24v or 12v ?!? ...going in circles ?

[Screwball]

Argh .... my head is spinning from reading and trying to finalize my (fulltime rv/avid boondocker) setup.
Here is what I have : 8 x 250w Trina panels permanently flat mounted on the roof (ocv 37.6v, pmax 30.3v, scc 8.85a pmax 8.27a) currently wired in two sets of 2s2p.
Two temporary 110ah12v deep cycle batts but plan on replacing with a (most likely) 8-12 x 280ah lifepo4 diy bank on overkill bms (2-3 groups of 4s/bms if I go 12v).
I understand the benefits of 24v, especially when it comes to $$ of the controller(s) needed, but it seems 24/12 converter(s) add almost as much $$ as I save in SCC as well as adding more complexity ?.
So my (latest) rest of the setup would be twin outback fm60a and a victron multiplus 12/3000 (what is imho a decent "bargain" for a lf inverter/charger/transfer switch)

Any and all input/ideas/suggestions is highly appreciated ?

 

[jwelter99]

How much equipment do you have that is 12V only?

The one that usually really influences this decision is the fridge.... if a compressor style if it runs on 12V only or would work on 24V is the deciding factor.

To run some 12V LED lights and fans is not a ton of power so a small 24V to 12V convertor is not a big cost or loss of efficiency.

 

[John Frum]

If you have 12 volt loads that is a vote for a 12 volt system voltage.
How much pure dc power do you need?
The 24_2_12 converter probably is a wash.
A 2000 watt inverter is a practical upper limit for 12 volts.
A low frequency 3000 watt inverter is doable but its pushing the limits.
How much ac power do you really need including locked rotor amps?

 

[time2roll]

I would try to stay at 2000 watts max inverter on 12 volts.

 

[jwelter99]

There are thousands of happy Victron MultiPlus 3000/12 owners who would say otherwise. In fact why would Victron release their new MultiPlus II 3000/12 in only 12V if this was something that doesn't work or not recommended?

Back in LA/AGM days it was tough to get 300A at 12V discharge needed but with todays lithium batteries this is not a challenge.

 

[Screwball]

How much equipment do you have that is 12V only?

The one that usually really influences this decision is the fridge.... if a compressor style if it runs on 12V only or would work on 24V is the deciding factor.

To run some 12V LED lights and fans is not a ton of power so a small 24V to 12V convertor is not a big cost or loss of efficiency.

Heavy toyhauler, so I have twin landing gears up front (12v 30A motors).
Diy bed elevating lift would be best with a 12v 2000lbs winch.
Sound system is car 12v head unit with rather large jbl sub amp (love a good bass base ?)
Fridge/freezer is a 11.6 cuft whirlpool residential (largest 24" wide model i could find) ... would be on inverter most of the time (thats why I really like the low consumption of the victron) ... rest is just basic rv stuff like wh, wp, furnace .... biggest ac load is 1000w micro, coffeemaker, toaster and occasional senville 9000btu inverter minisplit heat pump ... been offgrid & rving for a while now, so im used to only run one thing at a time ?

 

[John Frum]

There are thousands of happy Victron MultiPlus 3000/12 owners who would say otherwise. In fact why would Victron release their new MultiPlus II 3000/12 in only 12V if this was something that doesn't work or not recommended?

Back in LA/AGM days it was tough to get 300A at 12V discharge needed but with todays lithium batteries this is not a challenge.

3000 ac watts * 1.5 low frequency fudge factor / 12 volts low cutoff = 375 dc amps
375 dc amps / .8 fuse headroom = 468.75 fuse amps.
According to the abyc 4/0 awg is only rated to 440 amps without melting the insulation off 105c rated wire.
According to the nec 4/0 awg is only rated to 260 amps without melting the insulation off 90c rated wire.
I don't want my wire getting anywhere near 90c so I would be looking at 2x 4/0 awg.

 

[John Frum]

Heavy toyhauler, so I have twin landing gears up front (12v 30A motors).
Diy bed elevating lift would be best with a 12v 2000lbs winch.
Sound system is car 12v head unit with rather large jbl sub amp (love a good bass base ?)
Fridge/freezer is a 11.6 cuft whirlpool residential (largest 24" wide model i could find) ... would be on inverter most of the time (thats why I really like the low consumption of the victron) ... rest is just basic rv stuff like wh, wp, furnace .... biggest ac load is 1000w micro, coffeemaker, toaster and occasional senville 9000btu inverter minisplit heat pump ... been offgrid & rving for a while now, so im used to only run one thing at a time ?

The biggest ac load I see is the toaster which will be fine on a 2000 watt inverter.
One big load at a time of course.
I would call your dc loads significant.
Suggest you stay at 12 volts.

 

[Supervstech]

Heavy toyhauler, so I have twin landing gears up front (12v 30A motors).
Diy bed elevating lift would be best with a 12v 2000lbs winch.
Sound system is car 12v head unit with rather large jbl sub amp (love a good bass base ?)
Fridge/freezer is a 11.6 cuft whirlpool residential (largest 24" wide model i could find) ... would be on inverter most of the time (thats why I really like the low consumption of the victron) ... rest is just basic rv stuff like wh, wp, furnace .... biggest ac load is 1000w micro, coffeemaker, toaster and occasional senville 9000btu inverter minisplit heat pump ... been offgrid & rving for a while now, so im used to only run one thing at a time ?

You have a lot of 12 V loads. The winch and 30A motors would fry most 24/12 converters...
and the 120V loads should be fairly small. The mini will slow start, the fridge is likely a small startup load. I vote stay 12V.

 

[Screwball]

3000 ac watts * 1.5 low frequency fudge factor / 12 volts low cutoff = 375 dc amps
375 dc amps / .8 fuse headroom = 468.75 fuse amps.
According to the abyc 4/0 awg is only rated to 440 amps without melting the insulation off 105c rated wire.
According to the nec 4/0 awg is only rated to 260 amps without melting the insulation off 90c rated wire.
I don't want my wire getting anywhere near 90c so I would be looking at 2x 4/0 awg.

Iirc multiplus 12/3000 is 3000va ... around 2400w ... however, victron is very honest with ratings
I could do with the mp 12/2000 but $150 extra gets you the (better featured) 12/3000 so there is no point in going less ?

 

[GSXR1000]

which toy hauler? I want the GD 349m..
I would go with 24v with that much solar and battery.. then a victron 24-12 70a... and place a small riding lawn mower batter up front to handle surges.

 

[John Frum]

Iirc multiplus 12/3000 is 3000va ... around 2400w ... however, victron is very honest with ratings
I could do with the mp 12/2000 but $150 extra gets you the (better featured) 12/3000 so there is no point in going less ?

The 30 second surge rating is 6000 watts so its not much of a stretch to estimate 4500 watts for 90 seconds which flirts with the trip curve of most of the ocp options.

 

[GSXR1000]

check out my build for my 2007 octane toyhauler...
it's 12v.. but move a few buss bars and you get 24v.. I want 3x 24v@560ah in my future 5th wheel

Thread 'Just ordered Lifepo4 prismatic cell 3.2V 280Ah lithium lifepo4' https://diysolarforum.com/threads/j...smatic-cell-3-2v-280ah-lithium-lifepo4.14955/

 

[Screwball]

which toy hauler? I want the GD 349m..
I would go with 24v with that much solar and battery.. then a victron 24-12 70a... and place a small riding lawn mower batter up front to handle surges.

View attachment 44595View attachment 44596

Yes, you gave me this idea in another thread already ... still considering it
A multiplus 24/3000 and a single 150/70 SCC is very tempting ...as a fulltimer i kinda like the idea to stick with Victron ... its like with Honda gens: buy once, cry once ?

 

[Cdkipp]

I spent my first 5 years of RVing with a 12 volt system. I had 700 ahr of Calb cells. I have a magnum hybrid 3012 inverter and a morningstar mppt 60. The system served me well but I was at the very top of the 60 amp and often would push at the upper end of of the 3000 at times and I would get inverter shutdowns now and then. I decided to put in a mini split AC which I could run off solar and as part of that decision, I decided I would switch over to a 24 volt system. I added the Magnum 4024 and switched my morningstar over to 24 volts. I only have the packs connected with a 25 amp Victron 24-12 dc -dc. However, because my landing gear is 12 volt and runs electric mores I have retained a small 100 ahr lithium bank. I think this is the perfect arrangement. The heavy AC usage circuits are now run off my 4024 now. I feel like everything runs cooler.

 

[GSXR1000]

Yes, you gave me this idea in another thread already ... still considering it
A multiplus 24/3000 and a single 150/70 SCC is very tempting ...as a fulltimer i kinda like the idea to stick with Victron ... its like with Honda gens: buy once, cry once ?

I do like victron ... yes like Honda 4 sure... the other good thing about 24 is voltage drop on 24v system effects it less...

 

[John Frum]

I do like victron ... yes like Honda 4 sure... the other good thing about 24 is voltage drop on 24v system effects it less...

Will the lead acid battery last just being floated by the dc2dc converter?
I missed the 12volt winch.
That is going to take some serious juice.

 

[Cdkipp]

Will the lead acid battery last just being floated by the dc2dc converter?
I missed the 12volt winch.
That is going to take some serious juice.

In my set up the Victron holds a Lifepo4 at about 13.

 

[John Frum]

In my set up the Victron holds a Lifepo4 at about 13.

In this scenario its a 24to12 converter that will be supplying the lead acid battery.

 

[GSXR1000]

Will the lead acid battery last just being floated by the dc2dc converter?
I missed the 12volt winch.
That is going to take some serious juice.

yes so the life of the battery should be awesome... also let's say you have 100a draw for 5 minutes.. only 30a comes from the battery