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A few cons of 48V systems.

Thank you for the MS comment... Money always plays a role, and a Major role at that. But isn't 48v safer for even 2500 watts? Safety probably makes up 90% of the decision for me... but I also know 48v is closer to killing you. Eg4 having the built-in circuit breaker can just be turned off I always wear glasses and rubber gloves when I build or work on these things.

Safer in what way?
 
I want to share my experience with the cons of the 48v system that I did not know first.

1. We are almost certainly stuck with Growatt if going 48V, 48V MPP inverter are taking $1400+, and there are no other options. If we want to go with Victron, the issue is the biggest 48V AC-DC charger we can get in the market is a 48V 25A 120V Battery Charger by EG4, which is very inefficient for a 4KW RV generator because it only puts about 50% of the load.
2. There is no cheap Bluetooth battery monitor for a 48v system.
3. For some random reason, 12v batteries in a series could lose balance by themselves; it needs to be balanced every now and then.
4. If you go 24V batteries, 24V 100AH is often more expensive than 12V 200AH
5. Biggest issue: if you have a bunch of small areas that are not at the same angle, you will want more than one MPPT charger for each region. There is no dirt cheap MPPT for a 48v system! 48v MPPT is almost always for big arrays! The cheapest I can find is Victron 100 | 20 MPPT, which supports 48V, but is still $170+.
you got a new choice for 48v mppt chargers. I just got 3 80 amper's from signature solar, Growatt makes 60, 80, 100 & 120 amp models & they're cheap. The 3 80's I got cost less than 1 victron 150/100 & gives you 140 amps more power. I've had 3 victrons give out on me & was denied a warranty claim so they're on my shit list & will no longer get my $$$.
 
I ended up going 12v for the system at my parent's cottage. It was way more affordable. I could go with a small inexpensive inverter and use lots of cheap and available RV parts. Stuff like a 12v water pump, 12v lighting, 12v fridge(well that one is 12/24v). They only need to run the inverter when watching tv. I've installed 5v USB charging ports for device charging. In their case going 24v or 48v would have added like 25-30% or more in cost.

The fridge was quite expensive but it saved adding more panels, another charge controller and more batteries. It uses 1/2 the kWh of the best 120v fridge but isn't frost free. Then even more power is saved by not running an inverter 24/7.

That system has 1200W of panels and 1100Ah @ 12v of flooded cells(Going LiFePO4 when the time comes to replace). Before buying the 12v/24v fridge they were running the fridge in their motorhome off the system and coming up very short on power. The RV fridge is terribly inefficient and less than 1/2 the size of the new fridge. We were looking at doubling the system before buying the new fridge.

After the new fridge was installed back in July they never ran the battery bank down even after a few days of heavy cloud. They still run the inverter 24/7 when they are there to monitor things(also cell booster currently requires 120v). But shut it down when they leave. For the winter everything gets shutoff except the charge controller is still maintaining the batteries. They live very comfortably with that available power. Dad still uses his Honda generator to run large power tools, but that is about it.

On really big systems 48v and full time 120v makes sense. On smaller systems you really have to crunch the numbers. Balancing efficiency and cost. 12v stuff is cheap and available. It's harder to find 24v and 48v stuff and its often far more expensive.
 
Can I ask you why you are not a fan of this? I have to make a decision very soon. I have a 12v 800ah system now, I was going to go with a 24v EG$ but they aren't in stock... But 48v is. I want 3 eg4's A/C (Wife with MS needs some A/C) ... I'll start off with 2 and add another later in the summer as more money becomes available.
As you go up in voltage, you find some components won't readily run 48VDC. Take for instance a commonly used rotary battery disconnect switch. Usually these are rated up to 32V, not 48V. You can run 24V thru it but if you run 48V thru it and there is current running thru it, there will be an arc that can either weld the contacts or worse create a fire. There isn't an arc chute on the disconnect.

If given the choice to run one 48V inverter or two 24V for the same capacity, the 24V system wins hands down. Redundancy, easily sourced parts, can more readily charge off the vehicle 12V system, and much easier to step down for 12V accessories if needed.

If you have a 12V system and want an inverter 3000w or above, I recommend moving up to 24V. If you're living full time in an RV and want air conditioning, you should first look into an inverter mini split system instead of a roof air unit. This allows you to run much longer off the batteries with less amps and allows a much smaller inverter. . If the RV is quite large, 2 mini split units. Again, redundancy and you can turn one off when not needed. The idea is to conserve energy so the solar system is able to power the RV for extended time frames.

I don't know what you have for a RV but as you go up in size and amperage requirements, then higher volts such as 48V might be needed. But that also requires more robust parts than just a 12 or 24V system.
 
Safer in what way?
Well, I was more asking than stating. Lower Amperage which means less heat? I diy built my current battery, but with the welded bars and such In an RV the EG4 seems like a nice safety build. But I'm not a know it all, and I'm going to listen to you experts and appreciate it! It's little rushed because we are leaving for Florida in the first week of March. Thankyou for the help.
 
If you have a 12V system and want an inverter 3000w or above, I recommend moving up to 24V. If you're living full time in an RV and want air conditioning, you should first look into an inverter mini split system instead of a roof air unit. This allows you to run much longer off the batteries with less amps and allows a much smaller inverter. . If the RV is quite large, 2 mini split units. Again, redundancy and you can turn one off when not needed. The idea is to conserve energy so the solar system is able to power the RV for extended time frames.

I don't know what you have for a RV but as you go up in size and amperage requirements, then higher volts such as 48V might be needed. But that also requires more robust parts than just a 12 or 24V system.
Thank you I agree. I wanted the 24v version, but Signature Solar says they are at least 1 month out. Also, the 48 I can use on my soon to be built home solar when not in use in the camper. I would build a 24v system for myself but I'm not confident with these aluminum cased cells can really be self-made to be RV safe without a lot of extra money? maybe I'm wrong (I'd love to be). Right now, I have 16 Sinopoly 200ah cells and they are some much beefier and more solid. Thank you for the help and advice. I would love to build a dual 24v battery bank though.
 
I ended up going 12v for the system at my parent's cottage. It was way more affordable. I could go with a small inexpensive inverter and use lots of cheap and available RV parts. Stuff like a 12v water pump, 12v lighting, 12v fridge(well that one is 12/24v). They only need to run the inverter when watching tv. I've installed 5v USB charging ports for device charging. In their case going 24v or 48v would have added like 25-30% or more in cost.

The fridge was quite expensive but it saved adding more panels, another charge controller and more batteries. It uses 1/2 the kWh of the best 120v fridge but isn't frost free. Then even more power is saved by not running an inverter 24/7.

That system has 1200W of panels and 1100Ah @ 12v of flooded cells(Going LiFePO4 when the time comes to replace). Before buying the 12v/24v fridge they were running the fridge in their motorhome off the system and coming up very short on power. The RV fridge is terribly inefficient and less than 1/2 the size of the new fridge. We were looking at doubling the system before buying the new fridge.

After the new fridge was installed back in July they never ran the battery bank down even after a few days of heavy cloud. They still run the inverter 24/7 when they are there to monitor things(also cell booster currently requires 120v). But shut it down when they leave. For the winter everything gets shutoff except the charge controller is still maintaining the batteries. They live very comfortably with that available power. Dad still uses his Honda generator to run large power tools, but that is about it.

On really big systems 48v and full time 120v makes sense. On smaller systems you really have to crunch the numbers. Balancing efficiency and cost. 12v stuff is cheap and available. It's harder to find 24v and 48v stuff and its often far more expensive.
If I thought I could safely build a 12v 1200ah Battery that's RV bumpy road safe with those aluminum cells I would.
 
Well, I was more asking than stating. Lower Amperage which means less heat? I diy built my current battery, but with the welded bars and such In an RV the EG4 seems like a nice safety build. But I'm not a know it all, and I'm going to listen to you experts and appreciate it! It's little rushed because we are leaving for Florida in the first week of March. Thankyou for the help.

Any voltage is safe as long as it is properly designed and implemented with components rated for that voltage. That's a rather generic statement, but you get the idea.

Even in a 48 volt system you could have a bad connection that makes heat. The right cables, the right connections and it'll work.

I have the old style (circa 2020) 280Ah EVE cells that have threaded terminals that so many are worried about and look down on. My toy hauler is taken on some very rough roads (BLM, Forest Service, county, etc). My batteries are doing fine. I've checked the terminal connections and everything has stayed nice and tight. Maybe mine are anomaly or maybe I'm just a bit more anal that most about getting things secure.
 
If I thought I could safely build a 12v 1200ah Battery that's RV bumpy road safe with those aluminum cells I would.

I would have no qualms about building a 1200 Ah 12 volt battery bank. I would not build a single 1200 Ah 12 volt battery. I have two 280 Ah 12 volt batteries that I run in parallel (4s2p) without any issues. The two batteries stay well balanced on both charge and discharge.
 
If you have a 12V system and want an inverter 3000w or above, I recommend moving up to 24V. If you're living full time in an RV and want air conditioning, you should first look into an inverter mini split system instead of a roof air unit. This allows you to run much longer off the batteries with less amps and allows a much smaller inverter. . If the RV is quite large, 2 mini split units. Again, redundancy and you can turn one off when not needed. The idea is to conserve energy so the solar system is able to power the RV for extended time frames.
I'm probably going to buy this mini split Mr. Cool DIY Gen-3 12,000 BTU 22 SEER ENERGY STAR Ductless Mini Split Air Conditioner & Heat Pump w/ 25 ft. Install Kit 115-Volt .... It's a bit more money but more efficient and easier to install.
 
I would have no qualms about building a 1200 Ah 12 volt battery bank. I would not build a single 1200 Ah 12 volt battery. I have two 280 Ah 12 volt batteries that I run in parallel (4s2p) without any issues. The two batteries stay well balanced on both charge and discharge.
Ok I'm leaning towards 4 separate 12v 280ah batteries, but I would have to figure out the BMS Disconnects and Pre-chargers. I Do have a Victron Inverter Charger And Victron Smart Solar Charge Controller. Could I use the relays to disconnect? I also have a REC pre-charger.
 
Ok I'm leaning towards 4 separate 12v 280ah batteries, but I would have to figure out the BMS Disconnects and Pre-chargers. I Do have a Victron Inverter Charger And Victron Smart Solar Charge Controller. Could I use the relays to disconnect? I also have a REC pre-charger.

With four BMS, I suspect there is no need for a pre-charge circuit for the inverter. As long as all four BMS are active, they'll look at that pre-charge load with nothing more than a shrug. It's not wrong to put in a pre-charge circuit, I'm just saying you have enough on the supply side that it's likely not necessary.

I'm going to fire up my new Victron 12/3000 soon. No pre-charge circuit. I have 240 amps of BMS output available, so it will be interesting to see what happens.
 
Do I need to worry about
With four BMS, I suspect there is no need for a pre-charge circuit for the inverter. As long as all four BMS are active, they'll look at that pre-charge load with nothing more than a shrug. It's not wrong to put in a pre-charge circuit, I'm just saying you have enough on the supply side that it's likely not necessary.

I'm going to fire up my new Victron 12/3000 soon. No pre-charge circuit. I have 240 amps of BMS output available, so it will be interesting to see what happens.
I have a Victron 12/3000 (now I wont have to buy another 24v or 48v). I was wondering if a Contactor is needed?
 
Do I need to worry about

I have a Victron 12/3000 (now I wont have to buy another 24v or 48v). I was wondering if a Contactor is needed?

With the understanding that I have zero experience with contactors other than what I read here on the forum...

Coordinating a single contactor from four individual BMS would seem to be complicated to me. If you buy four good quality FET based BMS (JBD, Overkill Solar, etc.) with enough amp capacity I don't see a need for a contactor.
 
Thank you I agree. I wanted the 24v version, but Signature Solar says they are at least 1 month out. Also, the 48 I can use on my soon to be built home solar when not in use in the camper. I would build a 24v system for myself but I'm not confident with these aluminum cased cells can really be self-made to be RV safe without a lot of extra money? maybe I'm wrong (I'd love to be). Right now, I have 16 Sinopoly 200ah cells and they are some much beefier and more solid. Thank you for the help and advice. I would love to build a dual 24v battery bank though.
Go to Watts247 https://watts247.com/product-category/inverters/

I have the 24V Growatt SPF3000TL, works great in my truck camper. https://diysolarforum.com/threads/heres-my-truck-camper-setup.29488/
 
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I'm probably going to buy this mini split Mr. Cool DIY Gen-3 12,000 BTU 22 SEER ENERGY STAR Ductless Mini Split Air Conditioner & Heat Pump w/ 25 ft. Install Kit 115-Volt .... It's a bit more money but more efficient and easier to install.
What size RV?
 
As far as a precharge, I installed one on my system- I figure it will help protect my Multiplus 12/3000 and my contactor.

It would not be difficult at add a pre- charge and contactor to a system that used several overkill type bms’s.

On the power wires going to the inverter insert the contactor on the positive wire. Then wire the pre-charge to it. To turn it on/off- install a simple switch (or something with logic). Instead of a contactor you could have a large amp switch with the pre-charge as a manual process.

Part of the reason for a pre-charge is so the large amount of current does not slam the inverter and it’s capacitors - or the switch that applied the power.
 
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