24v battery but 12v use

STW

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Will, how about a video exploring the following:
Setup a 24v battery (2x 12v batteries in series) being charged by a 24v solar charger. Obvious benefit is cheaper controller since you can push 2x the watts.
However connect the inverter to just one of the batteries (12v).

What would this do negatively? Would the batteries stay balanced?

Just curious!
 

Short_Shot

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You gain nothing from your charging at a higher wattage then only using half the battery pack anyways.

All you'll do is horribly imbalance the system, degrade the one battery much faster, and increase total cost of ownership over time.

Just buy a 24 volt inverter.
 

Jordi

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When you discharge only one battery; their voltage will differentiate too much; therefore when charging at 24V you will probably damage the battery with higher voltage. The current you can send from one battery to the other via the BMS balancing function is small and only meant for the uneven speed of charge/discharge that each battery has (50-200 mA).

The reason I guess is the fact that the charge controller thinks that the batteries are still half empty and allows the solar panels charge to kick in; but in reality one battery is almost full already and when receiving extra charge it may get damaged (swelling).

Perhaps if a super fast BMS smart charger existed that could balance different cells with very high currents, then your set up could work. Yet I am sure many experienced people in this forum would not recommend.

Maybe a potent 24V to 12V transformer is your best option. I read step downs are more efficient than step ups. Then you use the battery as it is; 24V.
 

Short_Shot

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Maybe a potent 24V to 12V transformer is your best option. I read step downs are more efficient than step ups. Then you use the battery as it is; 24V.

I wouldn't even suggest this.
The price to do that would be significant vs just buying the inverter for 24v to begin with.

Even a 1000w output inverter will be pulling just shy of 100a at 12v and 85% efficiency.

A 100 amp 24v to 12v buck converter is around 140 for a cheap off brand unit. A victron one is 100 dollars more.

For $150 you can just buy a 1000w 24 volt pure sine inverter.

For the price of the victron converter you can just buy a nice 2kw inverter.


And that assumes the cheap one can handle any surge you might throw at it. Could be that it can't handle any surge and you need the victron anyways. At that point you're even further better off just getting a 24v inverter.


It just doesn't make sense from any angle, including financially, even if you get the 12v inverter for free.
 

captainrivet

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I think he wants to reduce costs by using one MPPT on 24V and the 2 12V batteries in series, can be one starter, one service…or put quite even loads on each of them to utilize 12V equipment he already has…
still a bad idea for daily use…
for emergency backup wire your 12V starter to one of the 12V batteries and your 12V windlass to the other is not a bad idea when your boat is 12V but you wanna go dual 12V/24V due to high loads like inverter and replace them by 24V ones when they break…

my problem going 24V as 2 new engines with 12V starter, spare 12V starter and new windlass in 12V came with the cat I bought. Have oversized 300AH lead starter for 50hp volvos due to windlass goes from starter…wanna get rid of the lead but cannot if I go 24V as no backup or cannot parallel if lead died. So i am forced to go 12V and run 2x3.5kw 12V inverter (use them till 2kw each, so 400A load) directly of the bank to keep loads on the rest of Installation small.
 
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Q-Dog

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Why attempt this?? Just get the voltage you need. In Victron list prices, there is no difference in price between a 12 volt and 24 volt version of the Multiplus.
 

captainrivet

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Why attempt this?? Just get the voltage you need. In Victron list prices, there is no difference in price between a 12 volt and 24 volt version of the Multiplus.
Because you already have a 12V inverter….
Or on 24V I would just need 2x 30/100 MPPT instead 3x 50/100 one for 12V, why still 12V see above…
 
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Q-Dog

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If you have a 12volt inverter, use a 12volt battery bank. If you have a 24volt battery bank, use a 24volt inverter. This isn't rocket surgery.
 

captainrivet

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But what about this idea if each of the 12V batteries has its own 12V BMS, that’s actually the case if you use 2 12V drop in series and works…
 
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captainrivet

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If you have a 12volt inverter, use a 12volt battery bank. If you have a 24volt battery bank, use a 24volt inverter. This isn't rocket surgery.
Yes you just to buy thicker cables, breakers and 2 MPPT instead of one….sell inverter and get 12V adds really up….
not everything is green field, you mostly have legacy…
 

Short_Shot

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I think he wants to reduce costs by using one MPPT on 24V and the 2 12V batteries in series, can be one starter, one service…or put quite even loads on each of them to utilize 12V equipment he already has…
still a bad idea for daily use…
for emergency backup wire your 12V starter to one of the 12V batteries and your 12V windlass to the other is not a bad idea when your boat is 12V but you wanna go dual 12V/24V due to high loads like inverter and replace them by 24V ones when they break…

my problem going 24V as 2 new engines with 12V starter, spare 12V starter and new windlass in 12V came with the cat I bought. Have oversized 300AH lead starter for 50hp volvos due to windlass goes from starter…wanna get rid of the lead but cannot if I go 24V as no backup or cannot parallel if lead died. So i am forced to go 12V and run 2x3.5kw 12V inverter (use them till 2kw each, so 400A load) directly of the bank to keep loads on the rest of Installation small.
We know what he's doing.

And it's not going to work out.

Also why would you use 3.5kw inverters for a 2kw load?
 

captainrivet

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Why attempt this?? Just get the voltage you need. In Victron list prices, there is no difference in price between a 12 volt and 24 volt version of the Multiplus.
Sorry wrong, the price difference between a Quattro 5000/12V and 24V is nearly 1000bucks…
 

Short_Shot

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Yes you just to buy thicker cables, breakers and 2 MPPT instead of one….sell inverter and get 12V adds really up….
not everything is green field, you mostly have legacy…
Did you even read the comment?

Why would you need 2 mppt units and thicker wires if you just get a 24v inverter?
 

Short_Shot

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Sorry wrong, the price difference between a Quattro 5000/12V and 24V is nearly 1000bucks…
Where are you shopping?

A 48v Quattro 5kva is on Amazon for $2542.
The 24v version is listed for 2825.
The 12v version is $3379. So it's a $554 difference.

But OP doesn't need 5kva.
And the person you quoted didn't even mention the quattro.

Op needs 1000w.

The 2k 12v multiplus is 1155.
The 24v version is also 1155.

Screenshot_20210917-085631_Chrome.jpgScreenshot_20210917-085642_Chrome.jpg

And none of that matters anyways because OP doesn't need a 1155 dollar victron inverter/charger if they can use a $150 one that doesn't do shore charging.
 
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captainrivet

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We know what he's doing.

And it's not going to work out.

Also why would you use 3.5kw inverters for a 2kw load?
World circum navigation catamaran with electric galley. First high temps reduce output, 2nd electronics especially inverters used to 60% load rating max live much longer, 3rd redudancy, 4th smaller cables and loads on the circuit, 5th had one 3.5kw already from old boat, 6th 2 complete isolated circuits for electric galley and legacy shore power installation=rest of boat. 7th Need real 5kw rarely and all 5kw delivering below 5kw and 8kw is too much. Key is reliability and backup as in remote areas no supply at all…
i love Victron and have all Victron except inverters as they are extremely overpriced, my 2x3.5kw costed 30% of Victron and are as reliable and deliver real 2x3.5V, Peak can be even 14kw....no problem with starting current in electric galley. Fan of having everything seperatly (charger, inverter,12V watermaker….), if one breaks the rest still works and most is doubled installed in the small version. my buddy boats charger on Multiplus failed and inverter was then not working meaning no 220V watermaker then too. He has problem with starting currents with cooktop on the Victron too where the same on my cheap Chinese inverters just works…clean but not as perfect clean 220V as Victron but all galley stuff don‘t care…have a 3rd 300W Victron inverter installed at the office/chart table and a clean 220V plugs in my owners cabin and one in salon for very sensitive stuff.
 
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