance blow when some daft person sustains overloads they system or from inrush currents.

Am on board with Matthias here on all the points. The fuses are there for the cables.