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3 minutes ago, nicknorman said:

Google doesn’t know what it is talking about. One problem with inverters is that they are constant power devices so if you want 3000 watts out (into a resistive load) you need 3000watts plus an allowance for efficiency in. Watts of course being current x voltage. If the voltage droops due to battery resistance, cable resistance, isolator resistance, connection resistance etc, the inverter compensates by taking more current. Which makes the voltage drop further, until the input voltage at the inverter is below the minimum and it trips.

 

if you plug your old kettle in and measure the voltage on the inverter input terminals, you’d find it drops below the minimum (say 10.5v) which trips the inverter. To drop 2v at 300A you only need 0.0066 ohms, which is not a lot.

Wrong my inverter is 2 foot away from the 6 x 140 ah LifePo4s the cables are very large it overloaded in seconds my 3000 watt inverter handled it easily and it was further away from the batteries 

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7 minutes ago, ivan&alice said:

So a 3000W inverter powering an LED and a 3000W inverter powering a kettle always use 3000W plus change for inefficiency? This is what I'm worried about - and why I want to size the inverter accurately to my load...

No, what I mean is that the load you place on it in terms of watts or va, has to be met by the 12v supply. So a 3000w load will result in 250A at 12v (inefficiency ignored) but if the voltage reaching the inverter drops to 10.5v, the output power will remain the same and current drain will now increase to 285A.

 

A decent inverter will use very little power when it isn’t powering anything, less than 1A. Which is why we leave ours on 24/7.

3 minutes ago, peterboat said:

Wrong my inverter is 2 foot away from the 6 x 140 ah LifePo4s the cables are very large it overloaded in seconds my 3000 watt inverter handled it easily and it was further away from the batteries 

You say “wrong” but it just demonstrates that you don’t understand the difference between w and va.

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4 minutes ago, nicknorman said:

No, what I mean is that the load you place on it in terms of watts or va, has to be met by the 12v supply. So a 3000w load will result in 250A at 12v (inefficiency ignored) but if the voltage reaching the inverter drops to 10.5v, the output power will remain the same and current drain will now increase to 285A.

 

A decent inverter will use very little power when it isn’t powering anything, less than 1A. Which is why we leave ours on 24/7.

You say “wrong” but it just demonstrates that you don’t understand the difference between w and va.

Nick you are wrong full stop victron rate their 2000 VA inverter at 1600 watts! Look at their data sheets and stop arguing yourself into a corner 

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3 minutes ago, nicknorman said:

No, what I mean is that the load you place on it in terms of watts or va, has to be met by the 12v supply. So a 3000w load will result in 250A at 12v (inefficiency ignored) but if the voltage reaching the inverter drops to 10.5v, the output power will remain the same and current drain will now increase to 285A.

 

A decent inverter will use very little power when it isn’t powering anything, less than 1A. Which is why we leave ours on 24/7.

OK, phew, thanks. So if that's the case, would you agree that the 2000VA inverter makes sense? I calculated that the 190A relay puts an upper limit on my load of 190A * 12V = 2280W, so I felt like this inverter fit nicely within a margin of comfort - but that was before this VA curve-ball. Should I rather look at a 3000 VA inverter - or would this want to draw more than my 190A current as it's presumably rated higher than 2280W?

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1 minute ago, peterboat said:

Nick you are wrong full stop victron rate their 2000 VA inverter at 1600 watts! Look at their data sheets and stop arguing yourself into a corner 

You still don’t understand the difference between w and va. Inverter manufacturers have a tendency to quote headline output power or va ratings as non-continuous ratings. Generator manufacturers do the same. If you want to contend that va and w into a resistive load are not the same, I can recommend some great websites explains how the Earth is flat and the Holocaust didn’t happen.

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1 hour ago, ivan&alice said:

Just checking - do you mean moving the red cable to here? This to me looks "better"...

Yes, That way the path through each of the three cells in a parallel group goes through two links. As done in the photo one cell has no links, one has two and one has four. Very small resistances will be enough to have large effects on the current flow and the cells not be worked equally hard.

 

I turned one of the blocks through 180 degrees compared to that photo, that way the interconnecting lead is short and doesn't have to cross anything else. The positive and negative connections are on the corresponding terminals at the other end.

Quote

 

image.png.4796c3404f74ebe5af0cf17ce68eaba8.png

 

Not to pass the buck but this is a photo that Jeremy sent me. He said that he'd make up the blocks with straps and end plates to compress the cells (which I didn't know was required!). I haven't taken delivery yet. he can't access his stock due to Covid unfortunately. Yes the price does seem good - he says the cells are a little older and not suitable for current draw > 200A such as for traction applications. I couldn't manage 200A if I tried anyway (maybe the starter motor?). Given the good price, do you think it would be outrageous to go for a 4p 4s configuration and get a whopping 640Ah? I want freedom to tinker and with 16 cells I could conceivably make a 24V or even 48V battery if I wanted to in the future...

I'd say that six cells are as heavy as you'd want as a single unit, so if you do upgrade, get them as four blocks of four, rather than two blocks of eight.

 

MP.

 
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29 minutes ago, ivan&alice said:

OK, phew, thanks. So if that's the case, would you agree that the 2000VA inverter makes sense? I calculated that the 190A relay puts an upper limit on my load of 190A * 12V = 2280W, so I felt like this inverter fit nicely within a margin of comfort - but that was before this VA curve-ball. Should I rather look at a 3000 VA inverter - or would this want to draw more than my 190A current as it's presumably rated higher than 2280W?

I had a look at the Victron blurb. They are a bit naughty because really, it is a 1600w inverter. It can supply up to 2000va with a non-unity power factor. But for a resistive load such as a kettle / heater etc it is limited to 1600w or 1600va (same thing).

This is still probably enough for your washing machine without heater, but for future provision (dishwasher, washing machine with heater, tumble drier etc) it might be more sensible to get a higher rated one that could manage at least 2kw. Perhaps it is a bad idea to size your inverter based on the current limit of the isolating relay. And when calculating input current for a given power, it is best to use 10v to allow for both voltage drop and inverter efficiency. Our inverter at 2kw takes nearly 200A, although less of course when the engine is running because the input voltage is higher.

 

Also to be honest, I am not a great fan of Victron, Mastervolt is better IMO. We have a Mastervolt 2500 which can run a 2kw electric kettle, a 2kw tumble drier, a compact washing machine with heater etc (not all at the same time, of course!).

 

Oh and electric kettles are good when cruising because they turn themselves off when they boil, unlike gas. And we can easily generate 2kw or more when the engine is running at cruising speed. We tend not to use the kettle when the engine isn't running, but we sometimes do. Although it takes 200A this is only for 3 minutes or whatever, not much in the way of AH.

31 minutes ago, peterboat said:

Nick you are wrong full stop victron rate their 2000 VA inverter at 1600 watts! Look at their data sheets and stop arguing yourself into a corner 

I see where your confusion arises. Victron do rate their 2000va inverter as 1600 watts. But really, it is a 1600w inverter that can supply up to 2000va when the power factor is not unity (inductive load etc). So you were fooled by the headline rating / name at 2000, when in fact it is really 1600.

Edited by nicknorman
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1 minute ago, nicknorman said:

it might be more sensible to get a higher rated one that could manage at least 2kw. Perhaps it is a bad idea to size your inverter based on the current limit of the isolating relay.

Sure, it just all seemed to fit happily into place around the 190A mark. Should I be worried about plugging in a 3000VA inverter into the isolating relay with a 200A fuse, or will I be fine as long as I never exceed a 3000VA AC load?

 

What would be the maximum current draw on the 3kVA Victron Phoenix inverter? https://www.victronenergy.com/upload/documents/Datasheet-Phoenix-Inverter-3000VA-120V-EN.pdf
 

6 minutes ago, nicknorman said:

Also to be honest, I am not a great fan of Victron, Mastervolt is better IMO.

Noted. As a newbie the integrated interface is quite appealing. It all just seems to go together like lego. Yet they seem also to be able to easily integrate with DIY stuff.

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14 minutes ago, ivan&alice said:

Sure, it just all seemed to fit happily into place around the 190A mark. Should I be worried about plugging in a 3000VA inverter into the isolating relay with a 200A fuse, or will I be fine as long as I never exceed a 3000VA AC load?

 

What would be the maximum current draw on the 3kVA Victron Phoenix inverter? https://www.victronenergy.com/upload/documents/Datasheet-Phoenix-Inverter-3000VA-120V-EN.pdf
 

Noted. As a newbie the integrated interface is quite appealing. It all just seems to go together like lego. Yet they seem also to be able to easily integrate with DIY stuff.

That Victron inverter can only supply 2400w so the 3kva is a bit misleading. At 2400w it will be taking around 240A. But as you suggest, it only takes that current if you plug it into a 2400w load. Of course the inverter can supply much more for a few moments (transient load).

The main limitation on the relay is two-fold, one being the heating effect of all that current flowing through its slight resistance. Because it has significant thermal mass, it won't instantly heat up and thus a short term overload wont be an issue. But the other consideration is its ability to break the circuit under heavy load and the resultant arcing. A not unfeasible situation is where a very heavy load (2400w, 240A) pulls the system voltage down below a safe limit for a LiFePO4 battery, and the emergency disconnect operates the relay to break the current. Lots of arcing and burning ensues! But everything is a compromise and provided you don't allow that to happen more than extremely rarely, it will probably be alright!

 

However I think you mentioned that you were not planning a low voltage disconnect? Which could be dangerous considering the ability of a big inverter to hoover up charge. No doubt you will not be foolish enough to plug in a 2kw load and then walk away, but in the lifetime of the batteries (10 years plus) can you be sure that someone else won't? LiFePO4 batteries maintain a very even voltage right up to the point where they "crash" and fall off a cliff. Also, you have to choose between top balancing and bottom balancing and normally folk choose top balancing, so that means that one cell can "crash" on discharge, whilst the others are OK and thus the system voltage isn't that low.

 

Yes you could plug the 3000va inverter in via a 200A fuse, it would certainly remind you when you had connected up a high a load. But keep some spare fuses at hand!

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6 minutes ago, nicknorman said:

At 2400w it will be taking around 240A.

Wouldn't this be 200A at 12V? Or is the 40A for inefficiencies? It looks like you're using 10V in your amperage calculations - I'm guessing this is to allow margin for error?

 

13 minutes ago, nicknorman said:

I think you mentioned that you were not planning a low voltage disconnect?

No, the 190A relay is intended to be the low voltage disconnect - triggering when either the battery voltage or any one cell drops too low. Would you recommend something like a Battery Protect in addition?

 

17 minutes ago, nicknorman said:

A not unfeasible situation is where a very heavy load (2400w, 240A) pulls the system voltage down below a safe limit for a LiFePO4 battery

I'm reading this as, provided I keep my load under say 2kW (definitely the plan for the medium term) the 3000kVA inverter should be just fine and allow a bit more room to load up the inverter should I need to. I plan to stick a 200A fuse in line as well and that should protect against the disaster situation you refer to.

 

23 minutes ago, nicknorman said:

No doubt you will not be foolish enough to plug in a 2kw load and then walk away, but in the lifetime of the batteries (10 years plus) can you be sure that someone else won't?

I wonder if it's possible to configure the output of the inverter to limit the power to lower than the maximum it can handle?

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43 minutes ago, nicknorman said:

I had a look at the Victron blurb. They are a bit naughty because really, it is a 1600w inverter. It can supply up to 2000va with a non-unity power factor. But for a resistive load such as a kettle / heater etc it is limited to 1600w or 1600va (same thing).

This is still probably enough for your washing machine without heater, but for future provision (dishwasher, washing machine with heater, tumble drier etc) it might be more sensible to get a higher rated one that could manage at least 2kw. Perhaps it is a bad idea to size your inverter based on the current limit of the isolating relay. And when calculating input current for a given power, it is best to use 10v to allow for both voltage drop and inverter efficiency. Our inverter at 2kw takes nearly 200A, although less of course when the engine is running because the input voltage is higher.

 

Also to be honest, I am not a great fan of Victron, Mastervolt is better IMO. We have a Mastervolt 2500 which can run a 2kw electric kettle, a 2kw tumble drier, a compact washing machine with heater etc (not all at the same time, of course!).

 

Oh and electric kettles are good when cruising because they turn themselves off when they boil, unlike gas. And we can easily generate 2kw or more when the engine is running at cruising speed. We tend not to use the kettle when the engine isn't running, but we sometimes do. Although it takes 200A this is only for 3 minutes or whatever, not much in the way of AH.

I see where your confusion arises. Victron do rate their 2000va inverter as 1600 watts. But really, it is a 1600w inverter that can supply up to 2000va when the power factor is not unity (inductive load etc). So you were fooled by the headline rating / name at 2000, when in fact it is really 1600.

No Nick its not confusion its practical. I was repairing generators when I was 17 they were rated in KVA but we always used .8 for conversion to watts load, its like the industry standard and Victron have done just that. I spoke to John V after I posted and he as an electrician that owned his own company. he said the same, his last big job was installing two 700 KVA and one 900 KVA  gennies and he  used the same conversion system, theory is one thing but in practice its less 400 watts in this case.

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1 minute ago, peterboat said:

No Nick its not confusion its practical.

Perhaps you're both right? As in the 0.8 conversion factor is a practical approximation, but in reality the conversion depends on the type of load (resistive, e.g. heating element vs non-resistive e.g. motor) and ranges between 0 for a perfectly non-resistive load and 1 for a perfectly resistive load?

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1 minute ago, ivan&alice said:

Perhaps you're both right? As in the 0.8 conversion factor is a practical approximation, but in reality the conversion depends on the type of load (resistive, e.g. heating element vs non-resistive e.g. motor) and ranges between 0 for a perfectly non-resistive load and 1 for a perfectly resistive load?

No in practice the maker of the equipment doesnt know the use of the equipment so they apply .8 and it always works, so their are no failures are their?

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27 minutes ago, ivan&alice said:

Perhaps you're both right? As in the 0.8 conversion factor is a practical approximation, but in reality the conversion depends on the type of load (resistive, e.g. heating element vs non-resistive e.g. motor) and ranges between 0 for a perfectly non-resistive load and 1 for a perfectly resistive load?

Exactly.

23 minutes ago, peterboat said:

No in practice the maker of the equipment doesnt know the use of the equipment so they apply .8 and it always works, so their are no failures are their?

You have no idea what you are talking about.

37 minutes ago, peterboat said:

No Nick its not confusion its practical. I was repairing generators when I was 17 they were rated in KVA but we always used .8 for conversion to watts load, its like the industry standard and Victron have done just that. I spoke to John V after I posted and he as an electrician that owned his own company. he said the same, his last big job was installing two 700 KVA and one 900 KVA  gennies and he  used the same conversion system, theory is one thing but in practice its less 400 watts in this case.

It is a rule of thumb. Like all rules of thumb, most of the time it isn't accurate. How embarassing for you that I&A gets it, when you, with your thousands of years experience, don't. Well you know what they say, 1000 years of getting it wrong is still experience, which is why experience without underlying knowlege is useless.

 

The bottom line is that you looked at an inverter with a specified max va, you tried to load it to that number of va when power factor was unity, and you were surprised when it tripped even though the wattage rating (va at unity power factor) of the inverter was somewhat less than the load. Clearly you didn't understand the issues.

Edited by nicknorman
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36 minutes ago, ivan&alice said:

1/Wouldn't this be 200A at 12V? Or is the 40A for inefficiencies? It looks like you're using 10V in your amperage calculations - I'm guessing this is to allow margin for error?

 

2/No, the 190A relay is intended to be the low voltage disconnect - triggering when either the battery voltage or any one cell drops too low. Would you recommend something like a Battery Protect in addition?

 

3/I'm reading this as, provided I keep my load under say 2kW (definitely the plan for the medium term) the 3000kVA inverter should be just fine and allow a bit more room to load up the inverter should I need to. I plan to stick a 200A fuse in line as well and that should protect against the disaster situation you refer to.

 

4/I wonder if it's possible to configure the output of the inverter to limit the power to lower than the maximum it can handle?

1/ Yes, due to voltage drop and inefficiency and it being a nice round number, I tend to use 10v. Perhaps slightly pessimistic but I'd use no more than 11v unless the engine is running with a powerful enough alternator to keep the system voltage well up.

2/ Not sure what that is. No I think the relay will be fine provided you don't overload it. I must have misread earlier, I thought you said you weren't doing low voltage disconnect

 

3/ Yes. However it doesn't take into account human error, and not all humans making the error will be you! But as you say, the 200A fuse will help.

 

4/ No, I dont think so.

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8 minutes ago, nicknorman said:

Exactly.

You have no idea what you are talking about.

It is a rule of thumb. Like all rules of thumb, most of the time it isn't accurate. How embarassing for you that I&A gets it, when you, with your thousands of years experience, don't. Well you know what they say, 1000 years of getting it wrong is still experience, which is why experience without underlying knowlege is useless.

When was the last time you installed a 900 KVA generator? to provide emergency power for two office blocks?

Well if I had not chimed in he would have followed your advice and installed an inverter that was 1600 watts when he wanted 2000 watts so who is wrong?

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2 minutes ago, peterboat said:

When was the last time you installed a 900 KVA generator? to provide emergency power for two office blocks?

When was the last time you understood the relationship between power factor, va and watts? Weilding a few spanners, screwdrivers and wiring something up in accordance with the manufacturer's instructions hardly makes you an expert on the science behind it.

2 hours ago, peterboat said:

What it's supposed to do and what it does are two different things! My old 3000 watt inverter powered my 2800 watt kettle my victron 3000 VA inverter tripped out on overload and that is a resistive load. I now have a new kettle  Google says 3000 VA is 2400 watts which would be why my kettle overloaded the inverter 

Unfortunately for you, this post says it all.

Edited by nicknorman
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1 minute ago, nicknorman said:

When was the last time you understood the relationship between power factor, va and watts? Weilding a few spanners, screwdrivers and wiring something up in accordance with the manufacturer's instructions hardly makes you an expert on the science behind it.

You still were wrong and the maker of the product agrees with me

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3 minutes ago, peterboat said:

You still were wrong and the maker of the product agrees with me

 

Dunning Kruger effect strikes again!

 

Anyway, enough bickerfest, folk will find it tiresome.

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1 hour ago, nicknorman said:

Yes you could plug the 3000va inverter in via a 200A fuse, it would certainly remind you when you had connected up a high a load. But keep some spare fuses at hand!

Was thinking exactly that about spares! Is there such a thing as a 200A 12V circuit breaker? Could save me a couple quid on fuses in the long run!

 

5 minutes ago, nicknorman said:

1/ Yes, due to voltage drop and inefficiency and it being a nice round number, I tend to use 10v. Perhaps slightly pessimistic but I'd use no more than 11v unless the engine is running with a powerful enough alternator to keep the system voltage well up.

2/ Not sure what that is. No I think the relay will be fine provided you don't overload it. I must have misread earlier, I thought you said you weren't doing low voltage disconnect

 

3/ Yes. However it doesn't take into account human error, and not all humans making the error will be you! But as you say, the 200A fuse will help.

 

4/ No, I dont think so.

2/ Victron Battery Protect is a programmable low voltage cutoff. The largest one is 220A and I was originally thinking of using this rather than the relay, but Victron recommends against using this device with an inverter.

 

12 minutes ago, peterboat said:

if I had not chimed in he would have followed your advice and installed an inverter that was 1600 watts when he wanted 2000 watts so who is wrong?

As I said I think you're both right! Thanks @peterboat for pointing out that inverters are measured in VA and not W, and giving a practical conversion, and thanks @nicknorman for explaining a bit more about the meaning behind it.

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15 minutes ago, nicknorman said:

 

Dunning Kruger effect strikes again!

 

Anyway, enough bickerfest, folk will find it tiresome.

Always have to have the last word dont you Nick? Practice is different to theory and the real world is practice

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11 minutes ago, ivan&alice said:

2/ Victron Battery Protect is a programmable low voltage cutoff. The largest one is 220A and I was originally thinking of using this rather than the relay, but Victron recommends against using this device with an inverter.

I have the 220A Bluetooth Victron Battery Protect as my low voltage protection. I saw it being used with an inverter in one of Will Prowses videos.

 

I'm a bit worried now.... What reason do Victron give for not using it with an inverter?

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I'm keeping out of this argument, but on our new bote being built I was offered a Victron 3000 VA combo which sounded great till I sussed out it was only rated to 2.5KW so I went for the 5000VA Quattro. My current 2000VA Victron combi, Like Peter says, is only rated to 1.6KW and only allows us to run our washing machine on a cold wash cycle.

 

I & A, I'll answer your other question to me tomorrow. Serious Bowmore overload.

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48 minutes ago, ivan&alice said:

Was thinking exactly that about spares! Is there such a thing as a 200A 12V circuit breaker? Could save me a couple quid on fuses in the long run!

 

2/ Victron Battery Protect is a programmable low voltage cutoff. The largest one is 220A and I was originally thinking of using this rather than the relay, but Victron recommends against using this device with an inverter.

 

As I said I think you're both right! Thanks @peterboat for pointing out that inverters are measured in VA and not W, and giving a practical conversion, and thanks @nicknorman for explaining a bit more about the meaning behind it.

Ivan if you plan to run your panels in series as per your diagram, the solar controller you have listed wont work, its only 150 volts and your panels have an open circuit voltage of over 40 volts, so you would have to put 2 into parallel twice and then series. Its a small point I know but I have fallen foul of it in the past, its because victron panels are rated at at 24 volts rather than much cheaper commercial ones for roof top systems on houses

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32 minutes ago, Richard10002 said:

I have the 220A Bluetooth Victron Battery Protect as my low voltage protection. I saw it being used with an inverter in one of Will Prowses videos.

 

I'm a bit worried now.... What reason do Victron give for not using it with an inverter?

Hi Richard, sorry to worry you. I was also planning on using the battery protect as my low voltage cutoff, using also the remote from the cell-level monitoring to trigger the batteryprotect when voltage of any cell dropped too low.

 

I wouldn't worry too much, but Will has since recanted on using a battery protect, updating the description on his video here: https://www.youtube.com/watch?v=_PgthByAYz4 - he unfortunately does not say why. He makes the following comments:


"This video is outdated!!!! DO NOT USE a battery protect in this system."

"Hi Will, can you explain why you now say to not use a Battery Protect?"

"It's because victron made an update saying not to use with inverters. Check out my community section and forum for more info on the update."

 

I couldn't find the information he refers to on his forum. I did find a reason on the Victron community that satisfied me as to why you shoudn't use it, but I can't find it again. I recall the risk being damaging the battery protect (and maybe the batteries if the cutoff stops working).

 

For one thing, current should definitely only flow in one direction on the battery protect, so if you have an inverter/charger this is an obvious no-no as it might damage the Battery Protect.

 

For another, the Battery Protect works on solid state Mosfets rather than switch relays, and...  "you shouldn't connect an inverter to a contactor or Mosfet due to the inrush current." (from Victron community site)

 

Sorry I don't have a definitive reason why you shouldn't use a battery protect with an inverter for at the moment, but I don't think your setup is posing you imminent danger! I'll look tomorrow if none of the electronics big guns on the forum have an explanation.

 

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