RV Solar: looking to connect large inverter with 60A Daly BMS with DIY lithium battery

[BNalette]

Hey guys, I'm new here, so please be gentle on me. I'm trying to get my trailer dialed in and I've got some questions/need advice.

I've been watching Will's videos for a while and they've been a huge help, but I need help with one last piece of my puzzle before completing my system.

What I have:

Epever Tracer 30A MPPT Charge Controller with Display (MT50?)
2x 100W Solar Panels
VariCore 3.2V LiFePO4 200ah cells x4
Daly 60A 4S BMS

So, the charge controller is currently installed in the RV and I'm using 6v lead acid batteries.

I need to balance my lithium cells, and get them installed with the BMS. I also want to add a 3,000 watt inverter. My main goal is to be able to brew a pot of coffee without running a generator. The inverter will also be used for lighter loads, but I think making coffee would be my biggest load. Maybe limited microwave use?

So, I know that it won't be wise to run a 3k watt inverter through the 60A BMS, so I think a 200A isolating relay is my solution. But, in my head, I'm trying to figure out how to wire this in a way that it works. Let me know if I'm on the right track/completely wrong/missing something...

If I wire the inverter directly to the battery (through the relay) and use the BMS lead to switch the relay, it would technically cut off the battery during a low voltage or over voltage situation....BUT....If I have the solar charge controller supplying a charge on the same circuit, wouldn't that power keep the relay energized and keep the inverter connected in a situation where I would want the inverter to disconnect?

If I run everything through the relay (coach 12v power, inverter, charger) and the BMS cuts off the relay due to low voltage, then no power would be able to reach the batteries in order to charge.

I'm hoping you guys might be able to shine some light on this situation. I'm open to any kind of advice or workaround to make sure my system is safe. Also, if you have a recommendation on a good pure sine wave inverter, that would be appreciated as well.

Thanks for your help!

 

[time2roll]

60 amps x 12 volts = 720 watts. Probably 600 watt inverter max with that BMS.

2000 watt inverter is plenty to brew coffee or run the microwave or any other single large item. Really need a 200 amp BMS to drive a 2000 watt inverter. Or a second battery in parallel each with an OverkillSolar 120 amp BMS. The single battery you have will be pressed close to the max if you get 150-200 amps out of it.

The solar will work fine to keep the battery charged. Will not really supply enough power to supplement what the inverter needs.

 

[BNalette]

60 amps x 12 volts = 720 watts. Probably 600 watt inverter max with that BMS.

2000 watt inverter is plenty to brew coffee or run the microwave or any other single large item. Really need a 200 amp BMS to drive a 2000 watt inverter. Or a second battery in parallel each with an OverkillSolar 120 amp BMS. The single battery you have will be pressed close to the max if you get 150-200 amps out of it.

The solar will work fine to keep the battery charged. Will not really supply enough power to supplement what the inverter needs.

Right, I don't plan to run the inverter through the BMS, that's why I'm asking how to properly wire in the relay in order to connect the inverter.

 

[John Frum]

Depending on your inverter, you might control it via an solid state relay.
I've done that and it works a treat.
You can drive the SSR from your BMS or from a Victron battery protect.
I'm doing the latter in my setup.
What inverter do you have?

 

[BNalette]

Depending on your inverter, you might control it via an solid state relay.
I've done that and it works a treat.
You can drive the SSR from your BMS or from a Victron battery protect.
I'm doing the latter in my setup.
What inverter do you have?

Thanks for your reply! I haven't purchased the inverter yet, and I'm open to adding other components (victron, etc) in order to make the system work. I'm currently open to suggestions on which inverter to buy.

 

[John Frum]

Thanks for your reply! I haven't purchased the inverter yet, and I'm open to adding other components (victron, etc) in order to make the system work. I'm currently open to suggestions on which inverter to buy.

Discrete inverter or inverter/charger?
Low frequency or high frequency?
System voltage?
Continuous watt rating?
120VAC or 120/240VAC?

 

[BNalette]

Discrete inverter or inverter/charger?
Low frequency or high frequency?
System voltage?
Continuous watt rating?
120VAC or 120/240VAC?

Just a discrete inverter.
I didn't give any thought to frequency.
12V system.
I don't think I'd need more than 2k continuous, but was looking at 3k to be safe.
120VAC

 

[John Frum]

Just a discrete inverter.
I didn't give any thought to frequency.
12V system.
I don't think I'd need more than 2k continuous, but was looking at 3k to be safe.
120VAC

2000 watts at 12 volts is big.
3000 is getting impractical.

Its really hard to find a discrete low frequency inverter so lets go with a high frequency, 2000watts, 120VAC model.
Notice the little green terminal block on the front left of this inverter.

Samlex PST-2000-12 2000W, 12V Pure Sine Inverter | DonRowe.com

The Samlex PST-2000-12, 12 Volt, 2000 Watt Pure Sine Wave Power Inverter features a commercial grade design for extreme reliability and is designed to accommodate tools and appliances in vehicles, RVs, boats, solar systems and more.

www.donrowe.com

I have the 1500watt@24volts version

page 51 of https://www.donrowe.com/v/vspfiles/pdf/pst-1500-2000-12-24_owners_guide.pdf shows how to set up the control signalling.


The inverter high current negative lead bypasses the bms.
The inverter high current positive lead bypasses the victron smart battery protect.
If you have any more questions I will be glad to help.

 

[John Frum]

This is a link to the battery protect https://www.victronenergy.com/uploa...rt-Battery-Protect-65-A--100-A--220-A-EN-.pdf
Notice it has nowhere close to the ampacity rating required for a 2000 watt inverter.
But that is fine because its not in the high current path it just "controls" the inverter.

 

[BNalette]

2000 watts at 12 volts is big.
3000 is getting impractical.

Its really hard to find a discrete low frequency inverter so lets go with a high frequency, 2000watts, 120VAC model.
Notice the little green terminal block on the front left of this inverter.

Samlex PST-2000-12 2000W, 12V Pure Sine Inverter | DonRowe.com

The Samlex PST-2000-12, 12 Volt, 2000 Watt Pure Sine Wave Power Inverter features a commercial grade design for extreme reliability and is designed to accommodate tools and appliances in vehicles, RVs, boats, solar systems and more.

www.donrowe.com

I have the 1500watt@24volts version

page 51 of https://www.donrowe.com/v/vspfiles/pdf/pst-1500-2000-12-24_owners_guide.pdf shows how to set up the control signalling.


The inverter high current negative lead bypasses the bms.
The inverter high current positive lead bypasses the victron smart battery protect.
If you have any more questions I will be glad to help.

So, I think the simplest answer to my question is the Victron smart battery protect. If I keep the inverter on the load side of the victron, and all other 12V loads/charger/BMS on the supply side, I should be good....assuming I wire the leads to the inverter as you mentioned.

So, the basically, the high current positive/negative from the inverter control go straight to the battery?

I'm not concerned about the other 12V loads on the trailer. The 60A BMS should be sufficient to handle all of those loads just fine.

You have been incredibly helpful, sir! Thank you so much for your advice.

 

[John Frum]

So, the basically, the high current positive/negative from the inverter control go straight to the battery?

That would work.
I would suggest connecting the inverter positive to a fused positive busbar and the inverter negative directly to the battery.
All the other negatives go to an un-fused negative busbar.
Its just a best practices/orthodoxy thing.

I'm not concerned about the other 12V loads on the trailer. The 60A BMS should be sufficient to handle all of those loads just fine.

You have been incredibly helpful, sir! Thank you so much for your advice.

You are welcome.
I have a weird feeling you are planning on using a "dumb" Daly bms, am I correct?

 

[BNalette]

Sorry, when I asked about wiring directly to the battery, I meant the 22ga control wires, not the actual power leads.

I think it’s a smart BMS…that’s what the ad said. It has Bluetooth and what not. I’ll try to attach a photo.

 

[John Frum]

Sorry, when I asked about wiring directly to the battery, I meant the 22ga control wires, not the actual power leads.

The positive control lead attachs the the protected side of the smart battery protect.
The negative control lead attaches to the un-fused negative busbar.
This way the smart battery protect is bms protected and the inverter is controlled by both.

I think it’s a smart BMS…that’s what the ad said. It has Bluetooth and what not. I’ll try to attach a photo.

The Daly smart bms has current accounting.
That feature won't work if the inverter bypasses the bms.

 

[BNalette]

The positive control lead attachs the the protected side of the smart battery protect.
The negative control lead attaches to the un-fused negative busbar.
This way both the smart battery protect is bms protected and the inverter is controlled by both.


The Daly smart bms has current accounting.
That feature won't work if the inverter bypasses the bms.

So my best option is to just get a big, 200a BMS?

 

[John Frum]

So my best option is to just get a big, 200a BMS?

You could just control the inverter directly via the bms.

If you want current accounting get a big smart bms or a dedicated shunt based battery monitor.

2000 ac watts / .85 conversion fact0r / 12 volts low cutoff = 196.078431373 service amps
Its prevailing wisdom here on the forum to de-rate daly's fairly optimistic ratings by .66 to .5.
200 amps / .66 de-rate = 303.03030303 amps
That means a 300 amp smart bms.

 

[HRTKD]

So my best option is to just get a big, 200a BMS?

That is AN option. There are other ways to power a big inverter. You need to do something different, that's for sure, because a 3000 watt inverter is going to bring that 60 amp BMS to its knees real quick.

I chose to buy eight 280Ah cells and create two 4s batteries, each with its own 120 amp BMS. I have ~240 amps of throughput for my future inverter. I currently run a 1000 watt inverter with zero problems, other than the inverter being too small to run my microwave. I knew that going in, so the inverter isn't connected to the RV's main distribution panel at all.