Good way to charge a 12V and 48V system—together

aangel

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I've already got a 200 a•hr (12V) battery that is running my RV. It's hooked up to a 2KW Giandel inverter. Works great. But it can't provide 240V the new a/c unit requires.

I've got a 48V EG4 that should be coming in next week (fingers crossed it's left the port of LA) and my Sigineer 6kW 48V inverter/MPPT charge controller just arrived.

I was going to replace the existing battery and inverter with the new system but a friend suggested, "Why not keep the 12V to run your lights, fans, Webasto heater, etc.?"

Why not indeed.

So let's say I remove the Giandel inverter and keep the 12V battery connected to the 12V lines around the RV. The equipment I have remaining is:
• Progressive Dynamics Converter/Charger already connected to the 12V battery
• GoPower! 30A transfer switch
• various switches and fuses

Now I add:
• a 120V to 48V charger
• The Sigineer 48V 240VAC Inverter

I no longer need the 48V to 12V step-down transformer I've bought; the 12V system is still in place.

The two questions I have are:
1. How do I charge these two systems from shore power? Do I have to have a switch that charges one system then the other—and I have to manually perform the switch? I likely can't charge both batteries without going over the 30A circuit at a typical RV park and I don't want to depend on 50A circuits going forward.
2. How do I charge these two systems from solar?

Of course a possible answer might be, "Save yourself some complication and switch over entirely to the new 48V battery." But then I lose my relatively new 200a•hr battery that a) cost me a load of cash a year ago and b) could keep a bunch of loads off the 48V system that is designed primarily to run the new mini-split a/c I just installed and the microwave.
 

sunshine_eggo

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I've already got a 200 a•hr (12V) battery that is running my RV. It's hooked up to a 2KW Giandel inverter. Works great. But it can't provide 240V the new a/c unit requires.

I've got a 48V EG4 that should be coming in next week (fingers crossed it's left the port of LA) and my Sigineer 6kW 48V inverter/MPPT charge controller just arrived.

That Sig is a HONGRY MONSTER. It's going to burn 100W just by being on. You're going to consume 50% of your battery capacity even if you don't use any loads.

No, you can't use power saving mode UNLESS you need NO AC loads of any kind. If you have any loads at all, there is no such thing as power saving mode. Power any clocks? Power an AC compressor fridge (needs AC for the thermostat to work)? No power saving mode.

I'm not going to address any of the other stuff because it makes me cross-eyed, but I'll let the above sink in.
 

Rednecktek

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I no longer need the 48V to 12V step-down transformer I've bought; the 12V system is still in place.

Your system will be more efficient if you just stick with the buck transformer to let your 48v system charge your 12v system. Better lo have 48v ->12v with efficiency loss than to have 48v -> 240v with loss -> 12v with loss.

As for how to do charging via solar and shore power, think of it more as building a complete 48v system for your inverter/charging/solar controller/etc. that just happens to also run a 12v buck transformer.
 

sunshine_eggo

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Your system will be more efficient if you just stick with the buck transformer to let your 48v system charge your 12v system. Better lo have 48v ->12v with efficiency loss than to have 48v -> 240v with loss -> 12v with loss.

As for how to do charging via solar and shore power, think of it more as building a complete 48v system for your inverter/charging/solar controller/etc. that just happens to also run a 12v buck transformer.

Except, the buck needs to output 13.8V if charging is planned. If taking the 12V battery out, 12V is fine.
 

Rednecktek

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Except, the buck needs to output 13.8V if charging is planned. If taking the 12V battery out, 12V is fine.

Aahh, didn't notice that. There's gotta be a variable adjustable version of that somewhere, right? Or just taking the battery out of the loop and providing all the 12v power from the buck like I do at my camp.
 

JoeHam

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I just buy them in 13.8v flavor but they do have idle consumption.

Like this one :


Last time I bought one they were around $20 so shop around.

I will hook mine up and put a clamp meter on to get an idle power estimate.

Edit: My 414W uxcell 13.8V buck converter is pulling 0.2 amps at 53.3 volts, no load, for an idle consumption of about 10.7W.

So you only want to connect it when you’re using it.
 
Last edited:

aangel

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@sunshine_eggo Yes, it definitely is hungry. I knew that before I bought it.

But I went ahead with this unit for a few reasons. First, after living full time in my RV for the past 8 months I've learned that I rarely turned my inverter on. I turn it on to charge my laptop and to fill another, smaller lithium battery (540Wh) that runs my internet router and weather station 24/7. Everything else in the rig runs on 12V. I'm even installing two USB-C chargers directly to the 12V to power the laptop thereby taking out the loss of the AC to DC wall transformer. This new inverter really will be just for the microwave and the a/c unit.

Second, I'm not using much power with the new a/c because it's so efficient. It's ok to lose another 80W to the inverter when it's turned on, especially once I get 1700W (rated) of solar installed.

The Sigineer manual says that the trip point is 500W, btw, then it will output full voltage and use 40W per hot line (80W total). If I'm using only 120V the loss is 40W. And I understand that the manufacturer's numbers may not reflect reality. We shall see.

@Rednecktek that's definitely one way to do it...make the Sigineer the priority then have it charge the 12V. I'm going to diagram it up.
 

sunshine_eggo

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@sunshine_eggo Yes, it definitely is hungry. I knew that before I bought it.

But I went ahead with this unit for a few reasons. First, after living full time in my RV for the past 8 months I've learned that I rarely turned my inverter on. I turn it on to charge my laptop and to fill another, smaller lithium battery (540Wh) that runs my internet router and weather station 24/7. Everything else in the rig runs on 12V. I'm even installing two USB-C chargers directly to the 12V to power the laptop thereby taking out the loss of the AC to DC wall transformer. This new inverter really will be just for the microwave and the a/c unit.

This unit is grossly oversized. You've bought a bazooka to shoot a 22LR. You don't need any kind of surge. It's rare that I recommend the cheaper high frequency inverters like the MPP Solar or Growatt, but they would likely be a better choice.

Second, I'm not using much power with the new a/c because it's so efficient. It's ok to lose another 80W to the inverter when it's turned on, especially once I get 1700W (rated) of solar installed.

Agree with the +80W, but you will need to turn your inverter on and off when you don't need it unless you want to accept the 100W burn.

The Sigineer manual says that the trip point is 500W, btw, then it will output full voltage and use 40W per hot line (80W total). If I'm using only 120V the loss is 40W. And I understand that the manufacturer's numbers may not reflect reality. We shall see.

It doesn't work like this. If power save is on, NOTHING GETS POWERED AT ALL, and it burns 25W. It continues to pulse until a >500W load is detected. Again, when power save is enabled, no loads below 500W will be powered. Furthermore, anything on this circuit is being turned on and off or at least being plugged in and unplugged every 3 seconds. Anything that relies on power to turn itself on and off will not perform reliably.

Power saving mode on all inverters is a useless feature in almost all situations.

80W on the datasheet, but then they say 100W in the manual.

1639856417266.png

Your plan to leave the inverter on and have it come on only when needed is almost certainly not going to work. I would be concerned it may damage electronics connected to AC power when in idle mode.
 

aangel

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@sunshine_eggo It's ok if the power save mode doesn't work out. I wasn't counting on it in my planning. I was anticipating continuing my current behavior i.e. turn the inverter on when I need it. If it doesn't work out, I'm happy to turn off the power save feature.

Yes, it's definitely over-sized. At the same time, it gives me all the things I want in one unit at an acceptable price.
 

sunshine_eggo

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The two questions I have are:
1. How do I charge these two systems from shore power? Do I have to have a switch that charges one system then the other—and I have to manually perform the switch? I likely can't charge both batteries without going over the 30A circuit at a typical RV park and I don't want to depend on 50A circuits going forward.

This is pretty tricky.

On 50A it's easy, AC in to inverter can charge the battery, and you can charge the 12V from the PD converter.

On 30A, you can't plug into your inverter AC in because you'll destroy it. 30A shorts L1 and L2 to allow 50A rigs to still power both legs. Your inverter output has to be isolated from the 30A AC input.

It almost seems like you need 2 ATS - 1 to isolate the inverter from the AC panel and one to select between 30A 120V in or 50A 240V in. I think I've seen a way that if the second leg is live, it will transfer to that. If not it feeds through the 120VAC to the panel.

When on 30A power, you'd use the 120VAC to 48V charger.


2. How do I charge these two systems from solar?

MPPT to 48V
48-13.8V DC buck and float the 12V from the 48V
 

sunshine_eggo

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One other thing...

Many of the Sigineer/AIMS inverters are rubbish for Lithium and AC charging. They have an absurd absorption duration. Please read page 8:


With regards to T0 and T1 timing.

Basically, absorption is 10X the charge time it takes to get to 0.3V below the absorption voltage with a 1 hour minimum.

MINIMUM absorption duration is 1 hour - LFP rarely needs more than 30 minutes. Absorption can be up to 12 hours.

The best way to deal with this is to set absorption to 3.40-3.45V/cell and float to 3.40V/cell - this way you're taking your time getting to 95-98% charge without overdoing it. Great for shore power. If charging from gen, you pretty much have to cut charging manually.
 

aangel

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I re-worked my wiring diagram to incorporate the new equipment according to @Rednecktek 's suggestion. I already have a Renogy DC to DC charger that I was going to use to get power from the alternator. I can repurpose that to charge the 12V battery off the 48V battery.

Not claiming perfection, just sorting through things as I go since I still consider myself a beginner at this:

1639866877994.png

@sunshine_eggo I haven't looked into charging profiles yet. Thanks for the heads up. I'll turn my attention to that as soon as I get the wiring all sorted out.

Agreed with 50A it would be easy. I could keep the PD converter.
As you point out, I can't connect the inverter to 120V shore power; it requires 240VAC input or 48VDC input.
It seems to get complicated if I attempt any sort of parallelization. This series design has simplicity going for it.

I keep seeing expressions like this but I don't know what "float the 12V from the 48V" means. Does that mean grab the positive only?
 

sunshine_eggo

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I re-worked my wiring diagram to incorporate the new equipment according to @Rednecktek 's suggestion. I already have a Renogy DC to DC charger that I was going to use to get power from the alternator. I can repurpose that to charge the 12V battery off the 48V battery.

Not claiming perfection, just sorting through things as I go since I still consider myself a beginner at this:

View attachment 76295

@sunshine_eggo I haven't looked into charging profiles yet. Thanks for the heads up. I'll turn my attention to that as soon as I get the wiring all sorted out.

Agreed with 50A it would be easy. I could keep the PD converter.
As you point out, I can't connect the inverter to 120V shore power; it requires 240VAC input or 48VDC input.
It seems to get complicated if I attempt any sort of parallelization. This series design has simplicity going for it.

I keep seeing expressions like this but I don't know what "float the 12V from the 48V" means. Does that mean grab the positive only?

No. It means that the 48 - 13.8V converter would "float" the AGM at a full state of charge all the time.
 
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