Get radical by getting simple: a 32kWh LFP house energy system

[nebster]

Originally Posted by mbullock

What's the model of 12V converter please? How efficient is it? Just comparing it to Victron 48-12 converter.

It is Meanwell RSP-1500-12, with claimed efficiency 87%. I'm sure that's at 25C and at something close to 1500W, though.

The idea of going LFP to 240/120V I like. Are you going to run your cooking off electric?

Yeah, the whole kitchen is electric and similar to one you'd have on land. We have a GE Advantium 240V microwave/speed oven, a Wolf induction cooktop, etc. Most larger RVs have moved away from propane over the last five years.

[john61ct]

Originally Posted by nebster

They are made by a company called Frey.

Would that be

Jiangsu Frey Battery Technology Co., Ltd.

and if so, did you just purchase through their public listing on Alibaba?

Ideal would be a link that would allow anyone to replicate your purchase

[john61ct]

Originally Posted by nebster

Meanwell RSP-1500-12

aka a power supply, used as an AC charger

IMO opinion much clearer terms than the confusing "converter", best used only for DC-DC buck/boost units.

Mean Well has a great rep within inexpensive adjustable Chinese gear.

Do you rely on its internal overcurrent protection, or use something else between it and the LFP to regulate how many amps are drawn by the bank + running loads?

[john61ct]

So total live capacity, 96 100AH cells each 3.2V

If 4s 12V we'd call it 2400AH ?

But more accurately and generalized

3.2V * 100AH = 320 wH

* 96 = 30.72 kWh

Is that right?

House circuit is at 48V, makes it a 640AH bank?

Have you got load devices like aircon that run native at that 48V?

Any plans for electric propulsion?

Or are you sure the high-voltage input inverters run that much more efficiently?

[nebster]

Originally Posted by john61ct

Would that be

Jiangsu Frey Battery Technology Co., Ltd.

and if so, did you just purchase through their public listing on Alibaba?

Ideal would be a link that would allow anyone to replicate your purchase

That's the company. I didn't purchase through Alibaba, and in fact they will not really sell through there at any quantity. (Maybe if you just want a few cells.) For a substantial pack, you work with one of their reps, and they help you understand what their stock is, what's in the pipeline, which cells you want, how you want them encased or enclosed (if desired), and so on.

If anyone wants to reach out to my rep, PM me and I'll share her contact info. She has been very easy to work with and totally honest and forthright. It is a little bit of an "adventure," though. It's probably best to think of it more as a procurement process. They are a pretty small company, though, so alternatively you could just inquire via their site.

[nebster]

Originally Posted by john61ct

aka a power supply, used as an AC charger

Yes, that's right, it's a DC power supply.

In my system, this power supply is used to create the 12V house power feed. It runs on the 120VAC side of the inverter. So I am not using it as a charger.

Do you rely on its internal overcurrent protection, or use something else between it and the LFP to regulate how many amps are drawn by the bank + running loads?

This power supply is only 1500W, and it has its own internal fuse (I think?) and is wired to its own dedicated 120VAC circuit with a traditional 20A breaker as well.

I have two of them connected in parallel, but it turns out we never draw 1500W in our setup, so I have turned one of them off and am just carrying it as a backup. Since I have no other "safe" way to make 12VDC for house systems, I wanted to have dual 12V supplies for redundancy.

The *only* load that the entire LFP pack*sees is the Victron inverter, and its internal overload protection provides the first layer of protection from overdemand. The pack is also fused at several layers to protect it directly from, e.g., a wiring fault.

Oversizing the inverter leaves a large cushion of thermal overhead for it to perform in less than ideal temperatures. Right now, my power bay is at 117F and climbing, so all of the hardware is well into its derate curve.

[nebster]

Originally Posted by john61ct

So total live capacity, 96 100AH cells each 3.2V

If 4s 12V we'd call it 2400AH ?

Yes, I think that's right. The cells are actually about 106AH, so the real pack size is slightly larger. I use a lot of that extra 6% as additional SOC cushion, to be discussed in more detail in a later post.

The real energy capacity is 636AH @ ~52V, or about 33kWh. Usable is quite a bit less, since I am conservative about it.

But more accurately and generalized

3.2V * 100AH = 320 wH

* 96 = 30.72 kWh

Is that right?

Yep, 30.72kWh nominal, as specified from the factory. Today running a little bigger thanks to the cells being over-provisioned from China.

House circuit is at 48V, makes it a 640AH bank?

The house DC bus is at 12V, hence the conversion discussed above.

Have you got load devices like aircon that run native at that 48V?

No, the largest DC load I have is a 400W sewage pump. The A/C are 120VAC units, 15kBTU.

Any plans for electric propulsion?

On the RV, yeah, as soon as Tesla makes that big truck. :-) Just kidding. Well, mostly kidding.

I don't think we'll opt for electric propulsion on the catamaran. Just a regular setup seems okay to me. If we could have a pure diesel-electric hybrid, with a single genset and two electric props, maybe that would be simpler and more reliable somehow. But it doesn't sound to me like much of a win... open to thoughts on that, and we have a couple years, so please invent something great for us?

Or are you sure the high-voltage input inverters run that much more efficiently?

Can you explain more about what this question means?

[john61ct]

Your inverter(s) from Victron are designed to take as input that 48-52VDC range?

I'm trying to get at why you didn't settle on a more mainstream voltage for your LFP configuration, as in 12V across the board, or maybe 24V, as is also common when needed.

Inverting to mains current, to then run that PS for all the House DC devices is going to be pretty inefficient.

But then you've got plenty to spare, too!

_______
I agree that there is little reason to go EP, but to others that disagree, let's not derail this so-far nicely coherent thread 8-D

[john61ct]

> microwave, a clothes dryer, and a water heater that provides continuous domestic hot water as well as hydronic radiator heating

Wow, yes, the 12V House loads will be a tiny fraction of that sort of mains powered gear.

I'll be very interested in your off-grid charging sources, especially staying for weeks in one place.

[nebster]

Originally Posted by john61ct

Your inverter(s) from Victron are designed to take as input that 48-52VDC range?

Victron's input range on the 48V line is 38-66V, so lots of flexibility!

I'm trying to get at why you didn't settle on a more mainstream voltage for your LFP configuration, as in 12V across the board, or maybe 24V, as is also common when needed.

The main reason is that no one runs 15kW at 24V or 12V, because the wires are too big. The equipment scales up to keep the wiring reasonable.

Also, there is a recent, developing automotive standard/preference to run DC systems at nominal 48V as well, although I don't care what they do too much (except that it may herald the coming of more 48VDC components one day, which would be interesting).

Inverting to mains current, to then run that PS for all the House DC devices is going to be pretty inefficient.

But then you've got plenty to spare, too!

Yeah, as you've observed, it's a relatively small loss on balance. (Another way to think of it: I intentionally made the pack larger to simplify the design!) I estimate the round trip inefficiency at about .93*.80 = ~75%. We average 100-200W of DC consumption. The simplicity gained by unifying the discharge sources was worth it.